ANALYTICAL CHEMISTRY
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Infrared Spectra of Propellant Ingredients
Glycerol triacetate (triacetin), E. K. white label, 5 % solution
Office of Scientific Research and Development (OSRD), KO. 1837, “Chromatographic Investigations of Smokeless Powders and Related Substances,” No. I. ( t 6 ) Ovenston, T. C., A n a l u s t , 74,344-51 (1949). (17) Philpotts, A. R . , Thain, W., and Smith, P. G., Ax.41..CHEM., 23, (15)
(21)
Pristera, F., Perkin-Elmer Instrument ,Vews, 2 , KO. 2 (Winter 1951).
(22) Schroeder, W. .I.,Keilin, B., and Lemmon, R. M . , Ind. Eng. Chem., 4 3 , 9 3 9 - 4 6 , (1951). ( 2 3 ) Schroeder, W. A , , Malmberg, E. W., Fong, L. L., Trueblood,
K. N., Landerl, J. D., and Hoerger, E., Ibid.; 41, 2818-27
268-72 (1951). (18) Picatinny Arsenal Tentative Specification, PXS-1197 (available through Office of Chief of Ordnance, Washington 25, D. C.). ( % l Y )l b i d . PXS-1250 (Revision 1 ) . (20) Pristera, F., A p p l . Spectroscopy, 6, No. 3 , 2 9 - 4 4 (1952).
1949).
(24) Torkington, P., and Thompson, H. W,, Trans. Faradall Soc., 41, 184-6 (1945). IIPCEIYED June 5 , 1952.
Accepted January 7, 1953.
Extraction of Metal Thiocyanate Complexes with Butyl Phosphate Iron Thiocynate LABEN MELNICKl
AND
HENRY FREISER
C’niversity of Pittsburgh, Pittsburgh 13, Pa.
H. F. BEEGHLY Jones & Laughlin Steel Corp., Pittsburgh 7, Pa.
P
REVIOUS work by Aven and Freiser ( 1 )indicated that butyl phosphate is a useful solvent for the extraction of iron(II1)
thioryanate. This is important in steel analysis, since iron interferes Kith the determination of various elements in steel and must be removed. Aven and Freiser found that with butyl phosphate, a commercially available, nonvolatile, nonflammable solvent, rapid extractions may be made without the inherent difficulties of the Rothe ether method. The time required per extraction and the cost of the method are both less where butyl phosphate is used instead of ether. Butyl phosphate may be readily recovered. Also, butyl phosphate is better for extracting iron(II1) thiocyanate than ether ( 3 ) . Precision obtained by 1
Present address, Jones & Laughlin Steel Corp , Pittsburgh 7, P a .
use of t h e two methods is comparable. This paper is a report on a more detailed study of various conditions affecting extraction of iron( 111)thiocyanate with butyl phosphate. REAGENTS AND APPARATUS
Unless otherwise stated, all reagents are C.P. or reagent grade. .411 pH measurements were made with a Beckman p H meter. Sodium thiocyanate. Stock solutions were standardized with silver nitrate. Ammonium hydroxide, filtered. 30% Hydrogen peroxide. Sodium hvdroxide. Sitric accd. Tributyl phosphate obtained from Commercial Solvents Corp. This was used without further Durification. Stock iron solutions prepared with Kational Bureau of Stand-
V O L U M E 2 5 , N O . 6, J U N E 1 9 5 3
857
The previously observed extractability of iron(II1) thiocyanate by n-butyl phosphate has been subjected to a thorough study to determine the relevant factors governing the extraction. The effects of temperature, pH, concentration of iron, and ratio of thiocyanate to iron were investigated, and the possibility of using carbon tetrachloride solutions of n-butyl phosphate rather than the ester itself was studied. I t was found that a suitable butyl phosphate-carbon tetrachloride mixture could be used which, in addition to extracting the iron quantitatively, was heavier than the aqueous phase, thus permitting greater convenience in extraction.
