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US-12618821-B2 - Powder composition, kit, and method for determining orthophosphate concentration

US12618821B2US 12618821 B2US12618821 B2US 12618821B2US-12618821-B2

Abstract

A kit and powder composition are described that can be used to determine a concentration of orthophosphate in a water system. The kit includes a first powder composition including molybdate; and a second powder composition including ascorbic acid. A powder composition is also described that includes molybdate, pyrosulfate, and less than 1 wt. % ascorbic acid. A method for determining the concentration of orthophosphate in a water system using the kit includes adding the first and second powder compositions to a water sample collected from the water system, measuring an absorbance of the water sample after the first and second powder compositions have been added to the water sample, and determining the concentration of orthophosphate in the water system based on the measured absorbance.

Inventors

  • Sarah ANCIAUX
  • Melinda BUYCK

Assignees

  • HACH COMPANY

Dates

Publication Date
20260505
Application Date
20220923

Claims (18)

  1. 1 . A kit comprising: a first powder composition comprising molybdate; and a second powder composition comprising ascorbic acid, wherein the first powder composition and the second powder composition are separated from each other, and wherein the first powder composition and the second powder composition show substantially no discoloration when stored at 50% humidity or higher for at least 4 months.
  2. 2 . The kit according to claim 1 , wherein the first powder composition includes molybdate in an amount in a range of 0.5 to 20 wt. % based on a total weight of the first powder composition and the second powder composition.
  3. 3 . The kit according to claim 1 , wherein the molybdate is selected from the group consisting of sodium molybdate, potassium molybdate, ammonium molybdate, and mixtures thereof.
  4. 4 . The kit according to claim 1 , wherein the first powder composition further includes pyrosulfate.
  5. 5 . The kit according to claim 4 , wherein the pyrosulfate is selected from the group consisting of potassium pyrosulfate, sodium pyrosulfate, ammonium pyrosulfate, and mixtures thereof.
  6. 6 . The kit according to claim 4 , wherein the pyrosulfate is present in the first powder composition in an amount in a range of 50 to 95 wt. % based on a total weight of the first powder composition and the second powder composition.
  7. 7 . The kit according to claim 1 , wherein the first powder composition further includes antimony.
  8. 8 . The kit according to claim 7 , wherein the antimony is potassium antimonyl tartrate.
  9. 9 . The kit according to claim 1 , wherein the first powder composition further includes a chelating agent.
  10. 10 . The kit according to claim 1 , wherein the first powder composition includes: pyrosulfate in an amount of in a range of 50 to 95 wt. %; molybdate in an amount in a range of 0.5 to 20 wt. %; antimony in an amount in a range of 0.01 to 5 wt. %; and a chelating agent in an amount in a range of 0.03 to 5 wt. %, based on a total weight of the first powder composition and the second powder composition.
  11. 11 . The kit according to claim 1 , wherein the ascorbic acid is present in the second powder composition in an amount in a range of 5 to 40 wt. % based on a total weight of the first powder composition and the second powder composition.
  12. 12 . The kit according to claim 1 , wherein the first powder composition is in a first container and the second powder composition is in a second container.
  13. 13 . A powder composition comprising: molybdate; and pyrosulfate; wherein the powder composition comprises less than 0.01 wt. % of ascorbic acid based on a total weight of the powder composition, and wherein the pox der composition shows substantially no discoloration when stored at 50% humidity or higher for at least 4 months.
  14. 14 . The powder composition according to claim 13 , further comprising antimony.
  15. 15 . A method for determining a concentration of orthophosphate in a water system using the kit according to claim 1 , the method comprising: adding the first powder composition to a water sample collected from the water system; adding the second powder composition to the water sample; and measuring an absorbance of the water sample after the first powder composition and the second powder composition have been added to the water sample.
  16. 16 . The method according to claim 15 , wherein the first powder composition reacts with orthophosphate in the water sample to produce a phosphomolybdic acid complex, and the phosphomolybdic acid complex is reduced by the second powder composition to a molybdenum blue.
  17. 17 . The kit according to claim 1 , wherein the first powder composition and the second powder composition do not suffer a loss of chemical function when stored at 50% humidity or higher for at least 4 months.
  18. 18 . The powder composition according to claim 13 , wherein the powder composition does not suffer a loss of chemical function when stored at 50% humidity or higher for at least 4 months.

