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Solvent extraction and spectrophotometric determination of iron(II) with di-2-pyridyl ketone benzoylhydrazone
MICROCHEMICAL
JOURNAL
33, 172- 178 (1986)
Solvent Extraction and Spectrophotometric Determination Iron with Di-2-pyridyl Ketone Benzoylhydrazone TSUTOMU *Departmen University,
of
NAKANISHI* ANDMAKOTO OToMot
of Solid Stare Electronics, Faculty of Engineering, Osaka Elecrro-communication Haisumachi, Neyagawa, Osaka 572; tDepartmenr of Synthetic Chemistry, Nagoya Institute of Technology, Showa-ku, Nogoya, Aichi 466, Japan
Received November 10, 1983 Di-2-pyridyl ketone benzoylhydrazone (DPKBH) was used for the spectrophotometric determination of trace amount of iron(U) in connection with the extraction process. The green iron(U) complex with a maximum absorbance at 379 and 686 nm is quantitatively extracted into benzene from aqueous solution buffered to pH 4.7-6.0. Beer’s law is obeyed over the range O-30 pg of iron in 10 ml of benzene at 686 nm. The molar absorptivity of the complex is 1.59 x 104 liters molFi cm- 1. The relative standard deviation for 16.8 pg of iron was 0.48% at this wavelength. The proposed method is relatively selective for iron and is satisfactorily applied to the determination of the total iron in natural waters. The proton dissociation constants of the ligand determined spectrophotometrically were pK,, = 3.18 and pK,z = 10.87 at 25°C and )I = 0.1. o 1986 Academic press. IX.
INTRODUCTION
In recent years a variety of nitrogen-containing heterocyclic hydrazone compounds have been synthesized and investigated for their potentiality as analytical reagents. We have pointed out in our recent papers that 2,2’-dipyridyl-2-quinolylhydrazone (5-7) and 2,2’-dipyridyl-2-furancarbothiohydrazone (3, 4), which contain a 2,2’-dipyridyl group in the aldehyde moiety of the ligand molecule, are particularly promising for the extractive spectrophotometric determination of trace metal ions including iron(I1). We synthesized a new hydrazone ligand, di-2pyridyl ketone benzoylhydrazone (I, abbreviated as DPKBH), containing the functionality - N = C - C = N - NH - C( = 0) - and investigated the proton
-N-
H
I dissociation behavior of the ligand and the color reaction between the reagent and iron(I1). A sensitive and selective method is proposed for the extractive spectro172 0026-265X/86 $1.50 Copyright 8 1986 by Academic Press, Inc. All rights of reproduction in any form reserved.
DETERMINATION
OF IRON(H)
173
photometric determination of iron(I1) with DPKBH. The method is satisfactorily applied to the determination of the total iron in natural waters. EXPERIMENTAL Reagents DPKBH. The ligand was prepared by interaction of di-2-pyridyl ketone and benzoylhydrazine in stoichiometric amounts and was recrystallized to a constant melting point (136- 137°C) from ethanol. The results of the elemental analysis of DPKBH were as follows: found, C 71.29%, H 4.66%, N 18.66%; calculated for Ci8Hi4N40, C 71.51%, H 4.67%, N 18.53%. The structural form of DPKBH (I), was also confirmed by the infrared spectrum of the ligand measured with a potassium bromide disk. A 1 x 10-3 M DPKBH in benzene was freshly prepared daily. Iron solution. Iron standards were obtained by dilution of 0.01 M ammonium iron(H) sulfate acidified with sulfuric acid and standardized compleximetrically. Ascorbic acid was used as a reducing agent for iron(II1) and a sodium chloride solution was added to prevent emulsification during the extraction. All other reagents were of analytical grade and were used as received. Apparatus
