Unit 1: Role of Materials in Engineering Fields PDF

Unit 1 Ro le of m ate ria ls in e ng inee ring fie lds Materials are probably more significant in our culture than we realize. Transportation, housing, clothing communication, reaction and food production and virtually every segment of our daily lives is influenced by materials. Mat...

Unit 1 Ro le of m ate ria ls in e ng inee ring fie lds Materials are probably more significant in our culture than we realize. Transportation, housing, clothing communication, reaction and food production and virtually every segment of our daily lives is influenced by materials. Materials have contributed to the advancement of a number of technologies, including medicine & health, information & communication, national security & space, transportation, structural materials, arts & literature, textiles, personal hygiene, agriculture & food science & the environment. These inter-disciplinary interactions between the Material sciences and other fields in the development of new materials and their applications is to be understood well. As the contribution of materials science and engineering to other disciplines increases, it will become necessary for scientists of all backgrounds to better understand it. Although it is not feasible for scientists to master a vast body of scientific knowledge over many disciplines, scientists must gain the skills that will allow them to master some specific topics. Our presentation attempts to present a relatively brief overview of Materials Science and Materials Engineering and their importance in the present day world. It will also attempt to examine the four components that make up the whole gamut of the discipline of materials science and engineering and their inter-relationship. 2. Materials Science and Engineering Materials Science and Engineering – (a) materials science, (b) materials engineering Materials science involves investigating the relationships that exist between the structures and properties of materials Materials engineering is based on the application of this structure-property correlations, in designing or engineering the structure of a material to produce a pre-determined set of properties From a functional perspective, the role of a materials scientist is to develop or synthesize new materials, whereas a materials engineer is called upon to create new products or systems using existing materials and/or to develop techniques for processing materials. 2.1 Elements of Materials Science and Engineering There are four essential elements in materials science and engineering 1) Processing/synthesis 2) Structure/composition 3) Properties 4) Performance/application These four elements of Materials Science and Engineering is primarily concerned with the study of the basic knowledge of materials: the relationships between the composition/structure, properties and processing of materials. Materials engineering is mainly concerned with the use of this fundamental knowledge to design and to produce materials with properties that will meet the requirements of society. As subjects of study, materials science and materials engineering are very often closely related. The subject ―materials science and engineering" combines both a basic knowledge and application and forms a bridge between the basic sciences (physics, chemistry and mathematics) and the various engineering disciplines, including electrical, mechanical, chemical, and civil and aerospace engineering. Q U A L I T Y A S S U R A N C E & Q U A L IT Y C O N T R O L Q u ality a ssur an ce (Q A) a nd qu ality c ont rol (Q C) a re tw o term s th at a re often use d in terc ha n g ea bly. Alth ou g h sim ilar , th er e a re distinc t diffe ren ces b et we en the t wo c on ce p ts. Th is p a g e w ill e xp la in th e differen ce s b etw een qu ality c on trol a nd qu ality m a na g em en t, an d p rov ide de fin ition s a nd exa mp le s of ea ch. D IF F E R E N C E S B E T W E E N Q A A N D Q C Q u ality a ssur an ce a n d qu a lity con trol a re tw o a sp ects of qua lit y m an ag e m ent. W hile som e qu ality a ssu ran ce a n d qu a lit y con trol a ctiv it ie s are in ter relat ed, the t wo a re define d differ en tly. Ty pic ally, Q A a ctiv it ie s an d resp on sib ilities cov er v irtu ally a ll of the qua lit y syste m in one fa shion or a n othe r, wh ile Q C is a su b set of th e Q A a ctiv it ie s. Also, e lem en ts in th e qua lity syst em mig h t not b e sp ec ifica lly cov ered b y Q A/ Q C ac tivities a n d re sp onsib ilities b ut m a y inv olv e Q A an d Q C. F ig u re 1 sh ow s ISO 9000 definition s from ISO 9000:2015: Q u ality m a na g em en t syste m s - F u nda m en tals a nd Voca b u la ry. Quality Assurance Qualityassurance canbe definedas "part of focusedon providingconfidence that will be fulfilled." The confidence provided byqualityassurance is twofold— internally tomanagement and externallyto customers,government agencies,regulators,certifiers,and thirdparties. Analternate definitionis "all theplannedand systematic activities implemented withinthe qualitysystem that canbe demonstrated to provide confidence that a product orservice will fulfill requirements forquality." Quality Control Qualitycontrol can be defined as"part of focused onfulfilling." While qualityassurance relates to how a processisperformed orhow a product is made, qualitycontrol ismore the inspectionaspect ofqualitymanagement.Analternate definitionis"the operational techniques andactivities usedtofulfill requirements for quality." INDUSTRY PERSPECTIVES ON QA AND QC For some serviceorganizations,the concept ofqualitycontrol maybe foreignbecause there is no tangible product to inspect and control.The qualityassurance functionin aservice organizationmay not include qualitycontrol ofthe service but mayinclude qualitycontrol ofanyproducts involvedin providingthe service. A service mayinclude productsthat are documents (such as areport, contract,ordesign)ortangible products (suchas arental carorunitsof blood).It maybe necessary to control product qualityinaservice organizationtoensure that the service meets customerrequirements. QA, QC, and Inspection Inspection isthe process of measuring,examining,and testing to gauge one ormore characteristics ofa product orservice andthe comparisonofthese with specified requirements to determine conformity. Products,processes,and various otherresultscanbe inspected to make sure that the object comingoffa productionline, or the service beingprovided, is correct andmeets specifications. Quality Assurance and Audit Functions Auditing ispart of the qualityassurance function. It isimportant to ensure qualitybecause it is usedtocompare actual conditions withrequirementsand to report those results to management. In (McGraw-Hill,1988), CharlesMill wrote that auditingand inspectionare not interchangeable: “ The auditor mayuse inspectiontechniquesas anevaluationtool,but the audit should not be involved incarrying out anyverificationactivities leading to the actual acceptance orrejectionof aproduct orservice. Anaudit shouldbe involvedwiththe evaluation ofthe processandcontrols covering the productionand verification activities.”  