Rapid semi-quantitative estimation of N-nitrosodibutylamine and N-nitrosodibenzylamine in smoked hams by solid-phase microextraction followed by gas chromatography-thermal energy analysis

A solid-phase microextraction (SPME) analytical method has been developed for the determination of N-nitrosodi-n-butylamine (NDBA) and N-nitrosodibenzylamine (NDBzA) in hams that is based on: (a) isolation of the compounds by steam distillation, (b) SPME from the distillate headspace using a polyacrylate coated silica fibre and (c) determination by gas chromatography-thermal energy analyzer technique or confirmation by gas chromatography-mass spectrometry. Recoveries of both NDBA and NDBzA from hams spiked at 5 to 160 micrograms/kg levels ranged between 41 to 112%. The overall method is fast, sensitive (detection limits, 1 to 3 micrograms/kg), precise (within 10%) and fairly accurate (average recoveries 86% and 70%, respectively). The results obtained by this technique for seven ham samples agreed fairly well with those obtained by an existing method (r2 = 0.97). The new method is solventless, environmentally friendly and useful for rapid monitoring purposes.

Formation of N-nitroso-N-methylurea in various samples of smoked/dried fish, fish sauce, seafoods, and ethnic fermented/pickled vegetables following incubation with nitrite under acidic conditions

In continuation of our previous studies on N-nitroso-N-methylurea (NMU) formation in cured meats following incubation with nitrite at gastric pH, we extended the investigation to other foods mentioned in the title of this paper. The main objective was to determine whether these foods have the potential to form NMU at pH's that can be found in the human stomach. This was done by nitrosating an aliquot (5 g for fish sauce, 10 g for the others) of each with 7.25 microM to 1.59 mM levels of sodium nitrite for 2 h at room temperature at pH 0.8--1.5 and measuring the amounts of NMU formed. Of the samples tested, fish sauce formed 2--712 ng of NMU, followed in decreasing order by herring (<0.3--688 ng); dried anchovy, shrimp, and other fishes (<0.3--134 ng); crab and lobster paté (<0.3--342 ng); sardines (6--59 ng); oysters and mussels (11--31 ng); dried squid (3--47 ng); kimchi (7--107 ng); and Japanese pickled radish (<0.3--72 ng). Incorporation of 200-2000 ppm of ascorbic acid in the fish sauce and other foods, prior to nitrosation, appreciably inhibited such NMU formation. Although previous researchers in China reported NMU formation in nitrosated samples of fish sauce, this is the first reported formation of NMU upon nitrosation of the other foods mentioned above, and the first reported inhibition of such formation by added ascorbic acid.

Investigation on the possible formation of N-nitroso-N-methylurea by nitrosation of creatinine in model systems and in cured meats at gastric pH

N-Nitroso-N-methylurea (NMU) is a highly potent direct-acting carcinogen that has been shown to induce cancer in a number of animal species. Although previous research has indicated that nitrosation of creatinine (CRN), a common constituent of meats, dried fish, and seafoods, can form traces of NMU, there is uncertainty as to (1) the yield of NMU and (2) whether detectable amounts of NMU can be formed from cured meats following nitrosation under acidic conditions given the low residual levels of nitrite found in cured meats at the present time. Lack of sensitive and specific analytical methods most likely has hindered progress in research in these areas. An HPLC postcolumn denitrosation-thermal energy analyzer technique and a GC-MS confirmation technique were developed for the determination of NMU in cured meats. Both techniques are highly sensitive (0.5 and 0.03 ppb, respectively) and specific. The optimum pH for NMU formation from CRN ranged between pH 1 and pH 3, and the yields of NMU under variable reactant concentrations ranged between 0.00004 and 0.0046%. When 27 samples of various cured meats (10 g aliquots each) were acidified with HCl (final pH values of 0.8-2.5) and incubated at room temperature for 2 h, without any additional nitrite, 24 gave results below detectable levels but 3 formed 2-26 ng of NMU/10 g of meat. Incubation of the negative meats with additional nitrite (50-500 microg/g of meat) formed 0.6-176 ng of NMU/10 g of sample. Although the amounts of NMU formed were extremely small, this seems to be the first reported formation of NMU from cured meats with and without additional nitrite.

Rapid and sensitive determination of nitrite in foods and biological materials by flow injection or high-performance liquid chromatography with chemiluminescence detection

A method is described for the determination of nitrite that is based on reduction of nitrite with potassium iodide followed by chemiluminescence detection of the liberated NO using a thermal energy analyzer. The method worked well both in the flow injection mode and upon interfacing with a reversed-phase high-performance liquid chromatography system. Limited data available indicated a good agreement between results obtained by the chemiluminescence method and those obtained by using a well established colorimetric procedure when they were applied for the determination of nitrite in a number of cured meats, human saliva, and baby foods. The chemiluminescence method is, however, much superior to the colorimetric one in its speed, versatility, as well as sensitivity (200 times more), and requires only a minimum of sample preparation. The detection limit of the new method is about 0.1 ng NaNO2 per injection or 5 micrograms/kg in cured meats and other substrates analyzed.

