Glucono-delta-Lactone as a Sequestering Agent in the Gravimetric Determination of Nickel SIR: Some of the commercially available standardized nickel ore samples used for student analyses are prepared by dilution of an acid soluble nickel compound with limestone (6). In the usual gravimetric determination with dimethylglyoxime (DMG), it is customary to sequester Fe(II1) with tartaric acid or citric acid (3, 4, 7, 8). Difficulty was encountered with this system in the presence of large amounts of calcium because calcium tartrate precipitates after adjustment of pH to the range suitable for the precipitation of nickel. Although the calcium precipitates slowly, it is frequently not possible to precipitate the nickel and to remove the precipitate before an appreciable quantity of calcium tartrate is formed. Substitution of citric acid for tartaric improves the situation since the solubility of calcium citrate is sufficiently high to prevent precipitation in all but extreme cases. Citric acid would be satisfactory for sequestering Fe(II1) except that the last traces of nickel appear to precipitate only after several hours standing. For a student whose time is limited to a given 3- or 4-hour period per week, delay in obtaining quantitative precipitation can be troublesome. Neither is prior removal of calcium feasible under these circumstances. The use of glucone-&lactone (presumably acting as gluconic acid in solution) permits rapid and complete precipitation of Ni(I1) as the DMG chelate while providing adequate control of small amounts of Fe(II1). Sequestering is also adequate for major amounts of iron such as would be encountered in steel samples. Replacement of citric or tartaric acid by glucono-8-lactone is satisfactory on a weight-for-weight basis. MATERIALS
Mich. The samples used in this study ranged from 1 to 5% Ni. Actual sample numbers and absolute values of nickel content have been coded to protect the integrity of the unknowns. REAGENT SOLUTIONS
Ammonia. Concentrated reagent diluted 1 : l with distilled water and filtered. 1% Dimethylglyoxime. 26 grams of Eastman white label disodium dimethvlglyoximate per liter. Citric acid monohydrate, 20% !w./y.) (Matheson Coleman & Bell) in distilled water. Tartaric acid 20% (w./v.) (General Chemical) in distilled water. Glucono-6-lactoneJ10% (w./v.) (Fisher Scientific) in distilled water, decolorized with carbon and preserved with 0.1% thymol. Ammonium chloride, 20% (w./v.) in distilled water. ANALYSIS O F ORE SAMPLES
Sample Preparation. Samples of ore were dried for 2 hours at 115' C. A 5.000-gram portion was dissolved in concentrated nitric acid and the solution was evaporated to dryness. The residue was taken up with hydrochloric acid, evaporated to dryness, and baked for a t least 1 hour. The baked residue was taken up with hydrochloric acid and water, filtered into a 250-ml. volumetric flask, and diluted to volume. One-tenth aliquots
Table 1. Precipitant Dimethylglyoxime,' disodium salt
were used for analysis after dilution with 150 ml. of distilled water. The procedure was essentially that recommended by the supplier (6), modified to accommodate the larger samples and using an aqueous solution of the sodium salt of DMG. The procedure is based on that given by Hillebrand and Lundell (3). Final drying of the precipitates w&s carried out a t 170' C. The results are summarized in Table 11. IDENTIFICATION O F CALCIUM TARTRATE
The interfering precipitate encountered with tartaric acid was identified aa calcium tartrate by its behavior on heating: charring, brilliant glow of the calx, flame color, and weight loss in comparison to that of an authentic sample of calcium tartrate. The slightly yellow crystals that continued to form after removal of nickel from a solution of sample A containing tartrate were collected and airdried. A 0.4005-gram portion of the crystals wae heated to about 550" C., as was a similar portion of calcium tartrate, to convert the salt to carbonate (9). Cafound %: Ca precip'itate 15.52 Calcium tartrate 15.43 Theoretical for CaC4H4Os.4Hp0 15.40 COMPOSITION O F A NPICAL ORE (SAMPLE A)
Acid Soluble RIOS. An aliquot of stock solution was made alkaline with ammonia in the presence of ammo-
Analysis of Nickel Ammonium Sulfate Hexahydrate
8-Quinolinol
Conditions No sequestrant Citric acid Tartaric acid Glucono-&lactone Acetate buffer, pH 4.5-5
Nickel Found, yo
Av.