Formal management systemshave evolved to direct and control organizations.There are qualitymanagement systems (QMSs) as well as environmental orothermanagement systems,and eachofthese systemsmaybe audited. Qualitative analysis and quantitative analysis Q u a lita tive a n a lys is a n d q u a n tita tive a n a lys is a re tw o m eth o d s u s e d to id e n tify a n d m ea s u re th e c h em ic a l c o m p o n en ts o f a s a m p le. Q u a litative a n a lys is is u s ed to id en tify th e p res e n c e o r ab s en c e o f c erta in c h em ic a l c o m p o u n d s o r ele m e n ts in a s a m p le. Q u a n tita tive a n a lys is is u s ed to d e te rm in e th e a m o u n t o r c o n c en tra tio n o f a p a rtic u la r c o m p o u n d o r elem e n t in a s a m p le. T h is m e th o d is o f te n u s ed in a n a lytic a l c h em is try to m ea s u re th e p u rity o f a s u b s ta n c e o r to d e te rm in e th e c o n c en tra tio n o f a p a rtic u la r ele m e n t in a s a m p le. B o th m eth o d s a re es s e n tia l in c h em is try a n d a re o ften u s e d to g eth er to p ro v id e a m o re c o m p le te a n a lys is o f a s a m p le. Qualitative Analysis Q u a lita tive a n a lys is is a m e th o d u s ed in c h em is try to id en tify th e p re s en c e o r a b s e n c e o f c e rta in c he m ic a l c o m p o u n d s o r elem en ts in a s a m p le. T h is m eth o d is o ften u s e d in o rg a nic c h e m is try to id e n tif y unkno w n s u b s ta n c es. Q u a lita tiv e a n a lys is in v o lv es o b s erv in g th e s a m p le's p h ys ic a l p ro p e rties , s u c h a s c o lo r, tex tu re, a n d o d o r, a n d p e rfo rm in g c h em ic a l te s ts to id e n tify s p ec if ic io n s o r f un c tio n a l g ro u p s. In o rd e r to p erfo rm q u a lita tiv e a n a lys is , a c h em is t m us t firs t p rep a re th e s a m p le b y d is s o lv in g it in a s o lve n t o r p erfo rm in g a c h em ic a l rea c tio n. O n c e th e s a m p le is p re p a red , th e c h e m is t c a n b e g in to o b s e rve its p h ys ic a l p ro p ertie s an d p e rfo rm c h e m ic a l tes ts. Example of Qualitative Analysis O n e c o m m o n typ e o f c h e m ic a l te s t u s ed in q u a lita tive a n a lys is is a f la m e te s t. It is a n in o rg a n ic q u a lita tive a n alys is te c h n iq u e. It is u s e d to id en tify th e p res e n c e o f c e rta in m eta l io n s in a s a m p le. In th is tes t, a s m a ll a m o u n t o f th e s a m p le is h ea te d in a fla m e , a n d th e c o lo r o f th e fla m e is o b s erve d. D iffere nt m eta l io n s p ro d u c e d iff eren t c o lo rs o f fla m e , w h ic h c a n b e u s ed to id en tify th e p re s en c e o f the m e ta l io n in th e s a m p le. F o r e xa m p le , s o d iu m io n s p ro d u c e a b rig h t yello w fla m e, w h ile z in c io n s p ro d u c e a g re en flam e. T h e fla m e te s t is o ften u s ed in c h em is try to id en tif y th e m e ta l io n s p re s en t in a s a m p le , s u c h a s in m in era ls o r b io lo g ic a l s a m p le s. A n o th e r c o m m o n typ e o f c h em ic a l tes t u s e d in q u a lita tive a n a lys is is a te s t fo r io d in e. It is a n in o rg a nic q u alita tiv e a n a lys is tec h n iq u e. T h is tes t is u s ed to d e term in e s ta rc h 's p re s en c e. In th is te s t, a s m a ll a m o u n t o f io d in e is a d d ed to th e s a m p le, a lo n g w ith a few d ro p s o f a s ta rc h s o lu tio n. If io d in e is p re s en t in th e s a m p le, it w ill re ac t w ith th e s ta rc h to fo rm a b lu e -b la c k c o lo r. T h is te s t is o fte n u s ed to id en tify th e p re s en c e o f io d in e in fo o d , s u c h a s in s a lt o r s ea f o o d. It c a n a ls o b e u s e d to d e te c t th e p res e n c e o f io d in e in la b o ra to ry s a m p les , s u c h a s in c h em ic a l s o lu tio n s o r b io lo g ic a l s a m p les. Quantitative Analysis Q u a n tita tive a n a lys is is u s ed to d e te rm in e th e a m o u n t o r c o n c en tra tio n o f a p a rtic u la r c o m p o u n d o r e le m e n t in a s a m p le. T h is m e th o d in v o lve s m e a s u rin g th e s a m p le's p h ys ic a l p ro p e rties , s u c h a s m a s s , vo lum e , a n d d en s ity, a n d p erfo rm in g c a lc u la tio n s to d e term in e th e a m o u n t o r c o n c en tra tio n o f th e c o m p o u n d o r ele m e n t. Example of Quantitative Analysis In q u a n tita tive a na lys is , tw o m e tho d s a re: T itra tio n m e th o d s , g rav im e tric m eth o d s , c o m b u s tio n a n a lys is m eth o d s , a n d c h e m ic a l re a c tio n s s u c h a s o x id a tio n , re d u c tio n , p rec ip ita tio n , a n d n e u tra liza tio n a re a ll e xa m p les o f c h em ic a l m e th o d s. P h ys ic a l m eth o d s lo o k at o n e o r m o re p h ys ic a l c h a ra c teris tic s o f a s a m p le. E x a m p les o f s u c h m e th o d s a re A E S (A to m ic em is s io n s p e c tro s c o p y), x-ra y flu o res c en c e, s p ec tro s c o p y, m a s s s p ec tro s c o p y, a n d o th e rs. T h e m a jo rity o f th e tim e, p h ys ic a l a n d c h em ic a l a n a lys is m e th o d s to g eth er w ith s p ec ific c a lc u la tio n s a re u s ed to d eterm ine th e p rec is e c o n c e ntra tio n o f a c o m p o n en t in a s a m p le. H o w ev er, a n u m b e r o f a s s u m p tio n s a n d e xp erim e n ta l m is ta k es c a n res u lt in in a c c u ra te en d re s u lts. Difference Between Qualitative And Quantitative Analysis S. Qualitative Analysis Quantitative Analysis No It m ea s u res th e a m o u n t o r It id e n tifies th e p re s en c e o r a b s e n c e o f a 1 c o n c en tra tio n o f a s u b s ta n c e in a p a rtic u la r s u b s ta n c e in a s a m p le. s am p le. It is p erfo rm ed u s in g s im p le c h em ic a l te s ts It is p e rfo rm e d u s in g in s tru m e n ta l 2 th a t p ro d u c e a vis u a l c h a n g e , s u c h a s a m e th o d s th a t p ro d u c e a n u m eric a l c o lo r c h a n g e o r a p rec ip ita te fo rm a tio n. re s u lt, s u c h a s a m a s s o r a vo lu m e. It is u s e d to id e n tify u n k n o w n s u b s ta n c e s o r It is u s ed to d eterm in e th e p u rity o r 3 to c o n firm th e id e n tity o f a k no w n c o m p o s itio n o f a s u b s ta n c e. s u b s ta n c e. It is le s s p rec is e an d le s s a c c u ra te th a n It is m o re p rec is e a n d m o re a c c u ra te 4 q u a n tita tiv e a n a ly s is b e c a u s e it re lie s o n th a n q u a lita tive a na lys is b e c a u s e it s u b jec tiv e o b s erv a tio n s. re lie s o n o b jec tiv e m ea s u rem en ts. It c a n b e p e rf o rm e d u s in g a s m a ll s a m p le It req u ire s a la rg er s a m p le s ize to 5 s iz e. o b ta in ac c u ra te res u lts. Summary Q u a lita tive a n a lys is a n d q u a ntita tiv e a n a lys is a re tw o e s s en tial m e th o d s u s e d in c h e m is try to id en tify a n d m ea s u re th e c h em ic a l c o m p o n e n ts o f a s a m p le. Q u a lita tiv e a n a lys is is u s ed to id e n tify th e p re s en c e o r a b s e n c e o f c erta in c h e m ic al c o m p o u n d s o r ele m e n ts in a s a m p le. T h is m eth o d in vo lv es o b s e rv in g th e s a m p le's p h ys ic a l p ro p ertie s , s u c h a s c o lo r, tex tu re, a n d o d o r, a n d p erfo rm in g c h em ic a l tes ts to id en tif y s p e c ific io n s o r fu n c tio n a l g ro u p s. Q u a n tita tive a n a lys is , on th e o th e r h a n d , is use d to d e te rm in e th e am ount or c o n c e n tra tio n o f a p a rtic u la r c o m p o u n d o r e lem en t in a s a m p le. In th is m eth o d , w e m ea s u re th e s a m p le 's p h ys ic a l p ro p ertie s , s u c h a s m a s s , vo lu m e , a n d d e n s ity, a n d p e rfo rm c a lc u la tio n s to d eterm in e th e a m o u n t o r c o n c e n tra tio n o f th e c o m p o u n d o r ele m e n t. B o th q u a lita tiv e a n d q u a n tita tive a n a lys is a re e s s en tia l in c h e m is try a n d a re o fte n u s e d to g eth er to p ro vid e a m o re c o m p lete a n a lys is o f a s a m p le. Q u a lita tiv e a n a ly s is is u s e d to id e n tify th e p re s en c e o f s p ec if ic c o m p o u n d s o r e le m en ts , w h ile q u a n tita tiv e a n a lys is is u s ed to d ete rm in e th e a m o u n t o r c o n c e n tra tio n o f th o s e c o m p o u n d s o r ele m e n ts. E