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Spectrophotometric determination of lodate, periodate, and persulfate in aqueous solution
MICROCHEMICAL
JOURNAL
29, 87-91 (1984)
Spectrophotometric Determination of lodate, Periodate, and Persulfate in Aqueous Solution S. Depurtment
A. RAHIM AND WADALA
of Chemistry,
College
of Science,
A. BASHIR
Universiry qf Mosd,
Mosul,
Irtry
Received December 3 I. 1981
INTRODUCTION The methods available for the spectrophotometric determination of the iodate, periodate, and persulfate ions are not complete satisfactory (I3, 6) for they need a rigorous control of the experimental conditions to ensure quantitative determination of the ions. Therefore, we have had the task to develop analytical procedures suitable for the trace determination of the intended ions. The following described methods are base on the oxidation of an acidic ferrous ion solution, by the ions under study, and subsequent reaction with ferrocyanide solution to form the intense Prussian blue color. This idea had previously been utilized for the spectrophotometric determination of chromium(W) (as dichromate) ion (4). The various experimental parameters related to an affecting the color reaction have been thoroughly investigated and optimized as to perhaps fill the required characteristics by the analytical chemist. MATERIALS
AND METHODS
Reagents All chemicals used were of analytical grade. Standard iodate solution (lOOyg/m/). Potassium iodate (0.1224 g) was dissolved in distilled water and the volume was completed to 1000 ml with distilled water. Standard periodate solution (100 &ml). Potassium periodate (0.1204 g) was dissolved in distilled water and the volume was completed to 1000 ml with distilled water. Standard persuf$ate solution (100 pglmf). Sodium persulfate (0.1239 g) was dissolved in distilled water and the volume was made to 1000 ml with distilled water. Potassium ferrocyanide solution (2 x 1O-3 M). The required weight of the trihydrate salt was dissolved in distilled water and the volume was diluted to 250 ml with distilled water. 87 0026-265X184 $1.50 Copyright e 1984 by Academic Press, Inc. All right\ of reproduction in any form reserved.
88
RAHIM
AND BASHIR
Ferrous ion solution (2 x fOd3M). The required weight of ammonium ferrous sulfate hexahydrate was dissolved in 1 N H2S04 and the volume was made up to 250 ml with 1 N H2S04. EDTA solution (2 x lo--’ M). Prepared from the dihydrate disodium salt in distilled water. Gelatin solution (0.1%). Gelatin (0.1 g) was dissolved in distilled water and the volume was completed to 100 ml with distilled water. This solution was prepared fresh daily. Apparatus
All spectrophotometric measurements were performed matched optical glass cells on a Bausch & Lomb Spectronic photometer.
with l-cm 20 spectro-
Procedure Determination of iodate. To a series of 25ml volumetric flasks, an aliquot of the aqueous sample solution containing 15-300 kg of iodate was transferred; 3 ml of 2 x lop3 M ferrocyanide solution, 2.5 ml of 0.1% gelatin solution, and 2.5 ml of 2 x 1O-3 M ferrous solution were added and the volume was made up to the mark with 1 N HZS04 solution. The reaction mixture was shaken and set aside for 70 min for complete color development. Then the absorbances were measured against a reagent blank prepared in the same manner but containing no iodate, within another 30 min, at 635 nm using l-cm glass cells. A straightline standard curve passing through the origin was obtained, indicating the Beer’s law was followed over the concentration range 15-300 ug of iodate in a final volume of 25 ml, i.e., 0.6-12 ppm. The apparent molar absorptivity and Sandell index of sensitivity (5), calculated from Beer’s law data, were 2.2 x lo4 liters mol-’ cm- ] and 0.0079 kg cm p2, respectively. Determination of periodate. To a series of 25-ml volumetric flasks, 4 ml of 0.1% gelatin solution, 2 ml of 2 x 10e3 M ferrocyanide solution, an aliquot of aqueous sample solution containing 5-60 pg periodate, and 3 ml of 2 x lop3 M ferrous solution were transferred and the volumes were diluted to the mark