A Hitachi Model 220A double-beam spectrophotometer and a Union Giken SM-401 high-sensitivity spectrophotometer were used for absorbance measurements with matched 1.OO-cm quartz cells. Toa Dempa HM-5B and digital HM-20B pH meters were used for pH adjustments. All measurements were made at 25°C. Recommended
Procedure
for the Determination
of Iron(II,Ill)
Place a suitable aliquot of the sample or standard solution containing less than 30 p.g of iron(II,III) in a 50-ml separatory funnel. Add 1 ml each of 1% ascorbic acid, I M acetate buffer adjusted to pH 5.0, and 1 M sodium chloride solution. Dilute to 20 ml with doubly distilled water and equilibrate with exactly 10 ml of 1 X IO-3 M DPKBH in benzene for 1 min. Measure the absorbance of the benzene extract at 686 nm against the reagent blank as a reference. Calculate the amount of iron present from a previously prepared calibration curve. RESULTS Proton
Dissociation
AND DISCUSSION
of DPKBH
The reagent, DPKBH, is a dibasic acid and colorless crystalline material soluble in most organic solvent, but not in water. The proton dissociation behavior of the ligand was studied spectrophotometrically in aqueous ethanol of various concentrations at an ionic strength of 0.1 (KCI). Figure 1 shows the absorption spectra of the ligand in 10% (v/v) aqueous ethanol at various pH values. The proton dissociation constants were therefore estimated by plotting the logarithmic ratio of the conjugated acid and base concentrations against the pH of the solution, according to the method described by Hildebrand and Reilley (I). An
174
NAKANISHI
0.5
AND
OTOMO
(A)
* 0.4 p0 0.3 b p” a
a2 0.1
d, 0.4I (B)
2z 0.3 i
0.2 0.1 0
350 Wavclcnpth
( nm )
1. Absorption spectra of DPKBH in 10% (v/v) aqueous ethanol at (*=O. 1. Concentration of DPKBH is 2 x IO-5 M. (A) Absorption spectra between pH 2.00 and 4.39: (1) pH 2.00, (2) pH 2.35, (3) pH 2.65, (4) pH 2.95, (5) pH 3.35, (6) pH 3.75, (7) pH 4.00, (8) pH 4.39. (B) Absorption spectra between pH 9.29 and 11.74: (1) pH 9.29, (2) pH 9.82, (3) pH 10.15, (4) pH 10.54, (5) pH 11.04, (6) pH 11.44, (7) pH 11.74. FIG.
approximately linear relationship was obtained between the pK,, and pK,, values thus estimated and the mole fraction of ethanol, n; pK,, = 3.25 - 0.20n and pK,, = 10.51 + 1.21n. The pK,, and pK,, values are ascribed to the removal of protons from the pyridine nitrogen atom and from the imino group existing in equilibrium with the tautomeric enol form, respectively. The Characteristics of the Iron(D) Complex The iron(I1) complex formed with the reagent is sparingly soluble in water, but readily soluble in various organic solvents such as benzene (A,,,,, = 379 and 686 nm, E = 4.11 x 104 and 1.59 x 104 liters mol-i cm-i), toluene (A,,, = 380 and 687 nm, E = 3.98 x 104 and 1.57 x 104), nitrobenzene (A,,, = 429 and 686 nm, E = 0.86 x 104 and 0.68 x 104), chlorobenzene (X,,, = 379 and 687 nm, E = 3.88 x 104 and 1.47 x 104), chloroform (A,,, = 374 and 680 nm, E = 2.46 x 104 and 0.93 x 104), 1,2-dichloroethane (A,,, = 374 and 682 nm, e = 3.09 x 104and 1.15 x 104), carbon tetrachloride (h,,, = 383 and 688 nm, E = 3.73 x 104 and 1.41 x 104), and methyl isobutyl ketone (A,,, = 374 and 684 nm, E = 1.72 x 104 and 0.43 x 104). Benzene was chosen as the extractant because the highest absorbance of the complex in the visible region was obtained in this solvent. Under the optimal conditions of the reagent concentration, pH, and shaking period, iron(I1) can be quantitatively extracted from aqueous solution with a
DETERMINATION
175
OF IRON(U)
2, 300
400
500 Wavelength
600
700
600
( “m)
FIG. 2. Absorption spectra obtained under the experimental conditions given under Experimental. Concentrations of iron(H) and DPKBH are 2 x IO-5 and I x 10-j M, respectively. (I) Reagent blank; (2) Fe(H)-DPKBH complex.
