Dual-channel semi-quantitative analysis method for particulate iron / manganese concentration in drinking water

Abstract

The present application relates to water quality detection and environmental monitoring technical field, specifically for a kind of for on-site rapid detection of the concentration of particulate iron / manganese in drinking water Dual-channel semi-quantitative analysis method, comprising the following steps: (1) take fixed volume of water sample to be measured;(2) by filtering mode, particulate iron / manganese in water sample is retained by filter membrane, and characteristic color is formed on filter membrane, i.e.filter membrane color layer;(3) dual-channel detection is carried out to filter membrane color layer and filtered water sample respectively;Filter membrane grade concentration range value C1 and colorimetric concentration value C2 are integrated by consistency correction algorithm to eliminate single detection path error, so as to output final particulate iron / manganese concentration, realize the closed-loop detection of dual-channel mutual calibration.The present application is suitable for on-site rapid detection, without complex laboratory equipment, realizes rapid semi-quantitative detection, and significantly reduces the subjective error of traditional manual colorimetric evaluation.

Description

Technical Field

[0001] This invention relates to the field of water quality testing and environmental monitoring technology, specifically a dual-channel semi-quantitative analysis method for rapid on-site detection of particulate iron / manganese concentration in drinking water. Background Technology

[0002] The safety of iron and manganese in drinking water is directly related to people's drinking water health and basic well-being. The safety issues of iron and manganese in drinking water mainly manifest in sensory problems and health risks. Sensory problems caused by iron and manganese at certain concentration levels are currently the most direct and common manifestation, with water exhibiting varying degrees of sensory appearance, from yellowish-brown to black, depending on the concentration range. The main health risk lies in long-term exposure to high concentrations of iron and manganese, which can damage the nervous system, especially for infants, children, the elderly, pregnant women, and vulnerable groups with underlying diseases, who are at higher risk from long-term iron and manganese intake. Currently, the most common manganese safety issue in drinking water is the sensory problem caused by the combined presence of iron and manganese. The limit for manganese in drinking water stipulated in the "Standards for Drinking Water Quality" (GB 5749-2022) and the World Health Organization's (WHO) "Guidelines for Drinking-water Quality" is 0.1 mg / L. However, related studies indicate that the 0.1 mg / L limit for manganese in treated water is not effective in controlling the sensory problems caused by manganese in drinking water. When the manganese concentration in treated water exceeds 0.02 mg / L, certain sensory risks arise.

[0003] Currently, methods for detecting iron / manganese in water are relatively mature. Electrochemical methods, spectrophotometry, atomic absorption spectrometry, and inductively coupled plasma atomic emission spectrometry are all common methods for detecting iron / manganese and other heavy metals. Different detection methods operate on different principles, and their applicable testing scenarios, testing cycles, and detection ranges vary. Due to limitations in the professional requirements of testing personnel, the equipment requirements, and the pretreatment requirements of test samples, the detection of iron / manganese ion concentrations can currently only be performed under laboratory conditions. This poses a challenge to achieving rapid on-site detection and appropriate emergency response measures.

[0004] The color limit stipulated in the "Standards for Drinking Water Quality" (GB 5749-2022) is 15 PCU. Existing cases show that even when the color value of drinking water is within the specified limit of 15 PCU, it can still be detected by users' senses, causing concerns about water safety and potentially leading to widespread public health incidents related to water safety. At low color levels, the human eye is not sensitive to the critical point of color change in water bodies, thus posing challenges to the daily management and emergency response efforts of relevant departments.

[0005] Existing research indicates that manganese in drinking water can transform between dissolved and particulate states. Particulate manganese is typically formed by the oxidation of dissolved manganese, and its concentration changes are strongly correlated with changes in water color. When the water body is free from interference from other color-producing substances, there is a functional correlation between water color and the concentration of particulate manganese. Similarly, particulate iron can also affect water color through a similar mechanism.

[0006] However, there is currently no semi-quantitative analytical method for rapid detection of particulate iron / manganese concentration in water that is highly correlated with color, so as to support relevant departments in carrying out daily management and emergency response work related to color sensory indicators of water safety. Summary of the Invention

[0007] To address the above problems, this invention provides a dual-channel semi-quantitative analysis method for rapid on-site detection of particulate iron / manganese concentration in drinking water.

