Ion chromatography detection method for simultaneously measuring sulfate radicals and sulfite radicals in desulfurized seawater
Technical Field
The invention belongs to the technical field of chemical analysis, and particularly relates to a detection method for simultaneously determining sulfate radicals and sulfite radicals in a water body containing calcium ions and magnesium ions, in particular to an ion chromatography detection method for simultaneously determining sulfate radicals and sulfite radicals in desulfurized seawater.
Background
The seawater flue gas desulfurization method is the preferred desulfurization method for coal-fired power plants in coastal areas, sulfur in the fire coal is converted into sulfur oxides after combustion, and sulfate and sulfite are generated after the sulfur oxides are dissolved in seawater. The solubility (wt%, 25 ℃) of calcium sulfite in water was 0.005g, the solubility (wt%, 25 ℃) of calcium sulfate was 0.2g, and the solubility (wt%, 25 ℃) of magnesium sulfite was 0.6 g. Therefore, trace sulfate radicals and sulfite radicals in the desulfurized seawater are simultaneously and accurately quantified, so that the thorough degree of seawater desulfurization can be monitored, and the significance of the combination of flue gas desulfurization and seawater desalination and decalcification technology can be understood.
The detection of sulfite comprises a pararosaniline hydrochloride method, a distillation method, an iodometry method and the like, the detection limit of the methods is 1mg/L, and sulfite ions with lower concentration in seawater are difficult to detect; the arbitration detection of sulfate ions adopts a gravimetric method, the method has long operation time, the detection limit of water quality detection is 2.5mg/L, the detection limits of an EDTA volumetric method and a potentiometric titration method are both more than 1mg/L, and the method is difficult to realize the analysis of sulfate ions with lower concentration.
In a desulfurization seawater system, sulfate ions and sulfite ions exist simultaneously, and sulfite is easily oxidized into sulfate in an acid solution; the existence of calcium and magnesium ions enables the mobile phase of a carbonate system to react with each other to form precipitates to block a chromatographic column, and an appropriate method needs to be selected to remove the influence of the calcium and magnesium ions; in addition, sulfate and sulfite have the same nuclear charge number and similar hydrated ion radius, so that baseline separation is difficult to realize in ion chromatography detection, and difficulty is brought to ion chromatography for simultaneously measuring sulfate and sulfite in the desulfurized seawater.
Disclosure of Invention
The invention aims to overcome the defects in the prior art: the method can only analyze and quantify single ions, has high detection limit, is difficult to analyze ions with the concentration lower than 1mg/L, and is difficult to respectively and simultaneously quantify two ions by the existing detection method under the condition that the two ions exist simultaneously. The invention provides an ion chromatography detection method for simultaneously measuring sulfate radicals and sulfite radicals in desulfurized seawater. The method realizes the pretreatment of the sample by the combination of solutions of formaldehyde, sodium hydroxide and disodium ethylene diamine tetraacetate with specific concentrations; and regulating specific ion chromatographic detection parameters to realize baseline separation of sulfite and sulfate radicals. On the basis of realizing the simultaneous accurate quantification of sulfate ions and sulfite ions, the invention also provides a novel sample pretreatment method to remove the influence of calcium and magnesium ions on the test, simultaneously inhibits the oxidation of sulfite, and solves the defects of the existing detection method.
The technical scheme of the invention is as follows:
an ion chromatography detection method for simultaneously measuring sulfate radicals and sulfite radicals in desulfurized seawater comprises the following steps:
a. drawing a sulfate ion and sulfite ion mixed standard curve:
weighing sodium sulfite and sodium sulfate solids, dissolving and diluting the sodium sulfite and sodium sulfate solids by using a pretreatment solution to prepare 5-12 groups of mixed standard solutions with the same sulfate radical and sulfite radical concentration and gradually increased concentration, wherein the ion concentration is 5.00-100.00 mg/L; filtering the mixed standard solution by an organic microporous filter membrane respectively, and testing by an instrument to obtain respective peak areas A (mu S & min) of sulfate ions and sulfite ions in the mixed solution; and (3) plotting by taking the ion concentration as an abscissa and taking the peak area as an ordinate, and obtaining two univariate linear equations of the ion concentration and the related peak area according to the plot: where a is the integral of conductance over time in μ S · min, C is the concentration in mg/L, and k and b are dimensionless constants, i.e. the univariate linear equation for the sulfate ion concentration and its peak area is: c1 ═ k1 · a1+ b 1; the unary linear equation of the concentration of sulfite ions and the peak area thereof is as follows: c2 ═ k2 · a2+ b 2;
the test instrument is specifically an anion chromatography detection system.
