Determination of Strontium in the Presence of Calcium KENNETH A. KOBE
AND WILLIAM
L. MOTSCH'
University of Texas, Austin, Tex.
ETHODS for the determination of strontium in the presence of calcium and barium are not numerous. They usually call for exactly controlled conditions and concentration of reactants. The most recent method is that of Kallmann (4), which uses a 20% solution of hydrogen chloride in n-butyl alcohol for the separation as chlorides of barium and strontium from calcium. Stewart and Kobe (7') reviewed previous methods for the separation of anhydrous nitrates and gave explicit directions for the use of acetone as a solvent to extract calcium nitrate from the anhydrous mixture of nitrates of calcium and strontium. An error curve was determined which showed that all analytical determinations were high and that a maximum deviation of 2.i'Y0 was reached at 33.3% strontium nitrate in the sample. The problem remains of importance because of the necessity of separating calcium and strontium nitrates produced from lower grade ores by meam of fractional crystallization (6). Barber ( 1 ) has shown that the monobutyl ether of ethylene glycol (butyl Cellosolve) will selectively dissolve calcium nitrate from the anhydrous mixed nitrates of strontium and calcium. A scheme of qualitative analyhis for these cations was based on this separation. The solubilities in butyl Cellosolve were given for calcium nitrate as 0.243 gram per ml. and for anhydrous strontium and barium nitrates as not greater than those of strontium carbonate and barium sulfate in mater. Results in qualitative analysis of unknown samples were excellent. Because of the excellent qualitative results obtained with this method, it was deeired to put it on a quantitative basis. I t was also desired to investigate all of the commercially available monoalkyl ethers of ethylene glycol, to ensure that the butyl ether was the best for this purpose. Although the word "Cellosolve" is a trade-name ( 8 )for the monoethyl ether of ethylene glycol, it is used here as a generic term for the monoalkyl ethers of ethylene glycol and the individual members distinguished by the name of the alkyl group, as methyl, ethyl, or butyl.
Table 1. Solubility of Calcium and S t r o n t i u m Nitrates in Cellosolves (Solubilitiesin grams of solute per 100 grama of solvent) Methyl Ethyl Butyl Ca(N0dz 1200 C. 123 4 71 1 27 2 5 90 58.4 30' C. 33.2 Sr(H0a)z 1200 c.
30' C. +l.O% Hz0 +2.0% HzO + 4 . 0 % HzO + 8 . 0 % HzO
0 187 1 60
0.021 0 048
0.015 0.023
... ...
0.048 0.069
. , .
... ... ...
... ...
0.195 1.21
EXPERIMENTAL
Salts. Reagent grade chemicals were used in all cases. Calcium nitrate tetrahydrate was dehydrated by heating in an oven a t 145' C., pulverizing the dried salt while still hot, and redrying it a t 145' for 12 hours. The anhydrous salt was kept either in a desiccator over phosphorus pentoxide or in an oven a t 105' C. The strontium nitrate was heated at 145" C. for a t least 6 hours before use. Solvents. The methyl, ethyl, and butyl Cellosolves were of commercial grade supplied by the Carbide and Carbon Chemicals Division. Each was distilled under vacuum using a Vigreux column, rejectin the first 15% and final 10% of the charge. Because all the 8ellosolves form azeotropes of minimum boiling 1
Present a d h e , Ethyl Corp., Baton Rouge, La.
point containing 71 to 78y0water ( 3 ) traces of water in the solvent should be removed with the rejected initial 15'%. Solubilities. The solubilities of anhydrous calcium and strontium nitrates in the three Cellosolves were determined over the temperature range 30' to 120' C. and complete phase diagrams are reported (6). Some solubilities are given in Table I. Butyl Cellosolve is much more selective than the others for the extraction of calcium nitrate. In order to ascertain the effect of water in the solvent on the solubility of strontium nitrate in butyl Cellosolve a t 30°, a solvent using 1.0, 2.0, 4.0, and 8.0% water was used. It is apparent that the solvent must be anhydrous for satisfactory results.
