ANALYTICAL CHEMISTRY
560 very stable in solution, being widely used as an artificial food and drink color. No attempt to determine the precision was made in this exploratory study of the reaction. More effective ways of bringing the supported lake into rapid contact with the sample solution would be desirable to enhance the precision of the method. The serious interference produced by sulfate, phosphate, and bicarbonate ions and p H values other than approximately neutral make it necessary that these ions be removed from a sample to be analyzed for fluoride ion. Fortunately, these are ions which are eliminated by accepted and well-studied distillatio; procedures (1, 4 ) . A high concentration of chloride ion might distill over as hydrochloric acid and cause some interference if not prevented by the addition of silver sulfate in the optional procedure using sulfuric acid ( 1 ) . Attempts to remove sulfate ion by preripitation as barium or lead sulfate also removed fluoride ion by coprecipitation. There is a possibility that this reaction might
be used for the colorimetric determination of sulfate ion, as the possible interferences-fluoride, bicarbonate, and monohydrogen phosphate ions-are removed by aluminum ion. This would require further investigation, as aluminum ion apparently does remove some of the sulfate ion if the aluminum-sulfate ratio is high LITERATURE CITED
(1) Am. Public Health Assoc., New Tork, and -4m. Water Works h s soc., “Standard Methods for the Examination of Water and Sewage,”9th ed., pp. 76-9, 1946.
(2) Gibson, K. S., McNicholas, H. J., Tyndall, E. P. T., Frehafer, h l . K., and Mathewson, W. E., Bureau of Standards, Sci. Papers, 18, KO.440, 121 (1922-3). (3) Snell, F. D., and Snell, C. T., “Colorimetric Methods of Analysis,” Vol. 11, 3rd ed., pp. 743-53, Ken, York, D. Van Xostrand Co., 1949. (4) Willard, H. H., and Winter, 0. B., IND.EYG.CHEM.,ASLL. ED.. 5, 7 (1933). RECEIVED Sor review July 30, 1953. Accepted October 23, 1953.
Separation of Magnesium from Calcium by Ion Exchange Chromatography Application to Determination of Calcium Oxide and Magnesia in limestones and Dolomites DAN N. CAMPBELL’ and CHARLES T. KENNER Department o f Chemistry, Southern M e t h o d i s t University, Dallas, Tow.
previous investigation, Banewicz and Kenner investiI(Versene) gated the application of the ethylenediaminetetraacetic acid method to the determination of calcium and magnes(1)
N A
ium in limestones and dolomites using the oxalate method of separation. More recently Cheng, Kurtz, and Bray ( 3 )have applied the Versenate method to the determination of calcium, magnesium, and iron in limestone using murexide as the indicator for the calcium determination. The proposed method involves the separation of magnesium from calcium by ion exchange chromatography followed by titration of the magnesium with Versenate. Calcium is determined by subtracting the titration for magnesium alone from that for both calcium and magnesium together. The separation technique is similar to that used by Beukenkamp and Rieman ( 3 ) for the Separation of sodium and potassium. APPARATUS AYD REAGENTS
The apparatus used was that recommended by Odencrantz and Rieman ( 4 ) . A borosilicate glass column 2.7 cm. in diameter, 10 cm. high. provided with a sintered-glass filter plate of coarse porosity (Ace GlassiCo., catalog No. 8571, porosity B ) was filled with the wet hydrogen form of the resin to a height of 6.3 f 0.3 cm. ,411 height measurements were made immediately after backwashing and regeneration. A 125-ml. dropping funnel was employed to hold the solutions for the column. The resin used was Dowex 50 (50 to 100 mesh). The resin was prepared by repeatedly mixing the dry form with water and decanting after settling. The wet resin was transferred to the column, regenerated with acid, and washed, and the level of liquid was adjusted to approximately 1 to 2 cm. above the resin ,411 reagents were C.P. or analytical grade chemicals which conformed to AMERICAN CHENXCAL SOCIETY specifications. Primary Rtandard grade disodium dihydrogen ethylenediaminetetraacetate was used to prepare the titrating solutions. The indicator was Potting Black C, Colour Index No. 203, made by the Ciba Co., Inc., and also known as Indicator F 241. SOLUTIONS
The standard calcium, magnesium, and Versenate solutions, the 1 Present address, Department of Chemistry, Louisiana State University, Baton Rouge, La.
