Hydrogen sulfide test kit and method for detecting hydrogen sulfide in an aqueous sample

Abstract

A hydrogen sulfide test kit includes: a first reactant powder containing citric acid, a second reactant powder containing sodium bicarbonate, and a test paper that changes color upon contact with hydrogen sulfide. The first and second reactant powders are physically isolated from each other. A method of using the hydrogen sulfide test kit and a method of detecting hydrogen sulfide in an aqueous sample both include: reacting citric acid and sodium bicarbonate in the aqueous sample to form bubbles, said bubbles releasing any hydrogen sulfide in the aqueous sample into a gaseous form; if the released hydrogen sulfide in gaseous form is present, contacting said released hydrogen sulfide in gaseous form with the test paper; and detecting the presence of hydrogen sulfide in the aqueous sample based on the color of the test paper.

Description

Background Technology

[0001] Hydrogen sulfide (H2S) is a common water pollutant that requires monitoring. It forms when soluble sulfides hydrolyze in water. In water, hydrogen sulfide dissociates to form hydrosulfide ions (1-)(HS-). - ) and sulfide ions (S 2- ).

[0002] Hydrogen sulfide can be produced by bacteria or released from naturally occurring geological sediments. For example, the presence of hydrogen sulfide in a water sample may indicate microbial activity or volcanic gas production. Therefore, its presence can reflect the existence of other potential problems.

[0003] In addition, hydrogen sulfide is highly corrosive and can cause premature damage and failure of equipment. When equipment is damaged and needs to be replaced, corrosion caused by hydrogen sulfide significantly increases the operating costs of production wells.

[0004] Hydrogen sulfide is also toxic, even in very low amounts. Once ingested, it forms a complex with the iron(III) ions of the mitochondrial metalloenzyme cytochrome oxidase, thereby blocking oxidative metabolism. It also alters or inhibits a variety of other enzymes, leading to rapid acute complications.

[0005] Exposure to trace amounts of hydrogen sulfide can cause symptoms ranging from mild irritation (such as eye and respiratory irritation, nausea, vomiting, and upper abdominal pain) (in the range of 20 to 250 ppm) to more serious neurological symptoms (coma and respiratory paralysis) (above 250 ppm). The National Institute for Occupational Safety and Health (NIOSH) considers a hydrogen sulfide concentration of 100 ppm to be immediately life-threatening or health-threatening. Concentrations greater than 500 ppm may cause unconsciousness within five minutes, while concentrations exceeding 700 ppm may cause immediate unconsciousness and death within just one or two breaths. Therefore, the Occupational Safety and Health Administration (OSHA) sets the permissible exposure limit for hydrogen sulfide at 20 ppm.

[0006] Although hydrogen sulfide has a recognizable odor similar to rotten eggs, this odor is only detectable at very low concentrations (less than 10 ppm in the air). Furthermore, the odor can have a deceptively sweet smell, and higher concentrations can numb the sense of smell. This means that someone could be exposed to potentially toxic amounts of hydrogen sulfide even in the absence of a detectable odor.

[0007] Current methods for detecting hydrogen sulfide in aqueous samples are generally limited to off-site testing applications. For example, hydrogen sulfide is typically detected using an acid displacement procedure, where it is displaced by acidification and detected by gas chromatography. While the so-called "dip strip" technique is more portable, it has lower accuracy.

[0008] Therefore, there is a need for a rapid and easy method to test for hydrogen sulfide in aqueous samples from sources such as wastewater, drinking water, and well water. To achieve this, the test should be able to accurately detect low concentrations of hydrogen sulfide and should be able to be performed in situ (at the water source). Summary of the Invention

[0009] The disclosed embodiments describe a hydrogen sulfide test kit, a method for using the hydrogen sulfide test kit, and a method for detecting hydrogen sulfide in an aqueous sample.

