Method for detecting and quantifying tetrakis(hydroxymethyl)phosphonium sulfate (THPS) in biocide products

Abstract

Disclosed herein are methods for detecting and quantifying tetrakis(hydroxymethyl)phosphonium sulfate (THPS) in a water sample. In the method, a water sample is mixed with a KMnO4 solution to form a mixture. The intensity of the KMnO4 absorption in the mixture at a wavelength of 525 nm is then measured. The measured intensity is normalized by subtracting the background intensity at a wavelength of 650 nm. The presence and concentration of THPS in the water sample can then be determined by comparing the normalized intensity to intensity values of KMnO4 absorption of calibration samples containing KMnO4 and known concentrations of THPS.

Description

Technical Field

[0001] The present disclosure generally relates to the detection and quantification of compounds in biocide compositions. Background of the Invention

[0003] Tetrakis(hydroxymethyl)phosphonium sulfate (THPS) is the main active ingredient in biocide products commonly used in the oil and gas industry for microbial control in water systems. THPS-based biocides are generally considered environmentally friendly because they readily degrade.

[0004] Traditionally, THPS has been detected and quantified using iodine titration or various commercial test kits. For example, the Solvay TOLCIDE Biocides Test kit and the LOVIBOND THPS kit are commonly used commercial test kits. However, these test kits have a limited detection range for THPS (e.g., 0-100 ppm).

[0005] Additionally, in large water pipe networks or other large water systems, after providing a batch of a biocide product at an upstream location, it is difficult to collect water samples at a downstream location for biocide residue measurement using currently available methods and test kits. This is because it is difficult to estimate the travel time of a biocide in a large pipe network due to the complexity of the pipe network (e.g., diameter, branches, etc.) and daily operational changes and fluctuations (e.g., flow rate).

[0006] Therefore, there is a need for effective on-site measurement methods for biocides, and in particular THPS-based biocides, in oil and gas facilities.The present application addresses these and other challenges associated with measuring THPS in water, particularly in the water grid of oil and gas facilities. Summary of the Invention

[0007] In a first aspect, a method for detecting tetrakis(hydroxymethyl)phosphonium sulfate (THPS) in a water sample is provided. In this method, a water sample is mixed with a KMnO4 solution to form a mixture. The intensity of KMnO4 absorption in the mixture at a wavelength of 525 nm is measured. The measured intensity is then normalized by subtracting the background intensity at a wavelength of 650 nm. The presence of THPS in the water sample is then determined by comparing the normalized intensity with the KMnO4 absorption intensity value of a calibration sample containing KMnO4 and a known THPS concentration.

[0008] In another aspect, the water sample is mixed with the KMnO solution for about 2 minutes. In another aspect, the water is fresh water or salt water. In a further aspect, the salt water is Arabian Gulf Seawater.

[0009] In another aspect, a mixture comprises equal volumes of a water sample and a KMnO4 solution. In another aspect, a sensor is used to measure the intensity of KMnO4 absorption in the mixture. In a further aspect, the sensor comprises a 565nm LED and a 650nm LED connected to a Z-flow cell. In a further aspect, the water sample is collected from water flowing in a conduit, and the sensor is an online sensor connected to the water conduit fluid and is configured to perform real-time measurements on the water flowing in the conduit.

[0010] On the other hand, the detection limit of THPS in water samples is about 2 ppm.

[0011] In a second aspect, a method for quantifying tetrakis(hydroxymethyl)phosphonium sulfate (THPS) in water flowing in a pipeline is provided. In this method, a water sample containing THPS from the pipeline is mixed with a KMnO4 solution, so that the THPS in the water sample reacts with the KMnO4 solution. The intensity of KMnO4 absorption in the mixture at a wavelength of 525 nm is measured. The measured intensity is then normalized by subtracting the background intensity at a wavelength of 650 nm. The concentration of THPS in the water sample is determined based on a comparison between the normalized intensity and the KMnO4 absorption intensity value of a calibration sample containing KMnO4 and a known THPS concentration.

