- Email: [email protected]
Determination of sulfate in presence of phosphate, arsenate, and other ions. Part II
MICROCHEMICAL
JOURNAL
13, 349-356
( 1968)
Determination of Sulfate in Presence of Phosphate, Arsenate, and Other Ions. Part II L. Chemical
Institute
SZEKERES
of the Veterinary
1
University,
Receizjed September
Budapest,
Hungary
16, 1967’
The microdetermination of sulfate ions in solutions containing calcium, magnesium, and trivalent cations is often necessary. Natural water samples (I ), belong to this category, and in addition, may also contain arsenate and phosphate. Sulfate in such samples may most easily be determined by precipitation titration. Volumetric precipitation titration of sulfate using barium chloride has been known since 1930 (4), but titrimetric determination of sulfate and phosphate in presence of each other has just recently been developed (3, 6, S-11). The end point of the well-known titration of sulfate with barium chloride may be indicated with metallochromic indicators (3, 4, 6). The titration of phosphate and arsenate ions to yield a precipitate of MgNHdPO, .6H20 or MgNH4As04. 6H20 can most easily be achieved with standard magnesium chloride in presence of ammonium chloride, ammonia, and a metallochromic indicator responsive to excess magnesium ions, (2, 3, 5, 7, IO, 12-14). The precipitation titration of phosphate and sulfate in presence of each other is very simple (6). The phosphate ions are titrated first with magnesium chloride in presence of ammonia, ammonium chloride, and eriochrome black-T. Sulfate ions do not interfere. After the end point has been reached, EDTA is added giving a blue solution. Then the sulfate ions are titrated with barium chloride until the excess barium ions replace magnesium in the EDTA complex giving a red end point. Our initial goal was to develop a simple procedure for the determination of 10 mg or less of sulfate in presence of alkaline earths, iron, aluminum, and possibly larger amounts of phosphate and arsenates. @e problem was solved in a number of dependent steps: 1 Present address:
Peterdy
u 12, 13udapest VII, 349
Hungary.
sm
350
a. A method was developed for the determination of sulfate ions, as well as the direct and indirect determination of magnesium and calcium ions. b. Methods were developed for alkaline earths and for phosphates and sulfates in presence of each other. c. The determination of sulfate in presence of alkaline earths, iron and aluminum was developed. d. The determination of phosphate and sulfate in presence of aIkaline earths, iron and aluminum was developed. f. Finally, the micro and macro determination of phosphate and/or arsenate and sulfate in presence of alkaline earths, iron, and aluminum was solved. EXPERIMENTAL
METHODS
Reagents EDTA solution, 0.01, 0.02, and 0.1 M DCyTA, 0.1 M Magnesium chloride, 0.02 and 0.1 M Barium chloride, 0.01, 0.02, and 0.1 M Acetic acid, 1 M Ammonia,
concentrated
Ethanol Buffer, pH 10, mix 50 g of NH&l and 400 ml of aqueous ammonia and dilute to 1 liter with water. Eriochrome
black-T indicator
Microburettes
of 3-S-ml total volume are employed in this work.
Procedure A DETERMINATIONOF SULFATE IN PRESENCE OF MAGNESIUMANDCALCXUMIONS A 2-5ml aliquot of the sample solution containing 2-10 mg of sulfate, l-10 mg of magnesium and l-20 mg of calcium is made neutral to weakly acid; l-2 ml of pH buffer and eriochrome black-T is added. The red solution is titrated with the appropriate EDTA standard @.Ol0.1 M) to a blue endpoint. The appropriate (0.02-0.1 M) magnesium
SULFATE IN PRESENCE OF PHOSPHATE AND ARSENATE
351
chloride standard is added until the red coloration reappears. The blue color is then carefully reestablished by titration with the appropriate (0.01-0.02 M) EDTA standard; 5-3 ml of ethanol is added and the sulfate titrated to a red end point with a suitable (0.01-0.02 M ) standard solution of barium chloride. The color change, caused by displacement of magnesium from the EDTA complex by excess barium ions, is easily perceived in spite of the precipitate. Solutions containing more than 40-50 mg of sulfate and 10 mg of magnesium in l-5 ml are titrated with 0.1 M EDTA and sulfate with 0.1 M barium chloride.
