Specific Colorimetric Reagents for the Determination of Palladium(ll) Krishna K. Saxena' and Arun K. Dey Chemical Laboratories, University of Allahabad, Allahabad, India The use of tropaeolin 0, tropaeolin 00, and tropaeolin 0 0 0 f o r the colorimetric determination of Pd(ll) was examined. TPO and TPOOO produce colored complexes with Pd(ll) at pH 3.5 and 4.0, respectively. No change i n color was noticed with TPOO. The composition of these chelates as determined by the continuous variations and mole ratio methods is 1to 2 (metal-ligand). The apparent stability constant of Pd-TPOO chelate, at pH 4.0 and 2 5 O C, is of the order of 10'0. A 5-fold concentration of reagents was necessary for the full development of color intensity with both reagents. Pd-TPO chelate is stable between pH 2.0 and 5.5 and Pd-TP000 chelate between 3.0 and 6.2, as indicated by the constancy of A,, values. The absorbance is constant only between pH 3.0 and 4.0 i n the first case and pH 3.0 and 5.2 i n the second. Beer's law i s valid over concentration 0.28 to 9.57 ppm with both TPO and TP000. The optimum range for the effective colorimetric determination is 0.5 to 7.2 ppm i n both cases. The sensitivity (for an absorbance of 0.001) is 0.085 and 0.026 pg of Pd per sq cm for TPO and TP000, respectively. Other platinum metals do not interfere i n the determinations.
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IN SPITE OF publications ( I , 2 ) on colorimetric reagents for palladium(II), few reagents may be considered suited from the viewpoint of both sensitivity and selectivity. Sogani and Bhattacharya (3) reported 3-hydroxy-l-p-sulfonatophenyl-3phenyltriazine as a highly selective reagent with a sensitivity (for an absorbance of 0.001) of 0.05 pg per ml. Burke and Yoe (4) found 1-thioglycerol to be selective, though with less sensitivity for Pd. Buscarons and Mene (5) showed that 2or 4-ethoxy or methoxy derivatives of hydroxyiminoacetanilides are nearly specific for Pd and the sensitivity is of the order of 1 pg per ml. A large number of compounds, mostly dyes, were examined by Popa and coworkers (6-9) for their color formation with Pd(I1); it was found that specific reagents are azo dyes of the type R1-N=N-R2 containing an -OH , gmup in QositEons adjacent to the azo group. The dyes tropaeqlin 0 fTPO), tropaeolin 00 (TPOO), and tropaeolin 000 (TPOOO) were mentioned for the colorimetric determination of Pd(I1). It was of interest to examine these dyes in detail for their 1 Present address, Department of Chemistry, Malaviya Regional Engineering College, Jaipur, India.
(1) F. E. Beamish and W. A. E. McBryde, Anal. Chim. Acta, 9, 349 (1953). (2) Ibid., 18, 551 (1958). 29, 397 (3) N. C. Sogani and S. C. Bhattacharya, ANAL.CHEM., (1957). (4) R. W. Burke and J. H. Yoe, Talanta, 10, 1267 (1963). (5) F. Buscarons and R. Mene, Chim. Anal., 45,72 (1963). (6) G . Popa, Wiss. 2. Friedric-Schiller- Uniu., Jena-Naturwiss. Reine, 10, 5 (1960-61). (7) G . Popa, V. Croitoru, and D. Costache, Studia Unil;. BabesBolyai, Ser. Chem., 1, 195 (1963). ( 8 ) G . Popa, V. Croitoru, and E. G. Radulescu, Ser. Stiint. Nut. Chim., 10, 197 (1961). (9) G . Popa, D. Negoin, and G. Baiulescu, Acad. Rep. Populare Romine Studii Cercetari Chem., I, 73 (1959).
