HJ 670-2013Water quality. Determination of orthophosphate and total phosphorus. Continuous flow analysis(CFA) and Ammonium molybdate spectrophotometry (English PDF)

4.1 Working principle of continuous flow analyzer

The sample and the reagent enter the chemical reaction module under the push of the peristaltic pump, and continuously flow in the closed pipeline, and are pressed by the bubble.

They are regularly spaced at regular intervals and mixed and reacted in a specific order and proportion. After the color development is completed, they enter the flow detection cell.

Photometric detection.

4.2 Principle of chemical reaction

4.2.1 Determination of phosphate

The orthophosphate in the sample reacts with ammonium molybdate to form a phosphorus molybdenum heteropoly acid in an acidic medium in the presence of a cerium salt, and the combination the material was immediately reduced by ascorbic acid to form a blue complex, and the absorbance was measured at a wavelength of 880 nm. See the workflow diagram, see figure 1.

4.2.2 Determination of total phosphorus

The sample was added with potassium persulfate solution, and subjected to ultraviolet digestion and acidic hydrolysis at 107 ° C ± 1 ° C. All forms of phosphorus were completely oxidized.

For the determination of normal phosphate and orthophosphate, see 4.2.1. Refer to the work flow chart, as shown in Figure 2.

1 Peristaltic pump 2 Mixed reaction ring 3 Dialyzer (unit) 4 Heating bath (circle) 40 °C

6.15 Potassium persulfate digestion reagent

Add.200 ml of sulfuric acid (6.1) to an appropriate amount of water, add 12 g of potassium persulfate (6.3), dissolve and cool to room temperature.

Dilute to 1000 ml with water and mix. The solution is stored at room temperature and protected from light for 1 month.

6.16 Ammonium molybdate solution

Measure 40 ml of sulfuric acid (6.1) dissolved in 800 ml of water. After cooling, add 4.8 g of ammonium molybdate (6.4) and add 2 ml of FFD6.

(6.10), dilute to 1000ml with water and mix. The solution was stored at 4 ° C and was stable for 1 month.

6.17 Potassium tartrate storage solution

Weigh 0.30g of bismuth potassium tartrate (6.5), dissolve in 80ml of water, dilute to 100ml with water and mix well, in brown with stopper in the glass bottle. The solution was stored at 4 ° C and was stable for 2 months.

6.18 Ascorbic acid solution

Weigh 18g ascorbic acid (6.6), dissolve in 800ml of water, add 20ml potassium bismuth tartrate stock solution (6.17), Dilute to 1000 ml with water and mix well in a brown stoppered glass bottle. The solution was stored at 4 ° C and was stable for 7 days.

6.19 Surfactant solution

Add 2 ml of FFD6 (6.10) in 1000 ml of water and mix. The solution was stored at 4 ° C and was stable for 7 days.

6.20 Standard stock solution of potassium dihydrogen phosphate. rho(P)=1000mg/L

Weigh 4.390g of potassium dihydrogen phosphate (6.7), dissolve in an appropriate amount of water, transfer to a 1000ml volumetric flask, add 2.5ml Sulfuric acid (6.1), make up to volume with water and mix and store in a stoppered glass reagent bottle. The solution can be stored for 6 months at 4 °C.

Or buy a commercially available certified standard solution directly.

6.21 Potassium dihydrogen phosphate standard intermediate solution. rho(P) = 100.0mg/L

Measure 10.00 ml of potassium dihydrogen phosphate standard stock solution (6.20) in a 100 ml volumetric flask, dilute to volume with water and mix. The solution the solution can be stored for 3 months at 4 °C.

6.22 Potassium dihydrogen phosphate standard use solution I. rho (P) =10.0 mg/L

Measure 10.00 ml of potassium dihydrogen phosphate standard intermediate solution (6.21) in a 100 ml volumetric flask, dilute to volume with water and mix. The solution the solution can be stored for 1 month at 4 °C.

6.23 Potassium dihydrogen phosphate standard use solution II. rho (P) = 2.50mg/L

The appropriate amount of potassium dihydrogen phosphate standard stock solution (6.20) was weighed and prepared by dilution with water. Available at the time of use.

6.24 Standard stock solution of sodium pyrophosphate. rho(P) =500mg/L

Weigh 3.600g sodium pyrophosphate (6.8), dissolve in an appropriate amount of water, transfer to a 1000ml volumetric flask, and dilute and mix with water.

uniform. The solution can be stored for 3 months at 4 °C.