7 results, 14.85-14.89 14.90, 14.88 14.87, 14.92, 14.87, 14.91 14.87, 14.85, 14.86, 14.91 14.84, 14.87
14.88 14.89 14.89 14.87 14.86 14.88 14.86
Weighted mean Theoretical Precipitates were allowed to stand overnight before being filtered. Results were 0.2 ta 0.40/, low in Ni when precipitates from citric acid solution were filtered within 2 hours of precipitation. All precipitates were heated to about 170' C. before final weighing. 0
Nickel ammonium sulfate hexahydrate. Prepared by mixing hot concentrated solutions of NiSOc .6Hz0 and (NH&SOi and collecting the bluish crystals obtained on cooling the mixture. The product was washed successively with cold water, alcohol, and ether followed by air-drying a t 25% relative humidity. The product was analyzed for Ni using DMG with and without sequestering agents, and using 8-quinolinol. All precipitates were dried to constant weight a t 160' to 170' C . (1). The results are summarized in Table I. Nickel ore samples. Obtained from Smith and Underwood, Royal Oak, 1286
ANALYTICAL CHEMISTRY
Table II.
Summary of Synthetic Ore Analyses for Nickel Nia Found in Sample, %
Sample A Sample B Sample C Sequestering Agent 2 Hrs? 2 Days 2 Hrs. 2 Days 2 Hrs. 2 Days Tartaric acid C Citric acid 1.03 1.07 2.76 2.81 4.54 4.58 Glucono-&lactone 1.05 1.04 2.81 2.82 4.57 4.58 Supplier's value 1.00 2.75 4.63 * yo Ni is reported relative to the supplier's value for sample A. b Time interval before filtration. In all case8 a dense crystalline precipitate formed before nickel could be removed.
nium chloride. The precipitate was collected and ignited a t 840’ C. Found: R203= 0.5270. Acid Soluble Calcium. The nickelfree filtrate from sample A containing gluconate was evaporated to 150 ml. and acidified. Ammonium oxalate and urea were added. The solution was diluted to 250 ml., heated, and treated with ammonia t o the first permanent turbidity. Heating was continued t o the methyl orange color change. The precipitate was collected, washed in the usual manner, and ignited at 510’ C. Found: Ca (as CaCOs) = 79.08%. EFFECT
OF
nium sulfate hexahydrate. Mohr’s salt (7.02 grams 1.00 grams Fe) was dissolved in 10 ml. of distilled water and 5 ml. of concentrated HN03. The solution was heated until evolution of NOz ceased and was diluted to 150 ml. Twenty-five milliliters of nickel stock solution was added. Further treatment of the solution and precipitation of the nickel were carried out using the procedure given by Willard and Diehl (9), but with the sodium salt of DMG and drying the precipitate at 170” C. Fe present, gram: 1.00; Ni taken, mg.: 25.0; Ni found, mg.: 24.9, 25.1 (tartrate); 25.1 (citrate); 25.2, 25.2 (gluconate).
LARGE AMOUNTS OF IRON
.4 nickel stock solution containing 1.00 mg. of Ni per milliliter waa prepared determinately using previously prepared and analyzed nickel ammo-
LITERATURE CITED
(1) Duval, C., “Inorganic Thermogravimetric Analysis,” pp. 230, 233, Elsevier,
New York, 1953.
(2) Ibid., p. 158.
(3) Hillebrand, W. F., Lundell, G. E. F.. “Applied Inorganic Analysis,” pp. 31517, Wiley, New York, 1929. (4) Kolthoff, I. M., Sandell, E. B., “Textbook of Quantitative Analysis,” pp. 689-90, 3rd ed., Macmillan, New York, 1952. (5) Smith, Rossman, Smith, and Underwood, Royal Oak, Mich., private communication. (6) Smith and Underwood, Royal Oak, Mich., Circular supplied t o purchasers of standardized samples. (7) Walton. H. F.. “Elementarv QuantitaQuantitative Analysis,” p. 883, D Nostrand, Princeton, N. J., 1943. (9) Ibid., p. 385. JAMESS. PROCTOR DAVIDC. FAR WELL^ Goessmann Laboratory University of Massachusetts Amherst, Mass. Present address, Box 46, Dover Road, Wilmington, Vt.
