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Copper(II) ion-selective sensor with electrolytically plated chalcogenide coating
544
Sensors and Actuators
B, 7 ( 1992) W-548
Copper( II) ion-selective sensor with electrolytically plated chalcogenide coating G. Papeschi, Dipartimento
S. Pinzauti
di Scienze Farmaceutiche,
and P. Gratteri Universitci di Firenze,
Via G. Capponi 9, 50121 Florence (Italy)
M. Larini E.C.D.
s.r.l.,
Via dell0 Steccuto
14, 50141 Florence (Italy)
Abstract The performance characteristics of a copper(H) ion-selective electrode, based on the copper selenide formed by cathodic deposition of selenium directly onto a copper substrate, are reported. The deposition is carried out at a constant current of 2 mA/cm2 from 0.1 M Na,SeO, solution whose pH is adjusted to between 6 and 4 with either sulphuric or hydrochloric acid. The electrodes exhibit a linear Nernstian response down to lo-’ M copper in non-buffered medium. Data on the electrode response time and pH dependence are also presented.
Introduction
Experimental
Monocrystalline, polycrystalline, homogeneous or heterogeneous chalcogenic compounds can be used as membranes in electrochemical sensors that are sensitive to heavy metal ions. Mixtures of a variety of copper chalcogenides (CuS, CuSe, CuTe) and Ag,S coprecipitated from aqueous solutions can be compacted at high pressure [ l-31 to obtain Cu( II)-sensitive electrode elements. Chalcogenic vitreous membranes based on CuAg-As-Se or Cu-As-S systems have been given extensive consideration as reliable copper( II) sensors [4]. The electrolytic codeposition of copper selenide has been a well-known fact for some time [5,6], as has its use for selenium determination [7]. Following this procedure, a copper-selective electrode has been prepared by electroplating copper selenide (Cu,.,Se) onto a conducting platinum base [8, lo]. In this case the chalcogenide coating was deposited cathodically from a solution of CuS04 and Na,SeO, dissolved in 0.5 M H,SO,. The present paper deals with the preparation and the performance of a copper ion-selective electrode based on the copper selenide formed by cathodic deposition of selenium directly onto a copper substrate from an NazSe03 solution at about pH 6.
To prepare the electrodes, strips 10 cm long and 0.7 cm wide were cut from a 0.03 cm thick pure (99.99%) copper foil, and used as a conducting basis on which a copper selenide coating was produced cathodically. The deposition was carried out at a constant current of 2 mA/cm2 from a 0.1 M Na2Se0, solution whose pH was adjusted to between 4 and 6 with sulphuric or hydrochloric acid. The anode was a platinum wire and the electrolysis was carried out in well-stirred solution. The e.m.f. measurements were carried out in the galvanic cell (1) with transference:
0925-4005/92/$5.00
CulCu(CuSe)I~~~~,~-~lIO.l M KN03 11 sat. KCl]Hg,Cl,(Hg[PtlCu
(1)
using a digital millivoltmeter (E.C.D., model 8702) connected to a potentiometric strip chart recorder (Kipp & Zonen, model BDlll). A saturated calomel electrode half-cell (E.C.D., model RC12) was used in the double-junction mode to minimize contamination of some test solutions; 0.1 M KN03 was used as the outer filling solution. When control of the pH was required, a combined glass electrode was introduced into the sample solution. @ 1992 -
Elsevier
Sequoia.
All rights
reserved
545
All measurements were taken at room temperature in solutions stirred with a magnetic stirrer. Copper standard solutions for pCu from 1 to 6 were prepared by successive ten-fold dilutions, starting from 0.1 M copper(I1) nitrate. Stock solutions of Cu( II) were prepared by dissolving a weighed amount of analytical reagent grade CU(NO,)~*~H~O in bidistilled water. The ionic strength of all solutions was adjusted to 0.1 by adding an appropriate volume of 1 M KN03 solution. Solutions with low copper concentration (lo-‘-lo-* M) were prepared in a polyethylene cell by addition of known quantities of concentrated copper(I1) nitrate solutions to a standard volume of supporting electrolyte (0.1 M KN03). The dynamic characteristics of the electrodes were measured by monitoring the potential changes following sudden Cu( II) concentration increases with the recorder, which was connected to the output of the pH meter. All chemicals used were of analytical reagent grade or Merck Suprapur.
