Method for detecting content of methylthio arsenic compound in water sample

Abstract

The invention relates to the technical field of detection of methyl arsenic sulfide, in particular to a method for detecting the content of a methyl arsenic sulfide compound in a water sample. According to the detection method, by establishing a standard curve, the molar concentrations of non-standard compounds DMMAV and DMDDTAV which are difficult to measure are transduced into peak areas which are easy to measure through the standard curve, and specifically, the peak area result of the HPLC-AFS is converted into the molar concentration of each methyl thioarsenic compound through each standard curve. Instruments required by the detection method are low in price, the operation cost is low, the operation is simple and convenient, the controllability and the repeatability are good, and a sample can be detected only through simple filtration. Meanwhile, the obtained compound content and purity information is high in accuracy, the data repeatability is good, a traditional measurement method can be effectively replaced, the detection cost is reduced, the detection efficiency is improved, and the problem of accurate analysis of the purity of DMMAV and DMDAV finished products in most laboratories is successfully solved.

Description

Technical Field

[0001] The invention relates to the technical field of methylthioarsenic detection, and in particular to a method for detecting the content of methylthioarsenic compounds in a water sample. Background Art

[0002] Arsenic (As) is an important pollutant in aquatic ecosystems worldwide and is widely present in freshwater and marine environments. Arsenic has certain bioaccumulation and biotoxicity, posing a serious threat to human health. Arsenic metabolites are diverse, the sample matrix is ​​complex, and the metabolic intermediates are unstable. Thioorganoarsenic compounds are a newly discovered class of arsenic metabolites, such as dimethylthioarsenic acid (DMMTA). V ) is as toxic as the more toxic arsenite, and dimethylarsenic acid (DMA V ), dimethylthioarsenic acid (DMMTA V ) and dimethyl dithioarsenic acid (DMDTA V ) These three thio-organoarsenic compounds can transform into each other.

[0003] In view of this, it is of great significance to conduct in-depth research on the physicochemical properties, health effects and toxicity mechanisms of thioarsenic compounds. Due to the poor stability of thioarsenic compounds and the lack of commercial standard products, laboratory synthetic samples are often used for subsequent experiments in scientific research. The high performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-IPC-MS) detection method is currently widely used. The steps of this method usually include sample preparation, chromatographic separation and mass spectrometry detection; however, this method has obvious defects. On the one hand, the cost of the instruments and equipment used in this method is high and the detection fee is expensive, which makes it difficult for many laboratories to afford it; on the other hand, the samples to be tested need to undergo a tedious process of removing salt ions, which is complicated and time-consuming.

[0004] Therefore, an efficient detection method for thiomethylarsenic is urgently needed to accurately analyze the unlabeled compound DMMTA. V and DMDTA V It can improve the purity of finished products, reduce testing costs, simplify operating procedures, and improve testing efficiency, so that it can be popularized and applied in various laboratories. Summary of the invention

[0005] The present invention aims to overcome the defect of the prior art that it relies on expensive equipment, and provides a method for detecting the content of methylthioarsenic compounds in a water sample to overcome the above defect.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for detecting the content of methylthioarsenic compounds in a water sample, comprising:

[0008] S1.DMA V Establishment of standard curve: prepare multiple groups of DMA with different molar concentrations V Solution, each group of DMA V The solutions were respectively fed into HPLC-AFS, and multiple groups of DMA were found according to the retention time matching method. V Peak and calculate the corresponding peak area value, draw DMA V Standard curve between peak area and molar concentration;

[0009] S2.DMDTA V Establishment of standard curve: prepare multiple groups of DMA with different molar concentrations V solution, and then each group was added with Na2S solution at a molar ratio of As:S of 1:500, and multiple groups of DMDTA were obtained through sulfidation reaction. V Solution, each group of DMDTA V The solutions were respectively put into HPLC-AFS, and multiple groups of DMDTA were found according to the retention time matching method. V Peak and calculate the corresponding peak area value, draw DMDTA V Standard curve between peak area and molar concentration;

[0010] S3.DMMTA V Establishment of standard curve:

