JP3090505B2 - Sample diluent for ion measurement and ion measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sample diluent for ion measurement and an ion measurement method, and more particularly to a method suitable for use in measuring ion concentration in a biological sample such as blood or urine with an ion selective electrode. The present invention relates to a diluent and an ion measurement method using the diluent.

2. Description of the Related Art When analyzing biological fluids such as blood and urine in a hospital laboratory or the like, sodium ions, potassium ions,
The number of chloride ion tests is extremely large. Flame photometry and coulometric titration have long been used for these measurements,
In recent years, the ion selective electrode method has also been used frequently. When using an ion selective electrode, the sample is appropriately diluted with a diluent in advance for the purpose of reducing the amount of sample used such as blood or adjusting the concentration of the component to be measured in a region where the electrode performance can be sufficiently exhibited. The measurement is often performed after diluting to a magnification. The dilution ratio varies depending on the type of the automatic analyzer used, etc., but is generally several tens of times without 10 times. When measuring the ion concentration in a biological sample using an ion selective electrode, a mixed solution of tris (hydroxymethyl) aminomethane and boric acid is used as a liquid for diluting the sample, as disclosed in Japanese Patent Application Laid-Open No. 60-228951 and JP-A-60-228951. Kaisho 61
-290353.

If an appropriate sample diluent is not used at the time of ion measurement, the pH of the diluted test sample varies from sample to sample. In particular, when urine is used as a sample, the pH of urine itself varies greatly between samples, so that the pH of the diluted measurement sample also varies greatly, resulting in a large error in ion concentration measurement results. In order to measure the ion concentration of a biological fluid sample using a polymer supporting membrane type ion selective electrode, even if the diluent shown in the above-mentioned prior art is used, the measurement error of the ion concentration does not become sufficiently small. . An object of the present invention is to provide a sample diluent that can maintain the pH of a biological fluid sample after dilution substantially constant for any sample and that does not adversely affect the ion-selective electrode. Another object of the present invention is to provide a method for measuring an ion concentration in a biological fluid using a sample diluent having a novel composition.

The sample diluent for ion measurement of the present invention is bis (2-hydroxyethyl) -iminotris (hydroxymethyl) methane (abbreviated as bis-tris).
And an aqueous solution containing boric acid. This diluent is used after being adjusted to a substantially neutral constant pH. Bis in diluent
The concentration of Tris is preferably between 5 mmol / l and 150 m
mol / l.

According to the diluent of the present invention, the p of the diluent used for measuring the ion concentration in the biological fluid sample with the ion selective electrode is measured.
H buffer capacity is increased. In this case, any diluent having a high pH buffering capacity may be used, and there are many restrictions on the diluent for the ion electrode. First, in a diluent containing the ion species to be measured, the ions themselves interfere with the measurement, so that such a diluent cannot be basically used. Also,
An aqueous solution having a high pH buffering capacity, which is generally called a buffer, is known, and most of these are sodium ions, potassium ions, chlorine ions such as phosphate buffer, borate buffer, and Tris-HCl buffer. Since one or more ions to be measured, such as ions, are contained, the ion cannot be used when these ions are to be measured. Also, many buffers that do not contain the ion species to be measured adversely affect any of the ion electrodes in terms of electrode characteristics such as slope sensitivity and lifetime. Such buffers are also unsuitable for use. Further, the storage stability and cost of the diluent itself are also important constraints. The present inventors have considered the diluent having a sufficient pH buffering capacity even when a sample having a remarkable fluctuation in pH such as urine is used as a measurement sample while considering the above restrictions,
The present invention has been completed. Bis-Tris is generally Bi
s (2-hydroxyethyl) -iminotris (hydroxymethyl) metha
This combination of bis-Tris and boric acid has a high pH buffer capacity near neutrality. The diluent of the present invention does not adversely affect the characteristics of any of the ion-selective electrodes for measuring sodium ions, measuring potassium ions, and measuring chlorine ions provided with a membrane containing an ion-sensitive substance. And even if there is a fairly large pH difference between the blood and urine samples, the pH of the diluted sample can be kept within an acceptable small width. The biological fluid sample is usually diluted 10 to 50 times with the diluent of the present invention, and then contacted with an ion selection electrode to measure the ion concentration in the sample. The pH of the diluent itself is usually 6.80 to 8.
It is adjusted in advance to a predetermined value within a range of 40, preferably 7.30 to 8.40. The pH of the biological fluid sample after being diluted with the diluent is 6.70 to 8.45. In the case of the same sample type (for example, blood or urine) at the same dilution ratio, the fluctuation range of the pH is 10 The standard deviation of the number of samples from 20 to 20 can be within 0.25.

EXAMPLE When a diluent consisting of bis-Tris and boric acid adjusted to pH 6.95 was used, when the concentration of bis-Tris and the dilution ratio were changed, the diluted sample solution after diluting urine was used. Table 1 shows the average value of pH and its fluctuation range (standard deviation, in parentheses in Table 1). The urine used as the sample was 20 samples, and the pH was 4.95 to 9.
01, with an average of 6.70 and a standard deviation of 1.
62. The dilution factor is the lower limit factor in a practical range of about 10 times. From this 10-fold dilution, it can be seen from Table 1 that if the bis-Tris concentration was 5 mmol / l, the pH fluctuation range of the diluted sample could be suppressed within the target deviation of 0.25.

