Eva M. Krupp

Potential and limits of speciated isotope-dilution analysis for metrology and assessing environmental reactivity

This paper describes the application of isotopically labelled elemental compounds for species-specific isotope-dilution (ID) analysis and for species transformation evaluation with the focus on organotin species and methylmercury in both analytical and environmental studies. Among others, the accurate measurement of organometallic compounds (speciation) in environmental samples can be hampered by processes such as incomplete extraction from solid samples, material loss, rearrangement reactions during extraction and/or derivatization, low recoveries, and signal drift. All these undesirable effects, with the exception of incomplete species extraction from the sample matrix, can be studied and/or corrected for using speciated ID analysis (IDA). The use of compounds enriched in stable isotopes with subsequent detection by inductively coupled plasma mass spectrometry (ICP-MS) is a powerful tracer technique to study dynamic environmental processes. We also present an overview of other work published in this area. We discuss limitations of the applicability of speciated IDMS.

Isotopic precision for a lead species (PbEt4) using capillary gas chromatography coupled to inductively coupled plasma-multicollector mass spectrometry

Precision and accuracy of lead isotope ratios of a volatile lead species (PbEt4) were determined by coupling a capillary GC to a magnetic sector multicollector ICP-MS. PbEt4 was prepared by ethylation of a certified lead isotope solution (NIST SRM 981). Coupling was achieved by a transfer line, which allowed simultaneous introduction of a thallium standard solution to correct for mass discrimination. Seven isotopes (202Hg, 203Tl, 204Pb, 205Tl, 206Pb, 207Pb, 208Pb) were monitored simultaneously with a transient resolution of 50 ms. Pb isotope ratios for the PbEt4 peaks were calculated using transient peak integrals of each isotope signal. Absolute detection limits were 20 (204Pb), 0.7 (206Pb), 1 (207Pb) and 0.3 pg (208Pb). Precision was assessed for five replicate injections of PbEt4 in iso-octane, corresponding to a total amount of 300 pg of Pb. Precision of isotope ratios for 206Pb, 207Pb and 208Pb were better than 0.07% (RSD), with ratios including 204Pb being one order of magnitude worse. Accuracy using mass bias correction via 203Tl/205Tl ranged from 0.18% for 208Pb/206Pb to 0.9% for 208Pb/204Pb.

Optimisation of the hyphenation between solid-phase microextraction, capillary gas chromatography and inductively coupled plasma atomic emission spectrometry for the routine speciation of organotin compounds in the environment

The hyphenation between solid-phase microextraction, gas chromatography and inductively coupled plasma atomic emission spectrometry (SPME-GC-ICP-AES) has been developed for the speciation of butyl- and phenyltin compounds in sediment and water samples. Factors determining the GC-ICP-AES analysis were optimised by an experimental design approach to evaluate critical parameters influencing the overall analytical performance system. Quasi-dry plasma conditions and a high helium carrier gas flow rate were required to obtain maximum performance in terms of sensitivity. The use of SPME to preconcentrate the analytes allowed detection limits within 1 to 42xa0ngxa0(Sn)xa0l−1 to be obtained for water samples. Validation of the technique was performed by the analysis of certified reference sediment (PACS 2) and a wastewater sample.

Rapid, accurate and precise determination of tributyltin in sediments and biological samples by species specific isotope dilution-microwave extraction-gas chromatography-ICP mass spectrometry

The rapid and precise determination of tributyltin (TBT) in sediments and biological tissues has been performed by species specific isotope dilution mass spectrometric analysis (IDMS) using an inductively coupled plasma mass spectrometer as detector after capillary gas chromatography (CGC-ICP-MS). A new labelled TBT standard (117TBTCl in methanolic solution) commercial isotope provided by LGC Limited (Teddington, UK) was used for these determinations. Parameters affecting the ICP-MS performances, such as correction for detector dead time and mass bias correction, were carefully studied. The mass bias was corrected using two different methods: the bracketing mode and an on-line mode based on a continuous nebulisation of an antimony solution (121Sb and 123Sb). The on-line mode has been successfully applied for mass bias corrections and allows simultaneous GC-ICP-MS analysis of organotins. Three spiking procedures were compared using isotopically enriched TBT (117TBT) to compare the efficiency of the extraction procedures for the different samples studied. A rapid method was developed (2 min) giving yield to good precision (uncertainty range between 0.7 and 13.7%) using a simultaneous microwave extraction and spiking procedure. The accuracy and precision of the different protocols has been validated on certified reference materials, such as PACS 2 (980 ng Sn g−1) and CRM 462 (70 ng Sn g−1) for the sediments, CRM 477 (2200 ng TBT g−1) and CRM 710 (135.1 ng TBT g−1) for the biological tissues. The results obtained were in all cases in good agreement with the certified reference values.