with 1 N H2SO4 solution. The reaction mixture was allowed to stand for 1 hr, and the absorbances were measured, within 5 min, against the reagent blank, at 640 nm using l-cm glass cells. A linear curve passing through the origin was obtained, showing that Beer’s law ruled over the concentration range 0.2-2.4 ppm of periodate. The conditional molar absorptivity and sensitivity index (5) were 5.1 x lo4 liters mol- * cm-’ and 0.0037 kg cme2, respectively. Determination of persufate. To a series of 25-ml volumetric flasks, 5 ml of 0.1% gelatin solution, 1.5 ml of 2 x toe3 M ferrocyanide solution, an aliquot of aqueous sample solution containing 50- 1000 pg persulfate,
SPECTROPHOTOMETRIC
DETERMINATION
IN AQUEOUS
SOLUTION
89
1.5 ml of 2 x lop3 A4 ferrous solution, and 3.5 ml of 1 x 10e3 A4 EDTA solution were introduced and the contents were diluted to the mark with 1 N HISO solution. After 35 min standing time, the absorbances were measured, within another I5 min, against the reagent blank at 630 nm with l-cm cells. Beer’s law ruled over the range 2-40 ppm of persulfate, with a molar absorptivity of 8.1 x IO3 liters mol-’ cm-’ and sensitivity index (5) of 0.0237 p-g cm-?. RESULTS
AND DISCUSSION
For the preliminary experiments, 100 p_g of each ion was taken and final volumes were 25 ml. The absorption spectrum of each anoin, after reaction, showed a single broad band with maximum absorbance at 635 nm (for iodate), 640 nm (for periodate), and 630 nm (for persulfate). At these wavelengths, the corresponding blanks showed a flat absorption. Therefore, all subsequent measurements were performed under the mentioned wavelength of the anion after the reaction. Optimization
of Conditions
Table 1, the result of an extensive study, shows the optimum concentration of each reagent for every ion. The effect of EDTA and gelatin on the color reaction can be found elsewhere. (4). Order of Addition of Reagents For optimal absorbance, one should follow the order given in the procedure, otherwise, a loss of sensitivity takes place. Development
Time and Stability Period
In spite of the rapid development of the blue color, it was necessary to stand for the given interval (see Procedure) to attain maximum absorTABLE 1 OPTIMUM CONCENTRATIONOF RE.+.GENTS
ml Reagent Ferrocyanide (2 x 10m3M) solution Ferrous (2 x 10e3 b4) solution EDTA(I x IO-‘M) solution Gelatin (0.1%) solution
bdate
Periodate
2.8-3.2
1.5-2.0
I-1.8
2.0-2.5
2.8-3.2
I-2.0
-
3.5-4.5
3-4.0 4.5-5.5
1.5-3.0
Persulfate
90
RAHIM AND BASHIR
ACCURACY AND
TABLE 2 PRECIUONOF THE METHODS
Amount taken ((Lg)
Accuracy WI%)”
Precision (RSD%)b
I.5 100 180
+5.5 0.0
+ 1.6
0.86 0.77 0.28
Periodate
5 20 60
+3.0 -0.7 0.0
0.96 0.44 0.14
Persulfate
50 600 1000
+4.5 -3.1 -0.5
0.56 0.31 0.08
Anion Iodate
a Relative error. * Relative standard deviation.
bance. Trials (4) made to further increase the stability period were not successful. Accuracy,
Precision, and Sensitivity
After construction of the standard curve, the accuracy and precision (five replicates) of the described methods were checked. The results are shown in Table 2. The sensitivity of the methods (5) (expressed as the amount of the ion corresponding to an absorbance of 0.001) in a l-cm cell at the wavelength given (under Procedure) was 0.0079 (for iodate), 0.0037 (for periodate), and 0.0237 (for persulfate) kg crnp2, The possible interfering effect caused by some cations can simply be eliminated using cation resin exchanger (H-form). By this method, the cation(s) containing the anion sample solution has to be percolated through the resin; thus, the cation(s) is trapped by exchanging the H-ions of the resin; the anion under test has no tendency for the resin and therefore, is excluded from the determination by the recommended procedure. SUMMARY Spectrophotometric methods for the trace determination of iodate, periodate, and persulfate have been worked out. They are based on the oxidation of ferrous ion, by the anions, in the presence of ferrocyanide to give an intense Prussian blue color. The methods do not resort to either solvent extraction or temperature control.
