Method for determining hexavalent chromium in domestic drinking water

Abstract

The invention belongs to the technical field of separation and detection, and particularly relates to a method for determining hexavalent chromium in domestic drinking water. Determining hexavalent chromium in the domestic drinking water by adopting a high performance liquid chromatography-ultraviolet detection method; taking a domestic drinking water sample solution for detection, and quantifying by an external standard method; the detection method comprises the following steps: adopting a Metrosep A Supp4-250 chromatographic column (250 mm * 4.0 mm, 5 m); the column temperature is 40 DEG C; the sample size is 100 L; the flow rate is 0.60 mL / min; and the mobile phase is 9.0 mmol / L Na2CO3. The detector is a DAD; and the detection wavelength is 372 nm. According to methodology verification, the method can be used for determining the hexavalent chromium in the domestic drinking water, is high in specificity, simple in pretreatment operation, high in accuracy, good in precision and stability and high in automation degree, has advantages in detection of large-batch samples, provides a reliable technical means for monitoring the hexavalent chromium in the domestic drinking water, and is suitable for popularization and application. And the practical value is high.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of separation and detection technology, and particularly relates to a method for determining hexavalent chromium in drinking water. BACKGROUND

[0002] Chromium can form various valence compounds, and chromium in water mainly exists in the form of trivalent and hexavalent. A small amount of trivalent chromium is beneficial to the human body, while hexavalent chromium is about 100 times more toxic than trivalent chromium and is considered to be one of the main human carcinogens. A large amount of intake of hexavalent chromium has many hazards, including damage to tissue cells, reduction of hemoglobin concentration, and also causes symptoms such as loss of appetite, abdominal pain, anemia and vomiting, and if long-term intake of hexavalent chromium, it can cause slow bone growth and poor development, and can also cause renal tubular epithelial cells and renal tubular necrosis, and even damage to the kidneys, leading to renal failure and thus harm to life. The "Drinking Water Health Index" promulgated in 2022 also includes hexavalent chromium in the toxicological index of the routine index of drinking water quality, therefore, it is necessary to monitor hexavalent chromium in drinking water.

[0003] At present, the methods for determining hexavalent chromium in drinking water mainly include diphenyl carbonyl hydrazine spectrophotometry, fluorescence spectrophotometry, continuous flow analyzer method, graphite furnace atomic absorption spectrometry, inductively coupled plasma mass spectrometry, inductively coupled plasma emission spectrometry, ion chromatography and high performance liquid chromatography. Among these methods, the diphenyl carbonyl hydrazine spectrophotometry is complicated to operate, needs to add multiple reagents, and uses toxic organic reagent acetone, cannot realize online automatic determination, the fluorescence spectrophotometry is easy to be interfered by ions, the continuous flow analyzer method and the ion chromatography need to be equipped with special instruments (continuous flow analyzer and ion chromatograph) and have limited determination substance range, the graphite furnace atomic absorption spectrometry can only determine total chromium, and the inductively coupled plasma mass spectrometry and the inductively coupled plasma emission spectrometry are expensive in instrument, and cannot be popularized. Therefore, it is urgent to establish a detection method which is simple to operate, strong in specificity, high in sensitivity, can realize online automatic detection on a large number of samples, and is beneficial to popularization and application at the grassroots level. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides a method for determining hexavalent chromium in drinking water.

[0005] The method for determining hexavalent chromium in drinking water is determined by high performance liquid chromatography-ultraviolet detection; the drinking water sample solution is detected by external standard method; the detection method is as follows: Metrosep A Supp4-250 chromatographic column (250 mm*4.0 mm, 5 µm) is used for separation; the column temperature is 25-40 DEG C; the flow rate is 0.60-1.20 mL / min; the mobile phase is 6.0-9.0 mmol / L Na2CO3; the detector is an ultraviolet detector; the drinking water sample solution is filtered through a 0.22 µm microporous filter membrane, and then directly detected by the machine.

[0006] The ultraviolet detection uses a DAD detector.