[0008] A dual-channel semi-quantitative analytical method for rapid on-site detection of particulate iron / manganese concentration in drinking water includes the following steps: (1) Take a fixed volume of water sample to be tested; (2) The particulate iron / manganese in the water sample is retained by the filter membrane through filtration, and a characteristic color is formed on the filter membrane, namely the filter membrane color layer; (3) Perform dual-channel detection on the color development layer of the filter membrane and the filtered water sample respectively: (a) Filter membrane channel detection: The color development layer of the filter membrane is compared with the step-type color-concentration standard scale to obtain the filter membrane grade concentration range C1; (b) Water sample channel detection: The colorimetry of the filtered water sample is measured using a portable colorimeter to obtain the colorimetry value, and the concentration value C2 is calculated based on the preset colorimetry-concentration relationship curve; (4) The concentration range C1 of the filter membrane grade is calibrated and calculated with the colorimetric conversion concentration value C2 to obtain the corrected target concentration C. f ; (5) Output the final semi-quantitative concentration results of the granular iron / manganese ratio C. f .

[0009] The calibration calculation is based on a preset joint calibration relationship between filter membrane grade and colorimetric value. The filter membrane grade concentration range value C1 and the colorimetric converted concentration value C2 are integrated through a consistency correction algorithm to eliminate single detection path error, thereby outputting the final particle iron / manganese concentration.

[0010] Achieve closed-loop detection with dual-channel mutual calibration.

[0011] The calibration calculation method in step (4) includes the following steps: (S1) Definition of interval parameters: The filter membrane detection result C1 represents the concentration range: C1∈[L,U] definition: ; ; C1: The concentration range value obtained from the filter membrane channel detection; C mid : The midpoint of the concentration range; ΔC: the half-width of the concentration range; L: is the lower limit of the concentration range corresponding to the filter membrane sample; U: The upper limit of the concentration range corresponding to the filter membrane sample; S2) Weight function definition: Filter membrane confidence weight: ; Colorimeter weights: ; Where: ω1: is the confidence weight of the filter membrane detection result; ω2: The weight of the colorimeter test results; e is the natural constant, with a value of 2.71828, used to construct the exponential decay function; λ is the interval sensitivity coefficient; β-colorimeter error sensitivity coefficient; σ² represents the colorimeter measurement error; (S3) The calibration calculation model is as follows: ; And satisfy the constraint: C f ∈[L,U] C f : The corrected target concentration obtained through calibration calculation; C2: The concentration value obtained by conversion based on the colorimetric-concentration relationship curve.

[0012] Preferred, Step (1) A fixed volume of water sample to be tested is obtained through a graduated quantitative container to ensure the consistency of the test volume and the repeatability of the colorimetric results.

[0013] Step (2) filtration is achieved through a negative pressure driven filtration process, preferably using a manual evacuation device, such as a manual vacuum pump.

[0014] Step (2) The filter membrane has a pore size of 0.45 μm, preferably a smooth, white PES microporous filter membrane. The characteristic color development on the filter membrane originates from the enrichment of particulate iron / manganese during the filtration process, thereby forming a concentration-related color gradient change.

[0015] After step (2) is completed, let the filter membrane stand for 10 minutes at room temperature and away from direct light to allow the color of the filter membrane to stabilize.

[0016] Step (3) The standard colorimetric card color patch concentration range of the step-type color-concentration standard scale is: Color block 1 represents the concentration of particulate iron / manganese: 0-20 μg / L Color block 2 represents the concentration of particulate iron / manganese: 20-50 μg / L Color block 3 represents the concentration of particulate iron / manganese: 50-100 μg / L Color block 4 represents the concentration of particulate iron / manganese: 100-200 μg / L Color block 5 represents the concentration of particulate iron / manganese: 200-500 μg / L Color block 6 represents the concentration of particulate iron / manganese: >500μg / L.

[0017] In step (3), the portable colorimeter directly measures the color of the water sample collected on site and outputs the color parameters.

[0018] The colorimetric-concentration relationship curve described in step (3) is established by standard concentration gradient sample calibration and is used to convert colorimetric values ​​into concentration values ​​C2.

[0019] Step (3) Water sample channel detection: The colorimetric value of the filtered water sample was measured using a Leici DGB-421F portable colorimeter. The instrument was preheated for 20 minutes. The same water sample was measured in parallel 3 times, and the average colorimetric value was taken.

