Nitrosamine, formation methods

Some of the methods used for decreasing nitrosamine formation are [41] ... 

To check that the NO exposure was necessary for nitrosamine formation, morpholine was gavaged to mice as usual, but the NO exposure was omitted. Five g mouse homogenate was worked up by the Iqbal method (after addition of 11 mg cis-DMM) and yielded neither NMOR nor cis-DMNM. Similarly, when 10 mg morpholine was added to 5 g homogenate prepared from an untreated mouse and... 

Reliable analytical methods are available for determination of many volatile nitrosamines at concentrations of 0.1 to 10 ppb in a variety of environmental and biological samples. Most methods employ distillation, extraction, an optional cleanup step, concentration, and final separation by gas chromatography (GC). Use of the highly specific Thermal Energy Analyzer (TEA) as a GC detector affords simplification of sample handling and cleanup without sacrifice of selectivity or sensitivity. Mass spectrometry (MS) is usually employed to confirm the identity of nitrosamines. Utilization of the mass spectrometer s capability to provide quantitative data affords additional confirmatory evidence and quantitative confirmation should be a required criterion of environmental sample analysis. Artifactual formation of nitrosamines continues to be a problem, especially at low levels (0.1 to 1 ppb), and precautions must be taken, such as addition of sulfamic acid or other nitrosation inhibitors. The efficacy of measures for prevention of artifactual nitrosamine formation should be evaluated in each type of sample examined. 

Major emphasis in studies of N-nitroso compounds in foods has been placed upon volatile nitrosamines, in part because these compounds are relatively easy to isolate from complex matrices by virtue of their volatility. Procedures utilizing atmospheric pressure or vacuum distillation have been used by most investigators, with variations of the method of Fine e al. (2) being among the most popular. This procedure employs vacuum distillation of a mineral oil suspension of the sample with optional addition of water to improve nitrosamine recovery from low moisture content samples (6) The usual approach to prevention of nitrosamine formation during analysis involves adding sulfamic acid or ascorbate to destroy residual nitrite at an early stage of sample preparation. 

Beer Samples. The beer samples were examined as part of the American Society of Brewing Chemists (ASBC) and Association of Official Analytical Chemists (AOAC) collaborative studies of NDMA in beer. Duplicate samples were analyzed by the column extraction procedure and the ASBC distillation procedure (35). The AOAC procedure (36) was similar, except that a larger sample (50 vs. 25 g) was examined and sulfamic acid was added to minimize artifactual formation of nitrosamines. Both methods utilize N-nitrosodipropylamine (NDPA) as an internal standard. 

Cured meat pigment (nitrosyl ferrohemochrome) may be prepared by gaseous NO treatment of hemin (Shahidi etal., 1985). O Boyle etal. (1990) used cured meat pigment produced by this method in the production of nitrite-free weiners, lowering the possibility for nitrosamine formation in these products during heat processing. This process also has not yet been incorporated into commercial practice. 

The content of free diethanolamine in particular is controlled in these products because secondary amines open the possibility of A-nitrosamine formation if they should come in contact with nitrites. The methods most frequently used nowadays for alkanolamine analysis are gas chromatography, ion chromatography, and capillary electrophoresis. The titration methods have become less useful over the last decade as the concentration of the free alkanolamines in commercial products continues to decline. 

Nonvolatile Nitrosamines In Tobacco. A method which we developed several years ago for the analysis of tobacco-specific nitrosamines (TSNA 31) involves extraction of tobacco with buffered ascorbic acid TpH 4.5) followed by partition with ethyl acetate, chromatographic clean-up on silica gel, and analysis by HPLC-TEA (Figure 9). Results obtained with this method for a large spectrum of tobacco products (Table IV), strongly support the concept that the levels of nitrate and alkaloids, and especially the methods for curing and fermentation, determine the yields of TSNA in tobacco products. Recent and as yet preliminary data from snuff analyses indicate that aerobic bacteria play a role in the formation of TSNA during air curing and fermentation. 

Direct Injection of Amines. In the course of developing methods for investigation of in vivo formation of NMOR and NPYR in rats treated with precursor amines and nitrite, it was necessary to determine the contamination levels of the amines by the nitrosamines. Spiegelhalder et al (32) reported the presence of nitrosamines in all secondary and tertiary amine samples which they examined, using vacuum steam distillation followed by extraction and GC-TEA determination. 

The concentrations of nitrosamines were reduced to undetectable levels by ultraviolet treatment of the amine solutions and were not increased by addition of 2 ppm NaN02> indicating that the nitrosamines were present originally in the amines and were not formed in the GC injection port. Similar concentrations were found when the amine samples were analyzed using the column extraction method. Direct injection is appropriate for analysis of relatively simple mixtures, if adequate precautions are taken ( ), but can result in significant artifact formation in more complex systems (42). 

Available detection and confirmation methods are adequate for establishing identity and amounts of nitrosamines in most environmental and biological samples. The validity of analytical results, especially at levels in the part-per-billion and lower range, depends upon the experience and skill of the analyst in preventing or detecting contamination or artifactual formation of nitrosamines. 

Egan, H. Preussmann, R. Walker, E.A. Castegnaro, M. Wasserman, A.E. Eds. "Environmental Carcinogens Selected Methods of Analysis Vol. 1 - Analysis of Volatile Nitrosamines in Food." lARC Scientific Publications No. 18. International Agency for Research on Cancer Lyon, 1978. Walker, E.A. Griciute, L. Castegnaro, M. Borzsonyi, M., Eds. "N-Nitroso Compounds Analysis Formation and Occurrence" lARC Scientific Publications No. 31. International Agency for Research on Cancer Lyon, 1980. Hedler, L. Schurr, C. Marquadt, P. J. Am. Oil Chem. Soc. 1979, 681-684. 

In view of the highly carcinogenic nature of many nitrosamines any experiments involving their isolation must be discouraged, and for this reason, this section has only been written for completeness. This high toxicity is unfortunate because the preparation of nitrosamines from the parent amines is often facile and they provide a route to highly pure nitramines. Other equally useful methods for the synthesis of nitramines, such as the chloride-catalyzed nitration of secondary amines, also suffer from the formation of nitrosamines in appreciable amounts and must also be viewed with caution. 

A novel method to degrade tertiary amines proceeds through the formation of secondary N-nitrosamines (l6). 

A modification of the mineral oil distillation procedure has been proposed using a gas purge system to trap nitrosamines on a ThermoSorb/N cartridge. This procedure eliminates solvent extraction and evaporation steps, hence reducing the possibility of artifact formation. On the other hand, some methods have also been described for the vacuum distillation of alkaline suspensions without mineral oil. The distillation is carried out from a slightly basified sample with carbonate potassium or from a highly basified sample with potassium hydroxide. 

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