Description of the thermal energy analyzer (TEA) for trace determination of volatile and nonvolatile N-nitroso compounds

Risk assessment of N-nitrosamines in food

EFSA was asked for a scientific opinion on the risks to public health related to the presence of N-nitrosamines (N-NAs) in food. The risk assessment was confined to those 10 carcinogenic N-NAs occurring in food (TCNAs), i.e. NDMA, NMEA, NDEA, NDPA, NDBA, NMA, NSAR, NMOR, NPIP and NPYR. N-NAs are genotoxic and induce liver tumours in rodents. The in vivo data available to derive potency factors are limited, and therefore, equal potency of TCNAs was assumed. The lower confidence limit of the benchmark dose at 10% (BMDL10) was 10 μg/kg body weight (bw) per day, derived from the incidence of rat liver tumours (benign and malignant) induced by NDEA and used in a margin of exposure (MOE) approach. Analytical results on the occurrence of N-NAs were extracted from the EFSA occurrence database (n = 2,817) and the literature (n = 4,003). Occurrence data were available for five food categories across TCNAs. Dietary exposure was assessed for two scenarios, excluding (scenario 1) and including (scenario 2) cooked unprocessed meat and fish. TCNAs exposure ranged from 0 to 208.9 ng/kg bw per day across surveys, age groups and scenarios. 'Meat and meat products' is the main food category contributing to TCNA exposure. MOEs ranged from 3,337 to 48 at the P95 exposure excluding some infant surveys with P95 exposure equal to zero. Two major uncertainties were (i) the high number of left censored data and (ii) the lack of data on important food categories. The CONTAM Panel concluded that the MOE for TCNAs at the P95 exposure is highly likely (98-100% certain) to be less than 10,000 for all age groups, which raises a health concern.

A Diagnostic Nitrosamine Detection Approach for Pharmaceuticals by Using Tandem Mass Spectrometry Based on Diagnostic Gas-Phase Ion-Molecule Reactions

N-Nitrosamines are strictly regulated in pharmaceutical products due to their carcinogenic nature. Therefore, the ability to rapidly and reliably identify the N-nitroso functionality is urgently needed. Unfortunately, not all ionized N-nitroso compounds produce diagnostic fragment ions and hence tandem mass spectrometry based on collision-activated dissociation (CAD) cannot be used to consistently identify the N-nitroso functionality. Therefore, a more reliable method was developed based on diagnostic functional-group selective ion-molecule reactions in a linear quadrupole ion trap mass spectrometer. 2-Methoxypropene (MOP) was identified as a reagent that reacts with protonated N-nitrosamines in a diagnostic manner by forming an adduct followed by the elimination of 2-propenol (CH₃C(OH)═CH₂]). From 18 protonated N-nitrosamine model compounds studied, 15 formed the diagnostic product ion. The lack of the diagnostic reaction for three of the N-nitrosamine model compounds was rationalized based on the presence of a pyridine ring that gets preferentially protonated instead of the N-nitroso functionality. These N-nitrosamines can be identified by subjecting a stable adduct formed upon ion-molecule reactions with MOP to CAD. Further, the ability to use ion-molecule reactions followed by CAD to differentiate protonated O-nitroso compounds with a pyridine ring from analogous N-nitrosamines was demonstrated This methodology is considered to be robust for the identification of the N-nitroso functionality in unknown analytes. Lastly, HPLC/MS² experiments were performed to determine the detection limit for five FDA regulated N-nitrosamines.

A Full Evaporation Static Headspace Gas Chromatography Method with Nitrogen Phosphorous Detection for Ultrasensitive Analysis of Semi-volatile Nitrosamines in Pharmaceutical Products

The recent detection of potent carcinogenic nitrosamine impurities in several human medicines has triggered product recalls and interrupted the supply of critical medications for hundreds of millions of patients, illuminating the need for increased testing of nitrosamines in pharmaceutical products. However, the development of analytical methods for nitrosamine detection is challenging due to high sensitivity requirements, complex matrices, and the large number and variety of samples requiring testing. Herein, we report an analytical method for the analysis of a common nitrosamine, N-nitrosodimethylamine (NDMA), in pharmaceutical products using full evaporation static headspace gas chromatography with nitrogen phosphorous detection (FE-SHSGC-NPD). This method is sensitive, specific, accurate, and precise and has the potential to serve as a universal method for testing all semi-volatile nitrosamines across different drug products. Through elimination of the detrimental headspace-liquid partition, a quantitation limit of 0.25 ppb is achieved for NDMA, a significant improvement upon traditional LC-MS methods. The extraction of nitrosamines directly from solid sample not only simplifies the sample preparation procedure but also enables the method to be used for different products as is or with minor modifications, as demonstrated by the analysis of NDMA in 10+ pharmaceutical products. The in situ nitrosation that is commonly observed in GC methods for nitrosamine analysis was completely inhibited by the addition of a small volume solvent containing pyrogallol, phosphoric acid, and isopropanol. Employing simple procedures and low-cost instrumentation, this method can be implemented in any analytical laboratory for routine nitrosamine analysis, ensuring patient safety and uninterrupted supply of critical medications.

