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Arazate Method for Estimating Copper in Water1
Arazate Method for Estimating Copper in Water' A. C. SMITH
Department of Animal Industries, University of Connecticut, Storrs 06268 presence of other metallic ions is reduced unless less than a few milligrams of Sb 3+,5+ and 0.1 mg of H g and Ag are present (6, 7). The presence of 0.1 mg Bi a+ will recover as 5.6 /~g Cu unless separation procedures are followed (6). Copper can be determined accurately with Arazate in the presence of large amounts (0.5g) of A1, As a+,~÷ Cd, Ca, Cr 3+, Fe 2÷, Pb, Mn 2÷, Sn 4÷, U 6+, and Zn (7). A method is described for estimating copper in water with Arazate as the sequesterant.
Abstract
A method using zinc dibenzyldithiocarbanmte (Arazate) for estimating copper in water was not significantly different from the Bathocuproine procedure. Repeatability trials at two levels of copper gave standard deviations of 0.001 and 0.002 ppm. Twelve samples with 0.1 and 0.2 ppm of added copper had recoveries of 93 to 104% and 93 to 103% with means of 100 and 99%. The presence of ~ 10 ppm of chlorine, however, interfered with the recovery of copper.
Experimental Procedure
Introduction
Post-milking contamination of milk with copper contributes to oxidized flavor. Copper transferred from copper tubing to water is adsorbed on metal surfaces during cleaning and sanitizing. The subsequent solution in milk of' copper contributes to oxidized flavor. Thus, a determination of copper in water is needed to minimize copper contamination during handling, cooling, and processing of milk. Standard methods for estimating copper in water (2) involve the chelates Cuprethol and Bathoeuproine. However, the zinc salt of dibenzyldithiocarhamic acid (Arazate) ~ which has been used successfully as a sequesterant in the copper analysis of plants (3, 4), soils (5), oils and fats (1), dyes and chemicals (6) and milk (8), offers several advantages. Arazate is specific for copper in acid solutions ( < p H 2) since copper is extractable from interfering elements, cobalt, iron and nickel (except when present in macro amounts) at low p H (1). The reagent is stable, permits fast extraction, and is soluble in carbon tetrachloride which has negligible solubility in water (6). Arazate does not require buffering after initial acidification nor addition of inorganic salts to prevent interference by other metals (1). However, to prevent interference from metals that might be reported as copper, the upper limits of 0.05 g Fe 3+, 0.01 g Ni and 0.01 g Co must not be exceeded (6, 7). Recovery of copper in Received for publication July 12, 1971. 1 Scientific Contribution 478, Connecticut Agricultural Experiment Station, University of Connecticut, Storrs. 39
Samples. W a t e r samples were from dairy farm sources throughout Connecticut. They were collected in plastio bags after the cold or hot water had flowed 2 min. Reagents. Arazate in carbon tetrachloride (0.05%): Make a 0.05% solution of reagentgrade zinc dibenzyldithiocarbamate in redistilled carbon tetrachloride and store in an amber bottle. 2.4 ~ HCI: Dilute 200 ml of 36.5 to 38% reagent grade HC1 with 800 ml deionized water. Copper-free glassware and reagents. Pass distillcd water through an ion exchange resin or deionizer. Glassware and glass wool. Soak clean glassware in 1 -}- 3 HNOa (v/v) overnight and follow with three thorough rinsings with deionized water. Carbon tetrachloride. Redistill in a copper free, all-glass apparatus. Standard curve procedure. Weigh exactly 1 g of chemically pure copper foil in a 150 ml beaker. Add 15 ml of 1 + 4 (v/v) nitric acid, cover with a watch glass and heat in a steam bath until completely dissolved and fumes are expelled. Cool, transfer to