Results Conditions for the copper selenide coating preparation
A 0.1 M NazSeO, solution was used as electrolyte in a cell with a copper cathode and a platinum anode. A constant current of 8 mA was maintained between the electrodes, the length of the copper strip dipping into the solution being about 2 cm with about 4 cm2 of copper surface wetted by the solution. The pH of the selenite solution was changed from the initial value (pH > 10) to about 6, either with 0.05 M H2S04 or with 0.1 M HCl (Fig. 1). In the pH range 10 to 7.5 we observed only very small hydrogen bubbles leaving the cathodic surface. From pH 7.5 to 6, hydrogen evolved at the cathode and selenium left the electrode in very small red flakes. Coatings were deposited in acidic solutions, but deposits were obtained which and mechanically were sufficiently adherent strong to permit prolonged use of the electrodes only for pH from 6 to 4.5. During selenium deposition hydrogen was not released. In more acid solutions the deposits were quickly obtained but a diffuse pitting corrosion occurred, leaving the
0PH
642.
V.
0
lb
20
30
VOLUME, ml(0.1MHCI)
Fig. 1. Influence of selenite solution pH on electrolysis onto copper cathode.
electrode studded with small spots of uncoated copper. Under the optimum conditions of pH and current density outlined above, ten minutes of electrolysis in well-stirred solution produced a lead-gray deposit. In the following we refer to this electrode as Cu{CuSe}, omitting assumptions about the stoichiometry of the copper selenide coating. The observed deposit formations imply that the following reactions take place at the cathodic surface: 2H+ + 2e- + H,(ads)
(2)
2H2(ads) + HSeOJ- + H+ + Se + %I20
(3)
Se + Cu 4 CuSe
(4)
Favourable conditions for a good deposit were reached when the amount of hydrogen atoms or hydrogen molecules produced by reduction (2) and adsorbed onto the cathodic surface did not exceed the amount of HSe03- ions that diffused from the bulk solution into the interfacial layer, where they undergo reduction according to eqn. (3). If a larger current was used, H2(gas) evolved at the cathode, and the reduction of HSeO,- to red selenium occurred too far from the cathodic surface and dispersed into the solution in the form of a light powder. Reaction (3) was revealed by using a gold cathode and observing in the same electroplating conditions a deposit of red selenium, which could be melted on the gold surface at about 220 “C.
546
TABLE I. Calibration data for Cu{CuSe} electrodes prepared by electrolysis in Na,SeO, solutions adjusted to about pH 6 either with H,SO, (mV-A) or with HCI (mV-B) PCH
mV-A
mV-B
I 2 3 4 5 6
50 21 -8 -31 -62 -11
52 22 -7 -36 -61 -15
Behaviour of the coatings as copper
electrode
Within the concentration range IO-‘-- lo-’ M the calibration was carried out in a Cu(NO,)* standard of constant ionic strength 0.1, prepared by serial dilution. Electrodes (Cu(CuSe}) prepared by electrolysis in Na,SeO, solutions at about pH 6 (adjusted either with sulphuric or hydrochloric acid) exhibited a steady and linear Nernstian response down to 10T5 M Cu(I1) in solutions of constant ionic strength, with a slope of 29 mV per decade (Table 1) and a detection limit of about lo-’ M. Figure 2 shows the potential-concentration relationships for a freshly prepared electrode (curve A) first equilibrated in 0.1 M KN03 solution, then exposed to increasing Cu(II) concentrations by spiking appropriate aliquots of Cu( II) standards into the background solution of 0.1 M KN03 to cover the concentration range pCu 8 to 4. The potentials at higher concentrations were measured by moving the electrode in Cu( 11) standards prepared by serial dilution.
