ERRORS IN THE ANALYSING OF PERFUMERY RAW MATERIALS straight-chain hydrocarbons. His system may be of an even more practical value to our industry, as he is working with natural essential oils, such as lime and mandarin orange. In our opinion such a "continuous" standard has many advantages. Whether the use of hydrocarbons as standards on columns of high polarity will still be a practical proposition remains to be seen. For stationary phases of this description the methyl esters of the even numbered saturated straight-chain carboxylic acids could eventually be chosen. The International Standard Organisation (ISO/TC 54) has created a sub-committee (WG 2) for the study of the problem of choosing the internal standard. What is your opinion on this subject ? T•E LECTURER: I should like to emphasise that, in routine analysis, the depreciation resulting from the use of any one column for a large number of determinations can result in incorrect interpretation of an analysis when standard curves are used as references. The retention times for the same components are frequently altered. We, as technicians, realise that the values that are obtained by means of GLC are not absolutely exact ones, but it is not always possible to make the commercial department of a company appreciate this fact. DR. •. H. KLouw•: In the GLC analysis of methyl- and ethylphenyl- glycidate spontaneous dehydration is observed, which in our opinion must be preceded by hydrogenation. The conditions are-- Support: Embacel Liquid phase: Apiezon L 20% W/W Detection: Flame ionisation Carrier gas: H2 Column temperature: 200 ø Do you know of other instances where hydrogen addition has been observed or must be taken for granted, in order to explain some other reactions ? Ta• L•½TUR•R: I am not aware of any cases similar to the one quoted, but with glycidate I think it would be better to use Reoplex 400 instead of the material suggested by you. •R. B. H. K•GsTo•: •ay I endorse the sentiments expressed in this and other papers on GLC techniques, that while the gas chromatograph is an extremely valuable analytical tool, great care must be exercised in the

42 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS interpretation of results. At the same time I would like to make some remarks which may be of value. With regard to experimental technique, reference has been made to the difficulty of reconciling conditions which favour high resolution and efficiency (e.g. long columns and high temperatures), with those which facilitate reasonably short retention times, symmetrical peaks, etc. Polarity of the packing and high temperatures have been mentioned as important sources of experimental error, especially when dealing with terpene chemicals. It would seem to me that more attention should be paid to the use of capillary columns for analysing complex mixtures of both perfumes and flayours. These would have the advantages of much speedier analysis on columns of 100 feet or more, extremely high efficiency and lower operating temperatures. But above all, they dispense with the use of a solid support. Catalytic and thermal breakdown of the more sensitive aromatic components would thus be reduced. I would also point out that errors in interpretation frequently occur when superimposing chromatograms for comparison purposes, especially with com- pound peaks. It is not often realised that when two or more peaks are very close together, their retention times may differ from the same peaks which have been completely separated. If single compounds or well-separated simple mixtures are used in the reference chromatogram, it should not therefore be assumed that coincidence with an unknown peak is a necessary indication of identity. Finally, I would support the general feeling that there is a lack of reliable published retention data of interest to the aromatics industry. It should, however, be remembered that the collation of such data depends on practical support from those using this technique. The Gas Chromatography Dis- cussion Group is well aware of such a need. Two years ago, in fact, industry and research organisations were approached for detailed information on retention times, etc. Unfortunately the response has been very poor, and, until more data is fed into this central body for conversion and tabulation, each individual will have to struggle on as best he can. This is a very unprogressive state of affairs which leads to unnecessary duplication. I feel certain that the aromatics industry as a whole could contribute to, and indeed benefit from, a much freer exchange of information of this kind. THE LECTURER: I do not particularly fayour the use of the reference chromatogram, for a number of reasons. Firstly, it is almost impossible to exactly repeat two chromatographs, using precisely the same material at almost the same time, let alone at different times, because conditions of injection, temperature and gas flow rates, are never, never exactly the same trouble is therefore likely to be encountered if that method is used.