Separated Isotopes as Internal Standards in Spark Source Mass Spectrometry

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Abstract
The use of separated stable isotopes as internal standards in spark source mass spectrometry is described. This method is useful for solution samples and complements the more classical isotope dilution technique. For powdered or insoluble samples, the isotopes are dried onto a conducting matrix material-usually high purity silver powder-followed by homogenization of the sample with this «spiked’ matrix. The resulting mixture can then be pressed into solid electrodes and analyzed by spark source mass spectrometry. This technique has proven useful for the determination of mononuclidic elements such as Co, As, and Mn in a variety of samples, and for multielement analysis of coal ash and fly ash, with a minimum of sample handling and resultant contamination. Use of an isotope which has a mass near to that of the element being measured gives more precise and accurate analyses than the common technique of using one internal standard.