ATOMIC SPECTROMETRY UPDATE - ATOMIC MASS-SPECTROMETRY

The format used for this annual review is broadly similar to that used last year with some refinement of headings. This update is intended t o cover all atomic stable isotopic MS techniques but not those used in studies of fundamental nuclear physics and 'exotic' nuclei far from s tability. Also excluded are those reports in which MS is used as a too l in the study of molecular processes or of gaseous components. The re view is based on critical selection of developments in instrumentation and methodology, notable for their innovation, originality or achieve ment of significant advances and is not intended to be comprehensive i n its coverage. Conference papers are only included if they contain en ough information to show they meet these criteria and our policy in ge neral remains one of waiting for a development to appear in a full pap er before inclusion in the review. A similar policy applies to those f oreign language papers unlikely to reach a wide audience. Routine appl ications of atomic MS are not included in this update and the reader i s referred to the updates on industrial analysis: metal, chemicals and advanced materials, environmental analysis and clinical and biologica l materials, food and beverages. Also excluded are those applications, even if not routine, which use atomic spectroscopy as a tool for the study of a non-atomic property, for example the use of stable isotope labelling of carbon or nitrogen in biomolecules in metabolic studies. There have been no general reviews on atomic MS of note in the period covered by this update. The book of Boutton and Yamasaki was notable, however, in that it gave a good comprehensive coverage in all MS techn iques used in the study of soils. The basic principles and operation o f each technique were described and examples of application given and the book would therefore be of interest and value to a wider readershi p than soil scientist alone. The Proceedings of the Seventh National S ymposium on Mass Spectrometry contained 30 invited papers and over 100 other contributions covering all aspects of MS, including most of the topics covered in this update. The invited speakers were leading rese archers who presented useful reviews of their areas of study. Several of the techniques covered in this update have found use in the analysi s of isotopic tracers used in metabolism studies. Yergey has reviewed (59 references) and discussed the individual advantages and limitation s of the four analytical techniques available for these studies: fast atom bombardment mass spectrometry (FABMS), gas chromatography mass sp ectrometry (GC-MS), inductively coupled plasma mass spectrometry (ICP- MS), and thermal ionization mass spectrometry (TIMS). The review of th e literature in the period covered by this update reveals strong advan ces in all areas with a continuing drive to achieve better analyses on smaller samples and in less time. Although significant advances in in strumentation and methodologies have been reported, the underlying tre nds are dominated by new and improved methods of sample introduction a nd, in particular, the coupling of chromotographic techniques with ato mic MS. The use of HPLC coupled with MS techniques has opened up new a reas of speciation studies which could be considered to be on the frin ges of atomic spectroscopy. In some applications the MS has in effect become a very sophisticated detector for the chromatographic technique s. In many applications, however, MS adds value to the analysis with a dditional information. Indeed MS is vital for the information obtained and it is therefore important to optimize instrumental operation and analytical methodologies for the coupled role. This is illustrated wel l by the increasingly reported use of electrospray mass spectrometry ( ESMS) which can provide either elemental or speciation information dep ending on the instrumental settings used. This information is given wh en coupled to high performance liquid chromatography (HPLC), capillary electrophoresis (CE) and ion chromatography (IC) or significantly, wh en operated alone. This dual role, elemental and speciation analysis, does bring into question whether this can be considered as true atomic spectroscopy. Glow discharge mass spectrometry (GDMS) continues to be an area of very active development. Instrumental modifications have i ncluded the coupling of an interchangeable GD/ICP source to a sector i nstrument in which the entire GD discharge chamber was inserted on a p robe, fitting of rf GD sources to sector instruments, coupling of GD s ources with ion traps and placing GD sources inside a Fourier transfor m ion cyclotron resonance mass spectrometer FTICR-MS. The last instrum ent required pulsed gas introduction to reduce the gas load. Microseco nd pulsed GD sources have received considerable attention, in particul ar for coupling with a time-of-flight (TOF) MS. Although the rf GD wou ld seem to be the method of choice for the analysis of non-conducting materials, the lack of availability of commercial instrumentation has directed researchers to the use of secondary cathodes with flat sample s in the dc GD. Some groups have made significant progress in developi ng the mathermatical modeling of the GD plasma (and plasmas in general ) to gain a better understanding of fundamental ion production process es. The aim is to be able to perform accurate analysis without the use of RMs. The use of cyclotrons continues to hold promise for smaller a ccelerator mass spectrometers (AMS) but progress appears to be slow. T he first reported coupling of an ICO source to AMS presents the possib ility of a new area of study. The rapid development and growth in appl ications of the GC-combustion-stable-isotope ratio mass spectrometry ( SIRMS) technique over a short period of time has been notable to such that it could almost be considered a conventional technique. Alternati ve interfaces are being developed for coupling both GC and LC to SIRMS and the scope for further growth appears to be considerable. The use of SIRMS for authenticity testing has also grown considerably. The per formance of high abundance sensitivity TIMS instruments continues to b e highly impressive. Replacing conventional Faraday cup detectors with charge collector devices has allowed noise levels and sensitivities t o be improved considerably. The unconventional isotope dilution (ID) d etermination of nitrate by TIMS and the use of direct loading procedur es are examples of the versatility of the technique.