HJ 778-2015Water quality. Determination of iodide. Ion chromatography (English PDF)

5.4 Iodide standard stock solution. rho (I -) = 1000 mg/L

Weigh 1.3080 g potassium iodide (5.1), dissolved in water and set to 1000 ml; frozen at 4 °C, dark can save for one year.

Or use a commercially available standard solution.

5.5 Iodide standard intermediate liquid. rho (I -) = 100 mg/L

Remove 10.00 ml of iodide standard stock solution (5.4), diluted with water volume to 100 ml, with the current allocation.

5.6 Iodide standard use of liquid. rho (I -) = 10 mg/L

Remove 10.00 ml of iodide standard intermediate (5.5), diluted with water volume to 100 ml, with the current allocation.

5.7 Potassium hydroxide solution. c (KOH) = 40 mmol/L

2.24 g of potassium hydroxide (5.2) was weighed and dissolved in water and allowed to settle to 1000 ml. The mixture was stored in a polyethylene bottle.

use.

5.8 Sodium hydroxide saturated solution. at room temperature, take appropriate sodium hydroxide solid (5.3) dissolved in 100 ml of water, stirring Dissolve it, and then continue to add sodium hydroxide solid (5.3), stirring until the solid precipitation is no longer continue to dissolve.

Standing, take clear solution, spare.

5.9 Carrier gas. High purity nitrogen (>=99.99%).

5.10 Water Microporous Membrane. 0.45 µm.

7.1 Collection and storage of samples

The collection of samples was carried out in accordance with the relevant provisions of HJ/T 91 and HJ/T 164. Place the water sample immediately after placing it in a polyethylene bottle or Brown glass bottle (6.6), add sodium hydroxide saturated solution (5.8) to adjust the pH to about 12, as soon as possible analysis. If not Timely analysis, should be 0 °C ~ 4 °C cold storage, dark preservation, and within 24 h to complete the determination.

7.2 Preparation of the sample

The collected sample (7.1) was filtered through a 0.45 µm water microporous membrane (5.10) and the initial filtrate was discarded. After collection, the filtrate is tested.

Note 1. For samples of unknown concentration, the sample (7.2) can be diluted 100 times into the sample, and then the appropriate dilution is selected according to the measurement result Multiple re-injection analysis.

Note 2. For samples that may be interfering, pretreatment should be performed. The Na-type or H-type cation exchange column (6.7) can be selected to remove metal ions Interference, select C18 or RP solid phase extraction column (6.7) to remove high levels of organic matter. The specific operation is to extract the sample (7.2) with a 5 ml syringe (6.4) A total of 15 ml was withdrawn and the pretreatment column (6.7) was placed on the front end of the syringe (6.4) and the sample (7.2) was gently pushed through the column. This process should be discarded initially Filtrate 3 ml, collected after the column filtrate, to be tested.

8.1 Chromatographic analysis of the reference conditions

Set the instrument according to the instrument manual. The chromatographic conditions are selected according to the column. Use potassium hydroxide eluent system isocratic wash the elution conditions were as follows. eluent was 40 mmol/L potassium hydroxide solution (5.7) at a flow rate of 1.00 ml/min, the inhibitor the current is 99 mA, the detector temperature is 30 °C, the injection volume can be selected according to the sample concentration of 50 µl ~ 250 µl.

Note 3. If an alcohol-based column is used, the carbonate eluent can also be used to separate the iodide, and its chromatographic analysis See Appendix A for details.

Note 4. The eluent should be degassed before use to avoid bubbling into the ion chromatographic system.

8.2 Standard curve drawing

Respectively, accurate absorption of 0.00 ml, 0.10 ml, 0.20 ml, 0.50 ml, 1.00 ml, 5.00 ml, 10.00 ml iodide Standard use of liquid (5.6) placed in a group of 100 ml volumetric flask, diluted with water to the mark and mix. Standard series of iodide the concentrations were 0.000 mg/L, 0.010 mg/L, 0.020 mg/L, 0.050 mg/L, 0.100 mg/L, 0.500 mg/L, 1.00 mg/L. With the iodide concentration as the abscissa, with its corresponding peak height or peak area as the ordinate, draw the standard curve.

The iodine reference chromatogram is shown in Fig.

8.3 Determination

The retention time of the chromatographic peak was recorded according to the same chromatographic conditions and procedures as the standard curve for drawing, Peak area or peak height.

Figure 1 Iodine chromatogram

8.4 Blank test

In the analysis of the sample at the same time, should do blank test. Use experimental water instead of sample, according to the preservation of the sample (7.1), try Preparation of the same procedure (7.2) and determination (8.3) for analysis.

