- Email: [email protected]
Spectrophotometric Determination of Iron and Chromium in Cr-Electroplating Baths at the Helwan Engineering Industrial Company Using Pyrocatechol as Indicator
JOBNAME: MIC 54#1 96 PAGE: 1 SESS: 2 OUTPUT: Wed Aug 7 11:57:35 1996 /xypage/worksmart/tsp000/72869f/16pu
MICROCHEMICAL JOURNAL ARTICLE NO. 0078
54, 72–80 (1996)
Spectrophotometric Determination of Iron and Chromium in Cr-Electroplating Baths at the Helwan Engineering Industrial Company Using Pyrocatechol as Indicator M. A. ZAYED,*,1 B. N. BARSOUM,*
AND
AMEL E. HASSAN†
*Chemistry Department, Faculty of Science, Cairo University, Giza A.R., Egypt; and †Helwan Engineering Industrial Company (HEIC, 99), Cairo A.R., Egypt Received September 22, 1995; accepted January 6, 1996 The pyrocatechol (P.C.) was used as a selective spectrophotometric reagent for Fe(III) and Cr(VI), under optimum conditions. The effects of pH and temperature on the spectra of iron–P.C. chelate and chromium–P.C. chelate were studied to select the optimum conditions for determination of iron(III) and chromium(VI) in synthetic and in electroplating bath solutions. The suitable conditions for determination of Cr(VI) and Fe(III) were 95°C, and 25°C at lmax 4 515 and 585 nm at the same pH 4 5.0, respectively. The method succeeded for determination of Cr(VI) and Fe(III) with recovery 99.31–101.6%. The standard deviation was found to be 0.98–1.6 which refered to the reproducibility and reliability of the applied procedures. The suggested procedures using P.C. indicator were applied successfully for analysis of Fe and Cr in 16 samples collected from the chromium-electroplating bath containing Fe(III) as contaminant. These procedures were also used for monitoring Fe(III) and Cr(VI) in the presence of each other during the electroplating of steel utensils at the Helwan Engineering Industrial Company, Factory 99. © 1996 Academic Press, Inc.
INTRODUCTION Vladimir Ruml (1) suggested a procedure for determination of several types of species in electroplating baths. CrO3, Cr(III), and Fe(III) were determined in Cr-electroplating bath. A rapid spectrophotometric method was recommended for determination of Fe(III) in chromium plating solution (2–5). The iodometric method was used for determination of Cr(III) and Cr(VI) which were the most important components contained in the Crelectroplating baths and Fe was determined after extraction with a amylacetate– isobutylmethylketones mixture by a complexometric method (6). The optimum conditions for determination of Fe(III) and other heavy metals were selected by Deng et al. (7) using the atomic absorption technique. The inductively coupled plasma atomic emission was used (8, 9) for determination of Fe and other heavy metals in electroplating waste water. The detection limits were <6.6 × 10−3 mg ml−1, relative standard deviation <4.0% in 10 measurements, and recoveries were 87 to 100%. Spectrophotometric methods were suggested (10–13) for determination of Cr(III) and Cr(VI). Detection limit precision and recovery were obtained. In this paper both Cr(VI) and Fe(III) were spectrophotometrically determined using P.C. indicator in chromium-electroplating bath samples. EXPERIMENTAL Materials and Solutions All chemicals used were of the highest purity coming from Merk and BDH. The water used was bidistilled from all glass equipments. 1
To whom all correspondence should be addressed. 72
0026-265X/96 $18.00 Copyright © 1996 by Academic Press, Inc. All rights of reproduction in any form reserved.
JOBNAME: MIC 54#1 96 PAGE: 2 SESS: 2 OUTPUT: Wed Aug 7 11:57:35 1996 /xypage/worksmart/tsp000/72869f/16pu
DETERMINATION OF Fe AND Cr USING PYROCATECHOL
73
Pyrocatechol (P.C.) solution (0.10 M) in 100 ml bidistilled water and 0.001 to 0.01 M sodium hydroxide solutions were prepared by dilution from a saturated solution (18 M carbonate free stock solution). Different solutions of Fe(III) were measured at lmax 4 585 and at 25°C and Cr(VI) at lmax 4 515 nm at pH 5.0 after heating the same mixture to 95°C for 4 min. The spectrophotometric data at both temperatures for the mixture are shown in Fig. 1. Spectrophotometric Analysis of Fe(III)–Cr(VI) in Synthetic Mixture This step is a preliminary one to analyze Fe(IV) and Cr(VI) in electroplating bath samples at the Helwan Engineering Industrial Company, Factory 99 (HEIC, 99) in Helwan (Egypt). This process starts with the measurement of spectra of different concentrations of Fe(III) (5.0 to 51.99 ppm) in the presence of excess constant Cr(VI) concentration (161.43 ppm) at pH 5.0. Sulfuric acid solutions (0.001 to 0.01 M) were prepared and standardized against standard Na2CO3 (0.01 M) as usual. The 0.001 M Fe(III) was prepared by dissolving 0.0399 g ferric sulfate in 100 ml bidistilled water acidified with a few drops sulfuric acid. The 0.001 M Cr(VI) was prepared by dissolving 0.0588 g of potassium dichromate in a suitable volume of bidistilled water. These solutions were standardized using recommended procedures (17).
FIG. 1. The spectra of (a) the Fe(III)–P.C. complex of 1.6 × 10−4 M, at temperature 25°C and (b) the Cr(VI)–P.C. complex of 0.8 × 10−4 M, at temperature 25°C.