[0011] S3.1 Get DMA V The sample is dissolved in water to obtain DMA with a molar concentration of Ma mol. V The solution was then added with Na2S solution at a molar ratio of As:S of 1:100, and DMMTA was obtained through sulfidation reaction. V A mixed solution;

[0012] S3.2 will contain DMMTA V The mixed solution enters HPLC-AFS detection: DMDTA is found according to the retention time matching method V The peak area was calculated and substituted into the DMDTA obtained by S2. V Standard curve to obtain DMDTA V The molar concentration is Mb mol; DMA is found by retention time matching method V The peak area is calculated and substituted into the DMA obtained by S1. V Standard curve obtained by DMA V The molar concentration is Mc mol;

[0013] S3.3 Calculate the DMMTA content as in formula (1) V DMMTA in the mixed solution V The molar concentration is Md mol,

[0014] Md=Ma-Mb-Mc (1);

[0015] S3.4 Dilute DMMTA in S3.3 V The molar concentration of DMMTA is Md mol V Mixed solutions of different DMMTA groups were obtained. V Molar concentration of DMMTA V The mixed solution was used to obtain DMMTA of each group by HPLC-AFS. V Peak area value corresponding to the peak, plot DMMTA V Standard curve between peak area and molar concentration;

[0016] S4. The sample solution containing various methylthioarsenic compounds is put into HPLC-AFS, and DMA is separated and found according to the retention time matching method. V Peak, DMDTA V Peak and DMMTA V Peak, calculate DMA V Peak, DMDTA V Peak and DMMTA V The peak area value corresponding to the peak was obtained using DMA obtained by S1 V The standard curve determines the DMA in the sample solution to be tested V Concentration, DMDTA obtained using S2 V The standard curve determines the DMDTA in the sample solution to be tested V Concentration, DMMTA obtained using S3 V The standard curve determines the DMMTA in the sample solution to be tested V concentration.

[0017] This application uses high performance liquid chromatography-atomic fluorescence spectrometry (HPLC-AFS) to establish DMA V Standard curve, DMDTA V Standard curve and DMMTA V The standard curve is used to determine the unlabeled compound DMMTA, which is difficult to measure. V and DMDTA V The molar concentration of DMMTA is converted into an easily measurable peak area through the standard curve. The conversion process is less affected by errors, so the obtained results are highly accurate and can solve the problem of DMMTA. V and DMDTA V The purity detection problem of finished products. In addition, the cost of HPLC-AFS instrument is low, which is about one tenth of the price of HPLC-IPC-MS instrument. It can effectively replace the traditional measurement method and reduce the detection cost.

[0018] Among them, in DMMTA V The establishment of standard curve is based on DMA V 、DMDT V and DMMTA V The conversion relationship between them. DMA V Sulfurized with DMMTA V As an intermediate, it eventually leads to DMDTA V conversion; therefore DMMTA V The solution often also contains DMA V 、DMDT V In this process, the molar concentration of arsenic is fixed, and arsenic exists in different forms, such as DMA. V Morphology, DMMTA V Morphology or DMDTA V The molecular formula of these three forms contains only one arsenic, so the molar concentration of each form is equal to the molar concentration of arsenic. The applicant uses this relationship to fix the initial DMA V Arsenic molar concentration of solution, using DMA V Standard curve and DMDTA V DMMTA was calculated from the standard curve V DMA in solution V Impurities and DMDTA V Impurity content, using initial DMA V Arsenic molar concentration of solution minus DMA V Impurities and DMDTA V Impurity content DMMTA V DMMTA in solution V The specific molar concentration of

[0019] Preferably, in S2, DMDTA V After the solution enters HPLC-AFS, only one peak appears, and DMDTA V After the solution entered ESI-TOF-MS, a characteristic peak with a mass-to-charge ratio of 169 was detected.

[0020] Due to DMDTA V For DMA V The final product under sulfurization conditions, so when HPLC-AFS detects only one peak, it may be DMDTA V At this time, when the electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS) detected a characteristic peak with a mass-to-charge ratio of 169, DMDTA was successfully synthesized. V Solution.

