Solid waste. Determination of lead and cadmium. Graphite furnace atomic absorption spectrophotometry (3)

(6) Analysis and testing

1.

Accurately pipette 0.

2.

Accurately pipette 0.

3.

The prepared blank sample is measured under the same conditions as the establishment of the calibration curve

4.

The prepared sample is measured under the same conditions as the establishment of the calibration curve

(7) Result expression and calculation

1.

The content w (mg/kg) of the element to be tested in the solid or desiccable semi-solid solid waste is calculated according to formula (3):

The content w (mg/kg) of the element to be tested in the liquid or semi-solid solid waste that does not need to be dried is calculated according to formula (4):

Where P ₁ -the mass concentration of the elements in the sample obtained from the calibration curve, mg/L;

P ₀ —The mass concentration of elements in the laboratory blank sample, mg/L;

V—Sampling volume when the solid waste leachate is digested, mL;

V ₀ —The constant volume of the sample after digestion, mL;

m ₁ —The weighed amount of solid waste sample before drying, g;

m ₂ —the mass of the solid waste sample after drying, g;

m ₃ —the weighed amount of the sample after grinding and sieving or the sampling amount of liquid solid waste, g

2.

The content of the element to be measured in solid, desiccable semi-solid solid waste, liquid, semi-solid solid waste that does not need to be desiccated is expressed in mg/kg

The mass concentration of the element to be tested in the solid waste leachate is expressed in mg/L

(8) Dry resistance elimination

When the mass concentration of Ca in the sample is higher than 500mg/L, the mass concentration of Fe is higher than 50mg/L, and the mass concentration of Mn is higher than 25mg/L, it will interfere with the determination of lead and cadmium.

Standard addition method calibration curve drawing method: respectively measure four equal amounts of the sample to be tested (mass concentration is cx), and prepare four solutions of the same total volume
.
No standard solution is added to the first part, and standard solutions of different mass concentrations are added in proportion to the second, third and fourth parts.
The mass concentrations of the four solutions are: c _x , c _x +c ₀ , c _x +2c ₀ , c _x +3c ₀ ; The mass concentration c _{0 of the} added standard solution is approximately equal to 0.
5 times the mass concentration of the sample, that is, c ₀ ≈0.
5c _x
.
Adjust the zero with the blank solution, and measure the absorbance of the four solutions in sequence under the same conditions
.
Draw a calibration curve with absorbance as the ordinate and the mass concentration of the added standard solution as the abscissa.
The intersection point of the reverse extension of the curve and the abscissa is the mass concentration of the sample to be tested
.
The relationship between the mass concentration of the sample to be tested and the corresponding absorbance is shown in Figure 5-1
.

Figure 5-1 The relationship between the mass concentration of the sample to be tested and the corresponding absorbance

(9) Quality assurance and quality control

(1) Make at least 2 laboratory blanks for each batch of samples, and the measurement results should be lower than the lower limit of measurement
.

(2) A calibration curve should be drawn for each analysis, and the correlation coefficient should be greater than 0.
999
.
Otherwise, the calibration curve needs to be redrawn
.

(3) Every 10 samples should be analyzed for an intermediate mass concentration point of the calibration curve, and the relative deviation of the measurement result from the mass concentration of the calibration curve should be less than 10%
.
Otherwise, the standard curve needs to be redrawn
.

(4) The zero point calibration of the instrument should be performed every 20 samples analyzed
.

(5) Each batch of samples should be tested in parallel at least at a ratio of 10%.
When the number of samples is less than 10, at least one parallel double sample should be tested.
The relative deviation of the two determination results should be less than 20%
.

(6) At least 10% standard addition recovery test should be done for each batch of samples.
If the number of samples is less than 10, at least one should be done.
The standard addition recovery rate should be 80%~120%
.

(7) When measuring samples in batches, every 10 samples are a group, and a quality control sample of the element to be measured is added to check the drift degree of the instrument
.
When the measured value of the quality control sample exceeds the allowable range, the instrument needs to be re-adjusted with a standard solution before continuing the measurement
.

(10) Matters needing attention

(1) The crucibles and glass containers used in the experiment should be soaked in nitric acid solution for more than 12 hours, rinsed with tap water and experiment water in turn, and placed in a clean environment to dry
.
For newly used or suspected contaminated containers, they should be immersed in hot hydrochloric acid solution (the temperature is higher than 80℃ and lower than the boiling temperature) for at least 2h, and then immersed in hot nitric acid solution for at least 2h, and rinsed with tap water and experimental water in turn.
Dry in a clean environment
.

(2) When the sample solution is heated to near dryness, the temperature should not be too high to avoid splashing
.

(3) Waste liquids and wastes generated during the experiment should be collected separately and entrusted to a qualified unit for disposal
.

Related Links: Determination of Lead and Cadmium in Solid Waste Graphite Furnace Atomic Absorption Spectrophotometry (2)