Rapid and accurate determination of thallium in seawater using SF-ICP-MS

We present a method for the rapid and direct determination of dissolved Thallium (Tl) using high resolution sector field inductively coupled mass spectrometry (SF-ICP-MS) suitable for the measurement of large time series (e.g. during monitoring). Thallium data are presented for a series of natural sea water samples, which were validated with sea water standards CASS-4 and NASS-5. The sea water samples and standards were diluted 10 times prior to measurement with SF-ICP-MS in low resolution mode (R=300, LR). For both CASS-4 and NASS-5 (salinity of 30.5) we calculated a concentration of about 11 ng L(-1) when using Tl values of 14±2 ng L(-1) (at salinity of 35±1) published by Flegal and Patterson for Atlantic and Pacific sea water. For CASS-4 we report a Tl value of 10.6±0.7 ng L(-1) (n=70), for NASS-5 a Tl value of 10.3±0.8 ng L(-1) (n=11). For Tl in both CASS-4 and NASS-5, the overall error in accuracy and precision is less than 4% and 8% (2s), respectively. Further, values of 7.7±0.3 and 6.7±0.2 ng L(-1) Tl were found for the estuarine standard SLEW-3 (salinity of 15) and the river water standard SLRS-4, respectively, for which no certified value exists so far. The detection and quantification limits of our method are 0.1 and 0.3 ng L(-1), respectively. Slight differences in the accuracy of our method and other published methods for the determination of Tl in sea water are discussed. Time-series of natural coastal water samples gave Tl values (6-12 ng L(-1)), which correspond to determined salinities, and hence, appear realistic and oceanographically consistent.