ANALYTICAL CHEMISTRY
1200 4.5
-
4.0
-
Table I. Absorbance Differences (against Blank Value) as Function of Ammonium Chlorate Contenta 70Ammonium Chlorate in Ammonium Perchlorate 1 0.01 045 0.02 088 0.04 180 0.06 275 0.08 359 0.10 430 a Five determinations.
A Absorbance X lo3 2 3 4 047 045 045 088 089 087 181 179 179 275 278 269 363 361 368 434 435 ...
8
5 042 088 180 273 361 446
-I
3.5
PO0
Table 11. No. of
Detn. Addeda 9 0.01 15 0.02 15 0.04 10 0.06 10 0.08 9 0.10 Calculated from potassium
Found 0.0096 10.00025 0.0194 f 0.00019 0.0398 f 0.00025 0.0606 =!= 0,00028 0.08 f 0.00033 0.096 =!= 0.00148 chlorate added.
300
1
350
WAVE LENGTH, Mp
Error in Chlorate Determination % Ammonium Chlorate
\
250
Figure 2. Absorption spectrum of brucine
Mean Difference - 0,0004 - 0.0006 0,0002
Brucine, 5.1 mg., in 1 ml. in glacial acetic acid, diluted successively with 30% sulfuric acid
-
0.0006 0 -0.004
The method gives excellent results below the 0.1% concentration of ammonium chlorate. For concentrations greater than O.l%, the results tend to become somewhat low. Regarding the possible interference of foreign ions, systematic experiments were carried out with chloride and ferric ions. As much as 0.1% of ammonium chloride in the ammonium perchlorate had no effect. The ferric ion did not interfere up to a quantity of 0.005%; larger amounts gave too high absorbance readings. Samples containing large quantities of iron ion should be treated with ammonia solution and then filtered to remove the iron ion. Periodate and nitrate interfere with this method. However, iodate gave no measurable color with the reagent below the 0.033 weight % concentration in the ammonium perchlorate. These ions are not likely to be present in samples of ammonium perchlorate. Heating of the solution from 15 to 30 minutes had no adverse effect on the accuracy of the analysis. DISCUSSION
Comparison of the absorption spectra of brucine (Figure 2) and the colored compound (Figure 1) leads to the hypothesis that the
ring system of the former is oxidized by the chloric acid. I t is most likely (supported by unpublished results on the determination of nitroglycerin with brucine), that all oxidizing agents convert brucine into the same compound or a t least compounds characterized by the same chromophoric groups. ACKNOWLEDGMENT
The author wishes to express his appreciation to Ernst D. Bergmann for his advice and to Shlomo Weinstock for providing the ammonium perchlorate used in this investigation. LITERATURE CITED
(1) Berl, E., and Lunge, G., “Chemisch-technische Untersuchungs(2)
(3) (4) (5)
(6) (7)
methoden,” 8th ed., Vol. 111, pp. 1170-1, Julius Springer, Berlin, 1932. Feigl, F., ”Spot Tests,” Vol. I, p. 301, Elsevier, New York, 1954. Kast, H., and Mete, L., “Chemische Untersuchung der Sprengund Zuendstoffe,” p. 379, Friedr. Vieweg und Sohn, Braunschweig, 1944. I h i d . , p. 384. Snell, F., and Snell, C. T., “Colorimetric Methods of Analysis,” 3rd ed., Vol. 11, p. 717, Van Nostrand, Xew York, 1949. Welcher, F. J., “Organic Analytical Reagents,” Vol. IV, p. 215, Van Nostrand, New York, 1948. Wischoe, F., J . Chem. SOC.,112,11, 539 (1917).
RECEIVEDfor review M a y 7, 19.54. Accepted December 29, 1954. These experiments were carried out under the auspices of the Scientific Department, Israeli Ministry of Defense.
Spectrophotometric Determination of Nickel in Tungsten Powder KENNETH L. ROHRER’ Tungsten and Chemical Division, Sylvania Electric Products, Inc., Towanda, Pa.
A rapid and accurate method has been developed for the determination of microgram quantities of nickel in tungsten powder. With this method the nickel is separated from all interfering elements by a chloroform extraction of the bivalent nickel complex of dimethylglyoxime in the presence of the hydrogen peroxide used to dissolve the metal powder. The determination is made by spectrophotometric measurement of the diethyldithiocarbamate complex of nickel. Nickel, 1 to 50 y, can be determined in tungsten powder with an average deviation of less than 1 y.