[0007] Preferably, the flow rate is 0.60 mL / min; the column temperature is 40 DEG C; and the mobile phase is 9.0 mmol / L Na2CO3.

[0008] The drinking water sample is pure water, tap water, mineral water or well water.

[0009] The application also provides the application of the above method in the determination of hexavalent chromium in drinking water.

[0010] Technical effects: (1) the application adopts the principle of ion exchange and the mode of diode array detection, and by using a high performance liquid chromatograph, selecting a suitable chromatographic column and a detection wavelength, and optimizing the composition, flow rate and column temperature of the mobile phase, a high performance liquid-ion exchange chromatography method for determining hexavalent chromium in drinking water is established. The method is used to determine hexavalent chromium in well water, mineral water, tap water and pure water, and no hexavalent chromium is detected. The method has strong specificity, simple pretreatment operation, high accuracy, good precision and stability, high automation degree, and advantages in the detection of a large number of samples, and provides a reliable technical means for monitoring hexavalent chromium in drinking water, and has high practical value.

[0011] (2) the LOD of the detection method is 2 µg / L, the LOQ is 4 µg / L, the sample is directly filtered on the machine, there is no complex pretreatment process, the accuracy, precision and stability are good, the specificity is strong, no toxic and harmful chemical reagents are used, and online automatic sampling can be realized, which has obvious advantages for a large number of samples; compared with inductively coupled plasma mass spectrometry, the instrument is relatively cheap, and is conducive to the popularization and application at the grassroots level. DETAILED DESCRIPTION

[0012] Figure 1 The ultraviolet spectrum of hexavalent chromium.

[0013] Figure 2Chromatograms of control and sample: (a) well water; (b) mineral water; (c) tap water; (d) pure water; (e) chromatogram of control solution.

[0014] Figure 3 Chromatograms of hexavalent chromium in the concentration range of 4.00-1000 µg / L. DETAILED DESCRIPTION

[0016] Agilent 1200 high-performance liquid chromatograph (Agilent, USA); Milli-Q ultrapure water machine (Millipore, USA). Anhydrous Na2CO3 (extra pure, Tianjin Kemeluo Chemical Reagent Co., Ltd.); NaHCO3 (extra pure, Tianjin Guangfu Science and Technology Development Co., Ltd.); hexavalent chromium solution standard material in water (100 mg / L, China Institute of Metrology); quality control samples (378826115, 378864087, Water Environment Monitoring and Evaluation Research Center of the Ministry of Water Resources); tap water from the terminal water of the laboratory building of Hunan Center for Disease Control and Prevention; well water from Baisha ancient well in Changsha; pure water and mineral water were purchased from supermarkets.

[0017] 1.2 Sample preservation and pretreatment The water sample was stored according to the national standard [GB 5750-2023], i.e., sodium hydroxide was added to adjust the pH to 7-9, and the sample was stored in a clean ground hard glass bottle or a clean polyethylene bottle (barrel or bag) with no wear on the inner wall, and the determination was completed within 48 h. The water sample was filtered through a 0.22 µm microporous filter membrane and directly loaded onto the machine.

[0018] 1.3 Preparation of standard solution The hexavalent chromium solution standard material in water was diluted with water in stages to obtain standard series solutions with concentrations of 4.0, 8.0, 10.0, 50.0, 100.0, 500.0, and 1000.0 µg / L, respectively.

[0019] 1.4 Liquid chromatography conditions Chromatographic column: Metrosep A Supp4-250 chromatographic column (250 mm×4.0 mm, 5 µm); column temperature: 40℃; injection volume: 100 µL; flow rate: 0.60 mL / min; mobile phase: 9.0 mmol / L Na2CO3. Detector: DAD; detection wavelength: 372 nm.

[0020] 2 Results and discussion

[0021] 2.1.1 Selection of detection wavelength ​The standard solution of hexavalent chromium (1.00 mg / L) was scanned under ultraviolet band to obtain the ultraviolet absorption graph of hexavalent chromium, as shown in Figure 1 . It can be seen from Figure 1 that the maximum absorption wavelength of hexavalent chromium is 372 nm. Since the DAD detector can provide the ultraviolet absorption graph of hexavalent chromium, it is more specific and more accurate in qualitative analysis than the conductivity detector of ion chromatography.

