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Large-volume injection using a system consisting of packed column GC, serially connected to capillary GC, and coupled to a microwave-induced plasma atomic emission spectrometric (MIP-AES) detector is described. The greater sample capacity of the packed column is exploited to allow large-volume injections to be accommodated. Preliminary chromatographic separation of the solvent and mercury species on the packed pre-column permits selective transfer of the analytes to a capillary GC system. There, the mercury species can be focused and further separated on the analytical column, minimizing the risks of extinguishing the plasma due to excess solvent reaching the MIP, and stationary phase or detector fouling, which accompany large-volume injections using alternative methods. Application to the determination of mercury species in natural waters following solid-phase extraction on a dithiocarbamate resin, elution into acidic thiourea, complexometric extraction into hexane and Grignard derivatization is used to illustrate the benefits and limitations of this approach. The relative limit of detection obtained for methylmercury is 8 pg 1-1 utilizing 50 pl injection on to the packed pre-column, compared with 40 pg 1-1 for direct injection of 13 pl into the capillary GC-MIP-AES system. This improved performance has enabled more detailed kinetic studies of the uptake of methylmercury from humic-rich natural waters on the dithiocarbamate resin to be undertaken, and shows that incipient and added analyte behave differently during enrichment, which may have implications for the use of spiking during method development.

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A key comparison on the determination of ethanol in aqueous matrix has been successfully completed. Nine national metrology institutes (NMIs) participated in this key comparison and used the techniques of gas chromatography with flame ionization detection (GC-FID), isotope dilution gas chromatography–mass spectrometry (GC-IDMS), gas chromatography–combustion–isotope ratio mass spectrometry (ID-GC-C-IRMS) and headspace-GC-FID for the determinations. Three samples were distributed to participants. Two of these samples (Samples A and B) were aqueous solutions that had been spiked gravimetrically with ethanol (at mass fractions of ethanol representing forensic standards, CCQM-K27a), the other (Sample C) was a commercial (red) wine (representing a traded commodity, CCQM-K27b). The KCRV for Sample A is 0.8040 ± 0.0080 mg g-1, that of Sample B is 120.90 ± 0.35 mg g-1 and that of Sample C is 81.23 ± 0.24 mg g-1 of ethanol in the appropriate aqueous matrix. These results are an improvement over those of the corresponding pilot study (CCQM-P35). The RSD for Sample A is 1.5% compared to 2.3% for a similar mass fraction for the pilot study. For the wine sample (Sample C) corresponding RSDs are 0.44% for this key comparison and 2.3% for the pilot study. This demonstration of capability will enable forensic ethanol standards to be compared across national boundaries. Likewise the ability to measure the typical mass fraction of ethanol found in wine is important since such commodities are traded worldwide and are liable to varying levels of excise duty. Thus this successful key comparison has demonstrated a broad range of capability by NMIs for the measurement of ethanol for both forensic and excise purposes.Main text. To reach the main text of this paper, click on Final Report.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the Mutual Recognition Arrangement (MRA).

A procedure was established for the determination of ethanol in water samples by isotope dilution analysis. After spiking the sample with labelled [13C2]ethanol, it was analysed by gas chromatography-combustion-isotope ratio mass spectrometry. Results are reported for two certified reference materials and also ethanol solutions prepared for a CITAC (Co-operation on International Traceability in Analytical Chemistry) interlaboratory comparison. The certified reference materials were certified using the dichromate titration method at nominal levels of 80 and 200 mg per 100 mL. The CITAC solutions were prepared gravimetrically at nominal levels of 50, 80 and 200 mg per 100 mL. The results of the analysis agree well to within 0.5% of the gravimetric values of the different samples. The relative expanded standard uncertainties (with a coverage factor equal to 2) associated with the results varied between 0.18 and 0.37%, a range that encompassed the gravimetric values for the different samples. A complete uncertainty budget was also drawn up so that the different contributions could be identified and quantified. The main contributions were due to variations in the measured isotope amount ratios and a 'between' blend component introduced to quantify the contribution of factors such as the degree of matching of the isotope amount ratios between standards and samples used in the isotope dilution analysis.

A thermal ionization mass spectrometric procedure was developed for the measurement of platinum. Single-and double-filament techniques were investigated. Negative Pt ions were produced in the source of a thermionic quadrupole mass spectrometer equipped with a secondary electron multiplier operated in ion counting mode. A high-purity platinum aqueous solution of natural isotopic composition was used as sample on a rhenium filament. This method allows the natural amount ratio of the major isotopes n( 194 Pt)/n( 195 Pt) to be measured with a repeatability of 0.3%.