[0021] Preferably, S3.1 contains DMMTA VAfter the mixed solution entered HPLC-AFS, three peaks appeared, and DMMTA V After the solution entered ESI-TOF-MS, a characteristic peak with a mass-to-charge ratio of 153 was detected.

[0022] Due to DMMTA V For DMA V The intermediate product under the sulfurization condition, so HPLC-AFS will detect three peaks, matching DMA according to the retention time method V and DMDTA V Substance, the remaining peak type is DMMTA V When ESI-TOF-MS detected a characteristic peak with a mass-to-charge ratio of 153, DMMTA was successfully synthesized. V of mixed solution.

[0023] Preferably, in S1 to S4, the detection conditions of HPLC are as follows: chromatographic column: Eclipse Plus C18 column, 3.5 μm, 4.6 mm×250 mm; flow rate: 1 mL / min; injection volume: 20 μL; 20 mM ammonium dihydrogen phosphate (pH=3) as the mobile phase, and the elution procedure is: the volume of the mobile phase is 100%.

[0024] The applicant found in the actual experiment that not all chromatographic columns and mobile phases can completely separate DMA V Peak, DMDTA V Peak and DMMTA V When the DMA separated under the above HPLC detection conditions is V Peak, DMDTA V Peak and DMMTA V The peak shape is more complete and the final measured result is more accurate.

[0025] Preferably, in S1 to S4, the specific method of using the retention time matching method to identify the peak is: the peak corresponding to the retention time of 2.6 to 3.1 min is DMA V The peak with retention time of 3.3 to 4.1 min is DMDTA V The peak with retention time of 6.2-7.3min is DMMTA V peak.

[0026] Preferably, in S1 to S4, the detection conditions of AFS are: carrier: 7% HCl aqueous solution; reducing agent: 5% NaOH + 20% NaBH4 aqueous solution; main current: 60mA; auxiliary current: 30mA; negative high voltage: 300V; carrier gas: 300mL / min; shielding gas: 900mL / min; atomizer height: 8mm; peristaltic pump: 60r / min.

[0027] Preferably, in S1 to S4, the detection conditions of ESI-TOF-MS are as follows: chromatographic column: Eclipse Plus C18, 3.5 μm, 4.6 mm×250 mm; flow rate: 1 mL / min; injection volume: 20 μL; 0.1% formic acid as mobile phase A, acetonitrile as mobile phase B, and the elution procedure: the volume of the mobile phase A is 90%, and the volume of the mobile phase B is 10%; ion mode: negative ion mode.

[0028] Preferably, the detection accuracy of the detection method is not affected by the salt ion concentration.

[0029] Preferably, the relative error of the detection method is within 4.5%.

[0030] Therefore, the present invention has the following beneficial effects:

[0031] (1) The present application provides an effective morphological qualitative and concentration quantitative detection method for methylthioarsenic compounds using HPLC-AFS, which effectively separates various forms of methylthioarsenic compounds and obtains their corresponding molar concentrations.

[0032] (2) This application uses DMA V 、DMDT V and DMMTA V DMMTA V Standard curve to solve DMMTA V Problems with testing cannot be directly identified.

[0033] (3) This application establishes a standard curve to determine the unstandardized compound DMMTA which is difficult to measure V and DMDTA V The molar concentration is converted into an easily measurable peak area through a standard curve, and the conversion process is less affected by errors, so the results obtained are highly accurate.

[0034] (4) This application uses a special HPLC column and a special HPLC mobile phase to completely separate DMA V 、DMDT V and DMMTA V , thereby improving the accuracy of the detection method.

[0035] (5) The detection method provided by this application requires low-priced instruments, low operating costs, simple operation, good controllability and repeatability, and the sample can be detected by simple filtration. At the same time, the obtained compound content and purity information are highly accurate, and the data repeatability is good. It can effectively replace traditional measurement methods, reduce detection costs, and improve detection efficiency. It successfully solves the problem of DMMTA without a standard compound in most laboratories. V and DMDTA V The problem of accurate analysis of the purity of finished products. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is the synthetic sample DMMTA in Example 1 V and DMDTA V Electrospray ionization time-of-flight mass spectrometry.

