Determination of 15N/14N and 13C/12C in solid and aqueous cyanides

The stable isotopic compositions of nitrogen and carbon in cyanide compounds can be determined by combusting aliquots in sealed tubes to form N₂ gas and CO₂ gas and analyzing the gases by mass spectrometry. Free cyanide (CN^-_aq + HCN_aq) in simple solutions can also be analyzed by first precipitating the cyanide as copper(II) ferrocyanide and then combusting the precipitate. Reproducibility is ±0.5‰ or better for both δ¹⁵N and δ¹³C. If empirical corrections are made on the basis of carbon yields, the reproducibility of δ¹³C can be improved to ±0.2‰. The analytical methods described herein are sufficiently accurate and precise to apply stable isotope techniques to problems of cyanide degradation in natural waters and industrial process solutions.