JP2816125B2 - How to measure chloride ion concentration - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a method for measuring chloride ion concentration, and more particularly to a method for use in biochemical analysis such as serum analysis. 2. Description of the Related Art An ion-selective electrode has the feature of selectively quantifying the concentration of a specific ion in a liquid, and has been used in a wide range of fields such as monitoring of a specific ion and water quality analysis. This is because the potential E of the ion-selective electrode and the logarithm of the concentration of the target specific ion have a linear relationship, and the target ion concentration can be easily calculated from the measured potential. Recently, as such an ion-selective electrode is medical, Na ⁺ in particular present in the blood, K ^+, Cl ^-, have come to be used for quantification of various ions and the like. Also, various types of analyzers using ion-selective electrodes have been manufactured. Incidentally, as the chloride-selective electrode among the ion-selective electrodes, conventionally, (1) an ion-selective membrane of a type in which a chloride-selective substance composed of a quaternary ammonium salt is dispersed in polyvinyl chloride. And (2) an electrode having a solid ion selective membrane formed by mixing and compressing Ag ₂ S and AgCl and the like have been developed and widely used for biochemical analyzers. [0005] However, the former electrode has a drawback that proteins and other organic substances are liable to adhere thereto and are easily hindered by other anions and proteins. In particular, protein adhesion is important, and when serum protein is adhered to the surface of an electrode during serum analysis, the sensitivity of the electrode is reduced and the response time is significantly delayed, resulting in a shortened electrode life. In the latter electrode, Ag ₂ S and AgCl
It is necessary to appropriately determine the mixing ratio of the electrode and to perform compression molding with strong stress, and this is accompanied by manufacturing restrictions, so that it has been difficult to reduce the size of the electrode or to mold it into an arbitrary shape. Further, in order to simultaneously analyze several types of electrolytes in blood, a flow-through type flow-through type in which a chloride ion selective electrode, another ion selective electrode, a reference electrode and an ion concentration measuring cell are integrated. Although it is desirable to constitute an ion sensor, it is extremely difficult to incorporate it into a flow-type ion sensor, especially in the case of the latter electrode, since it is difficult to form it into an arbitrary shape. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks, and uses an electrode that can be easily manufactured. It is an object of the present invention to provide a method for measuring a chlorine ion concentration without causing deterioration. The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, it has been a problem to use a silver / silver chloride electrode as a chloride ion-selective electrode. We found that it was effective to overcome the point. If this silver / silver chloride electrode is used, the chloride ion, which is an anion, selectively acts on the electrode surface and the electrode potential changes according to the chloride ion concentration. The ion concentration can be determined. The solubility product of silver iodide and silver bromide is smaller than the solubility product of silver chloride, and iodine ion and bromide ion tend to act more strongly on the electrode than chloride ion. Is usually about 1/10 of chloride ion
Since the concentration is less than 00, these ions do not interfere with the measurement of chloride ions. [0010] The silver / silver chloride electrode is formed by a silver plate, a silver wire, or the like.
l ^- can be produced in the electrode by electrolytic oxidation in a solution containing create a very is easy, and of various shapes if decide silver shape before the electrolysis. This silver /
The silver chloride electrode has high sensitivity to Cl ^- ions, shows a Nernst response, and has a very short response time. In addition, since it is not necessary to use an ion selective membrane in which a quaternary ammonium salt or the like is dispersed in a polymer, it is possible to prevent the electrode from deteriorating due to adhesion of proteins and the like. On the other hand, when the silver / silver chloride electrode is directly immersed in the solution for analysis, AgCl may elute and the electrode may be deteriorated. For example, AgCl may be damaged in any of the solution to be measured, the cleaning solution, the calibration solution, the storage solution, and the like. The concentration of AgCl is a saturation concentration or a concentration close to the saturation concentration. In a general measurement, for example, when a silver / chloride electrode is directly immersed in river water to measure a chloride ion concentration, AgCl is eluted from the electrode to deteriorate the electrode, so that it is difficult to use the electrode for a long time. However, even in this case, if AgCl is dissolved in the liquid to be measured, the life of the electrode can be extended. On the other hand, in the case of a biochemical analysis in which the method of the present invention is used, the measurement is performed in a so-called closed system as compared with a general measurement, and the amount of the liquid usually used is small. Therefore, it is extremely easy to dissolve AgCl in the liquid to be measured and the like. The solubility of AgCl is extremely small, and the influence of a relatively high concentration of chloride ion (10 ^-1 mol / l) in serum or the like on the measurement accuracy is extremely small. As described above, according to the method for measuring the chloride ion concentration of the present invention, the chloride ion selective electrode and the reference electrode are immersed in the liquid to be measured, and the chloride ion concentration in the liquid to be measured is measured by the potential difference between the two electrodes. In this case, a silver / silver chloride electrode is used as the chloride ion-selective electrode, and the solution in contact with the electrode has a saturated concentration of silver chloride. In the present invention, as a method for dissolving the solution in contact with the electrode, that is, the solution to be measured, the washing solution, the calibration solution or the preservation solution, for example, the following methods can be considered. That is, (1) a method in which solid or powdered AgCl is added to each of the above liquids in advance, and (2) AgC in a flow path through which each of the above liquids reaches the ion sensor.
