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Polarographic determination of copper and zinc in macromolecular compounds
Polymer Science U.S.S.R. Vol. 31, No. 4, pp. 979.-981, 1980 Printed in Poland
0032-3950/89 $10.00+ .00 :c3 1990 Pergamon Press pie
P O L A R O G R A P H I C D E T E R M I N A T I O N OF C O P P E R A N D ZINC IN M A C R O M O L E C U L A R C O M P O U N D S * V. G . SVIRIDENKO, I. M . Y'ELISEYEVA a n d D . G . LI~ Gomel' State University
(Receiced 21 September 1988) A method has been developed for the determination of copper and zinc by extraction and polarography without sample incineration. Extraction by cupferron (phcnyhai~rosohydr,~xyl~ amine) dissolved in an organic solvent yields the most satisfactory results wit!~ regard t~, d > termination of metals in polymers. The optimum concentration of the complex-forming c~:npound required for complete extraction of copper and zinc from the sample has been found.
QUANTITATIVE determination of copper and zinc is necessary for the elucidation of lhc m~'chani~m of reactions which proceed in polymers during their thermooxidative degradation on metallic substrates, accompanied by the dissolution of the metal and its transport into the po]ynlcr irverior [t, 2]. A non-destructive character of the analytical procedure is important h,:r¢ [3]. In ti~c pr,:~rnl paper we study the possibility to determine copper and zinc by extraction and pok~;~,graphv wil!~.,ut sample incineration. Polyethylene (GOST 16338-70) and several elastomers (butadiene-nitrilc SKN-40, GOST 7738-79; butadiene SKD, G O S T 14934-75; butadiene-styrene, G O S T 15627-79) in tile form of tllms w~;'e s~udied; the films were separated from a metal substrate after high-temperature thcrm,~oxidative degradation. Polarographic measurements (dropping mercury electrode) were pcrformt'd with tile PL-I polarograph. All potentials refer to the mercury pool potential. Calibration standards were prepared from copper and zinc sulphates according to [4]. Copper and zinc were extracted by cupferron (phenylnitrosohydroxylamine) dissolved in various organic solvents [5]. Aqu.:t~us solu~it~ns of cupferron were prepared from a reagent carefuly purified by recrystallizaiion. S~dulions ~q' ~wids were prepared from sealed standards. Redistilled water was used throughout. Ttlc c,~rrccnir.tl i,*~ t,f salts was monitored by titration. The polarographic behaviour of cupferron was first checked in 1-0 ~1 ~nd 0.1 ul amm~mium chloride supporting electrolytes [6]. An analysis of the electrode process pr,~ved tIlat undcr t[~:se conditions cupfcrron is reduced irreversibly on the dropping mercury cl¢cirode. This IL~CLh~/d io ~ taken into account in developing the method of quantitative determ;nation of copl)cr and zinc in polymer samples. Aqueous solutions of cupferron are unstable in acidic media, a circumstar~o~ wl Eclt ct~lnplicate3 its application as the extraction agent. We have therefore carried out a scNcs of prci[~;~ia ~.~'ycxp,~.,'~ments with extraction of cupferron into several organic solvents from aqueous stdui i~ls ot' ~tl~m~onium chloride with the aim to determine the partition coefficient, the dissociat ion c~n~t~nt and ~I~,: c xlraction coefficient. Extraction of cupferron depends both on pH and on the cheH~i~zd ti tlu~c t~l l]~.c ~:olvent. At p H 4"0 cupferron is extracted fully into chloroform, carbon tctrach!e:qdc, ar~d diethsi ctlxer (Fig. 1), Experimental conditions for the extraction of copper and zinc cupferronates were then investigated. The results have shown that the complexes must be treated by chloroform at p H 8 for 5 min to achieve quantitative extraction (Fig. 2). Copper a n d zinc cupferronates extracted * Vysokomol. soyed. A31: No. 4, 885-887, 1989. 979