single lo-ml portion of DPKBH in benzene over the concentration range studied. The absorption spectra of the reagent and the iron complex in benzene are shown in Fig. 2. The spectral pattern is characteristic for this ion, suggesting that by measuring the absorbance of the complex at the wavelength of the second maximum, iron(I1) can be determined without interference from other metal ions, because the latter complexes with DPKBH generally exhibited the absorption maxima below 450 nm. Iron(II1) did not react with the reagent and should be reduced by ascorbic acid. Effects of Experimental
Conditions
A pH study for the formation and extraction of the iron complex was carried out between pH 1 and 11, the results being plotted in Fig. 3. The absorbance of the organic phase, measured as a function of the pH of the aqueous phase, was maximal and constant over the pH range 4.7-6.0. A sample solution containing 16.8 kg of iron(I1) was equilibrated with various amounts of DPKBH in benzene. A maximal and reasonably constant absorbance was obtained by using more than 5 x 10-4 M of DPKBH in the organic phase. Addition of l-5 ml of 1 M sodium chloride was effective for rapid separation of the two phases. It was also found that only 1 min of a shaking period is sufficient for complete equilibrium, provided the volume ratio VO,: Vaq is between 1: 1 and 1:5. The color of the complex thus developed was very stable, the absorbance being constant for at least 5 h. Conformance to Beer’s Law The analytical species of interest obeys Beer’s law over the concentration range up to about 5 x IO-5 M (30 pg) iron(I1) in the organic phase. The molar
176
NAKANISHI
AND
OTOMO
0.6
0 1
2
3
4
5
6
7
6
a
10
11
PH FIG. 3. The pH dependence of the iron(H)-DPKBH complex formation. Initial iron concentration in the aqueous phase and DPKBH concentration in benzene are 3 x 10-x and 1 x IO-3 M, respectively. Measured at 686 nm.
absorptivity and the Sandell sensitivity for an absorbance of 0.001 were calculated as 1.59 x 104 liters mol - i cm- 1 and 3.5 ng cm-2 at 686 nm, respectively. It is found that the present reagent, DPKBH, is superior in sensitivity to those related hydrazone ligands recently proposed for iron( such as 2,2’-dipyridyl-2quinolylhydrazone (6), 2,2’-dipyridyl-2-furancarbothiohydrazone (3), and 2,2’-dipyridyl-2-benzothiazolylhydrazone (8). The precision of the method was estimated for 16.8 pg of iron, the coefficient of variation for 14 determinations being 0.48%.
0.6
a2 at
11) (Fe(l)l,([F~)l.(DPI(BH))
FIG. 4. Continuous variations plot for the iron(DPKBH and DPKBH is 5 x IO-5 M. Measured at 686 nm.
system. Total concentration of iron(I1)
DETERMINATION
177
OF IRON(H)
TABLE I Effect of Foreign Ions on Determination of 16.8 ug of Iron(H) Tolerance limit (Weight ratio, Ion/Fe)
Ion
Cl-, Br-, I-, NO,, NO?, SCN-, SO:-, &OS-, PO:- L-ascorbic acid, urea, thiourea Citrate, tartrate, Fm Li’, Ag+, Tl+, Be*+, Mg*+, Ca*+. Mn*+, Cu2+c, Zn*+, Sr*+, Pd*+, Cd*+. Hg*+, Pb*+, A13+. Cr3+, Ga3+0, Y3+, Sb3+, Au’+, Bi’+. La3+, Zti+d, Ce4+, Ti4+“, Pt4+, Mo6+, U6+ w6+0 &8-t CO~+~, Ni*+, Ir3+ Rhj+ CN - , EDTA,
G=l,OOO 2100
250 310 35 o-1 fl One b One r Two d Two
milliliter milliliter milliliters milliliters
of 0.5 M tartaric acid was added. of 0. I M citric acid was added. of 1 M potassium thiocyanate was added. of 0.5 M sodium fluoride was added.