[0037] Figure 2 The mixed standard solution of different arsenic forms and DMMTA in Example 1 V and DMDTA V Comparison of chromatographic results of synthetic sample mother liquors.

[0038] Figure 3 is the DMA in Example 1 V 、DMMTA V 、DMDT V Standard curve of peak area-molar concentration.

[0039] Figure 4 It is a comparison chart of the chromatographic results of the mixed standard solutions of different arsenic forms in Example 2 with and without the presence of borate.

[0040] Figure 5 It is a comparison chart of chromatographic results under different HPLC detection conditions. DETAILED DESCRIPTION

[0041] The present invention is further described below in conjunction with specific embodiments. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following description are generally only embodiments of a part of the present invention, rather than all embodiments. Therefore, based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work should fall within the scope of protection of the present invention.

[0042] Example 1

[0043] Step 1: Configuration of actual samples:

[0044] Accurately weigh DMA VThe standard sample was added to the ultrapure water solution and placed in an ultrasonic cleaner for slight sonication to dissolve the powder completely. A mother solution containing 10 μM total arsenic concentration was prepared and divided into three parts, one of which was used as DMA. V The other two were added with different concentrations of Na2S solution, so that the concentration of S(-II) in the solution was 1mM and 5mM, respectively, and mixed under argon atmosphere for 24h to obtain DMMTA V and DMDTA V Synthesize sample stock solution.

[0045] Step 2: Qualitative identification of synthesized arsenic species using ESI-TOF-MS:

[0046] DMMTA prepared in step 1 V and DMDTA V The synthetic sample mother solution was tested on an ESI-TOF-MS device to determine the species type (ESI-TOF-MS operating parameters are shown in Table 1). The mass-to-charge ratio was used to determine whether the synthesis of DMMTA was successful. V Mixed solution and DMDTA V of standard solution.

[0047] observe Figure 1 It can be seen that DMMTA V A characteristic peak with a mass-to-charge ratio of 153 appeared in the mother liquor of the synthetic sample. V A characteristic peak with a mass-to-charge ratio of 169 appeared in the mother liquor of the synthetic sample, and it was preliminarily determined that the synthesized product contained DMMTA. V Mixed solution and DMDTA V of standard solution.

[0048] Table 1 ESI-TOF-MS operating parameters

[0049] Pillar Eclipse Plus C18(3.5μm,4.6mm×250mm) Mobile phase 90% A phase: 0.1% formic acid in water; 10% B phase: acetonitrile Flow rate 1mL / min Injection volume 20μL Duration 10min Ion mode Negative ion mode

[0050] Step 3: Separate and analyze various arsenic forms in the two synthetic samples using HPLC-AFS:

[0051] DMMTA prepared in step 1 V and DMDTA V Synthetic sample stock solution and DMA V The standard solution was diluted with ultrapure water to 5 μM of the sample to be tested. V Standard solution, diluted DMMTA V and DMDTA V The sample mother solutions were synthesized and fed into HPLC-AFS equipment to determine the arsenic forms.

[0052] Instruments and equipment:

[0053] UltiMate 3000 liquid chromatograph (Thermo Scientific);

[0054] AFS-230E dual-channel atomic fluorescence spectrometer (Beijing Haiguang);

[0055] The operating parameters of the UltiMate 3000 liquid chromatograph and AFS-230E dual-channel atomic fluorescence spectrophotometer are shown in Tables 2 and 3:

[0056] Table 2 UltiMate 3000 HPLC operating parameters

[0057] Pillar Eclipse Plus C18(3.5μm,4.6mm×250mm) Mobile phase 20 mM ammonium dihydrogen phosphate aqueous solution, pH = 3 Flow rate 1mL / min Injection volume 20μL Duration 10min

[0058] Table 3 AFS-230E dual-channel atomic fluorescence spectrometer operating parameters

[0059]

[0060]

