Polymeric membrane selective to calcium (II) ions

Polymeric membrane selective to calcium (II) ions. The invention relates to a polymeric membrane selective to calcium (II) ions, formed by a solid film of plastic material, advantageously of poly(vinyl chloride), which contains an active neutral carrier in a plasticizer of the used plastic material. The active carrier is a complex of macrocyclic polyetherdiamides of the general formula ##STR1## where R.sub.1, R.sub.2, R.sub.3, R.sub.4 are H or alkyl containing 1 to 4 carbon atoms, advantageously methyl, R.sub.5 and R.sub.6 mean alkyl or arylalkyl with 6 to 10 carbon atoms, advantageously benzyl, with the calcium (II) ions and a lipophilic organic anion, advantageously with tetraphenylborate or tetra(p-chlorophenyl)borate anion.

The invention pertains to polymeric membranes selective to calcium(II) 
ions. 
Ion-selective electrodes for calcium, which are described in literature, 
employ various types of function membranes. In the first place, they are 
solid membranes from inorganic crystals, as CaF.sub.2 +LaF.sub.3 (Farren, 
G. M., Ger. 2,101,339) or CaWO.sub.4 (Vesely, J.; Jindra, J., 
Czech.163,358), and poly(vinyl chloride) membranes, which contain calcium 
(II) salt of octyl-phenylphosphoric acid (Tjell, J. C.; Ruzicka, J., Ger. 
Offen. 2 349 299) or of (1,1,3,3-tetramethylbutyl)phenylphosphoric acid 
(Cosgrove, R. E., U.S. Pat. No. 3,729,401) as an active component. The 
sensors based on single crystals did not find broader application, above 
all, because of their low selectivity and nonideal responses. A serious 
disadvantage of the electrodes based on calcium (II) alkylphosphates is a 
considerable dependence of the response on pH, which complicates their 
analytical utilization. The shortcomings of both types of above mentioned 
membranes are overcome in membranes with neutral carriers. A number of 
noncyclic neutral ionophores for the membranes selective to calcium were 
described by Simon et al. (Helv. Chim. Acta 58, 1535 (1975). Certain 
disadvantage of the sensors based on these neutral carriers consists in 
memory effects of the membranes, which make the response worse on passing 
from the more concentrated solutions to the more diluted ones. 
The objective of the invention is a membrane selective to calcium(II) ions, 
which is formed by a solid film of plastic material, advantageously of 
poly(vinyl chloride), containing an active neutral carrier in a 
plasticizer of the above plastic material. The active neutral carrier 
according to the invention is a complex of macrocyclic polyetherdiamides 
of the general formula I 
##STR2## 
where R.sub.1, R.sub.2, R.sub.3, R.sub.4 are H or alkyl containing 1-4 
carbon atoms, preferably methyl, R.sub.5 and R.sub.6 mean alkyl or 
arylalkyl with 6-10 carbon atoms, preferably benzyl, while the general 
composition of the complex with calcium(II) ion and a lipophilic organic 
anion, advantageously tetraphenylborate or tetra(p-chlorophenyl)borate 
anion, is 
EQU 2 polyetherdiamide.Ca.2A.sup.-, 
where A.sup.- is a lipophilic organic anion. 
Macrocyclic polyetherdiamides are prepared by the reaction of dichlorides 
of the correspondingly substituted 3,6-dioxa-octane-1,8-dicarboxylic acids 
with N,N'-dibenzyl-1,11-diamino-3,6,9-trioxaundecane by the earlier 
described method (Petranek, J.; Ryba, O., Collect.Czech.Chem.Commun. 45, 
1567 (1980)). 
As suitable plasticizers, they may be advantageously used plasticizers with 
the dielectric constants higher than 10, for example, nitrated 
alkylarylethers, preferably nitrated phenyl-n-alkylethers, where alkyl 
contains more than 6 carbon atoms in the chain. 
The advantage of calcium selective electrodes, based on the above given 
complex, consists in the precisely defined composition of active component 
and in a linear response with a theoretical course over the broad 
concentration range of 10.sup.-1 M to 10.sup.-5 M Ca.sup.2+. The response 
of electrode to the activity of calcium(II) ions is virtually 
instantaneous without memory effects. The electrodes exhibit a high 
selectivity to calcium(II) ions, namely with respect to ions of Na, Mg, K, 
Rb and Cs.

