Enhanced Accuracy and Precision of Analysis of Selenium in Clinical Matrices

Abstract

Conventional calibration procedures using external standards or standard additions provide sufficient precision and accuracy of selenium concentrations for clinical purposes, but an enhanced quality of analysis is required for accurate analysis of reference materials and for valid comparisons of inter-laboratory studies on a world-wide scale. Isotope Dilution (ID) mass spectrometry, a technique reputed for achieving high accuracy measurements, was investigated to improve the reproducibility and accuracy of selenium determinations by established methods. Low resolution inductively coupled plasma mass spectrometry (ICP-MS) using solution nebulisation (SN) was used for the accurate and precise determination of selenium isotopes. The addition of butan-1-o1 to the samples reduced the interferences normally experienced by direct analysis of selenium in biological matrices, and also enhanced signal response. Samples were spiked with a ⁷⁴Se-enriched isotopic standard, and accurate determinations of ⁷⁸Se: ⁷⁴Se ratios were converted into concentrations, using regression line equations obtained from calibrating solution ratios. This produced significant improvements in precision over conventional (single isotopic) ICP-MS analysis. Between-run relative standard deviations approached those obtained within-run, and were 1.0-6.0% for 0.25 - 1.90 μmol l^-1 selenium. An interlaboratory comparison showed improved accuracy, with a reduced overall spread of bias to 0.0 ± 0.05 μmol l^-1 selenium for ID, compared with -0.01 ± 0.07 μmol 1^-1 for conventional analysis.

Alternative methodologies/instrumentation for ICP-MS were investigated to establish the degree of accuracy and precision attainable for the measurement of selenium in serum. These techniques were compared to a method developed for conventional standard addition analysis of selenium, in which samples were diluted 1+14 in 0.5% v/v butan -1o1 and the signal at mass 78 monitored. The accuracy of the described method was demonstrated by the laboratory's excellent performance in two External Quality Control Assessment schemes, over 18 months. Hydride generation (HG) was evaluated as a method of sample introduction for ICP-MS. Multi-collector magnetic field (ICP-MC-MS) and Dynamic Reaction Cell (DRC-ICP-MS) instrumentation, which use collision or reaction cells to destabilise any polyatomic argon adducts, were also assessed for their potential to enhance precision in quantitative isotopic analysis. The order of both precision and accuracy of analysis was found to be ID-DRC-ICP-MS ≅ ID-SN- ICP-MS > DRC-ICP-MS ≅ SN-ICP-MS >>HG-ICP-MS.

More information

Identifiers

Catalogue record

Export record

ASCII CitationAtomBibTeXData Cite XMLDublin CoreDublin CoreEP3 XMLEndNoteHTML CitationHTML CitationHTML ListJSONMETSMODSMPEG-21 DIDLOpenURL ContextObjectOpenURL ContextObject in SpanRDF+N-TriplesRDF+N3RDF+XMLRIOXX2 XMLReferReference ManagerSimple Metadata