GB2154737A

GB2154737A - Test piece for measurement of concentration of chlorides

Info

Publication number: GB2154737A
Application number: GB08430153A
Authority: GB
Inventors: Osamu Tochikubo; Yoshihiro Kaneko; Yuzo Kosaka
Original assignee: Eiken Chemical Co Ltd
Current assignee: Eiken Chemical Co Ltd
Priority date: 1984-02-23
Filing date: 1984-11-29
Publication date: 1985-09-11
Also published as: DE3501826C2; DE3501826A1; GB8430153D0; GB2154737B

Abstract

A test piece for measurement of the concentration of chlorides comprises a support carrying a water-soluble silver salt such as silver nitrate, an adsorption indicator such as 2,7-dichlorofluorescein and a buffering agent having pH in the range of 4 to 7. The test piece does not contain any harmful chromate and enables easy and rapid measurement of the concentration of chlorides in for example urine with sufficient accuracy for practical use. A plurality of supports responsive to different concentrations of chloride may be mounted on a single plastic sheet. The test piece may carry standard colour, symbol, figure or letter markings.

Description

SPECIFICATION Test piece for measurement of concentration of chlorides BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a test piece suited for measurement of the concentration of chlorides in liquids.

Description of the Prior Art In recent years, a campaign for restricting the intake of salt has been developed since excess intake of salt is considered a serious factor in the causation of circulatory diseases such as hypertension and disorders of cerebral blood vessels. Accordingly, it has become necessary to monitor the daily intake of salt and it has been attempted to investigate and analyze the ingredients of food. However, the methods used all involve considerable errors and are unsatisfactory. As a more reliable method, the concentration of sodium or chlorides in urine has been measured so that the daily intake of salt may be determined. Detailed descriptions of these methods are found, for example, in the following literature: Takemori, Nippon Koshu Eisei Shi, 27, 588 (1980); Hirata et al, Nippon Iji Shinpo, 2931, 14 (1980).

In measuring the concentration of sodium or chlorides in body fluids, however, expensive machinery such as a flame photometer and an ion meter have heretofore been generally required. In addition, actual analysis has been conducted by technical experts and, simple and accurate measurement has been difficult.

There are also other known methods for measuring the concentration of chlorides in liquids and particularly in body fluids. The details of these methods are described, for example, in the following literature: Rinsho Kagaku Kensa II, edited by Ishii, p. 283 (1975), published by Igaku Shoin, Tokyo; J. Sendroy, Jr., J.B.C., 120, 405 (1937); and A. Saifer, J.B.C., 129, 273 (1939). These methods, however, all require special implements and involve complicated operations for analysis. Further, the Fantus method, a relatively simplified method, which involves titrating a sample with silver nitrate using potassium chromate as an indicator has been proposed (Kanai, Rinsho Kensa Ho Teiyo, Pll-54 (1974), published by Kinbara Shuppan, Tokyo).Furthermore, a test piece has been proposed which is prepared by applying the Fantus method although it is not used for the measurement of the concentration of chlorides in body fluids.

The conventional test piece for the measurement of the concentration of chlorides uses silver chromate which contains harmful hexavalent chromium. Hexavalent chromium is objectionable to pollution control and accordingly, special attention must be paid to its use and disposal.

Further, the test piece utilizes a precipitation reaction between silver chromate and chloride ions and therefore possesses poor stability, so that the upper limit of chloride ions that can be measured is approximately 0.2 wt%. Accordingly, the measurement of the concentration of chloride ions in urine, which is 0.5 to 1.5 wt%, is extremely difficult.

SUMMARY OF THE INVENTION It is. therefore, an object of the present invention to provide a test piece which enables easy, rapid and accurate measurement of the concentration of chlorides in liquids, e.g., in body fluids, particularly in urine, and which is prepared without the use of harmful silver chromate.

More specifically, the present invention provides a test piece for measurement of the concentration of chlorides in liquids, which comprises a support carrying a water-soluble silver salt such as silver nitrate, an absorption indicator such as 2,7-dichlorofluorescein and a buffering agent having a pH value in the range of 4 to 7.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of a first embodiment of a test piece for measuring the concentration of chlorides according to the present invention.