Curve B refers to the calibration of the Cu{CuSe) electrode after it had been immersed in lo-* M Cu(II) solution for five minutes. Potential values of curve B in the 10-l - 10e6 M concentration range are furnished by ‘used’ electrodes when the calibration is carried out either from high to low or from low to high concentrations in separate solutions. Strips of gold coated with glassy selenium obtained by melting the electrolytic deposit of red selenium were tested as a copper( II) sensor (Au{Se}). A linear response is attained between lop6 and 10-l M, but with a slope of 20 mV/ decade of Cu(I1). When the Au{Se) electrode was plated with copper from a CuSO, acid bath, a lead-gray deposit was observed to form, and the Au{CuSe) electrode gave exactly the same potential values as the Cu{CuSe} electrode in Cu(I1) solutions (Fig. 3). Response time
The time required for reaching a steady e.m.f. was examined by recording the electrode potential during the calibration with multiple standard Cu( II) addition. The electrode pair was immersed in a wellstirred 0.1 M KN03 solution (100 ml), and the potential was recorded with the recorder: After a steady potential had been reached, an aliquot of copper standard was spiked into the solution following the potential change. Several copper standard aliquots were spiked into the same solution
*\
-2001 0
2
4
6
6
, __
1U
PCU
Fig. 2. Response of Cu{CuSe} electrode to Cu( II) ion in 0. I M KNO,. A, freshly prepared electrode calibration. B, electrode calibration after immersion in 10m2 M Cu(II) solution for five minutes.
1
2
3
4
5
6
Pcu Fig. ,3. Response of Au{CuSe} electrode (curve B) and of the Cu{CuSe} electrode (curve C) in Cu(II) solutions. Curve A refers to the Cu(I1) sensitivity of a selenium coating on gold, from which Au{CuSe} is obtained by a light electrodeposition of copper.
100
\abpe-58mV
”
2
0
d
z 2
b 2
-100
-200
,
-3oc 2
4
6
6
10
PB Fig. 4. Response of Cu{CuSe} electrode to varying copper(B) ion concentrations as a function of pH. All solutions were 0.1 M KNO,.
without removing the electrodes, in order to increase the Cu(I1) concentration stepwise from about low6 to lop3 M. A steady electrode potential was attained in ten seconds in the micromolar concentration range, and simultaneously with the homogenization of the solution at higher concentrations. pH dependence of the electrode response The pH range of the Cu{CuSe) electrodes was studied in solutions with constant Cu(II) nitrate concentrations and with constant ionic strength (I = 0.1). The pH was adjusted by addition of nitric acid or potassium hydroxide (Fig. 4). It can be seen that the potential of the Cu{CuSe} electrode did not depend on pH at pH > 1.5. The decrease of electrode potential at pH < 1.5 was observed earlier for silver ion-selective chalcogenide glass sensors [9] and was related to changes in the liquid junction potential at the salt bridge electrolyte/test solution boundary as a result of the high hydrogen ion concentration. In pure 0.1 M KN03, the electrode potential is pH sensitive only at pH higher than 7, probably due to some surface adsorption of hydroxyl ions. In the presence of Cu(I1) ions, the electrode response was independent of pH until Cu(OH), began to precipitate.
tive chalcogenide sensors than the more complex existing technologies. The good performance of the Cu{CuSe} electrodes could be ascribed to the electrochemical/ chemical surface reactions implied in their preparation. The reaction of selenium with the copper surface as adsorbed hydrogen reduces HSeO,- ions to selenium, ensuring homogeneous coatings with a very stable copper compound. The Cu(CuSe} electrodes show: (a) a detection limit of 10e7 M Cu(I1); (b) very short response times even in the micromolar concentration range; (c) a high stability in time; (d) a wide pH-independent range within which direct potentiometric measurements could be carried out.
Acknowledgements
This work was supported by the National Research Council (CNR) of Italy, Progetto Finalizzato ‘Materiali e Dispositivi per 1’Elettronica a Stato Solido’.
