Trace analysis for total nitrogen in a water sample by isotopic dilution

Preliminary results of an investigation to test the feasibility of isotopic dilution analysis of aquatic samples for trace amounts of total-N (i.e. NH4-N, NO3-N, organic N, etc) are reported. Analysis of nine replicates of a kjeldahl-analysed subsoil water sample yielded an average value of 0.42 +- 0.02 mg total-N/l. water (ppm), which is in satisfactory agreement with the kjeldahl value of 0.38 +-0.03 ppm. So far, the detectivity of the isotope dilution method is in the vicinity of 100 ng total-N. Strict observance of 14N hygiene during sample preparation appears to be of paramount importance. (U.K.)