Analysis of National Bureau of Standards Potassium Dichromate, SRM-136b Harry J. Svec and Robert J. Conzemius Institute for Atomic Research and Department of Chemistry, Iowa State University, Ames, Iowa 50010 THENational Bureau of Standards makes available a variety of chemical primary standards which are of fundamental and practical importance to chemists. Extensive characterization of these materials is not provided, generally, other than an overall certification of purity. However, the oxidimetric standard-potassium dichromate, SRM-136b-has been the subject of a high precision assay by Marinenko and Taylor ( I ) by the coulometric method which gave a value of 99.977 for the purity. The latter value has been confirmed by Knoeck and Diehl (2) by the coulometric method incidental to their study of other oxidation-reduction primary standards. Inasmuch as a material of such a high level of purity may be of interest for several other purposes than that for which it was originally intended, we present here the semiquantitative results of an extensive analysis by spark source mass spectrography. While it is, of course, recognized that the results pertain specifically only to the batch in question, they should be of interest in indicating the types of trace contaminants that may be encountered in high purity potassium dichromate in general. The material was mixed with graphite (SP-1 graphite, National Carbon Co., Division of Union Carbide, New York) in a weight ratio of potassium dichromate to graphite of 6: 1. Indium oxide was present in the mixture as an internal standard at a level of 26 ppma indium. The mixture was pressed into a disk 1 cm in diameter and 1.5 mm thick. Polyethylene film was used to separate the metal parts of the die from the K2Cr20,-graphite mixture. The disk was broken in half and the halves were sparked against each other under the following conditions: repetition rate, 32 pulses second-’; pulse length, 32 psecond ; source chamber pressure while sparking, 1 X torr; ion accelerating voltage 24 kV. Ilford 4 - 2 photoplates were used as an ion detector and the plates were calibrated by the Churchhill two-line procedure. Results were calculated and corrections were made according to the method of Owens and Giardino (3). Corrections were made for line width, mass effect, energy effect, and blank levels in the graphite. Unit sensitivities were assumed for each element. The results are shown in Table I. Eight impurity elements were positively identified. The values shown for these impurities is the average of three determinations and the overall average deviation in these values is =k17%. No values are given for the matrix elements (K, Cr, 0, and C), hydrogen, lithium, and the rare gases. The remainder of the elements are reported as < or values on the basis of upper limits from clear regions of the recorded spectra or upper limits due to interferences from molecular ions. (A matrix such as graphitepotassium dichromate produces a large number of interfering molecular ions.) The sum of all the definite impurities is 55
