Problems in obtaining precise and accurate Sr isotope analysis from geological materials using laser ablation MC-ICPMS

This paper reviews the problems encountered in eleven studies of Sr isotope analysis using laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICPMS) in the period 1995–2006. This technique has been shown to have great potential, but the accuracy and precision are limited by: (1) large instrumental mass discrimination, (2) laser-induced isotopic and elemental fractionations and (3) molecular interferences. The most important isobaric interferences are Kr and Rb, whereas Ca dimer/argides and doubly charged rare earth elements (REE) are limited to sample materials which contain substantial amounts of these elements. With modern laser (193 nm) and MC-ICPMS equipment, minerals with >500 ppm Sr content can be analysed with a precision of better than 100 ppm and a spatial resolution (spot size) of approximately 100 μm. The LA MC-ICPMS analysis of 87Sr/86Sr of both carbonate material and plagioclase is successful in all reported studies, although the higher 84Sr/86Sr ratios do suggest in some cases an influence of Ca dimer and/or argides. High Rb/Sr (>0.01) materials have been successfully analysed by carefully measuring the 85Rb/87Rb in standard material and by applying the standard-sample bracketing method for accurate Rb corrections. However, published LA-MC-ICPMS data on clinopyroxene, apatite and sphene records differences when compared with 87Sr/86Sr measured by thermal ionisation mass spectrometry (TIMS) and solution MC-ICPMS. This suggests that further studies are required to ensure that the most optimal correction methods are applied for all isobaric interferences

On-line Automated Sample Preparation-Capillary Gas Chromatography for the Analysis of Plasma Samples.

An automated sample preparation module, (the automated sample preparation with extraction columns, ASPEC), was interfaced with a capillary gas chromatograph (GC) by means of an on-column interface. The system was optimised for the determination of the antidepressant trazodone in plasma. The clean-up of untreated plasma was carried out with disposable C18 cartridges, using several washing steps. The analyte was desorbed with methanol, the extract was diluted on-line with buffer and preconcentrated on a PLRP-S trapping column. The trapping column was dried by purging with nitrogen gas. Desorption (phase switching) of the trapping column was carried out with ethyl acetate which was introduced into a retention gap using partially concurrent solvent evaporation conditions. Trazodone was determined by GC with flame ionisation detection (FID). With a 1 ml sample, this resulted in a detection limit for trazodone in plasma of 3 ng/ml. The system showed good linearity and repeatability in the range 0.01-1 μg/ml, thus covering the range of pharmacokinetic/dynamic-to-therapeutic concentrations of trazodone in plasma. Preliminary results for benzodiazepines are promising. They indicate that the use of a selective detector such as the nitrogen/phosphorus detector, is to be recommended. © 1995 Friedr. Vieweg & Sohn Verlagsgesellschaft mbH

Sr and Pb isotopic composition of five USGS glasses (BHVO-2G, BIR-1G, BCR-2G, TB-1G, NKT-1G)

Sr isotopic compositions and Rb/Sr ratios of three USGS glasses (BHVO-2G, BIR-1G, BCR-2G) are identical to those of the original USGS reference materials. NKT-1G and TB-1G give values of 0.70351 and 0.70558, respectively. Pb isotopic ratios were measured by the standard-sample bracketing technique on an MC-ICP-MS, which give results that are comparable in accuracy and reproducibility to double spike analyses. However, assessment of the reproducibility of the technique is hampered by inhomogeneous contamination of all USGS reference materials analysed. This contamination is likely to be the reason why the USGS glasses do not all have the same Pb isotopic composition as their unfused originals. Powdered glasses, distributed for characterisation of the glasses by bulk analytical techniques, do not all have the same Pb isotopic compositions as the solid glass material, and can therefore not be used for this purpose. © 2005 Elsevier B.V. All rights reserved

Strontium and lead isotope ratios in human hair: investigating a potential tool for determining recent human geographical

Three cleaning techniques that remove external contamination of human hair are assessed to investigate the potential use of Sr and Pb isotope composition of hair for human provenancing. These techniques are; (i) a centrifugation technique using diiodomethane where hair and soil particles are separated by density difference; (ii) a leaching technique of the hair surface using 2 M HN

Growth rates, half-saturation constants, and silicate, nitrate, and phosphate depletion in relation to iron availability of four large, open-ocean diatoms from the Southern Ocean

Four large, open-ocean diatoms from the Southern Ocean (Actinocyclus sp., Thalassiosira sp., Fragilariopsis kerguelensis, and Corethron pennatum) were grown in natural (low iron) Southern ocean seawater with increasing Fe concentrations. With increasing dissolved iron (Fediss) concentrations, the growth rates increased three- to sixfold. The species with the smallest cells had the highest growth rates. The half-saturation constants (Km) for growth were low (0.19-1.14 nmol L-1 Fediss), and close to the ambient Fediss concentrations of 0.2 nmol L-1. The range in Km with respect to Fediss also varied with the size of the diatoms: the smallest species had the lowest Km and the largest species had the highest Km. As Fediss concentrations decreased, silicate consumption per cell increased, but nitrate consumption per cell decreased. Phosphate consumption per cell varied without clear relation to the dissolved iron concentrations. The differences in nutrient consumption per cell resulted in marked differences in elemental depletion ratios in relation to Fediss concentrations, with the depletion ratios being most affected by iron limitation in the largest cells. These experimental findings are in agreement with previous laboratory and field studies, showing the relatively high requirements of large diatoms for Fe. The size-dependent response of the diatoms with respect to nutrient depletion is a good illustration of the effects of Fe on silicate, nitrate, and phosphate metabolism.