阅读说明：本技术 一种地表水中总磷浓度的测定方法 (Method for measuring total phosphorus concentration in surface water ) 是由 朱红霞 袁懋 张霖琳 薛荔栋 于 2020-12-31 设计创作，主要内容包括：本发明涉及一种地表水中总磷浓度的测定方法,包括如下步骤：(1)利用氧化剂对地表水样品进行微波消解,待消解液自然冷却后混合得到待测样品,(2)以去离子水为空白组,重复步骤(1)的操作,得到空白对照样品,(3)用磷酸盐标准溶液配制不同浓度的待测标准系列溶液,重复步骤(1)的操作,得到消解后的待测标准系列溶液,利用离子色谱,绘制工作曲线,(4)将所述空白对照样品和待测样品通过离子色谱进行测定,利用所述工作曲线,对待测样品中的总磷浓度进行定量分析；其中,在步骤(3)和步骤(4)中,离子色谱的进样量为200～500μL。(The invention relates to a method for measuring total phosphorus concentration in surface water, which comprises the following steps: (1) carrying out microwave digestion on a surface water sample by using an oxidant, mixing after naturally cooling digestion liquid to obtain a sample to be detected, (2) repeating the operation of the step (1) by using deionized water as a blank group to obtain a blank control sample, (3) preparing standard series solutions to be detected with different concentrations by using a phosphate standard solution, repeating the operation of the step (1) to obtain the digested standard series solution to be detected, drawing a working curve by using an ion chromatography, and (4) determining the blank control sample and the sample to be detected by using the ion chromatography, and carrying out quantitative analysis on the total phosphorus concentration in the sample to be detected by using the working curve; wherein, in the step (3) and the step (4), the sample injection amount of the ion chromatography is 200-500 mu L.)

1. A method for measuring the total phosphorus concentration in surface water comprises the following steps:

(1) microwave digestion is carried out on the surface water sample by using an oxidant, the digestion solution is naturally cooled and then mixed to obtain a sample to be tested,

(2) repeating the operation of the step (1) by taking deionized water as a blank group to obtain a blank control sample,

(3) preparing standard series solutions to be detected with different concentrations by using a phosphate standard solution, repeating the operation of the step (1) to obtain the digested standard series solution to be detected, drawing a working curve by using ion chromatography,

(4) measuring the blank control sample and the sample to be measured through ion chromatography, and carrying out quantitative analysis on the total phosphorus concentration in the sample to be measured by utilizing the working curve;

wherein, in the step (3) and the step (4), the sample injection amount of the ion chromatography is 200-500 mu L.

2. The method according to claim 1, wherein the amount of the sample to be subjected to ion chromatography in step (3) and step (4) is 200 to 300. mu.L, and most preferably 200. mu.L.

3. The method according to any one of claims 1 to 2, wherein in the step (1), the oxidizing agent is potassium persulfate.

4. The method according to any one of claims 1 to 3, wherein 100 to 1000. mu.g of the oxidizing agent is added to 10mL of the surface water sample in the step (1).

5. The assay according to any one of claims 1 to 4, wherein in step (1), the digestion temperature is 100 to 150 ℃, preferably 100 to 130 ℃, most preferably 120 ℃.

6. The assay according to any one of claims 1 to 5, wherein in step (1), the digestion time is 5 to 30min, preferably 5 to 15min, most preferably 10 min.

7. The assay method according to any one of claims 1 to 6, wherein in step (1), microwave digestion is carried out using a microwave digestion apparatus.

8. The measurement method according to any one of claims 1 to 7, wherein in the step (3), the digested standard series solution to be measured is measured sequentially from low to high in mass concentration of phosphorus by using ion chromatography, and a working curve is drawn with the mass concentration of phosphorus as an abscissa and a corresponding peak area as an ordinate.

9. An assay according to any one of claims 1 to 8, wherein in step (3) the ion chromatography employs a carbonate eluent system.

10. The method according to claim 9, wherein the carbonate leacheate system is a mixed solution of sodium carbonate and sodium bicarbonate.

11. The assay method according to any one of claims 1 to 10, wherein, in step (4), the blank control sample and the sample to be tested are filtered, and then the filtered sample is assayed by ion chromatography.