a volumetric flask and dilute to 1 liter with deionized water. This stock solution (1 g Cu/liter) is then diluted by 5-ml transfers into 100-ml volumetric flasks to make solutions in the range of 0 to 15 /~g of copper. Determine standard curves in duplicate en three different days and develop the standard curve by least squares (9). Method for copper. To 50 ml of water in a 125-ml globe-shaped separatory funnel or an aliquot diluted to 50 ml, add 5 ml of 2.4 HC1. Mix and then add 5 ml of 0.05% Arazate in carbon tetrachloride. Shake vigorously for 2 min and allow solvent layer to settle. Transfer
40
SMITH
solvent layer into 12.7-mm diam test tubes from the separatory funnel through a plug of glass wool. Determine optical density at 435 m~ with a Spectronic 20 colorimeter or equivalent instrument adjusted with a blank prepared from deionized water carried through the same procedure as the sample. Estimate copper content in micrograms from a standard curve and multiply by 0.02 to obtain parts per million or milligrams per liter. Results and Discussion
Method ~,ompar~o~. A comparison of the Arazate method with the standard Bathocuproine procedure (2) for estimating copper in water is in Table 1. A paired t test (9) of the TABLE 1. Comparison of Arazate with Bathocuproine for estimating copper in water. Copper Sample 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Mean SD
Arazate (ppm) .095 .032 .262 .076 .026 .048 .046 .013 .010 .114 .022 .014 .254 .024 .308 .O08 .005 .056 .004 .157 .079 .092
TABLE 2. Recovery by Arazate of copper added to water. Copper added Sample
1 2 3 4 5 6 7 8 9 10 11 12 Mean
Natural .1 ppm copper Recovered (ppm) .114 .013 .128 .024 .004 .006 .082 .029 .063 .114 .094 .040 .059
(ppm) (%) .208 94 .117 104 .228 100 .131 107 .104 100 .099 93 .176 94 .128 99 .166 103 .211 97 .195 101 .140 100 .159 100
.2 ppm Recovered (ppm) (%) .299 93 .205 96 .327 100 .222 99 .201 98 .202 98 .276 97 .231 101 .264 ]00 .314 100 .293 100 .246 103 .257 99
Bathocuproine (ppm) .085 .025 .264 .077 .026 .039 .053 .016 .014 .114 .019 .013 .254 .027 .292 .012 .005 .054 .006 .160 .077 .090
data shows that the two methods are not significantly different. Recovery. The results of recovery experiments with the Arazate procedure presented in Table 2 confirm the conclusion of the cornparative trials that the method is precise. Trials in which 0.1 and 0.2 ppm of copper were added to 50 ml of water gave recoveries of 93 to 107 and 93 to 103% with means of 100 and 99%. Repeatability. The repeatability of the Ara,]'OURI~AL OF DAIRY SCIENO~ VOI,. 55, NO. 1
zate procedure in comparison to Bathocuproine (2) is in Table 3. Data are based on 10 replicate analyses of two water samples containing differing amounts of copper. Both methods are equally repeatable. Interference. Extent of interference from metals that might be reported as copper and the recovery of copper in the presence of other metals by the Arazate reagent has been reported (1, 6, 7). However, the interference by chlorine in Table 4 has not been noted. Increasing amounts of active chlorine as sodium hypochlorite were added to water containing TABLE 3. Comparison on repeatability of Arazate with Bathocuproine for estimating copper in water. Arazate Analysis
1 2 3 4 5 6 7 8 9 10 Mean SD
cv
1 (ppm) .057 .057 .056 .056 .055 .055 .056 .056 .053 .057 .056 .001 1.79
Bathocuproine 2
(ppm) .158 .158 .157 .160 .156 .156 .157 .160 .160 .158 .158 .002 1.27
1
2
(ppm) .055 .055 .053 .054 .054 .055 .054 .058 .056 .055 .055 .001 1.82
(ppm) .160 .158 .]60 .158 .157 .154 .160 .160 .161 .160 .159 .001 .63
COPPER
TABLE 4. Effect of chlorine on Arazate method for estimating copper in water. Chlorine added
(ppm) 0 5 10 15 20 25 30 0 5 10 15 20 25 30