Figure 2 is a perspective view of a second embodiment of a test piece for measuring the concentration of chlorides according to the present invention.

Figures 3 to 5 are perspective views of additional embodiments of a test piece for measuring the concentration of chlorides according to the present invention.

Figure 6 is a rear perspective view of the test piece according to Fig. 5.

Figure 7 is a graph showing the relationship between the measured values of sodium chloride concentration obtained with the test piece of the present invention according to Fig. 2 and the measured values of sodium chloride concentration obtained with an ion meter.

DETAILED DESCRIPTION OF THE INVENTION Representative water-soluble silver salts which can be used in the present invention are, for example, silver lactate, silver malonate, silver nitrate, silver acetate, silver chlorate, silver amidosulfonate, silver metaborate and silver phenolsulfonate. These water-soluble silver salts can be used alone or in combination. Of these water-soluble silver salts, silver nitrate, which has excellent stability and solubility, can be most advantageously used. The concentration of silver nitrate to be employed may appropriately be chosen depending upon the expected concentration of chlorides in a sample liquid. Where, however, an approximate quantitative assay is intended, it is preferred that the test piece be prepared to have a plurality of testing portions containing silver nitrate in stepwise increasing concentrations.

In the preparation of the test piece, the water-soluble silver salt is employed in the form of a mixture solution of the respective compounds to be carried on a support having a water-soluble silver salt concentration of 0.01 to 0.5 Mol/l (gram equivalent/l), preferably 0.03 to 0.3 Mol/l, and most preferably 0.07 to 0.27 Mol/l.

Examples of absorption indicators which can be used in the present invention include conventional indicators such as dichlorofluoresceins, e.g. 2,7-dichlorofluorescein, dibromofluorescein, tetrabromophenol blue, bromocresol green and 2,6-dichlorophenol indophenol. These indicators can be used alone or in combination. In the preparation of the test piece, the absorption indicator is employed in the form of an aqueous or organic solvent mixture solution of the respective compounds to be carried on a support having an absorption indicator concentration of 0.0001 to 0.02 Mol/l, preferably 0.001 to 0.01 Mol/l, and more preferably 0.003 to 0.005 Mol/l. For example, 2,7-dichlorofluorescein may be employed either in the non-dissociated form or in the form of an alkali metal salt.In the preparation of the test piece, 2,7-dichlorofluorescein is used in the form of a mixture solution of the respective compounds to be carried on a support having a 2,7-dichlorofluorescein concentration of 0.01 to 0.5 wt%, preferably 0.05 to 0.3wt%, and more preferably 0.1 to 0.2 wt%.

Any known buffering agent may be used as long as it is capable of maintaining a pH value of from 4 to 7. Where a high buffering capability is required due. to the type of sample liquid, it is preferred that a buffering agent be chosen which does not form a precipitate with silver nitrate.

Examples of buffering agents which can be used in the present invention include lactate, trislactate, and an aminoalkylsulfonate derivative known as Good buffering agent. These buffering agents can be used alone or in combination. Preferred examples of Good buffering agent includes 2-(N-morpholino)ethanesulfonic acid (M ES), bis(2-hydroxyethyl)-iminotris(hydroxymethyl)methane (BIS-TRIS), piperazine-N,N'-bis-(2-ethanesulfonic acid) (PIPES) and 3-(N-morpholino)propane-sulfonic acid (MOPS). In preparation of the test piece, the buffering agent is employed as a mixture solution of the respective compounds to be carried on a support having a buffering agent concentration of 0.05 to 1.0 Mol/l, preferably 0.3 to 0.7 Mol/l, and more preferably 0.4 to 0.5 Mol/l.

The ratio of the water-soluble silver salt to the adsorption indicator, which are both carried on the support, is most desirably chosen so that a color change of the adsorption indicator on the test piece due to the presence of chlorides may be easily observed by the naked eye. The molar ratio of the water-soluble silver salt to the adsorption indicator may be in the range of 2,000 to 10, preferably 200 to 20, and more preferably 100 to 40.

In the present invention, the chemical composition for the test is carried on an absorbent support such as paper, cotton, wood, or non-woven cloth. Of these supports, filter paper is particularly advantageous.

