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A highly sensitive spectrophotometric determination of beryllium with chromal blue G and cetyltrimethylammonium chloride
MICROCHEMICAL
JOURNAL
21, 438-444
(1976)
A Highly Sensitive Spectrophotometric Determination of Beryllium with Chromal Blue G and Cetyltrimethylammonium Chloride KATSUYA
UESUCI
MITSUO
AND
MIYAWAKI’
Laboratory of Chemistry, Himeji Institute of Technology, Shosha, Himeji, Japan Received
June
7, 1976
INTRODUCTION
Recently, the methods of spectrophotometric determination of metal ions based on the complex-formation in the presence of a quaternary ammonium salt have been suggested (1,2, 7, 12). Continuing the study on the application of ternary complex in the spectrophotometric determination of metals, it was found that submicrogram amounts of beryllium react very sensitively with chromal blue G (CBG) in the presence of a quaternary ammonium salt. Chromal blue G (sodium-2”-chloro-4”-nitro-4’hydroxy-3, 3’-dimethylfuchsone-5, S-dicarboxylate, color index 43835), a triphenylmethane dye, has been used as a spectrophotometric reagent for scandium (9)) beryllium (IO), and palladium (22). This paper describes a highly sensitive method for the determination of beryllium based on the formation of a colored complex with CBG in the presence of cetyltrimethylammonium chloride (CTMA). Several conditions under which microgram amounts of beryllium can be determined, the influences of coexisting ions, and the complex formation are discussed. EXPERIMENTAL
Reagents and Apparatus Standard beryllium solution. A standard stock solution (100 pg Be/ml) was prepared by dissolving 1.964 g of beryllium sulfate tetrahydrate in distilled water, adding small amounts of hydrochloric acid to prevent possible hydrolysis, and diluting the solution to 1 liter. This standard stock solution was diluted further as required. CBG solution. The CBG (Geigy Chemicals, New York) was purified by recrystallization from ethanol before use, and then 0.1 g of it was dissolved in 100 ml of distilled water. CTMA solution. The CTMA solution (3.0 x 1O-3 M/liter) was prepared * Present
address:
Kobe
Technical
College,
Tarumi, 438
Copyright All rights
@ 1976 by Academic Press. Inc. of reproduction in any form reserved.
Kobe,
Japan
DETERMINATION
by dissolving Buffer
439
OF BERYLLIUM
0.960 g of it in 1 liter of distilled
water.
solution (pH 5.5). A buffer solution of pH 5.5 was prepared by a 0.2 M acetic acid solution and a 0.2 M sodium acetate solution.
mixing All other chemicals used were analytical reagent grade. All absorbance measurements were made with a Hitachi automatic recording digital spectrophotometer, model 624, in 1 .OO-cm matched quartz cells. The pH measurements were carried out with a Toa Electronics, Ltd., pH meter, model HM-6A. The Standard
Procedure
for Beryllium
Determination
Transfer the sample solution containing 0.3-3 pg of beryllium to a 2%ml volumetric flask, and add 1 ml of the CBG solution, 2.5 ml of the CTMA solution, and then 5 ml of the acetate buffer solution. After diluting to the mark with distilled water, mix, let the color develop for 20 min, and measure the absorbance of the solution at 626 nm using a reagent blank as a reference. RESULTS
AND DISCUSSION
Absorption spectra. The absorption spectra of CBG and its beryllium complex are shown in Fig. 1. Curves A and B show the absorption spectra of CBG and its beryllium complex at pH 5.5, respectively, while curves C and D show the effect of the presence of CTMA to these solutions at pH 5.5. The presence of CTMA in the beryllium complex produces a somewhat bathochromic shift in the absorption maximum (610 to 626 nm) and
400 Wavelength,
500
600
700
nm
FIG. 1. Absorption spectra of CBG and its beryllium complex (pH 5.5). (A) Reagent blank of (B), reference: water. (B) Be-CBG complex (Be 6.67 x IO-” M, CBG 8.64 X 1OP M), reference: reagent blank. (C) Reagent blank of(D), reference: water. (D) BeXBG complex (Be 6.67 x lO-6 M, CBG 8.64 x 1O-5 M, CTMA 3.0 x lO-4 M), reference: reagent blank.
