Separation method and apparatus for As(III) and As(V)

Abstract

To provide a technique capable of simply separating As(III) ions and As(V) ions in a collected sample.SOLUTION: A method for separating As(III) and As(V) includes a fractionation and collection step of fractionating and collecting each of As(III) ions and As(V) ions by chromatography of passing a column filled with a column filler through a sample containing sodium ions, chloride ions, As(III) ions and As(V) ions, and a feed liquid containing a mobile phase having a pH of 2.5 or more and 3.5 or less. A column filler includes a silica gel carrier, and an alkyl group which is modified on the surface of the silica gel carrier and has 18 or more and 30 or less carbon atoms.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This application relates to a separation method and apparatus for fractionating and collecting trivalent arsenic (As(III)) ions and pentavalent arsenic (As(V)) ions present in a sample, and preparing them in a state suitable for supply to a detection device that detects the concentrations of As(III) ions and As(V) ions, respectively. [Background technology]

[0002] Arsenic, which is widely distributed in nature at low concentrations, exhibits different toxicity to the human body depending on its chemical form. Arsenic is found in the form of arsenobetaine ((CH3)3As), which is considered to be relatively less toxic. + CH2COO - Arsenic exists in environmental waters such as ocean water as organic arsenic compounds such as As(III), and inorganic arsenic such as As(V), which are relatively toxic. Among inorganic arsenic species, As(III) is the most toxic. Therefore, measuring the concentrations of inorganic arsenic As(III) and As(V) in environmental waters is very important for assessing their adverse effects on the human body.

[0003] A well-known method for measuring the concentrations of multiple substances in a sample is to use an analytical instrument such as LC-ICP-MS, which combines a separation instrument, such as a liquid chromatograph or gas chromatograph, to separate substances by their chemical form with a detection instrument, such as an inductively coupled plasma mass spectrometer, to quantitatively detect each of the substances separated by the separation instrument. However, due to the large size of these analytical instruments, they are usually installed in fixed locations within buildings. Meanwhile, in environmental water, As(III) ions (hereafter simply referred to as "As(III)") and As(V) ions (hereafter simply referred to as "As(V)") are interconverted. Therefore, the concentrations of As(III) and As(V) originally present in the sample become obscured after a certain period of time has passed since the sample was collected from environmental water.

[0004] For example, in marine surveys that require at least several weeks, collecting samples from ocean water on a ship at sea and measuring the concentrations of As(III) and As(V) in the samples using a detection device upon returning to port does not accurately measure the actual concentrations in the sample. Furthermore, considering the rocking of the ship, the salty atmosphere at sea, and the limitations on the instruments and electrical equipment that can be brought on board, it is not realistic to install the above-mentioned analytical equipment on board. Therefore, it is desirable to develop a technology that can separate As(III) and As(V) from other substances in a sample quickly after collection, without using precise, large-scale equipment, before measuring the concentrations using a detection device installed at a remote location. Summary of the Invention [Problem to be solved by the invention]

[0005] The present application has been made in view of the above circumstances, and aims to provide a technique that enables simple fractional collection of As(III) and As(V) in a sample. [Means for solving the problem]

[0006] The method for separating As(III) and As(V) of the present application includes a fractionation and collection step in which a sample containing sodium ions (hereinafter sometimes simply referred to as "sodium"), chloride ions (hereinafter sometimes simply referred to as "chlorine"), As(III) ions, and As(V) ions and a mobile phase having a pH of 2.5 to 3.5 are passed through a column packed with a column packing material by chromatography to fractionate and collect As(III) ions and As(V) ions, respectively. The column packing material comprises a silica gel carrier and alkyl groups having 18 to 30 carbon atoms modified on the surface of the silica gel carrier.