The above-mentioned absorbent support carrying the chemical composition thereon may itself be used as the test piece. Alternatively, the support may be cut into an appropriately sized and shaped pieces and attached to another appropriate support such as a plastic sheet to prepare a different type of test piece. The above-mentioned plastic sheet may be made of, for example, polystyrene, polyvinyl chloride and polyester.

Furthermore, if desired, the chemical composition for the test may be mixed with a suitabie adhesive such as starch or polyvinyl alcohol and coated on a support such as the abovementioned plastic sheet, followed by drying and fixing, to prepare a test piece.

The test piece of the present invention is prepared, for example, by the following method: The water-soluble silver salt, the absorption indicator and the buffering agent are dissolved in water or in an organic solvent soluble in water. Filter paper is immersed in the resulting solution and then the filter paper is withdrawn and dried. Alternatively, the filter paper is first immersed in a mixture solution of the water-soluble silver salt and the buffering agent and is then withdrawn from the mixture solution and dried. Then the filter paper is immersed in a solution of the absorption indicator and an organic solvent and is then removed from the solution and dried.

The filter paper resulting from either method is then attached to the aforementioned plastic sheet and cut into an appropriate size and shape to provide a test piece.

In measuring the concentration of chlorides in liquids with the test piece, the test piece is contacted with a sample liquid for a certain period of time. Thereafter, the color produced on the test piece is compared with a standard color table prepared in advance. Alternatively, a color, symbol, figure, or letter marking on the support is read to determine the concentration of chlorides in a liquid. Where a sample liquid contains large quantities of protein such as in blood or serum samples, it is preferred that the sample liquid first be treated with a known deproteinizing reagent solution such as a zinc sulfate solution and then that the resulting supernatant liquid be tested.

Representative methods for providing a color, symbol, figure or letter marking on the support include direct printing on the surface or the reagent portions of the support, attachment of printed matter on the support and press marking. However, any method is suitable as long as it achieves the objective of the present invention.

A single color or a plurality of colors may be provided on the support as the standard color; and the symbols, figures, or letters may be of any kind. Further, the location of the markings may be adjacent to or apart from the testing portions of the test piece. Their locations are most suitably selected from the objective of legibility.

It is apparent that by using the test piece of the present invention, the concentration of chlorides in liquids other than body fluids, e.g., seawater, industrial waste water, lubricating oil, and extracted liquors from concrete materials can also be analyzed. It is also apparent that for one skilled in the art, it is easy to make various modifications of the test piece of the present invention.

The present invention will now be described in more detail with reference to working examples. It should be noted, however, that these working examples are merely illustrative of the present invention and are not intended to be limiting in any way.

Example 1 Filter paper (Toyo Filter Paper No. 525) was immersed in the following first and second solutions successively, followed by drying.

First Solution: 2-(N-Morpholino)ethanesulfonic acid - 1 2.8 9 Sodium hydroxide - 2.0 g Silver nitrate - 4.4 g Purified water - 30.0 ml Second Solution: 2,7-Dichlorofluorescein - 0.1 g Acetone - 100.0 ml The obtained re-colored test paper sheet was cut into 10 mm X 10 mm pieces and attached to a 10 mm X 80 mm polystyrene sheet to prepare a test piece of the present invention. Fig. 1 is a perspective view of the test piece, wherein 1 is the test paper sheet and 2 is the polystyrene sheet.

The resulting test pieces were immersed in aqueous solutions of sodium chloride having the concentrations noted in Table 1. After about 10 seconds, the color development on the surface of the test paper sheets was observed. The results are shown in Table 1.

Table 1: Concentrations of Sodium Chloride and Color Development Concentration of Sodium Chloride (g/l) Color Development 5 100% red.

7.5 80% red and 20% yellow.

10 50% red and 50% yellow.

12.5 20% red and 80% yellow.

15 100% yellow.

Expressed in terms of the ratios of the red-colored area and yellow colored area to the entire area of the test paper sheet.

As is apparent from Table 1, the ratio of the yellow colored area on the test paper sheet increases as the concentraof sodium chloride increases.

