Use of CO.sub.2 absorbant for stabilization of dried alkaline reagent in creatinine assay

• US 5,610,073 A
• Filed: 09/26/1995
• Issued: 03/11/1997
• Est. Priority Date: 09/26/1995
• Status: Expired due to Term

• Current Assignee: Siemens Healthcare Diagnostics Incorporated (Siemens AG)
• Original Assignee: Bayer Corporation (Bayer AG)
• Inventors: Cooper, Howard A., Chu, Wei-Sen, Chu, Amy H.
• Primary Examiner(s): Warden, Jill
• Assistant Examiner(s): WALLENHORST, MAUREEN
• Application Number:
  US08/534,267
• Time in Patent Office: 532 Days
• Field of Search: 436/98, 436/164, 436/165, 436/167, 436/169, 436/170, 436/175, 436/176, 436/177, 436/178, 422/55, 422/56, 422/57, 422/58, 422/69, 422/83, 422/88
• US Class Current: 436/98
• CPC Class Codes: G01N 33/70 involving creatine or creatinine
• CPC Class Codes: Y10T 436/147777 Plural nitrogen in the same ring [e.g., barbituates, creatinine, etc.]
• CPC Class Codes: Y10T 436/25125 Digestion or removing interfering materials
• CPC Class Codes: Y10T 436/2525 Stabilizing or preserving
• CPC Class Codes: Y10T 436/255 including use of a solid sorbent, semipermeable membrane, or liquid extraction

Abstract

Disclosed is an improvement to the method for the detection of creatinine in which creatinine, in aqueous solution, is contacted with a dry reagent system of an indicator for creatinine. The assay is carried out at a pH above about 11.5 which is maintained by an alkaline material. The improvement involves packaging the reagent system with a material capable of absorbing CO₂ and at least some ambient water vapor. This inhibits the formation of carbonic acid thereby reducing the neutralization of the alkaline reagent system during storage to increase the shelf life and decrease the variability of the system.

Claims

1. In a method for the detection of creatinine in which creatinine in aqueous solution is contacted with a dry reagent system comprising an indicator for creatinine at a pH above about 11.5 which pH is maintained by an alkaline material, the improvement which comprises packaging the reagent system with a material capable of absorbing CO₂ and at least some ambient water vapor in sufficient amount to substantially inhibit the formation of carbonic acid in the area of the reagent system to thereby reduce the neutralization of the alkaline material during storage.

2. The method of claim 1 wherein the alkaline material is capable of maintaining the pH of the reagent system at a level of from about 12 to 14.

3. The method of claim 1 wherein the dry reagent system for detecting creatinine is carried by an absorbant carrier in the form of a test strip.

4. The method of claim 1 wherein the dry reagent system is contained in a reaction vessel which contains a first reaction zone in which is carried out an immunoassay for a protein in a urine test sample and a second reaction zone which contains the dry reagent system.

5. The method of claim 1 wherein the CO₂ absorbing material is selected from the group consisting of soda lime, sodium hydroxide coated silicate, lithium hydroxide, barium hydroxide, calcium hydroxide and potassium hydroxide.

6. The method of claim 5 wherein the CO₂ absorbing material is soda lime.

7. The method of claim 1 wherein the CO₂ absorbing material is present in an amount of from about 25 to about 200% (w/w) of the alkaline material.

8. The method of claim 1 wherein the indicator for creatine is 3,5-dinitrobenzoic acid and the alkaline material is sodium hydroxide.

9. A device for the detection of creatinine in an aqueous solution which device comprises a reagent system comprising an indicator for creatinine which indicator operates at a pH of above about 11.5 and an alkaline material, wherein the device is packaged with a material capable of absorbing CO₂ and water vapor and wherein the material capable of absorbing CO₂ is present in an amount sufficient to substantially inhibit the formation of carbonic acid in the area of the reagent system.

10. The device of claim 9 which is in the form of an absorbant carrier in which the reagent system for the detection of creatinine is contained.

11. The device of claim 9 which is in the form of a reaction vessel which contains a first reaction zone for carrying out an immunoassay and a second reagent zone containing the reagent system.

12. The device of claim 9 wherein the CO₂ absorbing material is soda lime.