The test instrument is preferably a quantitative loop volume of 25 mu L, a conductivity detector, an ASRS4mm anion suppressor and an IonPacAS9-HC separation column, and the test instrument is preferably under the working conditions of an eluent solution of 9mmol/L sodium carbonate and an eluent flow rate of 1.2 mL/min.
The pretreatment solution is a solution containing 0.5 mass percent of formaldehyde, 1 mole percent of sodium hydroxide and 0.5 mole percent of disodium ethylene diamine tetraacetate;
the number of the series of mixed standard solutions is preferably six, wherein the concentrations of sulfate radicals and sulfite radicals are 5.00mg/L, 10.00mg/L, 20.00mg/L, 50.00mg/L, 80.00mg/L and 100.00mg/L respectively;
taking the pretreatment solution with the same composition as a blank solution to be detected; k1 and b1, k2 and b2 are obtained by regression of actual instrument test.
Wherein, the concentration detection range C1 is 0.04-100.00 mg/L, and C2 is 0.03-100.00 mg/L;
the organic microporous filter membrane is a vinylidene fluoride resin membrane, and the pore diameter is preferably 0.22 μm.
b. Determining the concentration of sulfate ions and sulfite ions in the desulfurized seawater to be detected:
filtering the liquid to be measured through an organic microporous filter membrane, measuring the peak areas of sulfate ions and sulfite ions by adopting the same instrument in the step of drawing a mixed standard curve of the sulfate ions and the sulfite ions, and then substituting the peak areas into the linear equation obtained in the step a, wherein the unitary linear equation of the concentration of the sulfate ions and the peak areas thereof is as follows: c1 ═ k1 · a1+ b 1; the unary linear equation of the concentration of sulfite ions and the peak area thereof is as follows: c2 ═ k2 · a2+ b 2; and calculating the concentration of the ion according to the measured peak area A and the dimensionless constants k and b.
The invention has the substantive characteristics that:
in the invention, when the sulfite is pretreated, the influence of pH on the existence mode of the sulfite in the solution and the influence of pH on the oxidation rate of the sulfite are preferably considered, the pH is adjusted to 10 to eliminate the bisulfite easy to be oxidized, and the reducing agent formaldehyde with specific concentration is added on the basis, thereby achieving the purpose of better inhibiting the oxidation of the sulfite. And finally, selecting a method for adjusting the pH to 10 and treating an ethylene diamine tetraacetic acid solution to fix calcium and magnesium ions by screening the cationic fixative. Through selecting proper instrument parameters, the treated sample is analyzed, and the detection of sulfate ions and sulfite ions is not adversely affected by the EDTA ions.
The invention has the beneficial effects
The invention utilizes the oxidation rate property of sulfite in the solution to control the pH of the solution and simultaneously uses 0.5 percent formaldehyde solution as an oxidation inhibitor to effectively prevent sulfite ions from being oxidized. The interference of calcium and magnesium cations on ion chromatography detection is effectively fixed by innovatively adopting an ethylene diamine tetraacetic acid solution and a method for adjusting pH. The method is suitable for simultaneously and quantitatively detecting sulfate ions and sulfite ions in a seawater desulfurization system, and is also suitable for detecting single ions of the sulfate ions and the sulfite ions in water with calcium and magnesium cations.
The invention realizes the simultaneous and accurate quantification of sulfate ions and sulfite ions by using the ion chromatography, and solves the problem that the existing detection method has no suitable detection method under the condition that two ions exist at the same time and the concentration of the ions is low (lower than 1 mg/L). In the invention, the detection limit of sulfate radicals is 0.04mg/L, which is lower than 2.5mg/L of the prior optimal water quality detection method; the detection limit of the sulfite is 0.03mg/L, which is lower than 1mg/L of the prior method.
Drawings
FIG. 1 is a standard curve for sulfate ion and sulfite ion tests.
FIG. 2 shows the detection results of the desulfurized seawater sample.
Detailed Description
The present solution is further illustrated by the following specific examples.