Example 2 Six (6) test paper sheets were prepared in the same manner as mentioned in Example 1 except that the amount of silver nitrate in the first solution was changed to 1.75 g, 2.33 g., 2.91 g, 3.49 g, 4.07 9 and 4.65 g, respectively. The test paper sheets were designated A, B, C, D, E and F in the order of lower to higher concentrations of silver nitrate. Each of the test paper sheets was cut into a 5 mm X 5 mm piece. The six test paper sheets were successively attached to a 5 mm X 85 mm polyvinyl chloride sheet starting at the top thereof in the order of A, B, C, D, E and F at intervals of 1 mm to prepare a test piece. Fig. 2 is a perspective view of the test piece of this example wherein 3, 4, 5, 6, 7 and 8 represent test paper sheets A, B, C, D, E and F, respectively, and 9 represents the polyvinyl chloride sheet.

The test paper sheets were entirely colored yellow with aqueous solutions of sodium chloride of 6, 8, 10, 12, 14 and 1 6 g/l, respectively. Accordingly, it is possible to determine the concentration of sodium chloride in a body fluid from the degree of color change from red to yellow on each of the test paper sheets.

Example 3 Three (3) test paper sheets were prepared in the same manner as mentioned in Example 1 except that the amount of silver nitrate in the first solution was changed to 1.91 g, 2.87 g and 3.83 g, respectively.

The test paper sheet prepared using 1.91 g of silver nitrate was designated G. The test paper sheets prepared using 2.87 g and 3.83 g of silver nitrate were designated H and I, respectively.

Each of G, H and I was cut into a 5 mm X 5 mm piece and was attached to a polyethylene terephthalate sheet 10 having a size of 5 mm X 85 mm as shown in Fig. 3, to prepare a test piece for the measurement of the concentration of chlorides according to the present invention.

In Fig. 3, numerals printed on the polyethylene terephthalate sheet 10 indicate the concentrations of chlorides, and 11, 1 2 and 1 3 indicate test paper sheets G, H and I, respectively. What is printed on standard color mark 14 is the color (yellow) which is produced when the amount of chlorides in urine is larger than the equivalent amounts of silver nitrate contained in the test paper sheets.

Example 4 Test paper sheets were prepared, in addition to those prepared in Example 3, using 4.78 9, 5.73 g and 6.69 9 of silver nitrate and were designated J, K and L, respectively. After each of the test paper sheets G, H, l, J, K and L was marked with the corresponding concentration of chlorides, the test paper sheets were attached to a 5 mm X 85 mm polyethylene terephthalate sheet 10 in the same manner as in Example 3. Fig. 4 is a perspective view of the test piece of this example, wherein 15, 1 6 and 1 7 represent J, K and L, respectively, and the remaining numerals represent a concentration of chlorides. In this example, chloride concentrationindicating numerals are marked on each of the test paper sheets so that the intervals between the test paper sheets may be narrowed.Accordingly, more test paper sheets may be attached on the same length polyethylene terephthalate sheet than in Example 3. if the chloride concentration-indicating numerals are marked, for example, in the same color as that of the test paper sheets prior to color change (red), the legibleness of the numerals after the use of the test piece will be ensured, the numerals being viewed as contrasted to the color of the test paper sheets after the color change thereof (yellow).

Example 5 A test piece was prepared in the same manner as mentioned in Example 4 except that the numerals were marked on the corresponding reverse side of the support to which the test paper sheets were attached instead of being marked on the test paper sheets themselves. Fig. 5 is a perspective view of the test piece of this example and Fig. 6 is a perspective view of the test piece shown in Fig. 5 viewed from the reverse side thereof.

Comparative Test with the Prior Art Using the test piece of the present invention prepared in Example 2, the concentrations of sodium chloride in human urine were determined, which were then compared with the calculated concentrations of sodium chloride obtained by determining the concentrations of sodium with an ion meter (lonanalyzer Model 801 A, manufactured by Orion Company in the U.S.A.) and calculating. The results are shown in Table 2. In Table 2, X indicates the measured values obtained with the ion meter and Y indicates the measured values obtained with the test piece of the present invention.