STRONTIUM NITRATE FOUND, PERCENT
Figure 1. Calibration Calibration of Method. Samples were prepared in weighing bottles by weighing portions of strontium nitrate and adding from a buret enough standard calcium nitrate solution to give the desired ratio of salts. In all cases the total weight of salts was within 1% of 2.00 grams and contained from 2.5 to 95% strontium nitrate and sufficient water to dissolve both salts completely. The water in the solutions was evaporated in an oven a t 140' C. and the salts were dried for several hours a t 160' C. and cooled in a desiccator over phosphorus ntoxide. Ten milliliters of butyl Cellosolve were added and alrwed to stand 30 minutes to soften the sample, which was then pulverized with a stirring rod. The sample was allowed to stand for a t least 12 hours with occasional stirring to dissolve the calcium nitrate. The supernatant liquid was filtered through a glass filter cruc,ible of medium porosity. The solid was transferred from the weighing bottle to the filter, usin 10 ml. of butyl Cellosolve, and 5 ml. more of solvent were used for each of four washings of the solid salt on the filter; care was taken to agitate the precipitate thoroughly a t each washing. The filter crucible and residue were dried to constant weight in an oven a t 120' C. The deviations between true and found percentages of strontium nitrate are given in Table I1 and Figure 1. It is apparent that the results are much better than those obtained with acetone (6). At low and high concentrations of strontium nitrate the deviations are negative; this indicates that some strontium nitrate has been dissolved or lost mechanically through the filter. At medium concentrations the deviations ai e positive; this indicates that more calcium nitrate is left with the sample than the strontium nitrate dissolved. The method apparently has two disadvantages. (1) At low percentages of strontium nitrate the percentage deviations are large, about 50%, and it is difficult to filter the gelatinous piecipitate formed. For percentages of strontium nitrate above 25%, the solid residue will filter easily, if suction is not applied until the solid has been allowed to settle for several minutes. For percentages of strontium nitrate below 5%, acetone (7) can be used as a solvent with a smaller deviation than when butyl Cellosolve is used. (2) The vapors of the Cellosolves are toxic ( 8 ) , requiling proper protection for the analytical worker.
1498
V O L U M E 2 3 , NO. 10, O C T O B E R 1 9 5 1
1499
culated from the values read from Figure 1.
Table 11. Calibration of Analytical Procedure (Using mixtures of strontium nitrate and calcium nitrate) Per Cent Strontium Nitrate Present Trial 1 2 3 4 5 6 AV.
Av.deviation
2.50
5.00
7.50
25.00
35.00
50.00
60.00
75.00
85.00
95.00
14.20 14.86 14.55 14.48 14.80 15.02
25.20 25.20 25.23 25.25 25.16
50.50 51.01 50.71 50.88 50.86 50.22
60.08 60.57 60.40 60.58
75.22 75.20 75.93 75.13 74.86 75.33
85.20 85.20 85.17 85.17 85.20
94.72 94.78 94.83 94.95
...
35.11 35.88 35.42 35.36 35.57 35.22
...
.. .. ..
14.65 -0.35
25.21 +0.21
35.43 +0.43
50.69 +0.69
60.41 +0.41
75.28
85.19 f0.19
94.82 -0.18
Per Cent Strontium Nitrate Found
1.75 1.20 1.64 1.17 1.25 1.20
4.09 3.90 3.92 4.04
.. ....
6.29 6.48 6.78 6.37 6.18 6.99
1.37 -1.13
3.99 -1.01
6.52 -0.98
LITERATURE CITED
15.00
ANALYSIS OF SAMPLES
For analysis of unknown samples the alkaline earth group is eeparated by standard methods which precipitate the metals as carbonates. Barium may be separated by the method of Beyer and Rieman ( 2 ) . The calcium and strontium are then separated as nitrates, by the method used for the calibration. T o the percentage of strontium nitrate found is added a correction cal-
.. .
...
+0.28
( 1 ) Barber, H. H., IND. Esa.
CHEM., ANAL.ED., 13, 572-3 (1941). (2) Beyer, G. L.* and Rieman? W., 111, Ibid., 19, 35-7 (1947). (3) Carbide and Carbon Chemicals Corp., Xew York.
“Cellosolve and Carbitol
Solvents,” 1947. (4) Kallmann, S., As.4~.CHEM., 20, 449-51 (1948); 21, 1145-6 (1949). (5) Kobe, K. A., and hiotsch, 11’. L., J.Phvs. Chem., to appear (1952). (6) Kobe, K. A , and Stewart, P. B., J . Am. Chern. Soc., 64, 1301-3 (1942). (7) Stewart, P. B., and Kobe, K. A., IXD.ENG.CHEir., . ~ K A L .ED., 14, 298-9 (1942). (8) Werner, H. m’.,hlitchell, J. L., Miller, J. TV.,and Von Oettinger. W. F., J . I d . Hug. Tox~coZ., 25, 157-63 (1943). RECEIVED November 20, 1950.