Procedure B DETERMINATION OF LARGER AMOUNTS OF CALCIUM AND MAGNEXUM IN PRESENCE OF SULFATE
The 2-5-ml aliquot of the sample solution containing ,2-10 mg of sulfate, 10-20 mg of magnesium and 410 mg of calcium is made neutral to weakly acid; S-15 ml of 0.1 M DCyTA, 2-3 ml of pH 10 buffer, and eriochrome black-T indicator is added. Excess DCyTA is titrated with 0.1 M magnesium chloride to a red end point. Then 0.02 M EDTA is added dropwise until the so81ution just turns blue. Finally, S-10 ml of ethanol are added and the solution is titrated with 0.02 M barium chloride to reappearance of red.
Procedure C DETERMINATION OF SULFATE, PHOSPHATE AND ARSENATE IN PRESENCE OF MAGNESIUM AND CALCIIJM
A 2-5-ml aliquot of the sample solution containing 8-45 mg of sulfate, 2-5 mg of magnesium, 2-3 mg of calcium, and 20-30 mg of phosphate (or 30-70 mg of arsenate) is made weakly acid; 5-12 ml of 0.1 M DCyTA, 2-4 ml of pH 10 buffer, and eriochrome black-T is added. The blue solution is titrated with 0.1 M magnesium chloride to a red end point. Divalent cations may be determined by this titration. Now 5-10 ml of ethanol are added causing a blue color. The titration is continued in the following manner: One half the expected amount of magnesium chloride equivalent to the phosphate is added and the solution is shaken for 0.5 minute. The solution first turns red,
352
SZEXERES
MgNH4P04. 6HzO precipitates, then the solution turns blue. The titration is continued to a permanent red end point. Then the solution is carefully back titrated to incipient blue with 0.02 M EDTA. Finally, the solution is titrated to a red end point with 0.02-0.1 M barium chloride. The end point is clearly visible in spite of precipitation of barium sulfate.
Procedure D DETERMINATION OF SULFATE IN PRESENCE OF CALCIUM, MAGNESIUM, IRON, AND ALUMINUM IONS
A 2-5-ml aliquot of the weakly acid sample solution containing 410 mg of sulfate, 1-15 mg of magnesium, and 1-8 mg of calcium, l-l mg of iron, and aluminum is made alkaline by dropwise addition of ammonia until slight turbidity occurs. A few drops of N acetic acid and 10-12 ml of 0.1 M DCyTA are added, then the solution is boiled. After cooling and addition of 3 ml of pH 10 buffer and eriochrome black-T, the solution is titrated to incipient red with 0.1 it4 magnesium chloride. Then 0.02 M EDTA is added dropwise until a blue color is achieved, 10 ml of ethanol are added and the solution is titrated with 0.02 M barium chloride to a red end point.
Procedure E DETERMINATION OF SULFATE, PHOSPHATE, OR ARSENATE IN PRESENCE OF CALCIUM, MAGNESIUM, IRON, AND ALUMINUM
A 2-lo-mg aliquot of the weakly acid sample solution containing 5-50 mg of sulfate, 15-30 mg of phosphate or 20-70 mg of arsenate, 2-15 mg of magnesium, l-5 mg of calcium, l-3 mg of iron, and l-2 mg of aluminum is made alkaline by dropwise addition of ammonia until slight turbidity occurs. A few drops of 1 N acetic acid and 10-12 ml of 0.1 M DCyTA are added, and the solution is boiled. The solution clears, since iron and aluminum form complexes with DCyTA at pH 3 that are stable at pH 10. After cooling, 3 ml of pH 10 buffer and eriochrome black-T are added. The excess DCyTA in the solution is titrated to incipient red with magnesium chloride. Then add 5-10 ml ethanol to give a blue colored solution. Again, as in C, add one half the expected amount of magnesium chloride and
SULFATE IN PRESENCE OF PHOSPHATE
AND ARSENATE
353
shake for one half a minute. Continue titrating to a permanent red endpoint. This titration allows calculation of the phosphate or arsenate content. The red solution, containing MgNH4P04. 6Hz0 or MgNH4As04 . 6H20 precipitate, is treated dropwise with 0.02 M EDTA until blue, then, if needed, 2-3 ml additional ethanol and titrated with 0.02-0.1 M barium chloride to a red endpoint. RESULTS
The Tables 1 and 2 show that complex mixtures may be analyzed satisfactorily utilizing this simple method.