[0061] Figure 2 DMMTA V and DMDTA V Synthetic sample stock solution and DMA V Comparison of the chromatogram results of the standard solution. By comparing the retention time, it can be seen that the retention time of 2.6 to 3.1 minutes is DMA V Peak shape, 3.3~4.1min is DMDTA V Peak shape, 6.2~7.3min is DMMTA V Peak shape, DMDTA V The synthesized sample is pure DMDTA V Substances. Among them, DMMTA V Three peaks appeared in the mother liquor of the synthetic sample, corresponding to DMA V Peak, DMDTA V Peak and DMMTA V Peak, combined Figure 1 The results can confirm that DMMTA was successfully synthesized. V Mixed solution; DMDTA V Only one peak appeared in the mother liquor of the synthetic sample, corresponding to DMDTA V Peak, combined Figure 1 The results can confirm that DMDTA was successfully synthesized. V Standard solution. DMMTA V Synthetic samples contain DMA V and DMDTA V Impurities, calculated by subtracting DMA from total arsenic concentration VImpurity concentration and DMDTA V The concentration of impurities can be used to calculate DMMTA V The molar concentration of .

[0062] Step 4: Establish a standard curve:

[0063] DMA in step 1 V The standard solution was diluted with ultrapure water to obtain DMA with concentrations of 0.625 μM, 1.25 μM, 2.5 μM, 3.75 μM, 5 μM, and 6.25 μM. V The solution was tested in HPLC-AFS equipment and DMA was drawn. V Standard curve of peak area-molar concentration.

[0064] DMDTA in step 1 V Synthetic sample mother solution (DMDTA V The standard solution was diluted with ultrapure water to obtain DMDTA with concentrations of 1.25 μM, 3.125 μM, 5 μM, 6.25 μM, and 9.375 μM. V The solution was tested in HPLC-AFS equipment and DMDTA was drawn. V Standard curve of peak area-molar concentration.

[0065] DMMTA in step 1 V Synthetic sample stock solution (DMMTA V The mixed solution was diluted with ultrapure water to obtain DMMTA with total arsenic concentrations of 6.25 μM, 12.5 μM, 18.75 μM, 25 μM, and 31.25 μM. V The solution was tested by HPLC-AFS equipment to obtain DMA V Peak, DMDTA V Peak and DMMTA V The peak area was calculated by DMA V Peak and DMDTA V The peak area value was substituted into the standard curve of the corresponding substance to obtain the concentration value, and finally subtracted from the total arsenic concentration to obtain the DMMTA in the solution. V The concentration of DMMTA was plotted V The standard curve of peak area-molar concentration is shown in Table 2 and Table 3. The operating parameters of UltiMate 3000 liquid chromatograph and AFS-230E dual-channel atomic fluorescence spectrophotometer are shown in Table 2 and Table 3. The flow rate and pump pressure are constant during the whole experiment.

[0066] Finally get Figure 3 DMA in V 、DMMTA V 、DMDT VStandard curve of peak area-molar concentration.

[0067] Step 5: Method Validation

[0068] ① Detection limit and quantification limit

[0069] First, the baseline was collected by HPLC-AFS for 10 min, and the baseline was stabilized and the signal intensity was recorded as 61 mV. Then, the diluted DMA was injected V Standard solution, DMMTA V Synthetic sample stock solution and DMDTA V Synthesize sample stock solution. When the peak height of the corresponding substance reaches 2 times or more of the baseline signal intensity (i.e. 122mV), record the peak areas as 996mV*s, 1755mV*s, and 962mV*s, respectively, and substitute into the corresponding standard curve to obtain DMA V 、DMMTA V 、DMDT V The lower limits of detection of the concentrations of the substances were 0.31μM, 1.80μM, and 0.98μM, respectively. When the peak height of the corresponding substance reached 3 times or more of the baseline signal intensity (i.e., 183mV), the peak areas were recorded as 2510mV*s, 2571mV*s, and 1279mV*s, respectively, and the corresponding standard curves were substituted to obtain the DMA V 、DMMTA V 、DMDT V The lower limits of quantification of the concentrations were 0.70μM, 2.37μM, and 1.25μM, respectively.

