Abstract: The invention provides a calibrating method for use in a method of determining the quantity of an analyte labeled with an accelerator mass spectrometry (AMS) isotope in a test sample. The samples can include, for example, urine, faeces, plasma or blood. The analyte can be, for example, a drug or metabolite of a drug.

Abstract: The invention provides a calibrating method for use in a method of determining the quantity of an analyte labelled with an AMS isotope in a test sample, said calibrating method comprising: (i) contacting a plurality of samples contaminated with neither said analyte nor a non-labelled counterpart analyte with a known quantity of said counterpart analyte and a quantity C of analyte to afford a plurality of calibrating samples, wherein each of said calibrating samples contains a known quantity of counterpart analyte but a different quantity of C; (ii) measuring by AMS the quantity C of analyte added to each of the plurality of samples; (iii) separating the analyte and counterpart analyte from other species in the plurality of samples to afford a plurality of purified samples; (iv) measuring a quantity A of analyte in said purified samples by AMS; and (v) measuring a quantity B of counterpart analyte in said purified samples.

Abstract: The invention provides a biological composition comprising a biological compound of formula I B-A* ??(I) alone or together with B wherein B-A* is a biological compound or a derivative thereof formed as the product of reaction of the biological compound to introduce A*, A* is a radioisotopic moiety having MW in the range 10 to 500 comprising an AMS radioisotope * wherein the composition is characterised by a value for the percent incorporation of radioisotope which is a measure of maximum specific activity, wherein 100% incorporation is defined as the incorporation of one radioisotope per molecule, and wherein the percent incorporation is in the range from in excess of zero to 100%, wherein the quantity of organic radioisotope A* labelled molecules in a population of one thousand molecules is so low as to not alter the biological activity of the drug; a process for the preparation thereof; a method for AMS detection of one or more biological compositions as defined in any of claims 1 to 17 comprising B of