1. The amount of selenium in nationally representative samples of prepared and cooked groups of foods, and in a variety of raw individual foods, was determined fluorimetrically. 2. The average British diet was calculated to provide approximately 60 microgram Se/d, of which half was derived from cereals and cereal products and another 40% from meat and fish. Milk, table fats, fruit and vegetables provided little or no Se. 3. Individual foods which were particularly rich in Se (greater than 0.2 mg/kg) included 'bread-making' and wholemeal flours, kidney, fatty fish, brazil nuts (Bertholletia excelsa) and several other varieties of nut. In contrast, breast milk and other foods for babies (except some cereal products) contained little Se. 4. The total intake, and the amounts of Se in major foods, were lower than in most other studies. This is probably the result of the comparatively low levels of this element in British soil.

1. The amounts of iodine in nationally representative samples of prepared and cooked groups of foods and in a wide variety of individual foods and food products were determined colorimetrically. The amounts of erythrosine, a red food colour containing 577 mg I/g were also determined in selected foods and diets by high-performance liquid chromatography. 2. The average British diet was calculated to provide 323 micrograms I/d but only 255 micrograms if two fruit samples containing large amounts of glacé cherries were discounted. Of the total, 92 micrograms was derived from liquid milk. Meat and meat products provided 36 micrograms and cereal products 31 micrograms, but fresh fruits and sugars, vegetables and beverages provided little I. Fish and fish products, though rich in I, contributed only 5% to the total intake. 3. Milk was the most variable as well as the most important individual source of I. Summer milk samples contained 70 micrograms/kg and winter milk 370 micrograms/kg on average. Milk products, including butter and cheese, and eggs were also rich in I. 4. Some processed foods contained erythrosine, particularly glacé cherries and some pink or red confectionery items, biscuits, cherry cake, canned strawberries and luncheon meat. However, none of these are major foods in the average household diet and erythrosine would therefore contribute little more than 10 micrograms I/d to most diets. 5. The average daily intake of I was lower than in similar similar studies in the USA, but was twice the provisional UK recommended intake. This study provides no evidence that I intakes in the UK could be too low or too high for health.U

SEl 9NQA method is proposed for the extraction, separation, identification and quantitative measurement of synthetic organic colouring materials in a wide range of foodstuffs. The colours are extracted with a liquid anionexchange resin, and where irreversible binding of colours to the food has occurred during processing, the colours are released by a preliminary enzyme digestion prior to extraction. They are then re-extracted from the resin phase into aqueous solution, followed by clean-up and concentration by column chromatography on polyamide. The final eluate is concentrated and examined by high-performance liquid chromatography. For liquid foods and foods soluble in water, a shortened form of the method can be used. The method gives recovery values for most colours of 80% or better, and the reproducibility is within 5%.

The AOAC fluorometric method for determining selenium in foods is reviewed. A modified method of sample digestion is proposed, together with some minor alterations to the fluorometric method. A mixture of nitric and perchloric acids is used for sample digestion in place of nitric, perchloric, and sulfuric acids. Sulfuric acid is added after digestion to remove the other acids, and provide a constant and known matrix for complexation with DAN. Hydrogen peroxide is added in order to convert all Se(VI) to Se(IV). The pH of the digest is controlled by adding glycine/HCl buffer before adding ammonia. Samples are heated at a lower temperature and longer time for complexation. DAN reagent is prepared fresh daily.

The determination of nitrite with Cleve's acid has been investigated; the influence of composition of reagents and several experimental conditions have been evaluated. I t is shown that provided the standards used to prepare the calibration graph and samples are treated in a similar way, then the choice of conditions may largely be left to the operator. A recommended procedure is given.NITROGEN-CONTAINING compounds are widely distributed throughout nature and are found in most biologically active materials. Nitrite, an intermediate state in the nitrogen cycle, is found in soils, waters and effluents, and in some food products. Trace amounts of nitrites in potable waters may indicate organic pollution, while relatively large amounts of nitrites are frequently added to industrial cooling waters to inhibit metallic corrosion. Additionally, nitrite is often a convenient parameter by which, following a reduction step, to determine nit rate .1Sawicki, Stanley, Pfaff and D'Amico2 have compared many spectrophotometric methods for determining nitrite. In most of these methods the nitrite concentration is determined following the formation of a red azo dye. The Griess-Ilosvay procedure: in which diazotised sulphanilic acid is coupled with 1-naphthylamine, has been preferred by many workers. The advantages of this method are its good sensitivity, wide range, freedom from interference, rapidity and convenience. Unfortunately, 1-naphthylamine, because of its carcinogenic properties, is now regarded as hazardous, even for laboratory workers4 A recent Statutory Instrument5 further emphasises the need for care in the use of such substances.Several alternative coupling reagents were suggested by Professor Boyland of the Chester Beatty Research Institute, and were examined in this laboratory. Of these, Cleve's acid, 1-naphthylamine-7-sulphonic acid, was found to be most satisfactory from the analytical point of view, and a method for the determination of nitrite involving the use of this reagent was published by Crosby.6 Opinion of medical workers suggests that the possible hazards from the use of Cleve's acid are negligible,7,8 and there is no evidence to indicate that the sulphonic acid group is removed during metabolic processes. I t would appear that the loss of carcinogenic activity is associated with the increased solubility of the sulphonic acid derivative compared with the free base.* Experience in several laboratories with Cleve's acid reagent showed that for amounts of nitrite above that normally found in drinking water the experimental conditions needed to be more clearly defined. It was also desirable to relate composition and performance of the samples of Cleve's acid used in the various laboratories.