Colorimetric Determination of Nickel with AlphaFurildioxime A . K. GAHLER AND -4.M.MITCHELL' WITH &I. G. MELLON Purdue University, Lufayette, Znd. The work was undertaken to study the conditions under which nickel may be determined colorimetrically by means of a-furildioxime, especially as compared with dimethylglyoxime or 1,2-cyclohexanedionedioxime. The nickel-cu-furildioxime complex is a usable form for determining nickel, following extraction of the colored complex with 1,2-dichlorobenzene. This extractability facilitates separation of the metal from colored interfering solutions, such as iron or chromate salts. The pH of the solution must be regulated, but otherwise the system has satisfactory colorimetric properties. The general result is a method having some advantage over the earlier dioxime processes. Its applicability was shown by the determination of nickel in a magnesium alloy and in National Bureau of Standards steel So. 13c.
N
EARLY a decade ago ( 4 ) di(2-fury1)ethanedionedioxime(afurildioxime) was recommended for the colorimetric determination of nickel in magnesium alloys. Subsequently, the procedure was adopted by the American Society for Testing hlaterials ( 8 ) . Previously this compound had been investigated for use aa a reagent for spot testa (S) and as a precipitant for the gravimetric determination of nickel (7, IO). A critical study of the colorimetric method was started by Mitchell (6) following the observation of certain anomalies in the extraction operation. The method involves the extraction of the stable nickel(I1) complex with an immiscible organic solvent. The nickel is thus conveniently separated from many constituents in the sample, accompanied by the simultaneous formation of a yellow color suitable for colorimetric measurement. APPARATUS AND REAGENTS
Transmittancy measurements were made in 1.000-cm. cells with either a General Electric recording spectrophotometer set a t a spectral band width of 10 mr, or with a Beckman D.U. spectrophotometer operating close to 1 mp band width. The stock solution of nickel sulfate was prepared by suitable dilution of a solution analyzed electrolytically for nickel. The a-furildioxime, prepared by the method of Reed, Banks, and Diehl (8),had a melting point of 171-171.5' C. Solutions of the reagent were prepared in 95% ethyl alcohol Redistilled technical (95%, Eastman) lJ-dichlorobenzene was used in the extractions. Before use, the organic solvent was shaken with a solution of sodium acetate to remove traces of acidic substances that might be present. Solutions of chlorides, nitrates, or sulfates were used in the study of the effect of cations upon the extraction process and the color development. Alkali salts were used to study the effect of various anions. Separatory funnels (125-ml. Squibb type) were most convenient for the extractions. All p H measurements were made with a Beckman Model M pH meter.
acetate extract the complex from an aqueous solution. Carbon tetrachloride, n-amyl alcohol, nitromethane, nitropropane, tributylamine, and trichloroethylene do not extract the complex. The complex in the presence of ammonium hypobromite appears to be stable only in isopropyl alcohol and pyridine solutions. Oxidation in an alkaline potassium persulfate solution caused a hue to develop similar to that of the dimethylglyolrime complex, but the color faded rapidly. 1,2-Dichlorobenzene w m considered to be the best solvent tested because of its low volatility, nonflammable nature, immikcibility with water, and density (greater than that of water and of adequate difference for rapid separation of the layers). Extractions with this solvent required the presence of a small amount of ethyl alcohol to prevent turbidity in the organic phase. The nickel(I1) complex is unique for its color because nickel dimethylglyoxime and nickel 1,2-cyclohexanedionedioximeform almost colorless solutions in chloroform or 1,2-dichlorobenrene. Nickel(11)1,2-cycloheptanedionedioximeis similar to the a-furildioxime complex in that it is very soluble in chloroform, but it is not as highly colored. One milligram of nickel a-furildioxime can be readily extracted with 1,2-dichlorobenzene or chloroform, whereas the dimethylglyoxime ( 5 )and 1,2-cyclohexanedionedioxh e complexes are not appreciably soluble in these solvents. The extractability of these other complexes will be discussed in another paper. Effect of pH. The pH range for optimum color development occurs from p H 7.5 to 8.3. Below or above this range extraction is slow and incomplete. This narrow range necessitates the use of a buffer. Because the 1,2-dichlorobenzene was found to contain acidic constituents, the solvent is washed with a slightly basic solution prior to use. The effect of pH upon the extraction of nickel a-furildioxime is shown in Table I.
