y 5. P^- 7 ; ^^/^9S I MDDC - 1095 UNITED STATES ATOMIC ENERGY COMMISSION NIOXIME: A REAGENT FOR PALLADIUM by Roger C. Voter C. V. Banks Harvey Diehl Iowa State Cohege Date Declassified: July 9, 1947 > . Issuance of this document does not constitute authority for declassification of classified copies of the same or similar content and title and by the same authors. Technical Information Branch, Oak Ridge, Tennessee AEC, Oak Ridge, Tenn., 3-9-49--850-A379 Printed in U.S.A. PRICE 5 CENTS UNIV. OF FL LIB. DOCUMENTS DEPT i-»« t * U.S. DEPOSITORY Digitized by tlie Internet Arcliive in 2011 witli funding from University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation http://www.archive.org/details/nioximereagentfoOOio NIOXIME: A REAGENT FOR PALLADIUM By Roger C. Voter, Charles V. Banks, and Harvey Diehl The water soluble 1, 2-dioxlme, 1, 2-cyclohexanedionedioxime, called Nioxime, yields a yellow pre- cipitate with divalent palladium. This precipitate can be used as a qualitative and quantitative reagent for this ion and offers several advantages over its analogue, dimethylglyoxime. It effectively separates palladium from platinum with a single precipitation as well as from other cations. Palladium nioxime can be filtered from a hot solution after a brief digestion period. Qualitatively, nioxime is a more sen- sitive reagent for palladium than dimethylglyoxime. The preparation of 1, 2-cyclohexanedionedioxime, Nioxime, and its use in the analytical chemistry of nickel have already been reported (2, 5). Nioxime also yields an insoluble yellow compound with pal- ladium which can be used for the detection and determination of this metal. This reagent offers several advantages over dimethylglyoxime as a precipitant for palladium. Nioxime is soluble in water in con- trast to dimethylglyoxime which must be made up in alcohol or acetone, and the possibility of contami- nation of the palladium precipitate with excess reagent is eliminated. Palladium nioxime is very insol- uble and may be filtered from a hot solution after a brief digestion period whereas in many procedures it is recommended that the palladium dimethylglyoxime precipitate be allowed to cool and stand for long periods to insure complete precipitation (3, 6). Nioxime serves to separate palladium from large a- mounts of platinum, a feature not possessed by dimethylglyoxime (1, 6). REAGENTS An 0.8 per cent, aqueous solution of nioxime was used. A standard palladium solution was prepared from commercial palladium chloride. This salt was purified by first precipitating out platinum as ammonium chloroplatinate (4) and then by precipitating the palladium as palladium dimethylglyoxime. This complex was destroyed with aqua regia and the so- lution evaporated to near dryness five times with concentrated hydrochloric acid to eliminate nitrate ions. The palladium content of the diluted palladium chloride solution was determined by precipitating the palladium in weighed amounts of this solution with dimethylglyoxime. These solutions were allowed to stand overnight to insure complete precipitation of the palladium dimethylglyoxime. The results of this standardization are given in Table 1. A portion of this solution was evaporated to dryness and the residue spectrographically analyzed. Calcium, magnesium, aluminum, silicon, copper, chromium, bari- um, boron, and platinum were found to be present in less than 100 ppm quantities while only traces of manganese, silver, zinc, and nickel were found. Iridium, osmium, gold, rhodium, and ruthenium were not detected. SENSITIVITY Two series of five palladium solutions were made up in 100 ml volumetric flasks with concentrations ranging from one to ten parts in ten million. To one series of solutions was added one ml of nioxime solution and to the other, one ml of 1 per cent dimethylglyoxime in alcohol followed by vigorous shaking. MDDC - 1095 1 MDDC - 1095 Table 1. Standardization of palladium solution with dimethylglyoxime. Weight of palladium Weight of Weight of Gram of palladium Trial solution taken precipitate palladium per gram of solution Grams Gram Gram 1 20.30 0.1277 0.04044 0.001992 2 19.03 0.1197 0.03791 0.001992 3 21.70 0.1367 0.04329 Average 0.001995 0.001993 Observations made about five minutes after the addition of the reagent showed that the palladium solu- tions of ten, seven and five parts in ten million, which contained nioxime, exhibited a slight yellow col- oration while the corresponding concentrations of palladium with dimethylglyoxime did not. After stand- ing several hours, precipitates were noticeable in the flasks containing the higher concentrations in each of the series. Thus, it can be concluded that nioxime is a more sensitive qualitative reagent for palla- dium ions than dimethylglyoxime. In making the test care should be exercised and the weakly colored precipitate allowed to coagulate before drawing a definite conclusion. GRAVIMETRIC DETERMINATION OF PALLADIUM Although palladium nioxime, PdlCgHgOjN^), is formed by the union of one palladium ion with two molecules of nioxime with the liberation of two hydrogen ions, it