Technical Field

The invention belongs to the technical field of water quality environment monitoring, and particularly relates to a method for measuring total phosphorus concentration in surface water.

Background

The mainstream method for measuring the total phosphorus in water is to use potassium persulfate, nitric acid-perchloric acid or nitric acid for digestion, and use ammonium molybdate spectrophotometry or inductively coupled plasma emission spectrometry and a flow injection spectrophotometry based on the principle of the ammonium molybdate spectrophotometry for measurement. The detection limits for the three measurement methods for total phosphorus were 0.01mg/L, 0.04mg/L and 0.005mg/L, respectively, and the lower measurement limits (which were 4 times the detection limits) were 0.04mg/L, 0.16mg/L and 0.02mg/L, respectively. The lower limit of the three determination methods is higher than or equal to the limit requirement of class I surface water on total phosphorus, and accurate quantitative analysis cannot be carried out.

Therefore, the development of a determination method which can meet the standard limit requirement of class I water on total phosphorus in the environmental quality standard of surface water is urgently needed.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a method for measuring the total phosphorus concentration in surface water.

In order to achieve the purpose, the invention provides the following technical scheme:

a method for measuring the total phosphorus concentration in surface water comprises the following steps:

(1) microwave digestion is carried out on the surface water sample by using an oxidant, the digestion solution is naturally cooled and then mixed to obtain a sample to be tested,

(2) repeating the operation of the step (1) by taking deionized water as a blank group to obtain a blank control sample,

(3) preparing standard series solutions to be detected with different concentrations by using a phosphate standard solution, repeating the operation of the step (1) to obtain the digested standard series solution to be detected, drawing a working curve by using an ion chromatography,

(4) measuring the blank control sample and the sample to be measured through ion chromatography, and carrying out quantitative analysis on the total phosphorus concentration in the sample to be measured by utilizing the working curve;

wherein, in the step (3) and the step (4), the sample injection amount of the ion chromatography is 200-500 mu L.

In a preferred embodiment of the present invention, the amount of the sample to be subjected to ion chromatography in step (3) and step (4) is 200 to 300. mu.L, and most preferably 200. mu.L.

In a preferred embodiment of the present invention, in step (1), the oxidizing agent is potassium persulfate.

In a preferred embodiment of the present invention, in step (1), the digestion solution is cooled and then mixed uniformly to obtain the sample to be tested.

In a preferred embodiment of the present invention, in step (1), there is no particular limitation on the amount of the oxidizing agent, as long as it is sufficient to convert various forms of phosphorus in the surface water sample into orthophosphate, and preferably, 100 to 1000 μ g of the oxidizing agent is added per 10mL of the surface water sample.

In a preferred embodiment of the present invention, in step (1), the digestion temperature is 100 to 150 ℃, preferably 100 to 130 ℃, and most preferably 120 ℃.

In a preferred embodiment of the present invention, in step (1), the digestion time is 5 to 30min, preferably 5 to 15min, and most preferably 10 min.

In a preferred embodiment of the present invention, in step (1), microwave digestion is carried out using a microwave digestion apparatus.

In a preferred embodiment of the invention, in the step (3), the digested standard series solution to be measured is sequentially measured from low to high according to the mass concentration of phosphorus by using ion chromatography, and a working curve is drawn by taking the mass concentration of phosphorus as an abscissa and a corresponding peak area as an ordinate.

In a preferred embodiment of the present invention, in step (3), the carbonate rinse solution system is used for ion chromatography.

In a preferred embodiment of the present invention, the carbonate leachant system is a mixed solution of sodium carbonate and sodium bicarbonate.

In a preferred embodiment of the present invention, in the step (4), the blank control sample and the sample to be tested are filtered, and then the filtered sample is measured by ion chromatography.

The beneficial effects obtained by the invention are as follows:

the invention provides a method for measuring the total phosphorus concentration in surface water, which has the detection limit of less than 0.002mg/L and can meet the measurement requirement of the surface water with the total phosphorus concentration of less than 0.01 mg/L. The measuring method has good linear relation in the concentration range of 0.002-0.2 mg/L, the linear equation is that y is 845.71x-2.1491, and the linear correlation coefficient is 0.999. In addition, the determination method of the invention has stronger anti-turbidity and colorimetric interference capability, and has better accuracy, precision and parallelism in the determination process.