m e rg in g tren d s a n d a p p lic a tio n s o f a n a lytic a l te c h n iq u e s fo r en g in e erin g In en g in ee rin g a n d s c ie n c e , a n a lys is is im p o rta n t fo r p ro p er d e s ig n. M o s t a n a lys is a n d m o d eling te c h n iq u e s a re c o v ere d in n u m eric a l m e tho d s w h ic h h a s , in rec en t yea rs , b e en u n fo rtu n a te ly s a c rif ic ed in a n u m b er o f en g in eerin g p ro g ra m s in fa vo r o f a p u re s ig n a ls a n d s ys tem s c la s s. S o m e e n g in ee rin g p ro g ra m s in c lu d e n u m eric a l m e th o d s b y in c lu d in g a s ec tio n o r tw o in s ig n a ls a n d s ys tem s a n d va rio u s p ro g ram m ing c o u rs e s. It is im p o rta nt fo r a s tu d en t to m a k e s u re th ey h a v e s o m e b a c k g ro u n d in n u m eric a l m e tho d s. H e re w e w ill re vie w s o m e es s e ntia ls id ea s in n u m eric a l m e tho d s in c o m p u te r s c ie n c e. T h is w ill n o t b e a c o m p le te p ic tu re. A s ys tem is a p ro c e s s th a t c a n a c c o m p lis h a ta s k o r is a p ro c e s s th a t b y n a tu re a c c o m p lis h es a ta s k. T h e te rm s ys te m is s o g e n eric it c a n b e u s ed in th e s c ie n c e s , en g in e erin g , s o c ia l, c o m p u te r s c ie n c e , m u s ic , etc. In b io lo g y fo r in s ta n c e w e h a ve a d ig e s tive s ys te m th a t ta k es in fo o d a n d p ro c e s s es to o u tp u t m a teria ls th e b o d y n ee d s a n d w a s te, in c o m p u te r s ys tem yo u h a ve s ys te m c a lls th a t in p u t a c o m m a nd yo u w is h th e c o m p u ter s ys te m to d o a n d o u tp u ts the a c tio n o f th e c o m p u ters s ys te m (w h ic h is a s ys tem in its elf), in en g ine erin g yo u m a y h a ve a L E D w h ic h yo u in p u t a p o ten tia l a n d th e LE D o u tp u ts lig h t, an d s o o n. T h in k o f a ll th e term s w h e re s ys te m is u s ed...a g o ve rn m e n t s ys tem , a ra ilro a d s ys tem , a s ys te m o f s ta rs , a m u s ic a l s ys tem (s ta ve s ), n a tu ra l s ys te m , s o c ia l s ys tem , etc. T h is m a k e s a c o n s is ten t d ef in itio n o f s ys tem a little p ro b lem a tic , h o w ev er w e w ill try to d e fin e it to fit m o re o f a s c ien c e a n d en g in e erin g p u rp o s e. In s tru m e n ta l M e th o d s o f A n a lys is In s tru m en ta l m eth o d s o f c he m ic a l a n a lys is ha v e b ec o m e th e p rin c ip a l m e a n s o f o b ta in ing in f o rm a tio n in d ive rs e a re a s o f s c ien c e a n d tec h n o lo g y. T h e s p e ed , h ig h s en s itiv ity, lo w lim its o f d e te c tio n , s im u lta n eo u s d ete c tio n c a p a b ilities , a n d a u to m a ted o p e ra tio n o f m o d ern in s tru m en ts , w he n c o m p a re d to c la s s ic a l m e th o d s o f a na lys is , ha v e c re a te d th is p re d o m in a n c e. P ro fe s s io n a ls in a ll s c ie n c e s b a s e im p o rta n t d ec is io n s , s o lv e p ro b lem s , a n d a d v a n c e th e ir field s u s in g in s tru m en ta l m ea s u re m e n ts. A s a c o n s e q u e n c e , a ll s c ie n tis ts a re o b lig a ted to h a v e a fu n d a m en ta l u n d ers ta n d in g o f in s tru m e n ts a n d th eir ap p lic a tio n s in o rd er to c o n fid en tly a n d a c c u ra tely a d d res s th e ir ne ed s. It is u s efu l to o rg a n ize in s tru m e n ta l m eth o d s o f a n a lys is in to s ev era l g ro u p s b a s ed o n th e c h e m ic a l o r p h ys ic a l p ro p erties th a t w e u s e to g e n era te a s ig n a l th a t w e c a n m e a s u re a n d re la te to th e a n a lyte o f in teres t to u s. O n e g ro u p o f in s tru m en ta l m e th o d s is b a s ed o n th e in tera c tio n o f p h o to n s o f elec tro m a g n etic ra d ia tio n w ith m a tte r, w h ic h w e c a ll c o llec tive ly s p ec tro s c o p y. Lig h t a n d M a tter W h a t h a p p en s w h en a s a m p le is irra d ia te d b y lig h t? Fro m in tro d u c to ry c h e m is try c o u rs e s , yo u m ig h t h a ve a q u a n tu m m e c h a n ic al p ic tu re o f lig h t a b s o rp tio n , w h ic h e m p h a s iz es th a t lig h t e n erg y c o m es in q u a n tiz ed un its , c a lled p h o to n s , a n d th a t a m o le c u le’ s e n erg y a ls o c o m es in q u a n tiz ed u n its o r “ q u a n ta” , s o w he n a m o le c u le a b s o rb s a p h o to n , it ta k e s u p the p h o to n ’ s e n erg y to re a c h a n “ ex c ite d s ta te ” o f s o m e s o rt. Y o u r p ic tu re o f lig h t a b s o rp tio n m ig h t lo o k lik e th is B o th o f th e s e d e p ic tio n s g et o n e c ru c ial ele m e n t c o rrec t: c o n s erva tio n o f e n erg y. Th e p h o to n e n erg y d o e s in d e ed g e t tu rn e d in to m o le c u la r e n erg y. A ls o , s in c e m o le c u la r en erg y is q u a n tize d , th ere a re o nly m o lec u la r ex c ited s ta tes a t c erta in d is c rete e ne rg y le ve ls. Th e p h o to n e n erg y h a s to b e e q u a l to th e d iffe re n c e Δ E b etw ee n s o m e p a ir o f en erg y le ve ls o f th e m o le c u le in o rd e r fo r a b s o rp tio n to o c c u r. T he re a re m a n y typ e s o f s ta tes th a t th es e e n erg y le ve ls c o u ld c o rre s p o n d to , b u t in th is m o d u le yo u w ill o n ly c o n s id er elec tro nic , vib ra tio n a l, a n d s p in s tate s. What is Electromagnetic Radiation? — lig h t— is a fo rm o f en e rg y w h o s e b eh a vio r is d e s c rib ed b y the p ro p erties o f b o th w a v es a n d p artic les. S o m e p ro p ertie s o f elec tro m a g n etic ra d ia tio n , s u c h a s its refra c tio n w h en it p a s s es fro m o n e m ed ium to a n o th er (F ig u re 1 0.1. 1 ), a re ex p la in ed b es t w h en w e d e s c rib e lig h t a s a w a ve. O th er p ro p ertie s , s u c h a s a b s o rp tio n a n d e m is s io n , a re b ette r d es c rib ed b y trea tin g lig h t a s a p a rtic le. T h e e xa c t n a tu re o f ele c tro m a g n etic ra d ia tio n re m a in s u n c lea r, a s it h a s s inc e th e d ev elo p m e n t o f q u a n tum m ec h a nic s in th e firs t q u a rter o f th e 2 0 th c en tu ry [H o m e , D.; G rib b in , J. 1 99 1, 2 N o v. 3 0 – 3 3 ]. N ev erth e les s , th is d u a l m o d el o f w a ve an d p a rtic le b e h av io r p ro v id e a u s ef u l d es c rip tio n fo r ele c tro m a g n etic ra d ia tio n. Wave Properties of Electromagnetic Radiation E le c tro m a g n etic ra d ia tio n c o n s is ts o f o s c illa tin g elec tric a n d m a g n e tic fie ld s th a t p ro p a g a te th ro u g h s p a c e a lo n g a lin ea r p a th a n d w ith a c o n s ta n t v elo c ity. In a v ac u u m , ele c tro m a g n etic ra d ia tio n tra ve ls a t th e s p e ed o f lig h t, , w h ic h is 2.9 9 7 9 2 × 1 0 8 2.9 9 7 9 2 × 1 0 8 m /s. W h e n elec tro m a g n etic ra d ia tio n m o v es th ro u g h a m e d iu m o th e r th a n a v ac u u m , its ve lo c ity, , is le s s th a n th e s p e ed o f lig h t in a v a c u u m. T h e d iff eren c e b e tw e en and is s u ff ic ien tly s m a ll (< 0.1 % ) th a t th e s p ee d o f lig h t to th ree s ig n ific a n t fig u res , 3.0 0 × 1 0 8 3.0 0 × 1 0 8 m /s , is a c c u ra te e n o u g h f o r m o s t p u rp o s es. T h e o s c illa tio n s in th e e le c tric field a n d th e m a g n e tic fie ld a re p erp en d ic u la r to ea c h o th e r a n d to th e d irec tio n o f th e w a v e’ s p ro p a g a tio n. F ig u re 1 0.1.2 s h o w s a n ex a m p le o f p la n e -p o la rize d e le c tro m a g n e tic ra d ia tio n , w h ic h c o n s is ts o f a s in g le o s c illa tin g elec tric field a n d a s in g le o s c illa tin g m a g n e tic fie ld. A n e le c tro m a g n e tic w a ve is c h a ra c te riz ed b y s ev era l f u n d a m en ta l p ro p e rties , in c lu d in g its v elo c ity, a m p litu d e, f re q u e n c y, p h a s e a n g le, p o la riza tio n , a n d d irec tio n o f p ro p a g a tio n [B a ll, D. W. 1994, , 2 4 – 2 5 ]. F o r ex a m p le , th e a m p litu d e o f th e o s c illa tin g ele c tric fie ld a t a n y p o in t a lo n g th e p ro p a g a tin g w a ve is A t= A es in (2 π ν t+ Φ ) w h ere is th e m a g n itu d e o f th e elec tric fie ld at tim e , is th e e le c tric field ’ s m a xim um , ν 𝜈 is th e w a ve ’ s — th e n u m b er o f o s c illa tio n s in th e ele c tric fie ld p e r u n it tim e — a n d Φ is a th a t ac c o u n ts fo r th e fa c t th a t n ee d n o t h a ve a v a lu e o f z ero a t = 0. T h e id en tic a l eq ua tio n fo r th e m a g n etic fie ld is A t= A ms in (2 π ν t+ Φ ) w h ere is th e m a g ne tic field ’ s m a xim um a m p litu d e. O th er p ro p ertie s a ls o a re us e fu l fo r c h a ra c terizin g th e w a ve b eh a v io r o f ele c tro m a g n etic ra d ia tio n. T h e , 𝜆 , is d efin e d a s th e d is ta n c e b e tw e en s u c c es s iv e m a x im a (s e e F ig u re 1 0.1. 