A 2-stage in vitro enzyme system has been used to simulate gastric and intestinal digestion of food. Trace element species in the digest can then be separated chromatographically using ICP-MS as an on-line specific detector. This has been used in examination of the cadmium species in kidney, arsenic species in turkey and aluminium species in tea infusions. An alternative approach developed in collaboration with the University of Wales at Cardiff involves computer modelling to predict the major chemical forms of the method. The merits and limitations of the two techniques are discussed.

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 pg/kg with relative standard deviations ranging from 6% for a sample of kale containing 500 μg/kg to 20% for cabbage containing 3.0 μg/kg.

4. References > 1000 jAg/L. Typically, the concentration is low in wine and high in some spirits; the concentration is particularly high in some plum brandies but is low in gin and vodka. Literature methods [1,2,31 rely on sample clean-up followed by packedcolumn GC and detection by FID, alkali flame ionisation, electron capture, or Coulson electrolytic conductivity detector and allow measurements down to 10 Itg/L. The clean-up procedure required for levels below 100 jg/L is extensive and MS confirmation is still required. I.5 I~a 21 In the course of a study of ethyl carbamate levels in alcoholic beverages on sale in U.K., different methods of separation and measurement were as-

Figure 2. Multielement elution profiles: sample element solution (250 pL, 0.1 g/mL); elution ML, 2 M).

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. ATNC levels were below the detection limit in the sweet wort (aqueous extract of malt), bitter wort (malt extract boiled with hops) and also at the start of fermentation, but during the course of fermentation the concentration of ATNC increased appreciably and that of inorganic nitrate decreased; detectable, though transitory, levels of inorganic nitrite were observed. None of the brewing ingredients contained sufficiently high enough levels of ATNC to account for the concentration of these compounds present in the beer after fermentation. These findings suggest that the presence of detectable levels of ATNC in some beers is a result of N-nitrosation reactions occurring in the fermenting wort with the nitrosating species derived from reduction of nitrate, due probably to the presence of microbial species with nitrate reductase activity.

AbstractThe effect of phytate on the solubility of some minerals (Mg2+, Ca2+, Fe3+, Cu2+ and Zn2+) has been investigated in vitro at 37°C, under pH conditions which may be encountered in the duodenum. The observed solubility trends as a function of phytate concentration and pH result from the formation of complexes having different stoichiometries and solubilities as the conditions are varied. Possible structures for these complexes are proposed. In view of the ever‐increasing concern over cadmium toxicity and a recent report which indicates that intestinal absorption of Cd2+ is affected by phytate, this ion was included as part of this study.

A method has been developed for the analysis of individual alkanes in ducks and typical results are reported. Recoveries averaged 87% (+12% SD) with a detection limit of 0.05 mg/kg. Alkanes were observed on the duck skin at widely varying levels (e.g. 0.16 to 7.0 mg/kg skin for hexacosane) but were not observed in the duck flesh. These levels would therefore correspond to a total hydrocarbon concentration of 1 to 32 mg/kg duck which are small compared to other food products. Evidence is presented that the major source of these alkanes is from wax used in the duck defeathering process. Key Words: Analysisduckwaxhydrocarbons

The bioavailability of essential elements liberated from food during digestion depends upon their chemical form in vivo. The concentrations of these species are often so low that analytical determinations cannot be carried out using existing methods, and so computerised simulation techniques have been used to investigate chemical speciation in digested food. The food is considered to be completely broken down into its constituent amino acids and metal ions which then take part in a series of complex equilibrium reactions. The computer simulation of these equilibria uses a thermodynamic approach to determine the concentrations of up to 1000 different species which may be formed in vivo.

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.

The factors affecting the solubilisation of metals during digestion of food have been examined in a two‐stage model system comprising simulated gastric and intestinal juices. The solubilisation of iron, copper and zinc was examined in digests of white and wholemeal bread. Zinc solubility was principally governed by pH and the simulated digestion had little additional effect. In contrast both iron and copper solubility were markedly affected by digestion of the bread. In the case of copper the enzymolysis increased solubility appreciably at neutral pH. All of the cadmium in a simulated gastric digest of canned crab meat was associated with soluble low molecular weight species of less than 1000 daltons. Cadmium solubility resulted from the acidic conditions of the digest rather than enzymatic solubilisation of binding proteins. Ninety percent of the cadmium in the digest became rebound to the insoluble fraction on adjustment to pH7.0. Subsequent simulated intestinal digestion increased the level of soluble ...

The application of inductively coupled plasma mass spectrometry (ICP-MS) for trace and ultra-trace metal determination in foodstuffs has been investigated. The ICP-MS technique was compared with electrothermal atomisation atomic absorption spectrometry (ETA-AAS) for Cd and Pb in three biological standard materials. Results for Mo and V by ICP-MS were compared with the certified values. The ETA-AAS gave results that were closest to the certified values, with good precision. The ICP-MS results were encouraging and compared well for Cd and Pb, with both ETA-AAS and the certified results. The precision was acceptable at the higher element concentrations but degraded considerably at the lower levels. An investigation into the causes of the poor precision revealed molecular interferences and instrument hardware were partially to blame. Noticeable improvements in accuracy and dramatic improvements in precision were then obtained. Molecular ion interferences over the 51–81 a.m.u. mass range were investigated using several chemical matrices (HNO3, HCl, H2SO4, H3PO4, H2O2 and NH3) and the results confirmed that dilute HNO3 is the most suitable acid matrix. Data are presented on the problems of the determination of As and V in the presence of 51CIO+ and 75ArCl+ and the possibilities for data correction explored.

Measurements have been made of the amount of calcium, magnesium, zinc, iron, copper, manganese and nickel released into solution from three types of soya product prior to, and following the use of, in vitro enzymatic degradation procedures. The amount of solubilized metal has been shown to depend upon the enzymes used, the metal under consideration, the pH and the type of soya being studied. Such experiments may help to improve understanding of the behaviour of metals released from soya by the action of enzymes in the gastro‐intestinal tract.

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.

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. In cured meats, the coefficient of variation for unidentified N-nitroso compounds is 26% for a 0.3-g sample containing 600 micrograms/kg. Some interference from non-nitroso compounds is possible, but, in some commodities at least, these interfering compounds are not detectable. Conditions have been established that allow measurement of N-nitrosoamino acids in foods using a high-pressure liquid chromatograph interfaced to a Thermal Energy Analyzer, without the need for prior derivatization. After extraction of lipids with hexane, nitrosoamino acids are extracted with ethyl acetate and subjected to appropriate clean-up stages prior to high pressure liquid chromatography on Microbondapak CN with a hexane:ethanol:acetic acid mobile phase and Thermal Energy Analyzer detection. Recoveries from cured meat are in the 55-75% range for N-nitrososarcosine, N-nitrosoproline and N-nitrosohydroxyproline; elution is complete within seven minutes.

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). Only 3 out of 24 samples contained detectable quantities of nitro-PAHs; these were in the range 0.2-2.0 micrograms/kg. In contrast to the widespread occurrence of the parent PAHs in foodstuffs, the presence of nitro-derivatives appears to be minimal.

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. Potentially the method can be subject to some interference from compounds other than N-nitroso compounds, but at least in some commodities these interfering compounds do not exist in measurable amounts.

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.