[0070] Take 6.25μM, 9.37μM, 12.5μM, 18.75μM, 25μM DMA V Standard solution and DMDTA V The synthesized sample mother solution was injected into the HPLC-AFS from low to high concentrations, and the signal intensity of the instrument was observed. When the peak height of the corresponding substance exceeded the upper limit of the signal intensity of the instrument (i.e., 4000mV), the maximum peak area when a complete peak shape can appear was recorded as the detection upper limit of the present invention, and the DMA was obtained. V 、DMDT V The upper detection limits of concentrations were 9.37μM and 18.75μM, respectively.

[0071] Take DMMTA with total arsenic concentrations of 30 μM, 40 μM, and 50 μM V The mixed solution was injected into HPLC-AFS from low to high concentration, and the concentrations of DMMTA in the time period of 6.2 to 7.3 min were recorded. V The maximum peak area when the peak can show a complete peak shape is 48103mV*s, and DMMTA is obtained by substituting it into the corresponding standard curve. VThe upper limit of detection of the concentration is 34.19 μM.

[0072] The recorded results are shown in Table 4 below.

[0073] Table 4 Results of detection limit and quantification limit

[0074]

[0075] ②Stability test

[0076] Take DMMTA with a total arsenic concentration of 25 μM V The mixed solution was sampled and analyzed at 1h, 3h, 24h, and 48h under the parameters of Table 2 and Table 3, and the results are shown in Table 5. The results show that the method implemented by the present invention has a good effect on DMA V 、DMMTA V 、DMDT V The detection of three arsenic forms showed good stability within 48 hours.

[0077] Table 5 Peak area results of the same mixed sample within the specified time interval

[0078] <![CDATA[DMA V ]]> <![CDATA[DMMTA V ]]> <![CDATA[DMDTA V ]]> 1h 23793mV*s 10025mV*s 12805mV*s 3h 22918mV*s 9391mV*s 13988mV*s 24h 23228mV*s 9714mV*s 14056mV*s 48h 23051mV*s 9680mV*s 13577mV*s RSD 1.66％ 2.67％ 4.22％

[0079] ③Repeatability test

[0080] Take 5 equal portions of 6.25 μM DMA V The standard solution was tested in the HPLC-AFS device under the parameters in Table 2 and Table 3, and the results shown in Table 6 were obtained using the method in step 4. The results showed good repeatability.

[0081] Table 6 DMA V Repeatability test data

[0082] serial number 1 2 3 4 5 RSD Peak area 23890mV*s 24201mV*s 23685mV*s 24322mV*s 24110mV*s 1.06％ concentration 6.21μM 6.29μM 6.16μM 6.32μM 6.27μM 1.03％

[0083] Take 4 equal portions of 12.5 μM DMMTA V The mixed solution was tested in the HPLC-AFS device under the parameter conditions in Table 2 and Table 3, and the results shown in Table 7 were obtained using the method in step 4. The results showed good repeatability.

[0084] Table 7 DMMTA V Repeatability test data

[0085]

[0086] Take 5 equal portions of 6.25 μM DMDTA V The mixed solution was tested in the HPLC-AFS device under the parameter conditions in Table 2 and Table 3, and the results shown in Table 8 were obtained, which proved that the repeatability was good.

[0087] Table 8 DMDTA V Repeatability test data

[0088] serial number 1 2 3 4 5 RSD Peak area 7062mV*s 7190mV*s 7219mV*s 7104mV*s 7159mV*s 0.89％ concentration 6.16μM 6.27μM 6.30μM 6.20μM 6.25μM 0.90％

[0089] Step 6: Measure the concentration of methylthioarsenic in the actual water sample:

[0090] Prepare a total arsenic concentration of 10 μM (including DMMTA V 、DMDT V and DMA V The mixed standard solutions of three arsenic forms with a concentration of 3.33 μM were used. The mixed standard solutions of three arsenic forms were subjected to HPLC-AFS for determination, and the peak area values ​​obtained by the detection are shown in Table 9:

[0091] Table 9 Peak area of ​​each arsenic component in water samples / mV*s

[0092] Name <![CDATA[DMA V ]]> <![CDATA[DMMTA V ]]> <![CDATA[DMDTA V ]]> Area 12531 4153 3725

[0093] Substitute the peak area values ​​in Table 9 into Figure 3 DMA was obtained from three standard curves V 、DMMTA V and DMDTA V The molar concentration of .