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PH Figure 1. Effect of pH on stability of Pd-TP000 chelate Concentration of PdClz and TP000. 8.0 X 10-5M sensitivity and selectivity for Pd(I1) and the results of these studies are reported here. The chelate Pd-TPO has been described (IO). EXPERIMENTAL
Apparatus. Absorbance measurements were made with a Unicam SP-500 spectrophotometer, using IO-mm matched glass cells, against distilled water blanks. pH measurements were made with a k e d s & Northrup direct-reading pH meter. All measurements were at 25" C. Materials. PALLADIUM SOLUTION.A stock solution of palladium was prepared by dissolving PdClz (Johnson, Matthey & Co., London) in water acidulated with hydrochloric acid. The solution was standardized by estimating palladium as dimethyl glyoximate. COLORIMETRIC REAGENTS.Standard solutions of TPO, TPOO, and TPOOO (British Drug House indicators) were prepared in distilled water. OTHERREAGENTS.All other solutions were prepared from analytical grade chemicals and standardized by the usual methods. RESULTS
TPO, TPOO, and TPOOO were added separately to palladium (11) solution and the pH was adjusted to 4.0 by the addition of acid or alkali. The absorbances of the mixtures and of the reagents alone were measured at different wavelengths. (10) R. L. Seth and A. K. Dey, J. Indian Chem. Soc., 40,794 (1963).
Oi4 0
t ? I " '
k 2 S 4 5 6 7 IH Figure 2. chelate
Effect of pH on absorbance of Pd-TPO
Concentration of PdClz and TPO. 8.0 X 10-5M
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It is evident that Pd(I1) reacts with TPO and T P 0 0 0 , forming complexes as shown by the shift in, . , ,X whereas there is no shift in the Amax of TPOO on addition of Pd(I1) solution. This clearly shows that there is no reaction in this case. The absorbance of a solution of TPOO remains the same in either the absence or presence of Pd(I1). Properties of Colored Complex. EFFECT OF pH. Pd-TPO chelate is stable between pH 2.0 and 5.5 and P d - T P 0 0 0 between pH 3.0 and 6.2 (Figure l), as shown by the constancy of Amax within this pH range. However, the absorbance is constant only between pH 3.0 and 4.0 in the first case (Figure 2) and between 3.0 and 5.2 in the second (Figure 3). REACTION RATEAND STABILITY.With TPO, color formation is instantaneous but TPOOO produces a color only after standing for 15 minutes at room temperature. The color once formed is stable for at least 48 hours. ORDEROF ADDITION OF REAGENTS.The order of addition of reagents has practically no effect on the absorbance of the complex. EFFECT OF TEMPERATURE. Temperature has no effect on the absorbance of the chelates. ORGANIC SOLVENTS.Various organic solvents were used in an attempt to extract the organopalladium complex from its aqueous solution. No visible extraction was observed with many common organic solvents, including 1-butanol, benzene, carbon tetrachloride, chloroform, and ethyl acetate, an indication that the chelates are ionic in character. By use of ion exchange resins and electrophoresis methods also, the chelates were found to be anionic in nature. ADHERENCE TO BEER'SLAW. Beer's law is valid over the palladium concentration range of 0.28 to 9.57 ppm with both TPO and T P 0 0 0 . MOLERATIOSTUDIES.Two methods were employed to establish a mole ratio for Pd-reagent in the palladium chelate of TPOOO in solution. Seth and Dey (IO)have reported the composition of Pd-TPO chelate as 1 to 2. The mole ratio (11) and the continuous variations methods (12) (Figures 4 and 5 ) indicate the composition to be 1 to 2 (metal-ligand). SENSITIVITY AND PRECISION. For log Zo/Z = 0.001, the sensitivity is 0.085 and 0.026 pg of Pd per sq cm for TPO and T P 0 0 0 , respectively. The optimum range for the effective
(11) J. H. Yoe and A. L. Jones, IND. ENG. CHeM., ANAL.ED., 18, 111 (1944). (12) P. Job, Compr. rend., 180, 928 (1925); Ann. Chim. (France), 9, 113 (1928).