Fuchsin-Sulfite Reagent in Colorimetric Determination of Formaldehyde LEON SEGAJ, Southern Regional Research Laboratory, New Orleans, La.
OFFPAUIR, Buckaloo, and Guthrie ( 2 ) have described for organic compounds including cellulose formals a colorimetric method of determining combined formaldehyde which depends on the development of color in Schiff’s reagent when formaldehyde is present. The reagent is standardized against known amounts of formaldehyde, and because it changes sensitivity on standing arid does not follow the Lambert-Beer law, a new standardization or IT-orking curve must be plotted each time the reagent is used. This method is simple t o use and was selected by the author for determining combined formaldehyde in cottons that had been treated with various formaldehyde solutions. When the reagent was prepared from basic fuchsin (rosaniline hydrochloride) in the manner described ( 2 ) , appreciable color varying from tan to red mas found t o remain after addition of hydrochloric acid, when i t had been thought the color of the solution would he redured. I t was learned from one of the aut,hors of the method ( 1 )that, this had been observed by them but had heen overcome solely by use of a dyestuff of particular purity which, after addition of the acid, yielded a clear, slightly colored solution. For reliable analyt,ical result,s they recommended that only fuchsin which gave t.his color be used. Ten samples of basic fuchsin were tested, but none gave the rlesired color after addition of the acid. That the applicability of the procedure should be so limited by such a peculiarity of the rcagent did not seem reasonable, and a way was sought to use the fuchsin on hand. The color of the reagent was found to be removable h y decolorizing carbon (Xorit). This technique has been used for preparing Schiff’s aldehyde reagent for qualitative purposes (3,51, and Scott (4)satisfactorily accomplished the same thing using fuller’s earth. few minutes after addition of the acid, after the color had been lightened, about 1 gram of the decolorizing carbon was added to 500 ml. of the solution. The solution, after a vigorous shaking, was filtered through filter paper directly into the glasestoppered flask in which i t was t o be stored. Comparison of the working curve of the clear and water-ivhite filtrate with that of the decolorized reagent prepared from the
“satisfactory” dyestuff referred to above showed t,hat, they were almost, identical. After about 1 month’s storage of the two reagents in the dark, the shapes of the two working curves r e r e still almost identical, although they had changed from the original, as was expected. This evidence indicated that the decolorized res the reagent prepared agent from stock fuchsin m-as as suit,able a from the particular dyestuff. Results of formaldehyde analyses carried out with the decolorized reagent checked very well with t h o v given by the recommended, but slightly colored, reagent. Sub,sequent use of the decolorized reagent has shown it to be satisfactory. Caution. Use of too much carbon will result in complete loss of sensitivity of the reagent-that is, no color whatever will develop in the presence of formaldehyde. Whether this is due to withdrawal from the solution of the sulfur dioside or of the rerlured dyestuff, by the carbon, was not investigated. Although Norit was used here, other ~imilarcarbons such as those employed by Tobie (6) should be suitable. In the original paper ( 2 ) sodium acid sulfite (Rodium bisulfite, NaHSO?), is specified for use in reducing the fuchsin. If, instead, sodium pyrosulfite ( Na&05, commonly called sodium metabisulfite and labeled sodium hisulfite by some manufacturers) is used, then t he weight of sodium acid sulfite called for must, be multiplied by the factor 0.908 in order t,o obtain that weight of pyi.o.eulfite which will release the proper amount, of d f u r dioside. The effect of sulfur dioxide content on the sensitivity of the reagent has been indicated by Tobie (6). LITERATURE CITED ( I ) Hoffpauir, ‘2, L., personal communication. (2) Hoffpauir, C. L., Buckaloo, G. W., and Guthrie, .J. D., IND.ENG. CHEY.,ANAL.ED.,15,605 (1943). ( 3 ) Mann and Saunders, “Practical Organic Chemistry,” 2nd ed., p. 379, London, Longmans. Green & Co.. 1936. (4) Scott, F. C., Analyst, 70, 374 (1945). (.i) Tobie, W. C., IND.ENG.CHEY..i l x . 4 ~Eo., . 14,405 (1942). December 26, 1950. The mention of trade products does not RECEIVED imply their endorsement by ‘the Department of .4griculture over similar
products not mentioned.