Composition of the Complex The stoichiometry of the complex was established by Job’s method of continuous variations. The results showed a 1:2 ratio of iron to DPKBH in the extracted species (Fig. 4), suggesting that DPKBH acts as a tridentate ligand for iron(H) to give an extractable uncharged complex. Effect of Foreign Ions The effect of foreign ions was studied for the determination of 16.8 Fg of iron(H). The results obtained are presented in Table 1. An error of k 2% in the absorbance reading was considered tolerable. Cations were added in the form of chlorides, nitrates, or sulfates to a maximum of loo-fold weight ratio to iron(I1). The present method is found to be relatively interference free. The influence of
Determination
TABLE 2 of Total Iron in Natural Waters Iron founda (ppm)
Sample from Lake Lake Lake River River
Proposed method
Biwa (Ohmiohashi) Biwa (Maiami) Biwa (Wanihama) wani yasu
” An average
value
0.11 0.10 0.18 0.47 0.86
* * 2 -t ?
0.01 0.01 0.02 0.01 0.02
of triplicate determinations.
1, IO-Phenanthroline method 0.11 0.11 0.16 0.50 0.89
2 0.01 * 0.01 2 0.02 f 0.01 -+ 0.02
Atomic-absorption method 0.11 0.10 0.17 0.51 0.90
* 2 lr -c k
0.02 0.02 0.03 0.02 0.03
178
NAKANISHI
AND
OTOMO
copper( gallium(III), zirconium(IV), titanium(IV), and tungsten(V1) can be removed by addition of suitable masking agents as noted in Table 1. EDTA and cyanide, however, must be absent. Determination
of Iron in Natural
Waters
In order to confirm the usefulness of the proposed method, it was applied to the determination of the total iron in various water samples. The sample solutions were acidified with hydrochloric acid immediately after sampling and evaporated to an appropriate volume, so that the final solution contains lo-20 pg of iron. The results are summarized in Table 2, together with those obtained by the 1,10phenanthroline method and atomic absorption spectrophotometry (2) carried out for comparison. The method described here may also be adaptable for many samples, because of its high precision, high sensitivity, and simplicity. REFERENCES Hildebrand, G. P., and Reilley, C. N., New indicator for complexometric titration of calcium in presence of magnesium. Anal. Chem. 29, 258-264 (1957). 2. Iwamoto, K., “Jdsui Shiken HoHo,” pp. 275-276. Japan Water Works Assoc., Tokyo, 1977. 3. Nakanishi, T., and Otomo, M., Solvent extraction and spectrophotometric determination of iron(B) with 2,2’-dipryidyl-2-furancarbothiohydrazone. Microchem. J. 28, 99- 106 (1983). 4. Nakanishi, T., and Otomo, M., Solvent extraction and spectrophotometric determination of copper(H) with di-2-pyridyl ketone 2-fury1 (thiocarbonyl) hydrazone. Nippon Kugaku Kuishi 1.
1983,
518-522.
5. Otomo, M., 2,2’-Dipyridyl-2-quinolyhydrazone as a reagent for the spectrophotometric determination of metals. The extractive spectrophotometric determination of palladium(H). Anal. Chim. Acta 116, 161(1980). 6. Otomo, M., Ano, S., and Kako, H., Solvent extraction and spectrophotometric determination of iron(H) with 2,2’-dipyridyl-2-quinolylhydrazone. Microchem. J. 26, 228-235 (1981). 7. Otomo, M., Ito, A., and Doi, K., Solvent extraction and spectrophotometric determination of cadmium with 2,2’-dipyridyl-2-quinolylhydrazone. Jupun Anal. 31, E21-E26 (1982). [in English] 8. Singh, R. B., Odashima, T., and Ishii, H., Spectrophotometric and analog derivative spectrophotometric determination of micro-amounts of iron with 2,2’-dipyridyl-2-benzothiazolylhydrazone. Anulys? 108, 1120- 1127 (1983).