2 ). F o r u ltra vio le t a n d v is ib le ele c tro m a g n etic ra d ia tio n th e w a v elen g th u s u a lly is ex p res s e d in n a n o m e ters (1 n m = 1 0 – 9 m ), a n d fo r in fra re d ra d ia tio n it is ex p re s s ed in m ic ro n s ( 1 m m = 1 0 – 6 m ). T h e re la tio ns h ip b etw ee n w a v elen g th a n d freq u en c y is λ = c /ν A n o th e r u n it u s e fu l un it is th e , 𝜈 ¯, w h ic h is th e re c ip ro c a l o f w a ve le n g th ν¯=1/λ W a v en u m b e rs freq u en tly a re u s e d to c h a ra c terize in f ra red ra d ia tio n , w ith th e u n its g iv en in c m – 1. W h e n e lec tro m a g n e tic ra d ia tio n m o ve s b e tw e en d iffe re n t m ed ia — fo r ex a m p le , w h en it m o v es fro m air in to w a ter— its freq u en c y, 𝜈 , rem a in s c o n s ta n t. B e c a u s e its ve lo c ity d e p e n d s u p o n th e m e d iu m in w h ic h it is tra v elin g , th e e le c tro m a g n e tic ra d ia tio n ’ s w a ve le n g th , λ , c h a ng es. If w e re p la c e th e s p ee d o f lig h t in a v ac u u m , , w ith its s p e ed in th e m ed iu m , 𝑣 , th en th e w a ve le n g th is λ=𝑣 /𝜈 What is UV Spectroscopy? S p e c tro s c o p y is th e m e a s u re m en t a n d in terp re ta tio n o f e lec tro m a g n e tic ra d ia tio n a b s o rb ed o r em itted w h e n th e m o le c u les o r a to m s o r io n s o f a s a m p le m o v e fro m o n e en e rg y s tate to a n o th e r e n erg y s ta te. U V s p e c tro s c o p y is a typ e o f a b s o rp tio n s p e c tro s c o p y in w h ic h lig h t o f th e u ltra -v io let re g io n (2 0 0 -4 0 0 n m ) is a b s o rb e d b y th e m o lec u le w hic h re s u lts in th e e xc ita tio n o f th e ele c tro n s fro m th e g ro u n d s ta te to a h ig h e r en e rg y s tate. Principle of UV Spectroscopy 1. B a s ic a lly, s p e c tro s c o p y is re la te d to th e in tera c tio n o f lig h t w ith m a tter. 2. A s lig h t is a b s o rb ed b y m atter, th e res u lt is a n in c re a s e in th e e n erg y c o n ten t o f th e a to m s o r m o le c u les. 3. W h e n u ltra v io let ra d ia tio n s a re a b s o rb ed , th is res u lts in th e ex c ita tio n o f th e ele c tro n s fro m th e g ro u n d s ta te to w a rd s a h ig h er en e rg y s ta te. 4. M o lec u les c o n ta in in g π -e le c tro n s o r n o n b o n d in g e le c tro n s (n -e lec tro n s ) c a n a b s o rb en e rg y in th e fo rm o f u ltra vio le t lig h t to ex c ite th e s e e le c tro n s to h ig h er a n ti-b o n d in g m o lec ula r o rb ita ls. 5. T h e m o re e a s ily ex c ited th e e lec tro n s , th e lo n g er th e w a v ele n g th o f lig h t th ey c a n a b s o rb. T h ere a re fo u r p o s s ib le typ e s o f tra n s itio n s (π – π *, n – π *, σ – σ *, a n d n – σ *) , a n d th ey c a n b e o rd e red a s fo llo w s : σ – σ * > n – σ * > π – π * > n – π * 6. T h e a b s o rp tio n o f u ltra v io let lig h t b y a c h e m ic a l c o m p o un d w ill p ro d u c e a d is tin c t s p e c tru m th a t a id s in th e id en tif ic a tio n o f th e c o m p o u n d. Instrumentation or Parts of UV Spectroscopy Light Source T u n g s ten fila m e n t la m p s a n d H yd ro g en -D eu teriu m la m p s a re th e m o s t w id e ly u s e d a n d s u ita b le lig h t s o u rc es a s th e y c o ve r th e w h o le U V reg io n. T u n g s ten fila m e n t la m p s a re ric h in red ra d ia tio n s ; m o re s p ec ific a lly th ey e m it th e ra d ia tio n s o f 3 7 5 n m , w h ile th e in te n s ity o f H yd ro g e n -D e u te riu m la m p s fa lls b elo w 37 5 nm. Monochromator M o n o c h ro m a to rs g en e ra lly are c o m p o s ed o f p ris m s a n d s lits. M o s t o f th e s p e c tro p h o to m eters a re d o u b le b e a m s p ec tro p h o to m ete rs. T h e ra d ia tio n em itted f ro m th e p rim ary s o u rc e is d is p ers e d w ith th e h elp o f ro ta tin g p ris m s. T h e v a rio u s w a ve len g th s o f th e lig h t s o u rc e w h ic h a re s ep a ra te d b y th e p ris m a re th en s elec ted b y th e s lits s u c h th e ro ta tio n o f th e p ris m res u lts in a s eries o f c o n tin u o u s ly in c rea s in g w a v elen g th s to p a s s th ro u g h th e s lits fo r rec o rd in g p u rp o s es. T h e b ea m s e lec te d b y th e s lit is m o n o c hro m a tic a n d fu rth e r d ivid e d in to tw o b e a m s w ith th e h elp o f a n o th er p ris m. Sample and reference cells O n e o f th e tw o d ivid e d b e a m s is p a s s e d th ro u g h th e s a m p le s o lu tio n a n d th e s ec o n d b ea m is p a s s é th ro u g h th e re fere n c e s o lutio n. B o th s a m p le a n d refe re n c e s o lu tio n is c o n ta in e d in th e c ells. T h es e c e lls a re m a d e o f e ith e r s ilic a o r q u a rtz. G la s s c a n ’ t b e u s e d fo r th e c e lls a s it a ls o a b s o rb s lig h t in th e U V reg io n. Detector G e n era lly, tw o p h o to c ells s e rve th e p u rp o s e o f th e d e te c to r in U V s p ec tro s c o p y. O n e o f th e p h o to c e lls rec eive s th e b ea m fro m th e s a m p le c ell a n d th e s ec o n d d e tec to r rec eive s th e b ea m fro m th e re feren c e. T h e in ten s ity o f th e ra d ia tio n fro m th e re feren c e c ell is s tro n g er th a n th e b ea m o f th e s a m p le c e ll. T h is re s u lts in th e g en e ra tio n o f p u ls atin g o r a lte rna tin g c urren ts in th e p h o to c e lls. Amplifier T h e a ltern a tin g c u rren t g e n era ted in th e p h o to c e lls is tra n s ferred to th e a m p lifier. T h e a m p lifier is c o u p le d to a s m a ll s e rv o m e te r.  