In the method, the sample injection amount of the ion chromatography is set to be 200-500 mu L, so that the risk of polluting a chromatographic column due to overlarge sample injection amount is avoided, and the problems of low sensitivity and high detection limit due to too small sample injection amount are avoided.

The method uses microwave digestion for pretreatment, so that the time is saved; the ion chromatography is used for detection, so that the automation of the method is improved, and the method is convenient to popularize. The method only uses common potassium persulfate, sodium carbonate and sodium bicarbonate reagents, and has less varieties and less environmental pollution.

Drawings

FIG. 1 shows an ion chromatogram of a 10-fold diluted total phosphorus standard control sample (batch No. 203984) obtained by the method of the present invention (corresponding to example 1).

FIG. 2 shows an ion chromatogram of a surface water sample of Yanqing district of Beijing city obtained by the method of the present invention (corresponding to example 5).

FIG. 3 shows an ion chromatogram obtained by diluting a surface water sample of Mitsui region of Beijing city by a factor of 10 (corresponding to example 5).

Detailed Description

As described above, the present invention provides a method for measuring the total phosphorus concentration in surface water, comprising the steps of:

(1) microwave digestion is carried out on the surface water sample by using an oxidant, the digestion solution is naturally cooled and then is uniformly mixed to obtain a sample to be measured,

(2) repeating the operation of the step (1) by taking deionized water as a blank group to obtain a blank control sample,

(3) preparing standard series solutions to be detected with different concentrations by using a phosphate standard solution, repeating the operation of the step (1) to obtain the digested standard series solution to be detected, drawing a working curve by using an ion chromatography,

(4) and (3) determining the blank control sample and the sample to be detected through ion chromatography, and carrying out quantitative analysis on the total phosphorus concentration in the sample to be detected by utilizing the working curve.

Specifically, the invention provides a method for measuring the total phosphorus concentration in surface water, which comprises the following steps:

(1) taking potassium persulfate as an oxidant, performing microwave digestion on the surface water sample by using a microwave digestion instrument, converting phosphorus in various forms in water into orthophosphate, naturally cooling the digestion solution, uniformly mixing, transferring the digestion solution into a sample bottle, and obtaining the sample to be detected, wherein the digestion temperature is 120 ℃, and the digestion time is 10 min.

(2) Repeating the operation of the step (1) by taking deionized water as a blank group to obtain a blank control sample,

(3) preparing standard series solutions to be detected with different concentrations by using a phosphate standard solution, repeating the operation in the step (1) to obtain a digested standard series solution to be detected, setting the sample volume of an ion chromatograph to be 200 mu L, selecting a carbonate leacheate system, sequentially determining the digested standard series solution to be detected according to the mass concentration of phosphorus from low to high, drawing a working curve by taking the mass concentration of the phosphorus as a horizontal coordinate and the corresponding peak area as a vertical coordinate,

(4) and filtering the blank control sample and the sample to be detected, determining the filtered sample through ion chromatography, and quantitatively analyzing the total phosphorus concentration in the sample to be detected by utilizing the working curve, wherein the sample introduction amount of the ion chromatography is 200 mu L.

In order to facilitate understanding of the present invention, the technical solutions of the present invention are further described below with reference to specific embodiments, but the present invention is not limited thereto.

The following description of the manufacturers of the raw materials and instruments used in the examples, and the instruments and analytical methods used for product analysis, is provided below, and the reagents, instruments or procedures not described herein are all those that can be routinely determined by one of ordinary skill in the art:

TABLE 1 information on materials and instruments used in the present invention

Examples

Example 1

Measuring the total phosphorus concentration of the diluted 10 times total phosphorus standard quality control sample

The given concentration (1.14. + -. 0.05mg/L) of the total phosphorus standard quality control sample (lot number 203984) from the institute of Standard samples of the Ministry of ecological Environment was obtained by ammonium molybdate spectrophotometry, continuous flow-ammonium molybdate spectrophotometry or flow injection-ammonium molybdate spectrophotometry based on the principle of the national Standard (GB11893-89) method. The concentration of the total phosphorus standard quality control sample is verified by applying national standard GB11893-89 in the laboratory, and the measured value is 1.14mg/L, and the measured value is within the uncertainty range (1.09-1.19 mg/L) of the concentration of the total phosphorus standard quality control sample.