TABLE
1
DETERMINATION OF SULFATE IONS IN THE PRESENCEOF CALCIUM AND MAGNESIUM
Present ( mg ) Sulfate
Mg
1 2.040 2.040 2 4.080 3 4.080 4 4.630 5 4.630 6 4.630 7 4.630 8 9B a 4.630 2.640 10 46.56 11 2.045 12 2.045 13 4.630 14 4.630 15 4.630 16 4.630 17 9.260 18 9.260 19B
0.5 5.3 1.0 5.5 2.4 4.8 7.2 9.6 14.4 1.2 12.0 0.5 1.7 2.4 2.4 2.4 2.4 2.4 14.4
No.
a B = Procedure
B.
Ca
8.0 4.0 4.0 8.0 12.0 16.0 20.0 8.0
Found (w) (av)
Diff. (ms)
2.043 1.980 4.147 4.047 4.675 4.646 4.638 4.541 4.723 2.640 46.52 2.035 2.064 4.694 4.665 4.680 4.704 9.201 9.396
+0.003 4.06 +0.067 -0.033 +0.045 +0.016 +0.008 -0.089 $0.093 0.00 a.04 -0.01 +0.019 +0.064 +0.035 +0.05 +0.074 -0.059 t-O.136
SD calculated from 8 measurements 0.02 0.06 0.05 0.02 0.03 0.04 0.024 0.05 0.045 0.03 0.40 0.02 0.01 0.03 0.04 0.04 0.045 0.08 0.26
9.260 9.260 9.260 46.70 46.70 46.70 9.260 9.260 5.280 9.260 9.260 46.70 46.70 46.70 46.70 46.70 46.70 9.266 9.260 9.260 9.260
2oc 21c 22c 23c 24c 25C 26D 27D 28D 29E 30E 31E 32E 33c 34C 35C 38E 37c 38C 39E 40E
4.8 7.2 4.8 14.4 16.8 14.4 14.4 14.4 13.2 4.8 4.8 14.4 14.4 12.0 12.0 12.0 12.0 2.4 2.4 2.4 2.4
Mg 4.0 8.0 8.0 4.0 8.0 8.0 8.0 4.0 4.0 4.0 4.0 8.0 8.0 4.0 4.0 4.0 4.0
Ca
Present (mg)
1.2 1.2 1.2 1.2 2.4 1.2 3.0 1.2 1.2 3.0
Fe 1.5 1.5 1.5 1.5 3.0 1.5 3.0 1.5 1.5 3.0
Al 18.10 36.20 18.10 18.10 36.20 18.10 18.10 18.10 18.10 18.10 -
Phosphate
Qc = Procedure C; D = Procedure D; and E = Procedure E.
Sulfate
No. a
TABLE 2
27.38 68.46 27.38 27.38 27.38 68.46 27.38 27.38
-
Arsenate
-
18.22 18.25 18.20 18.22
-
18.05 36.10 18.00 18.22 36.42 18.20
Phosphate
27.42 68.33 27.30 27.25 27.33 68.33 27.30 27.30
-
Arsenate
Found (a) (av)
9.375 9.398 9.456 46.80 46.92 46.84 9.133 9.216 5.015 9.139 9.216 46.38 47.62 47.76 47.58 47.76 48.02 9.408 9.456 9.454 9.313
Found (a) (av)
DETERMINATION OF SULFATE AND PHOSPHATE (ARSENATE) IN THE PRESENCE OF CALCXJM, MAGNESIUM, ALUMINUM AND FERRIC IONS
to.115 to.138 to.196 to.10 to.22 to.14 -0.127 4.044 4.265 -0.131 -0.044 -0.32 j-0.88 tl.06 to.88 t1.06 t1.32 +O. 148 to.196 to.194 to.052
Diff. (mg)
Sulfate
0.045 0.09 0.07 0.03 0.20 0.50 0.08 0.05 0.08 0.08 0.07 0.30 0.45 0.24 0.22 0.24 0.40 0.09 0.05 0.06 0.05
SD calculated from 8 measurements
I
i
SULFATE
IN PRESENCE
OF PHOSPHATE
AND
ARSENATE
355
ACKNOWLEDGMENTS I wish to thank my colleague,
Miss E. Kardos,
for carrying
out the experiments.