[Table 1] On the other hand, from the viewpoint of the electrode life when urine or serum is sampled, it is desirable that the pH of the diluent composed of bis-tris and boric acid be 7.30 or more. The concentration of Bis-Tris for buffering also increases. However, if the bis-Tris concentration is 150
When the amount exceeds mmol / l, there is no significant change in the pH buffering capacity of urine or serum.
It is not advisable to make the concentration higher than 1 / l. The ion selective electrode used in the experiments described below is a polymer supporting membrane type ion selective electrode having a polymer membrane mixed with an ion-sensitive substance. The sensitive substance is crown ether for sodium ion measurement, valinomycin for potassium ion measurement, and quaternary ammonium salt for chloride ion measurement. These three types of ion selective electrodes are arranged in series with a reference electrode in a flow cell, and a sample diluted with a diluent flows into the flow cell. When a columnar ion selective electrode is used, three kinds of ion selective electrodes and a reference electrode may be inserted in the measuring tank, and the sample and the diluent may be supplied to the measuring tank. Other types of ion selective electrodes, for example, semiconductor electrochemical sensors, can be used. Hereinafter, embodiments of the present invention will be described. Example 1 A powdery boric acid was added little by little to a 10 mmol / l bis-tris aqueous solution while stirring well to prepare a solution whose pH was adjusted to 6.91. Using this as a diluent, human serum and urine were diluted 17-fold to obtain a diluted sample. Its pH
Table 2 shows the results of the measurement. Each sample number is 10 samples. PH of 17-fold diluted sample with sample diluent for ion-selective electrode commercially available for reference
Measurements were also made (shown in Table 2 for reference).

[Table 2] When the diluent of the present invention was used, the fluctuation range of the pH of the diluent sample solution could be reduced as compared with the case where the conventional diluent was used. Even when urine is used as the sample, the standard deviation is 0.20,
The diluent of the present invention showed remarkable pH buffering ability. Using a commercially available sodium ion selective electrode, potassium ion selective electrode, and chloride ion selective electrode, the effect of the diluent of Example 1 on the performance of the electrode was examined. Specifically, the time-dependent changes in the slope sensitivity when each electrode channel was immersed in a human pool serum and pool urine 17-fold diluted with this diluent were examined. As a result, in either case, 1
The electrode had a slope that could withstand practical use even after a long immersion time of 20 hours, and it was found that this diluent did not adversely affect the electrode performance. Thus, the use of the diluent according to the present invention makes it possible to reduce the pH fluctuation range of the diluted sample liquid without adversely affecting the electrode performance. Example 2 Powdered boric acid was added little by little to a 20 mmol / l bis-tris aqueous solution while stirring well to prepare a solution whose pH was adjusted to 6.91. This solution was loaded into a Hitachi 7150 type automatic analyzer as a diluent for electrolyte, and the urine of 36 actual samples was subjected to concentration analysis of sodium ion, potassium ion, and chloride ion. In this automatic analyzer, the sample was diluted 31-fold with a diluent, and these three types of ions were analyzed by an ion electrode method. For comparison, the same 36 actual samples were measured by the standard method. In the standard method, sodium ion and potassium ion are flame photometry, and chloride ion is coulometric titration. Table 3 shows the correlation coefficient and error variance with the reference method for each ion species. The error variance is expressed by the following equation, and the smaller the value, the more accurate the value by the ion electrode.

(Equation 1) Here, x: measured value by reference method y: measured value by ion electrode method x ': average value of measurement by reference method y': average value of measurement by ion electrode method b: slope of regression line n: number of samples is there. For comparison, a commercially available diluent was used with Hitachi 715.
Table 3 shows the results of the analysis performed on the same 36 actual samples loaded in a type 0 automatic analyzer, as reference values.

