CN105136695A - A kind of spectroscopic determination method and application of sulfite ion based on OPA-NH4+-SO32-reaction - Google Patents

Abstract

The invention discloses a spectroscopic determination method of sulfite ion based on OPA-NH ₄ ⁺ -SO ₃ ^2- reaction, which comprises: sequentially adding o-phthalaldehyde solution, EDTA-NaOH buffer solution and ammonia nitrogen solution, shake well, put them at a certain temperature to react to balance, take out and cool to room temperature, set up a spectrophotometer to measure the wavelength, measure the absorbance A of the solution, take the absorbance A as the ordinate, sulfurous acid Draw a working curve for the root ion concentration on the abscissa; in the sample solution, measure the absorbance A _s of the sample solution according to the above method; according to the working curve and the absorbance A _s of the sample solution, quantify the content of sulfite ions in the sample solution. The invention has the advantages of no need to use toxic reagents, low detection limit, high sensitivity and the like.

Description

A kind of spectroscopic determination method and application of sulfite ion based on OPA-NH4+-SO32-reaction

technical field

The invention relates to the determination of sulfite ions, in particular to a spectroscopic determination method and application of sulfite ions based on the OPA-NH ₄ ⁺ -SO ₃ ^2- reaction.

Background technique

At present, the methods for detecting sulfite ion in water samples mainly include pararosaniline hydrochloride spectrophotometry and o-phenanthroline-Fe ³⁺ spectrophotometry. The pararosaniline hydrochloride method uses more mercury salts in the determination process, which has certain potential hazards to people and the environment, and is not suitable for widespread use; the minimum detection concentration of the o-phenanthroline-Fe ³⁺ method is 0.052mg/L, and the detection The limit is relatively high, and it cannot do anything for samples with low sulfite ion content.

Contents of the invention

The purpose of the present invention is to provide a spectroscopic determination method of sulfite ion based on OPA-NH ₄ ⁺ -SO ₃ ^2- reaction. The method does not need to use toxic reagents, and has low detection limit, high sensitivity and rapidity.

The technical scheme that realizes the object of the present invention:

According to the present invention, when the pH is greater than 11, the sulfite ion in the water sample can react with o-phthalaldehyde (OPA) and ammonia nitrogen to generate a purple-red substance, and the absorbance of the purple-red substance can be compared with sulfurous acid under certain conditions. The concentration of sulfite ion is directly proportional, based on this, the spectroscopic determination method of sulfite ion is established.

A spectroscopic determination method based on OPA-NH ₄ ⁺ -SO ₃ ^2- reaction of sulfite ion, comprising the steps:

(1) Add 1.0mL of 10.6g/L o-phthalaldehyde solution to 25mL of sulfite ion standard solution in the range of 0.00-8.00mg/L, the concentration of EDTA is 52.0g/L and the concentration of NaOH is 12.0g 5.0mL of EDTA-NaOH buffer solution per L, 3.0mL of 5.0mmol/L ammonia nitrogen solution, that is, the dosage of OPA is 0.42g/L, the dosage of ammonia nitrogen is 0.60mmol/L, and the pH is 11.50; shake well; place at a certain temperature Lower the reaction to equilibrium; take it out and cool to room temperature, set the spectrophotometer to measure the wavelength as 550nm, and measure the absorbance A of the solution; take the sulfite ion concentration as the abscissa, and the absorbance A as the ordinate to draw a working curve;

(2) In 25mL sample solution, add 1.0mL10.6g/L o-phthalaldehyde solution, 5.0mL EDTA-NaOH buffer solution with EDTA concentration of 52.0g/L and NaOH concentration of 12.0g/L, 3.0mL5. 0mmol/L ammonia nitrogen solution, that is, the dosage of OPA is 0.42g/L, the dosage of ammonia nitrogen is 0.60mmol/L, and the pH is 11.50; The measuring wavelength of the meter is 550nm, and the absorbance A _s of the sample solution is measured;

(3) Quantify the content of sulfite ions in the sample solution according to the above working curve and the absorbance A _s of the sample solution.

Based on the OPA-NH ₄ ⁺ -SO ₃ ^2- reaction, the applicant has carried out specific experiments for determining the concentration of sulfite ions by means of spectrometry, and obtained the optimal reaction conditions for the method of the present invention from these experiments.

