Bias estimation in the certification of steroid reference materials for carbon isotope delta measurements via elemental analyser and gas chromatography-combustion-isotope ratio mass spectrometry.

RATIONALE: Two new certified reference materials (CRMs) have been prepared providing three steroids certified for stable carbon isotope delta values, δ(13 C) ‰. These materials have been designed to assist anti-doping laboratories in validating their calibration method or to be employed as calibrant for stable carbon isotope measurements of Boldenone, Boldenone Metabolite 1 and Formestane. These CRMs will allow for accurate and traceable analysis in compliance with World Anti-Doping Agency (WADA) Technical Document TD2021IRMS. METHODS: Certification was performed using an elemental analyser-isotope ratio mass spectrometry (EA-IRMS) primary reference method on the bulk carbon isotope ratios of nominally pure steroid starting materials. EA-IRMS analyses were carried out on a Flash EA Isolink CN coupled via a Conflo IV to a Delta V plus mass spectrometer. Confirmation analysis was performed by gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) using a Trace 1310 GC coupled to a Delta V plus mass spectrometer via GC Isolink II. RESULTS: Based on the EA-IRMS analysis, the materials were certified with δ(13 C) values of -30.38‰ (Boldenone), -29.71‰ (Boldenone Metabolite 1) and 30.71‰ (Formestane). Noting that the assumption of 100% purity in the starting materials has the potential to introduce bias, this was investigated using GC-C-IRMS analysis and theoretical modelling based on purity assessment data. CONCLUSIONS: Careful application of this theoretical model was shown to provide reasonable estimates of uncertainty while avoiding the introduction of errors associated with analyte-specific fractionation during GC-C-IRMS analysis.

Production of trace elements in coastal sea water certified reference material NMIA MX014.

A certified reference material (CRM) for trace elements in acidified sea water, NMIA MX014, has been produced by the National Measurement Institute Australia (NMIA). The CRM consists of natural coastal sea water with 12 elements (As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se and V) fortified to levels relevant to environmental regulatory testing in Australia ranging from 0.4 to 22 µg/kg. Certified values for these 12 elements were assigned using reference methods developed at NMIA, using either isotope dilution or standard addition with ICP-MS measurement. Specialised sample preparation (coprecipitation) and ICP-MS optimisation (online dilution, collision/reaction chemistry, high mass resolution) were used to negate the effect of the high level of dissolved solids. Multiple confirmatory experiments were performed in order to verify that ICP-MS spectral interferences were eliminated and to estimate the measurement uncertainty contribution from method precision and method trueness. Extensive homogeneity and stability testing was performed and the measurement uncertainty of certified values includes contributions from between-bottle homogeneity, short-term stability, medium-term stability and long-term stability. Special attention was paid to the stability of Hg due to well-known preservation problems. Acidified sea water matrix was satisfactory for stabilising Hg at 0.4 µg/kg for at least 4 years. Relative expanded uncertainties (k = 2) for the 12 certified values were between 1 and 11 %. NMIA MX014 is intended for use as a reference material for analytical method validation and quality control for quantification of trace elements in saline water and other similar sample types.

An evaluation of harmonic vibrational frequency scale factors.

Scale factors for obtaining fundamental vibrational frequencies, low-frequency vibrational frequencies, zero-point vibrational energies (ZPVEs), and thermal contributions to enthalpy and entropy have been derived through a least-squares approach from harmonic frequencies determined at more than 100 levels of theory. Wave function procedures (HF, MP2, QCISD, QCISD(T), CCSD, and CCSD(T)) and a large and representative range of density functional theory (DFT) approaches (B3-LYP, BMK, EDF2, M05-2X, MPWB1K, O3-LYP, PBE, TPSS, etc.) have been examined in conjunction with basis sets such as 6-31G(d), 6-31+G(d,p), 6-31G(2df,p), 6-311+G(d,p), and 6-311+G(2df,p). The vibrational frequency scale factors were determined by a comparison of theoretical harmonic frequencies with the corresponding experimental fundamentals utilizing a standard set of 1066 individual vibrations. ZPVE scale factors were generally obtained from a comparison of the computed ZPVEs with experimental ZPVEs for a smaller standard set of 39 molecules, though the effect of expansion to a 48 molecule data set was also examined. In addition to evaluating the scale factors for a wide range of levels of theory, we have also probed the effect on scale factors of varying the percentage of incorporated exact exchange in hybrid DFT calculations using a modified B3-LYP functional. This has revealed a near-linear relationship between the magnitude of the scale factor and the proportion of exact exchange. Finally, we have investigated the effect of basis set size on HF, MP2, B3-LYP, and BMK scale factors by deriving values with basis sets ranging from 6-31G(d) up to 6-311++G(3df,3pd) as well as with basis sets in the cc-pVnZ and aug-cc-pVnZ series and with the TZV2P basis.