N
ICKEL if present within the crystal structure of tungsten powder or as a dope will alter its physical properties. AS
an impurity, its accurate determination is usually lengthy and it requires a preliminary separation before a suitable colorimetric method can be utilized for the small amounts present.
Fettweis (3) has attempted to determine nickel in tungsten steels by precipitating with dimethylglyoxime, but found that the nickel precipitate of dimethylglyoxime retains some tungstic oxide and that results are from 0.05 to 0.1% high. However, no previous methods for the determination of small amounts of nickel in tungsten powder have been reported. Dimethylglyoxime has been mentioned frequently in the literature as a reagent forming a soluble, colored complex with nickel, either compleving with quadrivalent nickel, or if oxidized complexing u i t h bivalent nickel. This reagent has long been used for the detection of nickel ( 2 ) . Bivalent nickel can be separated by a chloroform extraction of the insoluble, bivalent nickel complex of dimethylglyoxime ( 6 ) . Oxidining agents such as nitrates, ferricyanides] peroxides, and permanganates have been reported to prevent the formation of this insoluble nickel prePresent address, Westinghouse Electric Corp., Elmira, N. Y.
V O L U M E 27, NO, 7, J U L Y 1 9 5 5 cipit,ate ( 7 ) ; however, reliable results have been obtained in the mixtures employed in the determination of nickel in steel. I n t,his work the bivalent nickel complex of dimethylglyoxime has been satisfactorily extracted with chloroform in the presence of an excess of hydrogen peroxide. The method employed had been first used by Alexander, Godar, and Linde ( I ) , who used two reactions of nickel together, a separation of nickel dimethylglyoxiiiie with chloroform and the extraction of a diethyldithiocarbamate co.mplex with isoamyl alcohol, the nickel being determined b y spectrophot'onietric measurement of the yellowgreen complex. APPARATUS AKD REAGENTS
Dimethylglyoxime, O.lgl,. Dissolve 0.25 gram of reagent grade dimethylglyoxime in 50 ml. of absolute alcohol and dilute to 250 ml. with distilled water. Ammonium Citrate (dimethylglyoxime, purified), 207& Dissolve 200 grams of ammonium citrate in 600 ml. of distilled water, adjust wit,h ammonium hydroxide to p H 9.0 to 9.5, and transfer to a separatory funnel. Add 10 ml. of dimethylglyoxime reagent and extract three times with 30-ml. portions of chloroform. Filter t,he aqueous layer and dilute to 1 liter with distilled water. Sodium Diethyldithiocarbamate, 0.2y0. Dissolve 1 gram of sodium diethyldithiocarbamate in 100 ml. of distilled water, filter, and dilute to 500 ml. x i t h distilled water. Ammonium Citrate (sodium diethyldithiocarbamate, purified), 20%. Dissolve 200 granis of ammonium citrate in 600 ml. of distilled water, adjust with ammonium hydroxide to p H 9.0 to 9.5, and transfer to a separatory funnel. Add 10 ml. of sodium diethyldithiocarbamate reagent and extract with 20-ml. portions of carbon tetrachloride until the organic layer is colorless. Add 5 ml. of carbamate reagent and again extract with carbon tetrachloride. If the organic layer remains yellow, add more carbamate reagent and continue the extractions until the layer is colorless. Hydrochloric Acid, 0.5N. Dilute 40 ml. of concentrated hydrochloric acid t o 1 liter with distilled water. Standard Nickel Stock Solution. Dissolve 0.500 gram of pure nickel in 20 ml. of (1 1) nitric acid and dilute to 1 liter with distilled water. Standard Nickel Working Solution (I ml. = 5 y of Ni). Dilute 10 ml. of the standard nirkel stock solution to 1 liter with 0.5N hydrochloric acid. All transmittance measurements 11ere made with a Beckman Model B spectrophotometer in combination with a blue-sensitive phototube and a Beckman No. 12216 filter, using 1.000-cm. Corex cells. The p H measurements were made with a Beckman Model 11 p H meter.
