^3.^^ 7''^ /jiMc. ^ MDDC - 985 u *' UNITED STATES ATOMIC ENERGY COMMISSION NIOXIME A REAGENT FOR NICKEL by Roger C. Voter Charles V. Banks Harvey Diehl Iowa State College This document consists of 8 pages. Date Declassified: May 29, 1947 This document is for official use. Its issuance does not constitute authority for declassification of classified copies of the same or similar content and title and by the same authors. '^^•., Technical Information Division, Oak Ridge Directed Operations Oak Ridge, Tennessee 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/nioximereagentfoOOiowa NIOXIME — A REAGENT FOR NICKEL By Roger C. Voter, Charles V. Banks, and Harvey Diehl The compound, 1,2-cyclohexanedionedioxime, designated Nloxlme, Is similar to dimethyl- glyoxime in yielding scarlet and yellow precipitates with nickel and palladium, which can be used for the gravimetric determination of these metals. It is soluble in water, in contrast to dimethylglyoxime, so that its use is theoretically unaccompanied by danger of contaminating the precipitates with excess reagent or of solubility loss by the addition of alcohol. On the other hand, nioxime is a more power- ful reducing agent than dimethylglyoxime, which introduces some complications in its use. One part of nickel in ten million may be detected with the reagent. The precipitation of nickel nioxime is complete at pH values of three ard greater, and the precipitation may be made from a solution of various anions, chloride, sulfate, perchlorate, nitrate, acetate, tartrate, and sulfo- salicylate. The precipitation effectively separates nickel from a variety of metals including zinc, beryllium, uranium, aluminum, the alkali and alkaline earth metals, manganese, cadmium, antimony, and arsenic. Attempts to separate nickel from iron failed, as no suitable complexing agent for the latter was found which would prevent the precipitation of the iron and not interfere in the determi- nation of the nickel. The unique and useful applications of the 1,2-dioximes to analytical chemistry were extensively reviewed in 1940.^ That 1,2-cyclohexanedionedioxime yielded a scarlet precipitate with nickel and in fact was a very sensitive qualitative test for nickel was early discovered by Wallach.^ FeigP pointed out that 1,2-cyclohexanedionedioxime should be the ideal reagent for nickel, inasmuch as its solubility in water would be a significant advantage over dimethylglyoxime, which must be made up in alcohol or acetone. Although this attracted the attention of various analytical chemists, the great difficulty in synthesizing 1,2-cyclohexanedionedioxime precluded a detailed study of its prop- erties and uses as an analytical reagent; indeed, numeroas, unreported attempts to prepare the rea- gent met with signal failure, and it was only in 1945 that Rauh, Smith, Banks, and Diehl' succeeded in obtaining sufficient of the material to make possible its investigation. One of their methods of preparation was later greatly improved by Hach,'' so that the compound is now available at moderate price.* A comman name, Nioxime, has been proposed for the reagent. The uses of nioxime in the analjfticai chemistry of nickel and palladium were investigated as part of the thesis for the MS degree by Banks. This work and also some by Voter, both interrupted for war service, have now been continued and form the subject matter of this paper. In the meantime work was done at Purdue University by Nellon and Grlffing^ on the use of the reagent in the colori- metric determination of nickel and iron. Publication of this work was unfortunately obstructed and during the ensuing delay a short paper by certain English workers,^ dealing with the gravimetric and colorimetric uses of nioxime, has appeared. *Hach Chemical and Oxygen Company, Ames, Iowa. MDDC- 985 2] MDDC - 985 PHYSICAL PROPERTIES Nioxime is a white, crystalline material, melting at 189 to 190°, which, when properly prepared, is