CS255160B1 - Calcium ion ion selective electrode membrane - Google Patents

Abstract

Membrane for a calcium ion-selective electrode with improved selective properties, especially towards potassium, rubidium and cesium ions, formed by a film of plastic, e.g. polyvinyl chloride, softened with plasticizers, such as o-nitrophenyl-n-octyl ether or o-nitrophenyl-n-dodecyl ether, where 4,4,5,5- -tetramethyl-3,6-dioxacortic acid diamide is used as a neutral carrier, selective for calcium ions, the imidiocytic nitrogen atoms of which are symmetrically substituted by two phenyls and two 2-n-alkyloxyethyls, of the schematic formula where -Ø is n-alkyl CnH2n+1 with a number of carbon atoms of 8 to 11, such as N,N'-diphenyl-N,N'-di- -(2-n-octyloxyethyl)diamide of 4,4,5,5- -tetramethyl-3,6-dioxacortic acid or 4,4,5,5-tetramethyl-3,6-dioxacortic acid N,N'-diphenyl-N,N'-di-(2-n-undecyloxyethyl)diamide.

Description

The invention relates to a membrane for a calcium ion-selective electrode with improved selective properties.

In practice, ion-selective calcium electrodes with a membrane formed by a plastic film, in which the active substance itself is embedded, are widely used. One group of substances used for the preparation of ion exchangers of these membranes are the so-called neutral carriers. The preparation, use and properties of neutral carriers with an acyclic chain were described by Simon and his collaborators (Ammán D., Bissig E., Giiggi M., Pretsch E., Simon W.: Hlev. Chim. Acta 58, 1 535 (1975)).

Neutral carriers based on tetramethyltriglycolic acid with an acyclic chain are described in the invention (Panooh M., Semler M., Ryba O., Petránek J., Czechoslovak patent number 214 057) and with a cyclic chain in the invention (Petránek J., Ryba O., Semler M., Panoch M., Czechoslovak patent number 213 944). By improving the selective properties of membranes with neutral carriers, the use of calcium ion-selective electrodes in practice has been expanded.

An even greater improvement in the selective properties of calcium ion-selective electrodes with a membrane formed by a film of plastic, for example high molecular weight polyvinyl alcohol, softened with plasticizers such as o-nitrophenyl-n-octyl ether or o-nitrophenyl-n-dodecyl ether, especially with respect to potassium, rubidium and cesium ions, is achieved according to the present invention, the essence of which lies in the fact that 4,4,5,5-tetramethyl-3,6-dioxacortic acid diamide is used as a neutral carrier selective for calcium ions, the amidic nitrogen atoms of which are symmetrically substituted by two phenyls and two 2-n-alkyloxyethyls, of the schematic structural formula where -R is n-alkyl ^c n ^H 2n-1 ^with P°^ ^tem of carbon atoms n = 8 to 11, such as N,N'-diphenyl-N,N'=-(2-n-octyloxyethyl)diamide 4,4,5,5-tetramethyl-3,6-dioxacortic acid or N,N-diphenyl-Ν,Ν ¹ -(2-n-undecyloxyethyl)diamide.

Membranes with these neutral carriers exhibit a wide range of linear Nernst response to calcium ion activity, fast response, small potential drift, and good selectivity, especially toward ammonium, potassium, rubidium, and cesium ions.

The membrane composition, response and selectivity properties are evident from the examples given below.

Example 1

A membrane with a thickness of 0.2 mm was prepared, consisting of 0.95 wt. % of a neutral carrier, specifically N,Ν'-diphenyl-N,Ν'-di-(2-n-octyloxyethyl)diamide of 4,4,5,5-tetramethyl-3,6-dioxacortic acid with the structural formula

0.46 wt. % sodium tetrafluoroborate, 60.01 wt. % o-nitrophenyl-n-octyl ether, 38.58 wt. percent high molecular weight polyvinyl chloride. An electrode with a reference electrolyte CaCl.,, c = 0.1 mol/1 and an internal reference electrode of silver chloride was made from the membrane. The measurement was carried out at a temperature of 293 - 5 K in the cell and with a reference saturated calomel electrode. For aqueous solutions of calcium chloride, the values of the electromotive force of the cell were measured as shown in Table I:

Table I

CaCl ₂ c (mol/1) electromotive force (mV,

-88.7 -60.4 -31.9 - 4.9 +20.6 + 45.0

By the method of separated solutions using chlorides of the respective cations with a concentration of 0.1 mol/l, the values of selectivity coefficients were determined for the electrode at a temperature of 293 - 5 K, as shown in Table XI.