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PH Figure 3. Effect of pH on absorbance of PdTPOOO chelate Concentration of PdCI, and TP000. 8.0 X 10-6M
Table I. Absorbancies of Reagents and Mixtures
System
PH
Color
Pd-TPO Pd-TPOO Pd-TP000
3.5 4.0
Violet
4.0
Violet
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Yellow
A,., mp Reagent Chelate 380 510 450 450 490 550
A
[Pd 2 t ] / @ d 2t] -tb P O O d
Figure 4. Composition of Pd-TP000 chelate by method of continuous variations pH 4.0. Temperature 25 "C. 570 mp Concentration A . 4.00 x 1 0 - 4 ~ B. 2.00 x 1 0 - 4 ~ C. 1.33 X IO-'M VOL. 40, NO. 8, JULY 1968
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[wa+pood Figure 5. Composition of Pd-TP000 chelate by mole ratio method
Figure 6. Effect of reagent concentration on Pd-TPO chelate pH 3.5. 550 mfi Concentration of PdCL 2.4 X 10-KM
pH 4.0. Temperature 25°C. 570 mp Concentration of TPOOO A . 1.00 x 1 0 - 4 ~ B. 6.66 X 10-5M
spectrophotometric determination was, however, found to be 0.5 to 7.2 ppm in both cases. A 5-fold concentration of the reagent was necessary for the full development of color intensity with both reagents (Figures 6 and 7). EFFECTOF DIVERSE IONS. The tolerance limits to diverse ions are summarized in Table I1 for both systems.
0'4
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Table 11. Tolerance to Diverse Ions
(4.27 ppm of palladium)
Ion
Added as
Fe(II1) Co(I1) Ni(I1) Ru(II1) Rh(II1) Os(" Ir(II1)
F~z(SO~)~ CO(NOa)z*6Hz0 NiS04.6Hz0 RuC13 RhCI3 OSCI, IrCh HzPtCls.6H20 CUSOa. 5H20 AuC13 KC1 KBr KI KzSO4 KNOI
W V )
Cu(I1) Au(II1) Chloride Bromide Iodide Sulfate Nitrate
Limiting concentration for f 2 . 0 x relative error, ppm TPO TPOOO (4 x 10-6M) (4 x 10-6M) 112 34
10 12
12 8 13 65 43 20 10 8
33
202 206 380 55
52 31 50
142 160
60
80 20 80 40
127
384 248
Table 111. Stability Constant of P d - T P 0 0 0 Chelate
Figure 7. Effect of reagent concentration on Pd-TP000 chelate pH 4.0. 570 mp Concentration of PdCI2. 2.4 X 10-KM STRUCTURE OF PALLADIUM CHELATES OH ( 1 3
(pH 4.0, 570 mb, 25 O C.) Method
log K
Mole ratio (11) Continuous variations (12) Dey and associates (13, 14) Av.
9 . 5 f 0.1 9.9 f 0.1 10.0 f 0 . 5
9.8
(13) A. K. Mukherji and A. K. Dey, J . Inorg. Nucl. Chem., 6, 314 (1958). (14) A. K. Mukherji and A. K. Dey, Anal. Chim. A d a , 18, 324 (1958). 1282
ANALYTICAL CHEMISTRY
Tropaeolin 0
Tropaeolin 000
In TPO there are three alternative positions, where chelation mav occur :
1. Between two hydroxyl groups numbered 1 and 2 2. Between OH(1) and nitrogen (3) of the azo group, or 3. Between OH(1) and nitrogen (4)of the azo group
In T P 0 0 0 , there are only two alternative positions:
of the color of the complex with the B.D.H. ion exchange resin
4. Between OH(1‘) and nitrogen (2’) of the azo group 5. Between OH(1’) and nitrogen (3’) of the azo group
Amberlite IR-45(OH). EVALUATION OF STABILITYCONSTANT.The apparent stability constant of the P d - T P 0 0 0 chelate was calculated from the absorbance data by three methods (Table 111).
