An isotope-derivative method for the detection and estimation of oestrogens

ABOUT ten years ago Keston and co-workers developed an isotope dilution method for the estimation of amino-acids1. This method, by which the amino-group of amino-acids is labelled with radio-active ‘pipsyl chloride’ (p-iodophenylsulphonyl chloride, labelled with iodine-131), was not found applicable for other types of compounds until recently. Last year, however, this method was also used for the detection and estimation of histamine2, pyrimidines3 and 17-hydroxycorticosterone4. In the last method the labelling agent was ‘pipsan’ (p-iodophenylsulphonylic acid anhydride).