As the linear range of the curve of the method is 0.002-0.2 mg/L, the total phosphorus standard quality control sample is diluted by 10 times and used for determination.

6 parts of the diluted 10-fold total phosphorus standard quality control sample are subjected to parallel determination, and the specific determination steps are as follows.

(1) A potassium persulfate aqueous solution (50. mu.L, concentration 10g/L) and a 10-fold diluted total phosphorus standard quality control sample (10mL) were added to a 30mL digestion tube, capped and mixed well. Then placing the digestion tube in a microwave digestion instrument for digestion for 10min at the digestion temperature of 120 ℃. And after the digestion solution is naturally cooled, uniformly mixing, and transferring the digestion solution into a sample bottle to obtain a sample to be detected.

(2) Repeating the operation of the step (1), wherein deionized water is used for replacing the diluted 10 times of the total phosphorus standard quality control sample to obtain a blank control sample,

(3) diluting a phosphate standard solution (calculated by phosphorus) with deionized water to prepare 7 standard series solutions to be detected with concentrations of 0.002mg/L, 0.005mg/L, 0.01mg/L, 0.02mg/L, 0.05mg/L, 0.1mg/L and 0.2mg/L, and repeating the operation of the step (1) to obtain the digested standard series solution to be detected. Setting the sample size of ion chromatography as 200 μ L, eluting solution as mixed solution of sodium carbonate (3.2mmol/L) and sodium bicarbonate (0.8mmol/L), regeneration solution as 100mmol/L phosphoric acid, eluting solution flow rate as 0.7mL/min, column temperature as room temperature, sequentially measuring standard series solution to be measured after digestion from low to high according to the mass concentration of phosphorus, and drawing working curve with the mass concentration of phosphorus as abscissa and the corresponding peak area as ordinate,

(4) and filtering the blank control sample and the sample to be detected, determining the filtered sample through ion chromatography, and quantitatively analyzing the total phosphorus concentration in the sample to be detected by utilizing the working curve, wherein the sample introduction amount of the ion chromatography is 200 mu L. The analysis results are shown in table 2 below.

TABLE 2

The experimental results in the table 2 are enlarged by 10 times and compared with the given concentration value (1.14 +/-0.05 mg/L) of the total phosphorus standard quality control sample, and the measurement results are all within the specified uncertainty range (1.09-1.19 mg/L), which shows that the method has good accuracy.

Example 2

Determination of detection limits for the methods of the invention

A total phosphorus simulation water sample with the concentration of 0.005mg/L is prepared from glyphosate and deionized water, and the concentration is calculated by phosphorus (P). The preparation method comprises the steps of taking 2.73mL of 1000mg/L glyphosate standard solution (calculated by glyphosate), diluting the solution with deionized water to be constant volume to 100mL to obtain a high-concentration total phosphorus simulation water sample of 5.00mg/L, and then gradually diluting the water sample to be 0.005 mg/L.

A duplicate of 7 10mL of 0.005mg/L total phosphorus containing simulant water was used in an amount of 50. mu.L each of 10g/L aqueous potassium persulfate solution, as described in example 1. The measurement results are shown in Table 3 below, and the average value of the measurement was 0.0053mg/L and the standard deviation was 0.000585 mg/L.

According to the measurement requirement of the detection limit in the HJ168-2010 environmental monitoring and analysis method standard system revision technical guide, and according to the formula MDL-t_(n-1,0.99)And calculating a method detection limit by S, wherein MDL is the method detection limit, n is the parallel measurement times of the sample, t is the t distribution (single side) with the degree of freedom of n-1 and the confidence coefficient of 99%, and S is the standard deviation of n parallel measurements. The detection limit of the method is calculated to be 0.002mg/L under the condition that the sample introduction amount of the ion chromatography is 200 mu L. It can be seen that the assay method of the present invention has a low detection limit.