REFERENCES I. Bruno, P., Caselli, M., and Fragale, Ultraviolet spectrophotometric iodides and iodates. Andyst
102, 966-969 (1977).
determination
of
SPECTROPHOTOMETRIC
DETERMINATION
IN AQUEOUS
SOLUTION
91
2. Escarrilla, A. M., Maloney, P. F., and Maloney, P. M., Calorimetric determination of periodate with benzhydrazide. And. Chim. Actu 45, 199-201 (1969) u .,nrl P..,C.t..,..L,+,,,+,;” Arlarhi.I., K K ? --Y..I’( unnna 9“.( l.yuI “. . ..) KcaLehi ..U.1.,.II, IX., v,,lii lURl, I.., c&n,” TQ!J;..m ICLRIUIC‘) $-. , “y~~rr”lJ,r”r”,r,rr,,~ determination of periodate with phenolphthalein. Anal. Chim. Acfa 78, 492-494 (1975). 4. Rahim, S. A., Abdulahad, H., and Milad, N. E., Microdetermination of chromium: Dichromate ion. J. lndiun Chem. Sot. 52, 853-854 (1975). 5. Sandell, E. B., “Calorimetric Determination of Traces of Metals.” 3rd ed.. pp. X3-84. Interscience, New York, 1959. 6. Truesdale, V. W., and Smith . C. J., Comparative study of three methods for determination of iodate in sea-water. Mar. Chcm. 7, 133-139 (1979).
JOURNAL
29, 87-91 (1984)
Spectrophotometric Determination of lodate, Periodate, and Persulfate in Aqueous Solution S. Depurtment
A. RAHIM AND WADALA
of Chemistry,
College
of Science,
A. BASHIR
Universiry qf Mosd,
Mosul,
Irtry
Received December 3 I. 1981
INTRODUCTION The methods available for the spectrophotometric determination of the iodate, periodate, and persulfate ions are not complete satisfactory (I3, 6) for they need a rigorous control of the experimental conditions to ensure quantitative determination of the ions. Therefore, we have had the task to develop analytical procedures suitable for the trace determination of the intended ions. The following described methods are base on the oxidation of an acidic ferrous ion solution, by the ions under study, and subsequent reaction with ferrocyanide solution to form the intense Prussian blue color. This idea had previously been utilized for the spectrophotometric determination of chromium(W) (as dichromate) ion (4). The various experimental parameters related to an affecting the color reaction have been thoroughly investigated and optimized as to perhaps fill the required characteristics by the analytical chemist. MATERIALS
AND METHODS
Reagents All chemicals used were of analytical grade. Standard iodate solution (lOOyg/m/). Potassium iodate (0.1224 g) was dissolved in distilled water and the volume was completed to 1000 ml with distilled water. Standard periodate solution (100 &ml). Potassium periodate (0.1204 g) was dissolved in distilled water and the volume was completed to 1000 ml with distilled water. Standard persuf$ate solution (100 pglmf). Sodium persulfate (0.1239 g) was dissolved in distilled water and the volume was made to 1000 ml with distilled water. Potassium ferrocyanide solution (2 x 1O-3 M). The required weight of the trihydrate salt was dissolved in distilled water and the volume was diluted to 250 ml with distilled water. 87 0026-265X184 $1.50 Copyright e 1984 by Academic Press, Inc. All right\ of reproduction in any form reserved.