1. Instruments and reagents

The main instruments are BT124D analytical balance (Beijing Sartorius Instrument System Co., Ltd.), electric heating constant temperature water bath (Shanghai Hede Experimental Equipment Co., Ltd.), UV-2550 ultraviolet-visible spectrophotometer (Shimadzu Corporation, Japan).

The reagents used in this study were of analytical grade unless otherwise specified, and the pure water used was reverse osmosis water. The main reagent solutions are:

(1) 10.6g/L o-phthalaldehyde solution: Weigh 2.12g of o-phthalaldehyde solid, dissolve it in 70mL methanol solution (chromatographically pure), after it dissolves, add 125mL ultrapure water, shake well and seal Store in tinfoil under refrigeration to obtain a 10.6 g/L o-phthalaldehyde solution.

(2) Na ₂ SO ₃ standard stock solution: Weigh 0.50 g of anhydrous Na ₂ SO ₃ solid, dissolve in 500 mL of ultrapure water, shake well and store in refrigerator. The exact concentration was calibrated by iodine-sodium thiosulfate titration.

(3) 0.050g/L Na ₂ SO ₃ standard solution: obtained by diluting Na ₂ SO ₃ standard stock solution. Prepare on the day of use.

(4) 20mmol/L ammonia nitrogen stock solution: Accurately weigh 0.33g of (NH ₄ ) ₂ SO ₄ , dissolve in a small amount of water and dilute to 150mL, store in refrigerator at 4°C.

(5) 5.0mmol/L ammonia nitrogen solution: obtained by diluting the ammonia nitrogen stock solution.

(6) EDTA-NaOH buffer solution: Weigh 26.0 g of EDTA solid and 6.0 g of NaOH solid, and then add 500 mL of ultrapure water to dissolve them completely.

(7) 0.10mol/L NaOH solution: Weigh 1.0g NaOH solid and dissolve it in 250mL ultrapure water. 2. Experimental method

Pipette 25mL of sulfite ion standard solution in the range of 0.00-8.00mg/L (prepared by diluting 0.050g/L Na ₂ SO ₃ standard solution) or sample solution into a 50mL colorimetric tube, and add 1.0 mL10.6g/L o-phthalaldehyde solution, 5.0mL LEDTA-NaOH buffer solution, 3.0mL5.0mmol/L ammonia nitrogen solution, that is, the amount of OPA (the amount mentioned in this study refers to the amount of reagent added to the unit water sample or standard solution) 0.42g/L (calculated by dividing the mass of the reagent OPA by 25mL), the amount of ammonia nitrogen is 0.60mmol/L, and the pH is 11.50. relevant), take it out, and after cooling to room temperature, set the spectrophotometer to measure the wavelength at 550nm, and measure the absorbance A of the solution.

3. The best reaction conditions obtained from the experiment

1. Absorption spectrum curve

Pipette 25 mL of the sulfite ion standard solution of 3.0 mg/L, add the reagent according to the above-mentioned experimental method, after the reaction is balanced, measure the absorption spectrum of the reaction solution in the visible light region with a UV-Vis spectrophotometer, the results are shown in Figure 1 Show. Figure 1 shows that the reaction solution has a maximum absorption plateau in the range of 540-560nm, therefore, 550nm is selected as the measurement wavelength for the following experiments.

2. Determination of reagent dosage

The main reagents used in the determination of sulfite ion based on the OPA-NH ₄ ⁺ -SO ₃ ^2- reaction are OPA and ammonia nitrogen solution, wherein the concentration of OPA and ammonia nitrogen solution will affect the completeness of the reaction, and then affect the absorbance of the reaction solution. For this reason, taking 25mL6.0mg/L standard solution of sulfite ion as the object of investigation, the influence of the amount of OPA and ammonia nitrogen on the absorbance of the reaction solution was investigated by single factor method.