The invention is further illustrated in examples of performance without 
limiting its scope by any means. 
EXAMPLE 1 
The solution of 0,5 g of potassium tetra(p-chlorophenyl) borate in 3 
cm.sup.3 of methanol was added to the solution of 0,55 g of 
polyetherdiamide of formula I (R.sub.1, R.sub.2, R.sub.3, R.sub.4 
=CH.sub.3 ; R.sub.5, R.sub.6 =benzyl) and 0,07 g Ca(SCN).sub.2 in 5 ml of 
methanol. The separating white precipitate was isolated by filtration, 
crystalized from nitromethane and dried at 110.degree. C. The yield was 
0,7 g of the complex; m.p. 218.degree.-220.degree. C. The composition was 
according to elemental analysis 2 C.sub.32 H.sub.46 N.sub.2 
O.sub.7.Ca.2(ClC.sub.6 H.sub.4).sub.4 B. 
EXAMPLE 2 
The complex of elemental composition 2 C.sub.31 H.sub.44 N.sub.2 
O.sub.7.Ca.2(ClC.sub.6 H.sub.4).sub.4 B and m.p. 238.degree.-241.degree. 
C. was obtained by the same procedure as in Example 1 from the solution of 
polyetherdiamide I (R.sub.1 =R.sub.2 =R.sub.3 =CH.sub.3 ; R.sub.4 =H; 
R.sub.5 =R.sub.6 =benzyl). 
EXAMPLE 3 
The complex of elemental composition 2 C.sub.30 H.sub.42 N.sub.2 
O.sub.7.Ca.2(ClC.sub.6 H.sub.4).sub.4 B and m.p. 104.degree.-106.degree. 
C. was obtained by the same method as in Example 1 (except the drying 
temperature, which was 80.degree. C.) from the solution of 
polyetherdiamide I (R.sub.1 =R.sub.3 =CH.sub.3 ; R.sub.2 =R.sub.4 =H; 
R.sub.5 =R.sub.6 =benzyl). 
EXAMPLE 4 
The complex of elemental composition 2 C.sub.28 H.sub.38 N.sub.2 
O.sub.7.Ca.2(ClC.sub.6 H.sub.4).sub.4 B and m.p. 95.degree.-97.degree. C. 
was prepared by the same procedure as described in Example 3 from the 
solution of polyetherdiamide I (R.sub.1 =R.sub.2 =R.sub.3 =R.sub.4 =H; 
R.sub.5 =R.sub.6 =benzyl). 
EXAMPLE 5 
The solution of 0,35 g of sodium tetraphenylborate in 3 cm.sup.3 methanol 
was added to the solution of 0,55 g of polyetherdiamide I (R.sub.1 
=R.sub.2 =R.sub.3 =R.sub.4 =CH.sub.3 ; R.sub.5 =R.sub.6 =benzyl) and 0,07 
g of Ca(SCN).sub.2 in 5 cm.sup.3 of methanol. The separating white 
precipitate was filtered, crystallized from a mixture of nitromethane and 
ethyl acetate, and dried at 110.degree. C. The complex of elemental 
composition 2 C.sub.32 H.sub.46 N.sub.2 O.sub.7.Ca.2(C.sub.6 
H.sub.5).sub.4 B and m.p. 241.degree.-243.degree. C. was obtained in the 
yield of 0,65 g. 
EXAMPLE 6 
The complex prepared in Example 1 (50 mg) was dissolved in 1 cm.sup.3 of 
(o-nitrophenyl)octylether and mixed with 10 cm.sup.3 of the 5% solution of 
high-molecular-weight poly(vinyl chloride) in cyclohexanone. The solution 
was cast on a horizontal glass plate 7.times.15 cm. Cyclohexanone was 
evaporated at ambient temperature and a foil of thickness about 0,15 mm 
was obtained. A ring cut from the foil was fixed in an electrode body. The 
electrode was filled with an internal standard solution and assembled by 
insertion of a silver-silver chloride electrode. The following selectivity 
coefficients log k.sub.CaM were measured with the electrode prepared in 
this way for the ions M: Mg=-3,77; Sr=-0,93; Ba=-2.10; Li=-2.44; Na=-3,73; 
K=-3,66; Rb=-4,09; Cs=-4,30. 
EXAMPLE 7 
The membrane and electrode were prepared from the complex according to 
Example 2 by the same procedure as described in Example 6. The following 
selectivity coefficients log k.sub.CaM were determined with the 
calcium-selective electrode for the ions M: Mg=-3,63; Sr=-0,71; Ba=-1.28; 
Li=-2,21; Na=-2,94; K=-2,84, Rb=-2,84; Cs=-2,68. 
EXAMPLE 8 
The electrode was made by the procedure described in Example 6 from the 
complex according to Example 3. The following selectivity coefficients log 
k.sub.CaM were measured for the ions M: Mg=-3,11; Sr=-0,69; Ba=-1,01; 
Li=-2,82; Na=-3,36; K=-3,07; Rb=-3,07; Cs=-2,77. 
EXAMPLE 9 
The calcium-selective electrode was prepared by the method described in 
Example 6 from the complex according to Example 4 and showed the following 
selectivity coefficients log k.sub.CaM for the ions M: Mg=-3,27; Sr=-1,82; 
Ba=-2,82; Li=-2,48; Na=-2,76; K=-2,21; Rb=-2,25; Cs=-1,76. 
EXAMPLE 10 
The calcium-selective electrode was prepared from the complex according to 
Example 1 in the same way as in Example 6, with the distinction that 
(2,4-dinitrophenyl)octylether was used instead of 
(o-nitrophenyl)octylether. The following selectivity coefficients log 
k.sub.CaM were obtained with this electrode for the ions M: Mg=-3,78; 
Sr=-0,85, Ba=-1,86; Li=-2,20; Na=-3,14; K=-3,32; Rb=-3,32; Cs=-3,27. 
EXAMPLE 11 
The calcium-selective electrode wad made from the complex according to 
Example 1 by the same method as in Example 6, with the distinction that 
(o-nitrophenyl)-n-decylether was used instead of 
(o-nitrophenyl)octylether. The following selectivity coefficients log 
k.sub.CaM were measured with this electrode for the ions M: Mg=-3,64; 
Sr=-0,78; Ba=-1,76; Li=-1,91; Na=-3,33; K=-3,32; Rb=-3,42; Cs=-3,38.