Analytik von N-nitrosoverbindungen: V. Spurenanalyse von N-nitrosoaminosäuren: Gaschromatographie und spektroskopie von N-nitrosoaminosäuremethylestern

Abstract

Analysis of N-nitroso compounds. V. Trace analysis of N-nitrosoamino acids: Gas chromatography and spectroscopy of N-nitrosoamino acid methyl esters N-Nitrosoamino acids (N-NO-sarcosine, N-NO- l-proline, N-NO-4-OH- l-proline and N-NO- d,l-piperidine-2-carboxylic acid) were reacted with methanol-H + or diazomethane to the corresponding methyl esters in preparative and analytical scale. N-NO-4-OH- l-proline methyl ester was reacted with N-methyl-N-trimethylsilyl-trifluoroacetamide to give N-NO-4-O-trimethylsilyl- l-proline methyl ester in quantitative yield. The N-nitrosoamino acid methyl esters were characterized by physical (b.p., m.p., R F values) and spectral data (infrared, mass spectrometry, 1H nuclear magnetic resonance (NMR), 13C NMR). The fragmentations of N-NO-sarcosine methyl ester, N-NO- l-proline methyl ester and N-NO- d,l-piperidine-2-carboxylic acid methyl ester induced by electron impact in the mass spectrometer, were studied by high-resolution measurements, metastabile ions, DADI-technique and defocusing method. The ratios of E- and Z-isomers of N-nitrosoamino acid methyl esters in solution are determined by 1H NMR spectroscopy. The resonances of the methyl ester protons appear as two singlets. This is explained by interaction of the N-NO-groups with the methyl ester protons via cyclic arrangements in equilibria of E- and Z-isomers and confirmed by the 1H NMR spectrum of N-NO-sarcosine-trideuteromethyl ester. The N-nitrosoamino acids are quantitatively converted to the corresponding N-nitrosoamino acid methyl esters by reacting with diazomethane. These derivatives of N-nitroso-amino acids (including N-NO-4-O-trimethylsilyl- l-proline methyl ester) can be separated by gas-liquid chromatography on OV-17 as stationary phase. This derivatization procedure allows separation and quantitative determination of N-nitrosoamino acids by gas-liquid chromatography and confirmation by gas-liquid chromatographic-mass spectrometric analysis in nanogram amounts.