Determination of OPA dosage

The amount of other reagents was fixed as described in the experimental method, and the influence of the amount of OPA on the absorbance of the reaction solution was investigated in the range of 0-0.42 g/L. The results are shown in Figure 2. Figure 2 shows that as the concentration of OPA increases, the absorbance of the reaction solution increases rapidly at first, and then gradually tends to be stable. Specifically, when the amount of OPA increases from 0 to 0.085g/L, the absorbance of the reaction solution shows a rapid increase trend; when it increases from 0.085 to 0.21g/L, the absorbance increase trend slows down; tends to a constant value. It shows that when the amount of OPA is 0.21-0.42g/L, the amount of OPA is enough to meet the needs of the reaction without affecting the progress of the reaction. It can be seen that the optimal use range of OPA is 0.21-0.42g/L. The following experiments control the amount of OPA to be 0.42g/L, that is, add 10.6g/1mL of LOPA solution to 25mL of the test solution.

Determination of ammonia nitrogen dosage

The amount of other reagents was fixed as described in the experimental method, and the single factor method was used to investigate the influence of the amount of ammonia nitrogen on the absorbance of the reaction solution in the range of 0-0.80mmoL/L. The results are shown in Figure 3. Figure 3 shows that as the amount of ammonia nitrogen increases, the absorbance increases first and then tends to be stable. When the amount of ammonia nitrogen changes within the range of 0.60-0.80mmoL/L, the absorbance tends to a constant value, that is, within this range, ammonia nitrogen The dosage can fully meet the needs of the reaction without affecting the progress of the reaction. It shows that the optimal use range of ammonia nitrogen is 0.60-0.80mmoL/L, and the amount of ammonia nitrogen used in the following experiments is controlled at 0.60mmoL/L, that is, 3.0mL of 5.0mmol/L ammonia nitrogen solution is added to 25mL of the test solution.

3. The influence of pH

The experiment found that the color of the reaction product of the OPA-NH ₄ ⁺ -SO ₃ ^2- system is related to the pH of the reaction solution. For this reason, the standard solution of sulfite of 6.0 mg/L was used as the object of investigation, and the amount of OPA was added according to the experimental method. And the amount of ammonia nitrogen, adjust the pH of the reaction solution by changing the amount of 0.1mol/L NaOH solution. Table 1 lists the colors of the reaction products of the OPA-NH ₄ ⁺ -SO ₃ ^2- system when the pH of the reaction solution varies within the range of 9.15-13.07. Table 1 shows that when the pH is in the range of 9.15-10.85, the reaction product is yellow; when the pH changes in the range of 11.20-12.85, the reaction product is a purple-red complex. This method is established based on the reaction to generate a purple-red complex. Therefore, the relationship between the absorbance and the pH was further investigated in the range of pH 11.20-12.85, and the results are shown in Figure 4. It can be seen from Figure 4 that within the investigated pH range, as the pH increases, the absorbance shows a slow increasing trend, and it can be seen that pH is one of the important factors affecting the absorbance of the reaction solution. Generally, the pH of the solution can be stabilized within a certain range by adding a buffer solution. Considering the control of the absorbance and the pH of the solution, the pH of the reaction solution is controlled to be 11.50 in the following experiments. Through repeated experiments, when 5.0 mL of the prepared EDTA-NaOH buffer solution is added to 25 mL of sulfite standard solution or actual water samples such as river water and groundwater, the pH of the reaction solution can be stabilized at about 11.50.

