HJ 824-2017Water quality - Determination of sulfide-Flow injection analysis (FIA) and methylene blue spectrophotometric method (English PDF)

4.1 Flow injection analyzer works

In a closed line, a volume of the sample is injected into the continuous flow of the carrier liquid, the sample and reagent in the chemical reaction module Specific order and ratio of mixing, reaction, in the non-complete reaction conditions, into the flow detection pool for photometric detection.

4.2 Principles of chemical reactions

In the acidic medium, the sample through 65 °C ± 2 °C on-line heating release of hydrogen sulfide gas is absorbed by sodium hydroxide solution. Absorbent liquid Sulfide reacts with p-aminodimethylaniline and ferric chloride to form methylene blue, and absorbance is measured at 660 nm. Specific work the process is shown in Figure 1.

1. Peristaltic pump; Heating pool (65 °C); Diffusion pool; Injection valve; Reaction ring; Heating pool (30 °C); Detection pool 10mm, 660nm;

R1 Phosphoric acid solution (6.20); Sodium hydroxide solution (6.23); R3. Picoline dimethylaniline solution (6.25); R4 Ferric chloride solution (6.24);

C. Carrier solution (sodium hydroxide solution, 6.23); Sample; Waste liquid

Figure 1 flow injection - spectrophotometric determination of sulfide reference work flow chart

6.24 Ferric chloride solution

Weigh 6.65 g of ferric chloride (6.5) in an appropriate amount of hydrochloric acid solution (6.18), dissolved and transferred to 500 ml volumetric flask, with salt Acid solution (6.18) constant volume to the marking, mixing.

6.25 P-aminodimethylaniline solution

Weigh 0.50 g of p-aminodimethylaniline (6.6) in an appropriate amount of hydrochloric acid solution (6.18), dissolved and transferred to 500 ml volumetric flask, with hydrochloric acid solution (6.18) constant volume to the mark, mix. If the color of the solution becomes darker, it should be re-formulated.

6.26 Standard solution of potassium dichromate

Weigh 2.4515 g potassium dichromate (6.15) dissolved in the amount of water, dissolved and moved to 500 ml volumetric flask, water volume to the mark, mix.

6.27 Iodine solution

6.35 g of iodine (6.13) was weighed into a 250 ml beaker and 20 g of potassium iodide (6.10) and an appropriate amount of water were added and dissolved to 500 ml Brown capacity bottle, the water volume to the mark, mix.

6.28 Sodium thiosulfate standard solution

Weigh 12.25 g sodium thiosulfate (6.7) in boiling water, add 0.1 g of sodium carbonate (6.9), move to 500 ml Capacity bottle, the water volume to the marking, mixing. The solution was stored in a brown bottle. Before use, use potassium dichromate solution (6.26) calibration.

Calibration method. 1 ml of potassium iodide (6.10), 50 ml of water, 15.00 ml of potassium dichromate standard solution (6.26), shake to completely dissolved and add 5 ml of sulfuric acid solution (6.17), immediately mix the dust. After standing for 5 min in the dark, use sulfur Sodium sulfate solution (6.28) titrated to light yellow, add 1 ml of starch solution (6.32), continue to titrate to blue just disappeared to the end Point, record the amount of sodium thiosulfate solution (6.28). At the same time do blank titration test.

The concentration of sodium thiosulfate standard solution (6.28) is calculated according to formula (1).

Where. c - sodium thiosulfate standard solution concentration, mol/L;

1 V - titration of potassium dichromate standard solution when the amount of sodium thiosulfate solution, ml;

0 V - the amount of sodium thiosulfate solution titrated in the blank solution, ml;

0.1000 - Concentration of potassium dichromate standard solution, mol/L.

6.29 Zinc acetate - sodium acetate solution.

Weigh 25 g of zinc acetate (6.11) and 6.26 g of sodium acetate (6.12) in 500 ml of water and mix well.

6.30 sodium sulfide standard stock solution. rho (S2-) ~100 mg/L.

Weigh 0.375 g of sodium sulfide (6.8) in an appropriate amount of sodium hydroxide solution (6.22) and move to a 500 ml brown volumetric flask.

Sodium hydroxide solution (6.23) constant volume to the mark, mix. The solution was stored in a brown volumetric flask and used after calibration. Or purchase evidence standard solution.

In a 250 ml iodine flask, add 10 ml of zinc acetate-sodium acetate solution (6.29), 10.00 ml to the standard sodium sulfide standard stock (6.28) and 20.00 ml of iodine solution (6.27), add 20 ml of water, then add 5 ml of sulfuric acid solution (6.17), immediately dense shake.

After standing for 5 min in the dark, titration with sodium thiosulfate standard solution (6.28) to pale yellow, add 1 ml of starch solution (6.32) Continue titration to blue just disappeared as the end point, record the amount of sodium thiosulfate standard solution (6.28). At the same time, with 10.00 ml water generation for the sodium sulfide standard solution to do blank test.

The concentration of sodium sulfide standard solution is calculated according to formula (2).

- sodium sulfide standard solution concentration, mg/L;

0 V - blank titration, the amount of sodium thiosulfate standard solution, ml;

1 V - titration sodium sulfide standard solution, the amount of sodium thiosulfate standard solution, ml;

C - sodium thiosulfate standard solution concentration, mol/L;

16.03--1/2 S2- molar mass, g/mol.

6.31 sodium sulfide standard use of liquid. rho (S2 -) = 10.00 mg/L.