6.25 Standard use solution of sodium pyrophosphate (test hydrolysis efficiency). rho(P) = 2.50mg/L

A suitable amount of sodium pyrophosphate stock solution (6.24) was weighed and prepared by dilution with water. Available at the time of use.

6.26 Standard stock solution of pyridoxal 5-phosphate. rho(P) =500mg/L

Weigh 0.8561 g (100% by purity) of pyridoxal 5-phosphate (6.9), dissolve in an appropriate amount of water, and transfer to.200 ml.

In a measuring flask, make up to volume with water and mix in a brown stoppered glass bottle. The solution can be stored for 3 months at 4 °C.

6.27 Standard use solution of pyridoxal 5-phosphate (test UV digestion efficiency). rho(P) = 2.50mg/L an appropriate amount of pyridoxal 5-phosphate stock solution (6.26) was weighed and prepared by dilution with water. Available at the time of use.

6.28 Cleaning solution (sodium hypochlorite solution).

A suitable amount of a commercially available sodium hypochlorite solution (6.11) was weighed and diluted with water to a solution having an effective chlorine content of about 1.3%.

9.1 Instrument Commissioning

Install the analysis system, set the operating parameters, and operate the instrument according to the instrument manual. After starting the machine, first replace the reagent with water, check Check the tightness of the flow path and the smoothness of the liquid flow. After the baseline is stabilized (about 20 min), the system starts to enter the reagent.

After the baseline is stabilized again, proceed to 9.2~9.4.

The determination of phosphate is generally carried out using a phosphate analysis module, see Figure 1, which can also be determined using an analytical module for total phosphorus.

See 13.7 for the method.

9.2 Calibration

9.2.1 Preparation of the calibration series

Phosphate calibration curve. separately take appropriate amount of potassium dihydrogen phosphate standard use solution (6.22), dilute to volume with water until 100 ml, a standard series of 6 concentration points was prepared. The phosphate concentrations were. 0.00 mg/L, 0.05 mg/L, 0.10 mg/L, 0.25 mg/L, 0.50 mg/L and 1.00 mg/L.

Total phosphorus calibration curve. separately take appropriate amount of potassium dihydrogen phosphate standard solution (6.21, 6.22), dilute to 100ml with water, A standard series of 6 concentration points was prepared. The total phosphorus concentrations were. 0.00 mg/L, 0.05 mg/L, 0.50 mg/L, 1.00 mg/L, 2.50 mg/L and 5.00 mg/L.

Note. When analyzing clean surface water, the linear range can be appropriately reduced.

9.2.2 Drawing of the calibration curve

Measure the appropriate amount of standard series solution (9.2.1), place it in the sample cup, and sample and measure according to the procedure. Test the fixed signal value (peak height) is the ordinate, and the corresponding phosphate or total phosphorus mass concentration (in P) is plotted on the abscissa.

curve.

9.3 Determination

The measurement of the sample was carried out under the same conditions as in the drawing of the calibration curve.

Note. If the sample phosphate or total phosphorus content exceeds the calibration curve range, the appropriate amount of sample should be diluted and measured on the machine.

9.4 Blank test

Replace the sample with experimental water and perform a blank test in accordance with step 9.3.

10.1 Calculation of results

The mass concentration of phosphate or total phosphorus (in terms of P, mg/L) in the sample is calculated according to formula (1).

Yaf

rho -= × (1)

In the formula.

rho--the mass concentration of phosphate or total phosphorus in the sample, mg/L;

y -- determine the signal value (peak height);

a -- the intercept of the calibration curve equation;

b -- the slope of the calibration curve equation;

f -- dilution factor.

10.2 Results are expressed

When the measurement result is less than 1.00mg/L, the result is retained to the second place after the decimal point; when it is greater than or equal to 1.00mg/L, the knot If you keep three significant digits.

11.1 Precision

Six laboratories tested the uniform samples with phosphate concentrations of 0.10mg/L, 0.50mg/L, and 0.90mg/L.

The relative standard deviations in the room are. 0.5%~4.1%, 0.3%~1.6%, 0.4%~2.4%; the relative standard deviation between laboratories the differences were. 5.4%, 1.2%, 1.7%; the repeatability limits were. 0.01 mg/L, 0.02 mg/L, 0.03 mg/L; reproducibility the limits are. 0.02 mg/L, 0.02 mg/L, 0.05 mg/L.

Six laboratories tested the uniform samples with total phosphorus concentrations of 0.50 mg/L, 2.5 mg/L, and 4.5 mg/, respectively.