TABLE 3

Example 3

This example was carried out in the same manner as in example 2, except that the total phosphorus-simulated water sample was prepared from glyphosate and deionized water at a concentration of 0.001mg/L in an amount of 500. mu.L by ion chromatography (P) (the concentration of the standard solution used for the determination of the detection limit was 2 to 5 times the detection limit of the method in accordance with the requirements for the determination of the detection limit in the revised technical guide of HJ168-2010 environmental monitoring and analysis Standard, when no target substance was detected in the blank test, and therefore 0.005mg/L of the total phosphorus-simulated water sample was not used). The measurement results are shown in table 4 below. The detection limit under the condition is lower than that under the condition of 200 muL, but considering that the large sample volume has the risk of polluting the chromatographic column, the sample volume below 500 muL can be selected on the basis of meeting the requirement of the quality standard limit value.

TABLE 4

Example 4

This example serves to illustrate the interference resistance of the method of the invention.

1. Preparing simulated water samples with different turbidity levels

Adding the same sediment with different masses into 500mL of deionized water respectively, mixing uniformly to prepare 6 parts of simulated water samples with turbidity of 6.5, 22.3, 22.1, 67.4, 115.1 and 172NTU respectively, and numbering the simulated water samples as water samples 1-6.

2. Determination of total phosphorus concentration of simulated water sample

Total phosphorus background concentrations were determined for 6 simulated water samples (10mL each) using 50 μ L of 10g/L aqueous potassium persulfate solution as described in example 1 and are shown in Table 5 below.

3. The 6 parts of simulated water sample is subjected to a labeling recovery test (the test not only further reflects the accuracy of the method, but also fully embodies the anti-turbidity interference effect of the method)

Step one, taking 2.73mL of a 1000mg/L glyphosate standard solution (calculated by glyphosate), diluting the glyphosate standard solution with deionized water to 100mL to obtain 5.00mg/L of total phosphorus standard solution (calculated by phosphorus); 27.3mL of 1000mg/L glyphosate standard solution (calculated as glyphosate) is diluted with deionized water to 100mL to obtain 50.0mg/L total phosphorus standard solution (calculated as phosphorus).

Secondly, adding 100 mu L of 5.00mg/L total phosphorus standard solution into 50mL of water sample 1 to ensure that the final concentration (called total phosphorus standard concentration for short) of the added total phosphorus in the water sample added with the glyphosate standard solution is 0.01 mg/L; adding 200 mu L of 5.00mg/L total phosphorus standard solution into 50mL of water sample 2 to ensure that the standard concentration of the total phosphorus is 0.02 mg/L; adding 50 mu L of 50.0mg/L total phosphorus standard solution into 50mL of water sample 3 to ensure that the total phosphorus standard concentration is 0.05 mg/L; adding 100 mu L of 50.0mg/L high-concentration total phosphorus standard solution into 50mL of water sample 4 to ensure that the total phosphorus standard concentration is 0.10 mg/L; adding 100 mu L of 50.0mg/L high-concentration total phosphorus standard solution into 50mL of water sample 5 to ensure that the total phosphorus standard concentration is 0.10 mg/L; to 50ml of water sample 6, 100. mu.L of 50.0mg/L total phosphorus standard solution was added so that the total phosphorus standard concentration was 0.10 mg/L.

And thirdly, determining the total phosphorus concentration (referred to as the 'concentration determined after adding standard substance') of the water samples 1 to 6 obtained in the second step after adding the total phosphorus standard substance according to the method in the embodiment 1, wherein the sampling amount of the water samples 1 to 6 is 10mL, the dosage of the 10g/L potassium persulfate aqueous solution is 50 muL, and the results are shown in the following table 5.

Step four, according to the formula: the spiked recovery rate (the measured concentration after spiking-the background concentration)/the spiked amount) is 100%, and the spiked recovery rates of the water samples 1 to 6 were calculated, and the results are shown in table 5 below.