The color of reaction product under the different pH conditions of table 1

4. Determination of reaction equilibrium time

In general, the reaction temperature will affect the reaction rate. In order to determine the equilibrium time at different reaction temperatures, take the 6.0 mg/L sulfite ion standard solution as the object, add reagents according to the experimental method, and investigate the change trend of absorbance with reaction time under different temperature conditions , so as to determine the reaction equilibrium time. The variation trend of absorbance with reaction time at 7 temperatures of 15°C, 23°C, 26°C, 30°C, 35°C, 40°C and 45°C were investigated respectively, and the results are shown in Figure 5-Figure 11. The results showed that no matter what the temperature was, the absorbance of the reaction solution increased first and then tended to a constant value with the prolongation of the reaction time. Figure 5 shows that when the reaction temperature is 15°C and the reaction time exceeds 150min, the absorbance tends to be stable and the reaction basically reaches an equilibrium state; Figure 6 shows that when the reaction temperature is 23°C and the reaction time exceeds 80min, the absorbance tends to be constant , the reaction reaches an equilibrium state and can be stabilized at least to the 150th minute; Figure 7 shows that at 26°C, when the reaction time exceeds 60 minutes, the reaction reaches equilibrium, but when the reaction time exceeds 100 minutes, the absorbance shows a slow downward trend, indicating that the reaction is in From the 60th minute to the 100th minute, the stable state is maintained, and can be stable for 40 minutes; Figure 8 shows that at 30 ° C, the reaction equilibrium time is 50 minutes, and the reaction maintains an equilibrium state within the range of 50 minutes to 90 minutes, that is, the equilibrium state can last for 40 minutes; Fig. 9 shows that at 35°C, the equilibrium time of the reaction is 30 minutes, and it can be stable to the 60th minute, and the equilibrium state can last for 30 minutes; Fig. The state can be maintained for 25 minutes; Figure 11 shows that at 45°C, the equilibrium time of the reaction is 15 minutes, it can be stable until the 30th minute, and it can be maintained for 15 minutes. It can be seen that as the reaction temperature increases, the time required for the reaction to reach equilibrium is gradually shortened, and at the same time, the equilibrium maintenance time also tends to shorten. The time required to reach equilibrium and the duration of equilibrium at each temperature are listed in Table 2.

Reaction start time and end time under table 2 different reaction temperatures

4. Working curve and detection limit

Under the optimal conditions selected, prepare a series of sulfite ion standard solutions within a certain concentration range, add reagents as described in the experimental method, react to equilibrium at a certain temperature, measure the absorbance, and investigate the relationship between absorbance and reaction concentration (Working curve). The results show that at 40°C, when the sulfite ion concentration is in the range of 0.00-8.00 mg/L, the working curve presents a linear relationship, as shown in Figure 12, the linear equation is A=0.103C+0.021 (n=7, R ² =0.9983), A in the equation is the absorbance, C is the concentration of sulfite ion, the unit is mg/L. At different times, due to slight differences in environmental conditions and the environment in which the instrument is located, the measurement results of the working curve will be different. Therefore, when measuring unknown samples, the working curve should be measured at the same time.

The detection limit refers to the minimum concentration or minimum amount of analyte that can be detected from a sample by an analytical method within a given degree of reliability. Configure 7 blank samples, add reagents according to the experimental method, react to equilibrium, measure the absorbance, the result is 0.005±0.00108 (n=7), calculate the detection limit with 3*SD/slope of the working curve, the working curve of the day is A=0.124C +0.022 (n=7, R ² =0.9966), therefore, the calculation result of the detection limit is 0.026 mg/L.

5. Recovery rate of substrate spiked

Base spike recovery for water samples:

River water (taken from the Huajiang River in Guilin City), groundwater (taken from the Huajiang Campus of Guilin University of Electronic Science and Technology), and mountain spring water (taken from the Yaoshan Scenic Area in Guilin City) were used as the base respectively, and the spiked concentrations of sulfite ions were 0, 0.250 , 0.500, 1.00, 2.00, 4.00 and 6.00mg/L, determine the base addition curve; at the same time determine the working curve of the day. The average base-spike recovery was calculated by dividing the slope of the base-spike curve by the slope of the working curve of the day, and the results are shown in Table 3. Table 3 shows that the recovery rates of the bases of river water, groundwater and mountain spring water are 99.4%, 104.3% and 102.9% respectively, indicating that the bases of river water, groundwater and mountain spring water do not interfere with the determination. The method established in this study is suitable for the determination of river water, Fresh water samples such as groundwater and mountain spring water.

Table 3 The substrate spiked curve and the substrate spiked recovery rate of different substrates

Base spike recovery of white sugar water sample:

Configure 4.0% (w/v) white sugar water sample. Take the white granulated sugar water sample as the base, and measure the recovery rate of the base spiked according to the concentration listed in Table 4. Table 4 shows that the average recovery rates of the two substrates of the 4.0% (w/v) white granulated sugar water sample are 107.4% and 100.2% respectively, indicating that the 4.0% (w/v) white granulated sugar water sample has no interference to the determination . That is, the method described in this study is suitable for determining the content of sulfite ion in white sugar water samples