[0012] In another aspect, the determined THPS concentration is accurate for water samples having a THPS content of about 2-500 ppm. In another aspect, the water sample comprises a THPS-based biocide. In another aspect, the water sample is mixed with the KMnO4 solution for at least 2 minutes.

[0013] In another aspect, the water is fresh water or salt water. In a further aspect, the salt water is Arabian Gulf Seawater (AGS). In a further aspect, the THPS concentration in AGS has a dynamic range of about 5-1500 ppm.

[0014] In another aspect, a mixture comprises equal volumes of a water sample and a KMnO4 solution. In another aspect, a sensor is used to measure the intensity of KMnO4 absorption in the mixture. In a further aspect, the sensor comprises a 565nm LED and a 650nm LED connected to a Z-flow cell. In a further aspect, the sensor is an in-line sensor connected to a pipeline fluid and configured to perform real-time measurements. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A flow chart showing the steps of a method for detecting and quantifying THPS in a water sample according to one or more embodiments;

[0016] Figures 2A-2B shows a graph showing KMnO4 absorption at 525 nm as a function of THPS concentration in samples of Arabian Gulf Seawater (AGS) and Milli-Q water according to one or more embodiments;

[0017] Figures 3A-3B a schematic diagram illustrating various aspects of an exemplary THPS sensor for use in the methods of the present invention, according to one or more embodiments;

[0018] Figure 4 shows a graph showing normalized measured KMnO4 absorption as a function of approximate THPS concentration (0-1000 ppm) in Arabian Gulf Seawater (AGS) samples containing a THPS-based biocide or pure THPS according to one or more embodiments;

[0019] Figure 5 shows a graph showing normalized measured KMnO4 absorption as a function of approximate THPS concentration (0-200 ppm) in AGS samples containing a THPS-based biocide or pure THPS according to one or more embodiments; and

[0020] Figure 6 An exemplary calibration curve showing KMnO4 absorption at 525 nm as a function of THPS concentration in freshwater and saltwater samples is shown, according to one or more embodiments. DETAILED DESCRIPTION

[0021] By way of overview and introduction, the present application discloses a method for detecting and quantifying tetrakis(hydroxymethyl)phosphonium sulfate (THPS) in a water sample. In one or more embodiments of the method, a water sample containing THPS (or suspected of containing THPS) is mixed with a KMnO4 solution to form a mixture. The intensity of the KMnO4 absorption in the mixture at a wavelength of 525nm is then measured. Once the KMnO4 absorption intensity at 525nm in the mixture is measured, the measured KMnO4 absorption intensity is normalized by subtracting the background intensity at a wavelength of 650nm. The normalized intensity of the KMnO4 absorption measurement is then used to determine the presence and / or concentration of THPS in the water sample by comparing the normalized intensity of the KMnO4 absorption with the KMnO4 absorption intensity value of a calibration sample containing KMnO4 and known THPS concentration.

[0022] These and other aspects of the inventive method are described in more detail below with reference to the accompanying drawings, in which one or more illustrative embodiments and / or arrangements of the method are shown. The method of the present application is not limited in any way to the illustrative embodiments and / or arrangements. It should be understood that the method as shown in the accompanying drawings is merely an exemplary method of the present application, which can be implemented in various forms understood by those skilled in the art. Therefore, it should be understood that any structural and functional details disclosed herein should not be interpreted as limiting the inventive method, but are provided as representative embodiments and / or arrangements for teaching those skilled in the art to implement one or more ways of the inventive method.

[0023] Further, it is to be understood that as used in this application, the term "about," when used in conjunction with a number, refers to any number within 5% of the recited number, inclusive of the recited number.

[0024] Now refer to Figure 1 According to one or more embodiments, a flow chart is provided showing the steps of a method 100 for detecting and quantifying THPS in a water sample. Method 100 begins at step S105, where a water sample is collected. The water sample contains or is suspected of containing THPS or a THPS-containing biocide. The water sample can be a freshwater sample or a saltwater sample, such as Arabian Gulf Seawater (AGS). AGS has a salinity of approximately 57,000 mg / L, which is much higher than the average salinity in the world's oceans (approximately 35,000 mg / L).