88
RAHIM
AND BASHIR
Ferrous ion solution (2 x fOd3M). The required weight of ammonium ferrous sulfate hexahydrate was dissolved in 1 N H2S04 and the volume was made up to 250 ml with 1 N H2S04. EDTA solution (2 x lo--’ M). Prepared from the dihydrate disodium salt in distilled water. Gelatin solution (0.1%). Gelatin (0.1 g) was dissolved in distilled water and the volume was completed to 100 ml with distilled water. This solution was prepared fresh daily. Apparatus
All spectrophotometric measurements were performed matched optical glass cells on a Bausch & Lomb Spectronic photometer.
with l-cm 20 spectro-
Procedure Determination of iodate. To a series of 25ml volumetric flasks, an aliquot of the aqueous sample solution containing 15-300 kg of iodate was transferred; 3 ml of 2 x lop3 M ferrocyanide solution, 2.5 ml of 0.1% gelatin solution, and 2.5 ml of 2 x 1O-3 M ferrous solution were added and the volume was made up to the mark with 1 N HZS04 solution. The reaction mixture was shaken and set aside for 70 min for complete color development. Then the absorbances were measured against a reagent blank prepared in the same manner but containing no iodate, within another 30 min, at 635 nm using l-cm glass cells. A straightline standard curve passing through the origin was obtained, indicating the Beer’s law was followed over the concentration range 15-300 ug of iodate in a final volume of 25 ml, i.e., 0.6-12 ppm. The apparent molar absorptivity and Sandell index of sensitivity (5), calculated from Beer’s law data, were 2.2 x lo4 liters mol-’ cm- ] and 0.0079 kg cm p2, respectively. Determination of periodate. To a series of 25-ml volumetric flasks, 4 ml of 0.1% gelatin solution, 2 ml of 2 x 10e3 M ferrocyanide solution, an aliquot of aqueous sample solution containing 5-60 pg periodate, and 3 ml of 2 x lop3 M ferrous solution were transferred and the volumes were diluted to the mark with 1 N H2SO4 solution. The reaction mixture was allowed to stand for 1 hr, and the absorbances were measured, within 5 min, against the reagent blank, at 640 nm using l-cm glass cells. A linear curve passing through the origin was obtained, showing that Beer’s law ruled over the concentration range 0.2-2.4 ppm of periodate. The conditional molar absorptivity and sensitivity index (5) were 5.1 x lo4 liters mol- * cm-’ and 0.0037 kg cme2, respectively. Determination of persufate. To a series of 25-ml volumetric flasks, 5 ml of 0.1% gelatin solution, 1.5 ml of 2 x toe3 M ferrocyanide solution, an aliquot of aqueous sample solution containing 50- 1000 pg persulfate,
SPECTROPHOTOMETRIC
DETERMINATION
IN AQUEOUS
SOLUTION
89
1.5 ml of 2 x lop3 A4 ferrous solution, and 3.5 ml of 1 x 10e3 A4 EDTA solution were introduced and the contents were diluted to the mark with 1 N HISO solution. After 35 min standing time, the absorbances were measured, within another I5 min, against the reagent blank at 630 nm with l-cm cells. Beer’s law ruled over the range 2-40 ppm of persulfate, with a molar absorptivity of 8.1 x IO3 liters mol-’ cm-’ and sensitivity index (5) of 0.0237 p-g cm-?. RESULTS
AND DISCUSSION
For the preliminary experiments, 100 p_g of each ion was taken and final volumes were 25 ml. The absorption spectrum of each anoin, after reaction, showed a single broad band with maximum absorbance at 635 nm (for iodate), 640 nm (for periodate), and 630 nm (for persulfate). At these wavelengths, the corresponding blanks showed a flat absorption. Therefore, all subsequent measurements were performed under the mentioned wavelength of the anion after the reaction. Optimization