References 1 Cl. J. M. Heijne and W. E. van der Linden, The formation of mixed copper sulfide-silver sulfide membranes for copper(II)selective electrodes, Anal. Chim. Acta, 93 (1977) 99-I IO. 2 R. D. Tsingarelli, A. F. Radchenko, E. A. Konshina, N. A. Ozeretskaya and I. P. Nikolenko, Selection of conditions for ionometric determination of copper in wastewater, Zh. Anal. Khim., 39 (1984) 437-441. 3 M. Neshkova and J. Havas, The ternary coppersilver selenide-a
new homogeneous solid state ion-selective electrode for copper( II), Anal. L.&r., 16 ( 1983) l567- 1580. 4 R. Jasinski, I. Trachtenberg and G. Rice, A chalcogenide glass electrode sensitive to cupric ions, J. Electrochem. SC., 121 (1974) 363-370. 5 E. Milller, Die kathodische
Abscheidung von Tellur und Selen aus ihren Saurstoffsauren und ihre elektroanalytische Bestimmung, Z. Phys. Chem., 100 (1922) 346-366. 6 J. Ladriere, Reduction of selenious acid by copper and by electrolysis in the presence of copper, Bull. Sot. Chim. Beige, 82
(1973) 87-98. 7 J. Norwitz, Electrolytic determination
Discussion
Electrolytic plating constitutes an easier and more economical way of preparing Cu(II)-sensi-
of selenium and tellurium and the separation of copper from selenium and tellurium, Anal. Chim. Acra, 5 (1951) lO9- 114. 8 M. Neshkova and H. Sheytanov, Ion-selective electrodes with sensors of electrolytically plated chalcogenide coatings. Part I. Copper ion-selective electrode based on plated copper selenide, J. Electroanal. Chem., 102 (1979) 189- 198.
548 9 Yu. G. Vlasov, E. A. Bychkov, E. A. Kazakova and Z. U. Borisova, Chalcogenide glass electrode for silver ions determination in corrosive media, Zh. Anal. Khim., 39 (1984) 452455.
10 M. Neshkova, Cu(I1) electrode function dependence on the membrane composition for selenide-based all solid-state copper ionselective electrodes, Proc. Ion-Selective Electrodes 5, Mbtraftired, Hungary, Oct. 9-13, 1988, pp. 503-517.
Sensors and Actuators
B, 7 ( 1992) W-548
Copper( II) ion-selective sensor with electrolytically plated chalcogenide coating G. Papeschi, Dipartimento
S. Pinzauti
di Scienze Farmaceutiche,
and P. Gratteri Universitci di Firenze,
Via G. Capponi 9, 50121 Florence (Italy)
M. Larini E.C.D.
s.r.l.,
Via dell0 Steccuto
14, 50141 Florence (Italy)
Abstract The performance characteristics of a copper(H) ion-selective electrode, based on the copper selenide formed by cathodic deposition of selenium directly onto a copper substrate, are reported. The deposition is carried out at a constant current of 2 mA/cm2 from 0.1 M Na,SeO, solution whose pH is adjusted to between 6 and 4 with either sulphuric or hydrochloric acid. The electrodes exhibit a linear Nernstian response down to lo-’ M copper in non-buffered medium. Data on the electrode response time and pH dependence are also presented.
Introduction
Experimental
Monocrystalline, polycrystalline, homogeneous or heterogeneous chalcogenic compounds can be used as membranes in electrochemical sensors that are sensitive to heavy metal ions. Mixtures of a variety of copper chalcogenides (CuS, CuSe, CuTe) and Ag,S coprecipitated from aqueous solutions can be compacted at high pressure [ l-31 to obtain Cu( II)-sensitive electrode elements. Chalcogenic vitreous membranes based on CuAg-As-Se or Cu-As-S systems have been given extensive consideration as reliable copper( II) sensors [4]. The electrolytic codeposition of copper selenide has been a well-known fact for some time [5,6], as has its use for selenium determination [7]. Following this procedure, a copper-selective electrode has been prepared by electroplating copper selenide (Cu,.,Se) onto a conducting platinum base [8, lo]. In this case the chalcogenide coating was deposited cathodically from a solution of CuS04 and Na,SeO, dissolved in 0.5 M H,SO,. The present paper deals with the preparation and the performance of a copper ion-selective electrode based on the copper selenide formed by cathodic deposition of selenium directly onto a copper substrate from an NazSe03 solution at about pH 6.