free from any pink coloration due to contamination by iron, and which remains white indefinitely. Its molecular weight is 142.16. The solubility of nioxime in water was determined by precipitating a measured volume of a sat- urated solution with an excess of nickel: 0.82 g per 100 ml water at 21.5°. REAGENTS A 0.8 per cent aqueous solution of nioxime was used. This solution keeps indefinitely. A standard nickel solution was prepared from Mond nickel obtained from the International Nickel Company. This nickel was analyzed spectrographically and found to be free from iron and cobalt. A weighed amount of this nickel was dissolved in aqua regia and the solution evaporated to dryness five times with concentrated hydrochloric acid to eliminate nitrate ions. By weighing the diluted nickel chloride solution, the weight of nickel per weight of solution was found. This nickel concentration was checked by an electroljrtic determination of the nickel, the sample being measured by a weight buret. The residual liquid was tested with nioxime to insure the complete deposition of the nickel. The nickel content of the solution, as determined by the two methods, agreed well. (See Table 1.) The value obtained by electrolysis was used. A 20 per cent solution of ammonium acetate was prepared from reagent-grade salt and filtered. Table 1. Standardization of nickel solution. Weighing nickel and solution Electr( Dlyti LC Determination g Ni/g solution 1 0.001990 Determination 1 2 3 4 Avg g Ni/g solution 0.001995 0.001994 0.001992 0.001993 0.001994 SENSITIVITY Ten nickel solutions were made up in 100-ml volumetric flasks, with concentrations ranging from one to ten parts in ten million. To each solution were added three drops of 0.8 per cent nioxime solution, followed by vigorous shaking. Observations made less than two minutes after the addition of the reagent showed that each solution exhibited a color ranging from red for the more concen- trated to pink for the one part in ten million. At the end of one hour, a red precipitate was found in each flask. The pH of the solutions as determined with a glass electrode was 6.4. A comparative test was performed using dimethylglyoxime (1 per cent in ethanol) on solutions of like concentrations at a pH of 8. No visible coloration was detected until thirty minutes after addition of the reagent and then only in those solutions of higher concentration. The sensitivity of the nioxime for nickel determined this way is greater than that reported by Wallach^ and the English workers, ^ who reported one part in two million and one part in five million, respectively. MDDC - 985 [3 GRAVIMETRIC DETERMINATION OF NICKEL Since hydrogen ions are liberated on the formation of the nickel derivatives of the 1,2-dioximes, it is necessary to buffer the solution or otherwise control the pH by the addition of ammonia. Whereas nickel dimethylglyoxime is generally precipitated from a mildly ammoniacal medium, it was found best to precipitate nickel nioximefrom a slightly acid solution. This is an advantage, because it makes possible the separation of nickel from certain metallic ions without the use of complexing agents. Quantitative precipitation of nickel was obtained at a pH of 3 or higher. The rate of precipitation and the pH of the solution determine the ease of filtration of the nickel nioxime precipitate. If the nickel was precipitated by the dropwise addition of the nioxime solution to the buffered nickel solution, the precipitate formed clogged the filtering crucible and filtration was quite difficult. If the pH of the solution was slowly raised from a point where the nickel nioxime would not precipitate to a pH of about 4.5, the precipitate was filtered without trouble. This slow precipitation was effected by the dropwise addition of a 20 per cent solution of ammonium acetate with constant stirring. Precipitates formed at pH values above 7 were somewhat gelatinous, were