JOBNAME: MIC 54#1 96 PAGE: 3 SESS: 2 OUTPUT: Wed Aug 7 11:57:35 1996 /xypage/worksmart/tsp000/72869f/16pu
74
ZAYED, BARSOUM, AND HASSAN
Procedures 1. Selection of Optimum Conditions for Determination of Iron(III) and Chromium(VI) in Free and Mixed States by P.C. Indicator (a) Selection of suitable pH. To 1 to 4 ml of 1.00 to 1.15 × 10−2 M Fe(III) add 5 ml of 0.1 M P.C. and adjust the pH to the range 4.0–9.0 in 25 ml final volume, in case of iron reaction with P.C. Add 9 ml of 0.1 M P.C. to 8–10 ml of Cr(VI) and adjust the pH to the range 4.0–8.0. Measure the absorbance of the colored solutions at different pH values and at the wavelength range 400–800 nm at 25°C. From these data select the pH at lmax, which gives the same maximum molar absorptivity characteristic for each of the Fe(III)–P.C. and Cr(VI)–P.C. complexes. (b) Effect of temperature on lmax of the Fe(III)–P.C. and Cr(VI)–P.C. complexes. To a definite volume of Fe(III) or Cr(VI) add 7 ml of 0.10 M P.C. indicator in 25 ml water of pH 5.0. Measure absorbances of the solutions and plot the A–l curve for each Fe–P.C. and Cr–P.C. complex at 25°C, at l 4 300 to 680 nm. Under these conditions only Fe–P.C. gives lmax 4 585 nm. Repeat this step for both complexes after heating each complex solution at 95°C for 4 min. Cool and measure the absorbances and plot again the A–l curves for each complex. Cr–P.C. was found to be of lmax 4 515 nm (Figs. 1 and 2). Mix equimolecular amounts of Fe(III) and Cr(VI) and add a suitable volume of P.C. indicator adjusting the pH to 5.0 in 25 ml as a final volume. Measure the absorbances and plot A–l curves at 25°C. Repeat this step with heating similar mixtures at 95°C for 4 min and measure absorbances after cooling. Then plot A–l curves for these mixtures. From the A–l curves at 25 and 95°C of Fe(III) and Cr(VI) in separate states and in mixtures, it was clear that Fe(III) could be determined at l 4 585 nm and Cr(VI) at 515 nm at pH 5.0 in the presence of each or in separate states using P.C. as indicator. (c) Obeyance to Beer’s law. In order to check the obeyance of Fe(III) concentration to Beer’s law when mixed with excess Cr(VI), various amounts of Fe(III) were added to excess Cr(VI) in the presence of P.C. indicator at pH 5.0 and at 25°C. The absorbance was measured at lmax 4 585. The calibration curve of Fe(III) was obtained by the plot of concentration against absorbance at l 4 585 nm. The obeyance of Cr(VI)–P.C. in a mixture of Fe and Cr at excess Fe(III) and various amounts of Cr is obtained by the plot of measured absorbances at l 4 515 nm of the mixture, after its heating at 95°C, against the concentration of the varied species. 2. Determination of Fe(III) and Cr(VI) in Chromium-Electroplating Bath This involved two steps. The first was the collection of the samples from the electroplating baths and the second was its preparation for spectrophotometric measurement as previously mentioned in synthetic mixtures (Procedure 1b). (a) Collection of electroplating bath samples. Sixteen samples were collected from different positions of the bath. Four samples were collected from the four corners of the bath and the other four from the sides of the bath at distances 20, 40, 60, and 80 cm from the surface. The other eight samples were collected from different depths at 10, 20, 30, 40, 50, 60, 70, and 80 cm. Each sample (0.5 ml) was diluted up to 100 ml in a measuring flask. (b) Spectrophotometric measurements. The diluted bath sample (0.5 ml) was treated with 5 ml of 0.1 M P.C. indicator at pH 5.0 in a 25 ml measuring flask and completed to the mark with water.
JOBNAME: MIC 54#1 96 PAGE: 4 SESS: 2 OUTPUT: Wed Aug 7 11:57:35 1996 /xypage/worksmart/tsp000/72869f/16pu
DETERMINATION OF Fe AND Cr USING PYROCATECHOL
75
FIG. 2. The spectra of (a) the Fe(III)–P.C. complex of 1.7 10−4 M, at temperature 95°C and (b) the Cr(VI)–P.C. complex of 0.8 × 10−4 M, at temperature 95°C.
The absorbance of the mixture was measured at 25°C and l 4 585 nm to determine Fe(III). Its concentration was determined by translating absorbance of electroplating bath solution from the calibration curve of Fe(III) in synthetic like mixtures (Table 1). The absorbance of the mixture heated at 95°C for 4 min and then cooled was measured at l 4 515 nm for Cr(VI). The Cr(VI) concentration in each electroplating bath sample TABLE 1 Spectrophotometric Microdetermination of Cr(VI) at lmax 4 515 nm, pH 5.0, and Temperature 95°C in Synthetic Mixture of (Cr + Fe) Using P.C. Indicator at High Concentration Limit Chromium Taken
Found
Recovery (%)
S.D.
51.99 51.99 51.99 51.99 51.99
48.56 47.40 48.06 46.94 46.91
93.40 91.17 93.58 90.28 90.22
0.858
JOBNAME: MIC 54#1 96 PAGE: 5 SESS: 2 OUTPUT: Wed Aug 7 11:57:35 1996 /xypage/worksmart/tsp000/72869f/16pu
76
ZAYED, BARSOUM, AND HASSAN
was determined from the constructed calibration curve of Cr(VI) in synthetic mixtures under similar conditions (Table 2). The concentration of Fe and Cr in these bath samples were measured by standard gravimetric and volumetric methods and by flame atomic absorption method. Instruments The spectrophotometric analysis was performed using a Milton Roy, USA (UV–Vis) instrument using a 1 cm quartz cell and water as a blank. The atomic absorption measurements were carried out using a PYE UNICAM 1900 spectrometer at the Cairo University Microanalytical Center. The pH values were adjusted by using NaOH or sulfuric acid solutions and using a pH–MV digital ion-analyzer, Model 701A. RESULTS AND DISCUSSION Spectrophotometric Study of the Fe(III)–P.C. and Cr(VI)–P.C. Complexes in Solution This study involves at first the effect of pH (in the range from 3.0 to 7.0) on the spectra of the iron complex. The suitable pH for the microdetermination of Fe(III) in its complex solution is found to be 5.0 using P.C. as indicator at the suitable lmax 4 585 nm (e 4 4.166 × 103 mol−1 cm−1) at 25°C. The concentrations of Fe(III) up to 9.38 ppm (Table 3) give percentage recovery ranging from 92.17 to 101.6%. The study of pH (4.0 to 6.5) on the spectra of the Cr(VI)–P.C. complex found that no sharp peaks were obtained at pH 5.0, at 25°C, and in the wavelength range from 350 to 750 nm. The effect of pH (at the same range) on Cr(VI)–P.C., after heating to 95°C for 4 min and cooling, gives a band at lmax 4 515 nm and pH 5.0 of maximum molar absorptivity 6 4 1.36 × 103 mol−1 cm−1. Under these conditions, Cr(VI) concentrations ranging from 8.31 to 41.5 ppm (Table 3) give percentage recovery from 82.16 to 105.08%. Therefore it is possible to analyze a synthetic mixture of both Fe(III) and Cr(VI) using P.C. spectrophotometrically, by measurement of iron at 25°C and lmax 4 585 nm. The Fe(III) obeys Beer’s law in the range from 18.0 to 125.0 ppm and the percentage recovery is found to be between 93.8 and 103.95%. The standard deviation is found to be 0.838 for five replicates of each concentration of iron in a mixture. The measurement of variable concentration of Cr(VI), 25 to 110 ppm, is made TABLE 2 Spectrophotometric Microdetermination of Fe(III) at lmax 4 585 nm, pH 5.0, and Temperature 25°C in Synthetic Mixture of (Cr + Fe) Using P.C. Indicator at High Concentration Limit Iron (ppm) Taken
Found
Recovery (%)
S.D.