is precipitated from a dilute mineral acid solution. Quantitative precipitation is obtained at pH values from 0.7 to 5 but at pH values below 0.7 quantitative precipitation is not assured. The effect of various anions upon the determination of palladium was investigated. In the cases of sulfate and nitrate, the chloride ions were expelled by evaporation with the respective acid before addi- tion of the ammonium salts. A small amount of chloride was present in samples to which ammonium acetate, ammonium tartrate and suUosalicylic acid were added. Results obtained indicate that these an- ions do not affect the determination, see Table 2. Table 2. The effect of various anions upon the determination of palladium. Anion Anion Palladium Weight of Palladium Error present Gram taken precipitate found Mg Gram Gram Gram Chloride 0.5 0.0107 0.0391 0.0107 0.0 Chloride 0.5 0.0122 0.0445 0.0122 0.0 Sulfate 1.0 0.0127 0.0461 0.0127 0.0 Sulfate 1.0 0.0119 0.0437 0.U120 +0.1 Nitrate 1.0 0.0117 0.0427 0.0117 0.0 Nitrate 1.0 0.0126 0.0470 0.0129 +0.3 Acetate 1.0 0.0130 0.0483 0.0133 +0.3 Tartrate 1.0 0.0121 0.0439 0.0120 -0.1 Sulfosalicylate 1.0 0.0120 0.0438 0.0120 0.0 MDDC - 1095 3 A series of determinations conducted in order to observe the effect of varying excesses of nioxime indicated that as much as 150 per cent excess reagent could be added without affecting the accuracy of results obtained. These data are shown in Table 3. The minimum excess of nioxime recommended is thirty per cent which is 0.43 ml of reagent per milligram of palladium present. Table 3. The effect of excess nioxime upon the determination of palladium. Trial Excess of Palladium Weight of Palladium Error nioxime added taken precipitate found Mg per cent Gram Gram Gram 1 30 0.0126 0.0462 0.0127 +0.1 2 60 0.0133 0.0481 0.0132 -0.1 3 100 0.0128 0.0467 0.0128 0.0 4 150 0.0125 0.0456 0.0125 0.0 Determinations conducted on a series of different sized samples indicated that palladium could be suc- cessfully determined over a range of 6 to 30 mg. However filtration becomes somewhat difficult with the larger samples. Table 4 gives the data obtained. Table 4. Determination of various amounts of palladium. Trial Palladium Weight of Palladium Error taken precipitate found Mg Gram Gram Gram 1 0.0065 0.0240 0.0065 0.0 2 0.0121 0.0444 0.0122 +0.1 3 0.0185 0.0672 0.0184 -0.1 4 0.0268 0.0970 0.0266 -0.2 RECOMMENDED PROCEDURE Adjust the volume of the solution containing from five to twenty mg of palladium to approximately 200 ml. The pH of the solution can vary from one to five depending upon 6ther cations present. Heat the solution to about 60°. Add slowly from a pipet with stirring 0.43 ml of 0.8 per cent nioxime for each mg of palladium present. Digest the solution with occasional stirring for thirty minutes at 60°. Filter through a weighed filter crucible of medium porosity and wash with five portions of hot water. Dry at 110° for one hour and weigh. The factor for palladium is 0.2743. The determination of palladium in the presence of platinum was investigated. The separation was ef- fected by simply using the procedure outlined above. The filtrates containing the platinum and excess nioxime yielded a blue precipitate only upon standing more than twenty-four hours after filtration. The data obtained is summarized in Table 5. Palladium was determined in the presence of uranyl, beryllium, ruthenium, aluminum, lanthanum, zinc, cadmium, alkali, and alkaline earth ions. The data obtained from these separations are shown in Table 6. Nioxime yields a precipitate with aurous ion at 60° which is contaminated with metallic gold. MDDC - 1095 Table 5. Determination of palladium in the presence of plat inum. Pt Palladium Weight of Palladium Trial present taken precipitate found Error Gram Gram Gram Gram Mg 1 0.010 0.0112 0.0412 0.0113 +0.1 2 0.025 0.0118 0.0436 0.0120 +0.2 3 0.040 0.0130 0.0479 0.0131 +0.1 4 0.050 0.0132 0.0487 0.0134 +0.2 5 0.100 0.0114 0.0423 0.0116 +0.2 Table 6. Determination of palladium in the presence of various cations. Palladium Weight of Palladium Cation Cation taken precipitate found Error present Gram Gram Gram Gram Mg Uranyl 0.030 0.0127 0.0468 0.0128 +0.1 Uranyl 0.070 0.0117 0.0430 0.0118 +0.1 Ruthenium 0.010 0.0135 0.0501 0.0137 +0.2 Ruthenium 0.025 0.0125 0.0460 0.0126 +0.1 Beryllium 0.015 0.0117 0.0428 0.0117 0.0 Beryllium 0.035 0.0130 0.0472 0.0130 0.0 Sodium Potassium Lithium Barium 0.05 ea. 0.0135 0.0494 0.0136 +0.1 Strontium Calcium ^ Aluminum^ Lanthanum Zinc > 0.05 ea. 0.0119 0.0428 0.0121 +0.2 Cadmium REFERENCES 1. Beamish, F. E. and M. Scott, Ind. Eng. Chem., Anal. Ed., 9:462 (1937). 2. Rauh, E. G., G. F. Smith, C. V. Banks, and H. Diehl, J. Org. Chem., 10:199 (1945). 3. Scott, Standard Methods of Chemical Analysis, Vol. I, p. 724, New York, D. Van Nostrand Co., Inc., 1939. 4. Treadwell, F. P. and W. T. Hall, Analytical Chemistry, Vol. 11, p. 141, John Wiley and Sons, New York, 1942. 5. Voter, R. C, G. V. Banks, and H. Diehl, submitted for publication. 6. Zschiegner, H. E., Ind. Eng. Chem., 17:294 (1925). END OF DOCUMENT /crroii T ur rLWRiUA 3 1262 08907 9528 1 ■i ■1