Absorption Analytical Techniques - Instrumental Analytical Chemistry - Lecture Slides, Slides of Analytical Chemistry

Download Absorption Analytical Techniques - Instrumental Analytical Chemistry - Lecture Slides and more Slides Analytical Chemistry in PDF only on Docsity! Atomic Absorption Spectrometry Atomic Absorption Analytical Techniques Docsity.com Sample Preparation 1. Flame Spectroscopic Methods Sample materials: • Soils • Animal tissues • Plants • Petroleum products • Minerals Common problem: most are insoluble in aqueous solutions so preliminary treatment to the sample is required Docsity.com Sample Introduction by Flow Injection • Introduce samples into a flame atomic absorption spectrometer • Peristaltic pump and valve arrangements help insure efficiency while conserving the sample • Carrier system: Deionized water or diluted electrolyte are used to provide continuous flushing of the flame atomizer • This reduces build up from samples containing high levels of salts or suspended solids Docsity.com Organic Solvents Low Molecular-weight organic solvents: 1. Alcohols 2. Esters 3. Ketones Why Organic Solvents? 1. Increased nebulizer efficiency- increases the amount of sample that reaches the flame 2. Rapid evaporation of the solvent Solvent Ratios: Leaner fuel-oxidant ratios must be used to offset the presence of any added organic material • This produces lower flame temperatures, which can increase the potential for chemical interferences Docsity.com Organic Solvents (cont.) Immiscible Solvents ex: Methyl isobutyl ketone • These solvents extract chelates of metallic ions – The resulting extract in then nebulized directly into a flame • Enhance absorption lines • Only small amounts are required to extract from relatively large volumes of aqueous solutions • Enhance the sensitivity of the sample, which reduces interferences Common Chelating Agents- 1. Ammonium pyrrolidinedithiocarbamate 2. Diphenylthicarbazone 3. 8-hydroxyquinoline 4. Acetylacetone Docsity.com Application of AAS • Sensitive men for the quantitative determination of more than 60 metals or metalloid elements Table 9-3 shows Detection Limits Columns 2 & 3 present detection limits for a number of common elements by flame and electrothermal atomic absorption Detection Limits 1. Flame Atomization: 0.001 – 0.020 ppm 2. Electrothermal Atomization: 2 x 10-6 – 1 x 10-5 ppm Accuracy Relative error • Flame Analysis: 1-2 % • Electrothermal Analysis: errors extend flame errors by a factor of 5-10 Docsity.com 9D ATOMIC ABSORPTION ANALYTICAL TECHNIQUES Docsity.com 9D-1 Sample Preparation • Sample has to be introduced into the excitation in the form of a solution (disadvantage).  Many materials are not soluble in common solvents; extensive treatment is required. – Treatment with hot minerals, oxidation with liquid reagent, ashing at high temperature, etc. • Some minerals can be atomized directly. Solid samples are weighed into cup-type atomizers (advantage). Docsity.com 9D-4 Calibration Curves • Theory is that calibration curves should follow Beer’s Law which does not happen very often • Absorbance should be directly proportional to concentration • Use two standards that bracket the concentration of the analyte. Docsity.com 9D-5 Standard Addition Method • Should use method found in Section 1D-3 • Need to compensate for chemical and spectral interferences of the sample Docsity.com 9D-6 Application of AAS • A sensitive way of determining 60 metals and metalloid elements Detection Limits • Flame Atomization Atomic Absorption Spectroscopy are in the range of 1-20ng/mL,or .001-.020ppm • Electrothermal Atomization are in the range of .002- .01ng/mL or 2x10-6 - 1x10-5ppm Accuracy • Error in Flame Ionization Atomic Absorption Spectroscopy 1-2% • Electrothermal Atomization increase by a factor of 5-10 Docsity.com