61.43 61.43 61.43 61.43 61.43 61.43 61.43
61.50 62.96 61.92 61.50 59.35 62.44 57.62
100.1 102.4 100.7 100.1 96.6 101.6 93.8
1.635
JOBNAME: MIC 54#1 96 PAGE: 6 SESS: 2 OUTPUT: Wed Aug 7 11:57:35 1996 /xypage/worksmart/tsp000/72869f/16pu
77
DETERMINATION OF Fe AND Cr USING PYROCATECHOL
TABLE 3 Spectrophotometric Microdetermination of Fe(III) by P.C. Indicator at pH 5.0, lmax 4 585, and Temperature 25°C in 25 ml Solution and Cr(VI) at pH 5.0, lmax 4 515 nm, and Temperature 95°C in 25 ml Solution Fe(III), ppm 1.34 (1.34) 2.68 (2.68) 4.02 (4.08) 5.36 (5.38) 6.70 (6.50) 8.04 (7.96) 9.38 (8.65)
Recovery (%)
Cr(VI), ppm
Recovery (%)
100.0
8.31 (7.89) 16.63 (14.29) 20.79 (18.0) 24.95 (20.5) 29.12 (30.6) 33.43 (32.2) 37.43 (38.5) 41.59 (39.7)
94.89
100.0 101.6 100.3 97.0 99.0 92.17
85.64 85.77 82.16 105.08 95.48 102.80 95.66
Note. The values in parenthesis are the found concentration spectrophotometrically.
at pH 5.0 after heating to 95°C in the presence of excess iron of 125 ppm to test the obeyance of chromium to Beer’s law. It is found that Cr(VI) obeys Beer’s law in the concentration range from 6.0 to 48.0 ppm and at l 4 515 nm. The percentage recovery is found to be between 89.5 and 93.4%, and the SD 4 1.88 for six replicates of each concentration of synthetic mixture. These values of SD refer to the accuracy and precision of the analysis of Fe(III) and Cr(VI) mixtures using P.C. indicator. The percentage recovery values of Fe(III) in excess Cr(V), or vice versa, refer to the reliability of the suggested procedures. Analysis of Iron and Chromium in Cr-Electroplating Baths at the HEIC, 99 Plants From the previous detailed analysis of the synthetic mixture of Fe(III) + Cr(VI), it possible to analyze their mixtures in Cr-electroplating baths of iron tools (spoons, forks, etc.) applying the same principles. The spectrophotometrically determined concentrations of Fe(III) and Cr(VI) in the electroplating bath samples collected from different positions in the bath are shown in Tables 4 and 5. The Fe(III) spectrophotometric values (Table 4) determined in samples collected at different corners are found to be 14.81, 14.70, 14.90, and 15.2 ppm ml−1 and the values analyzed by gravimetric techniques usually used in the plant (14) are 14.0, 12.9, 13.5, and 15.23 ppm ml−1. This shows the greater regularity of the spectrophotometric data than the conventional gravimetric data. The corresponding atomic absorption values of Fe(III) in the presence of Cr(VI) are 9.59, 10.41, 11.25, and 9.95 ppm ml−1. These are less than those obtained by both spectrophotometric and gravimetric techniques. This may be attributed to the problems
JOBNAME: MIC 54#1 96 PAGE: 7 SESS: 2 OUTPUT: Wed Aug 7 11:57:35 1996 /xypage/worksmart/tsp000/72869f/16pu
78
ZAYED, BARSOUM, AND HASSAN
TABLE 4 Microdetermination of Fe(III) Concentration Spectrophotometrically in the Cr-Electroplating Bath Using P.C. Indicator in Comparison with Gravimetric Data Fe(III) (ppm/ml) Sample no. Corner 1 Corner 2 Corner 3 Corner 4 Surface distance Surface distance Surface distance Surface distance Depth 10 cm Depth 20 cm Depth 30 cm Depth 40 cm Depth 50 cm Depth 60 cm Depth 70 cm Depth 80 cm
20 40 60 80
cm cm cm cm
Gravimetry
Spectrophotometry
14.000 12.900 13.500 11.230 12.900 11.500 10.700 11.000 13.080 12.000 11.150 11.125 10.450 11.149 11.500 11.250
14.812 14.700 14.900 15.200 13.900 13.900 12.380 13.670 13.159 13.418 11.353 12.643 11.350 11.766 12.900 11.330
usually faced in iron determination by FAAS in the presence of chromium species in electroplating baths as previously reported (15–19). At four surface distances from the bath sides at 10, 20, 30, and 40 cm, the iron(III) concentration determined by the gravimetric technique varied from 10.7 to 12.9 ppm ml−1, TABLE 5 Microdetermination of Cr(VI) Concentration Spectrophotometrically in the Cr-Electroplating Bath Using P.C. Indicator in Comparison with Volumetric Data Cr(VI) (ppm/ml) Sample no. Corner 1 Corner 2 Corner 3 Corner 4 Surface distance Surface distance Surface distance Surface distance Depth 10 cm Depth 20 cm Depth 30 cm Depth 40 cm Depth 50 cm Depth 60 cm Depth 70 cm Depth 80 cm
20 40 60 80
cm cm cm cm
Volumetry
Spectrophotometry
109.00 98.40 93.50 99.50 98.80 98.00 98.20 98.80 102.50 102.00 101.60 101.20 94.80 97.20 96.30 94.20
80.66 87.31 86.47 83.13 89.80 80.65 91.96 101.37 100.60 92.55 97.45 101.37 101.87 101.90 85.65 86.48
