Permanent modification in electrothermal atomic absorption spectrometry - advances, anticipations and reality

Permanent modification is an important recent development in chemical modif ication techniques which is promising in view of increasing sample throughp ut with 'fast' programs, reducing reagent blanks, preliminary elimination o f unwanted modifier components, compatibility with on-line and in situ enri chment, etc. An overview of this approach based on the authors' recent rese arch and scarce literature data is given, revealing both success and failur e in studies with permanently modified surfaces (carbides, non-volatile nob le metals, noble metals on carbide coatings, etc.), as demonstrated in exam ples of direct electrothermal atomic absorption spectrometric (ETAAS) appli cations to biological and environmental matrices and vapor generation (VG)- ETAAS coupling with in-atomizer trapping of hydrides and other analyte vapo rs. Permanent modifiers exhibit certain drawbacks and limitations such as: poorly reproducible treatment technologies - eventually resulting in poor t ube-to-tube repeatability and double or multiple peaks; impaired efficiency compared with modifier addition to each sample aliquot; relatively short l ifetimes; limitations imposed on temperature programs, the pyrolysis, atomi zation and cleaning temperatures being set somewhat lower to avoid excessiv e loss of modifier; applicability to relatively simple sample solutions rat her than to high-salt matrices and acidic digests; side effects of overstab ilization, etc. The most important niches of application appear to be the u tilization of permanently modified surfaces in coupled VG-ETAAS techniques, analysis of organic solvents and extracts, concentrates and fractions obta ined after enrichment and/or speciation separations and direct ETAAS determ inations of highly volatile analytes in relatively simple sample matrices. (C) 2000 Elsevier Science B.V. All rights reserved.