[0010] According to one aspect of the embodiments, a hydrogen sulfide test kit includes: a first reactant powder containing citric acid; a second reactant powder containing sodium bicarbonate; and a test strip configured to change color upon contact with hydrogen sulfide. The first reactant powder and the second reactant powder are physically isolated from each other.

[0011] Another aspect of the implementation includes a method for using the hydrogen sulfide test kit. The method includes: adding a first reactant powder and a second reactant powder to an aqueous sample; reacting the citric acid and sodium bicarbonate in the aqueous sample to form bubbles, wherein the bubbles release any hydrogen sulfide in the aqueous sample into a gaseous form; if gaseous hydrogen sulfide is present, contacting the gaseous hydrogen sulfide with the test strip; and detecting the presence of hydrogen sulfide in the aqueous sample based on the color of the test strip.

[0012] Another aspect of the implementation includes a method for detecting hydrogen sulfide in an aqueous sample. The method includes: adding citric acid and sodium bicarbonate to the aqueous sample; reacting the citric acid and sodium bicarbonate in the aqueous sample to form bubbles, wherein the bubbles release any hydrogen sulfide in the aqueous sample into a gaseous form; if the released hydrogen sulfide is present in gaseous form, contacting the released hydrogen sulfide in gaseous form with a test strip configured to change color upon contact with the hydrogen sulfide; and detecting the presence of hydrogen sulfide in the aqueous sample based on the color of the test strip. In this method, the citric acid and sodium bicarbonate are in contact with each other for no more than 24 hours before being added to the aqueous sample. Attached Figure Description

[0013] A more detailed description of the invention is provided by reference to the specific embodiments thereof shown in the accompanying drawings. While it is understood that these drawings depict only typical embodiments of the invention and are therefore not to be considered as limiting its scope, embodiments of the invention will be described and explained with the aid of additional features and details using the drawings, wherein:

[0014] Figure 1 This is a flowchart illustrating a method for detecting hydrogen sulfide in an aqueous sample according to the disclosed embodiment; and

[0015] Figure 2 This is a schematic diagram of a hydrogen sulfide test chart of the disclosed implementation scheme. Detailed Implementation

[0016] Existing methods for testing hydrogen sulfide in aqueous samples typically require off-site analysis or may only determine the amount of hydrogen sulfide with low accuracy. Therefore, there is a need for a kit that enables on-site testing of hydrogen sulfide in aqueous samples with high accuracy and resolution.

[0017] The inventors have discovered that by releasing hydrogen sulfide into a gaseous form and detecting the hydrogen sulfide in its gaseous form, hydrogen sulfide in aqueous samples can be detected and quantified with high accuracy.

[0018] For example, effervescent tablets (such as Alka-Seltzer Gold™) can be used to create bubbles in aqueous samples. These effervescent tablets contain sodium bicarbonate (NaHCO3) and citric acid (HOC(CH2CO2H)2), which are a base and an acid, respectively. When the tablet dissolves in water, bicarbonate ions (HCO3-) are formed. – ) and hydrogen ions (H + Once in solution, bicarbonate ions and hydrogen ions react as shown below.

[0019] HCO3 – (aq) + H + (aq) → H2O (l) + CO2 (g)

[0020] Carbon dioxide bubbles to the surface, causing any hydrogen sulfide in the aqueous sample to be released in gaseous form. Specifically, it is believed that hydrogen sulfide is released due to the pH change caused by the reaction, and that bubbling causes the hydrogen sulfide to come out of the solution.

[0021] Once hydrogen sulfide is in gaseous form, it can be brought into contact with a test strip configured to change color upon contact with hydrogen sulfide. It was found that when detected in gaseous form, even very small amounts of hydrogen sulfide could be detected at high resolution (e.g., concentration differences of 0.1 or 0.2 ppm). In contrast, a similar method using color-changing paper to detect hydrogen sulfide in liquid form (the so-called "strip dipping" method) cannot distinguish concentration differences smaller than approximately 2 ppm.