+
PREPARATION OF CALIBRATION CURVE
Add 0, 1, 2, 3, 4, and 5 ml. of standard nickel working solution to 125-m1. separatory funnels and dilute to exactly 25 ml. with 0.5N hydrochloric acid using a 25-ml. graduate. To these solutions add 5 ml. of ammonium citrate solution (carbamate, pyrified), a small piece of red litmus paper, and sufficient ammonium hydroxide to make slightly alkaline plus an excess of 8 drops. Add exactly 10.0 ml. of isoamyl alcohol and 5 ml. of carbamate reagent; stopper and shake vigorou-lv for 2 minutes. Allow the layers to separate completely, discard the aqueous layer, and drain the organic layer into a clean, dry spectrophotometer cell through a small piece of cotton placed in the tip of the stem of the separatory funnel. Determine the transmittance a t 386 mp using the combination of :t blue-sensitive phototube and a Beckman No. 12216 filter. Distilled water is used in the reference cell. PROCEDURE
Weigh a sample of tungsten powder containing preferably 10 to 50 y of nickel into a 100-ml. beaker. Carry through a reagent blank, following the same procedure and using the same amount of reagents used for treatment of the sample. Read reagent blank against the reference cell containing 1% ater and subtract from the mirrograms of nickel found in the sample or aliquot portion. Wash down the sides of the beaker with a few milliliters of distilled water, and add 5 ml. of 30% hydrogen peroxide; cover with a watch glass and allow to stand until the vigorous reaction has subsided. With distilled water wash doivn the sides of the beaker and the watch glass, and place on a hot plate until the solution begins to boil or until the metal powder has completely dissolved. Cool to room temperature, and add 10 ml. of ammonium citrate solution (dimethvlglvoxime, purified). If the nickel content is too high for direct treatment, dissolve an appropriately sized sample in 10 ml. of hydrogen peroxide, dilute to
1201
50 ml. and take an aliquot portion, and continue by adding 10 ml. of ammonium &rate solution. Dilute t o approximately 40 ml. with distilled water; add solid hydroxylamine hydrochloride until the solution is definitely acidic, and finally add a small excess. A large excess of hydroxylamine hydrochloride will neither interfere nor contribute to the blank, the excess only increasing the amount of ammonium hydroxide needed for subsequent neutralization. (Only one lot of hydroxylamine hydrochloride was used in this work; however, another lot supplied by a different, nianufacturer showed a different odor, smaller crystal size, lower acidity, and lower reducing power. Later work made use of this less acid reagent and made it necessary to add hydroxylamine hydrochloride before adding the citrate buffer to effect complete reduction, rather than after the buffer. The change in order of adding these two reagents produced the same effective reduction and desired results as those experienced with the more acid hydrosylamine hydrochloride.) Using a p H meter adjust the acidity of the solution to pH 8.5 by adding ammonium hydroxide. Cool the solution to room temperature, transfer to a 125-nil. separatory funnel, and add 5 ml. of dimethylglyoxime reagent, Upon adding this reagent carefully note whether the colorless solution changes to an orangered color; if a definite coloring of the solution is not,ed, oxidation has taken place. I n any case continue by adding 10 ml. of chloroform, stopper, and shake vigorously for 1 minute. Allow the layers to separate, and drain the chloroform layer into a second 50) animo125-ml. separatory funnel containing 25 ml. of (1 nium hydroxide. Add 5 ml. of chloroform and repeat the extraction, draining this into the second funnel. If the aqueous layer is noly colored, or coloration has been previously noted, indicating oxidat,ion has taken place, drain the layer into the original beaker. To this aqueous solution, add an excess of hydroxylamine hydrochloride, adjust to p H 8.5 with ammonium hydroside, transfer back into the first separatory funnel, and extract with an additional 5-ml. portion of chloroform. Combine this extract with the previous extracts; this last extraction is not necessary if there is no evidence of coloration. Shake the combined extracts for 1 minute and allow the layers to separate prior to draining the chloroform layer into a small, dry beaker. Add a few milliliters of chloroform to the remaining dilute ammonium hydroside, shake, allow the layers to separate, and drain the chloroform layer into the previous chloroform extract. Discard the aqueous layer, washing out the separatory funnel with distilled n-ater. Transfer the chloroform extracts in the beaker back into the separatory funnel, carefully rinsing out the beaker with n few milliliters of chloroform which is added to the separatory funnel. -4dd 25 ml. of 0.51%' hydrochloric acid, shake vigorously for 1 minute, allow the layers to separate completely, and discard the organic layer. Add a few milliliters of carbon tetrachloride, shake for a moment, and drain off the organic layer as completely as possible. The remaining aqueous layer is treated as in the preparation of the calibration curve beginning with the addition of the citrate buffer solution.
