Analytical Chemistry - Lesson 01 PDF

ANALYTICAL CHEMISTRY Chapter 1 Ma. Cecilia B. Bucasas, RCh Department of Chemistry College of Natural Sciences What is Analytical Chemistry? Analytical Chemistry Branch of Chemistry dealing with the chemical characterization of matter. Involves a range of techniques to...

ANALYTICAL CHEMISTRY Chapter 1 Ma. Cecilia B. Bucasas, RCh Department of Chemistry College of Natural Sciences What is Analytical Chemistry? Analytical Chemistry Branch of Chemistry dealing with the chemical characterization of matter. Involves a range of techniques to obtain and assess the: > qualitative; > quantitative; and, > structural information on the nature of matter.  Analytical Chemistry Involves separation, identification and determination of components in a sample.  Analytical Chemistry Chemical analyses can be selective or specific > selective – analysis that can occur with other substances but exhibits a degree of preference for the substance of interest or analyte > specific – analysis that can occur only for the substance of interest or analyte  The Chemical System Analyte: Specie of special interest Matrix: Part of sample outside the analyte  The Chemical System Analyte: Specie of interest Matrix: Part of sample outside the analyte Application and Importance  Application and Importance Quality control (QC); Monitoring and control of pollutants; Clinical and biological studies; Geological assays; and, Fundamental and applied research.  Analytical Methods Qualitative Methods “What is?” > Information about the identity of atomic or molecular species or the functional groups present in a sample. Quantitative Methods “How much?” > Numerical information as to the absolute or relative amounts of elements, species or compounds present in a sample.  Analytical Methods – performed either through wet-analysis or instrumental methods Wet-analysis – usually employs precipitation, titrimetric and gravimetric methods Instrumental methods – uses sophisticated instruments capable of measuring the analyte’s physical and chemical properties  Analytical Methods – can either be destructive or non-destructive analysis Destructive analysis – ends up consuming the sample or renders it unusable for the succeeding analyses; true for all, if not most, wet analyses Non-destructive analysis – renders the sample usable for the succeeding analyses as its composition are kept intact; true for some instrumental analyses  Analytical Methods According to amount of analyte or constituent present > Major – beyond 1% > Minor – 0.01 to 1.00% > Trace – less than 0.01%  Analytical Methods According to size of the sample > Macro – beyond 100 mg (or 100 μL)* > Semi-Micro – 10 to 100 mg (or 50-100 μL)* > Micro – 1.0 to 10 mg ( Ultramicro – less than 1.0 mg  Analytical Methods According to purpose > Proximate or partial – determines only a limited number of species in the sample > Ultimate – determines the amount of each element in the sample regardless of composition > Complete – determines the amount of each element in the sample present per composition  Analytical Methods Comparison of Different Analytical Methods Steps in Quantitative Analysis  Selecting a Method Some factors to consider: > The level of accuracy/ sensitivity required > Time and money available for the analysis > Tools and equipment available > The number/size/type of samples that will be analyzed > The complexity of the samples and the number of components in the sample  Sampling – requires proper storage and handling prior, during and after analysis to ensure stability of the sample – chain of custody should be observed Sampling Sampling Process  Sampling Process Gross Sample – representative sample obtained at the sampling site Laboratory Sample – homogenized gross sample brought in the laboratory Analysis Sample – portion of the laboratory sample used in the actual test method  Processing the Sample Sample pre-treatment – grinding and filtering – usually done on dry basis for solid samples to ensure accurate weight – dissolution to appropriate solvent – concentrating if the amount of the analyte is very low  Eliminating Interferences – done primarily to ensure elimination (or reduction) of interference in the sample > Selecting a method specific to the analyte > Masking – elimination of an interference from a substance by converting it to a non-interfering form > Separation – can be done by precipitation, electrodeposition, extraction, ion exchange, volatilization or chromatography  Calibration Calibration – process of standardizing analysis output or instrument readout – described by a calibration curve calibration curve – a plot of instrument response as a function of concentration  Calibration – achieved by using the method of standard addition standard addition – a given amount of sample is “spiked” with a known amount of standard and any increase in signal due to the added standard is observed  Calculating Results Series Series Series To calculate final results, take into 1 2 3 account the following: Item 1 > Stoichiometry of the reactions involved Item 2 in the analysis > Relationship of the gathered data to the Item 3 property being measured --> check for Item 4 equations from literature or derive when necessary  Estimating Reliability of Results Estimate reliability of results using statistical tests suitable for the data gathered and treatments employed in the analysis. THANK YOU