SUMMARY Sulfate ions are titrated with barium chloride in presence of ammonium chloride, ammonia, eriochrome black-T, and magnesium EDTA complex. Alkaline earth interference is avoided with EDTA, and iron and aluminum masked with DCyTA. After sequestration of cations, phosphate and arsenate may be titrated with magnesium chloride. Finally, sulfate titration is carried out in the same solution with barium chloride. REFERENCES 1. EFFENBERGER, M., Chelatometrische Sulfatbestimmung in Wbsern mit hohem Magnesiumgehalt unter Verwendung von Calcein als Indikator. Fortschr. Wawerchem. Ihrer Grenzgeb. 1, 173-176 ( 1964). 2. HAHN, F. L. AND MEYER, H., Massanalytische Bestimmung von Phosphat und Magnesium. Chem. Ber. 60, 975-977 ( 1927). 3. P~~SCHEL, R. AND LASSNER, E., The use of chelatochrome indicators in precipitation titrations. Chemist-Analyst 49, 58-62, 90-94, 120-124 ( 1960); 50, 26-29, 58-62 ( 1961) . 4. STRFBINGER, R. AND Z~MBORY, L., Ein neues Massanalytisches Verfaren zur Bestimmung von Barium-/und Sulfat-ionen. 2. Anal. Chem. 79, 1 ( 1930). 5. SZEKERES, L., Rapid volumetric determination of phosphate, sulphate and calcium amount in mineral raw phosphate and in superphosphate artificialfertilizers. Mugy. Kern. Lapju 19, 321-324 ( 1964). 6. SZEKERES,L. AND B. -POLAR, E., Simultaneous determination of phosphate and sulfate ions in the presence of metal contaminations. J. Agr. Food Chem. 8, 417-419 ( 1960). 7. SZEKERES, L. AND KARDOS, E., Data to the analysis of plantprotecting agents containing arsenate. Mugy. Kern. L&u 18, 617-619 ( 1963). 8. SZEKERES, L. AND KARDOS, E., Data to examination of arsenate containing plant protectors. Kiserl. Kozbmeny., C. Kertesz. 57, 153-160 ( 1964). 9. SZEKERES, L. AND KARDOS, E., Data to the determination of phosphate, arsenate and sulphate ions. Kised. Kozlemeny., A. Novenytermesz. 57, 169-172 (1964). 10. SZEKERES, L. AND KARDOS, E., Titrimetric determination of phosphate, arsenate, and sulfate. Ann. Chim. (Rome) 52, 844-848 ( 1962). 11. SZEKERES, L., KARDOS, E., AND SZEKERES, G. L., Determinazione degli ioni calcio, fosfato e solfato in presenza l’uno dell’altro con particolare riguardo all’analisi dei fosfati grezzi e dei fertilizzanti sintetici al superfosfato. Ann. Chim. (Rome) 53, 1704-1716 (1963). 12. SZEKERES, L., KARDOS, E., AND SZEKERES, G. L., Titrimetric determination of calcium and arsenate in the presence of iron, aluminum, fluoride and sulfate. Chemist-Analyst 53, 4041 ( 1964).
356
SZEXERES
13. SZEKERES, L., KARDOS, E., AND SZEKERES, G. L., Volumetrische
Bestimmung der Calcium/und Phosphationen neben Eisen (III)Aluminumund anderen Ionen. .I. Prukt. Chem. 28, (4R) 113-118 ( 1965). 14. SZEKERES, L., KARDOS, E., AND SZEKERES, G. L., Volumetric determination of calcium and phosphate ions in presence of iron, aluminum, fluoride, and sulfate. Microchem. J. 11, 1-12 ( 1966). 15. SZEKERES, L., KARDOS, E., AND SZEKERES, G. L., Microdetermination of arsenic by a precipitation titration. Microchem. J. 10, 184-193 ( 1966).
