We present a method for the determination of ultra-trace Te species (Te(IV) and Te(VI)) in open ocean waters. The proposed method is based on Mg(OH)2 coprecipitation, anion exchange resin column separation and inductively coupled plasma sector-field mass spectrometry (ICPSFMS) using a 125Te-enriched isotope spike. The largest advantage of the method is that the use of the spike allows accurate and precise determination when it combines with either isotope dilution or recovery correction. Tellurium-IV and VI are preconcentrated in a Mg(OH)2 precipitate and separated mutually by an anion exchange resin column. Te(IV) is retained to the column, while Te(VI) passing through the column is recovered by a subsequent column procedure after reduction of Te(VI) to Te(IV). Te(IV) is successfully eluted with a small amount of 0.01 M HCl. The additional merit of using this eluent is elimination of components that result in a memory effect during the measurement of Te(IV). Possible mass spectral interference on Te(IV) can be excluded by adjusting the mass window, and the Te(IV) concentrations determined by this approach agree well with those independently obtained by an oxidation procedure which removes the interference. The accuracy of the proposed method is verified with homemade standard seawater for which the measured concentrations agree well with results calculated from the value of the standard solution. Procedural blanks for Te(IV) and Te(VI) are 1.5 ± 0.9 pg kg-1 (n = 11) and 1.3 ± 0.9 pg kg-1 (n = 11) with corresponding overall detection limits of 3.0 pg kg-1 and 2.8 pg kg-1, respectively. Using the method, we have clarified vertical profiles of Te(IV) and Te(VI) in the subarctic western North Pacific for the first time.
Keywords: Anion exchange resin column separation; ICPSFMS; Mg(OH)(2) coprecipitation; Open ocean waters; Spike; Te species.
Copyright © 2024 Elsevier B.V. All rights reserved.