[0007] The separation device for As(III) and As(V) of the present application includes a column packed with a silica gel carrier and a column packing material having an alkyl group having 18 to 30 carbon atoms modified on the surface of the silica gel carrier, the column having an inlet and an outlet; a supply unit that supplies a sample containing sodium ions, chloride ions, As(III) ions, and As(V) ions and a mobile phase having a pH of 2.5 to 3.5 to the inlet; a first container that collects As(V) ions discharged from the outlet; a second container that is different from the first container and collects As(III) ions discharged from the outlet; and a control unit that guides As(V) ions to the first container during a first time period when As(V) ions are discharged from the outlet and guides As(III) ions to the second container during a second time period when As(III) ions are discharged from the outlet. [Effects of the Invention]

[0008] The present method and apparatus for separating As(III) and As(V) uses column chromatography with a packing material including a silica gel carrier whose surface is modified with an alkyl group having 18 to 30 carbon atoms and a mobile phase with a pH of 2.5 to 3.5. Therefore, the peaks of As(III) and As(V) in the chromatogram are sufficiently separated without too much time difference. Furthermore, the peaks of sodium and chloride in the chromatogram do not interfere with the peaks of As(III) and As(V). Therefore, the present method and apparatus for separating As(III) and As(V) can separate As(III) and As(V) from a solution containing sodium, chloride, As(III), and As(V). [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of an embodiment of a separation device for As(III) and As(V). [Figure 2] From top to bottom, the chromatograms are those of sodium, chlorine, and inorganic arsenic (Reference Example 1). [Figure 3] Chromatogram of Example 1. [Figure 4] Chromatogram of Comparative Example 1. [Figure 5] Graph showing the relationship between the pH of the mobile phase and the migration time of various components in the chromatogram (Reference Example 2). [Figure 6] Chromatogram of Comparative Example 2. [Figure 7] The top is a chromatogram of chlorine, and the bottom is a chromatogram of inorganic arsenic (Comparative Example 3). [Figure 8] The top is a chromatogram of chlorine, and the bottom is a chromatogram of inorganic arsenic (Example 5). [Figure 9] (a) Various chromatograms of the solution in the first container and (b) various chromatograms of the solution in the second container (Example 6). DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will now be described with reference to the drawings, based on embodiments and examples, with regard to the separation method for As(III) and As(V) and the separation device for As(III) and As(V). The As(III) and As(V) separation device, its components, and its peripheral components are shown schematically and may differ in size and dimensional ratio from the actual devices. Further, redundant explanations will be omitted where appropriate. The present invention also provides a separation method for As(III) and As(V) according to an embodiment of the present invention, which includes a fraction collection step. In this fraction collection step, As(III) and As(V) are fractionated and collected by chromatography, in which a solution containing a predetermined sample and a predetermined mobile phase is passed through a predetermined column.

[0011] The above-mentioned specific sample contains sodium, chlorine, As(III), and As(V). Examples of such samples include liquids such as environmental water and marine water, as well as extracts obtained by elution using acids, alkalis, or enzymes from solid materials such as soil, sediment, living organisms, agricultural crops, food, animals, and seafood. When a solution containing As(III) or As(V) also contains sodium and chlorine, NaCl produced by desolvation adheres to the detector, causing degradation. Furthermore, chlorine interferes with accurate measurement of inorganic arsenic content in inductively coupled plasma mass spectrometry (ICP-MS), which uses argon (Ar) gas as an excitation source.

[0012] According to the method for separating As(III) and As(V) of this embodiment, As(III) and As(V) can be separately fractionated and collected from a solution containing sodium, chlorine, As(III), and As(V), thereby easily separating interferents from the analyte. Furthermore, because As(III) and As(V) can be separately fractionated and collected from a solution containing sodium, chlorine, As(III), and As(V), this method for separating As(III) and As(V) of this embodiment is particularly suitable when the sample is ocean water.

[0013] If the sample is ocean water, the fraction collection process can be performed on board a vessel at sea. The pH of the specified mobile phase is between 2.5 and 3.5. A low pH, such as pH 2.0, can result in insufficient separation of As(III) and As(V). A high pH, ​​such as pH 4.0, can result in insufficient separation of As(III) and organic arsenic compounds. Examples of mobile phases include mixed solutions of acids, salts, bases, water, and aqueous solvents. The pH of the mobile phase is adjusted by adding an acid, such as a (1+1) nitric acid solution, or a base, such as a (1+1) aqueous ammonia solution, dropwise to the mobile phase while stirring and measuring the pH with a pH meter.

[0014] The specified column includes a column tube and a specified column packing material packed in the column tube. The specified column packing material includes a silica gel carrier and an alkyl group having 18 to 30 carbon atoms modified on the surface of the silica gel carrier. Because the silica gel carrier surface-modified with an alkyl group is used as the column packing material, the half-widths of the peaks of sodium, chlorine, As(III), and As(V) in the chromatogram are narrow. Note that if a silica gel carrier surface-modified with an alkyl group having a small number of carbon atoms, for example, an alkyl group having 8 carbon atoms, is used as the column packing material, chlorine and inorganic arsenic ions may not be separated.

