Multiple ion collector ICP

Figure 5.2 Overview of ICP-MS instrumentation quadrupole-based ICP-MS with and without colli-sion/reaction cell, sector field ICP-MS with single ion collector (ICP-SFMS) and multiple ion collector ICP-MS (MC-ICP-MS) and time-of-flight ICP-MS.

At present, the Nu Plasma from Nu Instruments, Wrexham, UK, the Isoprobe from GV Instruments, Manchester, UK, and the Neptune from Thermo Fisher Scientific, Bremen, Germany, are the most precise multiple ion collector ICP mass spectrometers available on the analytical market. 

Re-assessment of silicon isotope reference materials (IRMM-018 and NBS 28 isotope standard) has been performed using both high resolution multiple ion collector ICP-MS and gas mass spec-... 

Clough and co-workers reported on the uncertainty contribution using single and double isotopi-cally enriched spikes in the isotope dilution approach employing a multiple ion collector ICP-MS combined with an HPLC and with cold vapour generation (CV) to form HPLC-CV-MC-ICP-MS for the determination of MeHg in fish tissue.8 Two fish tissue reference materials DORM-2 (NRC, Canada) and BCR 464 were employed in these studies. The amount of each certified reference... 

The analyte was concentrated (enrichment factor 200) but high levels of natural strontium in the separated fraction (of about 1 jxg mF ) meant higher detection limits (80 pg 1 ) due to peak tailing of Sr+ atm/z = 90 and the relatively low abundance sensitivity of ICP-SFMS at a medium mass resolution of 6 x 10 . This detection hmit in the separated fraction corresponded to a detection limit of O.TpgT in the original urine sample. The recovery of °Sr, determined by the described analytical method in spiked urine samples, was in the range 82-86 %. Decreasing the detection hmit for °Sr determination is recommended by the apphcation of a multiple ion collector ICP-MS due to improved abundance sensitivity. The analytical methods described can also be applied for the analysis of other body fluids, such as blood or human milk or for the determination of °Sr in bones. 

A multiple ion collector device is required for the simultaneous determination of separated ion beams in precise and accurate isotope ratio measurements in order to study, for example, isotope fine variation in Nature or during tracer experiments using enriched stable isotope tracers. In thermal ionization mass spectrometers or in ICP-MS, mostly a system of several Faraday cups (up to 16) and/or ion counters (electron multipliers) is applied. In the photographs in Figures 4.7 and 4.8 examples of multiple ion collector systems are shown from the mass spectrometers MC-ICP-MS... 

Figure 4.7 Schematic (a) and photograph (b) of a multiple ion collector system of MC-ICP-MS IsoProbe (VC Instruments). (Reproduced by permission of Thermo Fisher Scientific, Bremen.)...

Instrumental developments (e.g., of sector field instruments with multiple ion collection, introduced in 1992, or the insertion of collision and reaction cells in order to reduce disturbing isobaric interferences), the progress in applications for ultratrace analysis, also in combination with on line hyphenated separation techniques (HPLC, CE), especially routine capability as well as decreasing price and user friendly maintenance mean that sales are increasing by 10 % every year. To improve the analytical performance of ICP mass spectrometers for precise isotope ratio measurements (e.g., for geochronology or for the study of fine isotope variation in nature) powerful instrumentation with high mass dispersion and multiple ion collector systems instead of single ion collection are commercially available on the analytical market. 

An overview of commercial ICP mass spectrometers from different companies (quadrupole based ICP-MS with and without collision/reaction cell, double-focusing sector field instrumentation with single and multiple ion collectors, time-of-flight (ToF), ICP-ion trap-MS and non-commercial ICP-Fourier transform ion cyclotron resonance (FTICR) mass spectrometers is given in Figure 5.2. By using ion traps and FTICR mass spectrometers in ICP-MS isobaric interferences of atomic ions... 

Sector field ICP-MS with single and multiple ion collectors ... 

For many decades, TIMS was the isotope analytical technique of choice, but due to instrumental developments in ICP-MS, especially with multiple ion collectors (MC-ICP-SFMS), and the advantages of ICP-MS in comparison to TIMS (e.g., higher element sensitivities, faster isotope ratio measurements, comparable precision and accuracy, practically no restriction on the ionization potential of chemical elements, time independent mass fractionation and the possibility of additional multi-element analysis at trace and ultratrace level and fewer, less time-consuming sample preparation steps75), TIMS will be replaced in future by powerful ICP-MS to an ever greater extent. 

An interesting approach is the application of multiple ion collector mass spectrometry (MC-TIMS and MC-ICP-MS) for the determination of Cd and T1 in high purity zinc metal after trace matrix separation by the certification of reference materials from the Bureau Communie de Reference (BCR).29 Accurate and precise element concentrations in high purity zinc metal have been obtained with both mass spectrometric techniques via precise isotope ratio measurements using the isotope dilution strategy the analytical data. 

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