A stable method for the direct detection of sulfite in water by ion chromatography

Abstract

A kind of stable method for ion chromatography direct detection of sulfurous acid radical in water belongs to the field of environmental science and technology.The method is as follows: a certain mass of KOH and citrate is placed in water to prepare a mixed concentrated solution, wherein the molar concentration ratio of KOH to citrate is in the range of 1:1 to 4; a certain volume of water sample containing sulfurous acid radical is taken and added to the above concentrated solution and mixed quickly; the mixing ratio is determined according to the concentration of sulfurous acid radical in the water sample, and the mixed solution is used for ion chromatography determination.The present application establishes a sulfurous acid radical ion chromatography determination method using safe and green citrate as stabilizer, citrate is used as stabilizer in alkaline solution to stabilize sulfurous acid radical in sample, and ion chromatography is used to directly determine sulfurous acid radical ions in water, solving the problem of instability of sulfurous acid radical in water during the whole process of sampling, preservation, transportation and determination.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of environmental science and technology, and particularly relates to a stable method for ion chromatography direct detection of sulfite in water. BACKGROUND

[0002] Sulfite is an important and widely used food additive, and sulfite is a kind of substance that is easy to be oxidized by oxygen in the air or dissolved oxygen in water. Excessive intake will cause a series of symptoms such as headache, diarrhea, liver damage, etc., and in the field of environment, it is also a pollutant that is concerned, and there are corresponding limit requirements in the national standards for surface water and atmosphere. At present, the detection methods of sulfite include colorimetry, titration, iodometric method and ion chromatography, etc., among which, ion chromatography has the advantages of simple operation, accuracy, high sensitivity, green, etc. However, due to the instability of sulfite, it is easy to be oxidized by oxidizing substances such as oxygen in the air or dissolved oxygen in water, so it is necessary to keep sulfite in a stable state in the whole process of sampling, preservation, transportation and determination. It has been shown that the addition of substances with stronger reducing property than sulfite can reduce the consumption of sulfite by dissolved oxygen or coexisting oxidizing substances in the solution, such as ascorbic acid, sodium hypophosphite, etc. However, the addition of reducing substances cannot completely prevent the occurrence of sulfite oxidation process, and once the added reducing substances are consumed, sulfite will soon be degraded before being accurately detected. In addition to adding reducing substances, stabilizers such as formaldehyde are recommended to be used in the relevant standards for determining sulfite by ion chromatography. However, formaldehyde is a toxic reagent and has an impact on the response value of sulfite in ion chromatography. Therefore, it is necessary to develop a safe and green method that can help to stabilize sulfite. SUMMARY

[0003] The purpose of the present application is to solve the problem of the instability of sulfite and the difficulty in accurately detecting sulfite by ion chromatography, and to provide a stable method for ion chromatography direct detection of sulfite in water.

[0004] To achieve the above purpose, the technical solution adopted by the present application is as follows:

[0005] A stable method for ion chromatography direct detection of sulfite in water, the method comprising the following steps:

[0006] Step one: a certain amount of KOH and citrate is placed in water to prepare a mixed concentrated solution, wherein the molar concentration ratio of KOH to citrate is in the range of 1:1 to 4; the citrate is sodium citrate, which is a safe and non-toxic chemical substance;

[0007] Step two: take a certain volume of water sample containing sulfite, add to the above concentrated solution, and mix quickly; the mixing ratio is determined according to the concentration of sulfite in the water sample, and the mixed solution is used for ion chromatography determination.

[0008] Further, in step two, when the concentration of KOH in the mixed solution is 1 mmol / L and the concentration of citrate is 1 mmol / L, the mixed solution has a good stabilizing effect on sulfite with a concentration lower than 0.2 mmol / L in the mixed solution; when the concentration of KOH in the mixed solution is 1 mmol / L and the concentration of citrate is 2 mmol / L, the mixed solution has a good stabilizing effect on sulfite with a concentration lower than 0.4 mmol / L in the mixed solution; when the concentration of KOH in the mixed solution is 1 mmol / L and the concentration of citrate is 4 mmol / L, the mixed solution has a good stabilizing effect on sulfite with a concentration lower than 0.8 mmol / L in the mixed solution.

[0009] Further, in step two, the ion chromatography detection conditions are as follows: instrument manufacturer and model: Thermo, Dionex Intergrion HPIC; analysis column: Dionex IonPac AS11-HC (4*250mm); detector: ECD; eluent: KOH solution; suppression current: 50mA; column temperature: 30 DEG C; flow rate: 1mL / min; sample volume: 25uL.

[0010] Further, in step two, the gradient elution conditions are as follows: 0.1-5min, 0→4mmol / L KOH; 5-5.1min, 4→8mmol / L KOH; 5.1-32min, 8mmol / L KOH; 32-32.1min, 8→25mmol / L KOH; 32.1-48min, 25mmol / L KOH; 48-48.1min, 25→4mmol / L KOH; 48.1-50min, 4mmol / L KOH.

