In Parts I and II of this series (1,2), degradation and foaming experiments on a number of commercially available alcohol polyethoxylates and alkyl phenol polyethoxylates are described. This paper describes an extension of the thin layer chromatographic work on which the experiments described earlier were based, supplemented by a variety of other chemical and physical tests to provide some insight into the initial mechanism of degradation of these materials before they disappear by the established oxidation and hydrolytic routes. In the case of the readily degradable alcohol ethoxylates, two distinct mechanisms are shown to proceed simultaneously: a fission of the molecule into hydrophobic and hydrophilic entities, and a rapid oxidation of the hydrophobic group. No fission occurs in the case of the alkyl phenol ethoxylates, the more usual route of degradation being slow oxidation and hydrolysis of the alkyl groups, the aromatic ring and the ethoxy chain simultaneously; occasionally, and at higher pH, the hydrolysis of the ethoxy chain proceeds at a considerably increased rate.

The thin-layer chromatographic method for determination of nonionie detergents has been used for the chemical assessment of alcohol polyethoxylates and material derived from them during degradation under simple laboratory conditions. Foaming capacity during degradation was also measured on a representative selection of the materials under test.With one exception (a material with a highly branched alkyl chain) the disappearance of all the aleohoi-ethoxylates tested was rapid; a small increase in time required for complete disappearance was observed with the more highly ethoxylated materials, and with the materials which had some slight branching in the alkyl chain. Residues of the polyethylene glycol type, which were generally more persistent than the original materials, were observed to build up as the original materials disappeared, increasing ethoxylation present in the original material giving rise to increasing quantities of residues.The foaming capacity at every stage of the degradation, that is, foam formation alone or synergistic effect on foam formation because of other detergents, could be closely correlated with the results obtained by using the thin-layer chromatographic procedure.

In this series of experiments, as in those described in Part I, the foaming capacity during degradation could be closely correlated with the results obtained by using the thindayer chromatographic procedure.

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.

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