A procedure for the determination of lead in green vegetables at concentrations down to 1 microgram/kg.

An accurate and highly sensitive dry ashing/graphite furnace atomic absorption spectrometry (GFAAS) procedure has been developed for the measurement of lead in green vegetables. The accuracy of the method was established by analysis of standard reference materials and confirmed by isotope dilution using an inductively coupled plasma-mass spectrometer (ICP-MS). The limit of detection (wet weight) of the technique is 1-3 micrograms/kg with relative standard deviations ranging from 6% for a sample of kale containing 500 micrograms/kg to 20% for cabbage containing 3.

An investigation of apparent total N-nitroso compounds in beer.

The concentration of apparent total N-nitroso compounds (ATNC) in beer has been investigated using a group-selective procedure based on chemical denitrosation with hydrogen bromide and chemiluminescence detection of the released nitric oxide. In a survey of samples of 40 brands of beer and lager, detectable levels of ATNC were present in 17 samples at concentrations of 20-100 micrograms N-NO/kg in 11 and 100-500 micrograms N-NO/kg in six. To determine the origin of ATNC in beer the production of a commercial batch was examined in detail.

Characterization studies on insoluble total N-nitroso compounds in bacon adipose connective tissue.

Enzymic hydrolysis was employed to solubilize 35% of the total N-nitroso compounds associated with bacon adipose connective tissue. Size exclusion chromatography of the digest showed that 95% of the solubilized N-nitroso compounds had molecular weights equivalent to those of di-, tri- and tetrapeptides. The likely identity of these compounds is discussed in the light of their extractability from acidified solution into ethyl acetate and their thermal and pH stability.

N-Nitrosopyrrolidine formation in bacon.

Evidence is presented that the likely major amine precursors to N-nitrosopyrrolidine in cooked bacon are free proline in the adipose tissue and to a lesser extent, collagenous connective tissues. A model system in which animal lipid is replaced with hydrogenated vegetable oil is described and used in investigating the potential role of prolyl derivatives as precursors to N-nitrosopyrrolidine.

Comparison of trace element solubility from food items treated separately and in combination.

Solubility of trace elements from various foods (beef, soya, crab, wholemeal and white bread) is assessed with various extractants, at different pH's and after enzyme treatment. Simple extractants do not solubilise trace elements to the same degree as when they are released after digestive enzyme action. Enzymic action can change the nature of the soluble species as well as their amount.

Some nitrosoamino acids in bacon adipose tissue and their contribution to the total N-nitroso compound concentration.

The levels of nitrosoamino acids and apparent total N-nitroso compounds in the adipose tissue of raw bacon have been examined. Nitrosoamino acids were detected in 80% of the samples in levels of up to 0.2 mg/kg.

Trace element solubility from food following enzymolysis.

Food items were treated with enzymes simulating gastric and intestinal digestive juices and the amounts of soluble lead, cadmium, zinc, iron, and copper, were determined. Enzyme treatment was conducted in two stages involving (I) pepsin at pH 2,5 followed by (II) pancreatin and amylase at neutral pH. Solubility was determined after each stage and additionally after post enzymolysis acidification.

Synthesis of three N-nitroso dipeptides N-terminal in proline and a method for their determination in food.

The terminal N-nitroso derivatives of L-prolyl-L-alanine, L-prolylglycine and L-prolyl-4-hydroxy-L-proline have been synthesized and characterized. A procedure suitable for their analysis in biological samples has been developed and is based on the preparation of an aqueous extract, extraction into an organic solvent, separation by high-performance liquid chromatography and detection by a chemiluminescence method. The average recovery in all cases was above 69% at the level of 200 micrograms/kg using cured meat as a food matrix; the detection limit was 10 micrograms/kg.

Incidence of some non-volatile N-nitroso compounds in cured meats.

Procedures are described for the use of high-performance liquid chromatography and gas chromatography with a chemiluminescence detector in the analysis of N-nitrosoamino acids, N-nitrosothiazolidine-4-carboxylic acid, N-nitroso-oxazolidine-4-carboxylic acids and N-nitroso dipeptides N-terminal in N-nitrosoproline in cured meat products. The detection limit is around 5-10 micrograms/kg. Evidence is presented for the presence of all these species except the N-nitrosated dipeptides.

Total N-nitroso group analysis of foods. II. Further studies on the precision and sensitivity of the assay.

The total N-nitroso content of foods can be measured by chemical denitrosation with hydrogen bromide and chemiluminescence detection of the cleaved nitric oxide radical. The denitrosation reagent itself causes a significant detector response which has limited the application of the technique to trace analysis. A procedure is described in which the errors associated with this interference are minimized.

N-nitroso compounds and polycyclic aromatic hydrocarbons in Icelandic smoked cured mutton.