[0022] Despite some improvements, the method was found to be disadvantageous due to its dependence on effervescent tablets. Because the method combines the reactants in tablet form, the amount of reactants cannot be adjusted. Therefore, the method is not readily adaptable to different applications.

[0023] In addition, tablets contain other ingredients to prevent premature reaction of the active ingredients. For example, Alka-Seltzer Gold™ tablets contain citric acid and sodium bicarbonate as active ingredients, potassium bicarbonate as a stabilizer, and magnesium stearate as a desiccant. Without the stabilizer and desiccant, citric acid and sodium bicarbonate will begin to react with each other. Therefore, the reacting ingredients cannot be packaged together without additional filler components. These filler components increase cost and volume and have the potential to interfere with the reaction process and reduce test accuracy.

[0024] The inventors conducted extensive research and discovered that by using powdered citric acid and sodium bicarbonate to release hydrogen sulfide into a gaseous form, and then detecting the hydrogen sulfide in its gaseous form, hydrogen sulfide in aqueous samples can be detected and quantified with high accuracy. Citric acid and sodium bicarbonate can be stored separately in powder form to prevent them from reacting with each other, and this allows for precise adjustment of the reaction amounts based on the characteristics of the test sample.

[0025] Specifically, the disclosed embodiments include a hydrogen sulfide test kit comprising citric acid and sodium bicarbonate. For example, the citric acid and sodium bicarbonate may be stored separately in different containers until ready for use.

[0026] In one embodiment, a first container contains a first reactant powder comprising citric acid, and a second container contains a second reactant powder comprising sodium bicarbonate. To keep the citric acid and sodium bicarbonate isolated from each other so that they do not react with each other, the first reactant powder is substantially free of sodium bicarbonate, and the second reactant powder is substantially free of citric acid. In this document, "substantially free of" means that the amount of the component does not significantly affect the reaction chemistry. For example, because the first reactant powder is substantially free of sodium bicarbonate, the extent to which any sodium bicarbonate present in the first reactant powder reacts with citric acid is negligible. In one embodiment, the first reactant powder does not contain any sodium bicarbonate, and the second reactant powder does not contain any citric acid.

[0027] The first reactant powder and the second reactant powder may optionally contain other non-reactive components. For example, the first reactant powder and the second reactant powder may contain stabilizers and / or desiccants. Alternatively, the first reactant powder and the second reactant powder may not contain any stabilizers or desiccants. In one embodiment, the first reactant powder is composed of citric acid, and the second reactant powder is composed of sodium bicarbonate.

[0028] Citric acid and sodium bicarbonate are essentially pure (meaning they contain less than 5% by weight of impurities). For example, citric acid and sodium bicarbonate contain less than 3% by weight, preferably less than 1% by weight, and more preferably less than 0.5% by weight of impurities.

[0029] For example, the particle size of sodium bicarbonate can be in the range of 50 to 600 µm, 75 to 500 µm, 100 to 400 µm, or 200 to 300 µm.

[0030] The kit also includes test strips configured to change color upon contact with hydrogen sulfide. For example, the test strips may contain copper sulfate, which reacts with hydrogen sulfide to form copper sulfide.

[0031] CuSO4 + H2S → CuS + H2SO4

[0032] Copper sulfate can be coated onto the surface of the test paper to ensure contact with hydrogen sulfide.

[0033] The amount of reaction product depends on the amount of hydrogen sulfide in contact with the test paper, which in turn depends on the amount of hydrogen sulfide present in the aqueous sample. A larger amount of reaction product can manifest as a color change. Therefore, this test paper allows for the simultaneous detection and quantification of hydrogen sulfide in aqueous samples.