[0022] 2.1.2 Selection of chromatographic column In this study, three chromatographic columns, Metrosep A Supp4-250, Metrosep A Supp5-250 and Metrosep A Supp7-250, were investigated, and the results are shown in Table 1. It can be seen from Table 1 that the peak height of Metrosep A Supp4-250 chromatographic column is the highest, the peak area is the largest, the retention time is moderate, and the pressure is the smallest; the retention time of Metrosep A Supp5-250 and Metrosep A Supp7-250 chromatographic columns is too long, which is not conducive to large-scale analysis, therefore, Metrosep A Supp4-250 is selected as the analysis chromatographic column.

[0023] Table 1 Selection of chromatographic column

[0024] 2.1.3 Selection of mobile phase Through preliminary screening of the previous experiments, Na2CO3 and NaHCO3 are selected as the components of the mobile phase.

[0025] When the flow rate is 1.0 mL / min, the concentrations of Na2CO3 and NaHCO3 in the mobile phase are investigated. With the increase of the concentration of Na2CO3, the peak height and peak area also gradually increase, and when the concentration of Na2CO3 is 10 mmol / L, the peak shape is a front peak; at the same time, compared with 5.0 mmol / L Na2CO3+1.7 mmol / L NaHCO3, the peak area is large and the peak height is low; compared with 9.0 mmol / L Na2CO3, there is no advantage in peak height and peak area, and the results are shown in Table 2. Considering the convenience of preparing the mobile phase, it is more convenient to prepare a component of the mobile phase, therefore, 9.0 mmol / L Na2CO3 is selected as the mobile phase.

[0026] Table 2 Investigation of mobile phase

[0027] 2.1.4 Selection of column temperature Since the temperature of Metrosep A Supp4-250 chromatographic column is in the range of 20-60℃, and the column temperature of 20℃ is not conducive to control, and the higher column temperature will affect the service life of the chromatographic column, therefore, the column temperature in the range of 25-50℃ is investigated, and the peak height is the highest at 40℃, and the peak shape is asymmetric at 50℃, and the peak height is the lowest, and the results are shown in Table 3. Therefore, the column temperature is selected as 40℃.

[0028] Table 3 Selection of column temperature

[0029] 2.1.5 Selection of flow rate The flow rate is investigated in the range of 0.60-1.20 mL / min, and with the increase of the flow rate, the peak height gradually decreases, and the pressure gradually increases, and the results are shown in Table 4. Considering that the retention time will continue to increase if the flow rate continues to decrease, in order to improve the analysis speed, therefore, the flow rate is selected as 0.60 mL / min.

[0030] Table 4 Selection of flow rate

[0031] Example 2: Experiment of specificity of the method of the application The method under item 1.4 described in Example 1 is tested, and the chromatogram of the standard solution of 1.00 mg / L hexavalent chromium is shown in (e) of Figure 2 , the theoretical plate number is 7299, and the tailing factor is 0.95, at this time, the chromatographic peak is sharp and symmetrical, and the chromatograms of the four kinds of drinking water, i.e. well water, mineral water, tap water and pure water are shown in (a) of Figure 2 , (b) of Figure 2 , (c) of Figure 2 , (d) of Figure 2 , it can be seen that there is no impurity interference before and after the hexavalent chromium in the chromatograms of well water, mineral water, tap water and pure water, which can meet the analysis requirements.

[0032] Comparative Example 1: Comparison with the reported method At present, the methods for determining hexavalent chromium in drinking water mainly include diphenyl carbonyl hydrazine spectrophotometry [9] , fluorescence spectrophotometry

[10] , continuous flow analyzer method

[11] , graphite furnace atomic absorption spectrometry

[12] , inductively coupled plasma mass spectrometry

[13] , inductively coupled plasma emission spectrometry [5] , ion chromatography

[14] , high performance liquid chromatography [15-16] and the like. Among these methods, Hu Yan [9]The operation of the diphenyl carbonyl dihydrazine spectrophotometric method is cumbersome, requires the addition of multiple reagents, and uses toxic organic reagent acetone, which is harmful to the environment and the health of the analyst, and cannot realize online automatic determination, and has no advantage for the determination of a large number of samples.