To prepare the electrodes, strips 10 cm long and 0.7 cm wide were cut from a 0.03 cm thick pure (99.99%) copper foil, and used as a conducting basis on which a copper selenide coating was produced cathodically. The deposition was carried out at a constant current of 2 mA/cm2 from a 0.1 M Na2Se0, solution whose pH was adjusted to between 4 and 6 with sulphuric or hydrochloric acid. The anode was a platinum wire and the electrolysis was carried out in well-stirred solution. The e.m.f. measurements were carried out in the galvanic cell (1) with transference:
0925-4005/92/$5.00
CulCu(CuSe)I~~~~,~-~lIO.l M KN03 11 sat. KCl]Hg,Cl,(Hg[PtlCu
(1)
using a digital millivoltmeter (E.C.D., model 8702) connected to a potentiometric strip chart recorder (Kipp & Zonen, model BDlll). A saturated calomel electrode half-cell (E.C.D., model RC12) was used in the double-junction mode to minimize contamination of some test solutions; 0.1 M KN03 was used as the outer filling solution. When control of the pH was required, a combined glass electrode was introduced into the sample solution. @ 1992 -
Elsevier
Sequoia.
All rights
reserved
545
All measurements were taken at room temperature in solutions stirred with a magnetic stirrer. Copper standard solutions for pCu from 1 to 6 were prepared by successive ten-fold dilutions, starting from 0.1 M copper(I1) nitrate. Stock solutions of Cu( II) were prepared by dissolving a weighed amount of analytical reagent grade CU(NO,)~*~H~O in bidistilled water. The ionic strength of all solutions was adjusted to 0.1 by adding an appropriate volume of 1 M KN03 solution. Solutions with low copper concentration (lo-‘-lo-* M) were prepared in a polyethylene cell by addition of known quantities of concentrated copper(I1) nitrate solutions to a standard volume of supporting electrolyte (0.1 M KN03). The dynamic characteristics of the electrodes were measured by monitoring the potential changes following sudden Cu( II) concentration increases with the recorder, which was connected to the output of the pH meter. All chemicals used were of analytical reagent grade or Merck Suprapur.
Results Conditions for the copper selenide coating preparation
A 0.1 M NazSeO, solution was used as electrolyte in a cell with a copper cathode and a platinum anode. A constant current of 8 mA was maintained between the electrodes, the length of the copper strip dipping into the solution being about 2 cm with about 4 cm2 of copper surface wetted by the solution. The pH of the selenite solution was changed from the initial value (pH > 10) to about 6, either with 0.05 M H2S04 or with 0.1 M HCl (Fig. 1). In the pH range 10 to 7.5 we observed only very small hydrogen bubbles leaving the cathodic surface. From pH 7.5 to 6, hydrogen evolved at the cathode and selenium left the electrode in very small red flakes. Coatings were deposited in acidic solutions, but deposits were obtained which and mechanically were sufficiently adherent strong to permit prolonged use of the electrodes only for pH from 6 to 4.5. During selenium deposition hydrogen was not released. In more acid solutions the deposits were quickly obtained but a diffuse pitting corrosion occurred, leaving the
0PH
642.
V.
0
lb
20
30
VOLUME, ml(0.1MHCI)
Fig. 1. Influence of selenite solution pH on electrolysis onto copper cathode.
electrode studded with small spots of uncoated copper. Under the optimum conditions of pH and current density outlined above, ten minutes of electrolysis in well-stirred solution produced a lead-gray deposit. In the following we refer to this electrode as Cu{CuSe}, omitting assumptions about the stoichiometry of the copper selenide coating. The observed deposit formations imply that the following reactions take place at the cathodic surface: 2H+ + 2e- + H,(ads)
(2)
2H2(ads) + HSeOJ- + H+ + Se + %I20
(3)
Se + Cu 4 CuSe
(4)
Favourable conditions for a good deposit were reached when the amount of hydrogen atoms or hydrogen molecules produced by reduction (2) and adsorbed onto the cathodic surface did not exceed the amount of HSe03- ions that diffused from the bulk solution into the interfacial layer, where they undergo reduction according to eqn. (3). If a larger current was used, H2(gas) evolved at the cathode, and the reduction of HSeO,- to red selenium occurred too far from the cathodic surface and dispersed into the solution in the form of a light powder. Reaction (3) was revealed by using a gold cathode and observing in the same electroplating conditions a deposit of red selenium, which could be melted on the gold surface at about 220 “C.
