Improved group determination of total N-nitroso compounds in human gastric juice by chemical denitrosation and thermal energy analysis.

Abstract

A procedure for the determination of total N-nitroso compounds (NOC) in human gastric juice was developed by modifying earlier methods. The gastric juice sample, treated with sulphamic acid to remove nitrite, is injected directly into refluxing ethyl acetate containing either acetic acid for determining thermo-and acetic acid labile thermal energy analyser (TEA) responsive compounds (TAC), or into hydrogen bromide for the determination of TAC and NOC. The nitric oxide (NO) levels released are measured using thermal energy analysis with chemiluminescence detection, and the difference between the two determinations represents the concentrations of NOC in gastric juice. This method is not affected by nitrate concentrations of up to 1000 µmol l–1.The method was found to be rapid, reproducible and sensitive (detection limit 0.02 µmol l–1 NOC), requiring only small volumes of gastric juice and no prior extraction. Because the difficulties arising from the system response to the denitrosating agent and variability of NO release by acetic acid from nitrite were eliminated, this improved method can more accurately distinguish NOC from most other TEA-responsive species. Suitable techniques for stabilising gastric juice samples from duodenal ulcer and atrophic gastritis patients and the influence of the time and storage conditions on NOC concentrations have been studied.