A new method for the measurement of argon isotope composition in a continuous flow of helium for potassium/argon geochronology is described. Extraction of argon from geological samples in multiple-sample holders was carried out in a chamber by heating with a continuous Nd-YAG laser. The extracted and pre-concentrated argon is passed through a chromatographic capillary column in a flow of helium. Argon is separated from possible contaminants in the column and is injected through an open split into the ion source of an isotope ratio mass spectrometer. Measurement of the (36)Ar, (38)Ar and (40)Ar isotopes was carried out in dynamic mode, using a triple-collector ion detector. These experiments have shown that continuous flow mass spectrometry can be used for the analysis of radiogenic argon in picogram quantities with an accuracy that is satisfactory for the solution of many geochronological problems. The method of argon isotope measurement in a continuous flow of helium is an alternative to the measurement of argon isotopes in the static mode. The sensitivity and accuracy of argon measurement by this method are comparable with those provided by the classical static method. The measurement of argon isotopes in a continuous flow of helium is simpler and more reliable than measurement in the static mode.
2009 John Wiley & Sons, Ltd.