Copper added .1 ppm .3 ppm Recovery Recovery (ppm) (ppm) 0.05% Arazate .106 .302 .102 .297 .107 .291 .104 .256 .096 .250 .040 .155 .020 .145 0.1% Arazate .I01 .302 .]O5 .3O5 .102 .297 .106 .308 .107 .281 .089 .256 .028 .156
0.1 and 0.3 ppm of copper. Chlorine in excess of 15 and 10 ppm in water containing 0.1 and 0.3 ppm of copper interfered with the recovery of copper with 0.05% Arazate in the solvent. Increasing Arazate to 0.1% permitted recovery of copper at 0.1 and 0.3 ppm in the presence of 20 and 15 ppm of chlorine. However, increasing Arazate might lead to more interference from iron, nickel and cobalt (7). Calcium hypochlorite gave similar results. Interference from chlorine is probably due to oxidation of the reagent. I t is recommended that water for copper analysis with 0.05% reagent contain less than 10 ppm of chlorine. General discussion. The Arazate reagent for estimating copper in water is equal in accuracy to the Bathocuproine reagent. Thus, it may be
41
IN WATER
used for screening farm and plant water supplies low in chlorine ( < 10 ppm) for copper to minimize adsorption of copper on metal surfaces during cleaning and sanitizing. Arazate permits greater efficiency in the laboratory since it requires only two reagents. Approximately twelve samples may be analyzed per hour. This method has been used successfully for two years in verifying the copper content in dairy farm water supplies. Acknowledgment The author thanks W. F. Dillman and M. E. Myers for collecting and transporting the water supplies. References (1) Abbott, D. C., and R. D. A. Polkill. 1954. The determination of copper in oils and fats by means of dibenzyldithioearbamic acid and its salts. Analyst, 7 9 : 5 4 7 . (2) American Public Health Association. 1965. Standard Methods for the Examination of Water and Wastewater, 12th ed. Amer. Publ. Health Ass. Inc., New York City. (3) Andrus, S. 1955. Determination of copper in plant tissues using zinc dibenzyldithiocarbamate. Analyst, 80 : 514. (4) Borchardt, L. G., and J. P. Butler. 1957. Determination of trace amounts of copper. Anal. Chem., 29: 414. (5) Hagstrom, G. R., and E. J. Rubins. 1961. Copper and molybdenum in Connecticut soils and vegetation. Part I. Determination of copper using zinc dibenzyldithiocarbamate (Arazate). Conn. Agr. Exp. Sta Bull., 360. (6) Martens, R. I., and R. E. Githins. 1952. Small amounts of copper in dyes and rubber chemicals. Anal. Chem., 24: 991. (7) Sandell, E. B. 1959. Colorimetric Determination of Traces of Metals. 3rd ed. Interscience Publ. Inc., New York City. (8) Smith, A. C. 1967. Rapid methods for determining copper content of milk. J. Dairy Sci., 50: 664. (9) Snedecor, G. W. 1956. Statistical Methods. 5th ed. Iowa State College Press, Ames.
JOURNAL OF DAIRY SCIE~'CE VOL, 55, NO. 1
Department of Animal Industries, University of Connecticut, Storrs 06268 presence of other metallic ions is reduced unless less than a few milligrams of Sb 3+,5+ and 0.1 mg of H g and Ag are present (6, 7). The presence of 0.1 mg Bi a+ will recover as 5.6 /~g Cu unless separation procedures are followed (6). Copper can be determined accurately with Arazate in the presence of large amounts (0.5g) of A1, As a+,~÷ Cd, Ca, Cr 3+, Fe 2÷, Pb, Mn 2÷, Sn 4÷, U 6+, and Zn (7). A method is described for estimating copper in water with Arazate as the sequesterant.
Abstract
A method using zinc dibenzyldithiocarbanmte (Arazate) for estimating copper in water was not significantly different from the Bathocuproine procedure. Repeatability trials at two levels of copper gave standard deviations of 0.001 and 0.002 ppm. Twelve samples with 0.1 and 0.2 ppm of added copper had recoveries of 93 to 104% and 93 to 103% with means of 100 and 99%. The presence of ~ 10 ppm of chlorine, however, interfered with the recovery of copper.