JOURNAL
33, 172- 178 (1986)
Solvent Extraction and Spectrophotometric Determination Iron with Di-2-pyridyl Ketone Benzoylhydrazone TSUTOMU *Departmen University,
of
NAKANISHI* ANDMAKOTO OToMot
of Solid Stare Electronics, Faculty of Engineering, Osaka Elecrro-communication Haisumachi, Neyagawa, Osaka 572; tDepartmenr of Synthetic Chemistry, Nagoya Institute of Technology, Showa-ku, Nogoya, Aichi 466, Japan
Received November 10, 1983 Di-2-pyridyl ketone benzoylhydrazone (DPKBH) was used for the spectrophotometric determination of trace amount of iron(U) in connection with the extraction process. The green iron(U) complex with a maximum absorbance at 379 and 686 nm is quantitatively extracted into benzene from aqueous solution buffered to pH 4.7-6.0. Beer’s law is obeyed over the range O-30 pg of iron in 10 ml of benzene at 686 nm. The molar absorptivity of the complex is 1.59 x 104 liters molFi cm- 1. The relative standard deviation for 16.8 pg of iron was 0.48% at this wavelength. The proposed method is relatively selective for iron and is satisfactorily applied to the determination of the total iron in natural waters. The proton dissociation constants of the ligand determined spectrophotometrically were pK,, = 3.18 and pK,z = 10.87 at 25°C and )I = 0.1. o 1986 Academic press. IX.
INTRODUCTION
In recent years a variety of nitrogen-containing heterocyclic hydrazone compounds have been synthesized and investigated for their potentiality as analytical reagents. We have pointed out in our recent papers that 2,2’-dipyridyl-2-quinolylhydrazone (5-7) and 2,2’-dipyridyl-2-furancarbothiohydrazone (3, 4), which contain a 2,2’-dipyridyl group in the aldehyde moiety of the ligand molecule, are particularly promising for the extractive spectrophotometric determination of trace metal ions including iron(I1). We synthesized a new hydrazone ligand, di-2pyridyl ketone benzoylhydrazone (I, abbreviated as DPKBH), containing the functionality - N = C - C = N - NH - C( = 0) - and investigated the proton
-N-
H
I dissociation behavior of the ligand and the color reaction between the reagent and iron(I1). A sensitive and selective method is proposed for the extractive spectro172 0026-265X/86 $1.50 Copyright 8 1986 by Academic Press, Inc. All rights of reproduction in any form reserved.
DETERMINATION
OF IRON(H)
173
photometric determination of iron(I1) with DPKBH. The method is satisfactorily applied to the determination of the total iron in natural waters. EXPERIMENTAL Reagents DPKBH. The ligand was prepared by interaction of di-2-pyridyl ketone and benzoylhydrazine in stoichiometric amounts and was recrystallized to a constant melting point (136- 137°C) from ethanol. The results of the elemental analysis of DPKBH were as follows: found, C 71.29%, H 4.66%, N 18.66%; calculated for Ci8Hi4N40, C 71.51%, H 4.67%, N 18.53%. The structural form of DPKBH (I), was also confirmed by the infrared spectrum of the ligand measured with a potassium bromide disk. A 1 x 10-3 M DPKBH in benzene was freshly prepared daily. Iron solution. Iron standards were obtained by dilution of 0.01 M ammonium iron(H) sulfate acidified with sulfuric acid and standardized compleximetrically. Ascorbic acid was used as a reducing agent for iron(II1) and a sodium chloride solution was added to prevent emulsification during the extraction. All other reagents were of analytical grade and were used as received. Apparatus
A Hitachi Model 220A double-beam spectrophotometer and a Union Giken SM-401 high-sensitivity spectrophotometer were used for absorbance measurements with matched 1.OO-cm quartz cells. Toa Dempa HM-5B and digital HM-20B pH meters were used for pH adjustments. All measurements were made at 25°C. Recommended