[0015] The inner diameter of the column tube is, for example, 3 mm to 5 mm, and the length of the column tube is, for example, 30 mm to 250 mm. The average particle size of the packing material is, for example, 3 μm to 15 μm. Various types of chromatography can be used, including progressive, reversed-phase, ion-exchange, and size-exclusion (gel filtration). Among these, reversed-phase chromatography is preferred. This is because it provides high resolution (theoretical plate count) and good separation of adjacent peaks, and also provides peaks with narrow half-widths, allowing for a small volume of As(III) and As(V) fractionated, and the resulting solution is less diluted with respect to the concentrations of As(III) and As(V).

[0016] According to the method for separating As(III) and As(V) of this embodiment, it is possible to separate As(III) and As(V) at the sample collection site. Therefore, the state of existence of As(III) and As(V) in the natural environment can be clearly understood. Furthermore, once As(III) and As(V) are separated, even if As(III) and As(V) subsequently change back and forth between them, the concentrations of As(III) and As(V) originally contained in the sample can be quantified. Therefore, a mass spectrometer, which was previously required to quantify the concentrations of As(III) and As(V), is no longer required at the sample collection site. Furthermore, the concentrations of As(III) and As(V) originally contained in the sample can be quantified using a detection device that quantifies the total amount of As(III) and As(V) without distinguishing between them.

[0017] The method for separating As(III) and As(V) according to this embodiment may further include the following setting step before the fraction collection step. That is, in this setting step, a first time period during which As(V) ions are discharged from the column and a second time period during which As(III) ions are discharged from the column are set using a setting solution containing As(III) ions, As(V) ions, and a mobile phase. By setting the first time period and the second time period in this setting step, in the fraction collection step, the solution discharged from the column and containing As(V) but not As(III) can be collected in a first container during the first time period, and the solution containing As(III) but not As(V) can be collected in a second container different from the first container during the second time period.

[0018] In other words, the fraction collection step includes an As(V) collection step in which the solution discharged from the column is collected in a first container during a first time period, and an As(III) collection step in which the solution discharged from the column is collected in a second container different from the first container during a second time period. In this way, by simply switching between introducing the solution into the first container and the second container depending on the retention time of the solution in the column, a solution containing As(V) but not As(III) and a solution containing As(III) but not As(V) can be fractionally collected.

[0019] The solutions fractionated into the first and second containers can be applied to atomic spectrometry instruments, such as ICP mass spectrometry, ICP atomic emission spectrometry, electrothermal atomic absorption spectrometry, and flame atomic absorption spectrometry, which are excellent for quantifying inorganic elements such as metals, as well as detection devices that combine these detectors. In other words, the present method for separating As(III) and As(V) is also a pretreatment method that can be applied to multiple detection devices.

[0020] FIG. 1 schematically illustrates the main components of an As(III) and As(V) separation apparatus 10 according to an embodiment of the present invention. The separation apparatus 10 includes a column 12, a supply unit 14, a first container 16, a second container 18, a control unit 20, and a fraction collection tray 21. The column 12 includes an inlet 12a and an outlet 12b. The column 12 includes a column tube 12c and a column packing material 12d. The column packing material 12d is packed in the column tube 12c. The column packing material 12d includes a silica gel carrier and an alkyl group having 18 to 30 carbon atoms modified on the surface of the silica gel carrier.

[0021] The supply unit 14 supplies the liquid 22 to the inlet 12a. The supply unit 14 and the inlet 12a are connected via a pipe P. The pipe P is made of a metal-free material, for example, a resin such as a fluororesin or an aromatic polymer. Similarly, pipes P are arranged between the outlet 12b and the control unit 20, and between the control unit 20 and the opening of the first container 16 or the second container 18. The liquid 22 contains a sample and a mobile phase.

