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Two different approaches for the derivatisation of selenomethionine and detection by gas chromatography-inductively coupled plasma mass spectrometry (GC-ICP-MS) are compared and applied for the determination of the amino acid in pharmaceutical preparations used as selenium nutritional supplements. The first derivatisation is accomplished in two steps, starting with the esterification of the carboxylic acid group of the seleno-amino acid using propan-2-ol, followed by the acylation of the amino group with trifluoroacetic acid anhydride. Alternatively, the ethyl chloroformate–ethanol method was carried out for the simultaneous esterification and acylation steps catalysed by a pyridine solution. The derivatives were finally extracted into chloroform and injected into the gas chromatograph. The different parameters affecting the efficiency of both derivatisation approaches were optimised, as well as the instrumental operating conditions. Standard GC-MS chromatograms and mass spectra for both derivatisation procedures were also obtained to confirm the structure of the corresponding derivatised amino acids. The propan-2-ol–trifluoroacetic acid anhydride procedure was finally selected and was used to determine selenomethionine in a parenteral solution by GC-ICP-MS. The advantages and disadvantages of both procedures are discussed.

The analytical potential of complementary chromatographic separations such as size exclusion (SEC) plus anion-exchange chromatography coupled with inductively coupled plasma time-of-flight mass spectrometry (ICP-TOF-MS), was evaluated for the multi-elemental speciation of trace elements associated with methallothionein-like proteins (MLPs) in mussel hepatopancreas. The initial separation of the proteins is performed by 'off-line' SEC, collecting fractions which are then analysed for the trace elements by ICP-TOF-MS in small sample volumes. Further purification is accomplished by the separation of the different proteins contained in the above obtained MLP fraction on a Mono Q (HR 5/5) anion-exchange column [fast protein liquid chromatography (FPLC)], using an ammonium acetate gradient at a physiological pH of 7.4 as the mobile phase. The separated proteins are detected 'on-line' by UV absorption at 254 and 280 nm. Specific detection (16 metals) with on-line ICP-TOF-MS was also performed. This hybrid approach was applied to investigate the metal binding patterns of the proteins expressed by mussels which had been previously exposed to 16 trace metals in an aquarium tank for 1 and 2 weeks. The exceptional characteristics of ICP-TOF-MS for quasi-simultaneous monitoring of many trace elements in transient signals are illustrated by this 'on-line' coupling to FPLC separation, paving the way to virtually simultaneous multi-elemental speciation of trace metals in biological material.

The design, construction and performance characteristics of an easily removable interface to couple a gas chromatograph (GC) to an inductively coupled plasma mass spectrometer (ICP-MS) for trace element speciation is described. The interface is based on the use of a heated metallic tube where the last part of the capillary GC column is inserted. This metallic tube is connected to a metallic T-piece where a flow of argon carrier gas is introduced perpendicularly and externally to the metallic tube, creating a high velocity flow of intermediate sheath gas, which prevents condensation of the analytes eluting from the column on the walls of the T-piece or on the connection tubing to the ICP-MS torch. A flexible non-heated PTFE tube is used to connect the exit of the T-piece to the ICP-MS torch. This new interface has been applied to the separation and detection of different organometallic compounds of Se, S, Pb, Hg and Sn.

A rapid and fairly accurate semiquantitative method for the determination of trace amounts of metals in water samples of low and high salinity was successfully applied to a double focusing inductively coupled plasma mass spectrometer. The method was used at both low (m/ Δm=300) and medium (m/Δm=3000) resolution, establishing the corresponding molar response curve in both modes. The ionisation conditions (Tionandne) were calculated through the Saha equation by adjusting the molar response of a multi-element solution to a third order polynomial equation by least squares. The validation of the proposed methodology was performed by elemental analysis of a Riverine Water reference material (SLRS-3) from the National Research Council of Canada. Results obtained were in good agreement with the certified values, working at low resolution when no polyatomic interferences were found and at medium resolution when necessary. Matrix effects were also evaluated using sea-water samples, after a 5-fold dilution. An increase in the analytical response for all the elements, used as internal standards, in comparison with the corresponding curve in Milli-Q water was observed. However, once the ionisation conditions had been calculated on the same saline matrix, recoveries of most of the elements under study were satisfactory for semiquantitative analysis.

A semiquantitative procedure for the determination of trace metals in natural waters and sediments by ICP-MS was developed. The method is based on the establishment of the instrumental molar response curveversus mass using a multi-elemental solution containing elements from Mg to Bi with different ionisation potentials. The ionisation conditions in the plasma (electron density, ne, and ionisation temperature, Tion) were determined by least-squares fitting, using the Saha equation, by adjusting the molar response curve to a third-order polynomial. The effect of matrix constituents, such as Na+, K+, Ca2+, Mg2+, Cl– and SO42–, on both the shape of the molar response curve and on the plasma ionisation conditions was evaluated. It was observed that the ionisation degrees calculated in the plasma did not change significantly in the presence of the matrix constituents. However, the shape of the molar response curve was affected by high concentrations of matrix components and this effect was corrected by adding internal standards to the samples. The semiquantitative procedure was applied to the analysis of local natural waters and the results were compared with those obtained by external calibration and standard additions. Validation was performed by analysis of riverine water (SLRS-3) and sediment (PACS-1 and MESS-2) reference materials from the National Research Council of Canada with satisfactory results.

For the analysis of biological and environmental materials by inductively coupled plasma mass spectrometry (ICP-MS), several quantification procedures can be used depending on the precision and accuracy required. Semiquantitative methods based on the molar response curve were compared with conventional external calibration and standard additions for the analysis of waters and sewage sludges. For the analysis of biological materials, where higher quality data were required, isotope dilution analysis using enriched isotopes was applied. It was observed that the molar sensitivity for different elements in ICP-MS was a simple function of the mass of the isotopes measured after normalization for ionization efficiency which could be fitted to a third-order polynomial equation. Element ionization adjustments for the third-order polynomial, using the Saha equation, allowed the calculation of the plasma ionization temperature and electron density. For the determination of trace metals in waters and sewage sludges, the samples were spiked with different internal standards, ionization corrections were performed and the results obtained agreed with those obtained by external calibration and standard additions within a factor of 2 but, on average, the agreement was within 20%. The determination of molybdenum in biological reference materials was performed by isotope dilution analysis taking into account possible sources of error in the measurements by ICP-MS such as mass discrimination, detector dead time, isobaric interferences and random error propagation. © 1997 by John Wiley & Sons, Ltd.