exceedingly difficult to filter, and exhibited a bluish coloration. The best results with respect to accuracy and precision were obtained when precipitation was made from a slightly acid solution. Nickel nioxime is formed by the union of one nickel atom with two molecules of nioxime with the liberation of two hydrogen ions, and the nickel derivative, NiCCeHgOjNjlj, molecular weight 340.99, should contain 17.21 per cent nickel. The results of nearly a hundred determinations indicate, however, that the nickel content is slightly lower than the theoretical. It has been shown that this departure is independent of the anion present in the solution, of any foreign cations present, and in general of any diverse ions present in the solution. The various reagents and distilled water were checked as possible sources of contamination and found to be without fault. A determination made on the nickel chloride in water without the addition of acetate gave the same results. The data all indi- cated that the positive error was caused by the coprecipitation of the reagent. Results from a series of determinations in which the per cent excess of the nioxime was varied showed that the error was nearly a linear function of the concentration of the excess nioxime for a given weight of nickel (Figure 1). RO / 1- z LiJ O 1^ 60 X y" 2 / UJ E X 40 y'i 1 z y in LiJ O •X 20 / y hi 0.1 0.2 0.3 ERROR IN MG Ni PER 0.025 G Ni 0.4 0.5 4] MDDC - 985 Since the volume of the solution was constant in these determinations, the per cent excess was proportional to the nioxime concentration and thus determined the amount of nioxime coprecipitated by the nickel nioxime precipitate. Washing the nickel nioxime precipitate with 95 per cent ethanol, in which nioxime is fairly soluble and the precipitate insoluble, did not free the precipitate of the reagent; nor did precipitation from 10 per cent alcohol solution change the result. Since the magnitude of this error was a linear function of the excess nioxime, an empirical equation was easily developed by which the correct results for nickel could be calculated from the weight of the precipitate and the total reagent added. The weight of nioxime used is the weight of the nickel precipitate multiplied by the factor 0.834. The volume of 0.8 per cent solution used is then ,, , , 0.834 (Wt Ni nioxime ppt) , „ . ,„,.„. . . ,, Vol used = ^ „ -„p '^^^ =104 (Wt Ni nioxime ppt) U.UUo with the volume added known, the per cent excess reagent is calculated. The correction is calcu- lated by _ .. , . (% excess nioxime) (Wt Ni nioxime ppt) (0.1721). Correction in g of Ni = tz—- ^^ duuu The result of the analysis is then calculated in the usual way ™ „. (Wt Ni nioxime) (0.1721) -(Corr in g Ni) /o Ni — „,, , x luu. Wt sample The factor 5000 results from the observation that each 20 per cent excess nioxime caused a positive error of one part in 250. As the correction is quite small, the per cent excess of nioxime need only be approximately known, and it is sufficient merely to measure the volume of nioxime solution added in a graduated cylinder. Determinations conducted on a series of samples of different size indicated that amounts of nickel from 5 to 25 mg could be successfully determined. The correction for the reagent carried down need only be applied for amounts of nickel above 1 5 mg. The precipitation of small amounts of nickel, less than 2 or 3 mg, is slow. In determination 1 of Table 2 the solution was refiltered after two hours through the filter crucible containing the first precipitate. Table 2. Determination of various amounts of nickel. Nickel Weight of Nickel Determination taken precipitate . found Error (gram) (gram) (gram) (milligram) 1 0.0018 0.0110 0.0019 +0.1 2 0.0049 0.0292 0.0050 +0.1 3 0.0107 0.0S31 0.0108 +0.1 4 0.0144 0.0847 0.0145 +0.1 5 0.0203 0.1186 0.0203 0.0 The nickel nioxime precipitate was dried at various temperatures from 100° to 155° . No further loss in weight