(3) For example, when a body fluid to be measured such as serum is diluted with a diluting solution to prepare a solution to be measured, or a stock solution of a washing solution or a calibration solution is prepared in advance, and these stock solutions are prepared. In the case of preparing a washing solution, a diluting solution or the like by diluting with a diluting solution, the following method is considered. (A) Compared with the solubility of AgCl in the solution to be measured, the washing solution, the calibration solution, etc., which actually come into contact with the electrodes, the AgCl in the diluting solution for diluting the undiluted solution of serum, washing solution, or calibration solution
If the solubility is higher, AgCl may be dissolved in the diluent in advance. Such AgCl
Is effective when the dissolved AgCl precipitates due to a decrease in temperature when the liquid to be measured or the like is stored inside or outside the apparatus, or when the solubility of AgCl increases due to an increase in temperature. . The above problem can be easily solved if the diluent is properly selected. An example of such a diluting solution is a tris-borate buffer solution (aqueous solution of trishydroxymethylaminomethane and boric acid). That is, the solubility of AgCl in the tris-borate buffer solution at around 0 ° C. is sufficiently larger than the solubility in the serum diluted 10-fold with the tris-borate buffer solution at the measurement temperature (usually 30 to 40 ° C.) If the above-mentioned problems are likely to occur, an appropriate diluent is used. (B) A required amount of Ag ⁺ is supplied to the diluent in the form of an easily soluble salt such as AgNO ₃ ,
A method of generating AgCl at the stage of adjusting a cleaning solution, a calibration solution, and the like. Usually, the solubility of AgNO _{3 in} aqueous solution is Ag
Because it is much larger than the solubility of Cl, this method can be applied to a wide range of diluents. Also Cl
^- , For example, 10 ^-1 mol
/ L of Cl ⁻ is included, AgCl can be generated in the liquid to be measured without adding extra Cl ⁻ . At this time, the solubility of AgCl is sufficiently small so that no measurement error occurs. Similarly, if the Cl ⁻ concentration in the stock solution of the washing solution and the calibration solution is made equal to the Cl ⁻ concentration in the serum in advance, the washing solution and the calibration solution can be diluted with the diluting solution supplied with Ag ⁺ to make the washing solution and the calibration solution contain AgCl. Can be generated. In the present invention, the ion concentration measuring cell is a chloride ion selective electrode, together with a silver / silver chloride electrode, other ion selective electrodes such as a Na ⁺ ion selective electrode, a K ⁺ ion selective electrode, and a reference. A flow-through type ion sensor incorporating electrodes can be used.
Since the silver / silver chloride electrode is easier to mold than a conventional chloride ion-selective electrode, even a flow-type ion sensor having a complicated shape as described above can be easily manufactured. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Hereinafter, an embodiment in which the method of the present invention is applied to the measurement of chloride ion concentration in serum will be described with reference to FIGS. FIG. 1 is a block diagram of an ion concentration analyzer used in the method of the present invention. First, a predetermined amount of 40 μl of serum is sent to the sample tube 3 by the serum suction pump 2.
Next, the diluent 4 is diluted to a predetermined amount by the diluent suction pump 5.