[0025] In one or more embodiments, water samples can be collected from existing bodies of water or from a water treatment facility or water distribution network known to contain THPS or THPS-based biocides. Thus, in embodiments where water is collected from a water treatment facility, for example, water can be collected from a pipe in the water treatment facility.

[0026] In step S110, the collected water sample is mixed with a potassium permanganate (KMnO4) solution to form a mixture. In one or more embodiments, equal amounts of the water sample and the KMnO4 solution are mixed together. In one or more embodiments, the KMnO4 solution is a 0.5 to 2.5 millimolar (mM) KMnO4 solution. In at least one embodiment, the KMnO4 solution is a 1-2 millimolar (mM) KMnO4 solution. According to one or more embodiments, the KMnO4 solution may have a pH of approximately 5.0. In at least one embodiment, the KMnO4 solution comprises water that has been deionized to a high degree and purified using a resin filter, such as using Water Purified by a Water Purification System ("MILLI-Q Water"). In at least one preferred embodiment, the KMnO4 solution is 1 mM KMnO4 in MILLI-Q water (pH 5.0).

[0027] The collected water sample and the KMnO4 solution are mixed for a period of time sufficient to allow a reaction between the KMnO4 solution and the THPS in the water sample to occur. According to one or more embodiments, the inventors have determined that the molar ratio of the reaction between THPS and permanganate in this reaction is approximately 2:1, meaning that 2 moles of THPS can decolorize 1 mole of KMnO4. In at least one embodiment, the water sample is mixed with the KMnO4 solution for at least 2 minutes. In one or more embodiments, the water sample is mixed with the KMnO4 solution for approximately 1 to 5 minutes. In one or more preferred embodiments, the water sample is mixed with the KMnO4 solution for approximately 2 minutes.

[0028] In step S115, the absorption of KMnO4 in the water-KMnO4 mixture at a wavelength of 525 nm is measured. As mentioned above, when the water sample and the KMnO4 solution are mixed, THPS present in the water sample reacts with the KMnO4 solution. Therefore, as determined by the inventors, when THPS is present in the water sample, the absorption of the KMnO4 solution obtained after the reaction with THPS at 525 nm is correlated with the THPS concentration in the water sample. Therefore, by measuring the change in the absorption of the KMnO4 solution after the reaction with THPS, the THPS concentration in the water sample (or the THPS concentration in the biocide product in the water sample) can be determined.

[0029] In one or more embodiments of the present methods, the THPS concentration in a water sample can be accurately determined for water samples containing THPS within a range of approximately 5-1500 ppm. In other words, in one or more embodiments, the present methods have a dynamic range for THPS of approximately 5-1500 ppm. This dynamic range is applicable to both freshwater and saltwater samples. This concentration range encompasses conventional biocide treatment and residual concentrations encountered in water treatment facilities and distribution networks in the oil and gas industry.

[0030] In step S120, the KMnO4 absorption measured at a wavelength of 525 nm is normalized by subtracting the background intensity at a wavelength of 650 nm. More specifically, the KMnO4 absorption measured at a wavelength of 525 nm represents the color change of KMnO4 after reaction with THPS. In step S120, the absorption of KMnO4 in the mixture at a wavelength of 650 nm is measured, which corresponds to the background absorption (background intensity) of the solution. The KMnO4 absorption measured at a wavelength of 525 nm is then normalized by subtracting the KMnO4 absorption measured at 650 nm (background intensity). Normalization by subtracting the 650 nm background absorption improves the lower limit of detection of THPS in the method of the present invention.

[0031] At S125, the presence and concentration of THPS in the water sample is determined by comparing the normalized absorbance measurement of KMnO4 at a wavelength of 525 nm with the intensity values ​​of calibration samples containing KMnO4 and known THPS concentrations.

