Determination of Trace Sulfur in Industrial Styrene by Oxidative Microcoulometric Method (3)

7 Analysis steps

Assemble and prepare the instrument used in accordance with the instrument instruction manual.

7.

7.

7.

7.

Table 1 Typical operating parameters

Note: According to the instrument used, under the condition of ensuring the accuracy and precision of the measurement, different operating parameters can be reasonably used to achieve a sulfur content of 0.

7.

7.

7.

When injecting, the needle tip should be inserted into the preheating zone, and the sample should be injected at a constant speed of 0.

7.

7.

The conversion rate F of sulfur is calculated according to formula (3):

Where: m ₁ ——the mass of sulfur in the injected sulfur standard solution measured by the microcoulometer, ng;

V ₁ -V ₂ ——The volume of the injected sulfur standard solution, uL;

A—Sulfur content of sulfur standard solution, ng/uL

7.

7.
3.
1 Clean the Ejector 3 to 5 times with the sample to be tested
.
Measure the sulfur content of the sample according to the steps described in 7.
2.
2 to 7.
2.
3
.
Repeat the measurement at least 3 times, and take the arithmetic mean as the measurement result
.

7.
3.
2 According to the sulfur content in the sample, the sensitivity of the instrument or the injection volume can be adjusted reasonably
.
For samples with sulfur content less than 5mg/kg, special attention should be paid to the blank errors caused by each operation step
.
If necessary, it should be calibrated in a timely and reasonable manner
.

During the measurement or calibration process, if the instrument has unstable readings, the conversion rate and sensitivity are reduced, and other phenomena that affect the measurement
.
It can be processed according to the corresponding steps introduced in the instrument manual and given the experience of skilled operators
.

Before the fourth sample is measured, it should be rechecked with a sulfur standard solution
.

8 Expression of analysis results

8.
1 Calculation

The sulfur (calculated as S) content X (mg/kg) in the sample is calculated according to formula (4):

Where: m ₂ ——the mass of sulfur in the injected sample measured by the microcoulometer, ng;

V ₁ —V ₂ ——Injected sample volume, uL;

p——The density of the sample, g/cm3
.

8.
2 Report

Use the mg/kg value to report the total sulfur content in the sample to the nearest 0.
1 mg/kg
.

9 Precision

9.
1 Repeatability

In the same laboratory by the same operator, using the same instrument and equipment, repeat the test twice on the same sample.
The difference between the test results obtained should not be greater than the value in Table 2 (95% confidence level)
.

9.
2 Reproducibility

In any two different laboratories, different operators, using different instruments and equipment, at different or the same time, the difference between the two single measurement results measured on the same sample should not be greater than that in Table 2.
Value (95% confidence level)
.

Table 2 Precision data