Isotopic standards, lead

SRM 979), Ni (nickel metal isotopic standard NIST SRM 986), Rb (rubidium chloride isotopic standard NIST SRM 984) and Sr (strontium carbonate isotopic standard NIST SRM 987). In addition, isotope reference materials are available for heavy elements such as T1 (thallium metal isotopic standard NIST SRM 997), Pb (NIST lead standard reference materials SRM 981-983) or U (uranium oxide NIST isotope standard U 005, U020, U350, U500 or U930) and others. The most important isotope standard reference materials applied in inorganic mass spectrometry are summarized in the table in Appendix V.17... 

Certified isotopic standards are available for some elements but by no means all. Such standards are available from the National Institute of Standards and Technology [52] and New Brunswick Laboratory [53] in the United States, and from the Institute for Reference Materials and Measurements [54] in Belgium. De Bievre et al. have published a review of reference materials available for isotope ratio measurements [55]. It is clearly desirable to use certified materials for instrument calibration if at all possible. If no standard is available for the element in question, the analyst has little choice but to obtain a pure sample of it and assume it has the composition listed by IUPAC [1]. A few elements, with lead being the outstanding example, have isotopic compositions that vary widely in... 

Isotopic Ratios of Common, Equal Atom and Radiogenic Lead Isotopic Standards, J. Res. Natl. Bur. Stand. Sec. A (1968) 72A, 261-267. 

A multilaboratory program is in progress to compare lead values obtained by ASV with the thin film with those determined by isotope dilution. Initial intercomparisons with samples of Southern California coastal waters were disheartening but were tentatively traced to procedural errors and contamination. Recent efforts have produced some values which are within a factor of two of the standardized lead value (10). Our own initial efforts to compare copper concentrations obtained using the system described herein with those obtained by extraction on Chelex 100 and subsequent analysis by atomic absorption showed ASV values to be considerably higher. This discrepancy was traced to interference by silver from the reference electrode. Recent work with a noncontaminating reference electrode yielded copper values that were essentially identical to those obtained by extraction followed by atomic absorption (11). 

Catanzaro, E.J., Murphy, T.J., Shields, W.R., Gamer, E.L. (1968) Absolute isotopic abundance ratios of common, equal-atom and radiogenic lead isotopic standards./owmaf of Research of the National Bureau of Standards, 72A, 261-267. 

Table II shows the precision and accuracy of the ICP-MS for tiie four lead isotopes b, Pb, and Pb based on measuremmits of the NIST Common Lead Isotopic Standard (SRM 981). For all of die lead isotopes except for b, our necision is under 0.2%, ai our percent error, or accuracy, is roughly 0.2%. This is etqiected, as Pb is the least abundant lead isotope, and in our analyses we measured amounts of ° Pb that w smaller than counts for the other isotopes by qq oximately a frctor of ten. In addititm, previous research used Pb Pb versus b/ Pb to identity clusters of majolica pottery manufactured in different areas 14), and it is with these isotopes that our method has its best precision and accuracy.

In elemental analysis by ICP-MS, a difference in the isotopic composition between the sample and the calibration standard leads to a bias in the measurement result, that is, the elemental content determined. In serious routine analysis, the isotopic variation of certain elements therefore needs to be considered. For lead determination, often the ion currents of the isotopes ° Pb, Pb, and Pb are summed and this sum is used for the calculations, because the sum of all isotope amount fractions is one and therefore is not susceptible to isotopic variations. However, two approximations are included first, the ion current of Pb is not used owing to its low isotope amount fractions and the interference from... 

Figure 1.116. Lead isotopic variation in Japanese Neogene ores. The majority of data fall in a relatively narrow range which is no more than twice the experimental uncertainty indicated by the replicate analyses of NBS-SRM-981 standard (Sasaki et al., 1982).

Gulson et al. (1998) used measured lead isotope ratios (207Pb/206Pb and 206Pb/204Pb) in mothers breast milk and in infants blood to establish that, for the first 60-90 days postpartum, the contribution from breast milk to blood lead in the infants varied from 36% to 80%. Maternal bone and diet appear to be the major sources of lead in breast milk. Mean lead concentration ( standard deviation) in breast milk for participants in the study was 0.73 0.70 pg/kg. 

Flegal and Stukas [406] described the special sampling and processing techniques necessary for the prevention of lead contamination of seawater samples, prior to stable lead isotopic ratio measurements by thermal ionisation mass spectrometry. Techniques are also required to compensate for the absence of an internal standard and the presence of refractory organic compounds. The precision of the analyses is 0.1 -0.4% and a detection limit of 0.02 ng/kg allows the tracing of lead inputs and biogeochemical cycles. 

A combination of FIA with ICP-MS was applied for direct determination of lead in aqueous samples. Calibration of the 208Pb signal by addition of standard was found to be better than external calibration and isotope dilution. In the 50 pg Pb/L range RSD was 1% for wine and 3.5% for urine62. 

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