[0022] Alternatively, the sample and the mobile phase may be supplied separately to the inlet 12a. In this case, the sample and the mobile phase are mixed immediately before the inlet 12a and supplied to the inlet 12a as a liquid. In this case, the supply unit 14 is the portion immediately before the inlet 12a where the sample and the mobile phase are mixed. The sample contains sodium ions, chloride ions, As(III) ions, and As(V) ions. The mobile phase has a pH of 2.5 or more and 3.5 or less. The first container 16 collects the As(V) ions discharged from the outlet 12b. The second container 18, which is different from the first container 16, collects the As(III) ions discharged from the outlet.

[0023] The control unit 20 moves the fraction collecting tray 21, for example, by an XY drive system, to move the first container 16 and the second container 18 on the fraction collecting tray 21 directly below the pipe P connected to the outlet 12b, and guides the solution 22 that has passed through the column 12 from the outlet 12b to predetermined containers set by the program for predetermined times, in this embodiment, to the first container 16 during a first time period and to the second container 18 during a second time period. In other words, the control unit 20 guides the As(V) ions to the first container 16 during a first time period when the As(V) ions are discharged from the outlet 12b, and guides the As(III) ions to the second container 18 during a second time period when the As(III) ions are discharged from the outlet 12b.

[0024] The separation device 10 also includes a sample tray, a degasser, a liquid pump, an autosampler, and a heater (none of which are shown). The sample tray accommodates a container containing a sample, such as a vial with a septum cap. The degasser removes gas dissolved in the liquid 22 by passing the gas through a resin tube into the liquid 22 in the supply unit 14.

[0025] The liquid delivery pump uses, for example, a double plunger system to deliver liquid 22 from supply unit 14 to inlet 12a at a flow rate of several μL / min to several mL / min. The autosampler uses, for example, a variable metering type total sample injection system to collect a predetermined volume of sample from a sample container in a sample tray at a rate of approximately 0.1 μL / min to 100 μL / min and introduce it into inlet 12a. The heater heats column 12 to an appropriate temperature of 100°C or less and maintains the temperature constant.

[0026] Using the separation device 10, As(III) and As(V) are separated, i.e., fractionally collected, according to the following procedure. First, the liquid to be analyzed, whose inorganic arsenic content is to be measured, is collected. If necessary, contaminants and large particles are removed from the liquid to be analyzed using, for example, a membrane filter with a pore size of 0.45 μm. Then, a portion of this liquid, for example, 1 mL or less, is collected as a sample in a vial with a septum cap and placed on a sample tray. Next, a liquid pump is used to send the mobile phase into the column 12, which is packed with column packing material 12d, to bring the column 12 into equilibrium.

[0027] A heater is also used to maintain a constant temperature for column 12. This allows for separation that is not dependent on environmental conditions such as the temperature at the sample collection site. A predetermined volume of sample is then collected from a sample container in a sample tray by an autosampler and supplied to column 12 through inlet 12a. The flow rate of the liquid delivery pump, the temperature of the heater, the positions of first container 16 and second container 18 on fraction collection tray 21, and the volume and collection time of liquid delivery 22 in first container 16 and second container 18 are set using a control panel mounted on control unit 20 or a personal computer connected to control unit 20.

[0028] The collection times of the solution 22 in the first container 16 and the second container 18, i.e., the first time zone and the second time zone, are set in advance by the method described in the fraction collection step of the method for separating As(III) and As(V) of the embodiment. The control unit 20 automatically controls the separation device 10 based on the set first time zone and second time zone and various other set conditions. Therefore, the separation device 10 can automatically fractionally collect a solution containing As(III) and a solution containing As(V). [Example]

[0029] Reference example 1 Using an LC-ICP-MS system in which a chromatograph equipped with an autosampler, a pump, and a column was directly connected to an inductively coupled plasma mass spectrometer (Agilent, 7700x) as a detector via a polyetheretherketone (PEEK) tube, column chromatography was performed on an aqueous solution containing sodium, an aqueous solution containing chlorine, and a mixed aqueous solution containing As(III) and As(V).

[0030] This mixed aqueous solution of As(III) and As(V) (hereinafter referred to as "mixed aqueous solution A") was prepared by mixing an As(III) aqueous solution (arsenic standard solution manufactured by Kanto Chemical Co., Inc., arsenic concentration 1000 mg / kg (hereinafter the same)) and an As(V) aqueous solution (certified reference material NMIJ CRM 7912-a, arsenic acid aqueous solution, arsenic concentration 99.53 ± 1.67 mg / kg (hereinafter the same)), and further diluting with water to prepare an As(III) and As(V) solution with concentrations of 10 ng / g each.