Development and Validation of a Method for the Semi-Quantitative Determination of N-Nitrosamines in Active Pharmaceutical Ingredient Enalapril Maleate by Means of Derivatisation and Detection by HPLC with Fluorimetric Detector

A novel HPLC method with fluorimetric detection was developed for the determination of potentially carcinogenic N-nitrosodimethylamine (NDMA) and N-nitrosodiethylamine (NDEA) in active pharmaceutical ingredient enalapril maleate. N-nitrosamines were subject to denitrosation followed by derivatisation with dansyl chloride or fluorenylmethoxycarbonyl chloride (Fmoc-Cl). Fmoc-Cl offers much better sensitivity and repeatability than dansyl chloride derivatisation. A satisfactory linearity was obtained for the method, with R2 = 0.9994 for NDMA and 0.9990 for NDEA, and a limit of quantification level of 0.038 μg/g for NDMA and 0.050 μg/g for NDEA. The precision decreased with the concentration to a maximum level of about 10%. The recoveries were in the range of 74.2 ± 4.2% to 101.6 ± 16.1% for NDMA and 90.6 ± 2.9% to 125.4 ± 7.4% for NDEA. Dansyl chloride was found to be an inappropriate derivatisation agent, mainly due to potential contamination with dimethylamine, leading to unrepeatable peaks in the blank solution. Since the method involves the derivatisation of amines liberated from the N-nitrosamines, it was necessary to remove the amines from the test sample. Several critical points in the standard/sample preparation have been mentioned, which affect the reproducibility of the method and are not covered in similar articles.

N-nitroso compounds: detection in ambient air

By use of a new, highly selective detection technique for N-nitroso compounds, which is sensitive to picogram quantities and which is based on the catalytic cleavage of the N-NO bond and the subsequent detection of the nitrosyl radical, dimethylnitrosamine has been found in concentrations of 0.02 to 0.96 part per billion in three out of five air samples from Baltimore, Maryland, and 0.014 to 0.051 part per billion in five out of six air samples from Belle, West Virginia. The sensitivity of the analytical procedures used was 1 part in 10(12). The presence of dimethylnitrosamine has been confirmed by using the new detector in conjunction with both a gas-liquid chromatograph and a high-performance liquid chromatograph. In addition, between one and three as yet unidentified N-nitroso compounds were detected in both cities. N-Nitroso compounds were not found in air samples from Philadelphia, Pennsylvania; Wilmington, Delaware; and Waltham, Massachusetts.

A review of the analysis of tobacco-specific nitrosamines in biological matrices

Tobacco use constitutes a leading cause of mortality and morbidity worldwide. Tobacco-specific nitrosamines (TSNAs) are an important class of biomarkers for tobacco carcinogen uptake. The current review focuses on the issues and developments in analysis of these compounds in human biological matrices. The two most widely used techniques for TSNA bioanalysis are gas chromatography coupled with thermal energy analysis and liquid chromatography coupled with mass spectrometry, employing various sample preparation techniques. The review provides an overview of the tools and techniques currently available for TSNA bioanalysis that will help towards the ultimate goal of understanding the mechanisms of cancer caused by the use of tobacco products. A contrast and comparison of the important aspects of bioanalysis such as sample preparation, compound detection, and throughput is discussed for the thermal energy analysis- and mass spectrometry-based techniques. Complex sample extraction procedures, throughput, and the ability to validate are important issues of concern for the gas chromatography-thermal energy analysis-based methods. On the other hand, addressing ion suppression matrix effects remains an important challenge for hyphenated mass spectrometry-based methods. The review also provides an extensive summary of analytical procedures for various studies measuring tobacco-specific nitrosamines in different biological matrices.