ards sample 5% (open hearth iron). \Veighed amounts of iron were dissolved in dilute nitric acid. The solutions were filtered and the filtrate was diluted with distilled water so that the pH was in the region of 1.0 to 2.0. The solutions were standardized gravimetrically by precipitating iron with ammonia and weighing as ferric oxide. Calibrated veights and buret. EXPERIMEhT4L PROCEDURE
The extraction of iron(II1) thiocyanate from aqueous solution is affected by various factors: thiocyanate to iron ratio, volume of butyl phosphate, acid concentration, and temperature. I n order to find the most favorable thiocyanate to iron ratio, sodium thiocyanate was added in varying amounts to 25-ml. aliquots of an 0.01627 M iron solution so that the ratio of thiocyanate to iron ranged from 0.5 to 1 to 10 to 1 on both a mole and weight ratio basis. (All thiocyanate to iron ratios are on a weight basis unless otherwise noted). For any particular value of thiocyanate to iron, the weight and mole ratios are approximately equal (see Figure 1). The solutions were adjusted to a volume of 60 ml. The pH values of the aliquots a t this point were 1.50 =t0.02. The solutions were then added in turn to a separatory funnel containing 25 ml. of butyl phosphate. The temperature of the aqueous phase was measured before and after shaking the mixture for 30 seconds. The phases were allowed to separate, and the aqueous layer, which was the denser of the two, was drawn off. Since the raffinate was sometimes contaminated with droplets of butyl phosphate containing the red iron(II1) thiocyanate, the aqueous layer was withdrawn from the separatory funnel directly into a funnel containing two thicknesses of filter paper which retained the butyl phosphate. Baker and Adamson Grade A paper was found to be most satisfactory for this purpose. The pH of the raffinate was measured, and then the filter paper was washed three times with dilute nitric acid of pH 1.52. Ten milliliters of concentrated nitric acid were added to the raffinate and the solution was boiled to destroy the remaining thiocyanate. After addition of excess ammonia to the solution, iron was determined gravimetrically; and the per cent of iron extracted was calculated. To determine the optimum volume of butyl phosphate needed, a series of extractions was carried out in which the volume of butyl phosphate was varied from 5 m]. to 35 m]. in 5-ml. increments. The pH values of the aliquots of 0.01014 M iron solution were 1.96 0.02, and the thiocyanate to iron ratio was 2.5 to 1. This ratio was chosen so that the amount of iron eytracted would be
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y - MRO ATIOLE Figure 1.
Extraction of Iron as a Function of ThiocJanate to Iron Ratio
less than loo%,, thus permitting a better study of the effect of varying volumes of butyl phosphate. Tv,~enty-five-milliliter aliquots of the iron solution were taken, and the iron(TI1) thiorym a t e was extracted as described above. Previous work by Aven and Freiser ( 1 ) showed that increaeing the acidity reduced the amount of iron that could be removed with a single extraction. I n order to find a quantitative relationship between pH and per cent of iron extracted, samples were run in the pH range 0.25 to 1.98. Two-milliliter aliquots of 0.4068 JI iron with pH values of 0.91 were diluted to 50 ml., and the pH values were adjusted downward by the dropwise addition of nitric acid. The final volumes were all between 50 and 52 ml. The thiocyanate to iron ratio was maintained constant a t 3 to 1. Extractions were made Kith 25 ml. of butyl phosphate, and the iron remaining in aqueous solution was again determind gravimetricallv.
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Figure 2. Comparison of Actual and Theoretical Amounts of Iron Extracted with Varying Ratio of Thiocyanate to Iron
The effect of iron concentration on the per cent of iron extracted was studied next. Two standard iron solutions differing in iron concentration by a factor of 10 were used (0.4068 and 0.04068 rM iron). Thiocyanate was added to aliquots of these solutions so that the thiocyanate to iron ratios for each group were 1, 3, 5, and 10. The volumes of the samples were then adjusted to 40 ml. All pH values were adjusted to 1.46 + 0.02 units by dropwise addition of dilute nitric acid. The sample solutions were washed, in turn, with a solution of hydrochloric acid of pH 1.35, into a separatory funnel containing 25 ml. of butyl phosphate. The temperature of the aqueous phase, before and after mixing, was measured. The per cent of iron extracted was determined as before. T o determine the effect of temperature on the per cent of iron extracted, two series of three samples each were run a t three different temperatures. Thege temperatures were approximately 13", 29", and 50" C. The thiocyanate to iron ratios for the two sets of samples were 3 to 1 and 4 to 1, respectively. Temperatures were measured immediately after mixing the organic and aqueous phases. Iron was again determined gravimetrically. Since the iron could not be quantitatively removed by a single extraction, the specific gravity of the organic layer was increased so that it would be heavier than the aqueous portion and could be withdrawn, leaving the aqueous phase in the separatory funnel. Thus, repeated extractions could be made without removing the raffinate until all or almost all of the iron had been extracted
858
ANALYTICAL CHEMISTRY
Because of its rather high density and miscibility with butyl phosphate, carbon tetrachloride was chosen as the diluent. A series of extractions was carried out with SCN/Fe = 5, the volume of butyl phosphate being maintained constant a t 20 ml., while the volume of carbon tetrachloride was varied in 5-ml. increments from 0 to 20 ml. After extraction the iron remaining in the raffinate was again determined gravimetrically.