980
V. G. SVIR~DENKOet al.
into chloroform are reduced in ammonium chloride solutions at pH 3 at the half-wave potentials of - 0.35 V (copper) and - 1.25 V (zinc). However, with increasing pH the half-wave potentials of the investigated complexes become more negative and the heights cease to depend linearly on concentration; at pH 7 the cupferronates are no longer reduced. The results proved the necessity of re-extrac-
¢,%
~%
100
J
I00
1
SO
50 12 3
,9
5
pH
I
I
q
8
pH
FIo. 1 FIG. 2 Fro. 1. Extent of cupferron extraction into diethyl ether (1), carbon tetrachloride (2), and chloroform (3) as a function of pH. FaG. 2. Extent of extraction of copper (1-3) and zinc cupferronates (4-6) into diethyl ether (1, 4), carbon tetrachloride (2, 3), and chloroform (3, 6) as a function of pH. tion before the polarographic analysis proper. Aqueous HCI was used in the re-extraction step and the subsequent polarographic measurements were carried out in an ammonium ckloride supporting electrolyte [7]. The following operations were found to be necessary for the determination of copper and zinc by extraction followed by polarography: the analysed metals are extracted (5 rain) from the aqueous solution into a chloroform solution of cupferron adjusted by ammonia to pH 8; the organic layer is separated, re-extracted with 0.1 M HC1, and the resulting solution is polarographed under the above conditions. When applied to the determination of trace amounts of copper and zinc the procedure yields satisfactory results (Table 1). TABLE 1. MICRODETERMINATION OF COl'PER'AND ZINC BY MEANS OF CUPFI~RRON
Amount of metal, 8 × 103, mole introduced
found
copper
zinc
copper
zinc
3.39 7"78 8-91
2.72 5"46 6.37
3"33 __0'06 7"65 4-0' 11 8.62 + 0' 15
2.72 + 0.05 5.40 + 0.10 6'29 + 0"11
The optimum conditions for quantitative determination of copper and zinc in polymers include t h e optimum cupferron concentration and the time of extraction. The experiments showed that with
decreasing cupferron concentration the time required for equilibrium extraction is prolonged and
Polarographic detcrmination of copper and zinc in macromolecular compounds
981
TABLE 2. DETERMINATIONOF COPPER AND ZINC IN POLYMERS BY EXTRACTIONAND POLAROORAPHY Sample Polyethylene SKN-40 SKD SKS-30-ARKPN
Content of metal, copper
zinc
copper*
zinc*
0.019 __0.001 0.022 + 0.002 0.02_.0.001 0.0018 + 0.0006
0.007 + 0-0009 0.018 + 0.0006 0.011 +0-0003 0.0009 + 0.00009
0.018 _ 0.001 0.022 + 0.002 0"021 +0.002 0.0017 ± 0.0004
0.0069 + 0.0009 0"017 + 0.0004 0.010+0.0003 0.001 + 0.00008
* By atomic-absorption spectroscopy.
only some 9 0 ~ of the metal is bound in the complex. The optimum copferron concentration is 6.2 x 10 -2 mole/l, where both copper and zinc arc fully extracted into the chloroform layer. Results of analytical determination of copper and zinc in various polymers are collected in Table 2. The method developed is selective and non-destructive, and can be recommended for quantitative determination of copper and zinc in studies concerned with oxidation of metal-supported polymer materials.
Translated by M. KUB/N REFERENCES 1. V. A. BELYI, N. I. YEGORENKOV and D. G. LIN, Vysokomol. soyed. BI4: 787, 1972 (Not translated in Polymer Sci. U.S.S.R.) 2. D. G. LIN, I. M. YELISEYEVA and N. I. YEGORENKOV, Kauchuk i rezina, 1, 13, 1986 3. Yu. A. Z O L O T O V , Ocherki analiticheskoi khimii (Introduction to Analytical Chemistry) 240 pp., Moscow, 1977 4. S. K. LAPITSKAYA and V. G. SVIRIDENKO, Zh. analit, khimii 37: 2007, 1982 5. V. B. ALESKOVSKII, S. K. LAPITSKAYA and V. G. SVIRIDENKO, Zh. analit, khimii 27: 602, 1972 6. V. B. ALESKOVSKH, S. K. LAPITSKAYA and V. G. SVIRIDENKO, Izv. vuzov. Khimiya i khim. tekhnol. 14: 847, 1971 7. V. G. SVIRIDENKO, D. G. LIN and S. K. LAPITSKAYA, Izv. vuzov. Khimiya i khim. tekhnol. 26: 1178, 1983
0032-3950/89 $10.00+ .00 :c3 1990 Pergamon Press pie
P O L A R O G R A P H I C D E T E R M I N A T I O N OF C O P P E R A N D ZINC IN M A C R O M O L E C U L A R C O M P O U N D S * V. G . SVIRIDENKO, I. M . Y'ELISEYEVA a n d D . G . LI~ Gomel' State University
(Receiced 21 September 1988) A method has been developed for the determination of copper and zinc by extraction and polarography without sample incineration. Extraction by cupferron (phcnyhai~rosohydr,~xyl~ amine) dissolved in an organic solvent yields the most satisfactory results wit!~ regard t~, d > termination of metals in polymers. The optimum concentration of the complex-forming c~:npound required for complete extraction of copper and zinc from the sample has been found.