JOBNAME: MIC 54#1 96 PAGE: 8 SESS: 2 OUTPUT: Wed Aug 7 11:57:35 1996 /xypage/worksmart/tsp000/72869f/16pu
DETERMINATION OF Fe AND Cr USING PYROCATECHOL
79
whereas that determined spectrophotometrically ranged from 13.6 to 12.45 ppm ml−1. This means that these spectrophotometric values are still very near to the values of Fe(III) at different corners of the bath. The values obtained by atomic absorption at different surface distances ranged from 9.0 to 11.37, which are still less than those obtained by both gravimetric and spectrophotometric techniques. At different depth distances (10–80 cm), Fe(III) concentration gravimetrically determined ranged from 13.08 to 11.25 ppm ml−1 and spectrophotometrically from 13.16 to 11.3 ppm ml−1, which shows correlation between the results. This also shows the decrease of Fe(III) on going deeper into the bath. The calculated SD 4 0.98 for eight replicates of iron in both samples shows the reproducibility of the spectrophotometric results obtained from the analyzed samples in chromium electroplating baths. On the other hand, the chromium concentration determined in its bath by the volumetric technique (Table 5a) is found to be in the range from 93 to 109 ppm ml−1 in bath samples, but it is not regularly varied at different surface or depth distances. The concentration of Cr in the samples determined spectrophotometrically (Table 5b) is found to be in the range from 80 to 111 ppm ml−1. At four corners in the bath, the difference between the volumetric and the spectrophotometric data is found to be 7–19 ppm, at the distance from the sides it is 3–16 ppm, and at different depths it is 3–10 ppm, which is actually attributed to the difference in efficiency between the volumetric and the spectrophotometric techniques (20–25). The atomic absorption data for Cr concentration in some selected samples are more or less the same as those obtained spectrophotometrically, which shows the success of using P.C. as indicator under optimum selected conditions to determine Cr by this fast (no more than 1 min for each sample), cheap, and accurate suggested procedure. The calculated standard deviation for one sample of five replicates is found to be 1.57%, which is comparable to the previously published work for similar bath analysis (26, 27). This also shows the reliability and reproducibility of the applied procedure for Cr analysis using P.C. indicator. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.
Rumel, V. Metallpraxis, 1971, 20(9), 352; Metallpraxis, 1971, 20(10), 406, 408, 412. Xiao, M. Diandu Yu Huanbao, 1988, 8(4), 23–25. Sumitoma Metal Industries Ltd., Jpn. Kokai Tokkyo Koho, 1984, 59, 212, 740. Ewald, G. Galvanotechnik, 1990, 81(4), 1365. Noelte, J. Galvanotechnik, 1990, 81(8), 2738. Bogenschuetz, A. F.; George, U. Oberflaechentechik, 1973, 2, 67–71. Deng, B.; Zhoa, X. H. Ching Hua Ta Hsuch Hsuch Pao, 1980, 20(3), 79–87. Dohi, K.; Wada, A.; Nakamura, S. R & D, Res. Dev. (Rube Steel Ltd.), 1991, 41(1), 146. Shan, Y.; Lihva, J. Huaxue Fence, 1989, 25(2), 93–94. Branstetr, J.; Huleja, J.; Sajo, I. Hutn. Listy, 1982, 37(10), 734. Dibenedetto, D.; Thomas, G. Eur. Pat. Appl., 1982, 59, 140. Sakurai, K.; Nishimura, K. Jpn. Kokai Tokkyo Koho, 1991, 104, 879. Xu, C. Youkuangye, 1991, 10(2), 612–614. Christian, G. D. Analytical Chemistry, 2nd ed. Wiley, New York, 1977. Savitskii, V. N.; Peleshenko, V. I.; Osadchii, V. I. Gidrobiol. Zh., 1986, 22(1), 62. Shen, Z.; Chen, Y.; Nie, F. Fenxi Huaxue, 1990, 18(1), 61. Bassett, J.; Denney, R. C. Text Book of Quantitative Inorganic Analysis, 4th ed., pp. 361, 440, Longman, 1985. 18. Ma, G.; Luo, J. Shanghai Huanjing Kexue, 1990, 9(6), 27.
JOBNAME: MIC 54#1 96 PAGE: 9 SESS: 2 OUTPUT: Wed Aug 7 11:57:35 1996 /xypage/worksmart/tsp000/72869f/16pu
80 19. 20. 21. 22. 23. 24. 25. 26. 27.
ZAYED, BARSOUM, AND HASSAN Xu, J.; Zhou, S. Diandu Yu Huanbao, 1991, 11(5), 33. Korol, L. S.; Levitman, K. Y.; Nagornaya, I. V. Khim. Kim. Technol. (Minsk), 1983, 16, 50–54. Feng, J.; Ving, W.; Zhang, B. Fenxi Huaxue, 1985, 13(8), 585. Feng, J.; Li, Y.; Zhang, B. Beijing Daxue Xuebao, Ziron Kexueban, 1988, 24(4), 436. Feng, J.; Wang, Z.; Zhang, B.; Liang, D. Fenxi Huaxue, 1983, 11(5), 384. Magyar, B. Atomspektrom. Spurenanal. Vortr. Kolloq., 1981, 401. Xu, C. Yonkuangye, 1991, 10(2), 61–64. Lieser, K. H.; Sondermeyer, S.; Kliemchen, A. Fresenius, Z. Anal. Chem., 1982, 517. Gordeev, S. K.; Krasnobryzhii, A. V. Zavod. Lab., 1982, 48(7), 23.