[0031] The column is made of octyldodecyl groups (-C 18 H 37 The column was packed with a column packing material (Osaka Soda Co., Ltd., C 18The column was run on a 1000 MW (MG, inner diameter 4.6 mm, length 150 mm, average particle size 3 μm) mobile phase, which consisted of an aqueous solution containing 10 mmol / L sodium 1-butanesulfonate, 4 mmol / L malonic acid, 4 mmol / L tetramethylammonium hydroxide, and 0.05% by mass of methanol, adjusted to pH 2.7 by adding dropwise a (1+1) nitric acid solution. This mobile phase was a reversed-phase eluent containing an ion-pair reagent.

[0032] This mobile phase was introduced into the column at a flow rate of 0.5 mL / min using a pump. Then, 20 μL of the sodium-containing aqueous solution, the chlorine-containing aqueous solution, and mixed aqueous solution A were each collected using an autosampler and introduced into the column. The chromatograms for sodium, chlorine, As(III), and As(V) are shown in Figure 2, starting from the top. As shown in Figure 2, As(V) was fractionated in the first time slot, with a retention time of approximately 155 to 175 seconds, and As(III) was fractionated in the second time slot, with a retention time of approximately 175 to 200 seconds. It was also found that the first and second time slots did not contain peaks for sodium or chlorine.

[0033] Example 1 Chromatography of sample B was performed in the same manner as in Reference Example 1, except that mixed aqueous solution A was replaced with sample B described below. Specifically, sample B was prepared by mixing an As(III) aqueous solution, an As(V) aqueous solution, and a 0.3% NaCl aqueous solution equivalent to the salinity of 10-fold diluted seawater, and further diluting the mixture with water to obtain a solution containing As(III) and As(V) at concentrations of 10 ng / g each. The chromatogram obtained is shown in Figure 3. In this chromatogram, As(III) and As(V) are inorganic arsenic compounds, and MMA (monomethylarsonic acid), DMA (dimethylarsinic acid), and AsB (arsenobetaine) are organic arsenic compounds (the same applies below).

[0034] As shown in Figure 3, the peaks of As(III) and As(V) were clearly separated, and there was no peak of an organic arsenic compound between the peaks of As(III) and As(V), nor was there any overlap between the peak of As(III) and the peak of an organic arsenic compound. It was also found that all inorganic arsenic components could be collected within the short retention time range of approximately 145 seconds to approximately 193 seconds. From the above, the chromatography of Example 1 enabled the fractionation and collection of As(III) and As(V) from a mixed aqueous solution containing sodium, chlorine, As(III), and As(V) easily and quickly without using a large amount of mobile phase.

[0035] Example 2 Chromatography of Sample B was performed in the same manner as in Example 1, except that the composition of the mobile phase was changed. The mobile phase in Example 2 was an aqueous solution containing 10 mmol / L sodium 1-butanesulfonate, 4 mmol / L tetramethylammonium hydroxide, 2 mmol / L ammonium dihydrogen phosphate, and 0.05 mass% methanol, with the pH adjusted to 2.7 by adding nitric acid. The chromatogram obtained in this case, like the chromatogram in Example 1, showed clearly separated peaks for As(III) and As(V), no peaks of organic arsenic compounds between the peaks of As(III) and As(V), and no overlap between the peaks of As(III) and organic arsenic compounds.

[0036] Example 3 Chromatography of Sample B was performed in the same manner as in Example 2, except that the pH of the mobile phase was changed to 2.5 by changing the amount of nitric acid added. In this chromatogram, the peaks of As(III) and As(V) were clearly separated, and there was no peak of an organic arsenic compound between the peaks of As(III) and As(V), and there was no overlap between the peak of As(III) and the peak of an organic arsenic compound.

[0037] Example 4 Chromatography of Sample B was performed in the same manner as in Example 2, except that the pH of the mobile phase was changed to 3.5 by changing the amount of nitric acid added. In this chromatogram, the peaks of As(III) and As(V) were clearly separated, and there was no peak of an organic arsenic compound between the peaks of As(III) and As(V), and there was no overlap between the peak of As(III) and the peak of an organic arsenic compound.