Table II

3 = ..Sweat j = "Sweat" Ca, j Ca, j NH+ 3.4 times 10 ^-5 Cs ⁺ 3.3 times 10 ⁵ Li ⁺ 2.6 times 10 ^-2 . Mg ²⁺ 9.4 times IO ^-5 On ⁺ 4.8 times 10 ^-4 Sr ²⁺ 2.7 times io ² To ⁺ 4.7 times 10' ⁵ Ba ²⁺ 7.9 times io ⁴ Rb ⁺ 1.9 times 10 ^-5

Example

A membrane of the same thickness as in Example 1 was made with a composition of 1.27 wt. % of neutral carrier as in Example 1, 0.63 wt. % of sodium tetrafluoroborate, 59.71 wt. % of o-nitrophenyl-n-dodecyl ether and 38.39 wt. % of high molecular weight polyvinyl chloride. An electrode was made from the membrane as in Example 1 and the electromotive force of the cell was measured in the same way, where the measured values are given in Table III and the selectivity coefficients, where the measured values are given in Table IV.

Table III electromotive force (mV)

CaCl ₂ c = (mol/1)

10 ^-6 -100.4 10' ⁵ - 72.4 10~ ⁴ - 43.7 10 ^-3 - 15.3 10- ² + 10.0 10 ^-1 + 33.7

Table IV

j = -.Pot 3 “ ..Sweat Ca, j Ca, 3 NH+ 3.3 times ΙΟ ^-5 Ca ⁺ 2.2 times 10' ⁴ Li ⁺ 2.7 times ΙΟ' ² Mg ²⁺ 5.9 times 10 ^-5 -3 2+ -2 On 2.2 times 10 Wed 3.6X 10 To ⁺ 6.3 times 10 ^-5 Ba ²⁺ 7.2 times 10 ⁴ 4· -4 Rb 1.5X 10

A membrane of the same thickness as in Example 1 was made with a composition of 1.55 wt. % of neutral carrier, namely N,Ν'-diphenyl-Ν,Ν'-di-(2-n-undecyloxyethyl)diamide of 4,4,5,5-tetramethyl-3,6-dioxacortic acid, 0.68 wt. % of sodium tetrafluoroborate, 59.51 wt. % of 6-nitrophenyl-n-dodeoyl ether and 38.26 wt. % of polyvinyl chloride. An electrode was made from the membrane as in Example 1, and the electromotive force and selectivity coefficients were measured in the same way. The measurement results are given in Tables V and VI.

Table V

CaCl ₂ c = (mol/1) electromotive force (mV)

10' ⁶ -98.1 10 ^-5 -72.8 -4 10 -44.2 -3 10 -15.8 -2 10 + 9.9 -1 10 Table VI +34.0 j = "Sweat" j = "Sweat" ^To Ca, j Ca,j NH+ 2.7 x IO ^-4 Ca ⁺ 2.0 x 10 ^-4 1.4 x 10 ^-2 Mg ²⁺ 5.4 x 10 ^-5 On ⁺ 5.4 x 10 ^-4 Sr ²⁺ 1.3 x 10 ^-2 To ⁺ 1.1 x 10 ^-4 Ba ²⁺ 4.1 x 10' ⁴ Rb ⁺ 5.2 x 10 ^-5

Claims (1)

SUBJECT OF THE INVENTION A membrane for a calcium ion selective electrode consisting of a plastic film, for example a high molecular weight polyvinyl alcohol, plasticized with a plasticizer such as o-nitrophenyl-n-octyl ether or o-nitrophenyl-n-dodeoyl ether, characterized in that diamide selective calcium carrier acid 4,4,5,5-tetramethyl-3,6-dioxakorkové whose imidioké nitrogens are symmetrically substituted with two phenyl groups and two 2n-alkyloxyethyly, the schematic structural formula wherein R is alkyl ^C n ^H 2n + l ^{3? em} ° ®r carbon atoms n = 8-11, such as N, N-diphenyl-N, N'-di- (2-n-oktyloxyethyl) diamide 4,4,5,5-tetramethyl-3,6- dioxacork or N, N'-diphenyl-N, N'-di- (2-n-undecyloxyethyl) 4,4,5,5-tetramethyl-3,6-dioxacorkic acid diamide.