[0011] The beneficial effects of the present application relative to the prior art are: a sulfite ion chromatography detection method is established, which uses safe and green citrate as a stabilizer; in an alkaline solution, citrate is used as a stabilizer to stabilize sulfite in a sample, and ion chromatography is used to directly determine sulfite ions in water, solving the problem of instability of sulfite in water in the whole process of sampling, storage, transportation and determination. Compared with other methods, the ion chromatography method has simple pretreatment process, is green and safe, and has accurate detection results. Compared with ascorbic acid which can stabilize sulfite for 2h, citrate can make sulfite exist stably for 28h, which will be beneficial to sample preservation when sampling at a long distance. When the sample volume is 25uL, in the range of 0.02-0.8mmol / L, the concentration of sulfite has a good linear relationship with the chromatographic peak area (R2=0.9999), and the detection limit is 0.02mmol / L.2 = 0.999), and the detection limit was 160 μg / L. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 chromatograms of each ion in the mixed standard solution;

[0013] Figure 2 chromatograms of three components in different solutions conversion diagrams;

[0014] Figure 3 chromatograms of three components in 1 mmol / L KOH solution containing VC;

[0015] Figure 4 conversion diagrams of three components in 1 mmol / L KOH solution containing VC over time;

[0016] Figure 5 chromatograms of stability comparison in citrate solution;

[0017] Figure 6 chromatograms of 0.2 mmol / L stability diagrams in different concentrations of citric acid solution;

[0018] Figure 7 chromatograms of 0.4 mmol / L stability diagrams in different concentrations of citric acid solution;

[0019] Figure 8 chromatograms of 0.8 mmol / L stability diagrams in different concentrations of citric acid solution;

[0020] Figure 9 linear relationship diagrams between concentration and peak area within 4 h

[0021] linear relationship diagrams between concentration and peak area after 24 h Figure 10 conversion diagrams before and after 24 h

[0022] Figure 11 conversion diagrams before and after 24 h

[0023] Figure 12 influence diagrams of KOH concentration on stability

[0024] influence diagrams of preparation time on stability Figure 13

[0025] Figure 14 ​​​​The standard curve is shown in the figure. DETAILED DESCRIPTION

[0026] The technical solutions of the present application are further described below in combination with the drawings and examples, but are not limited thereto, and any modification or equivalent replacement to the technical solutions of the present application without departing from the spirit and scope of the technical solutions of the present application shall be covered in the protection scope of the present application.

[0027] Example 1

[0028] A stable method for directly detecting sulfite in water by ion chromatography, comprising the following steps:

[0029] Step 1: A certain amount of KOH and citrate is added to water to prepare a mixed concentrated solution, wherein the molar concentration ratio of KOH to citric acid is 1:4;

[0030] Step 2: A certain volume of water sample containing sulfite is added to the above concentrated solution and mixed quickly; the mixing ratio is determined according to the possible concentration of sulfite in the water sample, and when the KOH concentration in the mixed solution is 1 mmol / L and the citrate concentration is 4 mmol / L, the mixed solution has a good stabilizing effect on sulfite with a concentration lower than 0.8 mmol / L in the mixed solution; the mixed solution is used for ion chromatography determination;

[0031] Step 3: The ion chromatography detection conditions are as follows: instrument manufacturer and model: Thermo, Dionex Intergrion HPIC; analysis column: Dionex IonPac AS11-HC (4x250mm); detector: ECD; eluent: KOH solution; suppression current: 50mA; column temperature: 30℃; flow rate: 1mL / min; injection volume: 25μL. Gradient elution conditions: 0.1-5min, 0→4mmol / L KOH; 5-5.1min, 4→8mmol / L KOH; 5.1-32min, 8mmol / L KOH; 32-32.1min, 8→25mmol / L KOH; 32.1-48min, 25mmol / L KOH; 48-48.1min, 25→4mmol / L KOH; 48.1-50min, 4mmol / L KOH.

[0032] Figure 1 The chromatographic peaks of each ion in the mixed solution of 9 standard substances are shown in the figure, and it can be seen from the figure that the above method can effectively separate a plurality of ions at the same time and has certain practicability. A certain amount of Na2SO3 is added to different solution systems to prepare a solution containing a certain concentration of sulfite, and an ion chromatograph is used for concentration monitoring. Figure 2This shows the effect of water and KOH solution system The transformation can be seen from the graph. The degree of conversion differs between the two systems, with alkaline conditions being more conducive to stability. A certain amount When added to a KOH solution containing vitamin C, the vitamin C concentration in the solution increased within 15 hours. Changes in chromatographic peaks, such as Figure 4 As shown in the figure, the peak area of ​​VC hardly changes with the extension of preparation time, indicating that VC is stable in the solution during this period. However, The peak area gradually decreased after 2 hours of preparation, accompanied by... The gradual increase in peak area indicates that although vitamin C was added to the solution as an antioxidant, it had an effect on... The antioxidant effect is still not ideal, only able to make Maintain stability for 2 hours.