COLOR REACTION
Table I. Effect of pH upon Extraction of Nicltel(I1) a-Furildioxime with 1,2-Dichlorobenzene
Effect of Solvent. Kickel(I1) forms a complex with afurildioxime which is insoluble in water and many water-organic solvent combinations. In a slightly alkaline aqueous solution a yellow hue develops which rapidly fades as the complex precipitates. The solubility and stability of both the nickel(I1j and the oxidized nickel complexes were tested in various solveds. The following solvents with water (1 to 1) did not form suitable colored systems for nickel(I1) a-furildioxime: acetone, dioxane, ethyl alcohol, ethyl Carbitol, ethyl Cellosolve, isopropyl alcohol, methanol, and methyl Carbitol. Pyridine fornu a yellow solution. Chloroform, 1,2-dichlorobenzene, diethyl ether, and ethyl 1
PH
(0.1 mg. of nickel) Recovery, %
6.5
7.0 7.5 7.7 8.1 8.3 8.5 9 1
9.5
Volumes. Aqueous phase, 25 ml.; successive extractions, 5.
Present address, Har\ard University, Cambridge, Mas3
500
72 99 100 100 100
100 99 78 23
organic solvent, 5 ml.
Number of
V O L U M E 23, NO. 3, M A R C H 1951
501
25" to 35" C. The transmittancy of a solution maintained a t 100' C. in a water bath for 1hour remained constant. EXTRACTION PROCESS
Volume of Aqueous Phase. Satisfactory extractions are obtained when the volume of 1,2-dichlorobenzene is 5 ml. and the aqueous solution is between 20 and 75 ml. When the volume ot the aqueous phase is greater than 75 ml., the extraction process is less efficient. An increase in the volume of the organic solvent to 10 ml. does not increase the extraction efficiency, as shown in Table 111. The data were obtained by extracting successively five times 17-ith the volume of solvent indicated.
Table 111.
Effect of Volume of Aqueous Phase upon Extraction Efficiency
Volume of Aqueous Phase
CONCENTRATION
I
2
3
4
5 400
450
500
550
WAVELENGTH,
Extraction Efficiency 10 ml. of 1,2dichlorobenzene
5 ml. of 1,Z-di-
chlorobenzene
M1.
%
%
20 80 80 100 150
100 100 96 98
100 100 98 96 63
,.
NI p p m Ni mg/romi 0.2 0.0 I O 0.5 1.0 2.0
3.0 600
0.025
0.050 0. I O 0 0.15 0 650 7(
mr
Effect of Ammonia and Ammonium Ion Concentration. Ammonia affects the extractability of the nickel(I1) complex in much the same way 119 it does the precipitation of nickel. High concentrations of ammonia prevent color formation and extraction of the nickel. However, small concentrations of ammonium ion added &s ammonium chloride up to 0.225 gram do not interfere with the extraction. Data in Table I1 show the effect of various concentrations of ammonium ion upon the color development and extraction process. Although a small amount of ammonia may be used to adjust the p H of the aqueous solution, it is recommended that sodium acetate or dilute sodium hydroxide be wed instead.
Table 11. Effect of Ammonium Ion upon Extraction of Nickel(I1) a-Furildioxime with 1,2-Dichlorobenzene (0.1 mg. of nickel) Ammonium Ion, G. Recovery, % 1.124 0.562 0.450 79 92 0.337 99 0.280 0.225 100 0.168 100 0.112 100 100 0,010
::
Volumes. Aqueous phase, 25 ml.; organic solvent, 5 ml. asssive extractions, 5 .
