Method for calibration of a measurement apparatus

• US 5,185,263 A
• Filed: 11/04/1991
• Issued: 02/09/1993
• Est. Priority Date: 10/23/1987
• Status: Expired due to Term

• Current Assignee: Avl Medical Instruments AG (Roche Holding AG)
• Original Assignee: Avl Medical Instruments AG (Roche Holding AG)
• Inventors: Kroneis, Herbert, Noormofidi, Taghi, Marsoner, Hermann
• Primary Examiner(s): Housel, James C.
• Assistant Examiner(s): CHAN, KWONG
• Application Number:
  US07/785,878
• Time in Patent Office: 463 Days
• Field of Search: 436/8-18, 436/50, 73/1 K
• US Class Current: 436/8
• CPC Class Codes: G01N 27/4165 for pH meters
• CPC Class Codes: Y10T 436/10 Composition for standardization, calibration, simulation, stabilization, preparation or preservation; processes of use in preparation for chemical testing
• CPC Class Codes: Y10T 436/107497 Preparation composition [e.g., lysing or precipitation, etc.]
• CPC Class Codes: Y10T 436/115831 Condition or time responsive

Abstract

In order to calibrate a measurement apparatus used for determining at least the pH and pCO₂ values in aqueous media, two aqueous base solutions A and B with good storage stability are mixed at a defined ratio immediately prior to calibration, the desired pH and pCO₂ values being provided for calibration of the measuring electrodes of the measurement apparatus only after chemical reaction of the base solutions A and B has taken place.

Claims

1. A method of calibrating a measurement apparatus that contains measuring electrodes and can be used to determine the pH and pCO₂ values of aqueous sample media, said method comprising the steps of providing two aqueous base solutions A and B which will react with one another when mixed but which will remain stable with respect to CO₂ content when exposed to ambient air, storing said two aqueous base solutions A and B in separate storage containers, mixing said base solutions A and B at a predetermined ratio such that they will react and form a calibration liquid having predetermined pH and pCO₂ values, immediately passing said calibration liquid to said measurement apparatus so as to contact said measuring electrodes, and taking calibration readings from said measuring electrodes, wherein said base solution A contains an acid component of a pH buffer system and said base solution B contains carbonate and bicarbonate, wherein a pCO₂ value resulting from the bicarbonate/carbonate ratio is obtained in said base solution B, which corresponds to a mean pCO₂ value of ambient air.

2. A method according to claim 1, wherein said base solution B additionally contains an alkaline component of said pH buffer system.

3. A method according to claim 1, wherein a pCO₂ value resulting from the bicarbonate/carbonate ratio is obtained in said base solution B, which corresponds to a mean pCO₂ value of ambient air.

4. A method according to claim 1, wherein inactive salts are added to at least one of said base solutions A and B, in order to adapt ionic strength to that of said aqueous sample media.

5. A method according to claim 3, wherein inactive salts are added to at least one of said base solutions A and B, in order to adapt ionic strength to that of said aqueous sample media.

6. A method according to claim 4, wherein at least one salt of a group consisting of NaCl and KCl is used as said pH inactive salt.

7. A method according to claim 1, wherein said pH buffer system is selected from a group of phosphate buffers and water-soluble organic amino buffers.

8. A method according to claim 1, wherein at least a two-point calibration is carried out, for which calibration at least two different mixing ratios of said base solutions A and B are selected.

9. A method according to claim 8, wherein said two selected mixing ratios are reciprocals.

10. A method according to claim 9, wherein said two selected mixing ratios are 1:

2 and 2;

1.

11. A method according to claim 1, wherein a dye is added to one of said base solutions A and B and wherein said mixing ratio of said base solutions is tested by means of optical methods, such as absorption measurements.

12. A method according to claim 1, wherein one of said base solutions A and B is equilibrated with oxygen from ambient air immediately before calibration, and wherein a pO₂ calibration is carried out in addition to said pH and pCO₂ calibrations.

13. A method according to claim 12, wherein equilibration of one of said base solutions A and B with oxygen is performed in a piece of silicone tubing between a storage container of said respective base solution and said corresponding measuring electrodes.

14. A method according to claim 13, wherein for zero point calibration of pO₂, oxygen is removed from one of said base solutions A and B by a cathodic reaction.

15. A method according to claim 13, wherein for zero point calibration of pO₂ a solution C is used which contains an oxygen-reducing agent.

16. A method according to claim 15, wherein said oxygen content of said solution C used for zero point calibration of pO₂ is checked by adding a redox indicator, wherein color of said redox indicator changes upon transition from oxidized to reduced state.

17. A method according to claim 15, wherein said oxygen-reducing agent is Na₂ SO₃ and wherein said oxygen content of said solution C is checked by adding a pH indicator which will undergo a change in color when the pH of said solution C is shifted from 9 to 7.