Treat the sample according to the recommended procedure for rhodium alone. If platinum is present, measure the absorbance of the solution at 420 and 490 mp against a reagent blank. The molar concentration of rhodium is then given by the equation (Rh) X
loj =
12.7 A,420 mp 4.55 A,490 mp
If iridium is present, measure the absorbance of the solution a t 420 and 460 mp against a reagent blank. The molar concentration of rhodium is then given by the equation (Rh) X lo5 = 20.1 A 4 2 0 mp 17.7 A,460 mp These procedures can be used jointly with the procedure given for palladium and rhodium.
Determine the palladium content a t 420 mp of a n aliquot by the procedure given for palladium in the presence of rhodium. From a calibration curve determine the amount of absorbance due to palladium a t 420, and a t 460 or 490 mp. Then subtract the absorbance of the palladium complex from the absorbances a t each wive length of the samples n-hich are carried through the procedure given above for platinum or iridium in the presence of rhodium. Beer’s law is obeyed by the palladium complex at all three n-ave lengths used. The results of the analysis of synthetic samples containing rhodium in the presence of palladium and platinum or iridium are given in Table 111. ACKNOWLEDGMENT
The author thanks the Mallinckrodt
Chemical Works for their gift of the LV,N’-bis(3-d i m e t h y1 a m i n o p r o p y1)dithio-oxamide used in this work. LITERATURE CITED
(1) Beaniish, F. E., hIcBr?.de, W. A. E., Annl C h i m . Acta 9, 349 (1953). ( 2 ) Ibzd., 18, 551 (1958). (3) Jacobs, TI-. D., A Y ~ LCHEM. . 32, 512
11960).
ed., p. 83, Interscience, S e w York, 1959. 16) Ibid.. D. 97. (7j Zbid.; p+103. ( 8 ) Zbid., p. 714.
RECEIVED for review September 14, 1957. Sccepted November 27, 1959. Southeastern Regional Meeting, ACS, Sovember 5 to 7, 1959, Richmond, Va.
Potassium Pyrosulfate Fusion Technique Determination of Copper in Mattes and Slags by X-Ray Spectroscopy THOMAS J.
CULLEN
United States Metals Refining Co., Carteret, N. 1.
b An x-ray spectrographic method
can be prepared with a uniform surface.
is reported for the determination of
By measuring standards simultaneously
copper in mattes and slags by grinding and briquetting a potassium pyrosulfate fusion. The fusions are carried out a t moderate temperatures in borosilicate glass beakers. Absorption and enhancement effects of the matrix are removed. No internal standardization is necessary. By dissolving the sample in the flux, heterogeneity effects are removed. The fusion is ground and briquetted to give a uniform surface exposed to the x-rays. An average deviation of 0.09% from the chemical analysis is reported.
or alternatively with the samples, instrument fluctuations can be detected and compensated. Several other techniques have been devised to remove these effects by dilution with a base material. One method entails the mechanical mixing of the sample with a base, which in general is of the relatively transparent type-starch, lithium carbonate, alumina, carbon, and paper pulp. Although class I effects are reduced, class I1 (heterogeneity) difficulties arise. Solution in a solvent such as mater may be used, but temperature affects the density of the solutions and in turn affects the analytical results. The use of rotating sample holders and cooled solution cells has reduced the difficulties of these techniques. Internal standardization, the addition of a properly chosen element, or the use of a scattered background line compensates for class I and I11 deviations. Some samples are too complex to utilize this technique, as one cannot be certain that the element added as an internal standard is always absent, or that the background line chosen as an internal standard is free from interference. Addition of a known amount of the element sought, the standard addition technique, to one portion of the sample
D
from proportionality complicate x-ray spectrographic methods. The main causes of these deviations fall into three classes: (I) absorption and enhancement effects, (11) heterogeneity in the samples, including surface effects, and (111) instrument instability. Deviations due to classes I and I1 can be greatly reduced by fusion in a properly chosen flux. By dilution of the sample to minimize the matrix change between individual samples, class I effects are reduced. If the flux chosen has a density close to that of the sample, this error can be removed. Class I1 effects are removed if the sample is soluble in the flux and if the fusion
516
EVIATIONS
ANALYTICAL CHEMISTRY
is another method of compensation for deviations. Results from this technique can be deceiving if self-absorption is taking place. Liebhafsky and Winslow (2) have reviewed deviations and compensation techniques. Claisse ( I ) found that a borax fusion reduced matrix effects in minerals without the use of internal standardization. He reports that the addition of barium peroxide or potassium pyrosulfate to the flux increases the accuracy by increasing the density of the flux. This laboratory required a rapid and accurate x-ray method for determining copper in matte and slag samples from miscellaneous scrap. The samples could not be used directly as received, because of absorption and enhancement eff’ects. The slag samples contained 0 to 60% copper, 0 t o 20% iron, and 0 to 10% zinc in a complex silicate base. The matte samples contained the same metals in the form of sulfides. It was desired to run both types of samples in the same manner. Diluting the samples with carbon dust in the ratio of 1 to 100 did not remove the matrix effects and introduced a heterogeneity error. Internal standardization by addition of a n element and use of scattered radiation was impracticable because the samples contained many elements varying from sample to sample. A standard addi-
tion of copper indica1,ed self-absorption of copper radiations. A series of samples was prepared as borax beads, as described by Claisse. Samples containing over 30% copper were insoluble in borax alone. When barium peroxide 1%-asadded to the borax flux, the deviations in the analysis were too great (Table I). Potassium pyrosulfate was tried as the flux, n i t h the addition of potassium persulfate for sarilples containing carbon. The results shoned only small deviations from the chemical analysis. Potassium pyrosulfate melts a t 30OoC. and starts to decompose a t about 700" C. By fusing below 700" C., reproducible fusions are made. The fusion absorbs moisture from the atmosphere. When the fusions are ground to a reproducible particle size, the amount of moisture absorbed is constant, and little or no error is introduced. Borax beads are prepared at high temperatures in platinum crucibles. The potassium pyrosulfate fusions can be carried out using a Bunsen burner and borosilicate beakers. Because potassium pyrosulfate is water-soluble, the beakers and mixer mills are easily cleaned. Sherman ( 3 ) found, from time to time, inexplicable losses of copper, when making borax fusions of the oxide. There was no question of incomplete fusion, as a remelt in the original crucible did not replenish any of the copper. Kickel and chromium oxide fusions also showed such losres.
to form a briquet 1.5 inches in diameter. Briquets formed between 12 and 28,000 p s i . give the same intensity for the CuK, line. The CuK, line is then read and the number of counts corrected to a weight basis of 10.200 grams. A straight-line calibration is obtained when per cent copper is plotted us. counts per second. Two hundred milligrams of the samples are prepared and measured in the same manner. If the sample contains carbon, 100 mg. of potassium persulfate is added to the flus. This additional weight must be calculated in the final result. Metallic copper is soluble in potassium pyrosulfate. Pieces of copper weighing more than 10 mg. dissolve slowly, and unless care is taken the decomposition of the pyrosulfate will introduce a n error.
Table I. 1 Week
PROCEDURE
Synthetic standards in the range of 0.0 to 79.88% copper are prepared by placing 10.00 grams of potassium pyrosulfate and 0, 5 , 25, 50, 100, 150, and 200 mg. of cupric oxide in 150-ml. borosilicate