9.1 Qualitative results

The components to be measured in the test sample are determined according to the retention time of the iodide ions in the chromatogram.

9.2 Quantitative results

9.2.1 Result calculation

The concentration rho (mg/L) of the iodide in the water sample is calculated according to the formula (1).

Hha

rho - - ×

Where.

rho - concentration of iodide in water sample, mg/L;

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

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

B - the slope of the regression equation;

A - the intercept of the regression equation;

F - the dilution factor of the sample.

9.2.2 Result representation

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

10.1 Precision

Six laboratories tested the standard solutions for iodide concentrations of 0.010 mg/L, 0.100 mg/L and 1.00 mg/L the relative standard deviations in the laboratory were 3.1% ~ 4.6%, 0.7% ~ 3.6% and 0.4% ~ 1.6%, respectively.

The standard deviations were 4.5%, 4.0% and 2.0%, respectively. The repeatability r was 0.001 mg/L, 0.005 mg/L and 0.025 mg/L, and reproducibility R were 0.002 mg/L, 0.014 mg/L and 0.060 mg/L, respectively.

Six laboratories were three different types of actual samples plus standard sample (each actual sample plus scalar were 0.050 Mg/L, 0.100 mg/L and 1.00 mg/L). The relative standard deviations in the laboratory were 0.6% ~ 5.5% 0.3% ~ 3.1% and 0.6% ~ 6.0% respectively. The relative standard deviations were 4.0% ~ 5.2%, 4.2% ~ 6.2% 0.8% ~ 1.0%; repeatability r were 0.003 mg/L ~ 0.004 mg/L, 0.003 mg/L ~ 0.005 mg/L and 0.058 Mg/L ~ 0.115 mg/L; reproducibility R were 0.006 mg/L ~ 0.008 mg/L, 0.014 mg/L ~ 0.020 mg/L and 0.060 mg/L to 0.122 mg/L.

10.2 Accuracy

Six laboratories were three different types of actual samples were 6 times the standard recovery rate of repeated determination, spiked concentration 0.050 mg/L, 0.100 mg/L and 1.00 mg/L, respectively. The recoveries were as follows. 87.7% ~ 102%, 87.1% ~ 100%, 92.3% ~ 103%, and the final recoveries were 94.6% ± 10.0% ~ 99.1% ± 1.4% 91.5% ± 11.4% ~ 98.8% ± 1.8%, 95.9% ± 8.0% ~ 102% ± 2.0%.

11.1 Blank test

Each batch of reagents to do a reagent blank test, reagent blank test results should be lower than the detection limit. Each batch (<=

20) samples at least do a full program blank test, blank test results should be lower than the method detection limit. Otherwise it should be identified the original Because the re-analysis until qualified after the determination of the sample.

11.2 Calibration

The correlation coefficient of the standard curve should be greater than or equal to 0.999.

For each batch (<=20) sample, a standard solution at the midpoint of a standard curve should be analyzed.

The relative error between the point and the standard curve should be <= 10%. Otherwise, the standard curve should be redrawn.

11.3 Parallel sample determination

Each batch of samples should be measured at least 10% of the parallel sample, the number of samples less than 10, should be measured at least a parallel double kind. The relative deviation of the results of the parallel sample determination should be less than 10%.

11.4 Sample spike recovery experiment

Each batch of samples (<= 20) at least to do a spike recovery determination, the sample spike recovery rate should be 80% to 120% of the between.

Appendix A

(Informative)

Carbonate eluent system reference conditions the carbonate eluent system can also be used for iodide analysis, but the performance of the matching column should meet the requirements. use Alkyl alcohol-based column, can be separated from the carbonate eluent system, determination of iodide. The reference chromatographic conditions are as follows.

The column is an anion separation column (polydivinylbenzene/ethyl vinyl benzene, with alkyl and alkanol quaternary functional groups) and anion protection column; detector type for the conductivity detector; temperature of 30 °C; eluent/mobile phase composition of carbonic acid Sodium and sodium bicarbonate mixed solution, wherein the concentration of sodium carbonate is 4.5 mmol/L, the concentration of sodium bicarbonate is 1.4 mmol/L, and the flow Speed of 1.2 ml/min; suppressor current of 31 mA; injection volume can be selected according to the level of sample concentration 50 µl ~ 250 µl.

The reference chromatogram of iodide analysis is as follows.

Figure A.1 Iodine chromatogram