Accurate determination of trace amounts of phosphorus in geological samples by inductively coupled plasma atomic emission spectrometry with ion-exchange separation

• We set up an effective ICP-AES procedure for determining trace P in rock samples.
• Some certified values of P for reference rock samples were proved to be doubtful.
• Accurate and reliable data were presented for a suite of geological reference rocks.

In order to determine trace amounts of phosphorus in geological and cosmochemical rock samples, simple as well as reliable analytical schemes using an ICP-AES instrument were investigated. A (conventional) ICP-AES procedure could determine phosphorus contents at the level of several 100 μg g−1 with a reasonable reproducibility (<10% for 200 μg g−1; 1σ). An ICP-AES procedure coupled with matrix-separation using cation and anion exchange resins could lower the quantification level down to 1 μg g−1 or even lower under the present experimental conditions. The matrix-separation ICP-AES procedure developed in this study was applied to twenty-one geological reference samples issued by Geological Survey of Japan. Obtained values vary from 1250 μg g−1 for JB-3 (basalt) to 2.07 μg g−1 for JCt-1 (carbonate). Matrix-separation ICP-AES yielded reasonable reproducibility (less than 8.3%; 1σ) of three replicate analyses for all the samples analyzed. In comparison of our data with certificate values as well as literature or reported values, there appear to be an apparent (and large) discrepancy between our values and certificate/reported values regardless of phosphorus contents. Based on the reproducibility of our data and the analytical capability of the matrix-separation ICP-AES procedure developed in this study (in terms of quantification limit, recovery, selectivity of an analyte through pre-concentration process, etc.), it is concluded that certified values for several reference standard rocks should be reevaluated and revised accordingly. It may be further pointed that some phosphorus data reported in literatures should be critically evaluated when they are to be referred in later publications.

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