Table I.
Effect of Butyl Phosphate Concentration on Extraction of Iron
Sample5
(C4He)sPOd Volume, M1.
cch Volume, MI. 0 5
10 15
20 a Samples are 0.01057 M i r o n , pH = 2.13, S C S / F e = 5 . separation = 24.5O i 0 . 5 O C .
Fe E x p c t e d , /o
97 28 96,60 95.24 94,63 95.24 Temperature a t
trated ammonia. The butyl phosphate is then shaken with several portions of water. In the extraction of iron( 111) thiocyanate from aqueous solution, the temperature, after mixing the phases, was about 1" higher than before mixing. The aqueous and organic phases need be mixed for only 30 seconds in order to establish equilibrium. Samples mixed for 3 minutes with butyl phosphate showed no improvement in separation. Also, 25 ml. of butyl phosphate were sufficient to obtain good extractions for the samples and conditions involved in this work (see Figure 3). There were no discernible volume changes of the phases upon equilibration. Acid concentration had a marked effect on iron extraction. Figure 4 shows that as the pH increases, the per cent of iron extracted also increases. KO conclusion has yet been reached as to
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Extraction of Iron as a Function of Butyl Phosphate Volume
Figure 3.
I n an effort to confine the extraction procedure to a minimum number of operations, iron was extracted with a mixture of 25 ml. of butyl phosphate and 30 ml. of carbon tetrachloride from a 5ml. aliquot of 0.4068 M iron diluted to 25 ml. The p H of the solution was 1.62. After removing about 90 to 95% of the iron, 10 ml. of 9% hydrogen peroxide were added to the aqueous solution remaining in the separatory funnel. The solution was shaken for a few seconds and allowed to stand for 1 or 2 minutes until the thiocyanate color disappeared. Ten milliliters of a concentrated sodium hydroxide solution were added, and the mixture was shaken, drawn off, and filtered. The filtrate was boiled for a few minutes to digest any colloidal hydrous iron oxide, and then it was filtered, washed, and ignited. RESULTS AND DISCUSSION
The smallest thiocyanate to iron ratio to give highest extraction is between 4 and 5 to 1 (see Figure 1). This ratio, unlike the amount of iron extracted, is independent of temperature or pH. Assuming that the iron compound extracted is [Fe(SCN)r]x, the theoretical optimum thiocyanate to iron ratio should be 3 to 1 on a mole basis or 3.12 to 1 on a weight basis. -4s can be seen from Figure 2, the actual amount extracted is fairly close to that theoretically possible if the only reaction that occurred between iron and thiocyanate were .^ Fef++
+ 3SCN- +Fe(SCS)a
and further, if this complex were quantitatively extracted by butyl phosphate. This emphasizes the strong solvent action of butyl phosphate. Duplicate determinations of extracted iron a t thiocyanate to iron ratios of 1, 3, and 5 agreed to within 0.44% or better. It should be pointed out that this extraction technique might also be applicable to the colorimetric determination of small amounts of thiocyanate, since having iron in excess results in essentially quantitative extraction of thiocyanate. Butyl phosphate recovery after extraction was found to be readily accomplished by stripping most of the iron(II1) thiocyanate from the solvent by shaking with 1 to 1 sulfuric acid. The small amount of iron remaining may be removed by shaking with concen-
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Figure 4.