JOURNAL
13, 349-356
( 1968)
Determination of Sulfate in Presence of Phosphate, Arsenate, and Other Ions. Part II L. Chemical
Institute
SZEKERES
of the Veterinary
1
University,
Receizjed September
Budapest,
Hungary
16, 1967’
The microdetermination of sulfate ions in solutions containing calcium, magnesium, and trivalent cations is often necessary. Natural water samples (I ), belong to this category, and in addition, may also contain arsenate and phosphate. Sulfate in such samples may most easily be determined by precipitation titration. Volumetric precipitation titration of sulfate using barium chloride has been known since 1930 (4), but titrimetric determination of sulfate and phosphate in presence of each other has just recently been developed (3, 6, S-11). The end point of the well-known titration of sulfate with barium chloride may be indicated with metallochromic indicators (3, 4, 6). The titration of phosphate and arsenate ions to yield a precipitate of MgNHdPO, .6H20 or MgNH4As04. 6H20 can most easily be achieved with standard magnesium chloride in presence of ammonium chloride, ammonia, and a metallochromic indicator responsive to excess magnesium ions, (2, 3, 5, 7, IO, 12-14). The precipitation titration of phosphate and sulfate in presence of each other is very simple (6). The phosphate ions are titrated first with magnesium chloride in presence of ammonia, ammonium chloride, and eriochrome black-T. Sulfate ions do not interfere. After the end point has been reached, EDTA is added giving a blue solution. Then the sulfate ions are titrated with barium chloride until the excess barium ions replace magnesium in the EDTA complex giving a red end point. Our initial goal was to develop a simple procedure for the determination of 10 mg or less of sulfate in presence of alkaline earths, iron, aluminum, and possibly larger amounts of phosphate and arsenates. @e problem was solved in a number of dependent steps: 1 Present address:
Peterdy
u 12, 13udapest VII, 349
Hungary.
sm
350
a. A method was developed for the determination of sulfate ions, as well as the direct and indirect determination of magnesium and calcium ions. b. Methods were developed for alkaline earths and for phosphates and sulfates in presence of each other. c. The determination of sulfate in presence of alkaline earths, iron and aluminum was developed. d. The determination of phosphate and sulfate in presence of aIkaline earths, iron and aluminum was developed. f. Finally, the micro and macro determination of phosphate and/or arsenate and sulfate in presence of alkaline earths, iron, and aluminum was solved. EXPERIMENTAL
METHODS
Reagents EDTA solution, 0.01, 0.02, and 0.1 M DCyTA, 0.1 M Magnesium chloride, 0.02 and 0.1 M Barium chloride, 0.01, 0.02, and 0.1 M Acetic acid, 1 M Ammonia,
concentrated
Ethanol Buffer, pH 10, mix 50 g of NH&l and 400 ml of aqueous ammonia and dilute to 1 liter with water. Eriochrome
black-T indicator
Microburettes
of 3-S-ml total volume are employed in this work.
Procedure A DETERMINATIONOF SULFATE IN PRESENCE OF MAGNESIUMANDCALCXUMIONS A 2-5ml aliquot of the sample solution containing 2-10 mg of sulfate, l-10 mg of magnesium and l-20 mg of calcium is made neutral to weakly acid; l-2 ml of pH buffer and eriochrome black-T is added. The red solution is titrated with the appropriate EDTA standard @.Ol0.1 M) to a blue endpoint. The appropriate (0.02-0.1 M) magnesium
SULFATE IN PRESENCE OF PHOSPHATE AND ARSENATE
351
chloride standard is added until the red coloration reappears. The blue color is then carefully reestablished by titration with the appropriate (0.01-0.02 M) EDTA standard; 5-3 ml of ethanol is added and the sulfate titrated to a red end point with a suitable (0.01-0.02 M ) standard solution of barium chloride. The color change, caused by displacement of magnesium from the EDTA complex by excess barium ions, is easily perceived in spite of the precipitate. Solutions containing more than 40-50 mg of sulfate and 10 mg of magnesium in l-5 ml are titrated with 0.1 M EDTA and sulfate with 0.1 M barium chloride.