With sodium hydroxide solution (6.22) to adjust the water pH = 10 ~ 12, take 150 ml in.200 ml brown volumetric flask, add 1 ~ 2 ml Zinc acetate - sodium acetate solution (6.29), mix well. Measure a certain amount of just calibrated sodium sulfide standard stock solution (6.30) side of the oscillation side drops Into the above brown volumetric flask, and then have been adjusted to pH 10 ~ 12 water diluted to the mark, shake well. The solution was stored in a brown bottle chamber Temperature can be saved for six months. Every time you use, should be fully shaken after access.

6.32 Starch solution. rho = 10 g/L.

Weigh 1 g of soluble starch, with a small amount of water into a paste, slowly add 100 ml of boiling water, after cooling stored in the reagent bottle, with the current distribution.

6.33 helium. purity >=99.99%.

9.1 Commissioning of the instrument

Install the analysis system, commissioning the instrument and setting the operating parameters according to the instrument manual. According to the order of the instrument after the boot, to pure water Instead of all reagents, check the integrity of the entire flow path and the smooth flow of the liquid. After baseline stabilization (about 20 min), the system Start pumping reagents, to be stable again after the baseline, according to 9.2 ~ 9.4 operation.

9.2 Calibration

9.2.1 Preparation of standard series

In a group of volumetric flask were the appropriate amount of sodium sulfide standard use of the liquid (6.31), with sodium hydroxide solution (6.23) diluted to the standard and the concentration of sulfide (in S2-terms) were 0.00 mg/L, 0.10 mg/L, 0.20 mg/L, 0.50 mg/L, 1.00 mg/L, 2.00 mg/L.

9.2.2 Drawing of calibration curves

Transfer to about 10 ml of the standard series of solution (9.2.1) were placed in the sample cup, from low to high concentrations of sequential sampling analysis to different concentrations of sulfide signal values (peak area). The signal value (peak area) as the ordinate, the corresponding sulfide mass concentration (to S2-meter, mg/L) as the abscissa, draw the calibration curve.

9.3 Determination

Measure the signal value (peak area) by measuring about 10 ml of the sample to be measured according to the same measurement conditions as the calibration curve.

If the concentration is higher than the highest point of the standard curve, the sample should be properly diluted.

9.4 Blank test

Replace the sample with 10 ml of water and perform the same procedure as the sample analysis to record the signal value (peak area).

10.1 Result calculation

The sulfide concentration in the sample (in S2-, mg/L) is calculated according to equation (3).

Where. - mass concentration of sulfide in sample, mg/L;

Y - measured signal value (peak area);

A - intercept of the calibration curve method;

B - the slope of the calibration curve method;

F - dilution factor.

10.2 Results are shown

When the determination result is less than 1.00 mg/L, it will be retained to three decimal places. If the result is greater than or equal to 1.00 mg/L, Bit effective number.

11.1 Precision

6 samples of the sulfide mass concentration of 0.20 mg/L, 1.00 mg/L, 1.80 mg/L of the unified samples were measured, the relative standard deviation of the laboratory was 1.9% ~ 3.4%, 1.0% ~ 5.0%, 0.3% ~ 5.0%; the relative standard deviation between the laboratory was 1.0% 1.0%, 0.5%, the repeatability limit was 0.013 mg/L, 0.045 mg/L, 0.048 mg/L, the reproducibility limit was 0.013 mg/L, 0.050 mg/L, 0.050 mg/L.

11.2 Accuracy

(0.713 ± 0.026) mg/L, (0.713 ± 0.062) mg/L, respectively, in six laboratories, the relative error was -6.5% -5.4%, - 1.9% -1.3%, and the relative error was (-4.9 ± 4.6)%, respectively, (-1.6 ± 0.6)%.

The concentration of sulfide in the six laboratories was 0.001 mg/L ~ 0.003 mg/L, 0.068 mg/L ~ 1.59 mg/L, 0.143 Mg/L ~ 1.29 mg/L of surface water, industrial wastewater and other actual samples were measured by spiked assays, spiked recovery were 91.4% 105%, 87.1% ~ 97.4%, 88.8% ~ 98.6%. The final recoveries were (99.1 ± 10.0)%, (93.3 ± 9.1)%, (93.4 ± 8.0)%.

12.1 Blank test

Each laboratory should be at least two laboratory blanks, the blank value shall not exceed the method detection limit. Otherwise it should identify the reasons for re-points Until the qualified sample can be measured.

12.2 Calibration validity check

Each batch of samples must be drawn with a calibration curve, and the correlation coefficient of the calibration curve is gamma >= 0.995.

Each of the 10 samples was calibrated with an intermediate concentration calibration solution with a calibration curve, and the results were compared with the last the relative deviation of the calibration curve should be <= ± 10%, otherwise the calibration curve should be redrawn.

12.3 Full program blank

At least one full program blank is set for each batch, and the blank value must not exceed the lower limit of the method. Otherwise it should identify the reasons for re-points Until the qualified sample can be measured.

12.4 Precision control

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, twice the relative deviation of the parallel measurement results should be <= ± 20%.

12.5 Accuracy control

Each batch of samples should be measured at least 10% of the spiked sample, the number of samples less than 10, should be measured at least a spiked sample, spiked the recovery rate should be between 70% and 120%.

If necessary, each batch of samples at least a certified reference material or laboratory self-prepared quality control samples, certified reference material determination the results should be given in the uncertain range, the laboratory self-prepared quality control test results should be controlled at 90% to 110%. laboratory Self-prepared quality control should pay attention to the state with the standard material comparison.