An alternative procedure for the O-18 measurement of nitrate oxygen

A new method for the preparation of nitrate samples for O-18 measurement is presented. The technique utilizes guanidine hydrochloride to convert the n itrate oxygen to CO2. The delta(18)O values of our KNO3 laboratory standard (K1) obtained by the guanidine method are compared with the results of the reaction of the potassium nitrate laboratory standard K1 with mercury cyan ide and with the silver nitrate-graphite method. The delta(18)O data produc ed by the high temperature (900 degrees C) cyanide and graphite technique a re comparable to the guanidine method only when the potassium nitrate is co nverted to silver nitrate. The reproducibility for the guanidine method is +/-0.2 parts per thousand b ased on the tests carried out using KNO3 (laboratory standard, K1) and the IAEA-N3 reference material. The yield of the conversion of nitrate oxygen t o CO2 is 95-100%. (C) 2000 Elsevier Science B.V. All rights reserved.