440
UESUGI
AND
MIYAWAKI
increases greatly the absorbance of the complex. In order to observe the spectral changes on varying pH, absorption curves for the beryllium complex were prepared at different pH values (Fig. 2). Between pH 5.0 and 6.2, the curves are of identical shape, with one absorption maximum at 626 nm. Below pH 4.6, the maximum absorption shifts toward a shorter wavelength. Effect ufpH on color development. The effect of the pH on the color development of the beryllium complex was examined by measuring the absorbance of a colored solution at 626 nm. The results are shown in Fig. 3, from which it can be seen that maximum intensity can be obtained in the pH range from 5.3 to 6.0. An acetic acid-acetate buffer solution, pH 5.5, was found to be satisfactory for this purpose. Effect of CBG concentration. The effect of variable concentration of CBG on the color development was examined by measuring the absorbance at 626 nm on solutions containing constant concentrations of beryllium and CTMA and varying amounts of CBG. Addition of 1 ml of a 0.1% CBG solution sufficed for less than 0.12 ppm of beryllium. This concentration represents a 6.5-fold molar excess of CBG over the maximum concentration of beryllium determination under the given conditions. Effect ofCTMA concentration. The effect of changes in the concentration of CTMA on the absorbance of beryllium complex was determined by measuring the absorbance. The maximum absorbance can be obtained over the range (2.5-3.3) x lo-* M of CTMA. The optimum amount of CTMA was 2.5 ml of a 3 x 1O-3 M CTMA solution in a final volume of 25 ml.
4
0.6 -
500
600 Wavelength.
FIG. 2. Absorption spectraofberylliumcomplex x IO-jM, CTMA 3.0 x 1O-4 M, reference:
reagent
i
nm at various pH. Be 6.67 x 10-6M, CBG 8.64 blank; pH: (1) 3.8, (2) 4.0, (3) 4.6, (4) 5.3.
DETERMINATION
OF
441
BERYLLIUM
Effect of time. The color of the beryllium complex developed gradually at room temperature; the full color was obtained in 20 min after preparation and then remained almost constant for at least 2 hr. Calibration CUYW, sensitivity, and precision. Calibration curves for the beryllium determination were prepared by the standard procedure. Beer’s law was obeyed over the range 0.012-o. 12 ppm of beryllium. The molar absorptivity was 9.38 x 104at 626 nm, and the spectrophotometric sensitivity was estimated to be 9.6 x 1O-5 pg Be cm-2, corresponding to logZ,,/Z = 0.001. The present method is very sensitive. Its sensitivity is much greater than that of the methods using chromal blue G (without CTMA, molar absorpitivity = 3.1 x 104) (ZO), Eriochrome brilliant violet B (II), aluminon (6), Eriochrome cyanine R (4)) and chromazurol S (8). A standard solution containing 1.5 pug of beryllium was analyzed 10 times by the standard procedure. The average absorbance was 0.625, with a standard deviation of 0.004 absorbance unit and a relative error of t 1.1%. Effect offoreign ions. The influence of foreign ions on the determination of beryllium was ascertained by the standard procedure. The most commonly encountered ions were added individually to a solution containing 1.5 ,ug of beryllium. The following metal ions did not interfere up to loo-fold weight excess: barium(II), calcium(II), cadmium(II),
_
o-
2
‘CA --Qx k --o-+--a I I I I
0
4 FIG. 3. Effect of pH. (1) Be-CBG 3.0 x IO-* M), reference: reagent
5
6
7
I 8
complex (Be 6.08 x 1OW M, CBG 8.64 x 10-5M, blank. (2) Reagent blank, reference: water.
CTMA
442
UESUGI
AND
MIYAWAKI
cobalt(II), lead(II), magnesium(II), manganese(II), mercury(II), nickel(II), strontium(II), tin(II), and zinc(I1). Aluminum(III), scandium(III), copper( iron(III), palladium(II), yttrium(III), and rare earth elements interfere seriously. EDTA was investigated as a masking agent for the more seriously offending ions. Scandium(III), copper( palladium(II), yttrium(III), and rare earth elements were effectively masked by EDTA and can be tolerated without further separation. However, more than 100 pg of aluminum and iron(II1) were not completely screened out by EDTA. In the presence of 50-fold weight excess of aluminum(II1) or iron(II1) 1.5 pg of beryllium were determined within the error of +-3% when EDTA is used as a masking agent. The optimum amount of EDTA used for masking these interfering ions was 1 ml of a 0.1 M EDTA solution. Chloride, sulfate, acetate, and nitrate were without effect even in large amounts, but fluoride, citrate, and tartrate prevent the formation of the beryllium complex. Complexfovmation. The method of the continuous variations (5) was employed to establish the molar ratio of the beryllium complex in the presence of CTMA. Figure 4 shows that a 1:2 complex formed between beryllium and CBG. These results were confirmed by the mole ratio method of Yoe and Jones (13). The formation constant was calculated from the curves obtained by the continuous variation method. As the mole ratio of the beryllium-CBG 0.8 I-
- 0
0.2
0.4
l3el/(CBeJ 4. Continuous variation method. [CTMA] A4 (pH 5.5). FIG.