of Conditions
Table 1, the result of an extensive study, shows the optimum concentration of each reagent for every ion. The effect of EDTA and gelatin on the color reaction can be found elsewhere. (4). Order of Addition of Reagents For optimal absorbance, one should follow the order given in the procedure, otherwise, a loss of sensitivity takes place. Development
Time and Stability Period
In spite of the rapid development of the blue color, it was necessary to stand for the given interval (see Procedure) to attain maximum absorTABLE 1 OPTIMUM CONCENTRATIONOF RE.+.GENTS
ml Reagent Ferrocyanide (2 x 10m3M) solution Ferrous (2 x 10e3 b4) solution EDTA(I x IO-‘M) solution Gelatin (0.1%) solution
bdate
Periodate
2.8-3.2
1.5-2.0
I-1.8
2.0-2.5
2.8-3.2
I-2.0
-
3.5-4.5
3-4.0 4.5-5.5
1.5-3.0
Persulfate
90
RAHIM AND BASHIR
ACCURACY AND
TABLE 2 PRECIUONOF THE METHODS
Amount taken ((Lg)
Accuracy WI%)”
Precision (RSD%)b
I.5 100 180
+5.5 0.0
+ 1.6
0.86 0.77 0.28
Periodate
5 20 60
+3.0 -0.7 0.0
0.96 0.44 0.14
Persulfate
50 600 1000
+4.5 -3.1 -0.5
0.56 0.31 0.08
Anion Iodate
a Relative error. * Relative standard deviation.
bance. Trials (4) made to further increase the stability period were not successful. Accuracy,
Precision, and Sensitivity
After construction of the standard curve, the accuracy and precision (five replicates) of the described methods were checked. The results are shown in Table 2. The sensitivity of the methods (5) (expressed as the amount of the ion corresponding to an absorbance of 0.001) in a l-cm cell at the wavelength given (under Procedure) was 0.0079 (for iodate), 0.0037 (for periodate), and 0.0237 (for persulfate) kg crnp2, The possible interfering effect caused by some cations can simply be eliminated using cation resin exchanger (H-form). By this method, the cation(s) containing the anion sample solution has to be percolated through the resin; thus, the cation(s) is trapped by exchanging the H-ions of the resin; the anion under test has no tendency for the resin and therefore, is excluded from the determination by the recommended procedure. SUMMARY Spectrophotometric methods for the trace determination of iodate, periodate, and persulfate have been worked out. They are based on the oxidation of ferrous ion, by the anions, in the presence of ferrocyanide to give an intense Prussian blue color. The methods do not resort to either solvent extraction or temperature control.
REFERENCES I. Bruno, P., Caselli, M., and Fragale, Ultraviolet spectrophotometric iodides and iodates. Andyst
102, 966-969 (1977).
determination
of
SPECTROPHOTOMETRIC
DETERMINATION
IN AQUEOUS
SOLUTION
91
2. Escarrilla, A. M., Maloney, P. F., and Maloney, P. M., Calorimetric determination of periodate with benzhydrazide. And. Chim. Actu 45, 199-201 (1969) u .,nrl P..,C.t..,..L,+,,,+,;” Arlarhi.I., K K ? --Y..I’( unnna 9“.( l.yuI “. . ..) KcaLehi ..U.1.,.II, IX., v,,lii lURl, I.., c&n,” TQ!J;..m ICLRIUIC‘) $-. , “y~~rr”lJ,r”r”,r,rr,,~ determination of periodate with phenolphthalein. Anal. Chim. Acfa 78, 492-494 (1975). 4. Rahim, S. A., Abdulahad, H., and Milad, N. E., Microdetermination of chromium: Dichromate ion. J. lndiun Chem. Sot. 52, 853-854 (1975). 5. Sandell, E. B., “Calorimetric Determination of Traces of Metals.” 3rd ed.. pp. X3-84. Interscience, New York, 1959. 6. Truesdale, V. W., and Smith . C. J., Comparative study of three methods for determination of iodate in sea-water. Mar. Chcm. 7, 133-139 (1979).