Table 4 Recovery rate of white granulated sugar water sample substrate spiked

The above experiments show that the reaction of OPA-NH ₄ ⁺ -SO ₃ ^2- can generate a purple-red substance, which has a maximum absorption plateau at 540-560nm. Based on this, a new spectroscopic method for the determination of sulfite ions in river water, groundwater, mountain spring water and white sugar water samples was established. The linear range of this method is 0.00-8.00mg/L, and the method detection limit is 0.026mg/L. The recoveries of base spiked water samples ranged from 99.4% to 107.4%. Compared with the existing method o-phenanthroline-Fe ³⁺ spectrophotometry, there is no significant difference in the determination results. When the reaction temperature exceeds 35°C, the time required for the reaction to reach equilibrium is less than 30 minutes. The invention is successfully applied to the determination of sulfite ions in river water samples, and the result has no significant difference from the determination result of o-phenanthroline-Fe ³⁺ spectrophotometry. Compared with the existing spectroscopic determination method of sulfite ion, the method established in this study does not need to use highly toxic mercury salt and other reaction reagents, and has the advantages of lower detection limit, higher sensitivity, and rapidity.

Description of drawings

The absorption spectrogram of Fig. 1 sulfite ion and OPA, ammonia nitrogen reaction product;

Fig. 2 is the figure of influence of OPA dosage on the absorbance of reaction solution;

Fig. 3 is the figure of influence of the amount of ammonia nitrogen on the absorbance of the reaction solution;

Fig. 4 is the figure of influence of pH on the absorbance of reaction solution;

Fig. 5 is when the reaction temperature is 15 ℃, the change trend diagram of the absorbance of the reaction solution with the reaction time;

Fig. 6 is when the reaction temperature is 23 ℃, the change trend diagram of the absorbance of the reaction solution with the reaction time;

Fig. 7 is when the reaction temperature is 26 ℃, the change trend diagram of the absorbance of the reaction solution with the reaction time;

Fig. 8 is when the reaction temperature is 30 ℃, the change trend diagram of the absorbance of the reaction solution with the reaction time;

Figure 9 is a trend diagram of the absorbance of the reaction solution with the reaction time when the reaction temperature is 35°C;

Fig. 10 is when the reaction temperature is 40 ℃, the change trend diagram of the absorbance of the reaction solution with the reaction time;

Figure 11 is a trend diagram of the absorbance of the reaction solution with the reaction time when the reaction temperature is 45°C;

Fig. 12 is a working curve diagram of absorbance and sulfite reaction concentration.

Detailed ways

A spectroscopic determination method based on OPA-NH ₄ ⁺ -SO ₃ ^2- reaction of sulfite ion, comprising the steps:

(1) Add 1.0mL of 10.6g/L o-phthalaldehyde solution to 25mL of sulfite ion standard solution in the range of 0.00-8.00mg/L, the concentration of EDTA is 52.0g/L and the concentration of NaOH is 12.0g 5.0mL of EDTA-NaOH buffer solution per L, 3.0mL of 5.0mmol/L ammonia nitrogen solution, that is, the dosage of OPA is 0.42g/L, the dosage of ammonia nitrogen is 0.60mmol/L, and the pH is 11.50; shake well; place at a certain temperature Lower the reaction to equilibrium; take it out and cool to room temperature, set the spectrophotometer to measure the wavelength as 550nm, and measure the absorbance A of the solution; take the sulfite ion concentration as the abscissa, and the absorbance A as the ordinate to draw a working curve;

(2) In 25mL sample solution, add 1.0mL10.6g/L o-phthalaldehyde solution, 5.0mL EDTA-NaOH buffer solution with EDTA concentration of 52.0g/L and NaOH concentration of 12.0g/L, 3.0mL5. 0mmol/L ammonia nitrogen solution, that is, the dosage of OPA is 0.42g/L, the dosage of ammonia nitrogen is 0.60mmol/L, and the pH is 11.50; The measuring wavelength of the meter is 550nm, and the absorbance A _s of the sample solution is measured;

(3) Quantify the content of sulfite ions in the sample solution according to the above working curve and the absorbance A _s of the sample solution.