Dietary meat, endogenous nitrosation and colorectal cancer

Colorectal cancer is the third most common cancer in developed countries such as the U.K., but incidence rates around the world vary approx. 20-fold. Diet is thought to be a key factor determining risk: red and processed meat, but not white meat or fish, are associated with an increased risk of colorectal cancer. The endogenous formation of N-nitroso compounds is a possible explanation because red and processed meat, but not white meat or fish, cause a dose-dependent increase in faecal ATNCs (apparent total N-nitroso compounds) and the formation of nitroso-compound-specific DNA adducts in humans. Red meat is particularly rich in haem which has been found to promote the endogenous formation of ATNC. Nitrosyl haem and nitroso thiols have been identified as major constituents of both faecal and ileal ATNC with a significant increase in the formation of these compounds following a diet rich in red meat. In vitro incubations show that, under simulated gastric conditions, nitroso thiols are the main species of nitroso compound formed, suggesting that acid-catalysed thionitrosation is the initial step in the endogenous formation of nitroso compounds. Nitrosyl haem and other nitroso compounds can then form under the alkaline and reductive conditions of the small and large bowel.

Detection of nitrosated proteins

Three methods are provided in this unit to detect nitrosated proteins. The Saville assay is the most commonly used and has the advantages that it is less sensitive to interference than the quinine sulfate-based fluorescent assay, uses simple chemical reagents, and requires a spectrophotometer. The diaminonaphthalene assay (a fluorescence assay) and chemiluminescence assay are used when the experiment requires high sensitivity. Mass spectrometry is employed for precise structural determinations.

Development of chemiluminescence-based methods for specific quantitation of nitrosylated thiols

While nitrosothiol compounds have been hypothesized to be important in the transport and function of nitric oxide (NO) in biological systems many important questions regarding their mechanism of formation and functional importance remain. In view of these fundamental questions there has been a great need for simple, sensitive, and specific methods for quantitation of nitrosothiols in biological samples. We report the development of two methods, for the measurement of nitrosothiol compounds using a chemiluminescence nitric oxide analyzer with a standard purging vessel. The first method is based on treatment with acidified solutions of potassium iodide in the presence or absence of dissolved free iodine. Quantitative release of NO occurs either from both nitrite and nitrosothiols or from nitrite alone, respectively. Subtraction of the amount of NO released without iodine from NO released in the presence of iodine allows estimation of the nitrosothiol concentration. To selectively measure nitrosothiols, we developed a redox quinone-hydroquinone alkaline reactant that selectively releases NO from nitrosothiols. This reactant quantitatively converts nitrosothiols to NO at elevated temperature, > 60 degrees C. Both methods were shown to detect nitrosothiols in biological buffers or blood plasma down to 10 nM concentration with high accuracy and reproducibility, variability less than 5%. These assays should be a useful addition to techniques used to characterize the biochemistry of NO.

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.

Detection of S-nitrosothiols and other nitric oxide derivatives by photolysis-chemiluminescence spectrometry

We have developed a method for the detection of biologically relevant derivatives of NO. that couples photolysis to chemiluminescence. S-Nitrosothiols, N-nitroso-L-tryptophan, and iron-nitrosyl derivatives can all be detected by this methodology, and these derivatives can be distinguished from free NO. by making measurements with and without photolysis. The limits of detection of this system are in the 10 nM range, with an intraassay variability of less than 2% and an interassay variability of less than 1.5%. The use of cutoff filters and alterations in pH and flow rate through the photolysis cell provide additional useful parameters with which to characterize specific NO. derivatives based on their intrinsic stability. This methodology is a useful addition to the growing armamentarium of techniques used to characterize the biochemistry and metabolism of NO..

Nitrosation of tryptophan residue(s) in serum albumin and model dipeptides. Biochemical characterization and bioactivity