Number of suc-
Effect of Nickel Concentration. With a 1,000-em. cell the transmittancy varies from 87.77, (0.2 p.p.m.) to 13.0% (3.0 p.p.m.) and the system conforms to Beer's law. The wave length of maximum absorption for the yellow solution occurs a t 438 mM (see Figure 1). The reference cell contained 1,2-dichlorobenzene, but water may be used. Stability of the Hue. The transmittancy does not change over a period of I4 days in diffuse light at a temperature from
Number of Extractions. From two to three successive extractions with 5-ml. portions of 1,2-dichlorobenzene are sufficient to remove the nickel complex from the aqueous solution Complete removal is readily detected by the absence of color in the organic solvent. Reagent Concentration. A volume of 3.5 ml. of a 0 . 1 7 ethanolic solution of a-furildioxime is required t o extract 0 1 mg. of nickel. As much as 15 ml. of reagent gave no adverw effect. Order of Addition of Reagents. Addition of the reagent before the organic solvent did not impair the efficiency of the extraction, even if a slight precipitate of nickel a-furildioxime formed in the aqueous phase. However, less shaking is necessary if the mixture is shaken before the precipitate is allowed t o form. Effect of Electrolytes upon Extraction. The effect of the presence of various electrolytes at different concentrations upon the extraction w119 studied. No deleterious effect is experienced when extractions are carried out from solutions 0.05 to 2.5 M with respect to sodium acetate. Chloride ion up to 3.6 M does not affect the extraction. In these extractions 2 ml. of 3 M sodium acetate were added to make the solution p H 7.6 to 7.8. Nitrate below 2.0 M and sulfate below 0.63 M with 5 ml. of 3 Af sodium acetate present (total volume of aqueous phase = 32 ml.) allow satisfactory results, but higher concentrations of both ions cause "salting-in" effects-Le., the complex is not extracted conipletely. ilddition of 5 ml. more of 3.0 AI' sodium acetate, or a total of 10 m]., eliminated the salting-in effect. Extractions from almost saturated solutions of electrolytes are more difficult to carry out than with dilute solutions because the small difference in density between the aqueous and 1,2-dichlorobenzene layers causes the phase to separate more slowly. Dilution with water decreases the density of the aqueous phase, so that the phases separate more quickly. If it is not feasible to increase the volume of the aqueous phase one may use chloroform, which has a higher density than 1,2-dichlorobenzene. Effect of Diverse Ions. In the study of the effect of diverse ions upon the color development and extraction process, 25 mg of diverse ion were tested n-ith 0.1 mg. of nickel(I1). I n all cases 5 nil. of 3 Jf sodium acetate (except in the test for acetate ion) and sufficient dilute hydrochloric acid or sodium hydroxide were added to adjust the solution to a pH of approximately 8.1. The pH was conveniently adjusted visually by addition of 2 drops of 0.5% ethanolic solution of phenolphthalein and then acid or base until the color due to the indicator was just perceptible.
ANALYTICAL CHEMISTRY
502 The pH of colored solutions was adjusted by means of a pH meter. If 25 mg. of diverse ion did not interfere, it was assumed that the ion would not interfere under the usual conditions of determination, although this may not hold true if certain combinations of ions should be present. The following ion3 do not interfere with the extraction of nickel a-furildioxime in concentrations as high as 25 mg. with 0.1 mg. of nickel(I1) present in the aqueous phase of approximately 25 ml.: acetate, arsenate, arsenite, barium, benzoate, bromide, cadmium, calcium, chloride, chlorate, dichromate, fluoride, formate, hydrogen sulfite, iodate, iodide, lactate, lithium, magnesium, molybdate, nitrate, nitrite, oxalate, orthoborate, orthophosphate, persulfate, potassium, pyroborate, salicylate, selenate, sodium, strontium, sulfate, sulfite, tartrate, thiocyanate, thiosulfate, tungstate, and vanadate. Lead and uranyl ions form a very slight precipitate that does not interfere with the extraction. The following ions, unless complexed, precipitate a t the pH of the extraction: aluminum, antimony, beryllium, bismuth, cerium, chlorostannate, chlorostannite, chromium(III), cobalt, copper, iron( 11),iron( 111),manganese( II), mercury, thorium, titanium, zinc, and zirconium. Permanganate interferes by reacting with the reagents. Gold, silver, platinum, and palladium form yellow solutions with the reagent. Perchlorate, pyrophosphate, cyanide, periodate, sulfide, and citrate prevent extraction of nickel. Silicate, in concentrations greater than 100 mg., slowly reacts with the ethyl alcohol to form a precipitate which interferes with the extraction. The extent of the error caused by the more important interferences is summarized in Table IV.
Table IV. Ion
Added
&s
Citrate
CN -
NaaCaHsOi KCN
CI04-
KClOi
Effect of Diverse Ions Amount
Errora
MQ.
%
1.0 1.0 0.2 25 10
-3 N o color formed -31
- 35
0 K104 1.0 N o color formed hlnO4KMn04 , .. Reacts with reagent -5 poi---- NarPlOi 0 XanS 0.1 - 50 *-;++ AuClr 1.0 +3 PdCh 0.05 +4 1.0 +5 Pt HxPtCI6 AgNOs 5.0 +3 Ag a Error in determination of 0.1 mg. of nickel.
104-
{
%++++ +
Amount Permissible MQ.