G e n era lly, th e c u rre n t g en era ted in th e p h o to c e lls is o f ve ry lo w in te n s ity, th e m a in p u rp o s e o f th e a m p lifier is to a m p lify th e s ig n a ls m a n y tim es s o w e c a n g et c lea r a n d rec o rd a b le s ig n a ls. Recording devices M o s t o f th e tim e a m p lifier is c o u p le d to a p en rec o rd e r w h ic h is c o n n e c ted to th e c o m p u ter. T h e c o m p u ter s to re s a ll th e d a ta g e n era te d a n d p ro d u c es th e s p e c tru m o f th e d e s ire d c o m p o u n d. Applications of UV Spectroscopy Detection of Impurities It is o n e o f th e b es t m e th o d s fo r th e d e te rm in a tio n o f im p u ritie s in o rg a n ic m o lec u le s. A d d itio n a l p ea k s c a n b e o b s erve d d u e to im p u ritie s in th e s a m p le a n d it c a n b e c o m p a red w ith th a t o f s ta n d a rd ra w m a teria l. B y a ls o m e a s u rin g th e a b s o rb a n c e a t a s p e c ific w a ve len g th , th e im p u rities c an b e d e tec te d. Structure elucidation of organic compounds It is u s e fu l in th e s tru c tu re elu c id a tio n o f o rg a n ic m o le c u les , s u c h as in d e te c tin g th e p re s en c e o r a b s e nc e o f u ns a tu ra tio n , th e p res e n c e o f h etero a to m s. 1. U V a b s o rp tio n s p ec tro s c o p y c a n b e u s ed f o r th e quantitative determination of compounds th a t a b s o rb U V ra d ia tio n. 2. U V a b s o rp tio n s p ec tro s c o p y c a n c h ara c te riz e th o s e typ e s o f c o m p o u n d s th a t a b s o rb U V ra d ia tio n th u s u s e d in th e q u a lita tiv e d eterm in a tio n o f c o m p o u n d s. Id en tif ic a tio n is d o n e b y c o m p a rin g the a b s o rp tio n s p ec tru m w ith th e s p ec tra o f know n co m p ound s. 3. T h is te c h n iq u e is u s ed to d etec t th e p re s en c e o r a b s e n c e o f a fu n c tio n a l g ro u p in th e c o m p o u n d. T he a b s e n c e o f a b a n d a t a p a rtic u la r w a ve len g th is re g a rd e d a s ev id e n c e fo r th e a b s en c e o f p a rtic u la r g ro u p. 4. K in etic s o f rea c tio n c a n a ls o b e s tu d ied u s in g U V s p ec tro s c o p y. T h e U V ra d ia tio n is p a s s ed th ro u g h th e rea c tio n c ell a n d the a b s o rb a n c e c h a n g e s c a n b e o b s e rv ed. 5. M a n y d ru g s a re eith e r in th e fo rm o f ra w m ate ria l o r in th e fo rm o f the fo rm u la tio n. T h ey c a n b e a s s a yed b y m a k in g a s u ita b le s o lu tio n o f th e d ru g in a s o lve nt a n d m ea s u rin g th e a b s o rb a n c e a t a s p ec ific w a v elen g th. 6. M o lec u lar w eig h ts o f c o m p o u nd s c a n b e m e a s u re d s p e c tro p h o to m etric a lly b y p re p a rin g th e s u ita b le d eriva tiv es o f th e s e c o m p o u n d s. 7. U V s p e c tro p h o to m eter m ay b e u s ed a s a d e tec to r fo r H P LC. High-performance liquidchromatography High-performance liquidchromatographyorcommonlyknownasHPLC, isananalyticaltechniqueusedtoseparate,identifyorquantifyeachcomponentina mixture. Themixtureisseparatedusingthebasic principleofcolumn chromatography and thenidentifiedand quantifiedbyspectroscopy. Inthe1960s, thecolumnchromatographyLCwithitslow-pressuresuitableglasscolumns wasfurtherdevelopedtotheHPLCwithits high-pressure adaptedmetal columns. HPLCisthusbasicallyahighlyimprovedformofcolumnliquidchromatography. Insteadofasolventbeingallowedtodripthroughacolumnunder gravity,it isforced throughunderhighpressuresofup to 400 atmospheres. HPLCPrinciple Thepurificationtakesplaceinaseparationcolumnbetweenastationaryandamobilephase. Thestationaryphaseisagranularmaterialwithverysmall porousparticlesinaseparationcolumn. Themobilephase,ontheotherhand,isasolvent orsolventmixturewhichis forcedathighpressurethroughtheseparation column. Viaavalvewithaconnected sampleloop, i.e. asmalltubeoracapillarymadeofstainlesssteel,thesampleisinjectedintothemobile phaseflowfromthepumptotheseparationcolumnusingasyringe. Subsequently, theindividual components ofthesamplemigratethroughthecolumnatdifferent ratesbecausetheyareretainedtoa varyingdegreebyinteractionswiththestationaryphase. Afterleaving thecolumn,theindividualsubstancesaredetectedbyasuitabledetectorandpassedonasasignaltotheHPLCsoftwareon thecomputer. Attheendofthisoperation/run, achromatogramintheHPLCsoftwareonthecomputerisobtained. Thechromatogramallowstheidentificationandquantificationofthedifferent substances. InstrumentationofHPLC Instrumentation of HPLC ThePump ThedevelopmentofHPLCledtothedevelopment ofthepumpsystem. Thepumpispositionedinthemostupperstreamoftheliquidchromatographysystemandgenerates aflowofeluent fromthesolvent reservoirintothesystem. High-pressuregenerationis a“ standard” requirementofpumps besideswhich, it shouldalsotobeabletoprovideaconsistent pressureatanyconditionandacontrollableandreproducibleflowrate. Mostpumps usedincurrent LCsystems generatetheflowbyback-and-forthmotionofamotor-drivenpiston(reciprocatingpumps). Becauseofthispistonmotion, it produces “ pulses”. Injector Aninjectorisplacednexttothepump. Thesimplestmethod istouseasyringe,and thesampleisintroducedtotheflowofeluent. Themost widelyused injectionmethodisbasedonsamplingloops. Theuseoftheautosampler(auto-injector)systemis alsowidelyusedthat allows repeatedinjectionsinasetscheduled-timing. Column Theseparationis performedinsidethecolumn. Therecentcolumns areoftenpreparedinastainlesssteelhousing,insteadofglasscolumns. Thepackingmaterial generallyusedissilicaorpolymergels comparedtocalciumcarbonate. TheeluentusedforLCvariesfromacidictobasicsolvents. Mostcolumnhousingismadeofstainless steelsincestainlessis tolerant towardsalargevarietyofsolvents. Detector Separationofanalytes is performedinsidethecolumn,whereasadetectoris usedtoobservetheobtainedseparation. Thecompositionoftheeluent isconsistent whennoanalyteispresent.Whilethepresenceofanalytechanges thecompositionofthe eluent. What detectordoesistomeasurethesedifferences. This differenceis monitoredasaformofanelectronic signal. Therearedifferenttypes ofdetectorsavailable. Recorder Thechangeineluent detectedbyadetectoris intheformofanelectronicsignal,and thusit isstill not visibletoour eyes. Inolderdays,thepen(paper)-chart recorderwas popularlyused. Nowadays, acomputer-baseddataprocessor(integrator)ismore common. Therearevarioustypesofdataprocessors;fromasimplesystemconsistingofthein-builtprinterandwordprocessorwhilethosewith softwarethat arespecificallydesignedforanLCsystemwhichnot onlydataacquisitionbut features likepeak-fitting, baselinecorrection, automaticconcentrationcalculation,molecularweight determination,etc. Degasser TheeluentusedforLCanalysis maycontaingasessuchas oxygenthat arenon-visibletooureyes.  Whengasis present intheeluent,thisisdetected asnoiseand causesanunstablebaseline. Degasserusesspecial polymermembranetubingtoremovegases. Thenumerousverysmallpores onthesurfaceofthepolymertubeallowtheairtogothroughwhilepreventinganyliquidtogothroughthe pore. ColumnHeater TheLCseparationisoftenlargelyinfluencedbythecolumntemperature. Inordertoobtainrepeatableresults,itisimportant tokeepconsistenttemperatureconditions. Alsoforsomeanalysis,suchassugarandorganicacid, betterresolutionscanbeobtainedat elevatedtemperatures (50to80° C). Thuscolumnsaregenerallykeptinsidethecolumnoven(columnheater). TypesofHPLC 1. Normalphase: Columnpackingispolar(e.gsilica)andthemobilephaseisnon-polar. Itisusedforwater-sensitivecompounds, geometric isomers, cis-trans isomers, andchiralcompounds. 2. Reversephase: Thecolumnpackingis non-polar(e.gC18),themobilephaseiswater+ misciblesolvent (e.g methanol). It canbeusedforpolar, non-polar,ionizable, andionic samples. 3. Ionexchange: Columnpackingcontainsionic groupsand themobilephaseisbuffer. It is usedtoseparateanionsandcations. 