Procedure
for the Determination
of Iron(II,Ill)
Place a suitable aliquot of the sample or standard solution containing less than 30 p.g of iron(II,III) in a 50-ml separatory funnel. Add 1 ml each of 1% ascorbic acid, I M acetate buffer adjusted to pH 5.0, and 1 M sodium chloride solution. Dilute to 20 ml with doubly distilled water and equilibrate with exactly 10 ml of 1 X IO-3 M DPKBH in benzene for 1 min. Measure the absorbance of the benzene extract at 686 nm against the reagent blank as a reference. Calculate the amount of iron present from a previously prepared calibration curve. RESULTS Proton
Dissociation
AND DISCUSSION
of DPKBH
The reagent, DPKBH, is a dibasic acid and colorless crystalline material soluble in most organic solvent, but not in water. The proton dissociation behavior of the ligand was studied spectrophotometrically in aqueous ethanol of various concentrations at an ionic strength of 0.1 (KCI). Figure 1 shows the absorption spectra of the ligand in 10% (v/v) aqueous ethanol at various pH values. The proton dissociation constants were therefore estimated by plotting the logarithmic ratio of the conjugated acid and base concentrations against the pH of the solution, according to the method described by Hildebrand and Reilley (I). An
174
NAKANISHI
0.5
AND
OTOMO
(A)
* 0.4 p0 0.3 b p” a
a2 0.1
d, 0.4I (B)
2z 0.3 i
0.2 0.1 0
350 Wavclcnpth
( nm )
1. Absorption spectra of DPKBH in 10% (v/v) aqueous ethanol at (*=O. 1. Concentration of DPKBH is 2 x IO-5 M. (A) Absorption spectra between pH 2.00 and 4.39: (1) pH 2.00, (2) pH 2.35, (3) pH 2.65, (4) pH 2.95, (5) pH 3.35, (6) pH 3.75, (7) pH 4.00, (8) pH 4.39. (B) Absorption spectra between pH 9.29 and 11.74: (1) pH 9.29, (2) pH 9.82, (3) pH 10.15, (4) pH 10.54, (5) pH 11.04, (6) pH 11.44, (7) pH 11.74. FIG.
approximately linear relationship was obtained between the pK,, and pK,, values thus estimated and the mole fraction of ethanol, n; pK,, = 3.25 - 0.20n and pK,, = 10.51 + 1.21n. The pK,, and pK,, values are ascribed to the removal of protons from the pyridine nitrogen atom and from the imino group existing in equilibrium with the tautomeric enol form, respectively. The Characteristics of the Iron(D) Complex The iron(I1) complex formed with the reagent is sparingly soluble in water, but readily soluble in various organic solvents such as benzene (A,,,,, = 379 and 686 nm, E = 4.11 x 104 and 1.59 x 104 liters mol-i cm-i), toluene (A,,, = 380 and 687 nm, E = 3.98 x 104 and 1.57 x 104), nitrobenzene (A,,, = 429 and 686 nm, E = 0.86 x 104 and 0.68 x 104), chlorobenzene (X,,, = 379 and 687 nm, E = 3.88 x 104 and 1.47 x 104), chloroform (A,,, = 374 and 680 nm, E = 2.46 x 104 and 0.93 x 104), 1,2-dichloroethane (A,,, = 374 and 682 nm, e = 3.09 x 104and 1.15 x 104), carbon tetrachloride (h,,, = 383 and 688 nm, E = 3.73 x 104 and 1.41 x 104), and methyl isobutyl ketone (A,,, = 374 and 684 nm, E = 1.72 x 104 and 0.43 x 104). Benzene was chosen as the extractant because the highest absorbance of the complex in the visible region was obtained in this solvent. Under the optimal conditions of the reagent concentration, pH, and shaking period, iron(I1) can be quantitatively extracted from aqueous solution with a
DETERMINATION
175
OF IRON(U)
2, 300
400
500 Wavelength
600
700
600
( “m)
FIG. 2. Absorption spectra obtained under the experimental conditions given under Experimental. Concentrations of iron(H) and DPKBH are 2 x IO-5 and I x 10-j M, respectively. (I) Reagent blank; (2) Fe(H)-DPKBH complex.