[0032] To begin step S125, a correlation equation (or calibration curve) is established between the THPS concentration in a given water sample and the measured normalized KMnO4 absorption (intensity). As determined by the inventors, the change in absorption (intensity) caused by the reaction of THPS and KMnO4 is correlated with the concentration of THPS in the water sample. Therefore, based on this correlation, a calibration curve is established between the THPS concentration in a given sample and the normalized KMnO4 absorption. As with the absorption measurement of step S120, the absorption of KMnO4 in the sample of the calibration curve is normalized by subtracting the 650nm background absorption. Using the established calibration curve, the concentration of THPS in the water sample is determined by matching the absorption of the KMnO4 normalized measurement at a wavelength of 525nm with its normalized absorption (intensity) value on the curve and the corresponding THPS concentration value on the curve.

[0033] Figures 2A-2B An example graph showing KMnO4 absorption at 525 nm as a function of THPS concentration in samples of Arabian Gulf Seawater (AGS) and Milli-Q water is shown, according to one or more embodiments. AGS is widely used in the Middle East for reservoir injection to maintain pressure in oil reservoirs. AGS is transported through a complex pipeline network for reservoir injection, and microbial activity in AGS is controlled by biocide treatment (e.g., THPS).

[0034] exist Figures 2A-2B In the example of , samples containing 0 to 1000 ppm of THPS were prepared in AGS and Milli-Q water. Equal volumes (1.5 mL) of the THPS-containing sample (both AGS and Milli-Q water) and 1.0 mM KMnO4 (pH 5.0) were mixed and allowed to react for 2 minutes. The permanganate (KMnO4) absorption at 525 nm was then measured and normalized by subtracting the background intensity at 650 nm. Figure 2A shows the KMnO4 absorption at 525 nm as a function of THPS concentration (0-1000 ppm), and Figure 2B Show Figure 2A Magnified version of the 0-200 ppm region of the graph.

[0035] like Figures 2A-2BAs shown in the graph, a linear relationship is established between THPS concentration and KMnO4 absorption. Specifically, according to one or more embodiments, the absorption of KMnO4 exhibits a linear relationship with THPS over a THPS concentration range between approximately 0 and 200 ppm, with a dynamic range of approximately 2-500 ppm. In one or more embodiments, the dynamic range can be extended to approximately 5-1500 ppm of THPS by increasing the concentration of the KMnO4 solution. For example, at 525 nm, when the KMnO4 concentration is 1 mM, the dynamic range is approximately 2-500 ppm. However, at 525 nm, when the KMnO4 concentration is 2 mM, the dynamic range increases to approximately 5-1500 ppm. Figures 2A-2B The results shown in also indicate that the function of THPS concentration as a function of 1 mM KMnO4 absorption at 525 nm is comparable in Milli-Q water samples and AGS samples, and according to one or more embodiments, THPS can be detected at levels as low as 2 ppm and as high as 500 ppm. In at least one embodiment, the dynamic range for detecting THPS in water samples at a KMnO4 concentration of 2 mM at 525 nm is approximately 10-700 ppm. The above dynamic range is applicable to both freshwater and saltwater samples.

[0036] Thus, in one or more embodiments, the detection limit is approximately 2 ppm. In one or more embodiments, the dynamic range of THPS concentration in a sample is approximately 2-500 ppm. Furthermore, in at least one embodiment, the dynamic range of THPS in AGS can be extended to approximately 5-1500 ppm by increasing the KMnO4 concentration from 1 mM to 2 mM.

[0037] Back to Figure 1 After determining the concentration of THPS in the water sample, the method ends at step S130. In at least one embodiment, the steps of the method of the present invention (steps S105-S130) are performed using a sensor. Figures 3A-3B Various aspects of an exemplary THPS sensor 200 for use with the method of the present invention are shown, according to one or more embodiments. Figure 3A The sensor 200 includes a sample reservoir 205 for a water sample containing THPS and a reservoir 210 for a KMnO4 solution. The THPS sensor 200 also includes a first conduit 215 for transferring the water sample containing THPS and the KMnO4 solution from their respective reservoirs to a mixing coil 220. In the mixing coil 220, the water sample containing THPS and the KMnO4 solution are mixed (step S110). After mixing, the mixture is transferred to a flow cell 230 via a second conduit 225. In one or more embodiments, the flow cell 230 is a Z-flow cell.

