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The microdetermination of sulfur in organic compounds containing phosphorus
MICROCHEMICAL
JOURNAL
The
606-608
(1967)
Microdetermination of Compounds Containing R. B.
Parke,
12,
BALODIS,~
Sulfur in Organic Phosphorus
A. COMERFORD, AND C. E. CHILDS
Davis and Co., Research Received
Laboratories, April
Ann
Arbor,
Michigan
7, 1967
INTRODUCTION
The determination of sulfur in phosphorus-containing compounds has always been a problem in organic analysis due to the phosphorus interference, and several procedures have been developed to overcome this (2, 3). The methods employing the oxygen flask combustion and subsequent titration with a barium salt usually lead to high results due to the slightly soluble barium phosphate formed. It is necessary, therefore, to eliminate the phosphate produced in the course of the combustion before an accurate measurementof sulfur can be made. In the present method the phosphate ions are masked with ferric ions, since the latter chelate more readily with phosphate than sulfate ions in an acidic solution, and the excess ferric ions are back-titrated with EDTA (I, 5). The sulfate is titrated in the usual way (4). EXPERIMENTAL Reagents
1. 2. 3. 4. 5. 6. 7.
Aqueous solution of 0.02~ BaCL 0.025~ Disodium ethylene dinitrilotetraacetate. 2H20 (EDTA) . 5y0 sulfosalicyclic acid solution. 0.1% Thorin. 0.0125% Methylene blue. 30% Hydrogen peroxide. Ferric chloride, reagent grade.
1 Present address: Chemical Abstract Ohio.
Service, Ohio State University, 606
Columbus,
MICKODETEKMINATION
OF
607
SULFUK
Proccdurr A 5-7 mg sample is burned in a 300 ml oxygen flask over 10 ml of triple-distilled water containing 7 drops of 30”~ hydrogen peroxide. The solution is transferred to a 100 ml beaker using absolute alcohol (ethanol) to rinse out the flask, and boiled down to 5 ml. The solution is then acidified with 1 drop of 0.1~ H(‘I and buffered with 1 drop of 51~ TABLE. TWI~AI.
.AvAI.~~-I~.\!.
1 Resr!,xx Sulfur
COmpOUMl
found
Sulfur ~.~
calculated
31.57y$ .3 1 .JY
31.49c/,
C,,H,,K.J),PS
9.46 Y56
9.3-l
C,,,H,!,Cl,NO,PS
x.20
s.19
(‘,H,
,O,PS.,-SH,,
Salt
8.16 C,:,H,!,Cl:INO,PS
(Isomer)
x.2;
x.19
8 ..i 1 c,,H,,C1,,~0,Ps
x.27
X.50
8.52 S-henzylthiuronium
chloride
l.j.69
l.i.82
I.<.97 16.03 16.03
sulfosalicylic acid. Enough Fe(‘1, crystals (several mgs) are added to make the solution dark red and the excess ferric ions are back-titrated with 0.025~ EDTA (.5-.8 ml) until the solution becomes pale yellow. The solution is then transferred to a 30 ml titration cell using absolute alcohol as the rinse with a final volume of 30 ml. Titration is carried out on an illuminated stand equipped with a masking plate (A. H. Thomas C-0.) using .02~ Ra(‘1, as the titrant with 2 drops of thorin and 4 drops of methylene blue as the combined indicator. The end point is a color change from green to grey. Overtitration produces a gey pink.
The results of a group
The main advantage phosphorus is required.
of known
compounds
are shown in Table
1
of this procedure is that no special separation of As the results indicate, the method is quite accurate
608
BALODIS,
COMERFORD,
AND
CHILDS
and simple, but there may be some difficulty in seeing the final end-point. With a little practice, however, it is readily distinguishable. An illuminated stand and masking plate are necessary to concentrate the light on the solution, and a colorless titration cell is mandatory. The titration was not tried on a regular titration stand but might be possible if a good light source were used. SUMMARY An oxygen-flask procedure is described for the microdetermination phosphorus-containing compounds. The phcsphate formed is masked and the sulfate is titrated directly with barium chloride.
of with
sulfur in ferric ions
REFERENCES 1. 2. 3. 4. 5.
CHENC, K. L., Increasing selectivity of analytical reactions by masking. Bnal. Chem. 33, 783-790 (1961). FRITZ, J. S., AND YAMAMURA, S. S., Rapid microtitration of sulfate. Anal. Chem. 27, 1461-1464 (1955). JASELSKIS, B., AND VAS, S. F., Titrimetric determination of semimicro amounts of sulfate in the presence of phosphate. Anal. Chem. 36, 1965-1967 (1964). THOMAS, ARTHUR H. COMPANY, Determination of Sulfate, Technological Service Bulletin 6470E-G, 5 (1958). VAN NIEUWENBURC, C. J,, ASD \‘AN LIGTEN, J. W. L., “Qualitative Chemical Microanalysis,” pp. 120-121, Elsevier, Amsterdam, 1963.
