The determination of low concentrations of the vitamins B,, nicotinic acid, nicotinamide, ascorbic acid, K, and K, in pure solutions by use of differential pulse polarography has been studied. The approximate limits of detection achieved for the different vitamins varied from 0.01 to 1 p.p.m., which is 10 to 100 times better than for d.c. polarography. A comparative determination of vitamin B, and nicotinamide in three complex multivitamin preparations showed that differential pulse polarography is more selective than d.c. polarography. With the former method the nicotinamide can be determined directly, i.e., without prior separation of interfering substances.Most of the vitamins can be determined po1arographically.l Even the vitamins of the A and D groups give polarographic waves in solvents such as benzeneacetonitrile,2 dioxan -water3 or dime t hylf~rmamide.~In textbooks that deal with methods of vitamin assay, several polarographic procedures are given, especially for determining water-soluble vitamin^.^^^ However, most of the applications are for pharmaceutical preparations in which the vitamins are present in relatively high concentrations. Only for ascorbic acid are polarographic procedures given even for determinations in biological materials such as fruits and vegetables. In those instances when the method is applicable it is often claimed to be simple, specific and accurate. One limitation of polarography has been the relatively low sensitivity attainable. The method is best suited to determinations at concentrations between about 1 x and 2 x 10-3M.' Analysis of 10-6 M solutions can be performed but only under favourable conditions and in the absence of interfering substances. In order to obtain accurate results it is advantageous if the waves are in the form of easily measurable steps, which condition occurs in the concentration range between 10-4 andThe lower limit can, however, be considerably extended by the use of other voltammetric methods. The application of a pulse technique to polarography results, for instance, in the possibility of detecting reversibly reduced species at concentrations as low as 10-8 M, and irreversibly reduced species at 5 x 10-8 ~. 8The polarographic method is rather selective, as waves are observed in finite ranges of potentials. A 100-mV interval between two half-wave potentials can be sufficient to permit measurement of the corresponding wave heights if the concentration ratio is not less than 10: 1. The differential pulse technique is even more efficient because it yields peak shapes that approximate closely to the theoretically predicted derivative of an ordinary d.c. polarogram. It thus enables one to obtain the maximum possible resolution between closely spaced waves. A 40-mV interval between two peak potentials can be enough for the corresponding peak heights to be measured, even if the concentration ratio is as high as lo4: l.9The applications of modern polarographic methods to vitamin assay have hitherto been very few; they include the determination of riboflavine ...

A new method for transforming trace amounts of elemental sulfur dissolved in hydrocarbons quantltatively to thiosulfate is developed. The sensltlvlty and accuracy of the method were checked by titratlng 1 m L samples of sodlum thlosulfate containlng sulfur in the range of 3.22 X to 6.85 X lo-'

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