Cation-selective polymeric electrodes

• US 5,395,505 A
• Filed: 04/28/1994
• Issued: 03/07/1995
• Est. Priority Date: 10/31/1991
• Status: Expired due to Term

• Current Assignee: Monitoring Technology Corporation
• Original Assignee: Monitoring Technology Corporation
• Inventors: Linton, Robert A. F., Band, David M.
• Primary Examiner(s): Niebling, John
• Assistant Examiner(s): Bell, Bruce F.
• Application Number:
  US08/211,926
• Time in Patent Office: 313 Days
• Field of Search: 204/418, 204/435, 128/668, 128/670, 128/696, 128/700
• US Class Current: 204/418
• CPC Class Codes: G01N 27/3335 the membrane containing at least one organic component G01N27/3271 takes precedence; aspects concerning the enzyme reagent in enzyme electrodes C12Q1/001

Abstract

A cation-sensitive electrode which comprises an internal reference electrode, an internal reference solution and a cation-responsive membrane, characterized in that the internal reference solution contains a saturated solution of a salt of a cation other than the cation for which the cation-responsive membrane is primarily selective, the internal reference solution being formed in situ by hydration of a combination of the salt of the cation with a hygroscopic material, bu absorption of water from the atmosphere and/or by hydration of the hygroscopic material when the electrode is put into use, thereby forming the internal reference solution.

Claims

1. A cation-sensitive electrode which comprises an internal reference electrode, an internal reference solution and a cation-responsive membrane, characterized in that the internal reference solution contains a saturated solution of a salt of a cation other than the cation for which the cation-responsive membrane is primarily selective, the internal reference solution is formed in situ by hydration of a combination of a hygroscopic material with the salt of the cation other than the cation for which the cation-responsive membrane is primarily selective, either by absorption of water from the atmosphere and/or by hydration of the hygroscopic material when the electrode is put into use, thereby forming the internal reference solution.

2. A cation-sensitive electrode as claimed in claim 1 wherein the cation-responsive membrane is formed from a polymeric material which has an inherent selectivity for the cation for which the membrane is primarily selective.

3. A cation-sensitive electrode as claimed in claim 1 wherein the cation-responsive membrane is formed from a polymeric material which has an ionophore, ligand or complexing agent incorporated into the membrane structure to impart selective permeability.

4. A cation-sensitive electrode as claimed in claim 3 wherein the cation-responsive membrane comprises a lithium selective polyvinylchloride membrane and the internal reference solution comprises a saturated solution of a sodium or potassium salt.

5. A cation-sensitive electrode as claimed in claim 4 wherein the lithium selective polyvinylchloride membrane contains as the lithium ionophore N,N-dicyclohexyl-N,N-diisobutyl-cis-cyclo-hexane-1,2-dicarboxamide or 6,6-dibenzyl-14-crown-4.

6. A cation-sensitive electrode as claimed in claim 3 wherein the cation-responsive membrane comprises a calcium selective polyvinylchloride membrane and the internal reference solution comprises a saturated solution of a sodium or potassium salt.

7. A cation-sensitive electrode as claimed in claim 6 wherein the calcium selective polyvinylchloride membrane contains as the calcium ionophore diethyl-N,N'"'"'-bis(12-methylamino-dodecanoate).

8. A cation-sensitive electrode as claimed in claim 3 wherein the cation-responsive membrane comprises a potassium selective polyvinylchloride membrane and the internal reference solution comprises a saturated solution of a calcium salt.

9. A cation-sensitive electrode as claimed in claim 8 wherein the potassium selective polyvinylchloride membrane contains as the potassium ionophore valinomycin.

10. A cation-sensitive electrode as claimed in claim 1 wherein the hygroscopic material is formed as a layer on the internal reference electrode in admixture with the salt of the cation for which the cation-responsive membrane is not primarily selective.

11. A cation-selective electrode as claimed in claim 1 wherein the hygroscopic material is sorbitol.

12. A method of measuring cardiac output in a human being which method is characterized in that it comprises:

(i) injecting into a central vein of the human being a bolus injection of a solution of a cation which is not normally present in blood;

(ii) measuring the dilution of the cation in the blood plasma flowing in a peripheral artery using a cation-sensitive electrode which is sensitive to the cation injected in step (i); and

(iii) calculating from the dilution data obtained in step (ii) the cardiac output.

13. A method as claimed in claim 12 wherein the cation-sensitive electrode comprises an internal reference electrode, an internal reference solution and a cation-responsive membrane, the internal reference solution containing a saturated solution of a salt of a cation other than the cation for which the cation-responsive membrane is primarily selective, the internal reference solution is formed in situ by hydration of a combination of a hygroscopic material with the salt of the cation other than the cation for which the cation-responsive membrane is primarily selective, either by absorption of water from the atmosphere and/or by hydration of the hygroscopic material when the electrode is put into use thereby forming the internal reference solution.

14. A method as claimed in claim 13 wherein the cation-responsive membrane of the cation-sensitive electrode is formed from a polymeric material which has an ionophore, ligand or complexing agent incorporated into the membrane structure to impart selective permeability.

15. A method as claimed in claim 14 wherein the cation-responsive membrane comprises a lithium selective polyvinylchloride membrane and the internal reference solution comprises a saturated solution of a sodium or potassium salt.

16. A method as claimed in claim 14 or claim 15 wherein the lithium selective polyvinylchloride membrane contains as the lithium ionophore N,N-dicyclohexyl-N,N-diisobutyl-cis-cyclo-hexane-1,2-dicarboxamide or 6,6-dibenzyl-14-crown-4.

17. A method as claimed in claim 13 wherein the hygroscopic material is formed as a layer on the internal reference electrode in admixture with the salt of the cation for which the cation-responsive membrane is not primarily selective.

18. A method as claimed in claim 13 wherein the hygroscopic material is sorbitol.

19. A method as claimed in claim 12 or claim 13 wherein the injection comprises a lithium solution.

20. A method as claimed in claim 19 wherein the lithium solution comprises lithium chloride or lithium carbonate.