Analytical Sciences

An in-syringe La-coprecipitation Method for the Preconcentration of Oxo-anion Forming Elements in Seawater Prior to an ICP-MS Measurement

Dwinna RAHMI,* Yanbei ZHU,** Eiji FUJIMORI,* Takuya HASEGAWA,* Tomonari UMEMURA,* Shigeji KONAGAYA,* and Hiroki HARAGUCHI*

*Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603, Japan
**Inorganic Analytical Chemistry Division, National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8563, Japan

A lanthanum (La) coprecipitation method with low sample consumption was explored for the preconcentration of oxo-anion forming elements prior to a measurement by inductively coupled plasma mass spectrometry (ICP-MS). The preconcentration procedure was composed of two main steps: (1) the formation of a coprecipitate with the lowest possible La and (2) the redissolution of target analytes with minimal use of nitric acid, and the elimination of high concentration La from the analysis sample. Each step was performed in a 25 mL-volume syringe to reduce the sample consumption and to avoid contamination from the experimental environment. Various parameters, such as the concentration and volume of La added into the sample solution, the precipitation pH, the aging time, and the volume of HNO₃ were optimized to obtain good recoveries and high detection sensitivities for V, As, Sb, and W, which could be hardly recovered by solid-phase extraction using a chelating resin. The obtained method was evaluated through the analysis of seawater reference materials (CASS-4 and NASS-5). The recoveries exceeded 80%, and the observed values were in good agreement with the certified values.

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