[0094] DMA V =(12531+207) / 3880=3.28μM;

[0095] DMMTA V =(4153+820) / 1431=3.48μM;

[0096] DMDTA V =(3725+192) / 1177=3.33μM;

[0097] Total arsenic concentration = 3.28 + 3.48 + 3.33 = 10.09 μM.

[0098] The HPLC-AFS test results are close to the actual concentration values, where the relative error of a single substance can be controlled within 4.5%, and the relative error of the total arsenic concentration is only 0.9%, with high accuracy, proving that the detection method provided in this application can be used to separate various arsenic forms in water samples and can accurately determine DMA V 、DMMTA V and DMDTA V molar concentration; can effectively replace traditional measurement methods, reduce detection costs, improve detection efficiency, and successfully solve the problem of DMMTA without standard compound in most laboratoriesV and DMDTA V The problem of accurate analysis of the purity of finished products.

[0099] Example 2

[0100] This example is basically the same as Example 1, except that: in step 6, three arsenic forms (including DMA) were prepared. V 、DMMTA V and DMDTA V The mixed standard solution of the three forms of arsenic was divided into two equal parts, one of which was added with boric acid solution to make the BO3 3- The ion concentration is 20mM; the other part does not add any substance. They are tested by HPLC-AFS equipment respectively, and the results are as follows Figure 4 shown.

[0101] observe Figure 4 It can be seen from the comparison of retention time and peak area that the effect of borate solution on the test results of HPLC-AFS instrument is negligible.

[0102] Comparative Example 1

[0103] This comparative example is basically the same as Example 1, except that the chromatographic column C18 in the HPLC detection conditions is replaced by PRP, and the mobile phase 20mM diammonium phosphate aqueous solution (pH=3) is replaced by 15mM diammonium phosphate aqueous solution (pH=6). The HPLC-AFS chromatographic results of the three arsenic forms mixed standard solution are shown in Figure 5 As shown, it can be found that DMMTA cannot be separated V Peak and DMDTA V Therefore, subsequent experiments could not be performed.

[0104] Comparative Example 2

[0105] This comparative example is basically the same as Example 1, except that the mobile phase of 20 mM ammonium dihydrogen phosphate aqueous solution (pH=3) in the HPLC detection conditions is replaced by 0.1% CH2O2. The HPLC-AFS chromatographic results of the three arsenic forms mixed standard solution are shown in Figure 5 As shown, it can be found that DMA can be separated V Peak, DMMTA V Peak and DMDTA V Peak, but DMA V Peak and DMDTA V The peaks are connected, resulting in incomplete peak shape, and DMDTA V Peak and DMMTA V The peaks have severe tailing, so this method is not suitable for DMAV 、DMMTA V 、DMDT V Separation and detection of mixed samples.