single lo-ml portion of DPKBH in benzene over the concentration range studied. The absorption spectra of the reagent and the iron complex in benzene are shown in Fig. 2. The spectral pattern is characteristic for this ion, suggesting that by measuring the absorbance of the complex at the wavelength of the second maximum, iron(I1) can be determined without interference from other metal ions, because the latter complexes with DPKBH generally exhibited the absorption maxima below 450 nm. Iron(II1) did not react with the reagent and should be reduced by ascorbic acid. Effects of Experimental
Conditions
A pH study for the formation and extraction of the iron complex was carried out between pH 1 and 11, the results being plotted in Fig. 3. The absorbance of the organic phase, measured as a function of the pH of the aqueous phase, was maximal and constant over the pH range 4.7-6.0. A sample solution containing 16.8 kg of iron(I1) was equilibrated with various amounts of DPKBH in benzene. A maximal and reasonably constant absorbance was obtained by using more than 5 x 10-4 M of DPKBH in the organic phase. Addition of l-5 ml of 1 M sodium chloride was effective for rapid separation of the two phases. It was also found that only 1 min of a shaking period is sufficient for complete equilibrium, provided the volume ratio VO,: Vaq is between 1: 1 and 1:5. The color of the complex thus developed was very stable, the absorbance being constant for at least 5 h. Conformance to Beer’s Law The analytical species of interest obeys Beer’s law over the concentration range up to about 5 x IO-5 M (30 pg) iron(I1) in the organic phase. The molar
176
NAKANISHI
AND
OTOMO
0.6
0 1
2
3
4
5
6
7
6
a
10
11
PH FIG. 3. The pH dependence of the iron(H)-DPKBH complex formation. Initial iron concentration in the aqueous phase and DPKBH concentration in benzene are 3 x 10-x and 1 x IO-3 M, respectively. Measured at 686 nm.
absorptivity and the Sandell sensitivity for an absorbance of 0.001 were calculated as 1.59 x 104 liters mol - i cm- 1 and 3.5 ng cm-2 at 686 nm, respectively. It is found that the present reagent, DPKBH, is superior in sensitivity to those related hydrazone ligands recently proposed for iron( such as 2,2’-dipyridyl-2quinolylhydrazone (6), 2,2’-dipyridyl-2-furancarbothiohydrazone (3), and 2,2’-dipyridyl-2-benzothiazolylhydrazone (8). The precision of the method was estimated for 16.8 pg of iron, the coefficient of variation for 14 determinations being 0.48%.
0.6
a2 at
11) (Fe(l)l,([F~)l.(DPI(BH))
FIG. 4. Continuous variations plot for the iron(DPKBH and DPKBH is 5 x IO-5 M. Measured at 686 nm.
system. Total concentration of iron(I1)
DETERMINATION
177
OF IRON(H)
TABLE I Effect of Foreign Ions on Determination of 16.8 ug of Iron(H) Tolerance limit (Weight ratio, Ion/Fe)
Ion
Cl-, Br-, I-, NO,, NO?, SCN-, SO:-, &OS-, PO:- L-ascorbic acid, urea, thiourea Citrate, tartrate, Fm Li’, Ag+, Tl+, Be*+, Mg*+, Ca*+. Mn*+, Cu2+c, Zn*+, Sr*+, Pd*+, Cd*+. Hg*+, Pb*+, A13+. Cr3+, Ga3+0, Y3+, Sb3+, Au’+, Bi’+. La3+, Zti+d, Ce4+, Ti4+“, Pt4+, Mo6+, U6+ w6+0 &8-t CO~+~, Ni*+, Ir3+ Rhj+ CN - , EDTA,
G=l,OOO 2100
250 310 35 o-1 fl One b One r Two d Two
milliliter milliliter milliliters milliliters
of 0.5 M tartaric acid was added. of 0. I M citric acid was added. of 1 M potassium thiocyanate was added. of 0.5 M sodium fluoride was added.