Procedure B DETERMINATION OF LARGER AMOUNTS OF CALCIUM AND MAGNEXUM IN PRESENCE OF SULFATE
The 2-5-ml aliquot of the sample solution containing ,2-10 mg of sulfate, 10-20 mg of magnesium and 410 mg of calcium is made neutral to weakly acid; S-15 ml of 0.1 M DCyTA, 2-3 ml of pH 10 buffer, and eriochrome black-T indicator is added. Excess DCyTA is titrated with 0.1 M magnesium chloride to a red end point. Then 0.02 M EDTA is added dropwise until the so81ution just turns blue. Finally, S-10 ml of ethanol are added and the solution is titrated with 0.02 M barium chloride to reappearance of red.
Procedure C DETERMINATION OF SULFATE, PHOSPHATE AND ARSENATE IN PRESENCE OF MAGNESIUM AND CALCIIJM
A 2-5-ml aliquot of the sample solution containing 8-45 mg of sulfate, 2-5 mg of magnesium, 2-3 mg of calcium, and 20-30 mg of phosphate (or 30-70 mg of arsenate) is made weakly acid; 5-12 ml of 0.1 M DCyTA, 2-4 ml of pH 10 buffer, and eriochrome black-T is added. The blue solution is titrated with 0.1 M magnesium chloride to a red end point. Divalent cations may be determined by this titration. Now 5-10 ml of ethanol are added causing a blue color. The titration is continued in the following manner: One half the expected amount of magnesium chloride equivalent to the phosphate is added and the solution is shaken for 0.5 minute. The solution first turns red,
352
SZEXERES
MgNH4P04. 6HzO precipitates, then the solution turns blue. The titration is continued to a permanent red end point. Then the solution is carefully back titrated to incipient blue with 0.02 M EDTA. Finally, the solution is titrated to a red end point with 0.02-0.1 M barium chloride. The end point is clearly visible in spite of precipitation of barium sulfate.
Procedure D DETERMINATION OF SULFATE IN PRESENCE OF CALCIUM, MAGNESIUM, IRON, AND ALUMINUM IONS
A 2-5-ml aliquot of the weakly acid sample solution containing 410 mg of sulfate, 1-15 mg of magnesium, and 1-8 mg of calcium, l-l mg of iron, and aluminum is made alkaline by dropwise addition of ammonia until slight turbidity occurs. A few drops of N acetic acid and 10-12 ml of 0.1 M DCyTA are added, then the solution is boiled. After cooling and addition of 3 ml of pH 10 buffer and eriochrome black-T, the solution is titrated to incipient red with 0.1 it4 magnesium chloride. Then 0.02 M EDTA is added dropwise until a blue color is achieved, 10 ml of ethanol are added and the solution is titrated with 0.02 M barium chloride to a red end point.
Procedure E DETERMINATION OF SULFATE, PHOSPHATE, OR ARSENATE IN PRESENCE OF CALCIUM, MAGNESIUM, IRON, AND ALUMINUM
A 2-lo-mg aliquot of the weakly acid sample solution containing 5-50 mg of sulfate, 15-30 mg of phosphate or 20-70 mg of arsenate, 2-15 mg of magnesium, l-5 mg of calcium, l-3 mg of iron, and l-2 mg of aluminum is made alkaline by dropwise addition of ammonia until slight turbidity occurs. A few drops of 1 N acetic acid and 10-12 ml of 0.1 M DCyTA are added, and the solution is boiled. The solution clears, since iron and aluminum form complexes with DCyTA at pH 3 that are stable at pH 10. After cooling, 3 ml of pH 10 buffer and eriochrome black-T are added. The excess DCyTA in the solution is titrated to incipient red with magnesium chloride. Then add 5-10 ml ethanol to give a blue colored solution. Again, as in C, add one half the expected amount of magnesium chloride and
SULFATE IN PRESENCE OF PHOSPHATE
AND ARSENATE
353
shake for one half a minute. Continue titrating to a permanent red endpoint. This titration allows calculation of the phosphate or arsenate content. The red solution, containing MgNH4P04. 6Hz0 or MgNH4As04 . 6H20 precipitate, is treated dropwise with 0.02 M EDTA until blue, then, if needed, 2-3 ml additional ethanol and titrated with 0.02-0.1 M barium chloride to a red endpoint. RESULTS
The Tables 1 and 2 show that complex mixtures may be analyzed satisfactorily utilizing this simple method.