JOURNAL
The
606-608
(1967)
Microdetermination of Compounds Containing R. B.
Parke,
12,
BALODIS,~
Sulfur in Organic Phosphorus
A. COMERFORD, AND C. E. CHILDS
Davis and Co., Research Received
Laboratories, April
Ann
Arbor,
Michigan
7, 1967
INTRODUCTION
The determination of sulfur in phosphorus-containing compounds has always been a problem in organic analysis due to the phosphorus interference, and several procedures have been developed to overcome this (2, 3). The methods employing the oxygen flask combustion and subsequent titration with a barium salt usually lead to high results due to the slightly soluble barium phosphate formed. It is necessary, therefore, to eliminate the phosphate produced in the course of the combustion before an accurate measurementof sulfur can be made. In the present method the phosphate ions are masked with ferric ions, since the latter chelate more readily with phosphate than sulfate ions in an acidic solution, and the excess ferric ions are back-titrated with EDTA (I, 5). The sulfate is titrated in the usual way (4). EXPERIMENTAL Reagents
1. 2. 3. 4. 5. 6. 7.
Aqueous solution of 0.02~ BaCL 0.025~ Disodium ethylene dinitrilotetraacetate. 2H20 (EDTA) . 5y0 sulfosalicyclic acid solution. 0.1% Thorin. 0.0125% Methylene blue. 30% Hydrogen peroxide. Ferric chloride, reagent grade.
1 Present address: Chemical Abstract Ohio.
Service, Ohio State University, 606
Columbus,
MICKODETEKMINATION
OF
607
SULFUK
Proccdurr A 5-7 mg sample is burned in a 300 ml oxygen flask over 10 ml of triple-distilled water containing 7 drops of 30”~ hydrogen peroxide. The solution is transferred to a 100 ml beaker using absolute alcohol (ethanol) to rinse out the flask, and boiled down to 5 ml. The solution is then acidified with 1 drop of 0.1~ H(‘I and buffered with 1 drop of 51~ TABLE. TWI~AI.
.AvAI.~~-I~.\!.
1 Resr!,xx Sulfur
COmpOUMl
found
Sulfur ~.~
calculated
31.57y$ .3 1 .JY
31.49c/,
C,,H,,K.J),PS
9.46 Y56
9.3-l
C,,,H,!,Cl,NO,PS
x.20
s.19
(‘,H,
,O,PS.,-SH,,
Salt
8.16 C,:,H,!,Cl:INO,PS
(Isomer)
x.2;
x.19
8 ..i 1 c,,H,,C1,,~0,Ps
x.27
X.50
8.52 S-henzylthiuronium
chloride
l.j.69
l.i.82
I.<.97 16.03 16.03
sulfosalicylic acid. Enough Fe(‘1, crystals (several mgs) are added to make the solution dark red and the excess ferric ions are back-titrated with 0.025~ EDTA (.5-.8 ml) until the solution becomes pale yellow. The solution is then transferred to a 30 ml titration cell using absolute alcohol as the rinse with a final volume of 30 ml. Titration is carried out on an illuminated stand equipped with a masking plate (A. H. Thomas C-0.) using .02~ Ra(‘1, as the titrant with 2 drops of thorin and 4 drops of methylene blue as the combined indicator. The end point is a color change from green to grey. Overtitration produces a gey pink.
The results of a group
The main advantage phosphorus is required.
of known
compounds
are shown in Table
1
of this procedure is that no special separation of As the results indicate, the method is quite accurate
608
BALODIS,
COMERFORD,
AND
CHILDS
and simple, but there may be some difficulty in seeing the final end-point. With a little practice, however, it is readily distinguishable. An illuminated stand and masking plate are necessary to concentrate the light on the solution, and a colorless titration cell is mandatory. The titration was not tried on a regular titration stand but might be possible if a good light source were used. SUMMARY An oxygen-flask procedure is described for the microdetermination phosphorus-containing compounds. The phcsphate formed is masked and the sulfate is titrated directly with barium chloride.
of with
sulfur in ferric ions
REFERENCES 1. 2. 3. 4. 5.
CHENC, K. L., Increasing selectivity of analytical reactions by masking. Bnal. Chem. 33, 783-790 (1961). FRITZ, J. S., AND YAMAMURA, S. S., Rapid microtitration of sulfate. Anal. Chem. 27, 1461-1464 (1955). JASELSKIS, B., AND VAS, S. F., Titrimetric determination of semimicro amounts of sulfate in the presence of phosphate. Anal. Chem. 36, 1965-1967 (1964). THOMAS, ARTHUR H. COMPANY, Determination of Sulfate, Technological Service Bulletin 6470E-G, 5 (1958). VAN NIEUWENBURC, C. J,, ASD \‘AN LIGTEN, J. W. L., “Qualitative Chemical Microanalysis,” pp. 120-121, Elsevier, Amsterdam, 1963.