[10] The fluorescence spectrophotometric method is easily interfered by ions, and needs to add a pH buffer solution to control the pH value of the solution, the reaction conditions are harsh, and it also cannot realize online automatic determination, and has no advantage for a large number of samples; Bai Siyu

[11] The continuous flow analyzer method needs to be equipped with a continuous flow analyzer special instrument, and needs to prepare a diphenyl carbonyl dihydrazine solution, and only determines tap water samples; Xue Xiaofang

[14] The ion chromatography method needs to be equipped with an ion chromatograph special instrument, and also only determines tap water samples; Zhang Xiaowei

[12] The graphite furnace atomic absorption spectrometry method can only determine total chromium, and cannot distinguish the form of chromium, that is, cannot distinguish between trivalent chromium and hexavalent chromium, so it cannot determine the content of hexavalent chromium; Wang Jinhua

[13] The inductively coupled plasma mass spectrometry method and Chen Bin [5] The inductively coupled plasma emission spectrometry method needs expensive instruments and cannot be popularized; Zhou Tanchun

[15] The high performance liquid chromatography method needs to prepare a diphenyl carbonyl dihydrazine solution, and the sample needs to be derivatized before determination, and the pretreatment is relatively cumbersome; Ling Yingru

[16] The mobile phase of the high performance liquid chromatography method is 120 mmol / L ammonium sulfate 10% ammonia solution, which needs two components.

[0033] Therefore, it is urgent to establish a detection method that is simple to operate, has simple mobile phase components, strong specificity, high sensitivity, can realize online automatic detection of a large number of samples, and is beneficial to the popularization and application of primary units.

[0034] Reference: [5] Chen Bin, Han Shuanglai. Online ion exchange-ICP-OES determination of trace hexavalent chromium in water [J]. China Environmental Monitoring, 2014, 30(2): 95-98. [9] Hu Yan. Method verification of spectrophotometric determination of hexavalent chromium in drinking water [J]. China Standardization, 2024(3): 215-219.

[10] Yu Qian. Research on the determination of chromium (VI) by roxithromycin fluorescence spectrophotometry [J]. Journal of Hunan City University, 2014(1): 49-51.

[11] Bai Siyu, Wang Shuo, Sun Lingli. Application of SKALAR SAN + + 5 block continuous flow analyzer in monitoring of hexavalent chromium in water quality [J]. China Health Inspection Journal, 2022, 32(10): 1179-1181, 1186.

[12] Zhang Xiaowei, Qu Ning, Wu Xiaofang. Determination of hexavalent chromium in drinking water by graphite furnace atomic absorption spectrometry [J]. Chinese Journal of Public Health, 2004, 20(12):1498-1499.

[13] Wang Jinhua, Fan Siyi. Determination of lead, manganese, chromium and aluminum residues in drinking water by inductively coupled plasma mass spectrometry [J]. Energy and Environment, 2020(2):71-72.

[14] Xue Xiaofang, Wu Yan, Chen Nan, et al. Simultaneous determination of hexavalent chromium and perchlorate in drinking water by ion chromatography [J]. Liaoning Chemical Industry Journal. Engineering, 2025, 54(1):180-185.

[15] Zhou Tanchun, Wang Hui, Zhou Peng, et al. Determination of hexavalent chromium in drinking water and liquor by high performance liquid chromatography [J]. Food Science and Technology, 2021, 46(6):278-282.

[16] Ling Yingru, Zhang Hao, Ji Wenliang. Determination of hexavalent chromium in drinking water by high performance liquid chromatography [J]. Jiangsu Preventive Medicine, 2021, 32(2):127-129

[0035] The methodological evaluation of the detection method of the present invention as described in Example 1 was carried out.