Nitrosation of bovine serum albumin with acidified NaNO2 was compared to that of carboxymethyl-bovine serum albumin in which the thiol group is covalently blocked. Differential ultraviolet-visible (UV-Vis) spectroscopy and a modified Saville assay indicated that a non-cysteine residue(s) in carboxymethyl-bovine serum albumin was nitrosated. The nitrosated carboxymethyl-bovine serum albumin exhibited similar vasorelaxation activity as that observed with nitrosated bovine serum albumin. Identification of the nitrosated non-cysteine residue(s) was studied using 16 model dipeptides, each of which contained a glycyl residue and a variable residue. Using photolysis-chemiluminescence analysis, modified Saville assay, differential UV-Vis spectroscopy, and bioassays, L-glycyl-L-tryptophan (Gly-Trp) was found to be the only dipeptide that underwent significant nitrosation under these conditions. Liquid chromatography-UV-Vis spectroscopy-mass spectrometry showed that the NO group was attached to the indole nitrogen of tryptophan. Nitrosated Gly-Trp exhibited dose-dependent vasorelaxation and platelet inhibiting activity with apparent EC50 values of 1.1 +/- 0. 3 and 3.5 +/- 0.9 microM, respectively. Because N-nitroso-Gly-Trp does not release NO radical via spontaneous homolytic N-NO bond fission nor freely diffuse through cellular membranes, the ability of this compound to induce NO.-like biological effects suggests the existence of a (membrane-associated) transnitrosation system that facilitates delivery of -NO to its specific biologic target(s).

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.

Tobacco-specific N-nitrosamines and Areca-derived N-nitrosamines: chemistry, biochemistry, carcinogenicity, and relevance to humans

Nicotine and the minor tobacco alkaloids give rise to tobacco-specific N-nitrosamines (TSNA) during tobacco processing and during smoking. Chemical-analytical studies led to the identification of seven TSNA in smokeless tobacco (< or = 25 micrograms/g) and in mainstream smoke of cigarettes (1.3 micrograms TSNA/cigarette). Indoor air polluted by tobacco smoke may contain up to 24 pg/L of TSNA. In mice, rats, and hamsters, three TSNA, N'-nitrosonornicotine (NNN), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), are powerful carcinogens; two TSNA are moderately active as carcinogens; and two TSNA appear not to be carcinogenic. The TSNA are procarcinogens, agents that require metabolic activation. The active forms of the carcinogenic TSNA react with cellular components, including DNA, and with hemoglobin (Hb). The Hb adducts in chewers and smokers serve as biomarkers for the uptake and metabolic activation of carcinogenic TSNA and the urinary excretion of NNAL as free alcohol and as glucuronide for the uptake of TSNA. The review presents evidence that strongly supports the concept that TSNA contribute to the increased risk for cancer of the upper digestive tract in tobacco chewers and for the increased risk of lung cancer, especially pulmonary adenocarcinoma, in smokers. The high incidence of cancer of the upper digestive tract especially among men on the Indian subcontinent has been causally associated with chewing of betel quid mixed with tobacco. In addition to the TSNA, the betel quid chewers are exposed to four N-nitrosamines that are formed during chewing from the Areca alkaloids, two of these N-nitrosamines are carcinogens. The article also reviews approaches toward the reduction of the carcinogenic potency of smokeless tobacco, betel quid-tobacco mixtures, and cigarette smoke. Although the safest way to reduce the risk for tobacco-related cancers is to refrain from chewing and smoking, modifications of smokeless tobacco and of cigarettes are indicated to lead to less toxic products. Another more recent approach for reducing the carcinogenic effect of tobacco products is the application of chemopreventive agents, primarily of micronutrients. Future aspects in tobacco carcinogenesis, especially as it relates to TSNA, are expected in the field of molecular biochemistry and in biomarker studies, with the goal of identifying those tobacco and betel quid chewers and tobacco smokers who are at especially high risk for cancer.

Reactions of nitrate and nitrite in foods with special reference to the determination of N-nitroso compounds

The stabilities of nitrate and nitrite in food systems and their reactions in such matrices are reviewed. Particular reference is made to reactions with haem proteins, smoke components and amines in foods, and the chemistry of formation of N-nitroso compounds from food components is discussed. Finally, the methodology available for determination of both volatile and non-volatile N-nitroso compounds is addressed.

Studies on endogenous formation of N-nitroso compounds in the guinea pig supplemented with proline or thioproline and sodium nitrate

