HJ 1082-2019Soil and sediment--Determination of Cr(VI)--Alkaline digestion/ flame atomic absorption spectrometry (English PDF)

7.1 Sample collection and storage

Collect and store soil samples in accordance with the relevant requirements of HJ/T 166 or HJ 25.2, and in accordance with HJ/T 91, HJ 494 or relevant requirements of HJ 495 for collection and preservation of water sediment samples.

Collection and preservation of marine sediment samples. Samples should be collected and stored in plastic or glass devices and containers.

Containers of metal products.

7.2 Sample preparation

According to HJ/T 166, the collected samples were air-dried, crushed, passed through a nylon sieve (6.7), and stored in the laboratory.

Note. The sample can also be dried by lyophilization.

7.3 Determination of moisture

Determine the dry matter content of soil samples (7.2) according to HJ 613, and determine the sediment samples (7.2) according to GB 17378.5 Moisture content.

7.4 Preparation of test specimens

Weigh accurately 5.0 g (accurate to 0.01 g) sample (7.2) in a 250 ml beaker, add 50.0 ml alkaline extract Take the solution (5.8) and add 400 mg of magnesium chloride (5.4) and 0.5 ml of dipotassium phosphate-potassium dihydrogen phosphate buffer solution (5.7).

Put the stirrer, seal it with a polyethylene film (5.13), and place it on the stirring heating device (6.3). Stir sample 5 at normal temperature After min, turn on the heating device, heat and stir to 90 °C ~ 95 °C, and keep it for 60 minutes. Remove the beaker and cool to room temperature.

Filter with a filter membrane (5.12), place the filtrate in a 250 ml beaker, and adjust the pH of the solution to 7.5 ± 0.5 with nitric acid (5.1).

Transfer this solution to a 100 ml volumetric flask, make up to volume with water, shake well, and test.

Note 1. When adjusting the pH value of the sample solution, if flocculent precipitation occurs, it needs to be filtered with a filter membrane (5.12).

Note 2. If the prepared sample cannot be analyzed immediately, it should be stored under seal at 0 °C ~ 4 °C for 30 days.

7.5 Preparation of blank sample

Without the sample, follow the same procedure as for sample preparation (7.4) to prepare a blank sample.

8.1 Instrument Reference Conditions

Different models of atomic absorption spectrophotometers have different measurement conditions, which can be selected according to the instrument's instruction manual.

Recommended instrument measurement conditions are shown in Table 1.

Table 1 Instrument reference conditions

Element Cr

Measurement wavelength (nm) Passband width (nm) 0.2 Flame properties are rich in combustion and reducibility (allow the light spot to pass through the bright blue part of the flame) Secondary sensitivity line (nm) 359.0; 360.5; 425.4 the height of the combustion head is adjusted so that the light source spot passes through the intermediate reaction zone

8.2 Establishment of working curve

Pipette 0 ml, 0.10 ml, 0.20 ml, 0.50 ml, 1.00 ml, and 2.00 ml hexavalent chromium standard solution (5.11) respectively Place it in a 250 ml beaker and follow the steps for sample preparation to prepare a working curve solution with a reference concentration of. 0 mg/L, 0.10 mg/L, 0.20 mg/L, 0.50 mg/L, 1.00 mg/L, 2.00 mg/L. Adjust the zero point of the instrument with a blank sample (7.5) and press the absorbance was measured in order from low to high. Set the working curve with the hexavalent chromium concentration as the abscissa and the absorbance as the ordinate line.

8.3 Sample determination

The measurement of the sample (7.4) is performed under the same analysis conditions as the establishment of the working curve (8.2).

8.4 Blank test

The blank sample (7.5) was measured under the same analysis conditions as the sample measurement (8.3).

9.1 Calculation of results

9.1.1 Calculation of results for soil samples

The content of hexavalent chromium in soil samples w (mg/kg) is calculated according to formula (1).

In the formula. w--the content of hexavalent chromium in the soil sample, mg/kg;

--concentration of hexavalent chromium in the sample, mg/L;

V--constant volume of sample, ml;

D--sample dilution factor;

m--weigh the weight of the soil sample, g;

Wdm-dry matter content of soil sample,%.

xVxD

mxWdm (1)

9.1.2 Results calculation of sediment samples

The content w (mg/kg) of hexavalent chromium in the sediment sample is calculated according to formula (2) in the formula. w--the content of hexavalent chromium in the sediment sample, mg/kg;

--concentration of hexavalent chromium in the sample, mg/L;

V--constant volume of sample, ml;

D--sample dilution factor;

m--weigh the weight of the sediment sample, g;

WH2O--Moisture content of sediment sample,%.

9.2 Representation of results

The number of digits after the decimal point of the measurement result is consistent with the detection limit of the method, and a maximum of 3 significant digits are retained.

10.1 Precision

Six laboratories performed soil samples with hexavalent chromium contents of 8.4 mg/kg, 31.6 mg/kg and 66.5 mg/kg Six repeated determinations. the relative standard deviations in the laboratory were. 5.0% to 14%, 3.8% to 5.8%, and 2.4% to 14%;

The relative standard deviations between laboratories were. 7.8%, 4.0%, and 9.1%; the repeatability limits were. 2.6 mg/kg and 4.1 mg/kg, respectively.

And 12 mg/kg; the reproducibility limits are. 3.0 mg/kg, 5.2 mg/kg, and 20 mg/kg.

Six laboratories performed six replicates of sediment samples with hexavalent chromium levels of 7.8 mg/kg and 24.9 mg/kg Measurement. The relative standard deviations in the laboratory were. 5.2% to 9.3% and 2.3% to 6.4%; the relative standard deviations between laboratories Respectively. 7.9% and 11%; repeatability limits are. 1.6 mg/kg and 3.4 mg/kg; reproducibility limits are. 2.3 mg/kg and 8.4 mg/kg.

Six laboratories performed 6 repeated determinations of blank spiked samples with a hexavalent chromium content of 2.0 mg/kg. experiments the indoor relative standard deviation is 2.6% to 8.5%; the relative standard deviation between laboratories is 4.1%; the repeatability limit is 0.34 mg/kg;

The reproducibility limit is 0.38 mg/kg.

10.2 Accuracy

Six laboratories tested soil standard samples with a hexavalent chromium content of 71.0 (26.6 to 115) mg/kg. relative the error is -18% ~ 5.8%; the final relative error is -6.3% +/-17.0%.

Six laboratories for soil samples with a hexavalent chromium content of 31.6 mg/kg and sediments with a hexavalent chromium concentration of 24.9 mg/kg the samples were spiked and recovered. The spiked recoveries were 86.2% to 108% and 80.9% to 115%, respectively.

The final values of the rate are. 94.6% +/-15.3% and 93.3% +/-28.4%.

xVxD

mx (1-WH2O) (2)

11.1 Working curve

A working curve should be drawn before the determination of each batch of samples, and the correlation coefficient should be greater than or equal to 0.999.

11.2 Blank test

Analyze at least 1 blank sample every 20 samples or each batch (less than 20 samples/batch), determination of blank samples Value should be below the method detection limit.

11.3 Parallel samples

Analyze at least 1 parallel sample every 20 samples or batches (less than 20 samples/batch).

For deviation <=20%.

11.4 Matrix Spiking

Analyze at least 1 matrix spiked sample every 20 samples or batches (less than 20 samples/batch). The spiked recovery should be it is between 70% and 130%.