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The internal and simultaneous correction of mass bias and spectral interferences (BrH+ and SeH+) in the determination of total selenium in biological samples by isotope dilution analysis is evaluated here using isotope pattern deconvolution (IPD). The procedure takes the measured intensities at masses 76 to 82 in the spiked samples (using 77Se as spike) and calculates the isotopic composition of selenium. This isotopic composition would be a linear function of the isotopic composition of natural abundance selenium and that of enriched 77-selenium if no mass bias or spectral interferences were present or if they were adequately corrected. So, the molar fractions of natural abundance selenium and isotopically enriched selenium are calculated using IPD along with the variance of the multiple linear regression model. The variance of the regression is first calculated when no correction is applied (either mass bias or spectral interferences) and then this value is minimised by applying different factors for mass bias and the ratios SeH/Se and BrH/Br. It is demonstrated that, using the SOLVER application of Excel, the regression variance can be minimized and the correction factors converge to those factor which could have been calculated by external correction. Hence, this procedure eliminates the need for any external correction of mass bias or isobaric interferences in isotope dilution analysis provided that enough isotopes of the element are measured. To illustrate the applicability of this method, raw data obtained by Hinojosa Reyes et al. in a previous paper (J. Anal. At. Spectrom., 2003, 18, 11) were recalculated using the proposed methodology with satisfactory results. [ABSTRACT FROM AUTHOR]

Enriched spikes of 53Cr, 57Fe, 67Zn, 95Mo, 111Cd, 143Nd, 150Sm, 199Hg and 207Pb were characterised on a multi-collector ICP-MS instrument both in terms of isotopic composition and concentration. The isotopic composition of the spikes was determined using either a natural abundance or certified standard for mass bias correction, except for lead where thallium internal correction was used. It was observed that the use of weighted regression lines for mass bias correction provided similar or, in most cases, lower uncertainties in the isotopic composition of the spikes in comparison with unweighted regression lines or single ratio measurements. For the establishment of the spike concentration by reverse isotope dilution analysis, isotope pattern deconvolution was evaluated and mass bias could be corrected internally in each blend by minimising the variance of the multiple linear regression model. It was also observed that isotope pattern deconvolution with internal mass bias correction provided lower uncertainties in the concentration of the spikes in comparison with the usual procedure based on external mass bias correction. [ABSTRACT FROM AUTHOR]

Large volume injection ion chromatography has been evaluated for the precise and accurate measurement of strontium isotope ratios by multicollector ICP-MS. On-line coupling of the ion chromatograph to the MC-ICP-MS instrument allowed the complete separation of isobaric rubidium and other matrix elements (Ca, Mg, Na and K) and the measurement of strontium isotope ratios on flat-topped chromatographic peaks of ca. 3 minutes duration. No drift in the strontium isotope ratios was observed during strontium elution and mass bias could be corrected using either the 86Sr/88Sr isotope ratio (internal correction) or the observed 87Rb/85Rb isotope ratio (external correction) in the real samples. Typical internal precisions obtained with the selected measurement and correction conditions were about 2 times lower than the precisions obtained with continuous sample introduction for a solution 50 ng g–1 of Sr NIST SRM 987 in HNO3 2% (typical standard deviations of 0.00022–0.00036 for the corrected 87Sr/86Sr ratio in comparison to 0.00014–0.00020 for continuous sample introduction). The method was applied to the measurement of strontium isotope ratios in cider samples and the results agreed with previous data obtained after an off-line Rb–Sr separation procedure using the Sr-Spec chelating material. The precision obtained for the real samples was poorer than previous data due to the low concentration of strontium in the measured samples. The method was also applied to other sample types (soil leachates, apple leaves and apples) to study the transference of strontium isotope ratios in the soil–tree–cider system. [ABSTRACT FROM AUTHOR]