TABLE
1
DETERMINATION OF SULFATE IONS IN THE PRESENCEOF CALCIUM AND MAGNESIUM
Present ( mg ) Sulfate
Mg
1 2.040 2.040 2 4.080 3 4.080 4 4.630 5 4.630 6 4.630 7 4.630 8 9B a 4.630 2.640 10 46.56 11 2.045 12 2.045 13 4.630 14 4.630 15 4.630 16 4.630 17 9.260 18 9.260 19B
0.5 5.3 1.0 5.5 2.4 4.8 7.2 9.6 14.4 1.2 12.0 0.5 1.7 2.4 2.4 2.4 2.4 2.4 14.4
No.
a B = Procedure
B.
Ca
8.0 4.0 4.0 8.0 12.0 16.0 20.0 8.0
Found (w) (av)
Diff. (ms)
2.043 1.980 4.147 4.047 4.675 4.646 4.638 4.541 4.723 2.640 46.52 2.035 2.064 4.694 4.665 4.680 4.704 9.201 9.396
+0.003 4.06 +0.067 -0.033 +0.045 +0.016 +0.008 -0.089 $0.093 0.00 a.04 -0.01 +0.019 +0.064 +0.035 +0.05 +0.074 -0.059 t-O.136
SD calculated from 8 measurements 0.02 0.06 0.05 0.02 0.03 0.04 0.024 0.05 0.045 0.03 0.40 0.02 0.01 0.03 0.04 0.04 0.045 0.08 0.26
9.260 9.260 9.260 46.70 46.70 46.70 9.260 9.260 5.280 9.260 9.260 46.70 46.70 46.70 46.70 46.70 46.70 9.266 9.260 9.260 9.260
2oc 21c 22c 23c 24c 25C 26D 27D 28D 29E 30E 31E 32E 33c 34C 35C 38E 37c 38C 39E 40E
4.8 7.2 4.8 14.4 16.8 14.4 14.4 14.4 13.2 4.8 4.8 14.4 14.4 12.0 12.0 12.0 12.0 2.4 2.4 2.4 2.4
Mg 4.0 8.0 8.0 4.0 8.0 8.0 8.0 4.0 4.0 4.0 4.0 8.0 8.0 4.0 4.0 4.0 4.0
Ca
Present (mg)
1.2 1.2 1.2 1.2 2.4 1.2 3.0 1.2 1.2 3.0
Fe 1.5 1.5 1.5 1.5 3.0 1.5 3.0 1.5 1.5 3.0
Al 18.10 36.20 18.10 18.10 36.20 18.10 18.10 18.10 18.10 18.10 -
Phosphate
Qc = Procedure C; D = Procedure D; and E = Procedure E.
Sulfate
No. a
TABLE 2
27.38 68.46 27.38 27.38 27.38 68.46 27.38 27.38
-
Arsenate
-
18.22 18.25 18.20 18.22
-
18.05 36.10 18.00 18.22 36.42 18.20
Phosphate
27.42 68.33 27.30 27.25 27.33 68.33 27.30 27.30
-
Arsenate
Found (a) (av)
9.375 9.398 9.456 46.80 46.92 46.84 9.133 9.216 5.015 9.139 9.216 46.38 47.62 47.76 47.58 47.76 48.02 9.408 9.456 9.454 9.313
Found (a) (av)
DETERMINATION OF SULFATE AND PHOSPHATE (ARSENATE) IN THE PRESENCE OF CALCXJM, MAGNESIUM, ALUMINUM AND FERRIC IONS
to.115 to.138 to.196 to.10 to.22 to.14 -0.127 4.044 4.265 -0.131 -0.044 -0.32 j-0.88 tl.06 to.88 t1.06 t1.32 +O. 148 to.196 to.194 to.052
Diff. (mg)
Sulfate
0.045 0.09 0.07 0.03 0.20 0.50 0.08 0.05 0.08 0.08 0.07 0.30 0.45 0.24 0.22 0.24 0.40 0.09 0.05 0.06 0.05
SD calculated from 8 measurements
I
i
SULFATE
IN PRESENCE
OF PHOSPHATE
AND
ARSENATE
355
ACKNOWLEDGMENTS I wish to thank my colleague,
Miss E. Kardos,
for carrying
out the experiments.
