THE ANALYSIS OF SYNTHETIC DETERGENTS 515 the extent being characteristic of the particular am/de. If the sample is a sulphate, or is a non-ionic compound, then more specific tests for the ester and amide links are needed. The hydroxamic test for esters is very useful •, while amides can be detected through the primary or secondary amine produced on hydrolysis. Hydrophobic groups The hydrophobic groups are examined after hydrolysis of the surfactant: mild alkaline hydrolysis is sufficient for carboxylic esters, moderate acid hydrolysis for sulphates without a linking group, prolonged acid hydrolysis for amides, hydrolysis with hydriodic or hydrobromic acid for ethers, and hydrolysis with concentrated phosphoric acid for sulphonates without a linking group. The liberated acid or alcohol may be analyzed for acid value or hydroxyl value, but a much more useful technique is gas chromatography, which is applicable to hydrocarbons also. Aromatic rings and ethylene bonds may be detected without hydrolysis ultra-violet spectroscopy is most useful for the former whilst other physical methods such as infra-red spectro- photometry and mass spectra analysis may also be used. PAPER CHROMATOGRAPHY This technique is one of qualitative analysis, but it is usefu!]y discussed under a separate heading. Over the past few years we have developed a comprehensive scheme of identification of detergent components using paper chromatography. Toluene and xy!ene sulphonates, urea, and alkano!arnines or metals used for neutralization are tested for in addition to the main surfactants which are examined in respect of their hydrophilic groups, linking groups and hydrophobic groups. Full details have recently been given by Drewry 5 and, therefore, the present paper will be restricted to a brief outline of the scheme and an account of the developments that have been made since the former paper was written. Paper chromatography is essentially a separation by partition between the stationary water and moving organic solvents, and the first requirement is an optimum irdtia! water content of the paper. In our laboratory it has been found that washing the paper (Whatman No. 1) in 50% ethanol, and allowing it to dry in the air is sufficient. In other laboratories it may be necessary to experiment with different drying conditions. Initially, a large number of solvents was tried, but a mixture based on tertiary butanol was the only one that gave a uniform development in the presence of surface active components. Later it was found that an ethyl acetate mixture as described by Gaspari• et al 6 gave equivalent results to the butanol solvent, though in a development time of only 2-3 hours instead of 15-20 hours. The solvent also contains a little ammonia and methanol.

516 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS It deteriorates after a few days, possibly because of reaction between the ester and ammonia. Upward development of the chromatogram is the preferred technique because of its simplicity. Pinacryptol yellow is a very useful reagent for detecting the surface- active agents in the chromatogram, giving under ultra violet illumination an orange fluorescence with most anionic surfactants, and blue with catiordcs. Amine oxides and non-ionics surfactants, of higher R F values, also give blue colours with pinacryptol yellow, and toluene and xylene sulphonates, of lower R F values, give orange colours. Characteristic changes occur in the spots on heating, and a subsequent spraying with Rhodamine B also modifies their appearance and makes many spots more definite. Exposure of the paper to iodine vapour gives dark brown spots with ethylene oxide derivatives, amine oxides and cationic surfactants. It also gives spots with alkanolamides, alkanolamines, and metals, but these dis- appear in a few minutes. Spraying the paper next with bromocresol green solution shows all alkaline regions due to the amine oxides and cationic surfactants already detected, to the various alkanolamines which can then be identified from their various R F values, and to alkali metals which remain at the origin. The metals can subsequently be separated on another chromatogram with a more mobile solvent of methanol and ammonia solution (9-51). A spray with cobalt thiocyanate is useful for confirming the presence of ethylene oxide derivatives and amines that were revealed by the iodine treatment, and a spray with dimethylaminobenzaldehyde is used to test for urea. l)uring the last few months the ninhydrin tests for amines has been found useful. Purple spots are developed after heating to 80øC with primary amines or 120øC for secondary and tertiary amines. These confirm the presence of the alkanolamines detected with bromocresol green, but also indicate the presence of mono- and diethanolamides in spots near the solvent front. It is suspected that these spots are due not to the substituted amides as such but to amine-ester impurities. The ninhydrin reagent is also sufficiently sensitive to detect the traces of free alkanolamine present in the alkanolamides added in the manufacture of the detergent. The ninhydrin spray may be followed by acetaldehyde and nitroprusside which gives a useful distinct/on between primary amines (khaki spots on clear paper, not readily visible after ninhydrin) and secondary amines (deep blue spots). I)rewry described the successive application of all spray solutions to the same chromatogram, but the incorporation of nin- hydrin into the list of treatments tends to overwhelm the paper and it is best to develop two chromatograms and apply the first five sprays to one series and the last two to a duplicated series of spots. Another small change