Abstract: Whereas flame atomic absorption spectrometry (AAS) lacks sensitivity at analyte concentrations below 0.1 and 10 µg g-1 in analyzes of liquid and solid samples, respectively, two modern AAS techniques with better detection power for quantitation at nanogram and picogram levels are employed: electrothermal AAS (ETAAS) and vapor generation AAS (VGAAS), viz. hydride generation AAS (HGAAS) or cold vapor technique for mercury (CVAAS). In this overview are discussed and illustrated the scope, merits, sample pretreatment requirements, methodological considerations and limitations of ETAAS, VGAAS and their recent hyphenations with each other (e.g. the VG-ETAAS coupling with in-atomizer trapping of hydrides and vapors) and with other separation/enrichment analytical techniques, aimed at solving important analytical problems of elemental trace analysis, microanalysis, speciation, etc. Optimum application fields are defined and examples from the authors recent research with biological and environmental matrices are given.

Abstract: Permanent modification is an important recent development in chemical modification techniques which is promising in view of increasing sample throughput with fast programs, reducing reagent blanks, preliminary elimination of unwanted modifier components, compatibility with on-line and in situ enrichment, etc. An overview of this approach based on the authors recent research and scarce literature data is given, revealing both success and failure in studies with permanently modified surfaces (carbides, non-volatile noble metals, noble metals on carbide coatings, etc.), as demonstrated in examples of direct electrothermal atomic absorption spectrometric (ETAAS) applications to biological and environmental matrices and vapor generation (VG)-ETAAS coupling with in-atomizer trapping of hydrides and other analyte vapors. Permanent modifiers exhibit certain drawbacks and limitations such as: poorly reproducible treatment technologies - eventually resulting in poor tube-to-tube repeatability and double or multiple peaks; impaired efficiency compared with modifier addition to each sample aliquot; relatively short lifetimes; limitations imposed on temperature programs, the pyrolysis, atomization and cleaning temperatures being set somewhat lower to avoid excessive loss of modifier; applicability to relatively simple sample solutions rather than to high-salt matrices and acidic digests; side effects of overstabilization, etc. The most important niches of application appear to be the utilization of permanently modified surfaces in coupled VG-ETAAS techniques, analysis of organic solvents and extracts, concentrates and fractions obtained after enrichment and/or speciation separations and direct ETAAS determinations of highly volatile analytes in relatively simple sample matrices.

Abstract: Analytical procedures for direct electrothermal atomic absorption spectrometric (ET-AAS) determination of selenium in urine, blood serum and solubilized hair, employing rhodium modifier (10-20 mug) in a transverse-heated graphite atomizer (THGA) with integrated pyrolytic graphite-coated platform and longitudinal Zeeman-effect background correction were developed. Results for urine were compared with flow injection hydride generation with in-atomizer trapping of hydrogen selenide in Ir-Zr treated THGA (FI-HG-ET-AAS) and with continuous flow hydride generation coupled with a non-dispersive atomic fluorescence spectrometry (CF-HG-ND-AFS). Two different bomb decompositions proved useful: (i) urine sample (1 ml) soaked overnight with HNO3, followed by pressurized digestion with HNO3 in a microwave oven, then H2O2 added, and bomb decomposition completed with HNO3-H2O2, then selenium pre-reduced to Se(IV) in 4.8 M HCl; and (ii) sample (1 ml) soaked overnight with HBr-BrO3-, then pressurized digestion in a microwave oven, followed by quantitation by FI-HG-ET-AAS or CF-HG-ND-AFS with standard addition calibration. Several certified reference materials (urine, blood serum and hair) as well as the NIES candidate CRM No. 18 Human Urine from the National Institute of Environmental Studies (NIES) (Tsukuba, Japan) were analyzed and the results are in agreement between techniques and with certified values. Preference is given to the direct ET-AAS determination of Se in biological liquids after two- to threefold dilution in the presence of 10 µg of Rh. Pyrolysis and atomization temperatures are within 1100-1200°C and 2100-2200°C, respectively, and the end-capped graphite tubes are preferred for better sensitivity and lower background absorbance. The limits of detection of the direct ETAAS are approximately 6 ng mL-1 Se in biological fluids. For 24 paired samples of blood serum and urine from non-exposed individuals (Sofia, Bulgaria), selenium levels are: serum 66.5±15.5 (45.5-116.4) ng mL and urine 16.8±8.1 (6.0-41.9) ng ml-2. (C) 2001 Elsevier Science B.V. All rights reserved.

Abstract: 1. Aims and scope 2. Modern flow techniques in VGAAS (FI-VGAAS and CF-VGAAS) 3. On-line decompositions (FI-MWD-VGAAS, CF-MWD-VGAAS, FI-UV-VGAASetc.) 4. On-line pre-reduction 5. On-line pre-concentration and separation (FI-VG-ETAAS, FI-ion-exchange-VGAAS, HG-CT-AASetc.) 5.1 VG-ETAAS 6. Hyphenated techniques for speciation analysis (VG-CT/GC-AAS, HPLC-VGAAS, HPLC-UV-VGAAS, HPLC-MWD-VGAASetc.) 6.1 On-line speciation by non-chromatographic HGAAS techniques 6.2 Coupling with GC 6.3 Coupling with HPLC 6.3.1 Scope, sensitivity and LODs 6.3.2 Hardware complexity 6.3.3 Mercury speciation 6.3.4 Availability and validation 7 Conclusion 8 References

Abstract: A review is presented of developments in the determination of 52 elements by the cited technique. Instrumentation, chemical modifiers, reaction media, sample decomposition, atomizer design, fast temperature programmes, in-situ ashing, flow injection pre-concentration and element speciation are critically discussed with respect to occupational and environmental health applications. (170 references).