AT-Nitroso compounds can be divided into either AT-nitro-samines or AT-nitrosamides. AT-Nitrosamines can be subdivided into two groups depending on their physical properties: (1) Volatile AT-nitrosamines (VNA), which are Af-nitrosated analogues of simple low molecular weight dialkylamines and cyclic compounds such as NDMA, N-nitrosodibutylamine (NDBA), AT-nitrosopiperidine (NPIP), AT-nitrosopyrrolidine (NPYR), AT-nitrosothiazolidine (NTHZ), and AT-nitrosomorpholine (NMOR), as shown in Figure 2; and (2) nonvolatile AT-nitrosamines (NVNA), which include a wide range of AT-nitrosated hydroxylated or polyfunctional compounds, as shown in Figure 3. The most commonly encountered NVNA are the Af-nitrosated amino acids Af-nitrosoproline (NPRO), AT-nitrososarcosine (NSAR), AT-nitrosohydroxyproline (NHPRO), and a wide range of AT-nitrosated heterocyclic carboxylic acids formed by nitrosation of the condensation products of the amino acids cysteine, serine, threonine, and tryptophan with simple aldehydes such as formaldehyde and acetaldehyde. The condensation of cysteine and formaldehyde to yield thia-zolidine-4-carboxylic acid produces the amine precursor to AT-nitrosothiazolidine-4-carboxylic acid (NTCA), which is the most frequently encountered AT-nitrosated heterocyclic carboxylic acid formed by this type of reaction. Other examples of AT-nitrosated heterocyclic carboxylic acids are AT-nitroso-2-(hydroxymethyl)thiazolidine-4-carboxylic acid (NHMTCA) formed by condensation of cysteine with glycolaldehyde and the oxazolidines AT-nitrosooxazolidine-4-carboxylic acid (NOCA) and AT-nitroso-5-methyloxazoli-
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