GB11893-89 adopts turbidity chrominance compensation agent to remove turbidity interference of water sample, and under the same digestion condition, the absorbance of water sample containing color-developing agent is deducted from the absorbance of water sample containing turbidity chrominance compensation agent, that is the actual content of total phosphorus in water sample. However, for a water sample containing suspended particles and having a relatively high turbidity, when the absorbance of the water sample is measured, the suspended particles can continuously obstruct the transmission of light, so that the stability of the absorbance is poor, and the accuracy of the measurement result is poor. The method of the invention also comprises the steps of digesting and determining water samples with different turbidity levels, converting dissolved and suspended particle phosphorus into phosphate, wherein the digested phosphate is water-soluble, and measuring by using ion chromatography after filtering to obtain the total phosphorus concentration in the water samples, thereby avoiding the interference of suspended matters. And because the detector is a conductivity detector and is combined with the separation of the ion chromatographic column, accurate qualitative and quantitative analysis can be carried out on the target object without turbidity and chromaticity compensation.

Compared with the national standard method principle and the verification of the standard adding recovery test, the method has stronger anti-interference capability.

TABLE 5

	Water sample 1	Water sample 2	Water sample 3	Water sample 4	Water sample 5	Water sample 6
							Turbidity of water sample (NTU)	6.5	22.3	22.1	67.4	115.1	172
Total background phosphorus concentration (mg/L)	0.013	0.042	0.057	0.083	0.103	0.095
							Total phosphorus standard concentration (mg/L)	0.010	0.020	0.050	0.100	0.100	0.100
Concentration (mg/L) determined after calibration	0.022	0.058	0.100	0.163	0.208	0.190
							Recovery rate of the added standard	97.8	83.4	85.4	81.1	105	95.3

Example 5

Surface water sampling is carried out in the Yanqing area and the dense cloud area. 6 parts of surface water samples of Yanqing area and 6 parts of surface water samples of densely covered area diluted 10 times were each subjected to parallel measurement in accordance with the method described in example 1, wherein 10g/L of an aqueous solution of potassium persulfate added to 10mL of the water sample was 50. mu.L, and the measurement results are shown in Table 6 below. The spiked recovery test was then performed as described in example 4, with the following specific steps. Firstly, 50 mu L of 5.00mg/L total phosphorus standard solution is added into 50mL of surface water samples in Yanqing areas, so that the total phosphorus addition standard concentration is 0.005 mg/L; and adding 100 mu L of 50.00mg/L total phosphorus standard solution into 50mL of surface water sample of the dense cloud area diluted by 10 times so that the standard concentration of the total phosphorus is 0.100 mg/L. Then, the total phosphorus concentrations (referred to simply as "measured after calibration") of the two surface water samples to which the total phosphorus standard solution was added were measured in the same manner as in example 1, wherein the sample volumes of the two surface water samples to which the total phosphorus standard solution was added were 10mL each, and the usage of the 10g/L potassium persulfate aqueous solution was 50. mu.L each, and the measurement results are shown in Table 6 below.

In general, the quality assurance and quality control requirements of different standard methods for measuring total phosphorus concentration are different, and the method of the present invention is not the current standard method, so the method can only be compared with the current standard method. The existing standard method for measuring the total phosphorus by the ammonium molybdate spectrophotometry requires that the relative standard deviation of a water sample with the total phosphorus concentration less than or equal to 0.03mg/L is less than or equal to 25 percent, and the standard recovery rate is 70-130 percent; the relative standard deviation of a water sample with the total phosphorus concentration of more than 0.03mg/L is required to be less than or equal to 10%, and the standard adding recovery rate is 80-120%.

As can be seen from Table 6, the total phosphorus background concentration of the surface water sample in Yanqing area is less than 0.03mg/L, the relative standard deviation of the measurement result is 12-23%, and the recovery rate of the added standard is 113%. The total phosphorus concentration of the surface water sample in the dense cloud area after being diluted by 10 times is more than 0.03mg/L, the relative standard deviation of the measurement result is 3.1-8.6%, and the standard addition recovery rate is 91.3%. Therefore, the relative standard deviation and the standard adding recovery rate of the method meet the relative standard deviation and the standard adding recovery rate range required by the existing standard method for measuring the total phosphorus by the ammonium molybdate spectrophotometry. Therefore, the method has better precision and parallelism.