Five samples of Icelandic smoked cured mutton were analysed for volatile N-nitrosamines, N- nitrosoamino acids, total N-nitroso content and several polycyclic aromatic hydrocarbons. Levels varied considerably from sample to sample but generally the levels of polycyclic aromatic hydrocarbons and N-nitrosamines (as judged by N- nitrosoproline , N- nitrosohydroxyproline and total N-nitroso content) varied in the same way. It is suggested that in this product the smoking procedure is responsible for both groups of contaminants and that the curing process is relatively unimportant.

Comparison of a capillary gas chromatographic and a high-performance liquid chromatographic method of analysis for polycyclic aromatic hydrocarbons in food.

Five food samples have been analysed for a number of polycyclic aromatic hydrocarbons (PAHs) by capillary gas chromatography with flame ionization detection (GC-FID) and high-performance liquid chromatography (HPLC) with fluorescence detection. The methods give similar results and there is no significant difference in their repeatability. The capillary GC method is favoured where it is desirable to analyse for a large number of PAHs, whereas the HPLC method is preferred for the individual analysis of a smaller number of PAH isomers.

The application of a chemical denitrosation and chemiluminescence detection procedure for estimation of the apparent concentration of total N-nitroso compounds in foods and beverages.

The apparent total N-nitroso content of foods can be measured by a procedure based on chemical denitrosation and chemiluminescent detection of the eliminated nitric oxide. Procedures have been established which substantially reduce the 'apparatus blank' response to the denitrosating agent and allow total nitroso contents down to 10 micrograms (N-NO)/kg to be measured reproducibly on a 1-g sample. Typically, duplicate analyses of samples containing 10-1000 micrograms (N-NO)/kg differ by less than 15% of their mean.

N-nitrosamine analysis in foods: N-nitrosoamino acids by high-performance liquid chromatography/thermal energy analysis and total N-nitroso compounds by chemical denitrosation/thermal energy analysis.

The total N-nitroso content of foods can be measured by chemical denitrosation and chemiluminescent detection of the eliminated nitric oxide. Appropriate procedures substantially reduce the 'system response' to the denitrosating agent, so that N-nitroso group contents down to 10 micrograms/kg can be measured on a one-gram sample. Using N-nitrosamine standards added to beer, the coefficients of variation are approximately 10% and 5% at N-nitroso contents of 19 and 94 micrograms/kg, respectively.

Estimation of nitropolycyclic aromatic hydrocarbons in foods.

A method is described for the sample clean-up and estimation of nitropolycyclic aromatic hydrocarbons (nitro-PAH) in foods. The analysis involves the novel use of a coupled capillary gas chromatograph/thermal energy analyser and provides a detection limit for 1-nitropyrene of 12 pg (equivalent to 0.02 micrograms/kg for a 50-g sample).

Analysis of polycyclic aromatic hydrocarbons in UK total diets.

Analysis of UK total-diet samples for polycyclic aromatic hydrocarbons was carried out using a simplified sample clean-up and a high-performance liquid chromatography dual fluorescence detector system. The results indicate that cereals and oils/fats contribute the major part (approximately one third each) of the polycyclic aromatic hydrocarbons in these total diets. Fruit, sugars and vegetables provide much of the remainder (approximately one quarter) while meat, fish, milk and beverages make relatively minor contributions.

Dietary surveys on a population at Shipham, Somerset, United Kingdom.

The results are reported of three dietary surveys and crop sampling surveys carried out at Shipham in 1979. Concentrations of cadmium, lead and zinc in crops were higher than would normally be expected. Copper concentrations in crops were normal, and the results for mercury showed that mercury translocation from soil to crops was very low.

The effect of oxygen on nitrosamine formation in bacon.

Bacon has been cooked in air and in nitrogen atmospheres and the effect on the formation of N-nitrosodimethylamine and N-nitrosopyrrolidine has been studied. Under nitrogen, reductions of 50%-90% were obtained in the concentrations of both nitrosamines in the cooking vapour. The results are discussed in terms of the likely role of nitric oxide in nitrosamine formation in cooking bacon.

Gas chromatographic determination of vinylidene chloride monomer in packaging films and in foods.

Headspace electron-capture-gas chromatographic methods are described for the quantification of vinylidene chloride monomer in poly(vinylidene chloride) containing films and in film-packaged foodstuffs. Quantification of vinylidene chloride was possible at levels down to 0.001 mg/m2 in the films and 0.

Model system studies on N-nitrosamine formation in relation to cured meat: the non-polar phase and S-nitroso peptides.

In view of recent findings that N-nitrosamine formation occurs principally in the adipose tissue of frying bacon, an heterogeneous protein-based model system has been developed which incorporates a 20% decane phase. The N-nitrosation reactions of a series of secondary amines, of varying lipophilicity, have been studied at 37 degrees C, pH 5.25, in the model system, formulated with and without the non-polar phase.

Some effects of phenol- and thiol-nitrosation reactions on N-nitrosamine formation.

C-Nitrosophenols, produced by the nitrosation of phenols, catalyse N-nitrosamine formation. The rate of N-nitrosation of pyrrolidine, catalysed by p-nitroso-o-cresol, is fastest at about pH 5. The catalytic species is thought to be the quinone monoxime tautomer of the nitrosophenol.