Determination of 90Sr at ultratrace levels in urine by ICP-MS

Abstract

Sr appears as a radionuclide in the decay series of nuclear fission and can therefore be found in nuclear waste or released by nuclear accidents. Current methods for the detection of this radionuclide are time consuming and may be prone to a large variety of interferents. In this work, inductively coupled plasma mass spectrometry is explored for the determination of 90 Sr in the presence of stable zirconium in urine. Specific techniques are investigated to remove this as well as other contributions to the background at m/z~90. A quadrupole ICP-MS equipped with a hexapole collision cell is first explored (final LOD~2 ng L 21 for water samples), however, the desired limit of detection for 90 Sr in urine is quite low (0.02 pg L 21). The performance of a double-focusing sector field ICP mass spectrometer (ICP-SFMS) is further investigated, which allows measurement of 90 Sr at the ultratrace level. Other potential interferences were investigated and instrumental detection limits are calculated as 3 pg L 21 for water samples. Final parameters include the use of a cool plasma and medium mass resolution in ICP-SFMS. The method is applied to the analysis of 90 Sr extracted from urine using a crown ether extraction resin and concentrated (enrichment factor: 200); high levels of natural strontium in the separated fraction (of about 1 mg mL 21 ) equate to higher detection limits (80 pg L 21) due to 88 Sr 1 at m/z~90 and the relatively low abundance sensitivity of ICP-SFMS at medium mass resolution of 6 6 10 27 . This detection limit in the separated fraction corresponds to the detection limit of 0.4 pg L 21 in the original urine sample. The recovery of 90 Sr, determined with the developed analytical method in spiked urine samples, was in the range of 82-86%.

Critical comparison of radiometric and mass spectrometric methods for the determination of radionuclides in environmental, biological and nuclear waste samples

“…This method gives an isotopic selectivity of 1.4×10 10 against stable strontium and a detection limit of 4 mBq. 90 Sr has also been determined by ICP-MS [36][37][38]70]. The main interference in the measurements of 90 Sr by ICP-MS is the isobar 90 Zr which has a natural abundance of 51%.…”

“…In spite of the improvements, detection limit reported for 90 Sr was still around 10 Bq/ml (equivalent to 2 pg/ml). Sector field ICP-MS has also been used for the determination of 90 Sr [37,38]. By using cold plasma and medium mass resolution, the Zr signal is significantly reduced, and a detection limit of 10 mBq/ml was achievable in a pure water sample.…”

Inductively coupled plasma- and glow discharge plasma-sector field mass spectrometry : Part II. Applications

“…Denaturing separation in the presence of SDS is shown to result in loss of iron ions which disappear even completely in the case of transferrin. The ratio of 56 Fe + to 32 S + proved a good measure for the determination of the iron load of the proteins.…”

Understanding reactions with O2 for 90Sr measurements by ICP-MS with collision-reaction cell

“…Several analytical approaches exist to avoid such supplementary step and lower irradiation of operators. The double focusing Sector Field Inductively Coupled Plasma Mass Spectrometry (ICP-SFMS) is an effective tool which may provide a sufficiently high resolution for separating ions differing in mass by a fraction of a mass unit, as in the case of the 90 Zr/ 90 Sr isobaric interference (mass of 90 Zr = 89.9047 uma and 90 Sr = 89.9077 uma) [3,4]. But the required mass resolution (m/ m = 30,000), beyond actual possibilities, and the purchase price of such apparatus constitute a major obstacle which explains the development of others solutions.…”

“…But the required mass resolution (m/ m = 30,000), beyond actual possibilities, and the purchase price of such apparatus constitute a major obstacle which explains the development of others solutions. Cold plasma has been examined for taking advantage of the differences in ionization potential (IP(Zr) = 639.2 kJ mol −1 and IP(Sr) = 561.8 kJ mol −1 ) [3], but such plasma conditions enhance the formation of matrix-derivated polyatomic ions and sensitivity becomes particularly dependent on the matrix of the sample [5]. As a result, the use of ICP-MS with collision-reaction cells is increasingly widespread to avoid the chromatographic step and lower irradiation of operators.…”