HJ 666-2013Water quality. Determination of ammonium nitrogen by flow injection analysis (FIA) and Salicylic acid spectrophotometry (English PDF)

3.1 Working principle of flow injection analyzer

In a closed pipeline, a volume of sample is injected into a continuous flow of carrier liquid, and the sample and reagent are in a chemical reaction mode.

The blocks are mixed and reacted in a specific order and proportion. Under the condition of incomplete reaction, the flow detection cell is entered for photometric inspection.

Measurement.

3.2 Principles of chemical reactions

In an alkaline medium, ammonia and ammonium ions in the sample react with hypochlorite to form chloramine. At 60 ° C and nitrosyl cyanide in the presence of potassium, chloramine reacts with salicylate to form a blue-green compound, and the absorbance is measured at a wavelength of 660 nm.

Refer to the work flow chart, as shown in Figure 1.

1-peristaltic pump 2 - injection valve 3 - reaction (mixing) ring 4 - heating pool (ring) 60 ° C 5-detection cell 10mm, 660nm R1-buffer solution (5.10) R2-chromogen (5.11) R3-sodium hypochlorite solution (5.12) S-sample C-carrier liquid W-waste liquid

Figure 1 Flow chart of flow injection-salicylic acid spectrophotometric determination of ammonia nitrogen

4.3 When the pH of the sample is >12 or pH5 reagents and materials

Unless otherwise stated, analytically pure reagents that meet national standards were used for the analysis. Experimental water is freshly prepared, resistor Ammonia-free water with a rate greater than 10 Mohm·cm. In addition to the standard solution, other solutions and experimental water are used with helium (5.17) or ultrasound.

Degas.

5.1 Sulfuric acid. rho(H2SO4) = 1.84 g/ml.

5.2 Ammonium chloride (NH4Cl). excellent grade pure. After drying at a constant temperature of 105 ± 5 ° C ° C, it is stored in a desiccator.

5.3 sodium hydroxide (NaOH).

5.4 Ethylenediaminetetraacetic acid disodium salt (C10H14N2Na2O8·2H2O).

5.5 Disodium hydrogen phosphate (Na2HPO4·7H2O)...

5.6 Sodium salicylate (NaC7H5O3).

5.7 Sodium nitrosoferrocyanide dihydrate (Na2[Fe(CN)5NO]·2H2O).

5.8 sodium thiosulfate (Na2S2O3).

5.9 sodium hypochlorite (NaOCl). a commercially available solution. The effective chlorine content is not less than 5.25%; see the method for determining the effective chlorine concentration.

HJ 536 Appendix A.

5.10 Buffer solution.

Weigh 30g sodium hydroxide (5.3), 25g ethylenediaminetetraacetic acid disodium salt (5.4) and 67g disodium hydrogen phosphate (5.5), dissolve After dissolving in 800 ml of water, dilute to 1000 ml with water and shake well. The solution is stable for 1 month.

5.11 Color developer. sodium salicylate solution

Weigh 144g sodium salicylate (5.6) and 3.5g sodium nitrosoferrocyanide dihydrate (5.7) dissolved in 800ml water, dissolved Dilute to 1000 ml with water and shake well. Stored in a brown bottle, the solution is stored at 4 ° C for 1 month.

5.12 sodium hypochlorite use solution.

Measure 60 ml of sodium hypochlorite solution (5.9), dilute to 1000 ml with water, and shake well. Available at the time of use.

5.13 Ammonia nitrogen standard stock solution. rho(N)=1000mg/L

Weigh 3.819g of ammonium chloride (5.2) dissolved in water, dissolve it, transfer it to a 1000ml volumetric flask, dilute to volume with water and mix. The the solution was stored at 4 ° C and was stable for 6 months. Or buy a commercially available certified reference material directly.

5.14 Ammonia nitrogen standard use solution. rho(N)=50.0mg/L

Measure 5.00 ml of ammonia nitrogen standard stock solution (5.13), transfer to a 100 ml volumetric flask, dilute to volume with water and mix. The solution the solution is stored at 4 ° C and is stable for 1 month.

5.15 Sodium thiosulfate solution. rho=3500mg/L

3.5 g of sodium thiosulfate (5.8) was weighed and dissolved in water and diluted to 1000 ml with water.