4. Sizeexclusion: Moleculesdiffuseintoporesofaporous mediumand areseparated accordingtotheirrelativesizetotheporesize. Largemolecules elutefirstand smallermoleculeselutelater. ApplicationsofHPLC TheHPLChasdeveloped intoauniversallyapplicablemethodsothatit findsits useinalmost all areas ofchemistry, biochemistry, and pharmacy. Analysis ofdrugs Analysis ofsyntheticpolymers Analysis ofpollutantsinenvironmental analytics Determinationofdrugs inbiological matrices Isolationofvaluableproducts Productpurityandqualitycontrolofindustrialproductsandfinechemicals Separationandpurificationofbiopolymerssuchas enzymes ornucleicacids Waterpurification Pre-concentrationoftracecomponents Ligand-exchangechromatography Ion-exchangechromatographyofproteins High-pHanion-exchangechromatographyofcarbohydratesandoligosaccharides GAS-LIQUIDCHROMATOGRAPHY Gas-liquid chromatography (oftenjustcalled gas chromatography) is a powerful toolin analysis. It has all sorts of variations in theway itis done-if you want full details,a Google search on gaschromatography will giveyouscaryamounts of information if you need it! This pagejust looksin a simple introductory way athowitcan be carried out. Carryingoutgas-liquidchromatography Introduction Allforms of chromatography involvea and a. In alltheother forms of chromatography you will meet atthis level,the mobilephaseis aliquid. In gas-liquid chromatography,themobilephaseis a gas such as heliumand the stationary phaseis a high boiling pointliquid adsorbed ontoa solid. Howfast a particular compound travels through the machine will depend on howmuch of its timeis spentmoving with thegas as opposed to being attached totheliquid in someway. Aflowschemeforgas-liquidchromatography Injection of the sample Very small quantities of the sample that you are trying to analyse are injected into the machine using a small syringe. The syringe needle passes through a thick rubber disc (known as a septum) which reseals itself again when the syringe is pulled out. The injector is contained in an oven whose temperature can be controlled. It is hot enough so that all the sample boils and is carried into the column as a gas by the helium (or other carrier gas). How the column works There are two main types of column in gas-liquid chromatography. One of these is a long thin tube packed with the stationary phase; the other is even thinner and has the stationary phase bonded to its inner surface. To keep things simple, we are just going to look at the packed column. The column is typically made of stainless steel and is between 1 and 4 metres long with an internal diameter of up to 4 mm. It is coiled up so that it will fit into a thermostatically controlled oven. The column is packed with finely ground , which is a very porous rock. This is coated with a high boiling liquid - typically a waxy polymer. The temperature of the column can be varied from about 50° C to 250° C. It is cooler than the injector oven, so that some components of the mixture may condense at the beginning of the column. In some cases, as you will see below, the column starts off at a low temperature and then is made steadily hotter under computer control as the analysis proceeds. One of three things might happen to a particular molecule in the mixture injected into the column: It may condense on the stationary phase. It may dissolve in the liquid on the surface of the stationary phase. It may remain in the gas phase. None of these things is necessarily permanent. A compound with a boiling point higher than the temperature of the column will obviously tend to condense at the start of the column. However, some of it will evaporate again in the same way that water evaporates on a warm day - even though the temperature is well below 100° C. The chances are that it will then condense again a little further along the column. Similarly, some molecules may dissolve in the liquid stationary phase. Some compounds will be more soluble in the liquid than others. The more soluble ones will spend more of their time absorbed into the stationary phase; the less soluble ones will spend more of their time in the gas. The process where a substance divides itself between two immiscible solvents because it is more soluble in one than the other is known as. Now, you might reasonably argue that a gas such as helium can't really be described as a "solvent". But the term is still used in gas-liquid chromatography. You can say that a substance partitions itself between the liquid stationary phase and the gas. Any molecule in the substance spends some of its time dissolved in the liquid and some of its time carried along with the gas. The time taken for a particular compound to travel through the column to the detector is known as its. This time is measured from the time at which the sample is injected to the point at which the display shows a maximum peak height for that compound. Different compounds have different retention times. For a particular compound, the retention time will vary depending on: the boiling point of the compound. A compound which boils at a temperature higher than the column temperature is going to spend nearly all of its time condensed as a liquid at the beginning of the column. So high boiling point means a long retention time. the solubility in the liquid phase. The more soluble a compound is in the liquid phase, the less time it will spend being carried along by the gas. High solubility in the liquid phase means a high retention time. the temperature of the column. A higher temperature will tend to excite molecules into the gas phase - either because they evaporate more readily, or because they are so energetic that the attractions of the liquid no longer hold them. A high column temperature shortens retention times for everything in the column. For a given sample and column, there isn't much you can do about the boiling points of the compounds or their solubility in the liquid phase - but you do have control over the temperature. The lower the temperature of the column, the better the separation you will get - but it could take a long time to get the compounds through which are condensing at the beginning of the column! On the other hand, using a high temperature, everything will pass through the column much more quickly - but less well separated out. If everything passed through in a very short time, there isn't going to be much space between their peaks on the chromatogram. The answer is to start with the column relatively cool, and then gradually and very regularly increase the temperature. At the beginning, compounds which spend most of their time in the gas phase will pass quickly through the column and be detected. Increasing the temperature a bit will encourage the slightly "stickier" compounds through. Increasing the temperature still more will force the very "sticky" molecules off the stationary phase and through the column. The detector There are several different types of detector in use. The flame ionisation detector described below is commonly used and is easier to describe and explain than the alternatives. In terms of reaction mechanisms, the burning of an organic compound is very complicated. During the process, small amounts of ions and electrons are produced in the flame. The presence of these can be detected. The whole detector is enclosed in its own oven which is hotter than the column temperature. That stops anything condensing in the detector. If there is nothing organic coming through from the column, you just have a flame of hydrogen burning in air. Now suppose that one of the compounds in the mixture you are analysing starts to come through. As it burns, it will produce small amounts of ions and electrons in the flame. The positive ions will be attracted to the cylindrical cathode. Negative ions and electrons will be attracted towards the jet itself which is the anode. This is much the same as what happens during normal electrolysis. At the cathode, the positive ions will pick up electrons from the cathode and be neutralised. At the anode, any electrons in the flame will transfer to the positive electrode; and negative ions will give their electrons to the electrode and be neutralised. This loss of electrons from one electrode and gain at the other will result in a flow of electrons in the external circuit from the anode to the cathode. In other words, you get an electric current. The current won't be very big, but it can be amplified. The more of the organic compound there is in the flame, the more ions will be produced, and so the higher the current will be. As a reasonable approximation, especially if you are talking about similar compounds, the current you measure is proportional to the amount of compound in the flame. The main disadvantage is that it destroys everything coming out of the column as it detects it. If you wanted to send the product to a mass