Determination of total chromium in soil. Flame atomic absorption spectrophotometry (2)

(6) Sample pretreatment

1.

Mix the collected soil sample (generally not less than 500g) and divide it into about 100g by quarter method

2.

(1) Total digestion method

Accurately weigh 0.

(2) Microwave digestion method

Accurately weigh 0.

Since there are many types of soil, the organic content varies greatly.

(7) Analysis steps

1.

Accurately pipette 0.

Draw the calibration curve by subtracting the blank absorbance and the corresponding mass concentration of chromium (mg/L)

2.

Use deionized water instead of the sample, use the same steps and reagents as the test solution to prepare a blank solution for the whole procedure, and perform the measurement under the same conditions as the curve

3.

Take an appropriate amount of test solution, and measure the absorbance of the test solution under the same conditions as the calibration curve

(8) Result calculation

The content of chromium in soil samples (mg/kg) is calculated according to formula (7):

In the formula, P—the absorbance of the test solution minus the absorbance of the blank solution, and then check the mass concentration of chromium on the calibration curve, mg/L;

V—the volume of the test solution at a constant volume, mL;

m—weigh the mass of the sample, g;

wH ₂ o—sample moisture content, %
.

(9) Quality assurance and quality control

(1) A calibration curve should be drawn for each analysis, and the correlation coefficient should be greater than 0.
999
.

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

(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 calibration curve needs to be redrawn
.

(4) 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%
.

(5) 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%
.

(10) Matters needing attention

(1) Chromium is easy to form high temperature resistant oxides and complexes, so it should be prevented from drying out during the digestion process
.

(2) All glass containers must be soaked in nitric acid solution for more than 12 hours, rinsed with tap water and experimental water in turn, and dried for use
.

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

(4) Waste liquid and waste generated during the experiment should be collected separately and entrusted to a qualified unit for disposal
.