Titration of Sulfate Following Separation with Alumina JAMES
S. FRITZ, STANLEY S.
YAMAMURA, and MARLENE JOHNSON RICHARD
Institute for Afomic Research and Department o f Chemistry, Iowa State College, Ames, Iowa
b In acid solution a column of activated alumina will retain sulfate more readily than most other anions. It is therefore possible to separate as little as 0.5 p.p.m. sulfate from large quantities of chloride, nitrate, and perchlorate, and from most metal ions. The sulfate is then eluted from the column with dilute ammonium hydroxide, passed through a small cation exchange column, and titrated with 0.01 M barium perchlorate using Thorin [2 (2 -hydroxy 3,6 -disulfo- 1 -naphthy1azo)benzenearsonic acid] as the indicator. Small amounts of sulfate in metal salts can be determined, except where the metal ion forms a slow-reacting sulfate complex. A simple modification permits separation of sulfate from zirconium(1V) or chromium(ll1). The alumina column is also used with a peroxide bomb combustion to determine sulfur in a wide variety of organic compounds, with an error of 1 % or less.
-
D
-
for the determination of macro (2) and micro (3) quantities of sulfate are simple, quick, and accurate, and can be applied t o a rather wide variety of samples. In common with other adsorption indicator methods, these procedures do not give good results when large quantities of foreign salts are present during the titration, especially u-hen small amounts of sulfate are titrated ( 3 ) . Nydahl and Gustafsson (5) and more recently Sydahl (4) have described the use of an acid-washed alumina column for separating sulfate from metal cations and from the bulk of other anions. Dean ( 2 ) has employed a column of this type for separating cobalt from other metals by taking up the cobalt complex of nitroso R salt on the column. The alumina column acts as a n anion exchange column, but has much greater affinity for some anions than for others. I n acid solutions it takes up sulfate (actually bisulfate at the p H used) avidly; it has a somewhat lower affinity for phosphate and fluoride, and a much
158
IRECT
TITRIhfETRIC METHODS
ANALYTICAL CHEMISTRY
lower affinity for chloride, nitrate, and perchlorate. Sulfate is taken up quantitatively from a solution with a chloride, nitrate, or perchlorate concentration many times that of the sulfate concentration. The greater affinity of the alumina for the hydroxide ion than for any of the other anions mentioned permits easy elution of sulfate from the column following the separation.
Table I.
Acid,
M
0.1 1.0
2.0 5 0 a
be more basic than 5 or 6. Dilute to 1 liter with water. Sulfuric acid, 0.005M. Prepare a 0.005 M solution and standardize against - 0.02&V sodium hydroxide. Thorin [2(2-hydroxy-3,6-disulfc-l-naphthg1azo)benzenearsonic acid]. Prepare a 0.27, solution in water. Methylene blue. Prepare a 0.05% solution in water. Potassium perchlorate and sodium peroxide, sulfur-free, produced by Parr Manufacturing Co., 211 53rd St., Moline, Ill. Sucrose. Grind reagent grade sucrose in a mortar. Smmonium hydroxide; reagent grade.
Effect of Acidity on Recovery of Sulfate
HClO, 1.02 1.01 1.02 1.04
Barium, MI.= HCI " 0 8 1.05 1.08 1.03 1.06 1.03 1.06 0.84 1.02
Theory 1.03 ml.
35 m m EXTERNAL DIAMETER I/ m m
EXTERNAL MAMETER
&-ZOO
MESH ABSORPTION
GLASS WOOL 2 - H O L E RUBBER
TO SUCTION PUMP I-LITER SUCTION FLASK WITH BOTTOM REMOMD
It is entirely feasible to determine small quantities of sulfate titrimetrically after separation from most other ions with an alumina column. I n the method developed, an acid solution of the sample is passed through an alumina column in the chloride or perchlorate form. All of the sulfate in the sample is taken up by the column; a small fraction of the other anions is also taken up. After washing, the sulfate is eluted from the column with dilute ammonium hydroxide. The eluate is then passed through a cation exchanger in the hydrogen form, and the sulfate is titrated with 0.0111f barium perchlorate according to the method of Fritz and Yamamura (3).
