Recent GC-MS Studies of Different Elements

Aggarwal et al. recently implemented methods for the determination of isotope ratios and concentrations of different elements in biological specimens. Thermally stable and volatile chelates were identified for a number of trace elements Ni [43], Cr [45], Pt [46], Cu [33], Se [47], Co [48], Cd [49], Pb [44], Hg [50], and Te [51]. Memory effect was evaluated and found to be insignificant. Precision and accuracy in the measurement of isotope ratios was evaluated. Finally, the isotope dilution GC-MS method was validated by analyzing NIST reference materials (e.g., urine, semm), by comparing the results with ETAAS and by using the standard addition approach. 

Memory effect, due to the carryover of previously injected sample, leads to an isotope ratio different (lower or higher) from the true value in the sample. The presence of the memory effect limits the utility of determining isotope ratios in unknown samples. Hence, it is ideal to identify a suitable chelating agent for each element which does not show any significant memory effect circumventing these limitations. 

A rigorous approach to evaluate the memory effect is the sequential analyses of natural sample, enriched isotope (internal standard or tracer), and again the natural sample. As shown in Fig. 1, no measurable memory effect was observed for Hg [50], a small memory effect was seen for Cd 

Evaluation of cross-contamination in consecutive analyses of synthetic mixtures of Hg(FDEDTC)2 with isotopic ratio differing by a factor of 40. 

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