Analysis of N-nitrosamines by high-performance liquid chromatography with post-column photohydrolysis and colorimetric detection.

N-Nitrosamines eluted from reversed-phase HPLC were quantitatively photohydrolysed in a UV photoreactor in aqueous solution to give the nitrite ion which could be determined colorimetrically with the Griess reagent. The chromatographic behavior of N-nitroso compounds (including 19 volatile dialkyl and 7 non-volatile N-nitrosamines) was studied on three octadecylsilane columns. The capacity factor varies linearly with the number of carbons atom of the n-dialkyl chains. N-nitrosamines bearing di-n-alkyl chains with the same number of carbon atoms could be separated with a highly polar mobile phase. The yield of photohydrolysis depends upon pH and time of exposure under UV light. The response was shown to be linear in the 0-200 ng range with a limit of detection of 8 pmoles injected for N-dialkyl nitrosamines. This limit was 20 pmoles for N-nitrosamines bearing two phenyl groups. Although N-nitrosamines could be detected at 230 nm without post-column reaction, such a reaction enhances the specificity of detection in biological matrices such as gastric juice or alcoholic beverages.