Composition of the Complex The stoichiometry of the complex was established by Job’s method of continuous variations. The results showed a 1:2 ratio of iron to DPKBH in the extracted species (Fig. 4), suggesting that DPKBH acts as a tridentate ligand for iron(H) to give an extractable uncharged complex. Effect of Foreign Ions The effect of foreign ions was studied for the determination of 16.8 Fg of iron(H). The results obtained are presented in Table 1. An error of k 2% in the absorbance reading was considered tolerable. Cations were added in the form of chlorides, nitrates, or sulfates to a maximum of loo-fold weight ratio to iron(I1). The present method is found to be relatively interference free. The influence of
Determination
TABLE 2 of Total Iron in Natural Waters Iron founda (ppm)
Sample from Lake Lake Lake River River
Proposed method
Biwa (Ohmiohashi) Biwa (Maiami) Biwa (Wanihama) wani yasu
” An average
value
0.11 0.10 0.18 0.47 0.86
* * 2 -t ?
0.01 0.01 0.02 0.01 0.02
of triplicate determinations.
1, IO-Phenanthroline method 0.11 0.11 0.16 0.50 0.89
2 0.01 * 0.01 2 0.02 f 0.01 -+ 0.02
Atomic-absorption method 0.11 0.10 0.17 0.51 0.90
* 2 lr -c k
0.02 0.02 0.03 0.02 0.03
178
NAKANISHI
AND
OTOMO
copper( gallium(III), zirconium(IV), titanium(IV), and tungsten(V1) can be removed by addition of suitable masking agents as noted in Table 1. EDTA and cyanide, however, must be absent. Determination
of Iron in Natural
Waters
In order to confirm the usefulness of the proposed method, it was applied to the determination of the total iron in various water samples. The sample solutions were acidified with hydrochloric acid immediately after sampling and evaporated to an appropriate volume, so that the final solution contains lo-20 pg of iron. The results are summarized in Table 2, together with those obtained by the 1,10phenanthroline method and atomic absorption spectrophotometry (2) carried out for comparison. The method described here may also be adaptable for many samples, because of its high precision, high sensitivity, and simplicity. REFERENCES Hildebrand, G. P., and Reilley, C. N., New indicator for complexometric titration of calcium in presence of magnesium. Anal. Chem. 29, 258-264 (1957). 2. Iwamoto, K., “Jdsui Shiken HoHo,” pp. 275-276. Japan Water Works Assoc., Tokyo, 1977. 3. Nakanishi, T., and Otomo, M., Solvent extraction and spectrophotometric determination of iron(B) with 2,2’-dipryidyl-2-furancarbothiohydrazone. Microchem. J. 28, 99- 106 (1983). 4. Nakanishi, T., and Otomo, M., Solvent extraction and spectrophotometric determination of copper(H) with di-2-pyridyl ketone 2-fury1 (thiocarbonyl) hydrazone. Nippon Kugaku Kuishi 1.
1983,
518-522.
5. Otomo, M., 2,2’-Dipyridyl-2-quinolyhydrazone as a reagent for the spectrophotometric determination of metals. The extractive spectrophotometric determination of palladium(H). Anal. Chim. Acta 116, 161(1980). 6. Otomo, M., Ano, S., and Kako, H., Solvent extraction and spectrophotometric determination of iron(H) with 2,2’-dipyridyl-2-quinolylhydrazone. Microchem. J. 26, 228-235 (1981). 7. Otomo, M., Ito, A., and Doi, K., Solvent extraction and spectrophotometric determination of cadmium with 2,2’-dipyridyl-2-quinolylhydrazone. Jupun Anal. 31, E21-E26 (1982). [in English] 8. Singh, R. B., Odashima, T., and Ishii, H., Spectrophotometric and analog derivative spectrophotometric determination of micro-amounts of iron with 2,2’-dipyridyl-2-benzothiazolylhydrazone. Anulys? 108, 1120- 1127 (1983).