0.6
OS
-t KBGJ) = 3.0 X 10m4M, [Be] + [CBG] = 4.0 X 1OF
DETERMINATION
complex
OF
BERYLLIUM
443
is 1:2, the reaction can be expressed as: Be + 2CBG e Be (CBG)*.
The formation constant, K, was estimated from the curves obtained by the continuous variation method on the basis of the following relationships (3, 12): K = C (1 - a)/(&)
(2&)2
where C is the total concentration of the complex in moles/per liter (assuming no dissociation), where (Yis the degree of dissociation, where E, is the maximum extinction of the complex when all the beryllium is present in the form of the complex, and where& is the actual absorbance of the complex. The formation constant at pH 5.5 and 25°C was estimated to be 4.6 x lOlo. SUMMARY Chromal blue G in the presence of cetyltrimethylammonium chloride is proposed for the spectrophotometric determination of microgram amounts of beryllium. The sensitivity of color reaction between beryllium and chromal blue Cl has been greatly increased by the sensitizing action of cetyltrimethylammonium chloride (ecZ6“,,, = 93,000). Beer’s law is obeyed over the range 0.012Jl. 12 ppm of beryllium. Full color development occurs in 20 min at pH 5.5 and at 626 nm. The mole ratio of beryllium and chromal blue G in the complex is estimated to be 1:2. The proposed method is very sensitive and selective for determination of beryllium when EDTA is used as a masking agent.
REFERENCES I. Bailey, B. W., Chester, .I. E., Dagnall, R. M., and West, T. S., Analytical applications of ternary complexes-V. Tu/anfa 15, 1359-1369 (1968). 2. Dagnall, R. M., West, T. S., and Young, P., The catechol violet colour reaction for tin(lV) sensitised by cetyltrimethylammonium bromide. Analyst 92, 27-30 (1967). 3. Harvey, A. E., and Manning, D. L., Spectrophotometric methods ofestablishing empirical formulas of colored complexes in solution. J. Amer. Chem. Sot. 72, 4488-4493 (1950). 4. Hill, U. T., Photometric determination of beryllium. Anal. Chem. 30, 521-524 (1958). 5. Job, P., Formation and stability of inorganic complexes in solution. Ann. Chim. 9,113-203 (1928). 6. Kosel, G. E., and Neuman, W. F., Color reaction between beryllium and aurin tricarboxylic acid. Anal. Chem. 22, 936-939 (1950). 7. Leong, C. L., Spectrophotometric determination of uranium(V1) with chromazurol S and cetylpyridinium bromide. Anal. Chem. 45, 201-203 (1973). 8. Silverman, L., and Shideler M. E., Spectrophotometric determination of beryllium and fluoride using chrome azurol S. Anal. Chem. 31, 152-155 (1959). 9. Uesugi, K., The spectrophotometric determination of scandium with chromal blue G. Bull. Chem. Sot. Jup. 42, 2051-2054 (1969). IO. Uesugi, K., The spectrophotometric determination of beryllium with chromal blue G. Bull. Chem. Sot. Jap. 42, 2998-3000 (1969).
444
UESUGI
AND
MIYAWAKI
Uesugi, K., The spectrophotometric determination of beryllium with eriochrome brilliant violet B. Anal. Chim. Acta 49, 89-95 (1970). 12. Uesugi, K., and Shigematsu, T., Highly sensitive spectrophotometric determination of palladium with chromal blue G and cetyltrimethyl ammonium chloride. Anal. Chim. Acta, in press. 13. Yoe, J. H., and Jones, A. L., Calorimetric determination of iron with disodium 1, 2-dihydroxybenzene-3, 5-disulfonate. Ind. Eng. Chem. Anal. Ed. 16, 11l-l 15 (1944). 11.