The endogenous formation of N-nitrosoproline (NPRO) and N-nitrosothioproline (NTPRO, N-nitrosothiazolidine-4-carboxylic acid) was studied by monitoring their excretion in the urine of guinea pigs given oral doses of 10 mg proline or thioproline after supplementation with 34 mg (0.4 mmol) sodium nitrate. In order to estimate the conversion of nitrate to nitrite, the animals were also supplemented with 3.5 mg (0.05 mmol) sodium nitrite instead of sodium nitrate. In animals fed commercial diets, the excretion of NPRO and NTPRO under supplementation with sodium nitrate was 2.0 micrograms and 28.7 micrograms/animal/day, respectively, whereas the excretion under supplementation with sodium nitrite was 0.7 micrograms and 13.3 micrograms/animal/day, respectively. The higher excretion of NTPRO than NPRO in each case shows that thioproline is more effective for nitrite trapping than proline. The animals supplemented with nitrate excreted more than twice the amounts of NPRO or NTPRO than those supplemented with nitrite. It is assumed, therefore, that more than 0.1 mmol nitrate is reduced to nitrite and takes part in the endogenous nitrosation of the guinea pig. When various concentrations of L-ascorbic acid (AsA), known to inhibit the formation of N-nitroso compounds, were also administered orally to animals immediately after supplementation with sodium nitrate, the NPRO excretion decreased with increasing AsA concentration. These data indicate that the guinea pig, which is unable to synthesize AsA as well as humans, may be an appropriate animal model for evaluation of the endogenous nitrosation ability of humans ingesting nitrate.

Direct measurement of nitric oxide in headspace gas produced by a chicken macrophage cell line in a closed culture system

A simple and rapid method was applied for direct measurement of nitric oxide (NO) gas produced by cultured macrophages using a modified chemiluminescence detector, the thermal energy analyzer (TEA). HD11 chicken macrophages (1-3 x 10(6)/ml) were cultured on microcarrier beads (100 mg/ml) in 140 ml air-tight glass jars (5 ml cell suspension per jar) containing 0.5 micrograms/ml of LPS and different concentrations of L-arginine. Headspace gas was sampled at 24 hours of culture via a rubber septum and directly injected into a TEA with a liquid nitrogen trap set at -130 to -140 degrees C. The concentration of NO in the gas sample was quantified using a standard gas mixture of NO (2 microliters/L) in nitrogen. Gas samples from L-arginine-supplemented cultures contained NO (0.028-0.066 pl/microliter), whereas NO was not detected in samples from controls. These results suggest that chicken macrophages synthesize NO gas in a dose-dependent manner relative to L-arginine concentration.

N-nitrosamine and mutagenicity formation in Chinese salted fish after digestion

Salted and dried fish (Nemipterus virgatus), acquired from Hong Kong, was treated with 0.43-110 mM nitrite during in vitro digestion using gastric enzymes and the volatile N-nitrosamine content and mutagenicity on Salmonella typhimurium TA100 assayed without concentration. N-Nitrosodimethylamine (NDMA; the only nitrosamine detected) formation was second order in nitrite concentration. When 10 g of fish was treated with 6.96 mM nitrite, 394 nM NDMA was formed. Thiocyanate was catalytic for NDMA formation at nitrite concentration greater than 0.87 mM and when the ratio of thiocyanate to nitrite was greater than 1. Approximately a 50% inhibition in NDMA formation by ascorbic acid was seen when the ratio of ascorbate to nitrite was approximately 2 or greater and the nitrite concentration was 1.74 mM. Mutagenicity increased with increasing nitrite concentration but the addition of thiocyanate did not increase mutagenicity over nitrite alone. Ascorbate increased mutagenicity even though NDMA formation was inhibited. Even at nitrite concentrations greater than 100-fold higher than expected in vivo, there was insufficient NDMA formed to account for the observed mutagenicity. These data do not exclude the possibility that the observed mutagenicity was due to non-volatile N-nitroso compounds, however, this possibility seems unlikely given the effects of ascorbate and thiocyanate which would be expected to inhibit and enhance non-volatile N-nitroso compound formation.

Analytical studies on tobacco-specific N-nitrosamines in tobacco and tobacco smoke

Chemical-analytical studies have led to the identification of approximately 3000 compounds in tobacco and 4000 in tobacco smoke. These include carcinogens in processed tobacco as well as tumor initiators, tumor promoters, cocarcinogens, and organ-specific carcinogens in tobacco smoke. The latter group includes N-nitrosamines, in particular those that derive from nicotine and other tobacco alkaloids, the TSNA. In vitro nitrosation of nicotine yields NNN, NNA, and NNK. Nitrosation of other tobacco alkaloids leads to the formation of NAT, and NAB. Our analytical studies using GC-TEA have led to the identification of seven TSNA in tobacco and tobacco smoke. In addition to NNN, NAT, NAB, and NNK, we also identified NNAL, iso-NNAL, and, most recently, iso-NNAC. Their levels range from 0.01 to 92 ppm in tobacco and from 6 to 530 ng/cigarette in tobacco smoke. The high levels observed in snuff are primarily due to fermentation and aging. Technological methods exist today to reduce the levels of TSNA in both tobacco and cigarette smoke.

