The coupling of automated combustion instruments with mass spectrometry has streamlined total N and 15 N analyses of soil and plant materials. New methods are needed for analysis of soil NH 4 and NO 3 15 N to take advantage of the efficiency in automated combustion analysis. We have developed a method to quantitatively determine NO 3 , NH 4 , and 15 N content of soil extracts by automated combustion/mass spectrometry. Soil extracts are made basic, and diffused into acid‐washed zeolite in tin combustion cups. Zeolite samples are then analyzed on the automated combustion/mass spectrometry system for N and 15 N. Ammonium‐ and NO 3 ‐N and 15 N can be quantitatively recovered and analyzed during this procedure, reliably collecting 97% of the N and 15 N in the extract, with a repeatability of ±2%.
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Burke et al. (1990) studied this question.