60 μl is sent to the sample tube 3. In addition, this diluting liquid 4 was prepared by adding AgCl to ion-exchanged water at a saturation concentration of 2.5 ×
It was dissolved at a concentration of 10 ^-5 mol / l. In the sample tube 3, the serum 1 and the diluting liquid 4 are stirred, and the liquid 6 to be measured in which the components in the serum are diluted to 1/10 is adjusted. The liquid to be measured 6 is subjected to Cl
^- silver / silver chloride electrode as an ion selective electrode, is sent to the Na ⁺ ion-selective electrode, flow type ion sensor 8 that integrates and the measuring cell K ⁺ ion-selective electrode and reference electrode, the ion-selective The potential difference between the electrode and the reference electrode is amplified by the amplifier 9, and the electric signal is sent to the calculation and display mechanism 10 to perform a predetermined ion concentration measurement. After the measurement, the liquid to be measured is sent to the waste liquid tank 11. After the measurement of the ion concentration in the serum has been completed as described above, only the diluent 4 is injected into the sample tube 3 for washing to measure the next serum. Further, a calibration solution having a known concentration and a high concentration is supplied from a container (not shown) to the flow-type ion sensor 8 to calibrate the electrode sensitivity. Further, the potential measurement value is calibrated using a calibration solution having an ion concentration close to the measured concentration. AgCl is also dissolved in this calibration solution. The flow ion sensor 8 has a structure as shown in FIG. 2A or 2B, for example. In the flow-type ion sensor of FIG. 2A, a Na ⁺ ion selective electrode 23, a K ⁺ ion selective electrode 24, a Cl ^{+ -} supporting in a state of being inserted a side liquid junction of one end of the ion sensitive portion and a reference electrode of silver / silver chloride electrode 25 and reference electrode 26 is an ion-selective electrode is formed in said flow passage 22 Then, lead wires 23a to 26a are connected to the other ends of the electrodes. In the flow ion sensor 8 shown in FIG. 2B, flow holes 32 for liquid to be measured or the like are provided at both end surfaces of a cylindrical cell body 31, and a central portion is formed inside the cell body 31. A Na ⁺ ion selective electrode 34, a K ⁺ ion selective electrode 35, and a silver / silver chloride electrode 36, which is a Cl ⁻ ion selective electrode, on a ring through a spacer 33 provided with a flow hole for the flow hole 32. And a reference electrode 37, and lead wires 34 a to 37 a are connected to a part of each of the electrodes and are drawn out of the cell body 31. Each of the ion-selective electrodes has an ion sensitive portion on the side of the flow hole, and the reference electrode 37 has a liquid junction on the side of the flow hole. According to the method described above, a silver / silver chloride electrode which is easy to produce is used, and unlike a conventional chloride ion selective electrode, for example, a quaternary ammonium salt is contained in a polymer substance. Since it is not necessary to use an ion selective membrane, it is possible to prevent deterioration of the electrode due to adhesion of proteins and the like. Further, since the elution of AgCl from the electrode does not occur, deterioration of the electrode can be prevented. AgC
Since the solubility of 1 is small, the cost is small even if a saturated solution of AgCl is prepared. FIG. 3 shows the results of the life test of the silver / silver chloride electrode by the above method (Example 1) and the method using ion-exchanged water to which AgCl was not added as a diluent (Comparative Example 1). As described above, the repetition of serum analysis and washing was one cycle, that is, one sample was measured.
The sensitivity on the vertical axis in FIG. 3 is 10 ⁻³ mol / l and 10 ⁻² m
It shows the potential difference of an ol / l NaCl aqueous solution, that is, the absolute value of the slope of the Nernst response. As is clear from FIG. 3, in Example 1, no decrease in sensitivity was observed even when more than 20,000 serum samples were analyzed.
