HJ 811-2016Water quality. Determination of total selenium.3, 3′-Diaminobenzidine spectrophotometric method (English PDF)

3.1 Total selenium

Samples were digested after the determination of selenium, that is, the sum of organic selenium and inorganic selenium in the sample.

6.15 Nitric acid - perchloric acid solution

Mixed with an equal volume of nitric acid (6.2) and perchloric acid (6.3).

6.16 Sodium hydroxide solution. rho = 100 g/L.

Weigh 50 g of sodium hydroxide (6.6) in the appropriate amount of water, to be cooled, diluted to 500 ml.

6.17 Cresol red solution. rho = 0.2 g/L.

Weigh 20.0 mg of cresol red (6.9) in the appropriate amount of water, add 1 drop of ammonia (6.5), dissolved and transferred to 100 ml capacity Measuring bottle, the water volume to the mark, shake.

6.18 Ethylenediamine tetraacetic acid disodium mixed test solution

Weigh 10.0 g of ethylenediaminetetraacetic acid disodium dihydrate (6.7) dissolved in water, dissolved in heat, cooled and added 10 ml Cresol red solution (6.17), the volume of water to.200 ml, shake. Stored in plastic bottles, refrigerated below 4 °C, sealed can be saved Six months.

6.19 Ethylenediamine tetraacetic acid disodium mixed test solution

Ethylenediamine tetraacetic acid disodium mixed test solution (6.18) diluted with water 10 times that is the use of liquid, with the current allocation.

6.20 Hydroxylamine Hydrochloride Solution. rho = 20 g/L.

Weigh 2.0 g hydroxylamine hydrochloride (6.8), dissolved in water, water volume to 100 ml, with the current allocation.

6.21 3,3'-diaminobenzidine tetrachloride solution. rho = 5 g/L.

Weigh 0.5 g of 3,3'-diaminobenzidine tetrachloride (6.11) in an appropriate amount of water and set to 100 ml with water. The solution Perishable, should be used with the current distribution.

6.22 Selenium standard stock solution. rho = 100 mg/L.

Accurate weighing 0.1 g (accurate to 0.0001 g) selenium powder (granules) (6.10) In a 100 ml beaker, add 10 ml nitric acid (6.2) Low temperature heating dissolved, add 2 ml of perchloric acid (6.3), in the hot plate slowly heated to the beaker filled with thick white smoke, Continue to heat until the white smoke gradually disappear to remove the nitric acid, remove. Add a small amount of water after the cold, add 8 ml of hydrochloric acid (6.1), following Continue to heat until the white smoke exhausted, remove, after cooling the full amount into the 1000 ml volumetric flask, diluted with water volume to the mark, shake. this Solution per gram of selenium containing 100 micrograms. You can also purchase commercially available standard solutions.

6.23 Selenium standard use of the solution. rho = 1.00 mg/L.

Accurately remove 10.00 ml of selenium standard stock solution (6.22) to 1000 ml volumetric flask and dilute the volume with hydrochloric acid solution (6.13) to the mark, shake. If the use of commercially available standard solution, can also be directly prepared into the standard use of selenium liquid.

8.1 Sample collection

Samples were collected according to the relevant regulations of HJ/T 91. The vials are glass or polyethylene bottles, whisked with nitric acid (6.14) and rinse with tap water and experimental water in turn. Each batch of samples should be accompanied by at least one full program blank (with the same batch of experimental water Instead of the sample).

8.2 Preservation of samples

After sampling, if not measured in time, should be in proportion (1000 ml of sample by adding 10 ml of nitric acid) by adding nitric acid (6.2), at 4 °C the following cold storage, 14 d to complete the analysis.

8.3 Preparation of sample

Remove.200 ml of the mixed sample into a 250 ml Erlenmeyer flask (7.4) (depending on the amount of total selenium in the sample, Water diluted to.200 ml), heated to 15 ml on the hot plate (set the temperature of 130 °C ~ 150 °C), remove the slightly cold, Add 5 ml of nitric acid - perchloric acid solution (6.15), continue to digest on the hot plate (set the temperature of 180 °C ~ 210 °C), to the bottle Filled with white smoke, continue to heat until the white smoke gradually disappeared, remove the slightly cold, add 2.5 ml hydrochloric acid solution (6.12), continue Heating the heating plate (set the temperature of 180 °C ~ 210 °C), to the white smoke exhausted, remove the cooling, add 5 ml of hydroxylamine hydrochloride solution (6.20), to be tested.

Note. In the process of heating and concentrating, it is strictly forbidden.

8.4 Preparation of laboratory blank samples

A laboratory blank sample was prepared in the same manner as in the preparation of the sample (8.3) using the same batch of experimental water instead of the sample.

