Isotope-ratio analysis for 15N in solid-phase samples such as animal tissue starts with transformation to gas phase by extremely rapid and complete flash combustion of the sample material. Ionized combustion product (dinitrogen) is mass-analyzed by means of differing mass/charge ratios among the various isotopic species of N2. More details about this method in the stable isotope overview.
Sample prep considerations
Animal samples must be oven-dried, ball-milled to less than 250 um particle size and weighed (~3 mg, with ug digits significant) into 5 x 5 mm tin capsules before combustion. Poor precision can often be traced to inadequate grinding that leaves fibrous matter or visible granules in the sample. Clients may send us unprocessed samples or may provide any of the above processing themselves at a major reduction in price.