Formation of iodoacetic acids during cooking: Interaction of iodized table salt with chlorinated drinking water

Iodoacetic and chloroiodoacetic acids were formed when municipal chlorinated tap water was allowed to react with iodized (with potassium iodide) table salt or with potassium iodide itself. Iodoacetic acid was recently shown to be a potent cytotoxic and genotoxic agent. For analysis, samples were extracted with t-amyl methyl ether and converted to the corresponding methyl esters using methanol and sulfuric acid. The concentration of iodoacetic acid was determined by gas chromatography-mass spectrometry (GC-MS) using an authentic standard. The identities of iodoacetic and chloroiodoacetic acids were further confirmed by gas chromatography-high-resolution mass spectrometry (GC-HRMS). Certain influences of sodium hypochlorite and humic acid as well as the concentration of potassium iodide on the yields of these acids were investigated. The concentration of iodoacetic acid in tap water samples boiled with 2 g l-1 of iodized table salt was found to be in the 1.5 microg l-1 range, whilst the concentration of chloroiodoacetic acid was estimated to be three to five times lower.

A method for the determination of methyl carbamate and ethyl carbamate in wines

A method is described for the simultaneous determination of methyl carbamate (MC) and ethyl carbamate (EC) in wines that is based on: (a) extraction of the sample with dichloromethane using an extraction tube or an alumina-Celite column, (b) concentration of the extract to a small volume, and (c) determination by gas-liquid chromatography-thermal energy analyser (N-mode). The method is highly sensitive (1-2 ng/ml), accurate (recoveries greater than 80%), and precise (CV, 5-10%). Nineteen of 27 samples of wines analysed contained traces (up to 2.7 ng/ml) of MC, and most contained EC (up to 70 ng/ml). Wines treated in the laboratory with 200 ppm dimethyl pyrocarbonate (DMPC)-a cold sterilant recently approved for use in wines-indicated that such a treatment may increase the MC contents of the wines to 10 ng/ml. Additional studies suggested that formation of MC in DMPC-treated wines is dependent on both pH and ammonia content of the wines. The identity of MC in a few selected samples was confirmed by gas-liquid chromatography-high resolution (10 K) mass spectrometry. The natural low levels of MC found in these wines are not considered to pose a risk to human health.

Determination of non-volatile N-nitrosamines in baby bottle rubber nipples and pacifiers by high-performance liquid chromatography-thermal energy analysis

A method is described for the determination of non-volatile N-nitrosamines in baby bottle rubber nipples and pacifiers. It consists of extraction of the sample with dichloromethane in the presence of ascorbyl palmitate (an inhibitor of artifactual formation of nitrosamines), clean-up on silica or basic alumina, and final analysis by high-performance liquid chromatography-thermal energy analysis, a technique which is highly specific for N-nitroso compounds. The method worked well for the determination of four rubber-related non-volatile nitrosamines, namely, N-nitrosomethylphenylamine, N-nitrosoethylphenylamine, N-nitrosodicyclohexylamine, and N-nitrosodibenzylamine (recoveries from spiked samples greater than 80%; detection limit, ca. 5 micrograms/kg for each). Eighteen out of twenty four samples analyzed were found to contain varying levels (mean, 41 micrograms/kg; range, 8-146 micrograms/kg) of N-nitrosodibenzylamine. The identity of the compound was confirmed by gas chromatography-thermal energy analysis as well as by gas chromatography-mass spectrometry analyses.

The analysis and significance of bound N-nitrosoproline in nitrite-cured meat products

An alkaline hydrolysis method is described for the release of bound N-nitrosoproline (NPRO) from cured meats that is more efficient than an enzymic method reported previously. The bound NPRO contents of 17 cured meats analysed ranged between non-detectable and 578 micrograms/kg (mean 143 micrograms/kg). Administration of defatted meat powder, prepared from such meats, to rats led to increased excretion of free NPRO in the urine that could not be inhibited by concurrent administration of ascorbic acid. The significance of these findings with regard to the use of such cured meats in in vivo N-nitrosation studies is discussed.

Analytical methods for the determination and mass spectrometric confirmation of 1-methyl-2-nitroso-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid and 2-nitroso-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid in foods

A method is described for the determination of the two title compounds that is based on: (a) extraction of the acidified sample with methanol, (b) removal of fats and lipids by partitioning of the extract with n-hexane, (c) clean-up on acidic alumina extraction cartridge, and (d) determination by a post-HPLC column chemical denitrosation-thermal energy analyser (TEA) technique or by conventional HPLC-TEA analysis after derivatization of the compounds with diazomethane. Confirmation was carried out by HPLC-mass spectrometry of the free acids and also by gas chromatography-mass spectrometry of the methyl esters. The formation of both 1-methyl-2-nitroso-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid and 2-nitroso-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid in nitrosated samples of several Japanese and Chinese pickled vegetables, one soy sauce, and two cheeses was demonstrated.

Mass spectrometric confirmation of the presence of N-nitrosopyrrolidine in instant coffee

Traces of N-nitrosopyrrolidine (NPYR) may occur in some samples of both instant coffee and fine-ground roasted coffee. The identity of NPYR in 2 samples of instant coffee was confirmed by mass spectrometry as well as by liquid chromatography-thermal energy analysis. A 2-step cleanup procedure, involving fractionation on basic alumina followed by gradient elution on reverse-phase C18 cartridge, is described that allows full-scan mass spectrometric confirmation of NPYR in tested samples.