Composition for the detection of redox reactions

Abstract: An agent composition for detecting a redox reaction comprising a redox reagent system, iodic acid or an iodate, and a monovalent thallium compound, which suppresses adverse influence of liberated iodine and provides accurate diagnosis results.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a composition for detecting a redox reaction. More particularly, the present invention relates to an agent composition which can suppress or remove an adverse influence of iodine which is liberated when an agent for detecting a redox reaction containing iodic acid or an iodate for removing an reducing substance is used. Description of the Related Art Various diagnostic agents are known for detecting various substances in a body based on redox reactions. Since a reducing substance present in a reaction system such as ascorbic acid interferes with the redox reaction, many measures for preventing or avoiding such interference have been proposed. Japanese Patent Publication No. 15280/1989 (corresponding to Japanese Patent Kokai Publication No. 109595/1981) discloses pretreatment of a sample to be analyzed with iodic acid or an iodate at pH of 3 to 5. Japanese Patent Publication No. 4861/1990 (corresponding to US Patent Nos. 4,743,559 and 4,957872 and EP-A-037 056) discloses a diagnostic agent for detecting a redox reaction which can avoid the influence of ascorbic acid by the presence of iodic acid or an iodate. However, the pretreatment of the former method makes the analysis (diagnostic procedures) complicated and is less preferable. When the said diagnostic agent, which removes the reducing substance with iodic acid or the iodate, is used, an accurate diagnosis cannot be performed by using conventional Trinder's reagent, because the iodine which is liberated through the reaction of the iodate with ascorbic acid oxidizes the Trinder's reagent and colors the background to give a false positive result. At a pH of less than 5, it is possible to remove not only ascorbic acid but also other reducing substances such as bilirubin, cysteine or aminopyrin with an iodate. However, at a pH of less than 5, an influence of the liberated iodine increases so that, with any color reagent, it is impossible to avoid this influence. When the pH is further decreased, the iodine is liberated in the absence of ascorbic acid as acidity increases and oxidizes the color reagent to color the background of the test piece. As explained above, a cause of the adverse influence on the diagnostic agent is the oxidizing property of the liberated iodine. If there were a method for quickly capturing the liberated iodine before it influences the color reagent, the adverse influence of the liberated iodine could be avoided. SUMMARY OF THE INVENTION An object of the present invention is to provide a novel agent composition for detecting a redox reaction, which contains iodic acid or an iodate for removing any reducing substance and avoiding the adverse influence of liberated iodine. According to the present invention, there is provided an agent composition for detecting a redox reaction, which comprises a redox reagent system, iodic acid or an iodate, and a monovalent thallium compound. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A to 1H are graphs showing the change in the background caused by ascorbic acid in Example 1, Figs. 2A to 2H are graphs showing sensitivities in Example 1, Fig. 3 is a graph showing the change of reflectance by ascorbic acid in Example 1, Fig. 4 is a graph showing the change in the background caused by ascorbic acid in Example 2, and Fig. 5 is a graph showing the change of reflectance caused by ascorbic acid in Example 2. DETAILED DESCRIPTION OF THE INVENTION In general, the reducing property of iodide is reduced by the addition of sodium thiosulfate and the like. However, since a thiosulfate itself has a strong reducing property, it decomposes iodic acid or the iodate. When the monovalent thallium compound is added in a system for removing the reducing substances with iodic acid or the iodate, the liberated iodine is effectively trapped and the diagnostic agent has improved utility. The reaction mechanism with which the monovalent thallium compound traps the iodine is not an oxidation-reduction reaction but an ionic reaction. In addition, since thallium iodide formed by the ionic reaction is a hardly soluble yellow compound, reliberation of iodide ions can be prevented. Since the compound formed is yellow, it has no material influence on optical detection in instrumental analysis. When a test paper is colored with a yellow dye, the color change through the redox reaction can be detected visually. As described above, the use of the monovalent thallium compound has various advantages in the diagnostic agent composition. But, since the monovalent thallium compound is a strong oxidizing agent, it is assumed that such strong oxidizing property may have some adverse influence on the reaction system. Unexpectedly, the oxidizing property of the monovalent thallium compound never adversely affects the analysis in the reaction time for analysis. Further, the monovalent thallium compound does not decompose ascorbic acid. In this connection, a trivalent thallium compound has some adverse influences on the reaction system due to its oxidizing property and cannot be used. In the present invention, any of the monovalent thallium compounds may be used. Among the compounds, salts with inorganic or organic acids are preferred. Specific examples of the monovalent thallium compound are