ガスクロマトグラフィーによる<I>N</I>-ニトロソアミンの分析

Recently much attention has been paid on the possible formation of carcinogenic N-nitrosamines in foods. Nitrates and nitrites are widely used in many countries for meat curing aims, in addition to preservation of canned meat products and smoked fish products or to manufacturing certain types of cheese. In Japan, sodium nitrite is permitted to use as a color fixative for preparing such types of foods as hams, sausages, fish hams, fish sausages and salted salmon roe. On the other hand, secondary amines especially dimethylamine are widely distributed in the edible portions of sea fish at comparatively high level.<BR>Recently, Howard et al., and Sen et al. have reported the methods for estimating dimethylnitrosamine (DMNA) in various foods by gas chromatography. However, many problems remain to be solved as to get more sensitive and accurate method for determining ultra-minute quantity of N-nitrosamines in foods (at 0.1 ng level).<BR>In the present studies, operating conditions on gas chromatography for N-nitrosamines such as types of detector, column packing materials and carrier gases were investigated and, in addition, basic studies on the qualitative and quantitative analyses for N-nitrosamines were conducted.<BR>Concerning the flame thermoionic detector as an emission electrode, a platinum-iridium coil coated with alkaline salt was found superior in the sensitivity than a tip type alkaline salt for detecting N-nitrosamines.Potassium salt (KCl) gave higher sensitivity than either sodium (NaCl) or lithium salt (LiCl) as an emission electrode. In points of stability and sensitivity, Na silicate-K silicate mixture may satisfactorily be used as a coating material for the coil type detector.<BR>As to the separating ability for N-nitrosamine, following types of column packing materials, diethylene glycol succinate (LEGS), polyethylene glycol 6000 (PEG 6000), Versamid 900, Porapak Q, and Chromosorb 101 were compared one another. Consequently, both PEG 6000 and Versamid 900 have been found to be fitted as the liquid phase of a column for analyzing N-nitrosamines.<BR>Retention times for various N-nitrosamines were determined on the two columns; one was being packed with 25% PEG 6000 on 6080 mesh Chromosorb W, and the other with 20% Versamid 900 on the same support, from which those values for relative retention index have been calculated. The PEG 6000 column exhibited lower sensitivity for detecting N-nitrosamines than the Versamid 900 column. The reason for lower sensitivity of the former column was found that N-nitrosamines might be partially converted into N-nitroamines during passing through the PEG 6000 column.<BR>Of carrier gases, it was found that helium gives much higher sensitivity for detecting N-nitrosamines than nitrogen.<BR>N-nitrosamines in the salted Alaska pollack roe sample being treated with sodium nitrite have been analyzed according to the above-mentioned conditions.