Week 3 - Analysis of Mixtures and Compounds PDF

CM8002 Forensic Science Analysis of Mixtures and Compounds explain how chromatography works, and three different types explain how to identify molecules using spectroscopy and spectrometry explain how to use “hyphenated techniques”  Forensic Scienc...

CM8002 Forensic Science Analysis of Mixtures and Compounds explain how chromatography works, and three different types explain how to identify molecules using spectroscopy and spectrometry explain how to use “hyphenated techniques”  Forensic Science Analysis of Mixtures and Compounds Analysis of fibres: cotton, wool, silk, polyester, nylon? if fibre has colour which dye is present : < made of diff coloured compounds Analysis of blood or urine from an athlete, drunk driver, drug user, suspicious death Analysis of suspected illegal drugs How many compounds in a mixture? Use Chromatography - Different components move at different speeds through an absorbent material (stationary phase). [ also called Components can be detected as they get to the end Movement is due to the flow of a liquid or gas (mobile phase) Thin Layer Chromatography (TLC) blank - Solvent TLC front plate phase) : where e stationary solvent to & end got thin absorbent layer usually silica or alumina inert backing e.g. glass -sample is placed here using a fine glass tube which is a capillary & submerged in mobile phase wait while i mobile phase travels up i The plate Thin Layer Chromatography Coloured compounds are visible to the eye Others can be made visible by chemical staining or under UV light from I TLC , there is unknown C one spot in standard A, B = standards that matchesI B & another that matches C = unknown e standard A > unknown a probably - includes standard compounds A &B PRESUMPTIVE TEST & not a definitive test , go on to do a definitive test impossible to have every cmpd showing a spot & at a diff positi on a small TLC plate & rate The 2 diff cmpds more save on & give spots I in same posit: Thin Layer Chromatography (TLC) unknown possibly same as cpdB ~ unknown contains there is spots match at least 4 components up terms in no CpdA of distance in unknown travelled ~ possibly save as upd standards Unknown mixture Gas Chromatography (GC) temp a ~ to contro Oven fine metal (steel) - tube ~ as solut (1) , sample is dissolved in solvent to make a sold diff components e in free mobile phase comes outo mixture separate as they a move diff speeds inside tube iscoated column ~ down e o absorbent material Islationary phases increasing time Gas Chromatography (GC) GC (oven door open) Gas Chromatography (GC) signal from recorder vs time 5 diff drugs solvent (can disregard) compare unknown to Hardard like TLC unknown sample time mixture of standards compare time retent I time : time of which they they (unknown us standard) come out of e column Quantitative: area under each peak proportional to amount of that compound (priminaly identificate) more accurate than The but not super accurate High Performance Liquid Chromatography (HPLC) Similar to GC, but using a liquid mobile phase solventswater & can be organic sample (as sol] bottle put liquid solvent of e pressure packed i stationary mobile which is phase an phase absorbent material sends diff components separate. as they flow through signal e column High Performance Liquid Chromatography (HPLC) Quantitative: area under each peak ~ presentia proportional to amount amount of that compound time HPLC vs. GC True for both methods efficient, highly selective, widely applicable only small sample required may be non-destructive of sample ~ can be used to determine readily adapted to quantitative analysis i art of I components high resolution present & unlike TLC both can distinguish compounds that are structurally similar , Advantages of HPLC ~ they don't more through of column can accommodate non-volatile and thermally unstable samples & of has reated over Advantages of GC simple and inexpensive equipment rapid use to avalyze of illegal drugs / suspected illegal drugs How do we tell what it is? L those components whether e spots or Th I - match standards by chromatographic comparison with authentic samples Istandard samples) ~ FR ↳ but this is not compare retent- by spectroscopy sufficiently times from o definitive toI court , a HPLC evidence , by spectrometry not ad leaves room for reasonable doubt Infra-red spectroscopy based on molecular vibrations (stretching and bending of chemical bonds) Stretching frequency depends on masses involved and stiffness of the bond but also various bending modes  diff molecular features absorb IR & vibrate& diff regt of Infra-red spectroscopy espectrum cm-1 Wareno. bonds to H triple double fingerprint region: (light weight!) bonds bonds single bonds and complex ~ 3000 crit (very stiff) + (stiff) deformations 2000 cm characteristic of the class of 1600 1700 characteristic of the individual ~ ~ - compounds, but not of the individual compound 1 cm - compound like a molecular fingerprint above below [ 1500 cm-1 3 take I unknown compas IP spectrum 2 = N < cyanide fingerprint regt a compares to standard If spectrum of known coupd's C =0 of interest Carbon monoxide) => if matches, I unknown upd it is I standard upd (strong conclusi Infra-red spectroscopy diamorphine diagnostic, (active component “fingerprint region” not characteristic of heroin)  Mass Spectrometry detectors acceleration by generate positive high voltage ions by electron (100 – 10,000V) bombardment (violent event as I the charged ions travel through MF they, are deflected from their introduce path & light weight in sample in vacuum are more strongly deflected sample is in magnetic field vaponvised then bombarded we light weight ion more strongly deflected heavy ion less strongly deflected can measure mass of ion f ↓ 1 art deflecti used to Molecular ion, M+ isI mass of molecular ion useful for cmpd ? identifyingI Yes & No  of molecule Molecular Weight ~ mass Cocaine is C17H21NO4 each Carbon = 12 Molecular weight: 17 x 12 = 204 Hydrogen = 1 21 x 1 = 21 Nitrogen = 14 1 x 14 = 14 Oxygen = 16 4 x 16 = 64 Total 303 only maybe But does not prove that it is cocaine Isomers have the same atoms, but in a different arrangement isoner of cocaine & e molecular of ion is insufficient to prove identity of a couped : looking mass Mass Spectrometry - fragmentation ~are much lighter & more fragments strongly deflected Most molecules will break up molecular in the spectrometer: ion isoner will fragmentation while each ion give ~ game molecular , each isovergive will a diff fragmentati pattern I mass spectrum including introduce all e fragments will act sample like a molecular fingerprint in magnetic field of e molecular , characteristic of that also defects diff fragments particular rather than molecule any of its isomers fragmentation mass amount of deflection  degree of deflect depends on moss-to-charge ratio (E) & usually I charge is Mass Spectrometry and Molecular Fingerprinting fragmentati ~ molecular ion F cocaine molecular ; fragmentate on ~ heroin GC-MS another hyphenated technique take i output of column in G2 & couple to MS & directly a use it as a detector Ms this gives you of each of components Gas Chromatography Mass Spectrometry combines separate & identificate into a single instrument GC-MS auto-sampler (robot) MS GC Analysis of Mixtures and Compounds Chromatography – separation of mixtures (TLC, GC, HPLC) Infra-Red –identification by molecular stretching and bending Mass Spec – identification by fragmentation Can combine GC-MS in one instrument