[0020] This invention addresses water supply scenarios where color increase is primarily caused by particulate iron / manganese. It employs a semi-quantitative detection method based on the fusion correction of filter membrane color development interval information and portable colorimeter measurement point values. Specifically, by establishing a closed-loop correction mechanism between filter membrane color development interval information and portable colorimeter measurement point values, it reduces single-detection errors. This method is suitable for rapid on-site detection, requires no complex laboratory equipment, and achieves rapid semi-quantitative detection, significantly reducing the subjective errors of traditional manual colorimetric assessment. This invention is applicable to various water supply systems. In a specific system scenario, by constructing an interval-point value fusion model, closed-loop correction and semi-quantitative output of detection results are achieved. It can be used in daily management monitoring and emergency response of water supply systems, with a simple detection process and strong applicability to various detection scenarios. Attached Figure Description

[0021] Figure 1 A schematic diagram of the detection process in this invention.

[0022] Figure 2 This is the stepped color-concentration standard scale in this invention.

[0023] Figure 3 This is the colorimetric-concentration relationship curve in this invention. Detailed Implementation

[0024] Establishment of a stepped color-concentration standard scale: (1) Preparation of standard solutions Particulate iron / manganese standard samples with different concentration gradients were prepared. The concentration gradients of the samples were: 0 μg / L (deionized water), 20 μg / L, 50 μg / L, 100 μg / L, 200 μg / L, and 500 μg / L, to cover the concentration range that may occur in actual drinking water.

[0025] (2) Filtration and enrichment treatment Take 200 mL of each of the above standard water samples and filter them under negative pressure through a 0.45 μm PES microporous membrane to enrich particulate iron / manganese on the surface of the membrane.

[0026] (3) Filter membrane color development and fixation After filtration, the filter membrane is left to stand for 10 minutes under standard environmental conditions to allow the particulate iron / manganese to dry naturally and be stably adsorbed on the filter membrane for color development.

[0027] (4) Color block image acquisition Image acquisition of color blocks is performed under uniform standard lighting conditions.

[0028] (5) Tiered color card division After performing colorimetric optimization on the collected color patches, the continuous color variation range was divided into 6 levels: Color block 1 represents the concentration of particulate iron / manganese: 0-20 μg / L Color block 2 represents the concentration of particulate iron / manganese: 20-50 μg / L Color block 3 represents the concentration of particulate iron / manganese: 50-100 μg / L Color block 4 represents the concentration of particulate iron / manganese: 100-200 μg / L Color block 5 represents the concentration of particulate iron / manganese: 200-500 μg / L Color block 6 represents the concentration of particulate iron / manganese: >500μg / L.

[0029] Establishment of the colorimetric-concentration relationship curve: The relationship between colorimetric and particulate manganese was established using a colorimeter (Leici DGB-421F) and inductively coupled plasma mass spectrometry (ICP-MS). Colorimetric detection employed the colorimeter's built-in standard detection method. Total manganese and dissolved manganese were calculated using the results from the ICP-MS, and particulate manganese content was calculated using the difference method. Unless otherwise specified in this instruction, water sample colorimetric measurements were performed at room temperature. Manganese content determination involved nitric acid acidification and filtration through a 0.45 μm filter membrane. Specific procedures are as follows: (1) Sample preparation: Large particles in the water are filtered out. The filtered solution is uniformly yellow. After standing for 2 hours, no significant sedimentation occurs at the bottom of the sample bottle. In subsequent procedures, sample colorimetry and water sample preparation are performed alternately. After the apparent colorimetry of the sample is determined, 10 mL is taken out of the cuvette, and the pH of the water sample is adjusted to <2 with dilute nitric acid. After standing for 24 hours, the digested water sample is filtered through a 0.45 μm microporous membrane for total manganese determination. The remaining 10 mL of water sample in the cuvette is filtered through a 0.45 μm microporous membrane. The filtered solution is transferred to the cuvette to determine the true color. After the determination is completed, the solution is removed from the cuvette, and the pH of the water sample is adjusted to <2 with dilute nitric acid. After standing for 24 hours, the dissolved manganese index is determined. (2) Colorimetric determination: The colorimeter is preheated for 20 minutes. Ultrapure water is placed in the cuvette for colorimetric determination. After the reading stabilizes, the measurement begins. Shake the water sample to be tested well, and then take 20 ml into the cuvette. Wipe the outer surface of the cuvette repeatedly with clean paper until it is clean, without marks, and without water residue. Place the cuvette in the colorimeter. After the absorbance stabilizes, read the apparent color of the water sample. Transfer the filtered liquid into the cuvette. Wipe the outer surface of the cuvette repeatedly with clean paper until it is clean, without marks, and without water residue. Place the cuvette in the colorimeter. After the absorbance stabilizes, read the true color of the water sample. (3) Determination of total manganese and dissolved manganese: Take 5 ml of the treated water sample and use an Agilent 7850 ICP-MS to determine the manganese content in the water sample. The manganese content of the water sample after digestion and filtration is the total manganese content, and the manganese content of the water sample after filtration and digestion is the dissolved manganese content. The difference between the two is the particulate manganese content. (4) Standard Curve Determination: A standard curve of chromaticity value versus particulate manganese content in the water sample under the detection scenario is obtained by linear regression fitting. The measured particulate manganese content of the water sample is substituted into the fitting equation to obtain the theoretical chromaticity value. The relative error between the theoretical chromaticity value and the measured chromaticity value is calculated using the formula:

[0030] A relative error threshold of 15% was set, and data samples with a relative error exceeding 15% in the curve were removed. The fitting was then performed again, the linear relationship between color and particulate manganese content was recalculated, and a color-concentration relationship curve in water was plotted. Figure 3 ).

[0031] Example 1 This embodiment uses particulate manganese in a water sample from the end of a water supply network as the detection target, employing... Figure 2 The illustrated step-by-step color-density standard scale and Figure 3 The colorimetric-concentration relationship curve shown was used for on-site semi-quantitative detection. Figure 3The corresponding linear regression equation is C = 13.59433 * x - 25.78794, R² = 0.95269, where x is the chromaticity value in PCU; C is the particulate manganese concentration converted from the chromaticity value in μg / L. The following detection data are used to illustrate the operation and calculation process of this invention.

[0032] (1) Water sample collection and pretreatment: 500 mL of water sample to be tested was collected, and 200 mL was taken as the water sample for on-site testing after thorough shaking. The water sample was tested at room temperature, and no obvious sedimentation was observed at the bottom of the sample bottle before testing.

[0033] (2) Filter membrane channel detection: 200 mL of the water sample to be tested was filtered under negative pressure through a PES microporous membrane with a pore size of 0.45 μm to trap and enrich particulate manganese in the water sample on the surface of the filter membrane. After filtration, the filter membrane was allowed to stand for 10 min at room temperature, away from direct light, to allow the color development of the filter membrane to stabilize. The colored layer of the filter membrane was then compared with... Figure 2 The result is closest to color block 3 when compared with the step-type color-concentration standard scale shown. Therefore, the concentration range C1 obtained by the filter membrane channel is 50-100 μg / L, that is, L=50μg / L, U=100 μg / L.

[0034] (3) Water sample channel detection: The colorimetry of the filtered water sample was measured using a Leici DGB-421F portable colorimeter. The instrument was preheated for 20 minutes. The same water sample was measured in parallel three times, and the colorimetric values ​​were 6.8 PCU, 7.0 PCU and 7.2 PCU, respectively. The average colorimetric value x was 7.0 PCU. The measurement error parameter σ2 was calculated to be 0.20 based on the sample standard deviation. Substituting x=7.0 PCU into the standard curve, C2=13.59433×7.0-25.78794=69.37 μg / L.

[0035] (4) Dual-channel calibration calculation: Calculate the median value C in the interval based on C1=[50,100]μg / L. mid =(L+U) / 2=75μg / L, interval half-width ΔC=(UL) / 2=25μg / L.

[0036] In this water supply scenario, the following should be taken: The interval sensitivity coefficient λ = 0.02; The colorimeter's error sensitivity coefficient β = 1.0; Then the confidence weight of the filter membrane ω1=e -λ·C =e ^(-0.02×25) =0.6065; The colorimeter weight ω2 = 1 / (1+βσ2) = 1 / (1+1.0×0.20) = 0.8333.

[0037] Substituting the above parameters into the calibration calculation formula, we get...

[0038] The calculation result satisfies C f Constraints ∈ [50, 100] μg / L.

[0039] (5) Result output: The corrected target concentration is rounded according to the semi-quantitative detection accuracy on site, and the particulate manganese concentration in the water sample is found to be approximately 72 μg / L, which is determined to be in the concentration range of 50-100 μg / L. This completes the closed-loop correction between the filter membrane color development range information and the colorimeter measurement point value information.