MICROCHEMICAL JOURNAL ARTICLE NO. 0078
54, 72–80 (1996)
Spectrophotometric Determination of Iron and Chromium in Cr-Electroplating Baths at the Helwan Engineering Industrial Company Using Pyrocatechol as Indicator M. A. ZAYED,*,1 B. N. BARSOUM,*
AND
AMEL E. HASSAN†
*Chemistry Department, Faculty of Science, Cairo University, Giza A.R., Egypt; and †Helwan Engineering Industrial Company (HEIC, 99), Cairo A.R., Egypt Received September 22, 1995; accepted January 6, 1996 The pyrocatechol (P.C.) was used as a selective spectrophotometric reagent for Fe(III) and Cr(VI), under optimum conditions. The effects of pH and temperature on the spectra of iron–P.C. chelate and chromium–P.C. chelate were studied to select the optimum conditions for determination of iron(III) and chromium(VI) in synthetic and in electroplating bath solutions. The suitable conditions for determination of Cr(VI) and Fe(III) were 95°C, and 25°C at lmax 4 515 and 585 nm at the same pH 4 5.0, respectively. The method succeeded for determination of Cr(VI) and Fe(III) with recovery 99.31–101.6%. The standard deviation was found to be 0.98–1.6 which refered to the reproducibility and reliability of the applied procedures. The suggested procedures using P.C. indicator were applied successfully for analysis of Fe and Cr in 16 samples collected from the chromium-electroplating bath containing Fe(III) as contaminant. These procedures were also used for monitoring Fe(III) and Cr(VI) in the presence of each other during the electroplating of steel utensils at the Helwan Engineering Industrial Company, Factory 99. © 1996 Academic Press, Inc.
INTRODUCTION Vladimir Ruml (1) suggested a procedure for determination of several types of species in electroplating baths. CrO3, Cr(III), and Fe(III) were determined in Cr-electroplating bath. A rapid spectrophotometric method was recommended for determination of Fe(III) in chromium plating solution (2–5). The iodometric method was used for determination of Cr(III) and Cr(VI) which were the most important components contained in the Crelectroplating baths and Fe was determined after extraction with a amylacetate– isobutylmethylketones mixture by a complexometric method (6). The optimum conditions for determination of Fe(III) and other heavy metals were selected by Deng et al. (7) using the atomic absorption technique. The inductively coupled plasma atomic emission was used (8, 9) for determination of Fe and other heavy metals in electroplating waste water. The detection limits were <6.6 × 10−3 mg ml−1, relative standard deviation <4.0% in 10 measurements, and recoveries were 87 to 100%. Spectrophotometric methods were suggested (10–13) for determination of Cr(III) and Cr(VI). Detection limit precision and recovery were obtained. In this paper both Cr(VI) and Fe(III) were spectrophotometrically determined using P.C. indicator in chromium-electroplating bath samples. EXPERIMENTAL Materials and Solutions All chemicals used were of the highest purity coming from Merk and BDH. The water used was bidistilled from all glass equipments. 1
To whom all correspondence should be addressed. 72
0026-265X/96 $18.00 Copyright © 1996 by Academic Press, Inc. All rights of reproduction in any form reserved.
JOBNAME: MIC 54#1 96 PAGE: 2 SESS: 2 OUTPUT: Wed Aug 7 11:57:35 1996 /xypage/worksmart/tsp000/72869f/16pu
DETERMINATION OF Fe AND Cr USING PYROCATECHOL
73
Pyrocatechol (P.C.) solution (0.10 M) in 100 ml bidistilled water and 0.001 to 0.01 M sodium hydroxide solutions were prepared by dilution from a saturated solution (18 M carbonate free stock solution). Different solutions of Fe(III) were measured at lmax 4 585 and at 25°C and Cr(VI) at lmax 4 515 nm at pH 5.0 after heating the same mixture to 95°C for 4 min. The spectrophotometric data at both temperatures for the mixture are shown in Fig. 1. Spectrophotometric Analysis of Fe(III)–Cr(VI) in Synthetic Mixture This step is a preliminary one to analyze Fe(IV) and Cr(VI) in electroplating bath samples at the Helwan Engineering Industrial Company, Factory 99 (HEIC, 99) in Helwan (Egypt). This process starts with the measurement of spectra of different concentrations of Fe(III) (5.0 to 51.99 ppm) in the presence of excess constant Cr(VI) concentration (161.43 ppm) at pH 5.0. Sulfuric acid solutions (0.001 to 0.01 M) were prepared and standardized against standard Na2CO3 (0.01 M) as usual. The 0.001 M Fe(III) was prepared by dissolving 0.0399 g ferric sulfate in 100 ml bidistilled water acidified with a few drops sulfuric acid. The 0.001 M Cr(VI) was prepared by dissolving 0.0588 g of potassium dichromate in a suitable volume of bidistilled water. These solutions were standardized using recommended procedures (17).
FIG. 1. The spectra of (a) the Fe(III)–P.C. complex of 1.6 × 10−4 M, at temperature 25°C and (b) the Cr(VI)–P.C. complex of 0.8 × 10−4 M, at temperature 25°C.