spectrometer, for example, for further analysis, you couldn't use a flame ionisation detector. The output will be recorded as a series of peaks - each one representing a compound in the mixture passing through the detector. As long as you were careful to control the conditions on the column, you could use the retention times to help to identify the compounds present - provided, of course, that you (or somebody else) had already measured them for pure samples of the various compounds under those identical conditions. But you can also use the peaks as a way of measuring the relative quantities of the compounds present. This is only accurate if you are analysing mixtures of similar compounds - for example, of similar hydrocarbons. The areas under the peaks are proportional to the amount of each compound which has passed the detector, and these areas can be calculated automatically by the computer linked to the display. The areas it would measure are shown in green in the (very simplified) diagram. Note that it isn't the peak height that matters, but the total area under the peak. In this particular example, the left-hand peak is both tallest and has the greatest area. That isn't necessarily always so.  There might be a lot of one compound present, but it might emerge from the column in relatively small amounts over quite a long time. Measuring the area rather than the peak height allows for this. Coupling a gas chromatogram to a mass spectrometer This can't be done with a flame ionisation detector which destroys everything passing through it. Assuming you are using a non-destructive detector... When the detector is showing a peak, some of what is passing through the detector at that time can be diverted to a mass spectrometer. There it will give a fragmentation pattern which can be compared against a computer database of known patterns. That means that the identity of a huge range of compounds can be found without having to know their retention times. Thermogravimetric Analysis: Principle, Instrumentation, and Application Thermogravimetric analysis, a ls o kno wn a s TGA is a te c h n iq ue fre q u en tly use d in th e rm a l a n a lys is in w h ic h a c h a n g e in th e w eig ht o f a s u b s ta n c e is rec o rd e d a s a fu n c tio n of te m p e ra tu re or tim e. C o m p o s itio n , p urity, d ec o m p o s itio n p ro c es s e s , d e c o m p o s itio n tem p e ra tu res , an d a b s o rb ed m o is tu re c o n te n t a re am ong th e c h a ra c te ris tic s a n d b e h a vio r th a t c a n b e m e a s u red b y TGA. TGA is o n e of th e b es t m e th o d s fo r d eterm in in g th e th e rm a l c h a ra c te ris tic s of s u b s ta n c e s in c lu d ing c h em ic a ls , p h a rm a c eu tic a ls , an d m a terials m a d e o f p la s tic s , ela s to m ers , a n d th erm o s e ts a s w ell a s m in e ra l c o m p o un d s a n d c e ra m ic s. Types of thermogravimetric analysis TGA T h erm o g ra v im e tric m eth o d s a re c a te g o riz ed in to th re e typ e s : Static (isothermal) thermogravimetry: S u c h a m eth o d in v o lve s a na lys is in w h ic h th e s a m p le w eig h t is rec o rd e d a s a fu n c tio n o f tim e a t a c o n s ta n t te m p era ture. Quasistatic thermogravimetry: In th is typ e o f a n a lys is , th e s a m p le is h e a te d to c o n s ta nt w eig h t a t in c re as in g te m p era tu re. Dynamic thermogravimetry: T h e s a m p le is h e a te d in a c o n d itio n w h e re th e tem p e ra tu re is ris in g o r fa llin g a t a p re d e fin e d ra te, u s u a lly lin e a rly. M o s t s tu d ies u s in g th e th e rm a l te c h n iq u e o f a n a lys is a re typ ic a lly c o n d u c te d u s in g d yn a m ic th erm o g ra vim etric a n a lys is. Thermogravimetric analysis Principle TGA g ive s a q u a n tita tiv e e va lu a tio n o f a n y w e ig h t c h a n g es b ro u g h t o n b y th erm a lly in d u c ed tran s itio n. T h e m eth o d in vo lve s h e a tin g a s a m p le a t a c o n tro lled ra te i.e. fo r a s u b s ta n c e w ith a k n o w n in itia l w eig ht, th e te m p era tu re is ra is e d s tea d ily, a n d a t va rio u s tim e in terva ls , th e w eig h t c h a n g es a re re c o rd ed a s a fu n c tio n o f tem p e ra tu re. T h e re s u lts m a y b e p re s en ted in th e fo llo w in g tw o w a ys : a s a TG curve (th erm o g ra v im etric c u rve ) in w hic h th e w eig h t c h a n g e is rec o rd e d a s a f u n c tio n o f tem p e ra tu re o r tim e a s a T G c u rv e d eriva tive (D T G ) , w h ere th e T G c u rve ’ s firs t d e riv a tiv e is p lo tte d a g a in s t eith er te m p era tu re o r tim e. T h e g ra p h p lo tted is k n o w n a s th e p yro lys is c u rv e. D u e to th e d is tin c t o rd er o f p h ys ic a l tra n s itio ns a n d c h e m ic a l re a c tio n s th a t ta k e p la c e o v er s p ec ified tem p e ra tu re ra n g es , th e TG curve is u n iq u e to a g iv en s ub s ta n c e o r m a te ria l. B ec a u s e o f p h ys ic a l c h a n g e s a n d th e b u ild in g a n d b rea k in g o f c h em ic a l b o n d s a t h ig h tem p era tu res , w e ig h t c h a n g e s re s u lt. In eith er ine rt o r rea c tiv e a tm o s p h ere s , T G typ ic a lly o p e rate s in th e 1 2 0 0 oC te m p era tu re ran g e. T h e m o lec u la r s tru c tu re freq u en tly a f fec ts th e th erm a lly in d u c e d rea c tio n ra te s. A typ ic al TG curve fo r C u S O 4.5 H 2O c a n b e s h o w n a s : Figure : T h e g ra p h p res e n te d h e re c a n b e c a teg o rize d in to h o riz o n ta l a n d ve rtic al p o rtio n s. T h e h o rizo n ta l p o rtio n s s ig nify reg io n s w h ere th e re is n o w e ig h t lo s s , w h ile th e c u rv ed reg io n in th e v ertic a l p o rtio n in d ic a tes w e ig h t lo s s. T h e c a lc u la tio n s o n c o m p o u n d s to ic h io m e try c a n b e d o n e a t a n y tem p e ra tu re s in c e th e TG curve is a q u a n tita tiv e eq u a tio n. C u S O 4.5 H 2O c o n s is ts o f fo u r d is tin c t reg io n s o f d e c o m p o s itio n a s illu s tra ted b elo w : A d e riv a tiv e th e rm o g ra vim etric (D T G ) c u rve is p ro d u c e d b y p lo ttin g th e w eig ht c h a n g e o v er tim e (d W / d T ) v s tem p e ratu re. W h en th e re is n o w eig h t lo s s , d W / D T is eq u al to ze ro in th e D T G c u rv e. A m a xim u m s lo p e o n th e T G c u rve is re p res e n te d b y th e d e riv a tiv e c u rv e’ s p ea k. A s h ift in s lo p e o c c u rs o n th e TG curve w h e n d W / d T is m in im u m b u t n o t z ero , w h ic h is k n o w n a s a n in f le c tio n. Figure : Thermogravimetric analysis instrumentation T h e fu n d a m e nta l in s trum e n t n ee d e d fo r TG is a p re c is io n b a la n c e w ith a fu rn a c e d e s ig n e d to lin e arly in c rea s e tem p e ra tu re o v er tim e. T h e b lo c k d iag ra m fo r th e in s tru m en ta tio n o f TGA is illu s tra ted b elo w : Figure : T h e m a jo r c o m p o n e n ts o f th e th e rm o g ra v im e tric a n a lyze r (th e rm o b a la n c e) a re: B a la n c e F u rn a c e a s s e m b ly o S a m p le c o n tain e r, te m p era tu re s e n s o r, fu rn a c e lin er, th erm o c o u p le , etc. R e c o rd er a n d d is p la y A p u rg e g a s s ys tem fo r p ro v id in g a n in e rt a tm o s p h ere. T h e b a la n c e a n d th e fu rn a c e a s s em b ly a re th e tw o k ey c o m p o n e n ts o f th e rm o b a la n c e. A s h a llo w p la tin u m c ru c ib le (a ls o k n o w n a s a s a m p le c o n ta in e r) is u s e d to h o ld th e s a m p les a n d is c o n n ec te d to a n a u to m a tic re c o rd in g m ic ro b a la n c e. In th erm o g ra vim etry, n u ll p o in t b a lan c es a re th e m o s t o ften u s ed fo rm o f th e b a la n c e s ys tem. T h e n u ll p o in t a p p ro a c