Measurements of natural uranium concentration and isotopic composition with permil‐level precision by inductively coupled plasma–quadrupole mass spectrometry

Abstract

A new analytical technique using inductively coupled plasma–quadrupole mass spectrometry (ICP‐QMS) has been developed that produces permil‐level precision in the measurement of uranium concentration ([U]) and isotopic composition ( δ 234 U) in natural materials. A 233 U‐ 236 U double spike method was used to correct for mass fractionation during analysis. To correct for ratio drifting, samples were bracketed by uranium standard measurements. A sensitivity of 6–7 × 10 8 cps/ppm was generated with a sample solution uptake rate of 30 μ L/min. With a measurement time of 15–20 min, standards of 30‐ng uranium produced a within‐run precision better than 3‰ (±2 R.S.D.) for δ 234 U and better than 2‰ for [U]. Replicate measurements made on standards show that a between‐run reproducibility of 3.5‰ for δ 234 U and 2‰ for [U] can be achieved. ICP‐QMS data of δ 234 U and [U] in seawater, coral, and speleothem materials are consistent with the data measured by other ICP‐MS and TIMS techniques. Advantages of the ICP‐QMS method include low cost, easy maintenance, simple instrumental operation, and few sample preparation steps. Sample size requirements are small, such as 10–14 mg of coral material. The results demonstrate that this technique can be applied to natural samples with various matrices.