8.5 Preparation of full program blank samples

Samples of the same batch will be sent to the sampling site, with the same batch of experimental water into the vial, in accordance with the preservation of the sample (8.2) and the preparation of the sample (8.3).

9.1 Drawing of calibration curves

9.1.1 Preparation

Remove 0.00 ml, 0.50 ml, 2.00 ml, 5.00 ml, 10.00 ml and 25.00 ml selenium standard solution (6.23) in a group of 250 ml Erlenmeyer flask (7.4), add water to.200 ml, the preparation of selenium concentration were 0.00 µg/L, 2.50 µg/L, 10.0 µg/L, 25.0 µg/L, 50.0 µg/L, 125 µg/L. According to the same procedure as the preparation of the sample (8.3) Digestion.

9.1.2 Color development

The digested standard series were transferred to a group of 250 ml pear-shaped separatory funnel (7.3), treated with 20 ml of ethylenediaminetetraacetic acid Disodium mixed test solution using liquid (6.19) fractional cleaning conical flask, lotion all transferred to the separatory funnel, this time the solution was pink color. The pH was adjusted to 1 to 3 with sodium hydroxide solution (6.16) or hydrochloric acid solution (6.12), the solution was pale orange, 5.0 ml 3,3'-diaminobenzidine tetrachloride solution (6.21), shake, keep away for 30 min.

9.1.3 Extraction

The color solution (9.1.2) was adjusted to pH 7 to 10 with sodium hydroxide solution (6.16) or hydrochloric acid solution (6.12) So that the solution slightly red, add 10.0 ml of toluene (6.4), fully shaking, standing stratification, abandoned the water phase, organic phase to be measured.

9.1.4 Draw the calibration curve

The absorbance was measured with toluene (6.4) as a reference at a wavelength of 420 nm with a 30 mm cuvette. To deduct the lab empty the absorbance of the white sample (8.4) corresponds to the total selenium content (µg) as the abscissa, after deducting the laboratory blank sample (8.4) of the absorbance value for the vertical axis, the establishment of calibration curve.

9.2 Determination of sample

The prepared sample (8.3) was subjected to color development according to the same procedure of coloring (9.1.2) and extraction (9.1.3) of the calibration curve the organic phase extracted and extracted was placed in a 30 mm cuvette and measured at a wavelength of 420 nm with toluene (6.4) as a reference Luminosity.

9.3 Determination of blank sample

The laboratory blank sample (8.4) and the whole program blank sample (8.5) were measured according to the same procedure as the test (9.2) of the sample.

10.1 Result calculation

The mass concentration of total selenium in the sample is calculated according to equation (1) Vb AAA - -= 0 (1) where. rho - the mass concentration of total selenium in the sample, µg/L;

A - the absorbance of the sample;

A0 - absorbance of laboratory blank samples;

A - the intercept of the calibration curve;

B - the slope of the calibration curve;

V - sample size, L.

10.2 Results are shown

When the result is less than 10 µg/L, the result is retained to one after the decimal point; when the result is greater than or equal to 10 µg/L, the result retains three significant digits.

11.1 Precision

6 samples of the total selenium concentration of 8.7 µg/L, 11.2 µg/L and 17.4 µg/L uniform standard samples were measured in parallel test. The relative standard deviations in the laboratory were 3.5% ~ 7.1%, 4.3% ~ 7.1% and 3.3% ~ 7.5% respectively. The relative standard deviation between the laboratory the differences were 2.5%, 4.1% and 3.7%, respectively. The reproducibility r was 1.3 µg/L, 1.7 µg/L and 2.1 µg/L, respectively.

Do not. 1.4 µg/L, 2.1 µg/L and 2.6 µg/L.

11.2 Accuracy

The concentration of total selenium in the six laboratories was 8.7 µg/L ± 1.0 µg/L, 11.2 µg/L ± 1.1 µg/L and 17.4 µg/L ± 1.7 µg/L the standard samples were tested. The relative errors were -6.9% ~ 1.1%, - 4.5% ~ 4.5% and -6.9% ~ 4.6%, respectively; the relative error was the final Values were -1.9% ± 5.7%, - 1.4% ± 6.8% and -3.1% ± 8.1%, respectively.

Standard drafting unit of domestic sewage, smelting wastewater and chemical wastewater were measured spiked, plus scalar were 3.76 µg/L, 9.30 µg/L and 7.00 µg/L. The recoveries were 88.8% ~ 112.2%, 87.0% ~ 114.0% and 88.0% ~ 109.1%, respectively.

The final recoveries were 98.7% ± 20.3%, 100% ± 22.2% and 98.6% ± 15.5%, respectively.