546
TABLE I. Calibration data for Cu{CuSe} electrodes prepared by electrolysis in Na,SeO, solutions adjusted to about pH 6 either with H,SO, (mV-A) or with HCI (mV-B) PCH
mV-A
mV-B
I 2 3 4 5 6
50 21 -8 -31 -62 -11
52 22 -7 -36 -61 -15
Behaviour of the coatings as copper
electrode
Within the concentration range IO-‘-- lo-’ M the calibration was carried out in a Cu(NO,)* standard of constant ionic strength 0.1, prepared by serial dilution. Electrodes (Cu(CuSe}) prepared by electrolysis in Na,SeO, solutions at about pH 6 (adjusted either with sulphuric or hydrochloric acid) exhibited a steady and linear Nernstian response down to 10T5 M Cu(I1) in solutions of constant ionic strength, with a slope of 29 mV per decade (Table 1) and a detection limit of about lo-’ M. Figure 2 shows the potential-concentration relationships for a freshly prepared electrode (curve A) first equilibrated in 0.1 M KN03 solution, then exposed to increasing Cu(II) concentrations by spiking appropriate aliquots of Cu( II) standards into the background solution of 0.1 M KN03 to cover the concentration range pCu 8 to 4. The potentials at higher concentrations were measured by moving the electrode in Cu( 11) standards prepared by serial dilution.
Curve B refers to the calibration of the Cu{CuSe) electrode after it had been immersed in lo-* M Cu(II) solution for five minutes. Potential values of curve B in the 10-l - 10e6 M concentration range are furnished by ‘used’ electrodes when the calibration is carried out either from high to low or from low to high concentrations in separate solutions. Strips of gold coated with glassy selenium obtained by melting the electrolytic deposit of red selenium were tested as a copper( II) sensor (Au{Se}). A linear response is attained between lop6 and 10-l M, but with a slope of 20 mV/ decade of Cu(I1). When the Au{Se) electrode was plated with copper from a CuSO, acid bath, a lead-gray deposit was observed to form, and the Au{CuSe) electrode gave exactly the same potential values as the Cu{CuSe} electrode in Cu(I1) solutions (Fig. 3). Response time
The time required for reaching a steady e.m.f. was examined by recording the electrode potential during the calibration with multiple standard Cu( II) addition. The electrode pair was immersed in a wellstirred 0.1 M KN03 solution (100 ml), and the potential was recorded with the recorder: After a steady potential had been reached, an aliquot of copper standard was spiked into the solution following the potential change. Several copper standard aliquots were spiked into the same solution
*\
-2001 0
2
4
6
6
, __
1U
PCU
Fig. 2. Response of Cu{CuSe} electrode to Cu( II) ion in 0. I M KNO,. A, freshly prepared electrode calibration. B, electrode calibration after immersion in 10m2 M Cu(II) solution for five minutes.
1
2
3
4
5
6
Pcu Fig. ,3. Response of Au{CuSe} electrode (curve B) and of the Cu{CuSe} electrode (curve C) in Cu(II) solutions. Curve A refers to the Cu(I1) sensitivity of a selenium coating on gold, from which Au{CuSe} is obtained by a light electrodeposition of copper.