REAGENTS AND SOLUTIONS
iilcohol. Absolute ethanol, 2-propanol, methanol, or mixed ethanol and methanol as purchased commercially. Barium perchlorate, 0.01M. Dissolve 3.9 grams of barium perchlorate trihydrate in 200 ml. of water and add 800 ml. of ethanol. Standardize against 10 ml. of 0.005M sulfuric acid. Entol, 0.5M. Dissolve 69.5 grams of
A' - hydroxyethylethylenediaminetriacetic
acid in water, adding sodium hydroxide pellets to aid solution. The pH should not
K GLASS PLATE
Figure 1. Alumina column and associated apparatus
Hydrochloric and perchloric acids, reagent grade. APPARATUS
Alumina Column. The alumina column and the apparatus used for its operation under reduced pressure are shown in Figure 1. Add some chroniatographic alumina, 80 to 200 mesh, to a beaker, wash with water, and allow- to settle. Decant the supernatant liquid and repeat the washing process until the very fine particles have been removed, as evidenced by the clear wash water. Transfer the alumina to the column and wash with 50 ml. of 1M ammonia, several 5-ml. portions of 0.1M ammonia, and finally m-ith approximately 50 ml. of water. Lastly, wash with 10 ml. of hydrochloric or perchloric acid of the same strength to be used in t h e sulfate sample that will be passed
through the column. The strength of perchloric acid used was 0.1 to 2 031; this is not critical. The column is now ready to receive the sample. I n all operations with the alumina column, do not allolv the column to run dry.
Table
II.
so,--
Taken, P.P.M. 0 98 0.49 5.00 5.00
Recovery of Sulfate from Dilute Solutions
so,--
Added Ion, Ba++ Found, P.P.M. M1. P.P.RI. 1.01 None 0.21 0.48 None 0 10 1.03 4 98 C1-, 1000 5.03 Not-, 1000 1.04
Ion Exchange Column. Use an ion exchange column approximately 1 inch in diameter and fill Kith a 3-inch bed of cation exchange resin (Dowex 60-X8, 20 to 50 mesh) in the hydrogen form. After passage of each sample through the column, transfer the resin to a used resin container and add fresh hydrogenform resin to the column. When a sufficient quantity of used resin has been collected, place in a large column, regenerate with 3M hydrochloric acid, and wash with distilled water.
Table 111.
from the column by adding successively 5 ml. of 1-44 ammonia, 20 ml. of 0.1M ammonia, 20 ml. of 0.1M ammonia in 5-ml. portions, and about 25 ml. of water. Pass the sulfate-containing effluent through a small cation exchange column and receive the effluent from this column in a 100-ml. volumetric flask. Wash the cation exchange column with enough water to fill the volumetric flask to the mark. Transfer a 10-ml. aliquot of this final effluent to a 100-ml. beaker, add 40 ml. of alcohol and 2 drops of Thorin indicator, then titrate with 0.01M barium perchlorate to a pale pink end point. SEPARATION OF SULFATE FROM INORGANIC IONS
The effect of acidity on the recovery of sulfate was studied by passing sulfate-perchloric acid solutions with increasing concentrations of perchloric acid through the column. It was found that sulfate is taken up quantitatively from solutions up to 5M in perchloric acid. Complete recovery was also obtained from hydrochloric acid solutions up to 21M and from nitric acid solutions up to about 2144 (see Table I). The results for the nitric acid solutions are slightly high, because of the anion positions of the alumina column not used by the sulfate. The bulk of the nitrate could have been removed by washing the column with 1-I4 hydrochloric acid.
Effect of Chloride on Recovery of Sulfate
(1.00 ml. of 0.1M SO, taken) 1M HCl
Taken, M1. 50 100 200 300 450 a
of sulfate, it is necessary to have a sample of sufficient volume so that enough sulfate is obtained from the total sainple to permit titration without large error. When the concentration of an aqueous sulfate solution is 0.5 p.p.m. (approximately 5 x 1 0 b V ) , a sample volume of approximately 2 liters is required. The effect of the recovery of sulfate of increasing the foreign anion-sulfate ratio was studied by adding a constant amount of sulfate to increasing volumes of 1M hydrochloric acid, passing these samples through the alumina column, then eluting and titrating the sulfate. Data for these experiments are given in Table 111. At a chloride-sulfate ratio of 4600 to 1 (the highest ratio used), sulfate was quantitatively recovered. Sulfate cannot be separated from phosphate or fluoride by the alumina column method, although a partial separation is effected by making the sample 1 to 5 M in perchloric acid before passage through the column. If phosphate or fluoride is present, it may be necessary to adjust the sample size so that the capacity of the alumina column is not exceeded by the combined sulfate and phosphate content. After elution from the column, precipitation with magnesium carbonate can be used to separate small quantities of sulfate and phosphate from each other ( 3 ) . Separation of sulfate from dichromate using the alumina column is nearly quantitative in acid solution. The
Ratio C1-z SO,-500: 1 1000: i 2000 : 1 3000 : 1 4500 : 1
Ba +-, M1.u 1.03 ~. ~. 1.03 1.02 1.05 1.03
Table IV.