[0038] Continue to refer Figure 3A and 3B In one or more embodiments, the sensor 200 further includes a 565-nm light emitting diode (LED) 235 and a reference 625-nm LED 236, which are operatively connected to the flow cell 230. In at least one alternative embodiment, the two LEDs 235 and 236 can be replaced with multi-color LEDs. In the flow cell 230, a mixture containing the water sample and the KMnO4 solution is exposed to light emitted by the two LEDs 235 and 236 for absorption measurement.

[0039] According to one or more embodiments, Figure 3B A preferred optical configuration for a Z flow cell is shown, wherein a 565-nm light emitting diode (LED) 235 and a reference 625-nm LED 236 are arranged orthogonally and directed toward a dichroic mirror 237. In such an embodiment, the THPS sensor 200 optimizes the light level coupled into the flow cell by introducing a reference channel (650 nm LED). In one or more embodiments, the Z flow cell is a typical Z flow cell with a Z-shaped fluid path that allows continuous upward flow through the flow cell and minimizes bubble entrapment. When combined with a spectrometer, a light source, and accessories, the Z flow cell allows for rapid analysis of samples by measuring the optical absorption of a fluid moving through a flow injection system. Different optical path lengths and internal volumes in the Z-cell are available depending on the analytical needs. As Figure 3A As shown, the Z-flow cell 230 may include SMA connectors for connection to the optical setup and the microcontroller, respectively. Figure 3B In the preferred optical configuration of the Z-flow cell shown, two LED lights 235, 236 with specific wavelengths (565 nm and 650 nm respectively) are passed through the fluid (KMnO4 and sample mixture) and the absorption is measured by a spectrometer.

[0040] Reference again Figure 3AIn one or more embodiments, the flow cell 230 (e.g., a Z-flow cell) has an absorption path length of approximately 1 cm. As the absorption of KMnO4 is collected by the flow cell 230, the signal is transmitted to a microcontroller 245 (e.g., a printed circuit board [PCB] microcontroller) via a patch cable 240 (e.g., a 1.5 mm patch cable with an SMA connector). A microprocessor platform 250 (e.g., Feather, Arduino technology) can process the analog signal and provide pulses to measure the absorption of KMnO4 (e.g., step S115). After the absorption of KMnO4 has been measured and the concentration of THPS in the sample has been determined, the mixture of the THPS water sample and KMnO4 is removed from the flow cell 230 via a third conduit 255 and can be disposed of as waste.

[0041] In one or more embodiments, the THPS sensor 200 is an online sensor operatively connected to, for example, a water treatment facility or a water distribution network, so that real-time measurements of the THPS in the water treatment facility or the water distribution network can be determined. In one or more embodiments, the sensor 200 can also be configured to transmit measurements (wired or wireless) and data to a control center remote from the sensor 200.

[0042] In at least one embodiment, the absorption measurement can be performed using an instrument other than a sensor. For example, a laboratory-based instrument can be used to measure the absorption of the KMnO4 mixture. Such a laboratory-based instrument can include, for example, a spectrometer or a spectrophotometer. Examples of suitable spectrophotometers are the Mettler Toledo Spectrophotometers UV5 and UV7 and the Konica Minolta Spectrophotometers CM-5 and CM-3600A.

[0043] The above and other aspects of the present method may be further understood through the following examples.

[0044] Example 1

[0045] In this experiment, a biocide product containing approximately 20-40% THPS and 10-20% surfactant was used. The biocide product was diluted in AGS to samples containing approximately 0, 1, 2, 5, 10, 25, 50, 100, 200, 500, and 1000 ppm THPS. Each of these samples was then mixed with an equal volume of 1 mM KMnO4 (pH 5.0) in MilliQ water and allowed to react for approximately 2 minutes. The KMnO4 absorbance at 525 nm was then measured and normalized by subtracting the background intensity at 650 nm. The process was then repeated, but using pure THPS instead of the THPS-containing biocide. A series of samples containing pure THPS (same concentrations as shown above for the biocide product) were then compared to the samples containing the biocide.