Seth and Dey (IO) suggested position 2 in the case of chelation with TPO. Similarly, position 4 is preferred in the case of the TPOOO chelate of palladium and the tentative structure of P d - T P 0 0 0 chelate is believed to be:
P d - T P 0 0 0 Chelate The anionic nature of the chelate has been confirmed by electrophoresis studies and also by the complete adsorption
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RECOMMENDED PROCEDURE
An aliquot of the palladium solution is suitably diluted to contain ca. 2 to 15 ppm of palladium. To 10 ml of the dilute solution, an equal volume of 5-fold concentration of either TPO or TPOOO is added. The pH of the mixture is adjusted to 3.5 (for TPO) and 4.0 (for T P 0 0 0 ) and the total volume raised to 25 ml. The mixture is allowed to equilibrate for 15 minutes and the absorbance is measured with a spectrophotometer using IO-mm glass cells at 550 mp (for TPO) and 570 mp (for TPOOO). The concentration of palladium is read from Beer’s law plots prepared under identical conditions. RECEIVED for review December 1 1 , 1967. Accepted March 14, 1968. Work supported by the Council of Scientific and Industrial Research, New Delhi.
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Determination of Impurities in Bromine by Infrared Spectrophotometric Methods Lynn H. Hahn and Loren E. Pauling Michigan Chemical Corp., 500 North Bankson, St. Louis, Mich. 48880 An analytical method was needed for rapidly determining the concentration of impurities in commercial bromine. Recent improvements in bromine quality have necessitated more sensitive and informative analytical techniques. Much about the quality of bromine can be determined from the infrared spectrum because bromine i s a very effective transmitter of infrared energy. Impurities encountered in bromine produced from brine can include water, hydrogen chloride, hydrogen bromide, carbon dioxide, nitric oxide, carbonyl bromide, carbon tetrachloride, bromotrichloromethane, chloroform, ethyl bromide, and dibromobenrene. One impurity, chlorine, which does not show infrared absorption, can be determined by causing reaction with hydrogen bromide which converts the chlorine to hydrogen chloride. The hydrogen chloride is infrared sensitive and its absorption can be related to chlorine concentrations. Cell path lengths of 2 centimeters have been used to provide detection of impurities in concentrations below 1 pg per ml.
INTHE PAST FEW YEARS, the quality of commercial bromine has been improved significantly through the use of purification techniques. Bromine in the past was sold with a purity specification of 99.8 while today purity specifications exceed 99.95 %. The analysis of 99.8 bromine generally consisted of determining the water content by some sort of absorption train technique, determining the chlorine content using a gravity change procedure, and determining the nonvolatiles concentration by evaporating down a sample and weighing the residue. These analyses do not tell anything about the several other impurities which codistill with bromine and these methods are not sensitive enough to be of practical use when
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analyzing 99.95 or better bromine. Analytical methods were needed which could detect concentrations of impurities in the 1 pg per ml of bromine range. Our laboratory work has shown that infrared methods can be used to detect most of the impurities in bromine and quantitative determinations made. A review of the literature shows that the use of infrared to analyze bromine is not new but has probably been used in some laboratories for at least 10 years. Duvall and Kiley reported in 1958 the use of infrared to determine water in bromine ( I ) . Wagner in 1963 reported that bromine transmits infpared energy (2, 3). Stenger reported in 1964 and 1966 the use of infrared to analyze bromine, particularly for organic impurities ( 4 5 ) . Except for the water determination, these papers do not give details of the technique. This paper describes the technique and also a method for determining chlorine in bromine by infrared techniques. EXPERIMENTAL
Equipment and Procedures. Infrared spectra of bromine are recorded using a cell designed to provide a path length so that sensitivities of the order of 1 pg of impurity per ml of bromine are obtained. A cell thickness of about 2 cm is sufficient. The cell is mainly inert to bromine and when handled with care is safe to use. (1) R. B. Duvall and L. R. Kiley, ANAL.CHEM.,30, 549 (1958). (2) H. Wagner, Narurwissenschaften, 50, 223 (1963). (3) H. Wagner, 2.Anorg. Allgem. Chem., 337, 54 (1965). (4) M. S. Chao and V. A. Stenger, Tulanta, 11, 271 (1965). (5) V. A. Stenger, Angew. Chem. Intern. Ed., 5 , (3), 280 (1966). VOL. 40, NO. 8, JULY 1968
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