Table 2: Measured Values of Sodium Chloride Concentration No. X Y No. X Y 1 11.30 10 16 7.90 8 2 9.08 8 17 11.84 12 3 9.48 8 18 11.92 12 4 9.89 10 19 13.56 14 5 15.78 16 20 6.43 6 6 11.57 12 21 14.50 14 7 13.79 14 22 15.20 14 8 12.86 12 23 14.73 16 9 10.81 11 24 8.91 10 10 13.91 14 25 16.37 14 11 11.40 12 26 10.64 10 12 12.74 12 27 11.05 12 13 13.56 12 28 8.37 8 14 11.40 10 29 13.21 12 15 7.08 8 30 12.86 12 Number of data: N = 30 Mean value: X (ion meter) = 11.738 g/l Y (test piece) = 11.433 g/l Correlation coefficient: r = 0.9368 Primary regression equation:Y = 0.920X + 0.636 Verification in differences: t(0.05)= 2.024; T value = 0.465 (no significant difference) Further, Fig. 7 is a graph showing the correlation between the measured values obtained with the test piece of the present invention and the measured values obtained with the ion meter.

The correlation coefficient is about 0.94 and shows a very good correlation of the measured values obtained with the test piece of the present invention and the measured values obtained with the ion meter. It is apparent therefrom that the test piece of the present invention enables measurement of the concentration of sodium chloride in urine with sufficient accuracy for practical use.

As described above, the test piece for measurement of the concentration of chlorides according to the present invention comprises a support carrying a water-soluble silver salt, an absorption indicator and a buffering agent having a pH value in the range of 4 to 7. Therefore, the test piece of the present invention does not contain harmful hexavalent chromium as do conventional test pieces using silver chromate. Accordingly, the test piece of the present invention can be safely handled without any need for special procedures for its use and disposal.

Further, no expensive machine or special implement for measurement is required and accordingly, measurement of the concentration of chlorides can be carried out at a relatively low cost.

At the same time, since no technical skill is required in measurement, anyone can perform the measurement in a simple and rapid manner. Furthermore, the test piece of the present invention is portable due to its small size and light weight and can therefore be used indoors and outdoors. Furthermore, it is possible to make various modifications of the test piece of the present invention and therefore, the test piece is of great use in qualitative and quantitative analysis of the concentration of chlorides in liquids.

Claims

1. A test piece for measurement of the concentration of chlorides, comprising: a support carrying a water-soluble silver salt, an absorption indicator and a buffering agent having a pH in the range of from 4 to 7.

2. A test piece according to claim 1, wherein said water-soluble silver salt is selected from the group consisting of silver nitrate, silver lactate, silver malonate, silver acetate, silver chlorate, silver amidosulfonate, silver metaborate and silver phenolsulfonate.

3. A test piece according to claim 2, wherein said water-soluble silver salt is silver nitrate.

4. A test piece according to claim 1, wherein said absorption indicator is selected from the group consisting of dichlorofluorescein, dibromofluorescein, tetrabromophenol blue, bromocresol green and 2,6-dichlorophenol indophenol.

5. A test piece according to claim 4, wherein said adsorption indicator is 2,7-dichlorofluorescein.

6. A test piece according to claim 1, wherein said buffering agent having a pH in the range of from 4 to 7 is selected from the group consisting of lactate, tris-lactate, 2-(N-morpholino)ethanesulfonic acid, bis(2-hydroxyethyl)-iminotris(hydroxymethyl)methane, piperazine-N,N'-bis(2- ethanesulfonic acid, and 3-(N-morpholino)propanesulfonic acid.

7. A test piece according to claim 6, wherein said buffering agent having a pH in the range of from 4 to 7 is 2-(N-morpholino)-ethanesulfonic acid.

8. A test piece according to claim 1, wherein said support is an absorbent material selected from the group consisting of paper, cotton, wood and non-woven cloth.

9. A test piece according to claim 1, wherein at least one test paper sheet carrying silver nitrate, 2,7-dichlorofluorescein and 2-(N-morpholino)ethanesulfonic acid is attached to a first side of said support.

10. A test piece according to claim 9, wherein said support is a plastic sheet and wherein said test paper sheet is an absorbent material selected from the group consisting of paper, cotton, wood and non-woven cloth.