[0034] To enable quantification of hydrogen sulfide, the test kit also includes test charts. Figure 2An example of a test diagram for the disclosed implementation is shown. Figure 2 As shown, the test strip becomes increasingly darker as the detected amount of hydrogen sulfide increases. By visually comparing the test strip with the test chart, the approximate amount of hydrogen sulfide in the aqueous sample can be determined. For example, if the test strip is approximately the same color as the 0.3 ppm example shown on the test chart, the amount of hydrogen sulfide in the aqueous sample is determined to be approximately 0.3 ppm. If the color is somewhere between the colors shown on the test chart for 0.3 ppm and 0.5 ppm, the amount of hydrogen sulfide in the aqueous sample is determined to be between 0.3 ppm and 0.5 ppm (e.g., approximately 0.4 ppm). In this way, differences as low as 0.03 ppm can be distinguished. The accuracy of the approximation can reach ±0.03 ppm.

[0035] like Figure 1 As outlined herein, the disclosed embodiments also relate to a method for detecting hydrogen sulfide in aqueous samples. In performing the hydrogen sulfide test, citric acid and sodium bicarbonate should be physically separated from each other until ready for use to avoid premature reaction, which may reduce the effectiveness of the test. In some cases, citric acid and sodium bicarbonate may be pre-combined and the mixture stored in a low-humidity environment (e.g., less than 10% relative humidity at 23°C, or under vacuum). However, such exposure should be limited to less than 24 hours before the test and preferably should be avoided entirely.

[0036] Preferably, citric acid and sodium bicarbonate are not combined until just before testing. For example, citric acid and sodium bicarbonate are in contact with each other for less than 15 minutes before being added to the aqueous sample for testing. Preferably, citric acid and sodium bicarbonate are in contact with each other for less than 10 minutes, less than 5 minutes, or less than 1 minute before being added to the aqueous sample. In one embodiment, citric acid and sodium bicarbonate are added to the aqueous sample separately, and therefore are not combined before being added to the aqueous sample.

[0037] For example, the water sample used for testing can be a water sample, such as wastewater, drinking water, or well water. The water sample must contain at least 95%, 98%, 99%, or 99.8% water by weight.

[0038] Aqueous samples may contain hydrogen sulfide. The hydrogen sulfide content in an aqueous sample can be below 10.0 mg H₂S / L (i.e., 10.0 ppm H₂S), below 5.0 ppm, below 2.0 ppm, below 1.0 ppm, below 0.7 ppm, below 0.5 ppm, below 0.3 ppm, or below 0.1 ppm. For example, the hydrogen sulfide content in an aqueous sample can be above 5.0 ppm, such as 8 ppm, 10 ppm, 15 ppm, or 20 ppm.

[0039] To improve the accuracy of the test, the water-containing sample should ideally be kept at a temperature below 50°C during the test. For example, the temperature can be in the range of 5°C to 40°C, 10°C to 37°C, 12°C to 30°C, or 10°C to 23°C.

[0040] The pH of an aqueous sample can range from 3.7 to 9.7. For example, the pH of an aqueous sample can range from 4.0 to 9.5, 5.0 to 8.0, or 6.5 to 7.5.

[0041] The hardness of a water-containing sample can range from 0 to 180 ppm of calcium carbonate (CaCO3). For example, the hardness of a water-containing sample can be in the range of 10 to 150 ppm, 25 to 130 ppm, or 50 to 100 ppm.

[0042] like Figure 1 As shown, the test method involves adding an aqueous sample to a test container. For example, the volume of the aqueous sample added to the test container can range from 50 to 500 mL, 75 to 200 mL, or 100 to 150 mL. The test container should be impermeable and chemically inert so as not to interfere with the test process. For example, the test container can be made of glass. Once the aqueous sample has been collected and added to the container, it should be analyzed immediately to ensure that the measurement accurately reflects the concentration of hydrogen sulfide in the source of the aqueous sample.

