HJ 669-2013Water quality. Determination of phosphate. Ion chromatography (English PDF)

6.4 Potassium hydroxide solution. c (KOH) = 100 mmol/L

Weigh 5.610g potassium hydroxide (6.1) dissolved in an appropriate amount of water, dissolved and transferred to a 1000ml volumetric flask, diluted with water to the standard Line, mix. The solution is a stock solution of the eluent and stored in a polyethylene bottle.

6.5 Potassium dihydrogen phosphate standard stock solution. rho(PO43-)=1000mg/L

Weigh 1.4329g potassium dihydrogen phosphate (6.2) dissolved in an appropriate amount of water, dissolved and transferred to a 1000ml volumetric flask, diluted with water to Mark the line and mix. The solution was stored in a polyethylene bottle and stored at 4 ° C for 6 months. You can also buy a commercially available certified standard liquid.

6.6 Potassium dihydrogen phosphate standard use solution. rho(PO43-)=10.0mg/L

Accurately measure 1.00ml of potassium dihydrogen phosphate standard stock solution (6.5) in a 100ml volumetric flask, dilute with water to the mark, mix uniform. The solution can be stored for three months at 4 °C.

6.7 Acetate microporous membrane. 0.45µm pore size (can be used with a syringe).

8.1 Collection and preservation of water samples

Sample collection was performed in accordance with the relevant regulations of HJ/T 91, HJ/T 164 and HJ 493.

The sample should be filtered through a 0.45 µm microporous membrane. The filtrate is collected in a polyethylene or glass bottle without any preservative.

It can be stored for 48h at 0°C~4°C.

8.2 Preparation of samples

The sample is clean and there is no water sample that interferes with heavy metals or organic matter. After on-site filtration (8.1), it can be directly injected.

Note 1. For samples of unknown concentration, the sample should be diluted 100 times before analysis, and then the appropriate dilution factor should be selected according to the results obtained.

Sample analysis.

Note 2. Samples with heavy metal interference are removed by on-site filtration using a cation exchange column (7.2).

9.1 Instrument Reference Conditions

Operate the instrument according to the instrument manual. Gradient elution reference conditions, see Table 1.

Table 1 Gradient elution reference conditions

t(min) COH-(mmol/L)

0~7 10

7~15 10~40

15~18.5 40

18.5~24 10

Note 3. Eluent flow rate. 1.0ml/min,)

9.2 Calibration

9.2.1 Preparation of the standard series

Accurately measure 0.00ml, 0.20ml, 1.00ml, 2.00ml, 5.00ml, 10.00ml and 20.00ml potassium dihydrogen phosphate respectively Standard use solution (6.6), dilute to 100 ml with water and mix. Phosphate concentration in the standard series (based on PO43-) Others. 0.000 mg/L, 0.020 mg/L, 0.100 mg/L, 0.200 mg/L, 0.500 mg/L, 1.00 mg/L, and 2.00 mg/L.

9.2.2 Drawing of the calibration curve

The above standard series were separately filtered through a microporous membrane (6.7), and injected sequentially from low to high concentration, the injection volume was 50 µl.

Chromatograms of different concentrations of phosphate were obtained. The concentration of phosphate (in terms of PO43-, mg/L) is plotted on the abscissa, peak height or peak the product is plotted on the ordinate and a calibration curve is drawn. The chromatogram of the phosphate ion is shown in Figure 1.

Figure 1 Phosphate ion chromatogram

9.3 Determination

The samples were measured according to the same chromatographic conditions and procedures as those used to draw the calibration curve.

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 concentration of phosphate in the sample (in terms of PO43-, mg/L) was calculated according to the formula (1).

rho= f

Ahh ×-- 0 (1)

In the formula.

rho--the concentration of phosphate in the sample, mg/L;

H--the peak height (or peak area) of the phosphate in the sample;

H0--the peak height (or peak area) of the phosphate in the blank sample;

B--the slope of the regression equation;

A--the intercept of the regression equation;

F--dilution factor.

10.2 Results are expressed

When the sample content is less than 1mg/L, the result is retained to three decimal places; when the sample content is greater than or equal to 1mg/L, Keep three significant digits.

11.1 Precision

Six laboratories performed uniform samples with phosphate concentrations of 0.033 mg/L, 0.923 mg/L, and 2.137 mg/L, respectively.

The relative standard deviations in the laboratory were 1.7% to 6.6%, 1.3% to 2.8%, and 0.5% to 2.7%, respectively.

The standard deviations were 5.0%, 1.2% and 1.8%, respectively, and the repeatability limits were. 0.004 mg/L, 0.058 mg/L and 0.087 mg/L, respectively.

Reproducibility limits were. 0.006 mg/L, 0.061 mg/L and 0.133 mg/L, respectively.

11.2 Accuracy

6 laboratory-certified reference materials with phosphate concentrations of 0.697 mg/L ± 0.040 mg/L and 0.301 mg/L ± 0.016 mg/L for the measurement, the relative errors were 0.2% to 3.9% and 0.4% to 2.7%, respectively. The relative error final values are 0.51% ± 0.32% and 1.35% ± 0.90%.

Phosphate concentrations in the six laboratories ranged from 0.012 mg/L to 0.344 mg/L, 0.034 mg/L to 0.595 mg/L, and 0.073 mg/L.

The three actual samples of ~1.14mg/L were spiked and recovered. The recoveries were 94.0% ~103%, 93.0%~102%.

And 97.0%~105%; the final recoveries were 97.2%±3.1%, 97.3%±3.9% and 99.4%±5.2%, respectively.

12.1 Blank test

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

12.2 Relevance test

The correlation coefficient of the calibration curve is r >= 0.995.

12.3 Intermediate concentration check

For each sample of 20 samples or one batch (less than 20 samples), the concentration of the middle point of a calibration curve should be analyzed.

For the standard solution, the relative error between the measurement result and the concentration of the point at the most recent calibration curve should be <=10%. Otherwise, you need to redraw Calibration curve.

12.4 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 double sample should be determined. when when the phosphate concentration of the sample is 0.028~0.280mg/L, the relative deviation of the parallel determination results should be <=20%; when the sample is phosphoric acid when the salt concentration is 0.280~2.00mg/L, the relative deviation of the parallel determination results should be <=10%.

12.5 Accuracy Control

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

When the phosphate concentration in the sample is 0.028~0.280mg/L, the spike recovery should be between 75~125%; when the sample is phosphate when the concentration is 0.280~2.00mg/L, the recovery rate of spiked standard should be between 85~115%.