On-line isotope dilution

Giusti, P., Schaumloffel, D., Encinar, J. R., and Szpunar, J., Interfacing reversed-phase nanoHPLC with ICP-MS and on-line isotope dilution analysis for the accurate quantification of selenium-containing peptides in protein tryptic digests. Journal of Analytical Atomic Spectrometry 20(10), 1101-1107, 2005. 

Figure 6.26 On line isotope dilution in LA-ICP-MS for determination of Cu in platinum nanoclusters, (j. S. Becker et al., Int. j. Mass spectrom. 237, 13(2004). Reproduced by permission from Elsevier.)...

A suitable calibration strategy has been demonstrated for the determination of selected elements, i.e., Pb, Ag and T1 in a small amount of platinum nanoclusters. In on line isotope dilution analysis with LA-ICP-MS, an isotope emiched tracer solution was nebulized by the Aridus microconcentric nebulizer with desolvator. After about 180 seconds, laser ablation of the investigated platinum nanocluster sample was started and after an additional time of 180 seconds 2 % nitric acid nebulized instead of the tracer solution. The isotope ratios of lead ( Pb/ ° Pb), silver ( ° Ag/ ° Ag) and thallium ( ° T1/ ° T1) - with Cu/ Cu for internal standardization - were monitored during the whole experiment. The measuring time for one experiment was <10 min. 

On line isotope dilution in LA-ICP-MS using a microflow nebulizer (DS-5) inserted in the laser ablation chamber (experimental setup is shown in Figure 6.23) for the analysis of uranium in NIST glass standard reference material (SRM) 612 and NIST apple leaves SRM 1515 is described by Pickhardt et al In the analysis of SRMs, firstly the isotope ratio in the standard was... 

Compact solid samples cannot be analyzed via LA-ICP-IDMS using the techniques mentioned above because a homogeneous mixture of the sample and spike -indispensable in isotope dilution analysis - cannot be realized for such a type of sample. To overcome this problem, an on-line solution-based calibration approach has been developed, which was called on-line isotope dilution LA-ICP-MS, suggesting that a real IDMS analysis is carried out. However, this is by no means tme. 

C. Pickhardt, A.V. Izmer, M.V. Zoriy, D. Schaumloffel, and J.S. Becker. On-line isotope dilution in laser ablation inductively coupled plasma mass spectrometry using a microflow nebulizer inserted in the laser ablation chamber. International Journal cfMass Spectrometry 248 136-141, 2006. 

Beauchemin, D. and A. A. Specht. 1997. On-line isotope dilution analysis with ICPMS using reverse flow injection. Anal. Chem. 69 3183-3187. 

Lasztity A, Viczian M, Wang X, Barnes R (1989) Sample analyses by on-line isotope dilution inductively coupled mass spectrometry. J Anal At Spectrom 4 761-766. 

Roltmann, L., and Heumann, K. G. (1994). Development of an on-line isotope dilution technique with HPLC/ICP-MS for the accurate determination of elemental species. Fresenius J.Anal. Chem. 350(4/5), 221. 

Specht, A. A, and Beauchemin, D. (1998). Automated on-line isotope dilution analysis with ICP-MS using sandwich flow injection, na/. Chem. 70(5), 1036. 

Viczian, M., Lasztity, A.,Wang, X., and Barnes, R. M. (1990). On-line isotope dilution and sample dilution by flow injection and inductively coupled plasma mass spectrometry. J. Anal. At. Spectrom. 5(2), 125. 

In an on-line isotope dilution technique used with LA-ICP-MS, an isotope-enriched spike solution, which can be a multielement solution containing all the spikes of interest, was nebulized using a low-flow nebulizer and introduced through a membrane desolvation unit in front of the sample ceU. The isotope ratio of the spike solution was measured (spike ratio), and after a distinct time, the laser was turned on and the isotope ratio of both the sample and the spike solution (blend ratio) was measured. After turning the laser off, the spike solution was replaced by blank solution and the isotope ratio of the blank was usedfor any blank correction. Using this setup, very accurate determination of trace impurities in small sample sizes was successfully performed. ... 

Determination of the spike mass flow is the most crucial point in on-line isotope dilution MS. Biased mass flow values will have the most influence on the expanded uncertainty of the final result. Two methods of mass flow assessment have been described in the literature. The first method determines the mass flow gravimetrically. The make-up flow /gp can be supplied by a pump able to deliver a precise and accurate flow (micro-HPLC pump, syringe pump) or by self-aspiration of the nebuliser. /gp is assessed gravimetrically by repeated measurement. The spike mass flow My t) is calculated as follows ... 

Once the accurate value for My(t) has been determined, the analyte mass flow Mxj at any point j of the transient profile can be calculated by equation 7.2. As a next step an analyte mass flow Mxversus time diagram is estabUshed. Figures 7.5(a) and 7.5(b) Ulustrate the principle of species-unspecific quantification via on-line isotope dilution MS. 

---