Microscopic Identification of Microgram Quantities of Mannoheptulose and Sedoheptulose SIB: Studies on the distribution of heptuloses in plants required sensitive tests to confirm chromatographic evidence for the occurrence of mannoheptulose (D-manno-heptulose) and sedoheptulose (D-altro-heptulose). This note describes an extension of the solvent diffusion technique for the identification of some pentoses (4, 6) and hexoses (6-7) to the identification of microgram quantities of these heptuloses. METHODS AND OBSERVATIONS
Prepare the plant extract and remove fermentable sugars (1, 8, 9). Chromatograph 10 pg. or more of mannoheptulose or 25 to 50 pg. or more of sedoheptulose on water-washed (7) Whatman No. 1 (chromatographic grade) sheets in ethyl acetate-pyridinewater (8 to 2 to 1) solvent until the maximum separation of the heptuloses from other sugars remaining in the plant extract has been effected. Wash the chromatogram with ethyl ether immediately after its removal from the tank. Locate the test area by means of adjacent guide strips using orcinol reagent (2) on some strips t o show the heptuloses and alkaline silver nitrate on others to show the nonheptulose components. Excise the test area eliminating as much nonheptulose material as possible. Using techniques described (6),elute the sugar with 3 drops of water and carry out the synthesis and observation of the sugar derivative using reagent A or B described below and 1 pl. of glacial acetic acid as the diffusing solvent. Compare the result-
ing products with those obtained with authentic heptuloses and with suitable blanks. To obtain the most sensitive, characteristic, and rapid tests, use reagents . - . A and B only for the sugar specified. Reanent A (for mannoheDtulose test). Grindvan equimolar mixt&e of recry& tallized 1-benzyl-1-phenylhydrazine hydrochloride and recrystallized phenylhydrazine hydrochloride and add, with gentle stirring, 1 mole of anhydrous spdium acetate for each mole of hydrazme. Reagent B (for sedoheptulose test). Grind recrystallized phenylhydrazine hydrochloride and stir in an equimolar amount of anhydrous sodium acetate. Prepare both reagent mixtures daily and keep dry.
-
-
1 Benzyl - 1 phenylhydrazinephenylhydrazine test for mannoheptulose. The compound synthesized in this test is mannoheptulose 1benzyl - 1 - phenylphenylosazone-a new derivative of this sugar. It appears in from 1 to 16 hours, depending on the amount of sugar present, as fine yellow needles growing from a common center in clusters. Growth is rapid after crystallization has started. With large amounts of sugar, the clusters are densely packed, regular in shape, and often have depressed centers. Small amounts of sugar produce larger, less densely packed clusters having needles of varying length. Dendritic formation or long runners may be present. As little as 1pg. of the pure mannoheptulose or 10 pg. (amount applied to the paper)
of the chromatographically separated sugar gives a characteristic product. Phenylhydrazine test for sedoheptulose. The reaction product is sedoheptulose phenylosazone. It appears in from 3 to 16 hours, depending on the amount of sugar present, as fragile, short, light yellow-orange needles in densely packed clumps with no apparent center of growth. The sensitivity of the test is 15 pg. for the pure sugar (5% aqueous sedoheptulosan monohydrate hydrolyzed 400 hours at room temperature with Dowex 50, hydrolysis assumed 10% complete) or from 25 to 50 pg. (amount applied to the paper) for the chromatographically separated sugar. The principal anhydrides of sedoheptulose, 2,7-anhydro-,%~-dtro-heptulopyranose and 2,7-anhydro-,%~-altroheptulofuranose, did not react under the conditions of either of the tests. DISCUSSION
Both mannoheptulose and sedoheptulose give a product in each of the tests described. However, they do not interfere in the tests for each other because they are readily separated chromatographically. Plant extracts contain other sugars that may react in one or both of the tests. Such interference can be eliminated or greatly minimized by fermentation of the plant extract, careful chromatographic separation, and judicious excision of the test area. A thorough study of interference by VOL 33, NO. 9, AUGUST 1961
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