11. A test piece according to claim 10, wherein said support is a plastic selected from the group consisting of polystyrene, polyvinyl chloride and polydster.

1 2. A test piece according to claim 10, wherein said test paper sheet is filter paper.

1 3. A test piece according to claim 1, wherein a standard color marking representing a standard color of said adsorption indicator after color change is provided on said first side of said support and wherein a marking corresponding to a measurable concentration of chlorides is provided on said support.

14. A test piece according to claim 9, wherein a standard color marking representing a standard color of said absorption indicator after color change is provided on said first side of said support and wherein a marking corresponding to a measurable concentration of chlorides is provided on said first side of said support.

1 5. A test piece according to claim 14, wherein said marking corresponding to a concentration of chlorides is located on said first side of said support between two adjacent test paper sheets.

18. A test piece according to claim 14, wherein said marking corresponding to a concentration of chlorides is located on a surface of said test paper sheet.

1 7. A test piece according to claim 13, wherein said marking corresponding to a concentration of chlorides is located on a second side of said support.

18. A method of measuring the concentration of chlorides in liquids, comprising the steps of: (a) contacting a test piece for measurement of the concentration of chlorides, said test piece comprising a support carrying a water-soluble silver salt, an adsorption indicator and a buffering agent having a pH in the range of from 4 to 7, with a sample liquid; and (b) comparing a color change of said adsorption indicator with a standard color table of said adsorption indicator.

19. A method of preparing a test piece for measurement of the concentration of chlorides, comprising the steps of: (a) dissolving a water-soluble silver salt, an adsorption indicator, and a buffering agent in a solvent selected from the group consisting of water and a water-soluble organic solvent to produce a mixture solution; (b) immersing an absorbent support in said solution; (c) withdrawing said absorbent support from said solution; and (d) drying said absorbent support.

20. A method of preparing a test piece according to claim 19, wherein said water-soluble silver salt in said mixture solution has a concentration of from 0.01 to 0.5 Mol/l, said adsorption indicator in said mixture solution has a concentration of from 0.0001 to 0.02 Mol/l, and said buffering agent in said mixture solution has a concentration of from 0.05 to 1.0 Mol/l.

21. A method of preparing a test piece according to claim 20, wherein said water-soluble silver salt concentration is from 0.03 to 0.3 Mol/l, said adsorption indicator concentration is from 0.001 to 0.01 Mol/l, and said buffering agent concentration is from 0.3 to 0.7 Mol/l.

22. A method of preparing a test piece according to claim 21, wherein said water-soluble silver salt concentration is from 0.07 to 0.27 Mol/l, said adsorption indicator concentration is from 0.003 to 0.005 Mol/l, and said buffering agent concentration is from 0.4 to 0.5 Mol/l.

23. A method of preparing a test piece according to claim 19, wherein said absorbent support is filter paper.

24. A method of preparing a test piece according to claim 19, further comprising the step of: (e) attaching said absorbent support to an additional support.

25. A method of preparing a test piece for measurement of the concentration of chlorides, comprising the steps of: (a) dissolving a water-soluble silver salt and a buffering agent in a solvent selected from the group consisting of water and a water-soluble organic solvent to produce a first solution; (b) dissolving an adsorption indicator in an organic solvent to produce a second solution; (c) immersing an absorbent support in said first solution; (d) withdrawing said absorbent support from said first solution; (e) drying said absorbent support; (f) immersing said absorbent support in said second solution; (g) withdrawing said absorbent support from said second solution; and (h) drying said absorbent support.

26. A method of preparing a test piece according to claim 25, wherein said absorbent support is filter paper.

27. A method of preparing a test piece according to claim 25, further comprising the step of: (i) attaching said absorbent support to an additional support.

28. A method of preparing a test piece for measurement of the concentration of chlorides, comprising the steps of: (a) dissolving a water-soluble silver salt, an adsorption indicator, and a buffering agent in a solvent selected from the group consisting of water and a water-soluble organic solvent to produce a first solution; (b) mixing said first solution with an adhesive selected from the group consisting of starch and polyvinyl alcohol to produce a second solution; (c) coating said second solution on a support; and (d) drying and fixing said coated support.

29. A method of preparing a test piece according to claim 28, wherein said support is plastic.