[0043] Next, place the test strip near the aqueous sample so that any hydrogen sulfide released from the sample will come into contact with the test strip. For example, place the test strip inside a test container, such as inside the lid. Figure 2 As shown, the test strip can be placed inside the lid so that it fits snugly against the lid and remains fixed inside the lid when it closes the opening of the test container. After testing, the test strip can be removed from the lid so that the container can be washed and reused with new test strips.

[0044] Once the test strip is placed inside the container (e.g., inside the lid), the first and second reactant powders are measured, and then added to the aqueous sample within the container. As discussed above, the first and second reactant powders can be added together or separately. The total amount of sodium bicarbonate and citric acid added to the aqueous sample can range from 1 to 8 mg / 100 mL of sample. For example, the total amount added can range from 2 to 6 mg or 3 to 4 mg.

[0045] Depending on the source of the aqueous sample, the amounts of the first and second reactant powders added to the aqueous sample can be adjusted as needed. For example, the first and second reactant powders can be added so that the ratio of sodium bicarbonate to citric acid added to the aqueous sample is 30-70:70-30. For example, this ratio can be 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, or 65:35.

[0046] As mentioned above, the aqueous sample should be analyzed as soon as possible after collection to ensure that the measurement results accurately reflect the hydrogen sulfide concentration in the source of the aqueous sample. Therefore, the first reactant powder and the second reactant powder should be added to the aqueous sample within 2 hours of collection, and preferably within 1 hour, 30 minutes, 15 minutes, 10 minutes, or 5 minutes or less.

[0047] After adding the first reactant powder and the second reactant powder, seal the container (e.g., by closing the lid) and allow the first and second reactant powders to react, thereby generating bubbles. For example, allow the reaction to proceed for 30 seconds to 10 minutes, 45 seconds to 5 minutes, 1 minute to 4 minutes, or 1.5 minutes to 2 minutes. During this time, the container may be stirred as needed to ensure the reaction is complete. For example, the container may be gently moved to allow the contents to swirl inside, thereby mixing the first and second reactant powders with the aqueous sample. It is expected that all hydrogen sulfide in 100 mL of the sample will be released from the solution within approximately 2 minutes.

[0048] After a waiting period, remove the test strip from the container and observe it visually. Observation can be performed with the naked eye or under magnification. If visual observation indicates a color change in the test strip, hydrogen sulfide is confirmed to be present in the aqueous sample. The test strip can be compared to a test chart to confirm the presence of hydrogen sulfide, and optionally, the amount of hydrogen sulfide present in the aqueous sample can be quantified. Visual observation is preferably performed within 15 minutes of removing the test strip from the container. For example, the test strip can be visually observed within 10 minutes, 5 minutes, 2 minutes, or 1 minute after being removed from the reaction conditions.

[0049] This test method can be improved. For example, the test paper can be added to the container before adding the aqueous sample, after adding the aqueous sample but before adding the first reactant powder and the second reactant powder, or even after adding the first reactant powder and the second reactant powder if the operation is rapid. The test can be performed under various environmental conditions (e.g., relative humidity in the range of 20% to 90%, 30% to 80%, or 40% to 60%).

[0050] It should be understood that the features and functions disclosed above, or their alternatives, can be suitably incorporated into different kits and methods. Furthermore, various alternatives, modifications, variations, or improvements can subsequently be made by those skilled in the art, and these are also intended to be covered by embodiments of this disclosure. Thus, various changes can be made without departing from the spirit and scope of this disclosure.

Claims

1. A hydrogen sulfide test kit, the hydrogen sulfide test kit comprising: The first reactant powder containing citric acid; A second reactant powder containing sodium bicarbonate; and Test paper configured to change color upon contact with hydrogen sulfide. The first reactant powder and the second reactant powder are physically isolated from each other.

2. The hydrogen sulfide test kit according to claim 1, wherein: The first reactant powder is substantially free of sodium bicarbonate; and The second reactant powder is essentially free of citric acid.