h c a u s es th e b a la n c e b e a m to m o v e a w a y fro m its n o rm a l p o s itio n w h e n ev er th ere is a c h a n g e in w eig h t. H e n c e, a s e n s o r d e te c ts th is d e via tio n a n d in itia tes a fo rc e th a t w ill res to re th e b a la n c e to th e n u ll p o s itio n. T h is res to rin g f o rc e is p ro p o rtio n a l to th e c h a n g e in w e ig h t. Some of the major requirements for the thermobalance are: S h o u ld b e a b le to m o n ito r th e c h a n g e in w eig h t o f th e s a m p le a s a fu n c tio n o f tem p e ra tu re. T h e ra te o f h ea tin g s h o u ld b e lin ea r. T h e s a m p le h o ld er s h o u ld b e in th e fu rn a c e’ s ho t zo n e, w h ic h s h o u ld h a ve a c o n s ta nt tem p e ratu re. T h e b a la n c e m e c h a n is m n ee d s to b e s h ield e d fro m c o rro s iv e g a s es a n d th e fu rn a c e. A c c u ra te m e a s u rem en t o f th e te m p e ra tu re o f th e s a m p le. Application of thermogravimetric analysis S o m e o f th e m a jo r a p p lic a tio n s o f T G A a re: T G A is u s ed fo r th e th e rm a l c h a ra c teriz a tio n o f p o lym e rs. D e term in a tio n o f th e c o m p o s itio n o f a llo ys a n d m ix tu re s. D e term in in g th e p u rity a n d th erm a l s ta b ility o f b o th p rim a ry a n d s ec o n d a ry s ta n d a rd s. It is em p lo ye d to in ve s tig a te th e m o is tu re c o n ten t o f s e ve ral in o rg a n ic an d o rg a n ic c o m p o n e n ts , in d u s tria l ra w m a teria ls , f o o d s , m ed ic a tio n s , etc. D e term in in g th e id ea l d ryin g te m p era tu re s a n d th e a p p ro p ria te n es s o f d if feren t w eig h in g m eth o d s fo r g ra vim etric a n alys is. U s e d fo r c o rro s io n s tu d ies. A ls o a p p lic a b le to th e s tu d y o f k in e tic o f is o th erm a l rea c tio n s. Advantages of TGA R a p id p ro c es s S h o rt c o o lin g tim e H ig h a c c u ra c y o f th e b a la n c e A fa s t h ea ting ra te w ith g o o d re s o lu tio n c a n b e m a in ta in e d. Limitations of TGA F o r b o th q u alita tiv e a n d q u a n tita tive a na lys is , o nly s o lid s a m p les a re a llo w ed. T G A d o e s n o t ex h ib it a n y c h em ic a l o r p h ys ic a l a lte ratio n s tha t d o n o t re s u lt in a c h a n g e in m a s s / w e ig h t w h e n h e a ted. C h a n g e in tem p e ra tu re a s a re s u lt o f b ein g s en s itiv e to h ea tin g ra te a n d s a m p le m a s s es. Lim ite d to s a m p les th a t u n d e rg o w eig h t c h a n g e. Scanning electron microscopy (SEM) ScanningElectronMicroscope(SEM) isatypeofelectronmicroscopethat scans surfacesofmicroorganismsthat usesabeamofelectronsmovingat lowenergyto focusand scanspecimens. Thedevelopmentofelectronmicroscopeswas duetotheinefficiencyofthewavelengthoflight microscopes. electronmicroscopeshaveveryshortwavelengthsincomparisontothelight microscopewhichenablesbetterresolutionpower. Thefirst Scanning ElectronMicroscope was initiallymadebyMafredvonArdennein1937withanaimtosurpass thetransmissionelectron Microscope. Heusedhigh-resolutionpowertoscanasmall rasterusingabeamofelectrons thatwerefocusedontheraster. Healsoaimedat reducingtheproblemsofchromaticaberrations images produced bytheTransmissionelectronMicroscopes. Morestudiesfollowedbyscientists andresearchinstitutions suchasCambridgeScientific InstrumentCompanywhoeventuallydevelopedafullyconstructed Scanningelectron Microscope, in1965andnamedit aStereoscan In an SEM, an electron beam is emitted from an electron gun, then narrowed to a size of approximately 0.4-5 nm in diameter through the use of one or two condenser lenses. The beam then passes through a pair of deflection coils in the electron column to deflect the beam in the x and y axes before interacting with the sample. This deflection ensures that the scan is in a raster fashion, which means it is a rectangular image capture pattern of the sample. When the electron beam interacts with the sample, it loses energy due to random scattering and absorption by the sample. A schematic showing the components of SEM and how it works is shown in Figure 1. Additionally, a video explaining how SEM works is provided. HowdoestheScanningElectronMicroscope(SEM)work? Thesourceoftheelectronsandtheelectromagnetic lensesarefrom tungsten filamentlamps thatareplacedatthetopofthecolumnand itissimilartothoseofthetransmissionelectronMicroscope. Theelectronsareemittedafterthermal energyisappliedtotheelectronsourceandallowedtomoveinafast motiontotheanode, which hasapositivecharge. Thebeamofelectronsactivates theemissionofprimaryscattered (Primary)electronsat highenergylevelsandsecondaryelectronsat low-energylevelsfromthespecimensurface. Thebeamofelectronsinteractswiththespecimentoproducesignalsthatgiveinformation about thesurfacetopographyandcompositionofthespecimen. Thespecimendoesnotneedspecial treatmentforvisualizationundertheSEM,evenair-driedsamples canbeexamineddirectly. However, microbial specimensneedfixation,dehydration,and drying inordertomaintainthestructural features ofthecells andtoprevent collapsingof thecells whenexposedtothehighvacuumofthemicroscope.  Thesamplesaremountedandcoatedwiththinlayerofheavymetalelementstoallowspatialscatteringofelectric chargesonthesurface ofthespecimenallowingbetterimageproduction,withhighclarity. Scanningbythis microscopeis attainedbytaperingabeamofelectrons backandforthoverathinsectionofthemicroscope. Whenthe electronsreachthespecimen, thesurfacereleasesatinystawofelectronsknownassecondaryelectronswhicharethentrappedbyaspecial detectorapparatus. Whenthesecondaryelectrons reachandenterthedetector,theystrikeascintillator(aluminescencematerial thatfluoresces whenstruck byachargedparticleorhigh-energyphoton). Thisemits flashesoflight whichget convertedinto anelectriccurrentbyaphotomultiplier, sending asignal to thecathoderaytube. Thisproducesanimagethat lookslikeatelevisionpicturethat canbeviewedand photographed. Thequantityofsecondaryelectronsthat enterthedetectorishighlydefinedbythenatureofthespecimeni.eraisedsurfaces to receive highquantities ofelectrons, enteringthedetectorwhiledepressedsurfaces havefewerelectrons reachingthesurfaceandhencefewer electronsenterthedetector. Thereforeraisedsurfaces willappearbrighteronthescreenwhiledepressedsurfacesappeardarker. PartsofaScanningElectronMicroscope(SEM) Themajorcomponents oftheScanningElectronMicroscopeinclude; ElectronSource– Thisiswhereelectronsareproduced underthermalheat at avoltageof1-40kV. theelectrons condenseintoabeam that isusedforthecreationofanimageandanalysis.Therearethreetypesofelectronsourcesthat canbeusedi.eTungstenfilament, Lanthanumhexaboride, andField emissiongun(FEG) Lenses– ithasseveralcondenserlensesthat focusthebeamofelectrons fromthesourcethroughthecolumnforminganarrowbeamof electronsthat formaspot calledaspot size. ScanningCoil – theyareusedtodeflectthebeamoverthespecimensurface. Detector– It’ smadeupofseveral detectors thatareabletodifferentiatethesecondaryelectrons,backscattered electrons, and diffracted backscatteredelectrons.Thefunctioning ofthedetectorshighlydependsonthevoltagespeed,thedensityofthespecimen. Thedisplaydevice(dataoutput devices) Powersupply Vacuumsystem LikethetransmissionelectronMicroscope, theScanningelectronmicroscopeshouldbefreefromvibrationsandanyelectromagnetic elements. ScanningElectronMicroscope(SEM)Images Figure: SEM image of Tradescantia pollen and stamens. Source: Wikipedia Figure: Low-temperaturescanningelectron micrographof soybeancyst nematode andits egg.Magnified 1,000 times.Source: Wikipedia Figure: Scanningelectronmicroscope image of a hederelloidfromthe Devonianof Michigan(largest tube diameter is0.75mm).Source: Wikipedia. Figure: Photoresist SEMmicrograph(1995) SEM= DSM982Gemini fromZeiss. Source: Wikipedia.