Experimental Procedure
Introduction
Post-milking contamination of milk with copper contributes to oxidized flavor. Copper transferred from copper tubing to water is adsorbed on metal surfaces during cleaning and sanitizing. The subsequent solution in milk of' copper contributes to oxidized flavor. Thus, a determination of copper in water is needed to minimize copper contamination during handling, cooling, and processing of milk. Standard methods for estimating copper in water (2) involve the chelates Cuprethol and Bathoeuproine. However, the zinc salt of dibenzyldithiocarhamic acid (Arazate) ~ which has been used successfully as a sequesterant in the copper analysis of plants (3, 4), soils (5), oils and fats (1), dyes and chemicals (6) and milk (8), offers several advantages. Arazate is specific for copper in acid solutions ( < p H 2) since copper is extractable from interfering elements, cobalt, iron and nickel (except when present in macro amounts) at low p H (1). The reagent is stable, permits fast extraction, and is soluble in carbon tetrachloride which has negligible solubility in water (6). Arazate does not require buffering after initial acidification nor addition of inorganic salts to prevent interference by other metals (1). However, to prevent interference from metals that might be reported as copper, the upper limits of 0.05 g Fe 3+, 0.01 g Ni and 0.01 g Co must not be exceeded (6, 7). Recovery of copper in Received for publication July 12, 1971. 1 Scientific Contribution 478, Connecticut Agricultural Experiment Station, University of Connecticut, Storrs. 39
Samples. W a t e r samples were from dairy farm sources throughout Connecticut. They were collected in plastio bags after the cold or hot water had flowed 2 min. Reagents. Arazate in carbon tetrachloride (0.05%): Make a 0.05% solution of reagentgrade zinc dibenzyldithiocarbamate in redistilled carbon tetrachloride and store in an amber bottle. 2.4 ~ HCI: Dilute 200 ml of 36.5 to 38% reagent grade HC1 with 800 ml deionized water. Copper-free glassware and reagents. Pass distillcd water through an ion exchange resin or deionizer. Glassware and glass wool. Soak clean glassware in 1 -}- 3 HNOa (v/v) overnight and follow with three thorough rinsings with deionized water. Carbon tetrachloride. Redistill in a copper free, all-glass apparatus. Standard curve procedure. Weigh exactly 1 g of chemically pure copper foil in a 150 ml beaker. Add 15 ml of 1 + 4 (v/v) nitric acid, cover with a watch glass and heat in a steam bath until completely dissolved and fumes are expelled. Cool, transfer to a volumetric flask and dilute to 1 liter with deionized water. This stock solution (1 g Cu/liter) is then diluted by 5-ml transfers into 100-ml volumetric flasks to make solutions in the range of 0 to 15 /~g of copper. Determine standard curves in duplicate en three different days and develop the standard curve by least squares (9). Method for copper. To 50 ml of water in a 125-ml globe-shaped separatory funnel or an aliquot diluted to 50 ml, add 5 ml of 2.4 HC1. Mix and then add 5 ml of 0.05% Arazate in carbon tetrachloride. Shake vigorously for 2 min and allow solvent layer to settle. Transfer
40
SMITH
solvent layer into 12.7-mm diam test tubes from the separatory funnel through a plug of glass wool. Determine optical density at 435 m~ with a Spectronic 20 colorimeter or equivalent instrument adjusted with a blank prepared from deionized water carried through the same procedure as the sample. Estimate copper content in micrograms from a standard curve and multiply by 0.02 to obtain parts per million or milligrams per liter. Results and Discussion
Method ~,ompar~o~. A comparison of the Arazate method with the standard Bathocuproine procedure (2) for estimating copper in water is in Table 1. A paired t test (9) of the TABLE 1. Comparison of Arazate with Bathocuproine for estimating copper in water. Copper Sample 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Mean SD
Arazate (ppm) .095 .032 .262 .076 .026 .048 .046 .013 .010 .114 .022 .014 .254 .024 .308 .O08 .005 .056 .004 .157 .079 .092
TABLE 2. Recovery by Arazate of copper added to water. Copper added Sample
1 2 3 4 5 6 7 8 9 10 11 12 Mean
Natural .1 ppm copper Recovered (ppm) .114 .013 .128 .024 .004 .006 .082 .029 .063 .114 .094 .040 .059
(ppm) (%) .208 94 .117 104 .228 100 .131 107 .104 100 .099 93 .176 94 .128 99 .166 103 .211 97 .195 101 .140 100 .159 100
.2 ppm Recovered (ppm) (%) .299 93 .205 96 .327 100 .222 99 .201 98 .202 98 .276 97 .231 101 .264 ]00 .314 100 .293 100 .246 103 .257 99
