5 Instruments
5.
1 Microcoulometer: All microcoulometers that can meet the minimum detection sulfur content of not more than 0.
5mg/kg can be used
.
5.
2 Micro syringe: 1uL, 5uL or 10uL
.
6 Analysis steps
6.
1 Adjust the instrument to the working state according to the instrument manual
.
6.
2 The recommended typical operating conditions are shown in Table 1
.
Table 1 Recommended typical operating conditions
6.
3 Calibration
Each analysis needs to use a sulfur standard solution with a sulfur content similar to that of the sample to be tested for calibration
.
Use a micro syringe to draw a certain volume of standard solution to eliminate air bubbles, dry the needle, slowly pull out the needle core to a certain volume, read the volume of the standard solution in the needle tube, inject the sample at a constant speed, and then slowly pull the needle core Calculate a certain volume and read the residual volume of the standard solution
.
The difference between the two is the injection volume
.
The conversion factor F of sulfur is calculated according to formula (2):
Where:
M—The electrochemical equivalent of sulfur, in milligrams per coulomb (mg/C) (M=0.
166);
Q—The integral value of the integrator;
Q 1 —The amount of electricity equivalent to the unit integral value of the integrator, in microcoulomb (uC) (Q 1 =100);
V 2 —The value of the volume of the standard solution added, in microliters (uL);
R—Attenuation resistance value of integrator;
C 1 —The value of the mass concentration of sulfur in the standard solution, in nanograms per microliter (ng/uL)
.
Each standard solution shall be measured at least three times, and the arithmetic mean value shall be used as the measurement result of the transformation coefficient.
The transformation coefficient should be between 0.
8 and 1.
2
.
If the conversion coefficient is not within the specified range, the instrument system should be checked in accordance with the instrument manual, and if necessary, electrolyte and electrode solutions can be prepared again, or standard solutions can be prepared
.
6.
4 Determination
Clean the syringe with the sample to be tested 3 to 5 times, and inject an appropriate amount of sample according to the operation steps in 6.
3
.
Record the reading of the micro-coulomb meter
.
7 Result calculation
The mass fraction w of sulfur, expressed in mg/kg, is calculated according to formula (3):
Where:
V—The value of the volume of the sample, in microliters (uL);
p—The value of the density of the sample at the test temperature, in grams per milliliter (g/mL);
M, Q, Qi, F, and R have the same meaning as formula (2)
.
Take the arithmetic mean of the two parallel measurement results as the measurement result, and round off the value according to GB/T8170
.
8 Precision
8.
1 Repeatability
In the same laboratory, the absolute difference of the two independent test results obtained by the same operator using the same equipment, using the same test method, and testing the same object under test independently in a short time shall not exceed the following repetitions The limit of r is based on the premise that the repeatability limit of r is not more than 5%
.
When the mass fraction of sulfur is 0.
5mg/kg～5mg/kg, r is 10% of the arithmetic mean of the two measured values; when the mass fraction of sulfur is greater than 5mg/kg, r is the two measured values 8% of the arithmetic mean
.
8.
2 Reproducibility
In different laboratories, different operators use different equipment, and according to the same test method, the absolute difference of the two independent test results obtained by testing the same object independently of each other, does not exceed the reproducibility limit R, and exceeds The reproducibility limit R does not exceed 5%
.
When the mass fraction of sulfur is 0.
5mg/kg～5mg/kg, R is 15% of the arithmetic mean of the two measured values; when the mass fraction of sulfur is greater than 5mg/kg, R is the two measured values 10% of the arithmetic mean
.
9 report
The report should include the following:
a) All information about the sample, such as sample name, batch number, sampling location, sampling date, sampling time, etc.
;
b) The code of this part of GB/T6324;
c) Analysis results and presentation methods;
d) Details and descriptions of any abnormal phenomena observed in the measurement;
e) The name of the analyst and the date of analysis, etc.
;
f) Any description of operation or test conditions not included in this part of GB/T6324
.
Related Links: Determination of Trace Sulfur in Organic Liquid Chemical Products by Microcoulometry (1)