JOBNAME: MIC 54#1 96 PAGE: 3 SESS: 2 OUTPUT: Wed Aug 7 11:57:35 1996 /xypage/worksmart/tsp000/72869f/16pu
74
ZAYED, BARSOUM, AND HASSAN
Procedures 1. Selection of Optimum Conditions for Determination of Iron(III) and Chromium(VI) in Free and Mixed States by P.C. Indicator (a) Selection of suitable pH. To 1 to 4 ml of 1.00 to 1.15 × 10−2 M Fe(III) add 5 ml of 0.1 M P.C. and adjust the pH to the range 4.0–9.0 in 25 ml final volume, in case of iron reaction with P.C. Add 9 ml of 0.1 M P.C. to 8–10 ml of Cr(VI) and adjust the pH to the range 4.0–8.0. Measure the absorbance of the colored solutions at different pH values and at the wavelength range 400–800 nm at 25°C. From these data select the pH at lmax, which gives the same maximum molar absorptivity characteristic for each of the Fe(III)–P.C. and Cr(VI)–P.C. complexes. (b) Effect of temperature on lmax of the Fe(III)–P.C. and Cr(VI)–P.C. complexes. To a definite volume of Fe(III) or Cr(VI) add 7 ml of 0.10 M P.C. indicator in 25 ml water of pH 5.0. Measure absorbances of the solutions and plot the A–l curve for each Fe–P.C. and Cr–P.C. complex at 25°C, at l 4 300 to 680 nm. Under these conditions only Fe–P.C. gives lmax 4 585 nm. Repeat this step for both complexes after heating each complex solution at 95°C for 4 min. Cool and measure the absorbances and plot again the A–l curves for each complex. Cr–P.C. was found to be of lmax 4 515 nm (Figs. 1 and 2). Mix equimolecular amounts of Fe(III) and Cr(VI) and add a suitable volume of P.C. indicator adjusting the pH to 5.0 in 25 ml as a final volume. Measure the absorbances and plot A–l curves at 25°C. Repeat this step with heating similar mixtures at 95°C for 4 min and measure absorbances after cooling. Then plot A–l curves for these mixtures. From the A–l curves at 25 and 95°C of Fe(III) and Cr(VI) in separate states and in mixtures, it was clear that Fe(III) could be determined at l 4 585 nm and Cr(VI) at 515 nm at pH 5.0 in the presence of each or in separate states using P.C. as indicator. (c) Obeyance to Beer’s law. In order to check the obeyance of Fe(III) concentration to Beer’s law when mixed with excess Cr(VI), various amounts of Fe(III) were added to excess Cr(VI) in the presence of P.C. indicator at pH 5.0 and at 25°C. The absorbance was measured at lmax 4 585. The calibration curve of Fe(III) was obtained by the plot of concentration against absorbance at l 4 585 nm. The obeyance of Cr(VI)–P.C. in a mixture of Fe and Cr at excess Fe(III) and various amounts of Cr is obtained by the plot of measured absorbances at l 4 515 nm of the mixture, after its heating at 95°C, against the concentration of the varied species. 2. Determination of Fe(III) and Cr(VI) in Chromium-Electroplating Bath This involved two steps. The first was the collection of the samples from the electroplating baths and the second was its preparation for spectrophotometric measurement as previously mentioned in synthetic mixtures (Procedure 1b). (a) Collection of electroplating bath samples. Sixteen samples were collected from different positions of the bath. Four samples were collected from the four corners of the bath and the other four from the sides of the bath at distances 20, 40, 60, and 80 cm from the surface. The other eight samples were collected from different depths at 10, 20, 30, 40, 50, 60, 70, and 80 cm. Each sample (0.5 ml) was diluted up to 100 ml in a measuring flask. (b) Spectrophotometric measurements. The diluted bath sample (0.5 ml) was treated with 5 ml of 0.1 M P.C. indicator at pH 5.0 in a 25 ml measuring flask and completed to the mark with water.
JOBNAME: MIC 54#1 96 PAGE: 4 SESS: 2 OUTPUT: Wed Aug 7 11:57:35 1996 /xypage/worksmart/tsp000/72869f/16pu
DETERMINATION OF Fe AND Cr USING PYROCATECHOL
75
FIG. 2. The spectra of (a) the Fe(III)–P.C. complex of 1.7 10−4 M, at temperature 95°C and (b) the Cr(VI)–P.C. complex of 0.8 × 10−4 M, at temperature 95°C.
The absorbance of the mixture was measured at 25°C and l 4 585 nm to determine Fe(III). Its concentration was determined by translating absorbance of electroplating bath solution from the calibration curve of Fe(III) in synthetic like mixtures (Table 1). The absorbance of the mixture heated at 95°C for 4 min and then cooled was measured at l 4 515 nm for Cr(VI). The Cr(VI) concentration in each electroplating bath sample TABLE 1 Spectrophotometric Microdetermination of Cr(VI) at lmax 4 515 nm, pH 5.0, and Temperature 95°C in Synthetic Mixture of (Cr + Fe) Using P.C. Indicator at High Concentration Limit Chromium Taken
Found
Recovery (%)
S.D.
51.99 51.99 51.99 51.99 51.99
48.56 47.40 48.06 46.94 46.91
93.40 91.17 93.58 90.28 90.22
0.858
JOBNAME: MIC 54#1 96 PAGE: 5 SESS: 2 OUTPUT: Wed Aug 7 11:57:35 1996 /xypage/worksmart/tsp000/72869f/16pu
76
ZAYED, BARSOUM, AND HASSAN
was determined from the constructed calibration curve of Cr(VI) in synthetic mixtures under similar conditions (Table 2). The concentration of Fe and Cr in these bath samples were measured by standard gravimetric and volumetric methods and by flame atomic absorption method. Instruments The spectrophotometric analysis was performed using a Milton Roy, USA (UV–Vis) instrument using a 1 cm quartz cell and water as a blank. The atomic absorption measurements were carried out using a PYE UNICAM 1900 spectrometer at the Cairo University Microanalytical Center. The pH values were adjusted by using NaOH or sulfuric acid solutions and using a pH–MV digital ion-analyzer, Model 701A. RESULTS AND DISCUSSION Spectrophotometric Study of the Fe(III)–P.C. and Cr(VI)–P.C. Complexes in Solution This study involves at first the effect of pH (in the range from 3.0 to 7.0) on the spectra of the iron complex. The suitable pH for the microdetermination of Fe(III) in its complex solution is found to be 5.0 using P.C. as indicator at the suitable lmax 4 585 nm (e 4 4.166 × 103 mol−1 cm−1) at 25°C. The concentrations of Fe(III) up to 9.38 ppm (Table 3) give percentage recovery ranging from 92.17 to 101.6%. The study of pH (4.0 to 6.5) on the spectra of the Cr(VI)–P.C. complex found that no sharp peaks were obtained at pH 5.0, at 25°C, and in the wavelength range from 350 to 750 nm. The effect of pH (at the same range) on Cr(VI)–P.C., after heating to 95°C for 4 min and cooling, gives a band at lmax 4 515 nm and pH 5.0 of maximum molar absorptivity 6 4 1.36 × 103 mol−1 cm−1. Under these conditions, Cr(VI) concentrations ranging from 8.31 to 41.5 ppm (Table 3) give percentage recovery from 82.16 to 105.08%. Therefore it is possible to analyze a synthetic mixture of both Fe(III) and Cr(VI) using P.C. spectrophotometrically, by measurement of iron at 25°C and lmax 4 585 nm. The Fe(III) obeys Beer’s law in the range from 18.0 to 125.0 ppm and the percentage recovery is found to be between 93.8 and 103.95%. The standard deviation is found to be 0.838 for five replicates of each concentration of iron in a mixture. The measurement of variable concentration of Cr(VI), 25 to 110 ppm, is made TABLE 2 Spectrophotometric Microdetermination of Fe(III) at lmax 4 585 nm, pH 5.0, and Temperature 25°C in Synthetic Mixture of (Cr + Fe) Using P.C. Indicator at High Concentration Limit Iron (ppm) Taken
Found
Recovery (%)
S.D.