[0040] (6) Laboratory Validation: Following the aforementioned methods for determining total manganese and dissolved manganese, the same water sample was validated using an Agilent 7850 ICP-MS. The total manganese concentration was measured to be 79.6 μg / L, and the dissolved manganese concentration was 2.8 μg / L. The particulate manganese concentration was obtained as 76.8 μg / L using the difference method. The relative error between the dual-channel semi-quantitative result and the ICP-MS difference method result was |71.74-76.8| / 76.8×100%=6.58%, which is lower than the preset relative error threshold of 15%.

[0041] This embodiment demonstrates that, in a water supply scenario where particulate manganese dominates the color variation of the water sample, this invention can enrich the water sample using a filter membrane on-site and compare it with a standard color chart to define a concentration range. The target concentration within this range is then corrected using a colorimeter channel, yielding a semi-quantitative result on-site that matches laboratory test results. For water samples containing particulate iron or a combination of iron and manganese, corresponding color-concentration scales and color-concentration relationship curves can be established, and the detection and calibration can be completed following the steps described above.

Claims

1. A dual-channel semi-quantitative analysis method for particulate iron / manganese concentration in drinking water, characterized in that, Includes the following steps: (1) Take a fixed volume of water sample to be tested; (2) By filtering, particulate iron / manganese in the water sample is retained by the filter membrane and a color development layer is formed on the filter membrane; (3) Perform dual-channel detection on the color development layer of the filter membrane and the filtered water sample respectively: (a) Filter membrane channel detection: The color development layer of the filter membrane is compared with the step-type color-concentration standard scale to obtain the filter membrane grade concentration range value C1; (b) Water sample channel detection: The colorimetry of the filtered water sample is measured using a portable colorimeter to obtain the colorimetry value, and the concentration value C2 is calculated based on the preset colorimetry-concentration relationship curve; (4) The filter membrane grade concentration range value C1 and the colorimetric conversion concentration value C2 are calibrated and calculated based on the preset filter membrane grade-colorimetric value joint calibration relationship to obtain the corrected target concentration C. f ; The calibration calculation algorithm includes the following steps: (S1) Definition of interval parameters: The filter membrane detection result C1 represents the concentration range: C1∈[L,U] Definition: Interval midpoint ; Interval half width ; C1: The concentration range value obtained from the filter membrane channel detection; C mid : The midpoint of the concentration range; ΔC: the half-width of the concentration range; L: is the lower limit of the concentration range corresponding to the filter membrane sample; U: The upper limit of the concentration range corresponding to the filter membrane sample; (S2) Weight function definition: Filter membrane confidence weight: ; Colorimeter weights: ; Where: ω1: is the confidence weight of the filter membrane detection result; ω2: The weight of the colorimeter test results; e is the natural constant, with a value of 2.71828, used to construct the exponential decay function; λ is the interval sensitivity coefficient; β-colorimeter error sensitivity coefficient; σ² represents the colorimeter measurement error; (S3) The calibration calculation model is as follows: ； And satisfy the constraint: C f ∈[L,U] C f : The corrected target concentration obtained through calibration calculation; C2: The concentration value calculated based on the colorimetric-concentration relationship curve.

2. The method according to claim 1, characterized in that, In step (1), a fixed volume of water sample to be tested is obtained through a graduated quantitative container.

3. The method according to claim 1, characterized in that, The filtration in step (2) is achieved through a vacuum filtration process driven by negative pressure.

4. The method according to claim 3, characterized in that, The filtration in step (2) is achieved by a manual air extraction device.

5. The method according to claim 1, characterized in that, The filter membrane pore size in step (2) is 0.45 μm.

6. The method according to claim 5, characterized in that, The filter membrane in step (2) is a smooth, white PES microporous filter membrane.

7. The method according to claim 1, characterized in that, The standard colorimetric card color patch concentration range of the step-type color-concentration standard scale in step (3) is: Color block 1 represents the concentration of particulate iron / manganese: 0-20 μg / L; Color block 2 represents the concentration of particulate iron / manganese: 20-50 μg / L; Color block 3 represents the concentration of particulate iron / manganese: 50-100 μg / L; Color block 4 represents the concentration of particulate iron / manganese: 100-200 μg / L; Color block 5 represents the concentration of particulate iron / manganese: 200-500 μg / L; Color block 6 represents the concentration of particulate iron / manganese: >500μg / L.

8. The method according to claim 1, characterized in that, In step (3), the portable colorimeter directly measures the color of the water sample collected on site and outputs the color parameters.

9. The method according to claim 1, characterized in that, The chromaticity-concentration relationship curve is established through standard concentration gradient sample calibration and is used to convert chromaticity values ​​into concentration values ​​C2.

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