SUMMARY Sulfate ions are titrated with barium chloride in presence of ammonium chloride, ammonia, eriochrome black-T, and magnesium EDTA complex. Alkaline earth interference is avoided with EDTA, and iron and aluminum masked with DCyTA. After sequestration of cations, phosphate and arsenate may be titrated with magnesium chloride. Finally, sulfate titration is carried out in the same solution with barium chloride. REFERENCES 1. EFFENBERGER, M., Chelatometrische Sulfatbestimmung in Wbsern mit hohem Magnesiumgehalt unter Verwendung von Calcein als Indikator. Fortschr. Wawerchem. Ihrer Grenzgeb. 1, 173-176 ( 1964). 2. HAHN, F. L. AND MEYER, H., Massanalytische Bestimmung von Phosphat und Magnesium. Chem. Ber. 60, 975-977 ( 1927). 3. P~~SCHEL, R. AND LASSNER, E., The use of chelatochrome indicators in precipitation titrations. Chemist-Analyst 49, 58-62, 90-94, 120-124 ( 1960); 50, 26-29, 58-62 ( 1961) . 4. STRFBINGER, R. AND Z~MBORY, L., Ein neues Massanalytisches Verfaren zur Bestimmung von Barium-/und Sulfat-ionen. 2. Anal. Chem. 79, 1 ( 1930). 5. SZEKERES, L., Rapid volumetric determination of phosphate, sulphate and calcium amount in mineral raw phosphate and in superphosphate artificialfertilizers. Mugy. Kern. Lapju 19, 321-324 ( 1964). 6. SZEKERES,L. AND B. -POLAR, E., Simultaneous determination of phosphate and sulfate ions in the presence of metal contaminations. J. Agr. Food Chem. 8, 417-419 ( 1960). 7. SZEKERES, L. AND KARDOS, E., Data to the analysis of plantprotecting agents containing arsenate. Mugy. Kern. L&u 18, 617-619 ( 1963). 8. SZEKERES, L. AND KARDOS, E., Data to examination of arsenate containing plant protectors. Kiserl. Kozbmeny., C. Kertesz. 57, 153-160 ( 1964). 9. SZEKERES, L. AND KARDOS, E., Data to the determination of phosphate, arsenate and sulphate ions. Kised. Kozlemeny., A. Novenytermesz. 57, 169-172 (1964). 10. SZEKERES, L. AND KARDOS, E., Titrimetric determination of phosphate, arsenate, and sulfate. Ann. Chim. (Rome) 52, 844-848 ( 1962). 11. SZEKERES, L., KARDOS, E., AND SZEKERES, G. L., Determinazione degli ioni calcio, fosfato e solfato in presenza l’uno dell’altro con particolare riguardo all’analisi dei fosfati grezzi e dei fertilizzanti sintetici al superfosfato. Ann. Chim. (Rome) 53, 1704-1716 (1963). 12. SZEKERES, L., KARDOS, E., AND SZEKERES, G. L., Titrimetric determination of calcium and arsenate in the presence of iron, aluminum, fluoride and sulfate. Chemist-Analyst 53, 4041 ( 1964).
356
SZEXERES
13. SZEKERES, L., KARDOS, E., AND SZEKERES, G. L., Volumetrische
Bestimmung der Calcium/und Phosphationen neben Eisen (III)Aluminumund anderen Ionen. .I. Prukt. Chem. 28, (4R) 113-118 ( 1965). 14. SZEKERES, L., KARDOS, E., AND SZEKERES, G. L., Volumetric determination of calcium and phosphate ions in presence of iron, aluminum, fluoride, and sulfate. Microchem. J. 11, 1-12 ( 1966). 15. SZEKERES, L., KARDOS, E., AND SZEKERES, G. L., Microdetermination of arsenic by a precipitation titration. Microchem. J. 10, 184-193 ( 1966).