Trace and Ultratrace Analysis of Lithium

High precision (2-7 %) is achieved by accumulation over 100 scans. Relative to the sensitivity of FDMS, the observed concentrations of lithium in mineral water are extremely high. The ion currents from l- d samples can be measured over several hours. Lithium at such levels can be determined by methods such as atomic absorption spectrophotometry (AAS) with approximately the same precision. Therefore, a comparison between the results of mineral water analyses by FDMS and AAS, gives evidence for the accuracy of both techniques (Table 7). 

Since the solutions studied contain only minor concentrations of accompanying substances, it is possible to determine lithium from microlitre samples at levels of 10 to 10 g/1 without any pretreatment. The time required for one analysis is about 20 to 30 min. In general, it is found that 1 pg of lithium present on the emitter is sufllcient for a determination. This means that lithium concentrations as low as SO ng/1 can be determined in microliter samples using stable isotope dilution and FDMS. 

In view of the influence of a complex matrix on the FD determination, e.g. in physiological fluids and tissues, and the importance of the use of lithium in medicine a further step was to exploit the utility of FDMS in combination w th signal accumulation and stable isotope dilution (internal standard) in this field. Lithium salts are used in the chemotherapy of manic-depressive psychoses . The transport phenomena of lithium through cell membranes and the mode of therapeutic action in elevated lithium levels are areas of biomedical research which are of special interest for the therapy of certain affective disorders. Concerning the accurate determination of very small lithium concentrations in the range of the normal physiological level, there is a special need for a reliable analytical technique, in particular, if only microliters of the sample are available. 

Water 1 Gerolsteiner Stem Heilwasser, Dolomitquelle, Gerolsteiner Sprudel GmbH  

Water 2 Gerolsteiner Stem Tafelwasser, Gerolsteiner Sprudel GmbH Water 3 Heilwasser Vulkania, Nurburg Quelle, H. Kreuter Co Water 4 Tap water of the Institute of Physical Chemistry, Bonn  

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Table 7. Trace- and ultratrace-analysis of lithium by FOMS . All samples are applied to the emitter by the syringe technique without pretreatment. For one analysis 1 /tl of mineral water and about 3 ftl of the other samples are needed...

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