[0046] Figure 4 Shown are the normalized absorbance as a function of the approximate THPS concentration in AGS for samples containing THPS biocide. For comparison, Figure 4 Also shown are corresponding samples containing pure THPS. Figure 5 Shown Figure 4 A zoomed-in version of the graph is dedicated to the 0-200 ppm region of interest. Figure 4 and 5 As shown in , KMnO4 absorption is an effective way to measure the THPS content in AGS with a linear range of 0 to 200 ppm, a dynamic range of approximately 2-500 ppm and a limit of detection (LOD) of approximately 2 ppm. Figure 4 and 5 There is a small shift in the values ​​between pure THPS and the THPS-biocide product samples, both of which were diluted in AGS. The most plausible explanation is that the actual THPS content of the biocide product may be lower than the 30% approximation used in the experiments to prepare the THPS-biocide dilutions.

[0047] Example 2

[0048] THPS samples of 0, 1, 4, 16, 64, and 256 ppm were prepared in fresh water, and 1.5 mL aliquots from each sample were transferred to respective reaction vials. 1.5 mL of acidic 0.6 mM KMnO was then added to each reaction vial to allow the THPS and KMnO to react with each other. For each sample, 2 mL was transferred to an absorption cuvette and the absorption measured in the 400-700 nm range. The process was then repeated, but using THPS samples in salt water (seawater) instead of fresh water.

[0049] Figure 6 Exemplary calibration curves for freshwater and saltwater samples are shown in FIG. Figure 6 As shown in the figure, KMnO4 absorption decreases as THPS concentration increases. Therefore, the change in KMnO4 absorption intensity in the mixture is correlated with the THPS concentration in the water sample. Therefore, based on this correlation, a calibration curve was established between the THPS concentration in a given sample and the KMnO4 absorption intensity.

[0050] Although much of the foregoing description is directed to methods for detecting and quantifying THPS in water samples, the methods disclosed herein may be similarly deployed and / or implemented in situations, circumstances, and settings far beyond the ones referenced. It should also be understood that any such implementations and / or deployments are within the scope of the methods described herein.

[0051] It should also be understood that throughout the several figures, similar elements represented by similar numerals in the figures, and not all embodiments or settings require all components and / or steps described and illustrated with reference to the figures. In addition, the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used herein, the singular forms "a", "an", and "the" are also intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that when used in this specification, the terms "comprise", "include", or "have", "contain", "involve" and variations thereof herein specify the presence of the features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or groups thereof.

[0052] It should be noted that the use of ordinal terms such as "first", "second", "third", etc. in the claims to modify claim elements does not itself imply any priority, precedence, or order of one claim element relative to another claim element or the temporal order of the actions of the method, but is merely used as a mark to distinguish one claim element with a specific name from another element with the same name (but using ordinal terms) to distinguish the claim elements.

[0053] It is noteworthy that the above drawings and examples are not meant to limit the scope of the present disclosure to a single implementation, because by some or all of the elements described or illustrated interchangeably, other implementations are possible. In addition, in the case where known components can be used to partially or completely implement some elements of the present disclosure, only those parts necessary for understanding the present disclosure of such known components are described, and detailed descriptions of the other parts of such known components are omitted to avoid confusing the present disclosure. In this specification, the implementation of a single component should not necessarily be limited to other implementations comprising a plurality of identical components, and vice versa, unless otherwise expressly stated herein. In addition, the applicant does not intend to reduce any term in the specification or claims to an uncommon or special meaning, unless clearly stated in this manner. In addition, the present disclosure covers the current and future known equivalents of the known components mentioned herein by way of example.