It shows good performance. On the other hand, in Comparative Example 1, the sensitivity is gradually lowered, and the sensitivity is lowered to such an extent that it cannot be used for the 15,000th sample. This is because AgCl is not eluted from the electrode in the method of Example 1, whereas AgCl is gradually eluted from the electrode into the liquid to be measured and the ion-sensing part does not function in the method of Comparative Example 1. is there. If AgCl is dissolved in the liquid to be measured or the like, the effect of improving the stability of not only the silver / silver chloride electrode but also other ion-selective electrodes can be expected. Embodiment 2 Another method for dissolving AgCl in the liquid to be measured and the like will be described. The configuration of the ion concentration analyzer in this case is the same as that shown in FIG. Serum was prepared in substantially the same manner as in Example 1 except that AgNO ₃ was dissolved in a so-called trisborate buffer solution consisting of an aqueous solution of H ₃ BO ₃ and trishydroxymethylaminomethane as the diluent 4. Was measured. The amount of serum used was 50 μl, the amount of diluent used was 450 μl, and the flow-type ion sensor shown in FIG. 2B was used. AgNO ₃ contained in the buffer solution constituting the above-mentioned diluent is present as Ag ⁺ , and reacts with Cl ⁻ (about 1 × 10 ^-2 mol / l) in the serum when the serum is diluted. Almost saturated concentration (6.5 × 10 ⁻⁵ mol /
Since it exists as AgCl in 1), elution of AgCl from the silver / silver chloride electrode can be prevented. In fact, a method using the above-mentioned diluent (Example 2) and a method using a diluent consisting only of a trisborate buffer solution without addition of AgNO ₃ (Comparative Example 2)
Fig. 4 shows a life test of silver / silver chloride electrodes at
As shown in FIG. 3, almost the same results as in FIG. 3 were obtained. The same can be said of the result as described in the first embodiment. [0033] In the case of using a dilution of the composition of Example 2, Cl contained in the serum ^- is other than halogen ions Br ^- and I ^- is ^I -> Br ^-> Cl ^- order in Ag ⁺ And easily precipitate as a result. Therefore, Br
^- and I ^- by can be reduced measurement errors, also it is possible to prevent the sensitivity decrease due to the Cl of the AgCl layer of ion sensitive portion is replaced with another halogen atom. In the above description, the case where AgCl is dissolved in the solution to be measured, the cleaning solution, and the calibration solution has been described. Desirably, it is dissolved. For the purpose of preservation, electrolytes that release Cl ⁻ such as NaCl and KCl can be used because they have the effect of preventing the elution of AgCl as long as the concentration does not become extremely high. For these reasons, a preferred storage solution is a solution containing AgCl at or near saturation and excess Cl ⁺ ions (10 ^-4 to 10 ^-1 mol / l). These additives may be dissolved in pure water,
Of course, it may be dissolved in a buffer solution. As described above in detail, according to the method for measuring chloride ion concentration of the present invention, a silver / silver chloride electrode which is easy to produce is used, and protein is attached and silver chloride is eluted from the electrode. Thus, it is possible to measure the chloride ion concentration stably over a long period of time by preventing deterioration of the electrode due to the above.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram of an ion concentration analyzer used in an embodiment of the present invention. 2A is a front view of a flow-type ion sensor used in the device, and FIG. 2B is a cross-sectional view of another flow-type ion sensor used in the device. FIG. 3 is a diagram showing the results of a life test of silver / silver chloride electrodes according to the methods of Example 1 and Comparative Example 1 of the present invention. FIG. 4 is a diagram showing a life test result of a silver / silver chloride electrode according to the method of Example 2 and Comparative Example 2 of the present invention. [Explanation of Signs] 1 ... Serum, 2 ... Serum suction pump, 3 ... Sample tube, 4 ...
Dilution liquid, 5: dilution liquid suction pump, 6: liquid to be measured, 7: sample suction pump, 8: flow-type ion sensor, 9: amplifier, 10: calculation display mechanism, 11: waste liquid tank, 21,
31 ... cell body, 22 ... flow passage, 22, 34 ... Na
⁺ Ion selective electrode, 24, 35 ... K ⁺ ion selective electrode, 25, 36 ... silver / silver chloride electrode, 26, 37 ... reference electrode, 23a to 26a, 34a to 37a ... lead wire, 32
... flow holes, 33 ... spacers.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Junji Hizuka 1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Toshiba Research Institute Co., Ltd. (56) References JP-A-60-71945 (JP, A) (58) ) Surveyed field (Int.Cl. ⁶ , DB name) G01N 27/416

Claims (1)

(57) [Claims] Use biochemicals for chloride ion selective electrode and reference electrode
In measuring the chloride ion concentration in the test solution based on the potential difference between the two electrodes, a silver / silver chloride electrode is used as the chloride ion-selective electrode, and the solution in contact with the electrode contains chloride. A method for measuring chloride ion concentration, characterized in that silver is dissolved in a saturated concentration.