Bathocuproine (ppm) .085 .025 .264 .077 .026 .039 .053 .016 .014 .114 .019 .013 .254 .027 .292 .012 .005 .054 .006 .160 .077 .090
data shows that the two methods are not significantly different. Recovery. The results of recovery experiments with the Arazate procedure presented in Table 2 confirm the conclusion of the cornparative trials that the method is precise. Trials in which 0.1 and 0.2 ppm of copper were added to 50 ml of water gave recoveries of 93 to 107 and 93 to 103% with means of 100 and 99%. Repeatability. The repeatability of the Ara,]'OURI~AL OF DAIRY SCIENO~ VOI,. 55, NO. 1
zate procedure in comparison to Bathocuproine (2) is in Table 3. Data are based on 10 replicate analyses of two water samples containing differing amounts of copper. Both methods are equally repeatable. Interference. Extent of interference from metals that might be reported as copper and the recovery of copper in the presence of other metals by the Arazate reagent has been reported (1, 6, 7). However, the interference by chlorine in Table 4 has not been noted. Increasing amounts of active chlorine as sodium hypochlorite were added to water containing TABLE 3. Comparison on repeatability of Arazate with Bathocuproine for estimating copper in water. Arazate Analysis
1 2 3 4 5 6 7 8 9 10 Mean SD
cv
1 (ppm) .057 .057 .056 .056 .055 .055 .056 .056 .053 .057 .056 .001 1.79
Bathocuproine 2
(ppm) .158 .158 .157 .160 .156 .156 .157 .160 .160 .158 .158 .002 1.27
1
2
(ppm) .055 .055 .053 .054 .054 .055 .054 .058 .056 .055 .055 .001 1.82
(ppm) .160 .158 .]60 .158 .157 .154 .160 .160 .161 .160 .159 .001 .63
COPPER
TABLE 4. Effect of chlorine on Arazate method for estimating copper in water. Chlorine added
(ppm) 0 5 10 15 20 25 30 0 5 10 15 20 25 30
Copper added .1 ppm .3 ppm Recovery Recovery (ppm) (ppm) 0.05% Arazate .106 .302 .102 .297 .107 .291 .104 .256 .096 .250 .040 .155 .020 .145 0.1% Arazate .I01 .302 .]O5 .3O5 .102 .297 .106 .308 .107 .281 .089 .256 .028 .156
0.1 and 0.3 ppm of copper. Chlorine in excess of 15 and 10 ppm in water containing 0.1 and 0.3 ppm of copper interfered with the recovery of copper with 0.05% Arazate in the solvent. Increasing Arazate to 0.1% permitted recovery of copper at 0.1 and 0.3 ppm in the presence of 20 and 15 ppm of chlorine. However, increasing Arazate might lead to more interference from iron, nickel and cobalt (7). Calcium hypochlorite gave similar results. Interference from chlorine is probably due to oxidation of the reagent. I t is recommended that water for copper analysis with 0.05% reagent contain less than 10 ppm of chlorine. General discussion. The Arazate reagent for estimating copper in water is equal in accuracy to the Bathocuproine reagent. Thus, it may be
41
IN WATER
used for screening farm and plant water supplies low in chlorine ( < 10 ppm) for copper to minimize adsorption of copper on metal surfaces during cleaning and sanitizing. Arazate permits greater efficiency in the laboratory since it requires only two reagents. Approximately twelve samples may be analyzed per hour. This method has been used successfully for two years in verifying the copper content in dairy farm water supplies. Acknowledgment The author thanks W. F. Dillman and M. E. Myers for collecting and transporting the water supplies. References (1) Abbott, D. C., and R. D. A. Polkill. 1954. The determination of copper in oils and fats by means of dibenzyldithioearbamic acid and its salts. Analyst, 7 9 : 5 4 7 . (2) American Public Health Association. 1965. Standard Methods for the Examination of Water and Wastewater, 12th ed. Amer. Publ. Health Ass. Inc., New York City. (3) Andrus, S. 1955. Determination of copper in plant tissues using zinc dibenzyldithiocarbamate. Analyst, 80 : 514. (4) Borchardt, L. G., and J. P. Butler. 1957. Determination of trace amounts of copper. Anal. Chem., 29: 414. (5) Hagstrom, G. R., and E. J. Rubins. 1961. Copper and molybdenum in Connecticut soils and vegetation. Part I. Determination of copper using zinc dibenzyldithiocarbamate (Arazate). Conn. Agr. Exp. Sta Bull., 360. (6) Martens, R. I., and R. E. Githins. 1952. Small amounts of copper in dyes and rubber chemicals. Anal. Chem., 24: 991. (7) Sandell, E. B. 1959. Colorimetric Determination of Traces of Metals. 3rd ed. Interscience Publ. Inc., New York City. (8) Smith, A. C. 1967. Rapid methods for determining copper content of milk. J. Dairy Sci., 50: 664. (9) Snedecor, G. W. 1956. Statistical Methods. 5th ed. Iowa State College Press, Ames.
JOURNAL OF DAIRY SCIE~'CE VOL, 55, NO. 1