Claims

1. A method for detecting the content of methylthioarsenic compounds in water samples, characterized in that: include: S1.DMA V Establishment of standard curve: prepare multiple groups of DMA with different molar concentrations V Solution, each group of DMA V The solutions were respectively fed into HPLC-AFS, and multiple groups of DMA were found according to the retention time matching method. V Peak and calculate the corresponding peak area value, draw DMA V Standard curve between peak area and molar concentration; S2.DMDTA V Establishment of standard curve: prepare multiple groups of DMA with different molar concentrations V solution, and then each group was added with Na2S solution at a molar ratio of As:S of 1:500, and multiple groups of DMDTA were obtained through sulfidation reaction. V Solution, each group of DMDTA V The solutions were respectively put into HPLC-AFS, and multiple groups of DMDTA were found according to the retention time matching method. V Peak and calculate the corresponding peak area value, draw DMDTA V Standard curve between peak area and molar concentration; S3.DMMTA V Establishment of standard curve: S3.1 Get DMA V The sample is dissolved in water to obtain DMA with a molar concentration of Ma mol. V The solution was then added with Na2S solution at a molar ratio of As:S of 1:100, and DMMTA was obtained through sulfidation reaction. V A mixed solution; S3.2 will contain DMMTA V The mixed solution enters HPLC-AFS detection: DMDTA is found according to the retention time matching method V The peak area was calculated and substituted into the DMDTA obtained by S2. V Standard curve to obtain DMDTA V The molar concentration is Mb mol; DMA is found by retention time matching method V The peak area is calculated and substituted into the DMA obtained by S1. V Standard curve obtained by DMA V The molar concentration is Mc mol; S3.3 Calculate the DMMTA content as in formula (1) V DMMTA in the mixed solution V The molar concentration is Md mol, Md=Ma-Mb-Mc (1); S3.4 Dilute DMMTA in S3.3 V The molar concentration of DMMTA is Md mol V Mixed solutions of different DMMTA groups were obtained. V Molar concentration of DMMTA V The mixed solution was used to obtain DMMTA of each group by HPLC-AFS. V Peak area value corresponding to the peak, plot DMMTA V Standard curve between peak area and molar concentration; S4. The sample solution containing various methylthioarsenic compounds is put into HPLC-AFS, and DMA is separated and found according to the retention time matching method. V Peak, DMDTA V Peak and DMMTA V Peak, calculate DMA V Peak, DMDTA V Peak and DMMTA V The peak area value corresponding to the peak was obtained using DMA obtained by S1 V The standard curve determines the DMA in the sample solution to be tested V Concentration, DMDTA obtained using S2 V The standard curve determines the DMDTA in the sample solution to be tested V Concentration, DMMTA obtained using S3 V The standard curve determines the DMMTA in the sample solution to be tested V concentration.

2. The detection method according to claim 1, characterized in that In the S2, DMDTA V After the solution enters HPLC-AFS, only one peak appears, and DMDTA V After the solution entered ESI-TOF-MS, a characteristic peak with a mass-to-charge ratio of 169 was detected.

3. The detection method according to claim 1, characterized in that S3.1 contains DMMTA V After the mixed solution entered HPLC-AFS, three peaks appeared, and DMMTA V After the solution entered ESI-TOF-MS, a characteristic peak with a mass-to-charge ratio of 153 was detected.

4. The detection method according to claim 1, characterized in that In S1 to S4, the detection conditions of HPLC are: Chromatographic column: Eclipse Plus C18 column, 3.5 μm, 4.6 mm×250 mm; flow rate: 1 mL / min; injection volume: 20 μL; 20 mM ammonium dihydrogen phosphate (pH=3) was used as the mobile phase, and the elution procedure was: the volume of the mobile phase was 100%.

5. The detection method according to any one of claims 1 to 4, characterized in that: In S1 to S4, the specific method of using the retention time matching method to identify the peak is: the peak corresponding to the retention time of 2.6 to 3.1 min is DMA V The peak with retention time of 3.3 to 4.1 min is DMDTA V The peak with retention time of 6.2-7.3min is DMMTA V peak.

6. The detection method according to any one of claims 1 to 4, characterized in that: In S1 to S4, the AFS detection conditions are: carrier: 7% HCl aqueous solution; Reducing agent: 5% NaOH + 20% NaBH4 aqueous solution; Main current: 60mA; auxiliary current: 30mA; negative high voltage: 300V; carrier gas: 300mL / min; shielding gas: 900mL / min; atomizer height: 8mm; peristaltic pump: 60r / min.

7. The detection method according to any one of claims 1 to 3, characterized in that: In S1 to S4, the detection conditions of ESI-TOF-MS are as follows: chromatographic column: Eclipse Plus C18, 3.5 μm, 4.6 mm×250 mm; flow rate: 1 mL / min; injection volume: 20 μL; 0.1% formic acid as mobile phase A, acetonitrile as mobile phase B, elution procedure: the volume of mobile phase A is 90%, the volume of mobile phase B is 10%; ion mode: negative ion mode.

8. The detection method according to claim 1, characterized in that The detection accuracy of the detection method is not affected by the salt ion concentration.

9. The detection method according to claim 1, characterized in that: The relative error of the detection method is within 4.5%.

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