A rapid method for the determination of nitrate and nitrite by chemiluminescence

Nitrite and nitrate + nitrite can be determined by selective chemical reduction to nitric oxide which is measured using a chemiluminescence analyser. The reducing agents are sodium iodide in acetic acid for nitrite and ferrous ammonium sulphate-ammonium molybdate for nitrate + nitrite. The concentrations of the reducing agents have been optimized to obtain the maximum yield of nitric oxide and the minimum coefficient of variation. Under these conditions, it is possible to inject repeated samples into the refluxing reducing agents and to obtain rapid evolutions of nitric oxide from which the determinations can be made. Nitric oxide has also been produced using the nitrite reagents from organic nitrites, a S-nitrosothiol, a pseudonitrole and N-nitrosamines. Similarly, an organic nitrate and some C-nitroso compounds respond to the method for nitrate but only to the extent of a yield of nitric oxide of about 10% of the theoretical. Very low or zero responses were evident from aliphatic and aromatic C-nitro compounds but not omega-N-nitroarginine which gave a large yield of nitric oxide using the reagents for nitrate. In general, however, concentrations of nitrate will be in considerable excess of those of related compounds which would interfere with the determinations. Nitrate can be determined either by difference in its mixtures with nitrite or by prior removal of the nitrite using ascorbic acid provided oxygen and nitric oxide are removed by degassing with nitrogen.

Analysis of human blood for volatile N-nitrosamines by gas chromatography-chemiluminescence detection

A method was developed to separate and measure trace levels of volatile N-nitrosamines (NAs) in human blood that either eliminated or accounted for in vitro artifactual formation of N-nitrosodimethylamine (NDMA) through the use of water blanks, added inhibitor (ascorbic acid) and added morpholine. The absolute minimum detectable limit was 8 pg; minimum level of reliable measurement was 0.05 microgram/kg for a 20-g blood specimen. Recovery of NDMA from blood was 93 +/- 5%. Coefficient of variation was 25%. Bloods from 242 people were analyzed for volatile NAs. NDMA was the only NA found. Positive specimens were presumptively confirmed by their non-detection after ultraviolet photolysis and/or mass spectrometry. This paper presents additional evidence that in vivo NA formation occurs.

Extraction and clean-up of contaminants and toxicants from food for mass spectrometric analysis--a literature review

This report presents a review of the literature on the extraction and clean-up procedures used prior to the analysis, by mass spectrometry, of organic contaminants and toxicants in foods and food-related materials. It includes a brief description of the uses of a mass spectrometer and shows how the mode of operation of the machine can influence the amount of clean-up necessary before a sample is presented for analysis. The review covers a variety of contaminants of different compound types in a wide range of foods and not only discusses sample preparation techniques that have been used for contaminant analysis by mass spectrometry but also considers some that could be used. The most commonly used techniques involve solvent extraction followed by a clean-up using liquid-liquid partition or column chromatography or both, although a number of newer methods being evolved are moving towards the ideal of a single-step extraction and clean-up process.

Chromatographic investigations of the configurational and geometrical isomerism of allylic N-terpenyl-N-hydroxyethyl-nitrosamines

A preparative adsorption column chromatographic method is reported for the separation of cis and trans geometrical isomers of two types of N-nitrosamines derived from allylic terpenyl ethanolamines (experimental fish toxicants). Column eluates were monitored by gas chromatography in which a Carbowax 20M stationary phase was used. Further separation of E and Z configurational isomers was achieved by reversed-phase and normal-phase high-performance liquid chromatography. In the reversed-phase high-performance liquid chromatography system (acetonitrile-water), the 6',7'-acetylenic nitrosamines ( NMOA ) were efficiently resolved by using an argentous (AgNO3) mobile phase, whereas the presence of sodium alkanesulfonate in the aqueous acetonitrile mobile phase favored the base-line resolution of the 6',7'-olefinic nitrosamines ( NDOA ). For normal-phase separation on a silica column, addition of tetrahydrofuran to the mobile phase (methylene chloride-2-propanol) resulted in a varying degree of improvement in peak resolution (R) and column selectivity (alpha). Effects of temperature on the chromatographic behavior of the nitrosamine components are described. The high-performance liquid chromatographic separation method has proved to be applicable for the trace analysis of the title nitrosamines in organic tissues by way of thermal energy analysis.