The method comprises the passage of a gaseous test portion through water to absorb acetone, acetonitrile, propan-2-ol and methanol, and subsequent gas chromatographic analysis of the aqueous solution, using a flame ionization detector, and comparison of the peaks obtained with those derived from an external standard. The method is applicable to products having acetone, propan-2-ol and methanol concentrations greater than 1 mg/kg, and acetonitrile concentrations greater than 10 mg/kg.