thallium (I) chloride, thallium (I) sulfate and thallium (I) acetate. An effective amount of the monovalent thallium compound is from 0.1 to 20 g, preferably from 1 to 10 g per 100 g of the reagent composition. The redox reagent system to be used in the present invention may be any of those conventionally used. Examples are disclosed in the above described Japanese Patent Publication No. 4861/1990 and its corresponding US Patent and EP Patent Publication. Examples of the iodate are potassium iodate, sodium iodate, magnesium iodate, ammonium iodate, etc. and a mixture thereof. The redox reagent system and iodic acid or the iodate may be used in the same manner and the same amounts as in the conventional composition. When the composition of the present invention is used, the pH of the reaction system is not critical, and even a pH of 5 or less may be used, though a higher pH can also be used. When a benzidine derivative is used as a color reagent, the pH is preferably in the range between 3 and 8. When the Trinder's reagent is used as a colour reagent, pH is preferably in the range between 4 and 8. The effects achieved by the present invention are as follows: Since the monovalent thallium compound is used, it is possible to use the generally used Trinder's reagent in the reagent composition (diagnostic agent) in which the reducing substances are removed by iodic acid or the iodate. The pH range, in the case where the Trinder's reagent is used, is from 4 to 8. Then, it is possible to remove the reducing substances such as bilirubin, cysteine and aminopyrin. When the benzidine derivative color reagent is used, the pH can be reduced to 3 so that the reducing substances such as bilirubin, cysteine and aminopyrin can be removed. The addition of the monovalent thallium compound can suppress the coloring of the background of the test paper (the amount of ascorbic acid being zero (0)). PREFERRED EMBODIMENTS OF THE INVENTION The present invention will be illustrated by the following Examples. Example 1 A test paper having a formulation of Table 1 was prepared, and the change of the background of the test paper was examined under the following conditions: Sizes of the test paper: 5 mm x 5 mm square Measuring procedures: Dipping and reading Measuring time: After one minute Apparatus: A photoelectric colorimeter (SZ-Σ80 manufactured by Nippon Denshoku Kabushikikaisha) Sample: An aqueous solution of ascorbic acid (concentration: 0, 20, 100 and 250 mg/dl) The results are shown in Figs. 1A to 1H, in which the vertical axes are in terms of Log1/R. Then, the sensitivity was examined by the same procedures as above except that, as a sample, a glucose solution (concentration: 0, 0.1, 0.5 and 1 g/dl) was used. The results are shown in Figs. 2A to 2H. To examine whether or not the coloration by the liberated iodine in the reaction of ascorbic acid and the iodate was suppressed by the thallium compound, the following experiment was carried out. That is, the suppression of coloration was determined by the same procedures as above but using the test paper of the formulation No. 3 or 4 in Table 1 and a solution of glucose having a concentration of 0, 100 or 500 mg/dl to which ascorbic acid was added at a concentration of 0, 20, 100 or 250 mg/dl. The results are shown in Fig. 3. Example 2 With a test paper for detecting occult blood, the same tests as in Example 1 were carried out. The formulation of the test paper was as follow: First layer The following mixture was absorbed by a filter paper (Toyo Filter Paper No. 514A) and dried at 80°C for 30 minutes to form a first layer: 50 ml of 1.5 M citrate buffer (pH 4) 20 ml of purified water 30 ml of ethanol 300 mg of sodium laurylsulfate 2 ml of cumene hydroperoxide 3.0 g or 0 g (comparison) of thallium sulfate Then, the following mixture was coated on the first layer and dried at 50°C for 30 minutes: 50 ml of purified water 50 ml of acetone 1.0 g of 3-aminoquinoline 500 mg of o-tolidine 500 mg of sodium iodate The change in the background was measured by the same procedures as in Example 1. The sensitivity was examined by the same manner as in Example 1 but using, as a sample, a hemoglobin solution (concentration: 0, 0.05, 0.1 or 1 mg/dl). The change in the reflectance was examined by the same procedures as in Example 1 but using, as a sample, a solution of hemoglobin having a concentration of 0, 0.05, 0.1 or 1 mg/dl to which ascorbic acid was added at a concentration of 0, 20, 100 or 250 mg/dl. The results are shown in Fig. 4, Table 2 and Fig. 5, respectively. In Fig. 4, the vertical axes is in terms of Log1/R. Results of Sensitivity Measurement Thallium compound Yes No Hb amount (mg/dl) 0 0.05 0.1 1.0 0 Log1/R 0.209 0.464 0.617 0.845 1.232 Wavelength for measurement: 640 nm.

Claims: A composition for detecting a redox reaction, which comprises a redox reagent system, iodic acid or an iodate, and a monovalent thallium compound. The composition according to claim 1, wherein said thallium compound is a salt of thallium with an inorganic or organic acid. The composition according to claim 1, wherein said thallium compound is one selected from the group consisting of thallium (I) chloride, thallium (I) sulfate and thallium (I) acetate. The composition according to claim 1, wherein said iodate is one selected from the group consisting of potassium iodate, sodium iodate, magnesium iodate and ammonium iodate.

Inventors: DOI KENICHI, DOI, KENICHI
Applicants: KYOTO DAIICHI KAGAKU KK, KYOTO DAIICHI KAGAKU CO., LTD.
Application year: 1991
Main classification: C12Q1
IPC codes: C12Q1, G01N31, G01N33