[0038] Comparative Example 1 Chromatography of sample B was performed in the same manner as in Example 2, except that the pH of the mobile phase was changed to 2.0 by changing the amount of nitric acid added. The chromatogram obtained is shown in Figure 4. As shown in Figure 4, the peaks of As(III) and As(V) were not sufficiently separated, and the peak of As(III) overlapped with the peak of the organic arsenic compound.

[0039] Reference example 2 The pH of the mobile phase was adjusted to 2.0, 2.3, 2.5, 2.7, 3.0, 3.5, and 4.0, and chromatography of Sample B was performed in the same manner as in Example 1. The pH 2.0 mobile phase was the same as in Comparative Example 1. The pH 2.3 mobile phase was prepared by varying the amount of nitric acid added to the mobile phase of Example 2. The pH 2.5 mobile phase was the same as in Example 3. The pH 2.7 mobile phase was the same as in Example 1. The pH 3.0 mobile phase was prepared by varying the amount of nitric acid added to the mobile phase of Example 2. The pH 3.5 mobile phase was the same as in Example 4. The pH 4.0 mobile phase was prepared by varying the amount of nitric acid added to the mobile phase of Example 2 and further adding (1+1) aqueous ammonia.

[0040] Figure 5 shows the relationship between the retention times (i.e., the peak times) of As(III), As(V), MMA, DMA, and AsB in the chromatogram and the pH of the mobile phase. As shown in Figure 5, with mobile phases at pH 2.0 and 2.3, the retention times of As(III) and As(V) are close together, causing the bases of the peaks to overlap in the chromatogram. This makes it difficult to separate As(III) and As(V).

[0041] Furthermore, with the mobile phase at pH 4.0, the retention time of MMA appeared between the retention times of As(III) and As(V), close to that of As(III). Therefore, there is a risk that MMA may be present in the As(III) fraction collected with the mobile phase at pH 4.0. In contrast, with the mobile phases at pH 2.5, 2.7, 3.0, and 3.5, the retention times of As(III) and As(V) were separated, and there was no retention time of organic arsenic compounds between the retention times of As(III) and As(V). Therefore, there was no closeness in retention time that would make separation of As(III) and organic arsenic compounds difficult.

[0042] Comparative Example 2 Chromatography of sample B was performed in the same manner as in Example 1, except that a column packed with an anion exchanger (Hamilton, PRP-X100, internal diameter 4.1 mm, length 150 mm, average particle size 10 μm) was used, and 10 mM (NH4)2HPO4 (pH 8.25), a common arsenic species separation agent, was used as the mobile phase. The chromatogram obtained is shown in Figure 6. As shown in Figure 6, the peaks of As(III) and As(V) were sufficiently separated, but their retention times were far apart. Furthermore, a peak of an organic arsenic compound was present between these peaks. Therefore, when separating and collecting As(III) and As(V) from a sample, a large amount of mobile phase was required, and a separate container for collecting the organic arsenic compound was also required.

[0043] Comparative Example 3 As a column, octyl groups (-C8H 17Chromatography of the sodium-containing aqueous solution, the chlorine-containing aqueous solution, and the mixed aqueous solution A was carried out in the same manner as in Reference Example 1, except that a column (Shimadzu Corporation, Shim-pack VP-C8, inner diameter 4.6 mm, length 250 mm, average particle size 5 μm) packed with a silica gel carrier modified with octyl groups was used. The chromatograms obtained are shown in Figure 7. Note that the sodium peak position was significantly separated from the peak positions of chlorine and inorganic arsenic, so the sodium chromatogram is not shown (the same applies below). As shown in Figure 7, the chlorine and inorganic arsenic peaks overlapped. This indicates that chlorine and inorganic arsenic cannot be fractionated and collected by chromatography using a silica gel carrier modified with octyl groups.

[0044] Example 5 As a column, triacontyl groups (-C 30 H 61 Chromatography of the sodium-containing aqueous solution, the chlorine-containing aqueous solution, and the mixed aqueous solution A was performed in the same manner as in Reference Example, except that a column (Nomura Chemical Co., Ltd., Develosil C30-UG, inner diameter 4.6 mm, length 150 mm, average particle size 3 μm) packed with a column packing material consisting of a silica gel carrier modified with HCl (As(III)). The chromatograms obtained are shown in Figure 8. As shown in Figure 8, it was found that all inorganic arsenic components could be collected within the short retention time range of approximately 175 seconds to approximately 225 seconds. It was also found that the chlorine peak was not included in the inorganic arsenic peak. Thus, the chromatography of Example 5 allows for the simple and rapid fractionation and collection of As(III) and As(V) from a mixed aqueous solution containing sodium, chlorine, As(III), and As(V) without using a large amount of mobile phase.