Ion Added Chromate
Phosphate
Ratio Ion Added:
so,
10: 1 50: 1 100: 1
1:l 1:l
Theory 1.03 ml.
1:l 1:l
Fluoride Peroxide Bomb. The macro peroxide bomb manufactured by the Parr Instrument Co. was used.
GENERAL PROCEDURE
Use a sample containing 0.12 to 12.0 mg. of sulfate. Adjust the pH to 0.5 to 1.0 with dilute perchloric or hydrochloric acid. Pass the sample through the alumina column a t the rate of approximately 120 drops per minute; Kash with 10 ml. of 1 to 20 hydrochloric acid and 25 ml. of water, added in several portions. Elute the sulfate
(1
1:l 10: 1 10: 1
Effect of Anions on Sulfate Determination
Acid
Barium, Me Actual
L1.I
Theory
0 . 6 HC1 0 . 6 HC1 0 . 6 HC1
2.05 2.05 2.05
2.06 2.09 2.08
+0.01 f0.04 +0.03
5 HClO4
1.03 1.03 1.03 1 03
1.08 1. O i 1.03 1.03
+o, 05 +o. 00 +o. 00
1.03 1.03 1.03
1.04 1.07 1 .06
+0.01 +0.01 + O . 03
2 HClO, 5 HClOa" 2 HC10," 5 HC10,
1 HClO, 5 HClOI
Diff.
$0.04
Phosphate precipitated with magnesium carbonate after elution from alumina column.
An alumina column is very effective in concentrating sulfate from very dilute solutions. With sulfate concentrations as low as 0.5 p.p.m. quantitative recovery of sulfate is still obtained (see Table 11), and this does not necessarily represent the lowest concentration of sulfate that will be quantitatively taken up by the column. K h e n working with very low concentrations
small amount of dichromate which accompanies the sulfate appears to be reduced by the alcohol added just before the final titration. Data for the analysis of sulfate mixtures with phosphate. fluoride, and dichromate are given in Table IV. The effect of various metal ions on the separation and titration of sulfate was studied. Solutions of sulfate and VOL. 2 9 , NO. 1, JANUARY 1957
159
Table V.
Metal Ion Al+++ Bi+++
Effect of Metal Ions on Sulfate Determination
Ratio Metal: SO, 10: 1 100: 1
10: 1 100: 1
C r + + +(violet)
10: 1 100: 1
Cr+++(green)
10: 1 10O:la
Cu++
10: 1 100: 1
Fe+++
10: 1 100: 1
La+++ >In + +
1O:l
10: 1
100: 1
Th + + + +
10: 1 10: la
Theory 5.12 1.05 1.05 1.05 2.05 2.05 2.05 1.42 1.05 1.05 2.02 2.05 1.26 1.05 1.05
1.04
++
metal chlorides, nitrates, or perchlorates (where the molar ratio of metal to sulfate was from 1O:l to 100:1) \\-ere passed through a small alumina column, and the sulfate m-as eluted and titrated. Results for representative metals are reported in Table V. Consistently good results were obtained except for certain metals, such as chromium(II1) and zirconium(IV), which form slow-reacting sulfate complexes. Recovery of sulfate from thorium nitrate solutions is quantitative up to about a 20 t o 1 mole ratio of thorium to sulfate, but at higher ratios the results are somewhat low. Separation of sulfate from iron(II1) is quantitative only from hydrochloric acid solutions, and the column must be washed with hydrochloric acid to remove all traces of iron. Sulfate can be separated from zirconiuni(IV), chromium(III), or thorium (IV) if the metal ion is removed from combination with sulfate by adding a substance which forms a strong complex with the metal ion. Ethylenediaminetetraacetic acid (Enta) forms strong complexes with these metals, but some of the metal-Enta complex appears to be broken up during passage of the sample through the alumina column. N - Hydroxyethylethylenediaminetriacetic acid (Entol) complexes these metals almost as strongly as Enta and none of the Entol is taken up by the alumina column.
160
0
ANALYTICAL CHEMISTRY
Diff. -0.02 -0.01
1.05 1.07 2.05 2.06
j=o.oo
2.06 1.43 1.04 1.03 2.02 2.06 1.25 1.07 1.27
+o. 01
1.56 1.09 1.13 UOZ 50: 1 1,16 10: 1 1.05 Yb+++ 10: 1 1.25 &+++' 20: l a 1.10 1.09 100: l a 1.42 1.42 lletal complexed with Entol before passage through alumina column. 50: la
1.56 1.10 1.29 1.17 1.05 1.26
Barium, MI. Actual 5,lO
and potassium perchlorate must be used, and these foreign salts make the subsequent sulfate determination less accurate and more difficult to carry out, especially if a direct titrimetric method is used to determine the sulfate.
