Solid waste. Determination of lead and cadmium. Graphite furnace atomic absorption spectrophotometry (2)

(5) Sample pretreatment

1.

Collect and store solid waste samples in accordance with the relevant regulations of HJ/T20 and HJ/T298

2.

(1) Solid waste

Prepare solid waste samples in accordance with the relevant regulations of HJ/T20

(2) Solid waste leachate

Prepare solid waste leachate in accordance with relevant regulations of HJ/T299, HJ/T300 or HJ557

3.

(1) Solid waste samples

① Electric heating plate digestion method

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Note 1: When heating, do not cause a lot of bubbles to emerge from the sample, otherwise it will cause the loss of the sample

Note 2: If the content of lead or cadmium in the solid waste is high, the fixed volume of the sample after digestion can be determined according to the actual situation

Note 3: If the graphite digestion apparatus is used instead of the electric heating plate to digest the samples, please refer to the above steps

②Microwave digestion method

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Table 5-9 Reference table of heating program for microwave digestion of solid waste

(2) Solid waste leachate sample
.

① Electric heating plate digestion method
.

Measure 50 mL of the extract in a 150 mL Erlenmeyer flask, add 5 mL of nitric acid, and shake well
.
Insert a small funnel into the mouth of the triangular flask, place it on an electric hot plate to heat at 120°C, heat and concentrate the sample to about 5 mL in a slightly boiling state, and remove it to cool
.
Add 3mL nitric acid and 1mL perchloric acid until the digestion is complete (the digestion solution is smooth and clear, or the color and transparency of the digestion solution does not change), continue to evaporate at 180°C to near dryness, remove and cool, add 1mL nitric acid solution, and dissolve by warming The soluble residue, after cooling, rinse the inner wall of the small funnel and the triangular flask with appropriate amount of experimental water, transfer the entire amount of the digestion solution to a 50mL volumetric flask, dilute to the mark with experimental water, shake well, and wait for testing
.
If the digestion solution contains more impurities, it needs to be filtered, centrifuged or settled naturally
.

(2) Microwave digestion method
.

Measure 50mL of the leaching solution (the volume of the leaching solution can be determined according to the volume of the digestion tank and the mass concentration of the sample, and the final solution volume should not exceed the limit specified by the instrument) into the microwave digestion tank, add 5mL nitric acid, and close the digestion tank according to the instructions , Place the digestion tank on the turntable of the microwave oven, and perform digestion according to the heating program in Table 5-10
.
After the digestion, the digestion tank is cooled to room temperature in the microwave digestion apparatus and then taken out
.
Put it in a fume hood and carefully open the lid of the digestion tank to release the gas
.
Transfer the entire amount of the digestion solution to a polytetrafluoroethylene crucible, rinse the inner wall of the digestion tank with an appropriate amount of experimental water, merge the washing solution into the polytetrafluoroethylene crucible, and heat it to nearly dry under a slight boiling state on the electric hot plate
.
Rinse the inner wall of the crucible with an appropriate amount of experimental water, transfer the entire contents of the crucible and the washing liquid to a 50mL volumetric flask, dilute to the mark with experimental water, shake it, and wait for measurement
.
If the digestion solution contains more impurities, it needs to be filtered, centrifuged or settled naturally
.

Note: Since there are many types of solid wastes, the organic content is quite different, the amount of various acids in the digestion can be increased or decreased according to the digestion situation; the temperature of the electric heating plate should not be too high to prevent the deformation of the PTFE crucible; when the sample is digested , It is necessary to prevent evaporation to avoid the loss of the elements to be tested
.

Table 5-10 Reference Table of Heating Program for Microwave Digestion of Solid Waste Leachate

(3) Preparation of blank samples

①Blank of solid waste
.

Use an empty container to prepare a blank sample according to the procedure for solid waste samples
.

②The solid waste leachate is blank
.

Use extractant instead of leachate, prepare blank sample and digest it according to the digestion procedure of solid waste leachate
.