Development of an ICP-HRIDMS method for accurate determination of traces of silicon in biological and clinical samples

An inductively coupled plasma-high resolution isotope dilution mass spectro metric (ICP-HRIDMS) method in combination with a microwave-assisted decompo sition technique has been developed for the determination of traces of sili con in biological and clinical samples. A 30Si-enriched spike solution was used for the isotope dilution step. Decomposition of the samples was achiev ed by use either of HNO3 or a mixture of HNO3 and HE By application of both methods of digestion to the sample it N as possible to differentiate betwe en a poorly soluble silicate fraction and an HNO3-soluble silicon species. Traces of silicon were determined in different reference materials, which a re not certified for this element, and in other biological and clinical sam ples. A concentration range of 1-600 mug g(-1) was covered by the different samples. For homogeneous samples relative standard deviations of 2-4% were obtained. The detection limit was strongly affected by the blank. In this connection purification of water, used in the analytical procedure. was esp ecially critical. ne blank contribution of the ICP-MS instrument could be m inimized by applying a nebulizer and a spray chamber made of PFA, a sapphir e injection tube, and a silicon nitride torch. Under these conditions detec tion limits of 0.15 mug g(-1) and 0.2 mug g(-1) were obtained for the HNO3 and HNO3-HF digestion methods, respectively, when a sample weight of 0.5 g was used. With regard to expected silicon content this enables determinatio n in almost all biological and clinical samples. The ICP-HRIDMS results wer e compared with those recently obtained in an interlaboratory study. This i sotope-dilution method is an potential option for certification of silicon in reference materials, a method for which is still required.