$0.02
10.00
+0.01
Table VI.
so.01
-0.01 -0.02 10.00
+0.01 -0.01 $0.02 +o .22 $0.00 -0.01
-0.16 -0.01
=ko.oo -0.01
Results of Sulfur Determination
Sulfur Compound Sulfanilamide Sulfathiazole Sulfapyridine Sulfaguanidine Sulfathalidine Sulfadiazine o-Tosylbromobenzene 10,lO-Diphenylphenoxathiasilin-5-dioxide N,N'-Diphenylthiourea 8-Sulfopropionic acid Inner anhydride of 8-sulfopropionic acid
-0.01
=to,00
To determine sulfate in the presence of zirconium, a n excess of Entol (based on formation of a 1 to I complex) is added to the acid solution, the p H is raised to between 5 and 6, and the solution is heated to boiling. Heating is necessary a t this point to speed up the rate a t which the complex zirconium sulfate species react with Entol. The solution is then cooled and acidified, and the sulfate is separated on the alumina column according to the general procedure. Essentially this same procedure is used to separate sulfate from chromium(II1) and thorium, except that 10 or 15 minutes' boiling is required to form the chromium-Entol complex completely.
TITRIMETRIC DETERMINATION OF SULFUR IN ORGANIC COMPOUNDS
The usual methods of determining sulfur in organic sulfur containing compounds involve oxidation of the organic sulfur to sulfate, with a subsequent gravimetric or titrimetric determination of the sulfate. The Carius, Pregl combustion, and sodium peroxide bomb procedures are the most widely used for the determination of sulfur in pure organic compounds. The peroxide bomb fusion is basically the most simple and rapid method for decomposing the sample. Its chief disadvantage is that a very large excess of sodium peroxide
Anilinium salt of propionanilide &sulfonic acid Thianthrene monosulfone Thianthrene monocarboxylic acid Sodium alizarin sulfonate 2-Phenoxyphenyl mercaptoacetic acid 4,6-Dicarboxylphenoxathiin-10-dioxide 2-Thioldiphenyl ether 2-ilminophendxathiin-10dioxide 2-Bromophenoxathiin Bis-(0-phenoxypheny1)disulfide Diethyl ester of 4,6-dicar boxvlphenoxathiinIO-oxideF e ( d i ~ y r )C?JS)Z ~( Fe( phen)z(CXS)*
Sulfur, % Calcd. Exptl. 18.6 18.6 25.1 25.0 12.9 1 2 . 8 12.8" 13.8 13.8 15.9 15.7 12.8 12.8 9,8 9.8 9.7" 8.0 8.0 14.1 14.1 20,8* 21.0
23.2b 23.0b 23.4b 23.3b
23.2 22.9 23.5 23.2
9.9 9.9 25. P 25.4O 24.W 24.0a 9. 4d 9 . 4 8.ge 8.9 12.3
12.3
9.9 15.8
15.8
12.9 11.5
12.8 11.5
15.9
15.9
8.4 10.1
12.0
9.5
8.4
10.1.' 12.1'
Semimicrobomb used. based on neutralization equivalent. 0 Result of gravimetric analysis. d Anhydrous salt. 6 Monohydrate salt. f Oxidation accomplished by alkaline peroxide followed by digestion with mixture of nitric and perchloric acids. a
b
In the method now proposed, a sample of the organic sulfur compound is decomposed by a bomb fusion with sodium peroxide. After the melt has been dissolved in water and acidified with hydrochloric acid, the sulfate is preferentially absorbed onto an alumina column in the perchlorate form, and thus separated from high concentrations of alkali metal salts and hydrochloric acid. The sulfate is eluted from the column with dilute ammonia, and the eluate is passed
through a small cation exchange column in the hydrogen form to remove the excess ammonia and convert the ammonium sulfate to the acid. The sulfate is then titrated in 80% alcohol with 0.01M barium perchlorate, using thorin as the indicator ( 3 ) . PROCEDURE
Keigh 0.2- to 0.3-gram samples into the macro peroxide fusion cup and add 0.5 gram of powdered sucrose, 0.5 gram of potassium perchlorate, and 12 grams of sodium peroxide. Mix thoroughly with a tiny spatula or \\-ire. Place 3 grams of sodium peroxide on top of the mixture. Assemble, screw tight, and ignite by placing the bomb over the sharp blue tip of a Bunsen flame for 90 seconds. Quench the reaction by immersing in cold distilled water. Open the cup and dissolve the fused contents by laying the cup in a 400-ml. beaker containing sufficient water to cover the cup. Cover with a watch glass and heat to near boiling. \\-lien the melt has dissolved, rinse the cup with mater and remove. K i t h cover glass in place, add sufficient concentrated hydrochloric acid (28 to 30