[Table 3] In any of the ion electrodes, it was found that the use of the diluent of the present invention had better correlation coefficients and error variances than the use of a commercially available diluent, and the measured values were more accurate. Example 3 Diluent consisting of 50 mmol / l bis-Tris, 20 mmol / l boric acid, 0.1% formalin (pH 7.58)
) Was loaded into a Hitachi 7150 automatic analyzer, and serum was measured. Good measurement results were obtained as in Examples 1 and 2. It was also clarified that this diluent had another effect, that is, the effect that the degree of decrease in the slope sensitivity of the electrode after measuring a large number of samples was smaller than when using a commercially available diluent. . Specifically, the decrease in slope sensitivity after measuring 10,000 specimens with a potassium ion electrode was 10 to 15% of the initial slope sensitivity when a commercially available diluent was used, whereas the decrease in slope sensitivity When was used, it was within 3% of the initial slope sensitivity. pH
The effect of extending the life of the electrode was further studied by using various diluents composed of bis-tris and boric acid, which differed from each other. FIG. 1 shows the results in the case of the chloride ion selective electrode. The vertical axis represents the relative slope sensitivity, where the slope sensitivity of the chloride ion electrode after measurement of 10,000 samples of serum is represented by setting an initial value to 1. The larger the value, the higher the effect of extending the life of the electrode. Bis-Tris has a relative slope sensitivity of 90% or more of the initial value when a diluent having a pH of 6.80 or more is used and 95% or more of an initial value when a diluent having a pH of 7.30 or more is used. The effect of prolonging the electrode life when using a diluent consisting of
It became clear that the effect was remarkable when a diluent of 90 or more, particularly a diluent of pH 7.30 or more was used. Note that p
A diluent comprising bis-tris and boric acid having an H of more than 8.40 has a high boric acid concentration, and this borate ion acts as an interfering ion particularly to the chloride ion electrode. It was also found to be impractical because it would worsen the accuracy of. In addition, the pH is 8.40.
The diluent composed of bis-tris and boric acid exceeds the amount of bis-tris used in comparison with its pH buffering capacity, which is not desirable in terms of economy. As described above, the present invention has an effect of preventing a decrease in the slope sensitivity of the ion electrode. In particular, this effect is remarkable in a diluent having a pH of 7.30 or more. Example 4 A diluent of the present invention consisting of 50 mmol / l bis-tris, 20 mmol / l boric acid, 0.1% formalin (pH
7.58) was loaded into a Hitachi 7150 automatic analyzer, and the same serum was subjected to 20 repeated measurements.
The reproducibility of the chloride ion concentration measurement result is 0.16% in CV value.
Met. For comparison, a diluent (pH 7.58) containing 50 mmol / l tris (hydroxymethyl) aminomethane, boric acid and 0.1% formalin was prepared, and the measurement was repeated (20 times) with the same serum as above. By the way, CV
The value was 0.45%. As described above, the diluent of the present invention has an effect of improving the reliability of the measurement result, as compared with the diluent comprising tris (hydroxymethyl) aminomethane and boric acid.

As described above, the use of the diluent according to the present invention makes it possible to maintain the pH of the sample solution within a certain range regardless of whether the biological fluid sample is serum or urine. In addition, the accuracy of the measurement result at the ion selective electrode can be improved. Also, this diluent does not adversely affect the characteristics of the ion selective electrode.

[Brief description of the drawings]

FIG. 1 shows the pH of a diluent containing bis-tris and boric acid,
It is a figure which shows the relationship of the relative slope sensitivity of a chloride ion selection electrode.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Daizo Tokinaga 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo Examiner, Central Research Laboratory, Hitachi, Ltd. Jun Koriyama (56) References JP-A 64-9353 (JP, A) JP-A-60-220854 (JP, A) JP-A-60-203849 (JP, A) JP-A-1-118762 (JP, A) JP-A-56-76041 (JP, A) JP-A-173450 (JP, A) JP-A-61-100652 (JP, A) JP-A-54-26791 (JP, A) JP-A-4-215057 (JP, A) (58) Fields investigated (Int. . ^7, DB name) G01N 27/28 G01N 1/36 G01N 27/416 JICST file (JOIS)

Claims (10)

(57) [Claims] 1. A sample diluent for ion measurement comprising an aqueous solution containing bis (2-hydroxyethyl) -iminotris (hydroxymethyl) methane and boric acid. 2. The diluent according to claim 1, wherein the concentration of bis (2-hydroxyethyl) -iminotris (hydroxymethyl) methane in the aqueous solution is 5 mmol / l.
A sample diluent for ion measurement, which is in the range of 1 to 150 mmol / l. 3. The diluent according to claim 1, wherein the pH of the aqueous solution is adjusted within a range of 6.80 to 8.40. 4. The diluent according to claim 3, wherein the pH is adjusted in the range of 7.30 to 8.40. 5. The diluent according to claim 1, wherein the aqueous solution contains formalin as a preservative. 6. The diluent according to claim 1, wherein the diluent is used for measuring the concentration of at least one ion selected from the group consisting of sodium ions, potassium ions, and chloride ions. A sample diluent for ion measurement, characterized in that: 7. A first step of diluting a biological fluid sample with a diluent comprising an aqueous solution containing bis (2-hydroxyethyl) -iminotris (hydroxymethyl) methane and boric acid to obtain a diluted biological fluid sample; An ion measurement method including a second step of measuring ions in the diluted biological fluid sample using an ion selection electrode. 8. The ion measuring method according to claim 7, wherein, in the second step, a polymer support membrane type ion selective membrane having a polymer membrane mixed with an ion-sensitive substance is used as the ion selective electrode. An ion measurement method using an electrode. 9. The ion measuring method according to claim 7, wherein in the second step, a sodium ion selective electrode,
An ion measuring method comprising measuring the diluted biological sample with a potassium ion selective electrode and a chloride ion selective electrode. 10. The ion measuring method according to claim 7, wherein in the first step, the pH of the diluted biological fluid sample is adjusted.
Is adjusted within the range of 6.70 to 8.45.