Under the selected optimal conditions, prepare a series of sulfite ion standard solutions within a certain concentration range, add reagents as described in the experimental method, react to equilibrium at a certain temperature, measure the absorbance, and investigate the work of absorbance and reaction concentration curve. The results show that at 40°C, when the sulfite ion concentration is in the range of 0.00-8.00 mg/L, the working curve presents a linear relationship, as shown in Figure 12, the linear equation is A=0.103C+0.021 (n=7, R ² =0.9983), A in the equation is the absorbance, C is the concentration of sulfite ion, the unit is mg/L. At different times, due to slight differences in environmental conditions and the environment in which the instrument is located, the measurement results of the working curve will be different. Therefore, when measuring unknown samples, the working curve should be measured at the same time. The detection limit refers to the minimum concentration or minimum amount of analyte that can be detected from a sample by an analytical method within a given degree of reliability. Configure 7 blank samples, add reagents according to the experimental method, react until equilibrium, measure the absorbance, the result is 0.005±0.00108 (n=7), calculate the detection limit with 3*SD/slope of the working curve, the working curve of the day is A=0.124C +0.022 (n=7, R ² =0.9966), therefore, the calculation result of the detection limit is 0.026 mg/L. The method established in this study was used to determine the content of sulfite ions in two river water samples. At the same time, the o-phenanthroline-Fe ³⁺ spectrophotometric method was used to measure the water samples, and the results were compared. The data are listed in Table 5. The results of the two river water samples measured by the method described in this study were 3.76±0.046 (n=4) and 6.65±0.17 (n=4) mg/L, respectively. Use the t test method to test the difference of the measurement results of the two methods, the statistical quantity t calculation value of the two sample measurement results is all less than the critical value when the confidence level is 95%, so this method is different from the existing o-phenanthroline-Fe There was no significant difference in the results of ³⁺ spectrophotometric determination of sulfite ion in water samples. It shows that the method established in this study can successfully determine the content of sulfite ion in actual water samples, and the determination results are reliable.

Table 5 Comparison between this method and o-phenanthroline-Fe ³⁺ spectrophotometric method

Claims (5)

1. one kind based on OPA-NH ₄ ⁺-SO ₃ ^2-the spectral photometry method of the sulfite ion of reaction, is characterized in that, comprise the steps:

(1) in the sulfite ion standard solution within the scope of 25mL0.00-8.00mg/L, add 1.0mL10.6g/L o-phthalaldehyde(OPA) solution successively, the EDTA-NaOH damping fluid 5.0mL of EDTA concentration to be 52.0g/L and NaOH concentration be 12.0g/L, 3.0mL5.0mmol/L ammonia nitrogen solution, namely, OPA consumption is 0.42g/L, and ammonia nitrogen consumption is 0.60mmol/L, pH is 11.50; Shake up; Under being placed in certain temperature, reaction is to balance; After taking-up is cooled to room temperature, spectrophotometric determination wavelength is set, measures the absorbance A of solution; Take ion concentration of inferior sulfate radical as horizontal ordinate, absorbance A is ordinate drawing curve;

(2) in sample solution, add 1.0mL10.6g/L o-phthalaldehyde(OPA) solution successively, the EDTA-NaOH damping fluid 5.0mL of EDTA concentration to be 52.0g/L and NaOH concentration be 12.0g/L, 3.0mL5.0mmol/L ammonia nitrogen solution, namely, OPA consumption is 0.42g/L, and ammonia nitrogen consumption is 0.60mmol/L, pH is 11.50; Shake up; Under being placed in certain temperature, reaction is to balance; After taking-up is cooled to room temperature, spectrophotometric determination wavelength is set, the absorbance A of working sample solution _s;

(3) according to the absorbance A of above-mentioned working curve and sample solution _s, the sulfite ion content in quantitative sample solution.

2. method according to claim 1, is characterized in that, the spectrophotometric determination wavelength of described setting is 550nm.

3. method according to claim 1, is characterized in that, the working curve of absorbance and reaction density is 40 DEG C time, and the range of linearity of working curve is 0.00-8.00mg/L.

4. method according to claim 1, is characterized in that, the detection of method of the present invention is limited to 0.026mg/L.

5. one kind based on OPA-NH ₄ ⁺-SO ₃ ^2-the spectral photometry method of the sulfite ion of reaction is measuring the application in river, underground water, mountain spring water or white sugar water.