[0036] 3. Methodological Validation

[0037] Following the chromatographic conditions described in section 1.4 of Example 1, the prepared series of standard solutions were injected into the liquid chromatograph for analysis. The horizontal axis represents the mass concentration of the standard. X (µg / L), with the vertical axis representing the peak area. Y Perform linear regression, with the method detection limit (LOD) being equal to the signal-to-noise ratio (SNR). S / N The concentration at which the signal-to-noise ratio is equal to 3 is the method limit of quantitation (LOQ) of the signal-to-noise ratio (SNR). S / N The concentration of hexavalent chromium was equal to 10. Results showed that hexavalent chromium ranged from 4.00 to 1000 µg / L (see...). Figure 3 The linear relationship is good within the range of ), and the linear equation is: Y =0.8995 X +0.0272, r =0.9999. The method's LOD is 2 µg / L, and LOQ is 4 µg / L.

[0038] 3.2 Stability of the reference standard Hexavalent chromium standard solutions in water with concentrations of 50 and 500 µg / L were determined six times each. The RSD values ​​for retention time and concentration were 0.02%–0.03% and 0.45%–0.62%, respectively. The stability of these solutions was also investigated. Measurements were taken after standing at room temperature for 0, 2, 4, 6, 8, 12, 24, and 48 hours. The RSD value for the concentration of hexavalent chromium standard solution in water after 48 hours was 0.63%–0.74%. The results indicate that the standard solutions showed good stability within 48 hours, and the instrument repeatability was good.

[0039] 3.3 Accuracy and Precision Spiked recovery experiments were conducted on well water, mineral water, tap water, and purified water using a three-level, six-parallel approach (see Table 5). The results showed that at spiked levels of 10.00, 100.0, and 800.0 µg / L, the average recoveries of hexavalent chromium in these samples ranged from 92.0% to 109.8%, with relative standard deviations (RSD, n=6) of 0.42% to 0.95%. This indicates that the method has good recovery and high accuracy, and can be used to determine the hexavalent chromium content in drinking water.

[0040] Table 5. Content, spiked recovery rate, and relative standard deviation of hexavalent chromium in actual samples (n=6)

[0041] 2.4 Quality Control The method was used to determine hexavalent chromium in water control samples. The absolute errors of the results from the labeled values ​​were 1.93% and 1.17%, respectively.

[0042] Example 4: Actual Sample Testing The method described in Example 1 was used to determine the hexavalent chromium content in well water, mineral water, tap water, and purified water. The results showed that none of the four types of drinking water contained hexavalent chromium, meeting the requirement of GB 5749-2022 "Standards for Drinking Water Quality" that the hexavalent chromium content is below 0.05 mg / L.

[0043] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Obviously, other related modifications can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for determining hexavalent chromium in drinking water, characterized in that: Hexavalent chromium in drinking water was determined by high performance liquid chromatography-ultraviolet detection. Drinking water samples were analyzed, and quantification was performed using the external standard method. The detection method was as follows: separation was performed using a Metrosep A Supp4-250 column (250 mm × 4.0 mm, 5 µm); column temperature: 25–40℃; flow rate: 0.60–1.20 mL / min; mobile phase: 6.0–9.0 mmol / L Na2CO3; detector: ultraviolet detector.

2. The method according to claim 1, characterized in that: Drinking water sample solutions were filtered through a 0.22 µm microporous membrane and then directly tested on the instrument.

3. The method according to claim 1, characterized in that: The ultraviolet detection uses a DAD detector.

4. The method according to claim 3, characterized in that: The detection wavelength of the ultraviolet detector is 372 nm.

5. The method according to claim 1, characterized in that: The flow rate was 0.60 mL / min.

6. The method according to claim 1, characterized in that: The column temperature is 40℃.

7. The method according to claim 1, characterized in that: The mobile phase was 9.0 mmol / L Na2CO3.

8. The detection method according to claim 1, characterized in that: The drinking water samples were purified water, tap water, mineral water, or well water.

9. The application of the method according to any one of claims 1-8 in the determination of hexavalent chromium in drinking water.

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