JOURNAL
21, 438-444
(1976)
A Highly Sensitive Spectrophotometric Determination of Beryllium with Chromal Blue G and Cetyltrimethylammonium Chloride KATSUYA
UESUCI
MITSUO
AND
MIYAWAKI’
Laboratory of Chemistry, Himeji Institute of Technology, Shosha, Himeji, Japan Received
June
7, 1976
INTRODUCTION
Recently, the methods of spectrophotometric determination of metal ions based on the complex-formation in the presence of a quaternary ammonium salt have been suggested (1,2, 7, 12). Continuing the study on the application of ternary complex in the spectrophotometric determination of metals, it was found that submicrogram amounts of beryllium react very sensitively with chromal blue G (CBG) in the presence of a quaternary ammonium salt. Chromal blue G (sodium-2”-chloro-4”-nitro-4’hydroxy-3, 3’-dimethylfuchsone-5, S-dicarboxylate, color index 43835), a triphenylmethane dye, has been used as a spectrophotometric reagent for scandium (9)) beryllium (IO), and palladium (22). This paper describes a highly sensitive method for the determination of beryllium based on the formation of a colored complex with CBG in the presence of cetyltrimethylammonium chloride (CTMA). Several conditions under which microgram amounts of beryllium can be determined, the influences of coexisting ions, and the complex formation are discussed. EXPERIMENTAL
Reagents and Apparatus Standard beryllium solution. A standard stock solution (100 pg Be/ml) was prepared by dissolving 1.964 g of beryllium sulfate tetrahydrate in distilled water, adding small amounts of hydrochloric acid to prevent possible hydrolysis, and diluting the solution to 1 liter. This standard stock solution was diluted further as required. CBG solution. The CBG (Geigy Chemicals, New York) was purified by recrystallization from ethanol before use, and then 0.1 g of it was dissolved in 100 ml of distilled water. CTMA solution. The CTMA solution (3.0 x 1O-3 M/liter) was prepared * Present
address:
Kobe
Technical
College,
Tarumi, 438
Copyright All rights
@ 1976 by Academic Press. Inc. of reproduction in any form reserved.
Kobe,
Japan
DETERMINATION
by dissolving Buffer
439
OF BERYLLIUM
0.960 g of it in 1 liter of distilled
water.
solution (pH 5.5). A buffer solution of pH 5.5 was prepared by a 0.2 M acetic acid solution and a 0.2 M sodium acetate solution.
mixing All other chemicals used were analytical reagent grade. All absorbance measurements were made with a Hitachi automatic recording digital spectrophotometer, model 624, in 1 .OO-cm matched quartz cells. The pH measurements were carried out with a Toa Electronics, Ltd., pH meter, model HM-6A. The Standard
Procedure
for Beryllium
Determination
Transfer the sample solution containing 0.3-3 pg of beryllium to a 2%ml volumetric flask, and add 1 ml of the CBG solution, 2.5 ml of the CTMA solution, and then 5 ml of the acetate buffer solution. After diluting to the mark with distilled water, mix, let the color develop for 20 min, and measure the absorbance of the solution at 626 nm using a reagent blank as a reference. RESULTS
AND DISCUSSION
Absorption spectra. The absorption spectra of CBG and its beryllium complex are shown in Fig. 1. Curves A and B show the absorption spectra of CBG and its beryllium complex at pH 5.5, respectively, while curves C and D show the effect of the presence of CTMA to these solutions at pH 5.5. The presence of CTMA in the beryllium complex produces a somewhat bathochromic shift in the absorption maximum (610 to 626 nm) and
400 Wavelength,
500
600
700
nm
FIG. 1. Absorption spectra of CBG and its beryllium complex (pH 5.5). (A) Reagent blank of (B), reference: water. (B) Be-CBG complex (Be 6.67 x IO-” M, CBG 8.64 X 1OP M), reference: reagent blank. (C) Reagent blank of(D), reference: water. (D) BeXBG complex (Be 6.67 x lO-6 M, CBG 8.64 x 1O-5 M, CTMA 3.0 x lO-4 M), reference: reagent blank.
