Samples are step-heated in a Modifications Ltd. Low-bland furnace connected on-line to the mass spectrometer. Temperature control is accurate to 1C. Extracted argon is purified in a two-stage process. First stage exposes the ssample to a liquid nitrogen cold finger and a Ti furnace at 700C for 20 minutes. Argon is then drawn onto activated charcoal for 20 minutes. Argon is then released from the charcoal and further purified using a SAES ST101 getter for 10 minutes. Purifiec argon isotopes are then measured using a Nuclide 6-60-SGA 15 cm mass spectrometer. Sensitivity of the instrument is 6.5 x 10^-15 mol/mV and system noise is generall around 0.02 mV.