Description

TECHNICAL FIELD The present disclosure relates to a kit and a powder composition for determining an orthophosphate concentration in a water system, and a method of using the kit to determine the orthophosphate concentration. BACKGROUND Phosphates, including orthophosphates, are widely used as corrosion inhibitors in many water systems, such as waste water streams and process streams in various industrial processes. However, when the concentration of orthophosphate is too high, it can cause scaling, fouling, and environmental issues. Therefore, it is important to accurately measure and control the orthophosphate concentration to be within an appropriate range. A known method for measuring orthophosphate in a water system is the molybdenum blue method (Standard Method 4500-P E, 1997) in which reagents are added to a water sample to react with the orthophosphate in the water sample and produce a blue color having an absorbance proportional to the orthophosphate concentration. A powder composition based on the molybdenum blue method includes molybdate and a reducing agent, such as ascorbic acid. The molybdate reacts with the orthophosphate in the water to produce a heteropoly acid complex, and the reducing agent reduces the complex to produce a blue color. The absorbance of the water sample can then be measured to determine the orthophosphate concentration. Although the powder composition was originally developed as a stable alternative to reagent solutions, it has long been known that the powder composition can suffer from discoloration during storage, which can result in a loss of chemical function and significantly reduce the accuracy of the measured orthophosphate concentration, as well as cause a poor perception of the powder composition. This problem has plagued the water treatment industry for more than two decades with no known cause or solution. Although there has been speculation as to the source of the problem, for example, that it is caused during the manufacture of one or more of the powder reagents, it has been difficult to determine the source of the problem, which in turn has made it difficult to find an effective solution. There has been a long felt need for an improved powder composition that can be stably stored without suffering from discoloration and that can be used to accurately measure the orthophosphate concentration in a water system. SUMMARY In view of the above, an object of the present disclosure is to provide a stable powder composition and kit that can be used to accurately determine the phosphate concentration. In one aspect, the disclosure provides a kit including a first powder composition that includes molybdate; and a second powder composition that includes ascorbic acid. In another aspect, the disclosure provides a powder composition including molybdate, pyrosulfate, and less than 1 wt. % ascorbic acid. In a further aspect, the disclosure provides a method for determining a concentration of orthophosphate in a water system using the kit. The method includes adding the first powder composition to a water sample collected from the water system, adding the second powder composition to the water sample, measuring an absorbance of the water sample after the first and second powder compositions have been added to the water sample, and determining the concentration of orthophosphate in the water system based on the measured absorbance. DETAILED DESCRIPTION OF EMBODIMENTS In the following description, numerous details are set forth to provide an understanding of the present disclosure. However, it may be understood by those skilled in the art that the methods and systems of the present disclosure may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. After extensively studying the problem of discoloration, the inventors surprisingly found that discoloration of the powder reagent composition for measuring orthophosphate concentration can be caused by one or more reactions between the reagents under humid conditions. In particular, as shown in the Examples, the inventors found that the ascorbic acid can react with molybdate under humid conditions to produce discoloration in the powder composition. The reaction between ascorbic acid and molybdate produces dark blue or black particles that are insoluble in water and can significantly reduce the accuracy of the orthophosphate concentration measurement. The reaction between ascorbic acid and molybdate in the presence of pyrosulfate produces orange or brown particles that can also interfere with the orthophosphate measurement, as well as cause a poor perception of the powder reagent composition. The inventors found that discoloration can occur in powder compositions that include ascorbic acid and molybdate, and in powder compositions that further include pyrosulfate under humid conditions, for example, at least 50% relative humidity. The kit and powder compositio