440
UESUGI
AND
MIYAWAKI
increases greatly the absorbance of the complex. In order to observe the spectral changes on varying pH, absorption curves for the beryllium complex were prepared at different pH values (Fig. 2). Between pH 5.0 and 6.2, the curves are of identical shape, with one absorption maximum at 626 nm. Below pH 4.6, the maximum absorption shifts toward a shorter wavelength. Effect ufpH on color development. The effect of the pH on the color development of the beryllium complex was examined by measuring the absorbance of a colored solution at 626 nm. The results are shown in Fig. 3, from which it can be seen that maximum intensity can be obtained in the pH range from 5.3 to 6.0. An acetic acid-acetate buffer solution, pH 5.5, was found to be satisfactory for this purpose. Effect of CBG concentration. The effect of variable concentration of CBG on the color development was examined by measuring the absorbance at 626 nm on solutions containing constant concentrations of beryllium and CTMA and varying amounts of CBG. Addition of 1 ml of a 0.1% CBG solution sufficed for less than 0.12 ppm of beryllium. This concentration represents a 6.5-fold molar excess of CBG over the maximum concentration of beryllium determination under the given conditions. Effect ofCTMA concentration. The effect of changes in the concentration of CTMA on the absorbance of beryllium complex was determined by measuring the absorbance. The maximum absorbance can be obtained over the range (2.5-3.3) x lo-* M of CTMA. The optimum amount of CTMA was 2.5 ml of a 3 x 1O-3 M CTMA solution in a final volume of 25 ml.
4
0.6 -
500
600 Wavelength.
FIG. 2. Absorption spectraofberylliumcomplex x IO-jM, CTMA 3.0 x 1O-4 M, reference:
reagent
i
nm at various pH. Be 6.67 x 10-6M, CBG 8.64 blank; pH: (1) 3.8, (2) 4.0, (3) 4.6, (4) 5.3.
DETERMINATION
OF
441
BERYLLIUM
Effect of time. The color of the beryllium complex developed gradually at room temperature; the full color was obtained in 20 min after preparation and then remained almost constant for at least 2 hr. Calibration CUYW, sensitivity, and precision. Calibration curves for the beryllium determination were prepared by the standard procedure. Beer’s law was obeyed over the range 0.012-o. 12 ppm of beryllium. The molar absorptivity was 9.38 x 104at 626 nm, and the spectrophotometric sensitivity was estimated to be 9.6 x 1O-5 pg Be cm-2, corresponding to logZ,,/Z = 0.001. The present method is very sensitive. Its sensitivity is much greater than that of the methods using chromal blue G (without CTMA, molar absorpitivity = 3.1 x 104) (ZO), Eriochrome brilliant violet B (II), aluminon (6), Eriochrome cyanine R (4)) and chromazurol S (8). A standard solution containing 1.5 pug of beryllium was analyzed 10 times by the standard procedure. The average absorbance was 0.625, with a standard deviation of 0.004 absorbance unit and a relative error of t 1.1%. Effect offoreign ions. The influence of foreign ions on the determination of beryllium was ascertained by the standard procedure. The most commonly encountered ions were added individually to a solution containing 1.5 ,ug of beryllium. The following metal ions did not interfere up to loo-fold weight excess: barium(II), calcium(II), cadmium(II),
_
o-
2
‘CA --Qx k --o-+--a I I I I
0
4 FIG. 3. Effect of pH. (1) Be-CBG 3.0 x IO-* M), reference: reagent
5
6
7
I 8
complex (Be 6.08 x 1OW M, CBG 8.64 x 10-5M, blank. (2) Reagent blank, reference: water.
CTMA
442
UESUGI
AND
MIYAWAKI
cobalt(II), lead(II), magnesium(II), manganese(II), mercury(II), nickel(II), strontium(II), tin(II), and zinc(I1). Aluminum(III), scandium(III), copper( iron(III), palladium(II), yttrium(III), and rare earth elements interfere seriously. EDTA was investigated as a masking agent for the more seriously offending ions. Scandium(III), copper( palladium(II), yttrium(III), and rare earth elements were effectively masked by EDTA and can be tolerated without further separation. However, more than 100 pg of aluminum and iron(II1) were not completely screened out by EDTA. In the presence of 50-fold weight excess of aluminum(II1) or iron(II1) 1.5 pg of beryllium were determined within the error of +-3% when EDTA is used as a masking agent. The optimum amount of EDTA used for masking these interfering ions was 1 ml of a 0.1 M EDTA solution. Chloride, sulfate, acetate, and nitrate were without effect even in large amounts, but fluoride, citrate, and tartrate prevent the formation of the beryllium complex. Complexfovmation. The method of the continuous variations (5) was employed to establish the molar ratio of the beryllium complex in the presence of CTMA. Figure 4 shows that a 1:2 complex formed between beryllium and CBG. These results were confirmed by the mole ratio method of Yoe and Jones (13). The formation constant was calculated from the curves obtained by the continuous variation method. As the mole ratio of the beryllium-CBG 0.8 I-
- 0
0.2
0.4
l3el/(CBeJ 4. Continuous variation method. [CTMA] A4 (pH 5.5). FIG.