5.16 Aqueous filter. The pore size is 0.45 µm.

5.17 Helium. Purity >=99.99%.

7.1 Sample collection and preservation

Samples should be collected in polyethylene or glass bottles and analyzed as soon as possible. If necessary, add sulfuric acid (5.1) to pH8 Analysis steps

8.1 Commissioning of the instrument

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 has stabilized (about 15 minutes), the system begins to test After the baseline is stabilized again, proceed to 8.2~8.4.

8.2 Calibration

8.2.1 Preparation of the standard series

Transfer the appropriate amount of ammonia nitrogen standard solution (5.14) separately, dilute to 100ml with water, and prepare the standard for 6 concentration points.

Quasi-series. Ammonia nitrogen concentrations were. 0.00 mg/L, 0.05 mg/L, 0.25 mg/L, 0.50 mg/L, 2.50 mg/L, and 5.00 mg/L, respectively.

8.2.2 Drawing of the calibration curve

Measure the appropriate standard series (8.2.1), place in the sample cup, and take the sample from the low concentration to the high concentration according to the program.

Sample, measurement. Taking the measured signal value (peak area) as the ordinate, the corresponding ammonia nitrogen concentration (in N, mg/L) is the abscissa, Draw a calibration curve.

8.3 Determination

The measurement of the sample (7.2) was carried out under the same conditions as in the drawing of the calibration curve.

Note. If the ammonia nitrogen content of the sample exceeds the detection range of the calibration curve, the appropriate amount of the sample should be diluted and measured on the machine.

8.4 Blank test

Replace the sample with experimental water and perform a blank test in accordance with step 8.3.

9.1 Calculation of results

The mass concentration of ammonia nitrogen in the sample (in N, mg/L) is calculated according to formula (1).

Yaf

rho -= × (1)

In the formula.

rho--the mass concentration of ammonia nitrogen in the sample, mg/L;

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

a -- the intercept of the calibration curve equation;

b -- the slope of the calibration curve equation;

f -- dilution factor.

9.2 Results representation

When the measurement result is less than 1.00 mg/L, the result is retained to two decimal places; when it is greater than or equal to 1.00 mg/L, the result Keep three significant digits.

10.1 Precision

Six laboratories tested the uniform samples with ammonia nitrogen concentrations of 0.02 mg/L, 0.54 mg/L, and 2.74 mg/L.

The relative standard deviations in the laboratory are. 1.2%~8.6%, 0.3%~1.0%, 0.2%~0.7%;

The quasi-bias were. 4.6%, 1.5%, 1.7%; the repeatability limits were. 0.003mg/L, 0.010mg/L, 0.037mg/L;

The reproducibility limits were. 0.004 mg/L, 0.025 mg/L, and 0.134 mg/L, respectively.

10.2 Accuracy

Six laboratories had ammonia nitrogen concentrations of 0.54 mg/L ± 0.03 mg/L, 1.33 ± 0.03 mg/L, and 2.74 ± 0.12 mg/L, respectively.

Determination of the standard substance. relative error. 0.2% ~ 3.2%, 0.0% ~ 3.1%, 0.7% ~ 2.6%; relative error the final values were. 1.6% ± 2.8%, 1.7% ± 2.6%, 1.7% ± 1.6%.

The concentrations of ammonia nitrogen in the six laboratories were 0.05 mg/L ~ 0.45 mg/L, 0.44 mg/L ~ 1.70 mg/L, and 1.08 mg/L, respectively.

~2.20 mg/L 3 kinds of actual samples (surface water, domestic sewage, industrial wastewater) were spiked and measured, and the recoveries were spiked.

For. 104%~114%, 98%~105%, 93.8%~104%; the final recoveries of the spiked recovery are. 108%±7.8%, 101% ± 4.8%, 98.9% ± 7.2%.

11.1 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, the cause should be ascertained.

The sample can be measured after reanalysis until it is qualified.

11.2 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.

11.3 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 ammonia nitrogen concentration of the sample is <=0.10 mg/L, the allowable relative deviation of the parallel sample is <=20%; when the ammonia nitrogen concentration is when 0.10~1.0mg/L, the allowable relative deviation of parallel samples is <=15%; when the ammonia nitrogen concentration is >1.0mg/L, the allowable phase of parallel samples the deviation is <=10%.

11.4 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.

The spiked recovery rate should be between 80% and 120%.

If necessary, each batch of samples shall have at least one known quality control sample, and the test results shall be in the uncertainty given by it.

Inside.