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(6) Analysis and testing
The original fluorophotometer is turned on and preheated, and the lamp current, negative high pressure, carrier gas flow, shielding gas flow and other working parameters are set according to the instrument manual.
Table 5-53 Working parameters of atomic fluorescence photometer
1.
Use standard solutions of 100ug/L mercury, selenium, and bismuth respectively, which are diluted step by step into a series of standard solutions of mass concentration, and the samples are injected separately
Use standard solutions of 100ug/L arsenic, and dilute them gradually into a series of standard solutions of mass concentration.
2.
Prepare a blank sample for determination according to the steps of sample digestion
3.
Take the supernatant for injection, use potassium borohydride as the reducing agent, measure the fluorescence intensity of mercury, selenium, and bismuth on an atomic fluorescence spectrometer, and find out the mass concentration of the corresponding elements from the standard curve
Take a certain amount of arsenic and antimony supernatant in a colorimetric tube, add 10% hydrochloric acid, 100g/L thiourea solution, dilute to the mark with pure water, shake well, place at room temperature for 30 minutes, and measure on an atomic fluorescence photometer For the fluorescence intensity of arsenic and antimony, find out the corresponding mass concentration of arsenic and antimony from the standard curve
(7) Calculation and expression of results
When the measurement result is less than 1mg/kg, the number after the decimal point is retained at most three digits; when the measurement result is greater than 1mg/kg, three significant digits are retained
(1) Calculate the mass ratio w (mg/kg) of arsenic, selenium, antimony and bismuth in the soil with formula (4):
In the formula, p——the mass concentration of the sample found on the working curve, ug/L;
p 0 ——the mass concentration of the blank sample, ug/L;
V 0 ——The constant volume of the sample after microwave digestion, mL;
V 1 ——The volume of the aliquoted sample, mL;
V 2 ——Measure the constant volume of the sample after aliquoting, mL;
m——weigh the mass of the sample, g;
wdm-sample dry matter content, %,
(2) Calculate the mass ratio ω (mg/kg) of arsenic, selenium, antimony and bismuth in the sediment with formula (5):
In the formula, p——the mass concentration of the sample found on the working curve, ug/L;
p 0 ——the mass concentration of the blank sample, ug/L;
V——The constant volume of the sample after microwave digestion, mL;
V 1 ——The volume of the aliquoted sample, mL;
V 2 ——Measure the constant volume of the sample after aliquoting, mL;
m——weigh the mass of the sample, g;
wH 2 O-- soil moisture content,%
(8) Quality assurance and quality control
(1) Each batch of samples shall be tested for at least 2 full-process blanks.
(2) For each batch of samples, 10% parallel samples are required
(3) For each batch of samples, 10% quality control samples are required
.
For specific accuracy requirements, see HJ166-2004 .
(4) If excessive pressure is generated during the sample digestion process, causing pressure relief and destroying its closed system, the sample data should not be used
.
(5) The correlation coefficient of the calibration curve should not be less than 0.
999
.
(9) Matters needing attention
(1) After the sample is digested, the volume should be fixed and then filtered and tested on the machine or centrifuged to take the supernatant for determination
.
(2) The stability of atomic fluorescence is inversely proportional to the sensitivity.
Under the premise of ensuring the detection limit, the sensitivity of the instrument can be reduced to ensure the stability of the instrument
.
(3) Nitric acid and hydrochloric acid are highly corrosive, so the sample digestion process should be carried out in a fume hood
.
(4) The daily cleaning and maintenance of the digestion tank is critical
.
The digestion tank is difficult to clean, so a blank digestion should be performed first (add 6mL hydrochloric acid , then slowly add 2mL nitric acid, mix well, remove the residue on the liner tube and the sealing cap; then carefully clean the liner tube and pressure with water and a soft brush Sleeve; put the inner liner and ceramic outer sleeve into the oven, heat at 200~250℃ for at least 4h, and then cool down naturally at room temperature)
.
Related Links: Atomic Fluorescence Method of Soil and Sediment Mercury, Arsenic, Selenium, Bismuth and Antimony (1)