QUANTITATIVE determination of copper and zinc is necessary for the elucidation of lhc m~'chani~m of reactions which proceed in polymers during their thermooxidative degradation on metallic substrates, accompanied by the dissolution of the metal and its transport into the po]ynlcr irverior [t, 2]. A non-destructive character of the analytical procedure is important h,:r¢ [3]. In ti~c pr,:~rnl paper we study the possibility to determine copper and zinc by extraction and pok~;~,graphv wil!~.,ut sample incineration. Polyethylene (GOST 16338-70) and several elastomers (butadiene-nitrilc SKN-40, GOST 7738-79; butadiene SKD, G O S T 14934-75; butadiene-styrene, G O S T 15627-79) in tile form of tllms w~;'e s~udied; the films were separated from a metal substrate after high-temperature thcrm,~oxidative degradation. Polarographic measurements (dropping mercury electrode) were pcrformt'd with tile PL-I polarograph. All potentials refer to the mercury pool potential. Calibration standards were prepared from copper and zinc sulphates according to [4]. Copper and zinc were extracted by cupferron (phenylnitrosohydroxylamine) dissolved in various organic solvents [5]. Aqu.:t~us solu~it~ns of cupferron were prepared from a reagent carefuly purified by recrystallizaiion. S~dulions ~q' ~wids were prepared from sealed standards. Redistilled water was used throughout. Ttlc c,~rrccnir.tl i,*~ t,f salts was monitored by titration. The polarographic behaviour of cupferron was first checked in 1-0 ~1 ~nd 0.1 ul amm~mium chloride supporting electrolytes [6]. An analysis of the electrode process pr,~ved tIlat undcr t[~:se conditions cupfcrron is reduced irreversibly on the dropping mercury cl¢cirode. This IL~CLh~/d io ~ taken into account in developing the method of quantitative determ;nation of copl)cr and zinc in polymer samples. Aqueous solutions of cupferron are unstable in acidic media, a circumstar~o~ wl Eclt ct~lnplicate3 its application as the extraction agent. We have therefore carried out a scNcs of prci[~;~ia ~.~'ycxp,~.,'~ments with extraction of cupferron into several organic solvents from aqueous stdui i~ls ot' ~tl~m~onium chloride with the aim to determine the partition coefficient, the dissociat ion c~n~t~nt and ~I~,: c xlraction coefficient. Extraction of cupferron depends both on pH and on the cheH~i~zd ti tlu~c t~l l]~.c ~:olvent. At p H 4"0 cupferron is extracted fully into chloroform, carbon tctrach!e:qdc, ar~d diethsi ctlxer (Fig. 1), Experimental conditions for the extraction of copper and zinc cupferronates were then investigated. The results have shown that the complexes must be treated by chloroform at p H 8 for 5 min to achieve quantitative extraction (Fig. 2). Copper a n d zinc cupferronates extracted * Vysokomol. soyed. A31: No. 4, 885-887, 1989. 979
