An improved method for analysis of total N-nitroso compounds in gastric juice

An improved procedure for the analysis of total N-nitroso compounds (NOC) in human gastric juice was developed by modifying previous methods. The gastric juice sample, treated with sulfamic acid to remove nitrite, is injected directly into refluxing ethyl acetate containing either acetic acid for determining thermo/acetic acid-labile-thermal energy analyser (TEA)-responsive compounds (TAC), or into hydrogen bromide for the analysis of TAC and NOC. The nitric oxide (NO) levels released are measured by chemiluminescence by TEA, and the difference between the two determinations represents the concentrations of NOC in gastric juice. This method also allows the determination of nitrite and is not affected by nitrate concentrations up to 1,000 mumol/l. The method was found to be reproducible and sensitive (detection limit, 0.02 mumol NOC/l), 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 stabilizing gastric juice samples from duodenal ulcer/atrophic gastritis patients and the influence of the time and storage conditions on NOC concentrations have been studied.