occurred at the higher temperatures. At temperatures above 155°, however, the pre- cipitate turned brown and lost weight rapidly. The precipitate could not be ignited to the oxide for weighing, as sublimation occurred before the decomposition could be effected. MDDC - 985 [5 RECOMMENDED PROCEDURE Adjust the volume of the solution containing about 25 mg of nickel to approximately 250 ml. If a complexing agent is needed to prevent the precipitation of other metals, it should be added before continuing with the procedure. Add 8 ml of a solution of 0.8 per cent nioxime for each 10 mg of nickel present, measuring with a graduated cylinder the volume of reagent added. Slowly add with stirring enough concentrated hydrochloric acid to cause any red precipitate of nickel nioxime to dissolve. Then add ammonia dropwise until a faint red coloration persists. Heat the solution to about 60°. From a buret add dropwise and with constant stirring 25 ml of the 20 per cent ammonium acetate. Digest the solution with occasional stirring for 30 to 40 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. Calculate the results as previously described. The pH of the solution just before filtration will be between 4 and 5, if the procedure is carefully followed. Table 3. Effect of various anions upon the determination of nickel. Weight of Anion Anion Nickel taken precipitate Nickel found Error present (grams) (gram) (gram) (gram) (mg) Acetate 4.5 0.0265 0.1554 0.0236 +0.1 Acetate 4.5 0.0258 0.1516 0.0259 +0.1 Chloride 0.5 0.0229 0.1346 0.0230 +0.1 Chloride 0.5 0.0245 0.1439 0.0246 +0.1 Chloride 0.5 0.0294 0.1712 0.0293 -0.1 Chloride 0.5 0.0243 0.1417 0.0242 -0.1 Chloride 0.5 0.0229 0.1335 0.0228 -0.1 Sulfate 1.0 0.0246 0.1440 0.0246 0.0 Sulfate 1.0 0.0262 0.1531 0.0262 0.0 Sulfate 1.0 0.0233 0.1361 0.0233 0.0 Sulfate 1.0 0.0252 0.1476 0.0252 0.0 Sulfate 1.0 0.0264 0.1548 0.0264 0.0 Nitrate 0.2 0.0255 0.1497 0.0256 +0.1 Nitrate 0.2 0.0263 0.1545 0.0264 +0.1 Nitrate 0.2 0.0253 0.1486 0.0254 +0.1 Nitrate 0.2 0.0247 0.1449 0.0248 +0.1 Nitrate 0.2 0.0252 0.1480 0.0253 +0.1 Perchlorate 0.2 0.0264 0.1531 0.0262 -0.2 Perchlorate 0.2 0.0266 0.1567 0.0268 +0.2 Perchlorate 0.2 0.0249 0.1450 0.0250 +0.1 Perchlorate 0.2 0.0247 0.1440 0.0246 -0.1 Perchlorate 0.2 0.0246 0.1437 0.0246 0.0 Tartrate* 8.0 0.0238 0.1389 0.0237 -0.1 Tartrate* 8.0 0.0246 0.1434 0.0245 -0.1 Tartrate* 8.0 0.0261 0.1534 0.0262 +0.1 Tartrate* 8.0 0.0263 0.1534 0.0262 -0.1 Tartrate* 8.0 0.0266 0.1554 0.0266 0.0 Sulfosalicylate* 5.7 0.0239 0.1400 0.0239 0.0 Sulfosalicylate* 5.7 0.0246 0.1441 0.0246 0.0 ♦Small amount of chloride present MDDC - 985 The effect of various anions upon the determination of nickel was studied. The weighed nickel chloride solution was evaporated with sulfuric acid, nitric acid, or perchloric acid to eliminate the chloride. The nickel nioxime was precipitated by the addition of the nioxime reagent to the acid solution and neutralized with a 20 per cent solution of ammonium acetate. As shown in Table 3, satisfactory results are obtained from chloride, nitrate, sulfate, and perchlorate solutions. Further determinations in which tartrate, acetate, and sulfosalicylate were added as the ammonium salts to the nickel chloride solution showed that these anions do not affect the determination. The determination of nickel in the presence of beryllium was studied. The separation was effected both with and without sulfosalicylic acid as a complexing agent for the beryllium ion. As beryllium hydroxide does not precipitate below a pH of 5.7,'° the complexing agent is not necessary when the determination is conducted in the manner suggested. Table 4 summarizes the data obtained. The precipitate from determination "three" was decomposed with nitric acid and ignited to the oxide. Spectrographic analysis revealed the presence of less than 100 ppm beryllium, indicating a success- ful separation. Table 4. Determination of nickel in the presence