| Popis: |
Inductively coupled plasma mass spectrometry (ICP-MS) is an extremely powerful tool for the analysis of most elements. It has been used to find the composition of a wide variety of matrices important to man. This thesis primarily deals with the determination of selenium concentrations in blood serum. Instrumental parameters such as nebuliser flow rate (NFR) and forward power to the plasma were investigated and their significance to the signal response for selenium and interfering polyatomic ions shown. The simple, robust and inexpensive technique of organic solvent addition (essentially methanol, as well as other alcohols) was shown to greatly enhance the signal response for selenium (≈ 4.2 times for methanol) whilst at the same time setting up a competing reaction to remove the polyatomic ion 40Ar 37Cl+ on the 77Se+ isotope. This technique was then applied to the analysis of an acid digested certified reference material, namely Seronorm(TM) Trace Elements in Serum, giving excellent results of 83 +/- 3 mug 1- using 82Se+ and 87 +/- 4 mug1-1 using 77Se+. This compares with a reference value of 86 mug1-1 (range 79-89 mug1-1). The above experiment was repeated using an ultrasonic nebuliser instead of a V-groove, high solids nebuliser and the characteristics compared. An assessment was made of a hydride generation system coupled to the ICP-MS for the analysis of selenium in blood serum. This included validation of an acid digestion technique and modification of the HG system so a separately nebulised internal standard could be used to correct for signal drift. Analysis of Seronorm(TM) reference material gave values of 77Se+ = 77 +/- 13 mug 1-1, 78Se+ = 82 +/- 9 mug 1-1 and 82Se+ = 80 +/- 4 mug 1-1 selenium when utilising 74Ge+ as an internal standard. The feasibility of using diluted serum in 1% HNO3 as a method of sample preparation prior to analysis was investigated. Results for diluted serum samples were not as good as those using digested samples. Other problems encountered were blockage of the glass injector tube and sampling cone orifice leading to poor long-term stability. Overall, this work shows that the analysis of selenium in digested serum is precise and reproducible using ICP-MS with methanol addition and could be considered for routine mono-elemental analysis. The use of methanol addition allows the use of multiple isotope studies for selenium analysis with ICP-MS. Interferences are still a problem on certain selenium isotopes. The benefits of Se+ signal enhancement and the elimination of interferences on 77Se+ when using methanol addition to sample prior to analysis for selenium in serum by ICP-MS, have clearly been demonstrated. |
