The oxidation of pyridoxine and related compounds in ammonia buffer solutions is described and a fast and simple method for the determination of pyridoxine in pharmaceutical preparations is given. The only interferences are from ascorbic acid and iron(II), both of which can be removed by ionexchange chromatography. A comparison of the proposed method with a colorimetric method has also been made ; the voltammetric method has a better relative standard deviation.

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spectrometer, as reported in the literature (5). The spectrometric resolution is about 1500 (10% valley), the total amount of the peak corresponding to -ionone is about 0.7 Mg (0.02% of the sample).In the scanning conditions described in the caption of Figure 5, this corresponds to about 10 nanograms of a-ionone to get the spectrum. Nevertheless, the spectrum is still very intense and the trace of the intermediate galvanometer is sufficient to unequivocally identify the compound.The spectrum of Figure 5 has been taken in routine work. Chromatographic efficiency and mass spectrometric sensitivity and resolution are both nearly as good as possible. The number of theoretical plates is about 6500.The possibility of using a wide range of flow rates is helpful for obtaining mass spectra of minor components in complex organic mixtures. In fact, columns of high loading capacity can be exploited. This allows the major peaks not to be overloaded and the minor ones to be present in sufficient amount to take interpretable mass spectra. The (5) K. Biemann, "Mass Spectrometry," Organic Chemical Applications, McGraw-Hill, New York, N.Y., 1962.main advantages of this system are that one can get mass spectra from a very complex chromatogram without the need of doing it at least twice, and that a very large range of linear gas velocities can be used without problems for the operating conditions of the mass spectrometer.

A voltammetric method is described for determining tocopherols in vegetable oils, foods and pharmaceuticals by a newly developed carbon paste electrode. The samples are saponified and the unsaponifiable fraction is extracted and determined voltammetrically. No elaborate purification method is necessary as the substances that interfere with photometric procedures are electrochemically inactive in the potential range of operation. Detailed procedures for the preparation and the working of the electrode, and results for the precision of the method, are presented.

It has been shown that the oxidation of ascorbic acid at a carbon paste electrode is similar to that a t a platinum electrode. The half-peak potential is somewhat higher than the half-wave potential a t a dropping-mercury electrode. The peak current is proportional to the concentration of ascorbic acid in the range 10-6-10-3 M and the reproducibility is better than f l per cent. Chloride and sulphur compounds, such as sulphides and thiols, do not interfere, and sulphite can be determined a t the same time as the ascorbic acid. Some substituted phenols interfere but can often be detected by reversing the direction of polarisation. Reductones interfere but tin(I1) and manganese(I1) do not, A method has also been developed to determine ascorbic acid in the presence of an excess of iron. Different extraction media are discussed in terms of their influence on the redox potential of iron.Comparative titrimetric determinations of ascorbic acid in some fruits, vegetables and beverages gave higher results than the voltammetric method.