The relative standard deviations in the room are. 0.8%~3.8%, 0.4%~1.9% and 0.2%~1.2%; the relative standard deviation between laboratories They were. 1.8%, 3.1%, 2.7%; the repeatability limits were. 0.03 mg/L, 0.08 mg/L, 0.09 mg/L; reproducibility limit They were. 0.04 mg/L, 0.23 mg/L, and 0.36 mg/L, respectively.

11.2 Accuracy

11.2.1 Phosphate

6 laboratory-certified reference materials with phosphate concentrations of 0.30 mg/L ± 0.02 mg/L and 0.70 mg/L ± 0.04 mg/L the measured values were. 0.0%~2.7%, 0.0%~2.2%, and the relative error final values were. 1.3%±2.2%, 0.9% ± 1.9%.

Phosphate concentrations in the six laboratories ranged from 0.05 mg/L to 0.29 mg/L, from 0.21 mg/L to 0.43 mg/L, and from 0.52 mg/L to 0.72 mg/L.

The three actual samples were tested by spiked recovery. The recoveries of the spiked samples were 94.5%~109% and 99.3%~104%, respectively.

95.0%~104%; the final values of the spiked recovery were. 100%±12%, 102%±3.6%, and 99.1%±6.8%.

11.2.2 Total phosphorus

Six laboratories conducted standard substances with total phosphorus concentrations of 0.22 mg/L ± 0.01 mg/L and 1.58 mg/L ± 0.06 mg/L.

The relative errors are. 0.5%~2.3%, 0.0%~1.3%; the relative error final values are. 1.2%±1.5%, 0.5% ±1.0%.

The total phosphorus concentration in 6 laboratories was 0.15mg/L~1.33mg/L, 1.15mg/L~1.61 mg/L, 1.97 mg/L~4.16 mg/L.

The three actual samples were spiked and recovered. The recoveries were 96.0%~105% and 92.8%~104%.

95.6%~103%; the final values of the spiked recovery were. 100%±6.7%, 98.6%±7.9%, 100%±5.8%.

12.1 Blank test

At least 2 blank samples shall be measured for each batch of samples, and the blank value shall not exceed the method detection limit. Otherwise, you should find out the reason and re the sample can only be determined after analysis until it is qualified.

12.2 Calibration validity check

A calibration curve must be drawn for each batch of samples. The correlation coefficient of the calibration curve is gamma >= 0.995.

For each sample analyzed, a calibration curve intermediate concentration solution is used for calibration verification, and the measurement results are relatively biased.

The difference should be <= 5%, otherwise the calibration curve should be redrawn.

12.3 Precision Control

At least 10% of the parallel samples should be determined for each batch of samples. When the number of samples is less than 10, at least one parallel sample should be determined.

When the phosphate or total phosphorus concentration of the sample is <=0.04mg/L, the relative deviation of the parallel samples is <=25%; when the phosphate or total phosphorus is concentrated when the degree is >0.04 mg/L, the relative deviation of the parallel samples is <=10%.

12.4 Accuracy Control

Each batch of samples must be subjected to 10% spiked recovery samples. When the number of samples is less than 10, at least one spiked recovery should be determined.

Sample, spiked recovery should be controlled between 80~120%.

Or each batch of samples with at least one known concentration of quality control samples, the test results should be within the range of uncertainty given.

12.5 System Performance Check

Regularly use the sodium pyrophosphate standard use solution (6.25) to verify the hydrolysis efficiency of the method, using pyridoxal 5-phosphate standard the digestion efficiency of the solution (6.27) verification method is generally 1 time in 2 weeks.

Calibrate the system (9.2) first. Then, parallel analysis of sodium pyrophosphate standard use solution (6.25) or pyridoxal 5-phosphate standard Calculate the hydrolysis or digestion efficiency R,R according to formula (2) using solution (6.27) and potassium dihydrogen phosphate standard solution (6.23).

Should be greater than 90%.

100%R rhorho= × (2)

In the formula.

R--hydrolysis or digestion efficiency, %;

rho1--Sodium pyrophosphate standard use solution (6.25) or pyridoxal 5-phosphate standard use solution (6.27), mg/L;

The measurement result of the standard use solution of rho2--potassium dihydrogen phosphate (6.23), mg/L.

Note. For the total phosphorus analysis module, when the test result of the certified reference material is lower than the lower limit of the uncertainty range, the above test is required.