F 241 indicator, and ammoniacal buffer solutions were prepared as reported in the previous investigation (1). Known Solutions. The solutions containing known amounts of calcium and magnesium were repared by mixing accurately measured volumes of the standarf calcium and magnesium solutions and diluting in volumetric flasks. Aliquots of 20.00 ml. of these solutions were used in the analysis. The samples for single runs were prepared by direct addition of measured volumes of the two standard solutions. EXPERIMENTAL
Elution Curves. The elution curves in Figure 1 were obtained by adsorbing known samples on the resin and eluting with hydrochloric acid of the molarity designated a t a flow rate of 8 i 2 ml. per minute (1.3 f 0.3 ml. per minute per square centimeter). Aliquots of 25 ml. were collected consecutively in 25-ml. graduates and titrated by the F 241 procedure for total magnesium and calcium. As it was difficult to determine calcium in small quantities in the absence of magnesium by the F 241 procedure, a known volume of standard magnesium solution was added t o each elution aliquot before titration. Solution of Samples. Accurately weighed samples of limestone or dolomite of approximately 1 gram were dissolved in 10 ml. of hydrochloric acid (1 to 1) and 25 ml. of water. The samples were eva orated to dryness, baked for 1 hour, and redissolved in 10 m?. of hydrochloric acid (1 to 1) and 25 ml. of water, filtered, and washed. The filtrates were diluted to 500.0 ml. in a volumetric flask. Aliquots of 10.00 ml. of these solutions were then used for the determination of total calcium and magnesium and for the determination of magnesium alone. Preparation of Column. Before each separation, the resin in the column was backwashed for several minutes by connecting the lower end of the column to a 5-gallon jug of distilled water to which pressure was applied by means of a rubber pressure bulb. During the backwashing, the resin was forced into the dropping funnel and then allowed to settle back into the column. The resin was then regenerated with 300 ml. of 3 X hydrochloric acid and washed with 150 ml. of distilled water a t a flow rate of 10 i2 ml. per minute (1.8 & 0.4 ml. per minute per square centimeter). Adsorption of Aliquots. Sample aliquots of 10.00 ml. were pipetted into a beaker, transferred with washing to the dropping funnel, and diluted to 75 ml. The aliquot was run onto the resin a t a flow rate of 5 i 2~ ml. per minute, and the dropping funnel was washed with three separate 10-ml. portions of distilled water.
56 1
V O L U M E 2 6 , NO. 3, M A R C H 1 9 5 4 I
0
r
I
I
1
I
I
I
I
I
Table 11. Analysis of Known Solutions
h
Raniple So. 1
l\Ig Taken 0.24
2
1,l5
(All values in milligrams) Ca Found Difference Taken 0.26 0.02 3.24 0.24 0.00 0.26 0.02
Ifg
1.15 1.16
1.16
VOLUME OF ELUATE, ML.
Figure 1. Elution Curves Flow rate. 8 =t2 ml. per minute Resin height. 6.3 cm. 1. 1.50 mg. of h l g +A a n d 4.43 mg. of CaT2. 1.51 mg. of hlg.*+ a n d 4.50 Ing. of Ca+3. 1.47 mg. of bIg.++ and 4.47 mg. of Ca*+
Table I.
Analysis of Bureau of Standard Samples
CaO DifferPresent, n ence ," Dolomite, S B S 88 1 21.48 21.4YU 0.01 30.49 2 21.49" 0.01 3 21.44b 0.04 4 21.5Ob 0.02 Limestone, XBS" 1 2.19 2.260 0.07 41.32 (i 2.2fja 0.07 7 2.34s 0.15 8 2.32b 0.13 a Average of quadruplicate aliquots. b Average of duplirate aliquots. 3190
S:ailiple
1-0,
Piebent, L-9
3IgO Found,
Yo
CnO
Found, L-9
Difference
Difference 0.01 0.00 0.02
0.00 0.01 0.01
2.61
2.62 2.59 2.59
0.01 0.02 0.02:
3
2.28
2.28 2.26 2.27
0 00
1.73
1.74 1.76 1.75
0.01 0.03 0.02-
4
3.46
3.44 3.45 3.46
0.02 0.01 0.00
0.88
0.89 0.89
0.01 0.01 O.O&
0.0% 0 01
0.88
5
5.74
5.73 2.74
0.01 0.00
0.00
0.00 0.00
0.00
6
0.00
0.01 0.02
0.01 0.02
4.29
4.29 4.28
0.00 0.01
8.37 8.44 5.36 4.44 0.00 0.00
..
0 30 0.01 0.30 0.01 2.35 0.02 loa 2.96 0.00 11" j.83 0 04 12a 5.92 3.88 0.04 Single samples; calcium not determined.
7" 8a 9a
Elution of Magnesium. After the sample was washed onto the column, magnesium was eluted from the resin with approsimately 600 ml. of 1.05 i 0.02M hydrochloric acid a t a flow rate of 8 zt 2 ml. per minute. The first 75 ml. of the eluate were discarded and the nest 475 ml. were collected in a 1000-ml. Erlenmeyer flask previously marked for the correct volume. Titration of Magnesium. Approximately 100 ml. of concentrated ammonium hydroxide and 15 drops of indicator solution were added to each flask which was then titrated with the standard T'ersenate to a blue end point. -4 blank of 0.13 ml. of Versenate was normal. However, the blank was determined on each new bottle of concentrated ammonium hydroxide used and ran as high as 0.45 ml. for some. The end point was determined by comparison with a previously titrated blank or known solution in a box completely lined with white paper. Titration for Total Calcium and Magnesium. Aliquots of 10.00 ml. were pipetted and diluted to approximately 100 ml.; 3 ml. of the ammoniacal buffer solution and 5 drops of indicator were added, and the solution was titrated to a pure blue end point. To those samples in which iron was present, a few drops of 1097, (by weight) potassium cyanide solution were added before the addition of the indicator. Interference by iron v a s furt'her minimized hy withholding the indicator until just before the end point.
Ca Found 3.23 3.24 3.22
0.29 0.31 2.37 2.96 3.87
0.00
..
,.
,. ,. ,.
..
..
.. ,