ml.) to make the solution distinctly acidic. After allowing the carbon dioxide to escape, transfer the solution (with filtration if necessary) to a 500-ml. volumetric flask. Dilute to volume and pipet 50- or 100-ml. portions into 150ml. beakers. Dilute to approximately 125 ml. Pass the solution through the alumina column in the perchlorate form a t the rate of 2 drops per second. Rinse the beaker with a little water and pass this through the column. Rinse the column with 10 ml. of water added in two portions, then place the original 150-ml. beaker beneath the column. Elute the sulfate by passing through the column 5 ml. of 1M ammonia and 20 nil. of 0.1M ammonia added in four portions. Finally, rinse with 10 ml. of water. Pass the eluate through the cation exchange column, and collect in a 100-ml. volumetric flask. Dilute to volume. To IO-ml. portions, add 40 ml. of ethanol and titrate with 0.01M barium perchlorate to the first permanent pink color using a drop each of thorin and methylene blue. The above procedure was applied to the determination of sulfur in a wide variety of organic compounds. The experimental results tabulated in Table VI are the averages of two or more
analyses. The average deviation from the mean was approximately *0.03%. Some of the compounds were very hygroscopic; consequently, it was necessary to establish their purity on the basis of their neutralization equivalent. The separation and titration methods described may also be applied in the determination of sulfur following oxidation of the sample by the Carius procedure, or with nitric and perchloric acids. I n the Carius method the alumina column separation may be eliminated if the excess nitric acid is removed by careful evaporation. LITERATURE CITED
(1) Dean, J. A , , ASAL. CHEM.23, 1096 f19.51l \ - - - - ,
(2) Fritz, J. S., Freeland, M. Q., Ibid., 26, 1593 (1954). (3) Fritz, J. S., Yamamura, S. S., Ibid., 27, 1461 (1955). (4) Nydahl, F., Ibid., 26,580 (1954). (5) Nydahl, F., Gustafsson, L., Acta Chem. Scand. 7, 143 (1953).
RECEIVEDfor review March 14, 1956. Accepted October 19, 1956. Contribution from Ames Laboratory, U. S. Atomic Energy Commission.
Color Reaction between 17-Ketosteroids and 3,5Dinitrobenzoic Acid SASSON COHEN and ASHER KALUSZYNER Medical Research laboratories, Medical Corps, Israel Defence Forces, Israel
b A number of dinitro compounds were investigated as substitutes for m-dinitrobenzene in the determination of 17ketosteroids with the view to reducing the interference from urinary chromogens. 3,5-Dinitrobenzoic acid, under controlled conditions, reacts with the more important urinary 17-ketosteroids, giving a color with maximum abInterference sorbance at 550 mp. from urinary chromogens is negligible. When applied to urine extracts, the method gives results 18% lower than the Nathanson-Wilson method, and 8% higher than the Callow method. The method may b e adapted, with advantage, to the quantitative determination of urinary 17-ketosteroids.
U
extracts, prepared by the usual methods for the determination of 17-ketosteroids, contain a nonketonic fraction that possesses a RIXE
significant absorption in the region of nonketonic material by adsorption on 520 mp when treated with m-dinitrocharcoal ( 9 ) . benzene, the reagent of the Zimmermann reaction (19, 20). The use of Girard’s reagent (6, 15) seems to be the most effective means for the removal of the interfering nonketonic fraction, but it does not lend itself to rapid routine work. I n the Callow modification (W), a correction may be applied for the interfering chromogens (4, 5 ) ; however, the instability of the ethanolic potassium hydroxide solution used in this method is a major drawback. The Nathanson-Kilson modification (11, 18) of the Holtorff-Koch method ( 7 ) is perhaps the most suitable for routine work, but no valid correction for the 1 2 3 L 5 6 1. DINlTROSEU201C ACID urinary chromogens can be applied (4). Other methods for the elimination of Figure 1. Effect of concentration of interference depend either on the ex- 3,fi-dinitrobenzoic acid (curve A) and traction of the color with an immiscible of potassium hydroxide (curve E ) on color intensity solvent (10, 17) or on the remoyal of the VOL. 29, NO. 1 , JANUARY 1957
161