[0033] A certain mass Placed in a citrate solution, Figure 5 The results showed that under alkaline conditions More stable. Figure 6 The images show citrate solutions of different concentrations placed in 1 mmol / L KOH. The stability at a preparation time of 4 hours is shown in the figure, 0.2 mmol / L The peak areas were almost equal at 1, 2, and 4 mmol / L citrate concentrations, and at 0.4 mmol / L. So it is ( Figure 7 ). And 0.8 mmol / L It has similar peak areas in 2 and 4 mmol / L citrate solutions, and in 1 mmol / L citrate solution... The peak area decreased significantly. Figure 8 This indicates that low concentrations of citrate (1 mmol / L) have an effect on high concentrations of citrate. The protective effect of (0.8 mmol / L) is limited, due to Figure 8 It can be seen that a large number of Transformed into

[0034] Figure 9 and Figure 10 The figures show the results in 1 mmol / L KOH solution prepared over 4 hours and at 28-hour intervals. The linear relationship between concentration and peak area, as shown in the figure, indicates that after 24 hours, in a system containing 1 mmol / L citric acid... The linear relationship between concentration and peak area was poor (R² = 0.813), while in systems containing 2 mmol / L or 4 mmol / L citric acid, The linear relationship between concentration and peak area is good. For example... Figure 11 As shown, after a 24-hour interval, in the system containing 4 mmol / L citric acid, The conversion rate should not exceed 5%. Figure 12 The results showed that, in the presence of 4 mmol / L citric acid and with a preparation time of 4 h, the effects of 1–4 mmol / L KOH concentrations on [the specific effects of these concentrations]. The effect of KOH concentration on conversion is shown in the figure. Within the concentration range of 1–4 mmol / L, the concentration of KOH significantly affects the conversion process. The stability is not significantly affected. To save reagents, it is recommended to use 1 mmol / L KOH as a stable solvent.

[0035] Figure 13 It showed 0.8 mmol / L The stability of the solution in a KOH (1 mmol / L) containing 4 mmol / L citrate over 24 hours is shown in the figure. The peak area was relatively stable for the first 20 hours. From the 20th hour onwards, the peak area decreased slightly, while the citrate group remained stable, indicating that the citrate group had a relatively stable effect on the peak area. Stability does not come at the expense of citrate. Figure 14 for The standard curve was prepared using a KOH solution containing 4 mmol / L citrate (1 mmol / L) as a protective agent, and the above-described ion chromatography method was employed. For concentration detection, the minimum detectable concentration is 160 μg / L.

Claims

1. A stable method for facilitating direct detection of sulfite in water by ion chromatography, characterized by: The method comprises the following steps: Step one: a certain mass of KOH and citrate is placed in water to prepare a mixed solution; Step two: a certain volume of water sample containing sulfite is added to the mixed solution and mixed quickly to obtain a final mixed solution, which is used for ion chromatography determination; when the concentration of KOH in the mixed solution is 1 mmol / L and the concentration of citrate is 1 mmol / L, it is suitable for sulfite with a concentration lower than 0.2 mmol / L in the final mixed solution; when the concentration of KOH in the mixed solution is 1 mmol / L and the concentration of citrate is 2 mmol / L, it is suitable for sulfite with a concentration lower than 0.4 mmol / L in the final mixed solution; when the concentration of KOH in the mixed solution is 1 mmol / L and the concentration of citrate is 4 mmol / L, it is suitable for sulfite with a concentration lower than 0.8 mmol / L in the final mixed solution.

2. The stable method of facilitating direct detection of sulfite in water by ion chromatography according to claim 1, characterized in that: In step two, the ion chromatography detection conditions are as follows: instrument manufacturer and model: Thermo, Dionex Intergrion HPIC; analysis column: Dionex IonPac AS11-HC; detector: ECD; eluent: KOH solution; suppression current: 50 mA; column temperature: 30 DEG C; flow rate: 1 mL / min; sample volume: 25 μL; gradient elution conditions: 0.1-5 min, 0→4 mmol / L KOH; 5-5.1 min, 4→8 mmol / L KOH; 5.1-32 min, 8 mmol / L KOH; 32-32.1 min, 8→25 mmol / L KOH; 32.1-48 min, 25 mmol / L KOH; 48-48.1 min, 25→4 mmol / L KOH; 48.1-50 min, 4 mmol / L KOH. 5.1-32 min, 8 mmol / L KOH; 32-32.1 min, 8→25 mmol / L KOH; 32.1-48 min, 25 mmol / L KOH; 48-48.1 min, 25→4 mmol / L KOH; 48.1-50 min, 4 mmol / L KOH.

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