Effect of pH on Extraction of Iron
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RATIO
Effect of Iron Concentration on Extraction of Iron
V O L U M E 25, NO. 6, J U N E 1 9 5 3
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T EM P E R A T U R E OCFigure 6 . Extraction of Iron as a Function of Temperature why this occum This pH dependence might be expected if thiocyanic acid were a weak acid. Then increasing the pH would result in higher SCN- concentrations and hence better extractions. However, thiocyanic acid has been shown to be as strong RS perchloric acid (8). Iron concentration had little or no effect on extraction. It was found (see Figure 5 ) with the two solutions, differing in iron concentration by a factor of 10, that the respective pairs of values of per cent of iron estracted a t thiocyanate to iron ratios of 3) 5,
and 10 were approxiniately the same. However, a t a ratio of 1 to 1 about 6% more iron was extracted from the more concentrated solution. Increased solution temperature resulted in decreased eutraction. Figure 6 indicates that between 13" and 50' C. the per cent of iron extracted is independent of the thiocyanate to iron ratio. the rate of change of iron extracted with temperature being -0.3y0 per 1' C. for both the 3 to 1 and 4 to 1 thiocyanate to iron ratios. The temperature dependence of extraction of iron is most probably due to solubility effects, the distribution of the iron(111) thiocyanate probably favoring the aqueous phase a t higher temperature. The use of mixtures of carbon tetrachloride and butyl phosphate resulted in about 95% removal of iron with a single extraction (see Table I), Best separations were obtained with the volume of carbon tetrachloride equal to or greater than that of butyl phosphate, the specific gravity of the organic layer then being high enough so that there was a clear-cut meniscus between the aqueous and organic phases. With the combined extractionprecipitation procedure, an average of two determinations showed 99.38% of the iron to have been removed. LITERATURE CITED
(1) Aven, M., and Freiser, H., Anal. Chim. Acta, 6,412-15 (1952). and Connell, J., J . Am. Chem. Soc., 6 9 , 2 0 6 3 - 4 (1947). (2) Gorman, M., (3) Kerns, B., and Freiser, H., unpublished results.
RECEIVED for review August 7, 1952. Accepted March 10, 1953. Presented before the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, March 1952. Joint contribution of the Chemistry Department, University of Pittsburgh, and the Jones and Laughlin Steel Corp.
Determinations of Trace Elements Combining Chemical Enrichment and Spectrochemical Methods G . E. HEGGEN' AND L. W. STROCK' Albany Medical College, Albany, N.Y . , a n d Saratoga Springs Commission Research Laboratories, Saratoga Springs, N . Y .
0
NE of the problems in most types of analyses is that of
changing the material received to another form, 60 that existing standardized methods may be used. This is especially true in spectrochemical analyses by the direct current arc, where it may be necessary to have as many standardized methods for a given element as there are different materials containing that element. For example, standardized methods for the determination of chromium or tin in silicates would be different from methods for determining the m e elements in limestone, petroleum, or tissue. The amounts of these elements in the original sample may be too low to be determinable in a direct analysis of the sample. During the past few years, the Saratoga Springs Commission Research Laboratories have been concerned with the determination of certain minor and trace elements in widely different types of materials in geochemical, agricultural, and biological fields. Sample treatment varied for different materials. Brines, water, and snow were evaporated. Rocks, minerals, and soils required fusion, solution, and separation; for other purposes these were leached with various agents, followed by concentration of the leachates. Coals, petroleum, plant materials, biological tissues, and fluids required ashing. All these treatments concentrated the trace elements to a certain extent, but in many cases insufficiently for direct spectrochemical analysis. In addition, the 1 Present add=, Saratoga Springs Commission, The Saratoga Spa, Saratogs Springs, N. Y. 9 Present address, Physics Department, Sylvania Research Center, Bayside, L. I., N. Y.
same trace elements were still found in widely differing base materials, and, thus, further enrichment and separations were necessary. Among the procedures that have been used is precipitation from solutions as hydroxides and as sulfides. However, organic complesing reagents have been found very satisfactory for concentrating and separating metallic elements, especially when those elements are present in minute or trace amounts. Different reagents may be used for different elements, and in many cases the same reagent will precipitate different elements under different conditions. Therefore, the choice of the reagent dependboil the problem. The reagents do not have to be specific, if the final stage of the analysis is by spectrographic means. Generally speaking, procedures involving the precipitation of comple\es of the desired elements are more satisfactory than extraction procedures, if the final analysis is by direct current arc spectrography. The handling of the sample is much less complex for direct precipitation procedures, unless the techniques involve the spark excitation of solutions. Cupferron has been used by the authors as a precipitating agent for some time in the spectrochemical determination of titanium, vanadium, and zirconium in mineral waters (8). In some later work, a larger group of elements had to be determined. Among those studied most frequently were cobalt, rhromium, copper, iron, gallium, molybdenum, nickel, lead, tin, vanadium, and zinc. Cupferron precipitates a large group of elements from acid solution, including iron, gallium, molybdenum, tin, and vanadium.
