I have read in several publications the use of nitrosation assay procedure (NAP Test). The NAP test was originally designed in 80’s by the International Agency for Research on Cancer of the WHO to simulate in vivo formation of nitrosamines in the stomach.
In the publication below, All samples were incubated at 37°C for 4 h with an API concentration
of 10 mmol/l in a 40‐mol/l sodium nitrite solution at pH 3.5 (with 1 mol/l hydrochloric acid). The pH was adjusted in the sodium nitrite solution, measured (pH 3.5 ± 0.5), and corrected if necessary after the addition of sample material. After incubation, samples were centrifuged and the particle‐free supernatant was analyzed.