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3.
Take samples according to the technical requirements specified in GB/T13290
3.
3.
Draw TBC standard solution (3.
Subtract the absorbance of the reagent blank from the absorbance of the above-mentioned standard solutions, and draw the calibration curve with the mass of TBC in the standard solution as the abscissa and the corresponding net absorbance as the ordinate
Table 1 Correspondence table of volume and concentration of calibration curve of spectrophotometry
3.
3.
Take a 100mL±1mL butadiene sample with a graduated cylinder cooled to -20℃ , and measure the temperature of the liquid sample with a thermometer to the nearest 1℃
Add 30mL of water to the Erlenmeyer flask, cap and shake well
Note: Butadiene is a flammable gas, which can form explosive peroxides when exposed to the air.
3.
After adding the ferric chloride solution, let it stand for 5 min, and use water as the reference to measure the absorbance value of the sample solution with a spectrophotometer
At the same time as a reagent blank, the absorbance of the sample is subtracted from the absorbance of the reagent blank, and the difference is the net absorbance
3.
3.
6.
1 Calculation
On the calibration curve, calculate the TRC content (mg) based on the net absorbance measured in 3.
5.
2.
2, and then calculate the TBC content in the sample according to formula (1):
Where:
w— The content of TBC in butadiene , in milligrams per kilogram (mg/kg);
m—The mass of TBC found on the calibration curve, in milligrams (mg);
V—sample volume, in milliliters (mL);
P—The density of the sample at a certain temperature (see Table 2), in grams per milliliter (g/mL)
.
Table 2 Comparison table of temperature and density of butadiene
3.
6.
2 Expression of analysis results
Take the arithmetic average of the two repeated determination results as the analysis result
.
The measurement result shall be rounded according to the provisions of GB/T8170, and the accuracy shall be 0.
1mg/kg
.
3.
7 Precision
3.
7.
1 Repeatability
In the same laboratory, the absolute value of the two independent test results obtained by the same operator using the same instrument, using the same test method, and testing the same object under test independently in a short period of time should not exceed the repetition of Table 3.
Repetitive limit (r), exceeding the repeatability limit (r) does not exceed 5%
.
Table 3 Repeatability of spectrophotometry