[0054] The above description of specific implementations will fully reveal the general nature of the present disclosure so that others can easily modify and / or adapt the various applications of such specific implementations without departing from the general concept of the present disclosure by applying the knowledge within the technology of the relevant fields, without the need for excessive experimentation. Therefore, based on the teachings and guidance presented herein, such adaptations and modifications are intended to be within the meaning and scope of the equivalents of the disclosed implementations. It should be understood that the wording or terminology herein is for descriptive and not restrictive purposes, so that the terms or wording of this specification should be interpreted by those skilled in the art based on the teachings and guidance presented herein and in combination with the knowledge of those skilled in the relevant fields. It should be understood that the dimensions discussed or shown in the accompanying drawings are shown according to an example, and other dimensions can be used without departing from the present disclosure.

[0055] The foregoing subject matter is provided by way of illustration only and is not to be construed as limiting. Various modifications and changes may be made to the subject matter described herein without following the exemplary embodiments and applications illustrated and described, and without departing from the true spirit and scope of the invention encompassed by the present disclosure, which is defined by the set of statements in the appended claims and by structures and functions or steps equivalent to those statements.

Claims

1. A method for detecting tetrakis(hydroxymethyl)phosphonium sulfate (THPS) in a water sample, comprising: mixing the water sample with the KMnO4 solution to form a mixture; measuring the intensity of KMnO4 absorption in the mixture at a wavelength of 525 nm; The measured intensity was normalized by subtracting the background intensity at a wavelength of 650 nm; as well as The presence of THPS in the water sample was determined by comparing the normalized intensity with the KMnO 4 absorbance intensity values ​​of calibration samples containing KMnO 4 and known THPS concentrations.

2. The method according to claim 1, wherein The water sample was mixed with the KMnO 4 solution for approximately 2 minutes.

3. The method according to claim 1, wherein The water sample is fresh water or salt water.

4. The method according to claim 3, wherein: The brine is Arabian Gulf sea water.

5. The method according to claim 1, wherein The mixture contained equal volumes of water sample and KMnO4 solution.

6. The method according to claim 1, wherein The intensity of the KMnO4 absorption in the mixture was measured using a sensor.

7. The method according to claim 6, wherein: The sensor comprises a 565 nm LED and a 650 nm LED connected to a Z-flow cell.

8. The method according to claim 6, wherein: The water sample is collected from water flowing in a pipe, and wherein the sensor is an in-line sensor fluidly connected to the water pipe and configured to make real-time measurements of the water flowing in the pipe.

9. The method according to claim 1, wherein The detection limit of THPS in the water sample was approximately 2 ppm.

10. A method for quantifying tetrakis(hydroxymethyl)phosphonium sulfate (THPS) in a water sample flowing in a pipe, the method comprising: mixing a water sample containing THPS from the pipeline with a KMnO4 solution to form a mixture, wherein the THPS in the water sample reacts with the KMnO4 solution; measuring the intensity of KMnO4 absorption in the mixture at a wavelength of 525 nm; Normalizing the measured intensity by subtracting the background intensity at a wavelength of 650 nm; and The concentration of THPS in the water sample was determined based on a comparison between the normalized intensity and the KMnO 4 absorbance intensity values ​​of calibration samples containing KMnO 4 and known THPS concentrations.

11. The method according to claim 10, wherein: For water samples with a THPS content of 2-500 ppm, the determined THPS concentration in the water sample is accurate.

12. The method according to claim 10, wherein: The water sample contained a THPS-based biocide.

13. The method according to claim 10, wherein: The water sample was mixed with the KMnO4 solution for at least 2 minutes.

14. The method according to claim 10, wherein: The water sample is fresh water or salt water.

15. The method according to claim 14, wherein The brine was Arabian Gulf Seawater (AGS).

16. The method according to claim 15, wherein The dynamic range of THPS concentration in AGS is 5-1500 ppm.

17. The method according to claim 10, wherein The mixture contained equal volumes of water sample and KMnO4 solution.

18. The method according to claim 10, wherein The intensity of the KMnO4 absorption in the mixture was measured using a sensor.

19. The method according to claim 18, wherein The sensor comprises a 565 nm LED and a 650 nm LED connected to a Z-flow cell.

20. The method according to claim 18, wherein The sensor is an online sensor fluidly connected to the pipeline and is configured to perform real-time measurements.

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