100
\abpe-58mV
”
2
0
d
z 2
b 2
-100
-200
,
-3oc 2
4
6
6
10
PB Fig. 4. Response of Cu{CuSe} electrode to varying copper(B) ion concentrations as a function of pH. All solutions were 0.1 M KNO,.
without removing the electrodes, in order to increase the Cu(I1) concentration stepwise from about low6 to lop3 M. A steady electrode potential was attained in ten seconds in the micromolar concentration range, and simultaneously with the homogenization of the solution at higher concentrations. pH dependence of the electrode response The pH range of the Cu{CuSe) electrodes was studied in solutions with constant Cu(II) nitrate concentrations and with constant ionic strength (I = 0.1). The pH was adjusted by addition of nitric acid or potassium hydroxide (Fig. 4). It can be seen that the potential of the Cu{CuSe} electrode did not depend on pH at pH > 1.5. The decrease of electrode potential at pH < 1.5 was observed earlier for silver ion-selective chalcogenide glass sensors [9] and was related to changes in the liquid junction potential at the salt bridge electrolyte/test solution boundary as a result of the high hydrogen ion concentration. In pure 0.1 M KN03, the electrode potential is pH sensitive only at pH higher than 7, probably due to some surface adsorption of hydroxyl ions. In the presence of Cu(I1) ions, the electrode response was independent of pH until Cu(OH), began to precipitate.
tive chalcogenide sensors than the more complex existing technologies. The good performance of the Cu{CuSe} electrodes could be ascribed to the electrochemical/ chemical surface reactions implied in their preparation. The reaction of selenium with the copper surface as adsorbed hydrogen reduces HSeO,- ions to selenium, ensuring homogeneous coatings with a very stable copper compound. The Cu(CuSe} electrodes show: (a) a detection limit of 10e7 M Cu(I1); (b) very short response times even in the micromolar concentration range; (c) a high stability in time; (d) a wide pH-independent range within which direct potentiometric measurements could be carried out.
Acknowledgements
This work was supported by the National Research Council (CNR) of Italy, Progetto Finalizzato ‘Materiali e Dispositivi per 1’Elettronica a Stato Solido’.
References 1 Cl. J. M. Heijne and W. E. van der Linden, The formation of mixed copper sulfide-silver sulfide membranes for copper(II)selective electrodes, Anal. Chim. Acta, 93 (1977) 99-I IO. 2 R. D. Tsingarelli, A. F. Radchenko, E. A. Konshina, N. A. Ozeretskaya and I. P. Nikolenko, Selection of conditions for ionometric determination of copper in wastewater, Zh. Anal. Khim., 39 (1984) 437-441. 3 M. Neshkova and J. Havas, The ternary coppersilver selenide-a
new homogeneous solid state ion-selective electrode for copper( II), Anal. L.&r., 16 ( 1983) l567- 1580. 4 R. Jasinski, I. Trachtenberg and G. Rice, A chalcogenide glass electrode sensitive to cupric ions, J. Electrochem. SC., 121 (1974) 363-370. 5 E. Milller, Die kathodische
Abscheidung von Tellur und Selen aus ihren Saurstoffsauren und ihre elektroanalytische Bestimmung, Z. Phys. Chem., 100 (1922) 346-366. 6 J. Ladriere, Reduction of selenious acid by copper and by electrolysis in the presence of copper, Bull. Sot. Chim. Beige, 82
(1973) 87-98. 7 J. Norwitz, Electrolytic determination
Discussion
Electrolytic plating constitutes an easier and more economical way of preparing Cu(II)-sensi-
of selenium and tellurium and the separation of copper from selenium and tellurium, Anal. Chim. Acra, 5 (1951) lO9- 114. 8 M. Neshkova and H. Sheytanov, Ion-selective electrodes with sensors of electrolytically plated chalcogenide coatings. Part I. Copper ion-selective electrode based on plated copper selenide, J. Electroanal. Chem., 102 (1979) 189- 198.
548 9 Yu. G. Vlasov, E. A. Bychkov, E. A. Kazakova and Z. U. Borisova, Chalcogenide glass electrode for silver ions determination in corrosive media, Zh. Anal. Khim., 39 (1984) 452455.
10 M. Neshkova, Cu(I1) electrode function dependence on the membrane composition for selenide-based all solid-state copper ionselective electrodes, Proc. Ion-Selective Electrodes 5, Mbtraftired, Hungary, Oct. 9-13, 1988, pp. 503-517.