TABLE 6

Example 6

This example was carried out as described in example 1, except that the digestion temperature was set to 120 ℃ and the digestion times were set to 1min, 5min, 15min and 30min, respectively. The measurement results are shown in Table 7. And (3) comparing the measurement average value enlarged by 10 times with a given concentration value (1.14 +/-0.05 mg/L) of a total phosphorus standard quality control sample, and finding that the measurement values of the quality control sample are within a given concentration range within 5-15 min of digestion time and have good accuracy. However, when the digestion time was 1min, the measurement result was less than the given concentration range. At a digestion time of 30min, although the assay mean was within the given concentration range, some values were below or above the given concentration range in the replicate assay results. Therefore, in order to improve the sample pretreatment efficiency, the digestion time is set to be 5-30 min, preferably 5-15 min.

TABLE 7

Example 7

This example was carried out as described in example 1, except that the digestion temperatures were 100 deg.C, 130 deg.C, 140 deg.C, 150 deg.C, respectively. The measurement results are shown in Table 8. The measured average value is enlarged by 10 times and compared with the given concentration value (1.14 +/-0.05 mg/L) of the total phosphorus standard quality control sample, and the measured values of the quality control sample are all in the given concentration range at the temperature of 100-130 ℃, so that the accuracy is good. However, when the temperature was 140 ℃ and 150 ℃, although the mean value was within the given range, some values were lower than the given concentration range in the parallel measurement results. It can be seen that the digestion temperature has an important influence on the efficiency of sample pretreatment and the accuracy of the measurement method. Therefore, the digestion temperature is set to 100 to 150 ℃, preferably 100 to 130 ℃.

TABLE 8

As can be seen from examples 6 and 7, the concentration determined by the method is accurate under the digestion time of 5-15 min and the digestion temperature of 100-130 ℃, and the optimal digestion time and digestion temperature are obtained by the two examples. On the premise of ensuring that the target substance is not lost, the digestion time and temperature determine whether total phosphorus in the sample is completely digested or not, and the chromatographic condition of the ion chromatography determines the size of the measurement result, as can be seen from examples 5 and 6, the total phosphorus with the concentration of 0.114mg/L can be completely digested at the digestion time of 5-15 min and the digestion temperature of 100-130 ℃, and is not lost, so that the total phosphorus can be completely digested for a low-concentration solution which is far lower than the value and is used for measuring the detection limit, and the ion chromatography is used for measuring after the total phosphorus is completely digested. Example 2 is a detection limit test performed after digestion was completed within the temperature and time ranges of the present invention, and the detection limit was 0.002 mg/L. In connection with example 3, it can be seen that after complete digestion, the detection limit of the method is largely determined by the chromatographic conditions of the ion chromatography.

Example 8

This example was carried out in the same manner as described in example 1 except that 10g/L of potassium persulfate was added in an amount of 10. mu.L, 20. mu.L, 100. mu.L, 200. mu.L and 500. mu.L, respectively. The measurement results are shown in Table 9. The measured mean value is enlarged by 10 times and compared with a given concentration value (1.14 +/-0.05 mg/L) of a total phosphorus standard quality control sample, and the result shows that the measured requirement can be met when the addition of 10g/L of potassium persulfate is 10-100 mu L, and the sulfate radical is overloaded when the addition is more than 200 mu L, and the phenomenon that the tail of a phosphate radical peak is higher than the base line exists, so that the measured value is low. Therefore, in the method, 100-1000 mu g of the oxidant is preferably added into every 10mL of the surface water sample.

TABLE 9

Comparative example 1

This comparative example was conducted in the same manner as described in example 2 except that the amount of the ion chromatogram to be fed was set to 100. mu.L. The measurement results are shown in the following table. Under the condition of the sample introduction amount, the detection limit of the total phosphorus is 0.003mg/L, and the measurement lower limit is 0.012mg/L, so that the requirement of the measurement of the total phosphorus in the surface water of the lake or the reservoir of the class I cannot be met. It can be seen that the amount of sample introduced by ion chromatography has an important influence on the detection limit and the lower measurement limit of the measurement method. Therefore, in order to satisfy the requirement of measuring total phosphorus in the surface water of the class I lake or reservoir, the sample volume of the ion chromatography is set to 200 to 500. mu.L, preferably 200 to 300. mu.L, in accordance with the experimental result of example 3.

Watch 10

The foregoing is considered as illustrative and not restrictive in character, and that various modifications, equivalents, and improvements made within the spirit and principles of the invention are intended to be included within the scope of the invention.