61.43 61.43 61.43 61.43 61.43 61.43 61.43
61.50 62.96 61.92 61.50 59.35 62.44 57.62
100.1 102.4 100.7 100.1 96.6 101.6 93.8
1.635
JOBNAME: MIC 54#1 96 PAGE: 6 SESS: 2 OUTPUT: Wed Aug 7 11:57:35 1996 /xypage/worksmart/tsp000/72869f/16pu
77
DETERMINATION OF Fe AND Cr USING PYROCATECHOL
TABLE 3 Spectrophotometric Microdetermination of Fe(III) by P.C. Indicator at pH 5.0, lmax 4 585, and Temperature 25°C in 25 ml Solution and Cr(VI) at pH 5.0, lmax 4 515 nm, and Temperature 95°C in 25 ml Solution Fe(III), ppm 1.34 (1.34) 2.68 (2.68) 4.02 (4.08) 5.36 (5.38) 6.70 (6.50) 8.04 (7.96) 9.38 (8.65)
Recovery (%)
Cr(VI), ppm
Recovery (%)
100.0
8.31 (7.89) 16.63 (14.29) 20.79 (18.0) 24.95 (20.5) 29.12 (30.6) 33.43 (32.2) 37.43 (38.5) 41.59 (39.7)
94.89
100.0 101.6 100.3 97.0 99.0 92.17
85.64 85.77 82.16 105.08 95.48 102.80 95.66
Note. The values in parenthesis are the found concentration spectrophotometrically.
at pH 5.0 after heating to 95°C in the presence of excess iron of 125 ppm to test the obeyance of chromium to Beer’s law. It is found that Cr(VI) obeys Beer’s law in the concentration range from 6.0 to 48.0 ppm and at l 4 515 nm. The percentage recovery is found to be between 89.5 and 93.4%, and the SD 4 1.88 for six replicates of each concentration of synthetic mixture. These values of SD refer to the accuracy and precision of the analysis of Fe(III) and Cr(VI) mixtures using P.C. indicator. The percentage recovery values of Fe(III) in excess Cr(V), or vice versa, refer to the reliability of the suggested procedures. Analysis of Iron and Chromium in Cr-Electroplating Baths at the HEIC, 99 Plants From the previous detailed analysis of the synthetic mixture of Fe(III) + Cr(VI), it possible to analyze their mixtures in Cr-electroplating baths of iron tools (spoons, forks, etc.) applying the same principles. The spectrophotometrically determined concentrations of Fe(III) and Cr(VI) in the electroplating bath samples collected from different positions in the bath are shown in Tables 4 and 5. The Fe(III) spectrophotometric values (Table 4) determined in samples collected at different corners are found to be 14.81, 14.70, 14.90, and 15.2 ppm ml−1 and the values analyzed by gravimetric techniques usually used in the plant (14) are 14.0, 12.9, 13.5, and 15.23 ppm ml−1. This shows the greater regularity of the spectrophotometric data than the conventional gravimetric data. The corresponding atomic absorption values of Fe(III) in the presence of Cr(VI) are 9.59, 10.41, 11.25, and 9.95 ppm ml−1. These are less than those obtained by both spectrophotometric and gravimetric techniques. This may be attributed to the problems
JOBNAME: MIC 54#1 96 PAGE: 7 SESS: 2 OUTPUT: Wed Aug 7 11:57:35 1996 /xypage/worksmart/tsp000/72869f/16pu
78
ZAYED, BARSOUM, AND HASSAN
TABLE 4 Microdetermination of Fe(III) Concentration Spectrophotometrically in the Cr-Electroplating Bath Using P.C. Indicator in Comparison with Gravimetric Data Fe(III) (ppm/ml) Sample no. Corner 1 Corner 2 Corner 3 Corner 4 Surface distance Surface distance Surface distance Surface distance Depth 10 cm Depth 20 cm Depth 30 cm Depth 40 cm Depth 50 cm Depth 60 cm Depth 70 cm Depth 80 cm
20 40 60 80
cm cm cm cm
Gravimetry
Spectrophotometry
14.000 12.900 13.500 11.230 12.900 11.500 10.700 11.000 13.080 12.000 11.150 11.125 10.450 11.149 11.500 11.250
14.812 14.700 14.900 15.200 13.900 13.900 12.380 13.670 13.159 13.418 11.353 12.643 11.350 11.766 12.900 11.330
usually faced in iron determination by FAAS in the presence of chromium species in electroplating baths as previously reported (15–19). At four surface distances from the bath sides at 10, 20, 30, and 40 cm, the iron(III) concentration determined by the gravimetric technique varied from 10.7 to 12.9 ppm ml−1, TABLE 5 Microdetermination of Cr(VI) Concentration Spectrophotometrically in the Cr-Electroplating Bath Using P.C. Indicator in Comparison with Volumetric Data Cr(VI) (ppm/ml) Sample no. Corner 1 Corner 2 Corner 3 Corner 4 Surface distance Surface distance Surface distance Surface distance Depth 10 cm Depth 20 cm Depth 30 cm Depth 40 cm Depth 50 cm Depth 60 cm Depth 70 cm Depth 80 cm
20 40 60 80
cm cm cm cm
Volumetry
Spectrophotometry
109.00 98.40 93.50 99.50 98.80 98.00 98.20 98.80 102.50 102.00 101.60 101.20 94.80 97.20 96.30 94.20
80.66 87.31 86.47 83.13 89.80 80.65 91.96 101.37 100.60 92.55 97.45 101.37 101.87 101.90 85.65 86.48