of beryllium. Beryllium Nickel Weight of Nickel Determination present taken precipitate found Error (gram) (gram) (gram) (gram) (mg) 1* 0.2 0.0212 0.1243 0.0212 0.0 2* 0.2 0.0210 0.1232 0.0211 0.1 3 0.1 0.0242 0.1409 0.0241 0.1 4 0.2 0.0252 0.1482 0.0253 0.1 5 0.2 0.0270 0.1578 0.0270 0.0 6 0.3 0.0233 0.1363 0.0233 0.0 7 0.3 0.0241 0.1390 0.0238 0.3 ♦Contained 6.5 grams of sulfosalicylic acid. Table 5 shows results that were obtained in separating nickel from various amounts of zinc. There was no evidence of coprecipitation of zinc hydroxide with the nickel nioxime. Table 5. Determination of nickel in the presence of zinc. Zinc Nickel Weight of Nickel Determination present taken precipitate found Error (gram) (gram) (gram) (gram) (mg) 1 1.0 0.0252 0.1474 0.0252 0.0 2 0.8 0.0234 0.1371 0.0234 0.0 3 0.5 0.0272 0.1595 0.0272 0.0 4 0.3 0.0239 0.1401 0.0239 0.0 5 0.1 0.0210 0.1226 0.0210 0.0 Nickel was determined in the presence of uranyl, manganous, sodium, potassium, lithium, barium, calcium, strontium, magnesium, cadmium, and arsenite ions. When aluminum and antimonite ions are present with the nickel, tartrate must be added as a complexing agent to prevent copre- cipitation of aluminum hydroxide and antimonous hydroxide with the nickel nioxime. The data from these separations are also shown in Table 6. MDDC - 985 [7 Table 6. Determination of nickel in the presence of various cations. Nickel Weight of Nickel Cation Cation taken precipitate found Error present (gram) (gram) (gram) (gram) (mg) Uranyl 0.55 0.0236 0.1385 0.0237 +0.1 Uranyl 0.23 0.0234 0.1368 0.0234 0.0 Manganous 0.50 0.0236 0.1381 0.0236 0.0 Manganous 0.10 0.0231 0.1351 0.0231 0.0 Sodium ^ Potassium > 0.10 each 0.0235 0.1375 0.0235 0.0 Lithium Barium ^ Calcium > 0.10 each 0.0255 0.1491 0.0255 0.0 Strontium J Magnesium' 0.20 each 0.0220 0.1291 0.0221 +0.1 Cadmium Antimonite* 0.14 0.0221 0.1301 0.0222 +0.1 Aluminumf 0.20 0.0233 0.1362 0.0233 0.0 Arsenite 0.34 0.0234 0.1373 0.0235 +0.1 ♦Complexed with 0.2 gram of tartrate. -j-Complexed with 1.2 grams of tartrate. A method for the satisfactory quantitative separation of nickel from iron was not found. The difficulty lay in finding a complexing agent for the ferric iron. The possibility of using tartrate and citrate was exhaustively investigated. However, these anions are known to reduce iron to the ferrous state/ which forms a very stable complex with nioxime, and incomplete precipitation of the nickel results. Nioxime will also reduce ferric to ferrous iron. Ferric sulfosalicylate complex inhibits the precipitation of the nickel nioxime, and postprecipitation occurs as much as twenty four hours after filtration. Fluoride, phosphate, and pyrophosphate precipitate ferric iron, whereas dextrose, glycerine, salicylate, d-mannitol and thiocyanate do not prevent hydrous ferric oxide from precipitating under the conditions of the recommended procedure. Ferrocyanide was ruled out, since nickel ferrocyanide is insoluble. 2,2 -Bipyridine complexes nickel as well as ferrous iron,^ and nickel nioxime is not precipitated in its presence. 8] MDDC - 985 REFERENCES 1. Diehl, H. "The Application of the Dioximes to Analytical Chemistry," G. Frederick Smith Chemical Company, Columbus, Ohio, 1940. 2. Feigl, F., "Qualitative Analyse mit Hilfe von Tiipfelreaktionen," p 73, Akademische Verlags- gesellschait M.B.H., Leipsig, 1931. 3. Griffing, M., Ph.D. Thesis, Purdue University, Lafayette, Ind. 1944. 4. Hach, C. C, C. V. Banks, and H. Diehl, unpublished work. 5. Johnson, W. C, and M. Simmons, Analyst 71:554 (1946). 6. Moss, M. L., with M. G. Mellon, Ind. Eng. Chem., Anal. Ed., 14:862 (1942). 7. Rauh, E. G., G. F. Smith, C. V. Banks, and H. Diehl, J. Org. Chem. 14:862 (1945). 8. Schoras, J., Bar. 3:11 (1870). 9. Wallach, O., Ann. 437:175 (1924). 10. Willard, H. H. and H. Diehl, "Advanced Quantitative Analysis." p 45, D. Van Nostrand Co.,' New York, 1943. UNIVERSITY OF FLORIDA 3 1262 08909 7082 ^