0.6
OS
-t KBGJ) = 3.0 X 10m4M, [Be] + [CBG] = 4.0 X 1OF
DETERMINATION
complex
OF
BERYLLIUM
443
is 1:2, the reaction can be expressed as: Be + 2CBG e Be (CBG)*.
The formation constant, K, was estimated from the curves obtained by the continuous variation method on the basis of the following relationships (3, 12): K = C (1 - a)/(&)
(2&)2
where C is the total concentration of the complex in moles/per liter (assuming no dissociation), where (Yis the degree of dissociation, where E, is the maximum extinction of the complex when all the beryllium is present in the form of the complex, and where& is the actual absorbance of the complex. The formation constant at pH 5.5 and 25°C was estimated to be 4.6 x lOlo. SUMMARY Chromal blue G in the presence of cetyltrimethylammonium chloride is proposed for the spectrophotometric determination of microgram amounts of beryllium. The sensitivity of color reaction between beryllium and chromal blue Cl has been greatly increased by the sensitizing action of cetyltrimethylammonium chloride (ecZ6“,,, = 93,000). Beer’s law is obeyed over the range 0.012Jl. 12 ppm of beryllium. Full color development occurs in 20 min at pH 5.5 and at 626 nm. The mole ratio of beryllium and chromal blue G in the complex is estimated to be 1:2. The proposed method is very sensitive and selective for determination of beryllium when EDTA is used as a masking agent.
REFERENCES I. Bailey, B. W., Chester, .I. E., Dagnall, R. M., and West, T. S., Analytical applications of ternary complexes-V. Tu/anfa 15, 1359-1369 (1968). 2. Dagnall, R. M., West, T. S., and Young, P., The catechol violet colour reaction for tin(lV) sensitised by cetyltrimethylammonium bromide. Analyst 92, 27-30 (1967). 3. Harvey, A. E., and Manning, D. L., Spectrophotometric methods ofestablishing empirical formulas of colored complexes in solution. J. Amer. Chem. Sot. 72, 4488-4493 (1950). 4. Hill, U. T., Photometric determination of beryllium. Anal. Chem. 30, 521-524 (1958). 5. Job, P., Formation and stability of inorganic complexes in solution. Ann. Chim. 9,113-203 (1928). 6. Kosel, G. E., and Neuman, W. F., Color reaction between beryllium and aurin tricarboxylic acid. Anal. Chem. 22, 936-939 (1950). 7. Leong, C. L., Spectrophotometric determination of uranium(V1) with chromazurol S and cetylpyridinium bromide. Anal. Chem. 45, 201-203 (1973). 8. Silverman, L., and Shideler M. E., Spectrophotometric determination of beryllium and fluoride using chrome azurol S. Anal. Chem. 31, 152-155 (1959). 9. Uesugi, K., The spectrophotometric determination of scandium with chromal blue G. Bull. Chem. Sot. Jup. 42, 2051-2054 (1969). IO. Uesugi, K., The spectrophotometric determination of beryllium with chromal blue G. Bull. Chem. Sot. Jap. 42, 2998-3000 (1969).
444
UESUGI
AND
MIYAWAKI
Uesugi, K., The spectrophotometric determination of beryllium with eriochrome brilliant violet B. Anal. Chim. Acta 49, 89-95 (1970). 12. Uesugi, K., and Shigematsu, T., Highly sensitive spectrophotometric determination of palladium with chromal blue G and cetyltrimethyl ammonium chloride. Anal. Chim. Acta, in press. 13. Yoe, J. H., and Jones, A. L., Calorimetric determination of iron with disodium 1, 2-dihydroxybenzene-3, 5-disulfonate. Ind. Eng. Chem. Anal. Ed. 16, 11l-l 15 (1944). 11.