Example 1
a. Drawing a sulfate ion and sulfite ion mixed standard curve, accurately weighing 1.5741g of anhydrous sodium sulfite and 1.4785g of anhydrous sodium sulfate superior pure reagent in the same beaker, diluting the anhydrous sodium sulfite and anhydrous sodium sulfate superior pure reagent to a 1000ml volumetric flask by using a mixed solution, and preparing a mixed standard stock solution; continuously using the mixed solution to dilute step by step to prepare a series of mixed standard solutions with the concentrations of sulfate radical and sulfite radical of 5.00mg/L, 10.00mg/L, 20.00mg/L, 50.00mg/L, 80.00mg/L and 100.00mg/L, drawing a sulfate radical ion and sulfite radical ion test standard curve by using the relation of anion concentration C (mg/L) in the prepared standard solution to ion chromatographic characteristic peak area A (mu S.min) under the working conditions of the elution solution with the parameters of 9mmol/L sodium carbonate solution, the elution solution flow rate of 1.2mL/min and the IonPACA 9-HC separation column, and referring to the attached figure 1, wherein the figure 1 shows that the concentrations in the detected concentration range are 5.00mg/L, 10.00mg/L, 20.00mg/L, 50.And the ion concentration and the integral area of the corresponding ion characteristic peak are in a linear relation, and the obtained linear regression equation is as follows: c (SO)4 2-) 28.4171a +0.0042 and C (SO)3 2-) 13.7005a + 0.0031; according to the signal-to-noise ratio of 3 times, the detection limit of sulfate ions is 0.04mg/L, and the detection limit of sulfite ions is 0.03 mg/L; by detecting the sample, the integral area A of the characteristic peak conductance of sulfite and sulfate ions to time can be directly obtained, and the concentration of the corresponding ions can be calculated by directly reading the integral area and substituting the integral area into the linear equation of the corresponding ions; wherein the solvent of the mixed solution is ultrapure water, the solutes are formaldehyde and sodium hydroxide, the mass percentage concentration of the formaldehyde in the mixed solution is 0.5%, the molar percentage concentration of the sodium hydroxide is 0.5%, and the molar percentage concentration of the disodium ethylene diamine tetraacetate is 0.5%;
TABLE 1 customized ion Standard series to be tested
b. Pretreating the desulfurized Schleicher artificial seawater, inhibiting sulfite oxidation, fixing calcium and magnesium cations, transferring 1mL of desulfurized seawater to be detected, diluting the desulfurized seawater to be detected to be 100mL by using a mixed solution of 0.5% by mass of formaldehyde, 1% by mole of sodium hydroxide solution and 0.5% by mole of disodium ethylenediamine tetraacetate, filtering the diluted solution by using a 0.20-micrometer water-based microporous filter membrane, and removing calcium hydroxide and magnesium hydroxide precipitates to prepare a liquid to be detected; synchronously preparing blank solution to be detected by using ultrapure water;
c. performing ion chromatographic analysis on the solution to be detected, performing ion chromatographic analysis on the desulfurized seawater pretreated in the step b, referring to the attached drawing 2, wherein the eluent is 9mmol/L sodium carbonate solution, the flow rate of the eluent is 1.2mL/min, the volume of a quantitative ring is 25 mu L, and the integral area of the characteristic peak of the desulfurized seawater after blank correction of sulfate ions and sulfite ions is measured; the characteristic peak position of sulfite is 15.067min, the concentration is 20.88mg/L, the characteristic peak position of sulfate is 17.217min, and the concentration is 4.74 mg/L;
the applicable detection concentration of the ions related to the scheme is respectively as follows: the concentration of sulfite is more than 0.03mg/L of detection limit concentration, the concentration of sulfate is more than 0.04mg/L of detection limit concentration, and the error can be kept within 1% by gradually diluting to the concentration range of a standard curve in the solubility range of sulfite and sulfate.
Example 2
The precision, accuracy and recovery rate of the detection method are tested.
The accuracy and precision of the method are confirmed by the standard addition recovery experiment and the precision experiment of the sample.
In the recovery experiment, after a certain amount of sulfate radical and sulfite radical ion standard solution is added into the desulfurized Schleicher artificial seawater, the sample standard addition recovery rate after treatment is detected according to the method, and the test result is shown in Table 2.
Table 2 sulfate and sulfite ion precision and standard recovery test results (n ═ 3)
The method is used for simultaneously and quantitatively detecting sulfate radicals and sulfite ions in the desulfurized seawater, the linearity is good in the concentration range of 5.00-100.00 mg/L, the correlation coefficient is above 0.999, the standard recovery rate range of the sulfate radicals and the sulfite ions is 96.5-104.3%, and the RSD is 0.3-1.9%. The detection limit of sulfite is 0.03mg/L, and the detection limit of sulfate is 0.04 mg/L. The method has the advantages of rapid detection, high sensitivity and good accuracy, and provides technical support for the research of the seawater flue gas desulfurization technology.
The invention is not the best known technology.