3. The hydrogen sulfide test kit according to claim 1, further comprising: A first reactant container that contains the first reactant powder; and A second reactant container that contains the second reactant powder.

4. The hydrogen sulfide test kit according to claim 3, wherein: The first reactant container contains only the first reactant powder; and The second reactant container contains only the second reactant powder.

5. The hydrogen sulfide test kit according to claim 1, wherein the first reactant powder and the second reactant powder do not contain any desiccant.

6. The hydrogen sulfide test kit according to claim 1, wherein the first reactant powder and the second reactant powder do not contain any stabilizers.

7. The hydrogen sulfide test kit according to claim 1, wherein the first reactant powder and the second reactant powder do not contain any potassium bicarbonate.

8. The hydrogen sulfide test kit according to claim 1, wherein the test strip contains copper sulfate.

9. The hydrogen sulfide test kit according to claim 1, wherein the degree to which the test strip changes color upon contact with hydrogen sulfide depends on the amount of hydrogen sulfide in contact with the test strip.

10. The hydrogen sulfide test kit according to claim 1, further comprising: A test container configured to contain a water-containing sample, the test container comprising: Opening; and A removable cover, wherein the removable cover is configured to: Seal the opening of the test container, and The test strip is held in such a way that when the cap closes the opening of the test container, the test strip is exposed to the interior of the test container.

11. The hydrogen sulfide test kit according to claim 1, further comprising: Test charts containing color-coded results for various hydrogen sulfide concentrations.

12. A method of using the hydrogen sulfide test kit according to claim 1, the method comprising: The first reactant powder and the second reactant powder are added to the aqueous sample; The citric acid and sodium bicarbonate are reacted in the aqueous sample to form bubbles, wherein the bubbles release any hydrogen sulfide in the aqueous sample into a gaseous form. If released hydrogen sulfide in gaseous form is present, then bring the released hydrogen sulfide in gaseous form into contact with the test paper; and The presence of hydrogen sulfide in the aqueous sample is detected based on the color of the test strip.

13. The method according to claim 12, wherein: The hydrogen sulfide test kit also includes: a test chart containing color-coded results for various hydrogen sulfide concentrations, and The presence of hydrogen sulfide in the aqueous sample is detected by visually comparing the color of the test strip with the color coding result.

14. A method for detecting hydrogen sulfide in an aqueous sample, the method comprising: Citric acid and sodium bicarbonate were added to the aqueous sample; The citric acid and sodium bicarbonate are reacted in the aqueous sample to form bubbles, wherein the bubbles release any hydrogen sulfide in the aqueous sample into a gaseous form. If there is released hydrogen sulfide in gaseous form, the released hydrogen sulfide in gaseous form is brought into contact with the test paper, which is configured to change color upon contact with the hydrogen sulfide. as well as The presence of hydrogen sulfide in the aqueous sample is detected based on the color of the test strip. The citric acid and sodium bicarbonate are in contact with each other for no more than 24 hours before being added to the aqueous sample.

15. The method of claim 14, wherein the citric acid and the sodium bicarbonate are in contact with each other for no more than 15 minutes before being added to the aqueous sample.

16. The method of claim 14, wherein the citric acid and the sodium bicarbonate are added to the aqueous sample separately from each other.

17. The method of claim 14, wherein the presence of hydrogen sulfide in the aqueous sample is detected by visually observing the color of the test paper.

18. The method of claim 14, wherein: The citric acid was added to the aqueous sample in the form of a first reactant powder that was substantially free of sodium bicarbonate; and The sodium bicarbonate was added to the aqueous sample in the form of a second reactant powder that was substantially free of citric acid.

19. The method of claim 18, wherein: The first reactant powder is added from the first reactant container to the aqueous sample; and The second reactant powder is added from the second reactant container to the aqueous sample.

20. The method of claim 19, wherein: The first reactant container contains only the first reactant powder; and The second reactant container contains only the second reactant powder.

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