[0045] Example 6 Chromatography of the mixed aqueous solution A was performed in the same manner as in Reference Example 1 using the chromatograph of Reference Example 1. A solution containing As(V) eluted from the chromatograph during a first time period (retention time 150 seconds to 180 seconds) was fractionated into a 2 mL amber glass vial with a septum as a first container, and a solution containing As(III) eluted from the chromatograph during a second time period (retention time 180 seconds to 210 seconds) was fractionated into another 2 mL amber glass vial with a septum as a second container. Solutions eluted during other retention times were discarded.

[0046] Because As(III) and As(V) are unstable at low concentrations, they easily undergo redox reactions and are easily converted to each other. In other words, if the solutions from which As(III) and As(V) were fractionated were subjected to chromatography again, As(V) would be observed in the As(III) solution, and As(III) would be observed in the As(V) solution. Therefore, the arsenic concentrations in the solutions from which As(III) and As(V) were fractionated were evaluated stoichiometrically. Specifically, the inorganic arsenic concentrations in the solutions in the first container and the second container were measured using the LC-ICP-MS of Reference Example 1.

[0047] Figure 9(a) shows the chromatogram of the solution in the first container, and Figure 9(b) shows the chromatogram of the solution in the second container. In Figure 9(a), the peak of As(V) originally present in the first container was observed almost unchanged. In contrast, in Figure 9(b), a peak of As(V) was also observed, which was a partial conversion of the As(III) originally present in the first container. The inorganic arsenic concentrations of the solutions in the first and second containers were calculated to be 1.60 ng / g based on the inorganic arsenic concentration in mixed aqueous solution A (20 ng / g), the amount of mixed aqueous solution A introduced into the column (20 μL), the flow rate of the solution (0.5 mL / min), and the time for fraction collection (30 seconds).

[0048] The inorganic arsenic concentrations in the solutions in the first and second containers quantified by LC-ICP-MS were 1.58 ng / g and 1.60 ng / g, respectively. The recovery rates of inorganic arsenic in the first container were 1.58 / 1.60 × 100 = 98.8%, and the recovery rates of inorganic arsenic in the second container were 1.61 / 1.60 × 100 = 100.6%. Thus, the theoretical concentrations of inorganic arsenic were quantified in each fractionated solution. Therefore, if either As(III) or As(V) is observed in the chromatogram of a fractionated solution, this is due to a chemical change that occurred after fractionation. In other words, the inorganic arsenic obtained from the fractionated solution, whether As(III) or As(V), is the inorganic arsenic contained in the original sample solution. [Explanation of symbols]

[0049] 10 Separation device 12 columns 12a Column inlet 12b Column outlet 12c Column Tube 12d Column Packing Material 14 Supply section 16 First container 18 Second container 20 Control Unit 21 Fraction collection tray 22 Fluid Delivery P piping

Claims

1. a fractionation and collection step of fractionating and collecting the As(III) ions and the As(V) ions by chromatography in which a sample of ocean water containing sodium ions, chloride ions, As(III) ions, and As(V) ions and a mobile phase having a pH of 2.5 to 3.5 are passed through a column packed with a column packing material; the column packing material comprises a silica gel carrier and an alkyl group having 18 to 30 carbon atoms modified on the surface of the silica gel carrier; A method for separating As(III) and As(V), wherein the fraction collection step is carried out on a ship on the ocean where the ocean water is present.

2. In claim 1, The method for separating As(III) and As(V), wherein the chromatography is reverse phase chromatography.

3. In claim 1 or 2, The method further includes a setting step of setting, before the fraction collection step, a first time period during which the As(V) ions are discharged from the column and a second time period during which the As(III) ions are discharged from the column, using a setting solution containing As(III) ions, As(V) ions, and the mobile phase; A method for separating As(III) and As(V), wherein the fraction collection step comprises an As(V) collection step in which the effluent discharged from the column is collected in a first container during the first time period, and an As(III) collection step in which the effluent discharged from the column is collected in a second container different from the first container during the second time period.

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