+
DISCUSSION OF METHOD
Dissolution of tungsten powder n ith hydrogen peroxide seems to be the most effective and rapid method available but previous reports seem to indicate its presence would prevent the complete precipitation of nickel dimethylglyoxime and cause the formation of a soluble, orange-red complex which Lyould subsequently be insoluble in the chloroform extract. If the reported interference of hydrogen peroxide could be eliminated, after separation ait,h dimethylglyosime and chloroform, the nickel could be converted to the diethyldithiocarbamate comples and estracted with isoamyl alcohol. The literature shows that metals giving colored precipitates with diethyldithiocarbamate, soluble in organic solvents, are nickel, copper, bismuth, and iron ( 4 ) . The use of ammoniacal citrate solutions prevent,s the reaction with iron, and the nickel is separated completel- from other potential interfering elements, such as cobalt and bismuth, by t'he dimethylglyosime estraction (1). High concentrations of copper are partially extracted with the dimethylglyoxime, but may easily be removed by an intermediate wash with dilute ammonium hydroxide. 3Iaximum absorbance for the nickel diethyldithiocarbamate conlplex occurs a t 385 nip a t the very edge of the visible spectrum. The calibration rurve, Figure 1, very nearly approaches a straight line. This slight curvature is said to be due to the failure of the optical systems of certain spectrophotometers to produce light beams that are spec-
1202
ANALYTICAL CHEMISTRY
trally pure rather than failure of the measured color to obey Beer's law ( 1 ) . The experiments below showed nickel could be satisfactorily extracted as the bivalent nickel complex of dimethylglyoxime with chloroform in the presence of as much as 5 ml. of 80% hydrogen peroxide. Standard solutions of nickel, to which 5 ml. of 30% hydrogen peroxide was added, were treated as unknowns and carried through the entire procedure. Satisfactory recoveries were obtained as evidenced in Table I with an average deviation of nickel recovered from the nickel added of 0.4 r; there was never any evidence of oxidation, indicated by a colored, aqueous layer during the dimethylglyoxime separation, when standard nickel solutions were put through the procedure. If partial precipitation of nickel dimethylglyoxime in the presence of hydrogen peroxide is due t o the formation of quadrivalent nickel, the ammonium citrate, which is present during the determination to keep iron in solution, may act as a reducing agent and counteract the effect of the hydrogen peroxide (8). However, in the presence of a tungst,en pori-der, designated here as sample A, and hydrogen peroxide, incomplete recovery of known amounts of nickel is evidenced in Table 11. Sandell ( 6 ) has said manganese in the oxidized state has a tendency to oxidize the nickel present, making the addition of hydroxylamine hydrochloride necessary t o reduce any manganese present. Such may be the case in the presence of tungsten, one possible explanation being that dissolution of tungsten powder forms soluble peroxytungstic acid, which may in t'urn ouidize the nickel. T'o counteract this effect solid hydroxylamine hydrochloride kyas zdded until the solution was definitely acid. When treated in the prescribed manner satisfactory results were obtained. The effect of hydroxylamine hydrochloride on a tungsten powder A and on mEtal powder A to which known amounts of nickel were added, in Table 111, can be compared to values in Table I1 using the same sample of metal povider but n-it,h no hydroxylamine hydrochloride added. The average deviation of nickel recovered from the nickel present is 1 y. ' T o test the procedure further, tungsten poxder samples of high nickel content, samples B, C, D, and E, were analyzed, n-ith results as shown in Table IT. These samples were dissolved in 10 nil. of 30% hydrogen peroxide, diluted to 50 ml. with distilled water, and appropriately sized aliquots \$-eretreated as befow.
Tahle I.
Effect of Hydrogen Peroxide on Standard Nickel Solutions
Detn.
Added 24.9 24.9 24.9
0.500
Sample
B
hlicrograms of Sickel Added Recovered 3.6 Sone 28.0 24.9 1 0.5 10 0 1.5 None
Analysis of Tungsten Powders of High Nickel Content Gram Sample 0,4499 0,4499
Aliquot Portion 0.2 0.1 0.2 0.1 0.2 0.1 0.1 0.2 0.1 0.2 0.1 0.2 0.1
C
D
0.3188 0.3188 0.4119 0.4119
E
Table V. Gram of Sample A 0.3032 0.3037 0.3041 0.3132
Yo Ni 0,0155 0.0162
AY. 0,0159 0,0536
0.0416 0.0417 0.0159 0.0178
0.0417 0.0169
Blends of High and Low Nickel Content Samples Gram High Nickel Content Samples 0.1032 (B) 0.2164 ( C ) 0 . l l R 5 (D) 0.1473 (E)
Aliquot Portion Total 0.2 0.2 Total
Total Ni Present Recovered 21.6 20.8 24.1 23.5 10.8 12.0 30.2 29.8 Av. dev.