JOBNAME: MIC 54#1 96 PAGE: 8 SESS: 2 OUTPUT: Wed Aug 7 11:57:35 1996 /xypage/worksmart/tsp000/72869f/16pu
DETERMINATION OF Fe AND Cr USING PYROCATECHOL
79
whereas that determined spectrophotometrically ranged from 13.6 to 12.45 ppm ml−1. This means that these spectrophotometric values are still very near to the values of Fe(III) at different corners of the bath. The values obtained by atomic absorption at different surface distances ranged from 9.0 to 11.37, which are still less than those obtained by both gravimetric and spectrophotometric techniques. At different depth distances (10–80 cm), Fe(III) concentration gravimetrically determined ranged from 13.08 to 11.25 ppm ml−1 and spectrophotometrically from 13.16 to 11.3 ppm ml−1, which shows correlation between the results. This also shows the decrease of Fe(III) on going deeper into the bath. The calculated SD 4 0.98 for eight replicates of iron in both samples shows the reproducibility of the spectrophotometric results obtained from the analyzed samples in chromium electroplating baths. On the other hand, the chromium concentration determined in its bath by the volumetric technique (Table 5a) is found to be in the range from 93 to 109 ppm ml−1 in bath samples, but it is not regularly varied at different surface or depth distances. The concentration of Cr in the samples determined spectrophotometrically (Table 5b) is found to be in the range from 80 to 111 ppm ml−1. At four corners in the bath, the difference between the volumetric and the spectrophotometric data is found to be 7–19 ppm, at the distance from the sides it is 3–16 ppm, and at different depths it is 3–10 ppm, which is actually attributed to the difference in efficiency between the volumetric and the spectrophotometric techniques (20–25). The atomic absorption data for Cr concentration in some selected samples are more or less the same as those obtained spectrophotometrically, which shows the success of using P.C. as indicator under optimum selected conditions to determine Cr by this fast (no more than 1 min for each sample), cheap, and accurate suggested procedure. The calculated standard deviation for one sample of five replicates is found to be 1.57%, which is comparable to the previously published work for similar bath analysis (26, 27). This also shows the reliability and reproducibility of the applied procedure for Cr analysis using P.C. indicator. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.
Rumel, V. Metallpraxis, 1971, 20(9), 352; Metallpraxis, 1971, 20(10), 406, 408, 412. Xiao, M. Diandu Yu Huanbao, 1988, 8(4), 23–25. Sumitoma Metal Industries Ltd., Jpn. Kokai Tokkyo Koho, 1984, 59, 212, 740. Ewald, G. Galvanotechnik, 1990, 81(4), 1365. Noelte, J. Galvanotechnik, 1990, 81(8), 2738. Bogenschuetz, A. F.; George, U. Oberflaechentechik, 1973, 2, 67–71. Deng, B.; Zhoa, X. H. Ching Hua Ta Hsuch Hsuch Pao, 1980, 20(3), 79–87. Dohi, K.; Wada, A.; Nakamura, S. R & D, Res. Dev. (Rube Steel Ltd.), 1991, 41(1), 146. Shan, Y.; Lihva, J. Huaxue Fence, 1989, 25(2), 93–94. Branstetr, J.; Huleja, J.; Sajo, I. Hutn. Listy, 1982, 37(10), 734. Dibenedetto, D.; Thomas, G. Eur. Pat. Appl., 1982, 59, 140. Sakurai, K.; Nishimura, K. Jpn. Kokai Tokkyo Koho, 1991, 104, 879. Xu, C. Youkuangye, 1991, 10(2), 612–614. Christian, G. D. Analytical Chemistry, 2nd ed. Wiley, New York, 1977. Savitskii, V. N.; Peleshenko, V. I.; Osadchii, V. I. Gidrobiol. Zh., 1986, 22(1), 62. Shen, Z.; Chen, Y.; Nie, F. Fenxi Huaxue, 1990, 18(1), 61. Bassett, J.; Denney, R. C. Text Book of Quantitative Inorganic Analysis, 4th ed., pp. 361, 440, Longman, 1985. 18. Ma, G.; Luo, J. Shanghai Huanjing Kexue, 1990, 9(6), 27.
JOBNAME: MIC 54#1 96 PAGE: 9 SESS: 2 OUTPUT: Wed Aug 7 11:57:35 1996 /xypage/worksmart/tsp000/72869f/16pu
80 19. 20. 21. 22. 23. 24. 25. 26. 27.
ZAYED, BARSOUM, AND HASSAN Xu, J.; Zhou, S. Diandu Yu Huanbao, 1991, 11(5), 33. Korol, L. S.; Levitman, K. Y.; Nagornaya, I. V. Khim. Kim. Technol. (Minsk), 1983, 16, 50–54. Feng, J.; Ving, W.; Zhang, B. Fenxi Huaxue, 1985, 13(8), 585. Feng, J.; Li, Y.; Zhang, B. Beijing Daxue Xuebao, Ziron Kexueban, 1988, 24(4), 436. Feng, J.; Wang, Z.; Zhang, B.; Liang, D. Fenxi Huaxue, 1983, 11(5), 384. Magyar, B. Atomspektrom. Spurenanal. Vortr. Kolloq., 1981, 401. Xu, C. Yonkuangye, 1991, 10(2), 61–64. Lieser, K. H.; Sondermeyer, S.; Kliemchen, A. Fresenius, Z. Anal. Chem., 1982, 517. Gordeev, S. K.; Krasnobryzhii, A. V. Zavod. Lab., 1982, 48(7), 23.