980
V. G. SVIR~DENKOet al.
into chloroform are reduced in ammonium chloride solutions at pH 3 at the half-wave potentials of - 0.35 V (copper) and - 1.25 V (zinc). However, with increasing pH the half-wave potentials of the investigated complexes become more negative and the heights cease to depend linearly on concentration; at pH 7 the cupferronates are no longer reduced. The results proved the necessity of re-extrac-
¢,%
~%
100
J
I00
1
SO
50 12 3
,9
5
pH
I
I
q
8
pH
FIo. 1 FIG. 2 Fro. 1. Extent of cupferron extraction into diethyl ether (1), carbon tetrachloride (2), and chloroform (3) as a function of pH. FaG. 2. Extent of extraction of copper (1-3) and zinc cupferronates (4-6) into diethyl ether (1, 4), carbon tetrachloride (2, 3), and chloroform (3, 6) as a function of pH. tion before the polarographic analysis proper. Aqueous HCI was used in the re-extraction step and the subsequent polarographic measurements were carried out in an ammonium ckloride supporting electrolyte [7]. The following operations were found to be necessary for the determination of copper and zinc by extraction followed by polarography: the analysed metals are extracted (5 rain) from the aqueous solution into a chloroform solution of cupferron adjusted by ammonia to pH 8; the organic layer is separated, re-extracted with 0.1 M HC1, and the resulting solution is polarographed under the above conditions. When applied to the determination of trace amounts of copper and zinc the procedure yields satisfactory results (Table 1). TABLE 1. MICRODETERMINATION OF COl'PER'AND ZINC BY MEANS OF CUPFI~RRON
Amount of metal, 8 × 103, mole introduced
found
copper
zinc
copper
zinc
3.39 7"78 8-91
2.72 5"46 6.37
3"33 __0'06 7"65 4-0' 11 8.62 + 0' 15
2.72 + 0.05 5.40 + 0.10 6'29 + 0"11
The optimum conditions for quantitative determination of copper and zinc in polymers include t h e optimum cupferron concentration and the time of extraction. The experiments showed that with
decreasing cupferron concentration the time required for equilibrium extraction is prolonged and
Polarographic detcrmination of copper and zinc in macromolecular compounds
981
TABLE 2. DETERMINATIONOF COPPER AND ZINC IN POLYMERS BY EXTRACTIONAND POLAROORAPHY Sample Polyethylene SKN-40 SKD SKS-30-ARKPN
Content of metal, copper
zinc
copper*
zinc*
0.019 __0.001 0.022 + 0.002 0.02_.0.001 0.0018 + 0.0006
0.007 + 0-0009 0.018 + 0.0006 0.011 +0-0003 0.0009 + 0.00009
0.018 _ 0.001 0.022 + 0.002 0"021 +0.002 0.0017 ± 0.0004
0.0069 + 0.0009 0"017 + 0.0004 0.010+0.0003 0.001 + 0.00008
* By atomic-absorption spectroscopy.
only some 9 0 ~ of the metal is bound in the complex. The optimum copferron concentration is 6.2 x 10 -2 mole/l, where both copper and zinc arc fully extracted into the chloroform layer. Results of analytical determination of copper and zinc in various polymers are collected in Table 2. The method developed is selective and non-destructive, and can be recommended for quantitative determination of copper and zinc in studies concerned with oxidation of metal-supported polymer materials.
Translated by M. KUB/N REFERENCES 1. V. A. BELYI, N. I. YEGORENKOV and D. G. LIN, Vysokomol. soyed. BI4: 787, 1972 (Not translated in Polymer Sci. U.S.S.R.) 2. D. G. LIN, I. M. YELISEYEVA and N. I. YEGORENKOV, Kauchuk i rezina, 1, 13, 1986 3. Yu. A. Z O L O T O V , Ocherki analiticheskoi khimii (Introduction to Analytical Chemistry) 240 pp., Moscow, 1977 4. S. K. LAPITSKAYA and V. G. SVIRIDENKO, Zh. analit, khimii 37: 2007, 1982 5. V. B. ALESKOVSKII, S. K. LAPITSKAYA and V. G. SVIRIDENKO, Zh. analit, khimii 27: 602, 1972 6. V. B. ALESKOVSKH, S. K. LAPITSKAYA and V. G. SVIRIDENKO, Izv. vuzov. Khimiya i khim. tekhnol. 14: 847, 1971 7. V. G. SVIRIDENKO, D. G. LIN and S. K. LAPITSKAYA, Izv. vuzov. Khimiya i khim. tekhnol. 26: 1178, 1983