Der. -0.8 -0.6
+1.2 -0.4 0.8
I n Table V are shown the results of blending metal powders with high and low nickel content. The total nickel recovered in each case is compared to the total nickel present calculated from the average percentages of high and IOK nickel content samples from Tables 111 and IV. The average deviation of nickel recovered from the nickel present is 0.8 y . A reagent blank was run along n-ith each set of determinations, the average blank being approximatelj- 5 y of nickel. Distilled water was used the majority of the time, since distilled l\-ater passed through a demineralizer column did not appreciably reduce the reagent blank. SCMM\IARY
hlicrogram amounts of nickel may be determined in tungsten powder with satisfactory precision and accuracy by a preliminary separation of nickel with dimethylglyoxime and the subsequent spectrophotometric measurement of the developed diethyldithiocarbamate complex. However, the addition of hydroxylamine hydrochloride is necessary in the presence of hydrogen peroxide and tungsten to effect complete recovery of nickel. One explan-
RIicrograms of Nickel Recovered Deviation 25 3 4-O.G 24 5 -0.4 -0.3 24 6 Ar. der. 0 4
Table 11. Effect of Hydrogen Peroxide in Presence of Tungsten Tungsten Powder A Taken, G. 1 00 1.00 1 00
Table IV.
100
90
eo
E
70
2 k 52
60
E
50
2
a c
z
W
Table 111. Effect of Hydroxj-lamine Hydrochloride in Presence of Hydrogen Peroxide and Tungsten Tungsten Powder A Taken, G. 1.00 1 .00
Added None 24.9
0.7013 0.7079 0,5026
10.0 24.9 24.9
llicrograms of Nickel Total Total recovpresent ered ne\-. 17.5 .. .. 41.
I. J ~ N E S DALL , n. L(LnL.n, ana L n r n i N C E M. WHITE
.....
Western Utilization Research Branch, Agricultural Research Service, United Stater Department of Agriculture,
HE preparation of o-fructose 2,4-dinitrophenylhydazone T pyridine . . solvate (ClrHteNIOp.CsHiN)has been described by White and Secor ( 1 ) . Some of their yellow crystalline preparations were used in this study. It was necessary to use fresh material when determining refrmtive indices by immersion in order to avoid trouble from a thin film of decomposed material which developed on the crystals after aging. Old crystals could be used if they were broken to expose fresh surfaces at.the time of immersion. A crystal mounted on a goniometer head was used for x-ray measurements, optical goniometry, and microscopical observations. The faces of the crystals were always striated, usually giving poor and multiple signals on the optical goniometer. Twinning also caused trouble, but the average of severd seta of measurements an severd crystals was used for the values given here (Figure 1). T h e angles cslculated from x-ray data agree i.%l"eS.
elongittion is pesdlel to b. The blade8 usually lie on I1001i and s,how an obtuse end angle. Except for {loo) the form:? s h o w1 in Figure 2 are inconspicuous on most crystals. Loost> n o d l o . S V P ~ o m m o n Tha sheaf1ibln ~Instnmnf .._.____I -..-nnt,i?nl - ..--.n.rt,ivit,x -. .... ., of this compound ( 1 ) requires the ahmnee of a plane of symmetry but as ordinarily developed (Figure 2) they appear to have one. - Interfacial Angles. 100 A 403 = 1 2 j 0 (120" 12' x-ray), 403 A 101 = 126"(126" 13'x-ray), 1OOA 101 = 114°(1139 35' x-ray). Twinning. End views of mounted crystals usually show from two to several lamellae, which appear parallel t o (100); how-ever, x-ray evidence shows t h a t the twins share the a and b axe8 rather than c and b and t h a t the twinning plane is perpendicular t,o a. The striations or steps on (100) prevent certsin recognition of the h e.e n t,he twin line and small angle (1" IS') t h a t should exist b e. (100). X-RAYDIFFRACTION DATA Space Group. C; - P2, (only 6rst 6 0:rders of b axis observed). Cell Dimensions. a = 20.133 A,, b = 5.746 A,, c = 8.i88 A. .LxialRatio. a : b : e = 3.504:1:1.529. "..l Beta Angle = 91" 15'. T h e choice oL diffraction pattern (Weissenberg). Thefe is no crystal face containing axis a, although it is perpendicular to the twinning
...-
".
.-
yyyly
.. b--' Figure 1. O r t h o g r a p h i c projection of &fructose 2 4 d i n i t r o p h e n y l h y d r a z o n e pyridine solvate
pyridine Solvate lOOX
-..
