GB/T 6324.10-2020Test method of organic chemical products - Part 10: Determination of trace sulfur in organic liquid products - Ultraviolet fluorescence method (English PDF)

4.1 Carrier gas

argon or helium, with a purity of not less than 99.99% (volume fraction).

4.2 Oxygen

The purity is not less than 99.99% (volume fraction).

4.3 Thiophene (C4H4S) or dibenzothiophene (C6H4C6H4S)

analytically pure, with a purity of not less than 98% (mass fraction), used to prepare sulfur standards

Quasi solution.

4.4 Solvent

analytical grade. Isooctane, toluene, etc., or other solvents similar to the sample to be tested, are used to prepare standard solutions and dilute samples.

The sulfur content in the solvent should not be higher than 0.2mg/kg, and the sulfur content of the selected solvent should be blank corrected if necessary.

4.5

Standard stock solution (sulfur content is about 1000mg/L). Add a small amount of solvent to a 100mL volumetric flask, and accurately weigh the sulfur standard substance (Thiophene is about 0.26g or dibenzothiophene is about 0.58g), accurate to 0.0001g, transferred to a volumetric flask, and diluted to the mark with solvent. Sulfur Standard

The validity period of the quasi-stock solution is three months. The sulfur standard stock solution should be sealed and stored.

4.6 Sulfur series standard solution

The sulfur standard stock solution (4.5) can be diluted to prepare a series of sulfur standard solutions of suitable concentration, in mg/L.

A commercially available certified sulfur standard solution can also be used.

5.1 Burning furnace

Electric heating, the temperature can reach enough to oxidize and burn the sample, and oxidize the sulfur in it to sulfur dioxide.

5.2 Combustion tube

It is made of quartz, and can use quartz tubes with two structures. direct injection mode and boat injection mode. The direct injection method is directly with a syringe

The sample is injected into the high temperature oxidation zone; the boat sampling method is to inject the sample into the sample boat, and use the sampler to push it to the high temperature zone of the sampling tube. Burn

The burner tube should have oxygen and carrier gas inlet branches. The oxidation zone of the combustion tube should be large enough to ensure complete oxidation and combustion of the sample.

5.3 Flow controller

A stable supply of oxygen and carrier gas should be ensured.

5.4 Drying tube

The instrument should be equipped with a membrane drying tube to remove water vapor from the reaction product before it enters the detector.

5.5 UV fluorescence detector

The quantitative detector can measure the fluorescent signal emitted when the excited sulfur dioxide formed after being irradiated by the ultraviolet light source returns to the ground state.

5.6 Syringe

Can choose 100µL, 20µL, 10µL or other suitable volume micro syringe.

5.7 Sampling system

5.7.1 Direct sample injection system

The sampler can inject the sample in the syringe into the carrier gas flow of the combustion tube at a uniform speed, and the vaporized sample is loaded with it.

The gas enters the oxidation zone of the combustion tube.

5.7.2 Boat sampling system

The sampling boat is made of quartz. The sampler can completely push the sample boat into the high temperature zone of the combustion tube, or it can be removed from the combustion tube.

The tube is pulled out. The injection port is equipped with a cooling device. When the injection boat pulled out from the high temperature zone is returned to the injection port, this device can make the injection boat completely cold.

However, the next sample measurement can be performed after cooling. You can choose to place a quartz wool chip on the sample boat to prevent low-boiling samples from before the sample

Volatile.

5.8 Balance (optional)

Sense amount 0.01mg.

7.1 Instrument preparation

7.1.1

Put the quartz combustion tube into the combustion furnace and connect the carrier gas and reaction gas pipelines.

7.1.2

Turn on the power, turn on the gas source, adjust the furnace temperature, gas flow, sampling speed and other parameters to the conditions recommended by the instrument manual, and press the instrument

Check the air tightness of the gas circuit. After the baseline of the instrument is stable, the sample can be measured.

Note. For high-carbon samples, in order to prevent carbon deposition, the operator can optimize the operating conditions according to the instrument manufacturer's recommendation to improve the repeatability and stability.

7.2 Drawing the standard curve

7.2.1

Selection of standard curve range and standard solution concentration. use sulfur series standard solution (4.6) as the standard solution for calibration. Against

Different standard curves can be used for samples with the same concentration range. The recommended concentration range of the standard curve is shown in Table 1.Standard curve

The quasi-solution concentration range should include the concentration of the sample to be tested.

7.2.2 Cleaning of the syringe

Before the analysis, rinse the syringe with the standard solution. If there are bubbles in the liquid column, rinse the injection again

And redraw the standard solution.

7.2.3

The pipetting method of the standard solution can be one of the following two methods.

a) Volume method. Take the sample with a syringe and adjust it to the required scale, pull back the plunger of the syringe, and inhale a period of air to make the lowest liquid level

Fall to the 10% mark and record the volume of liquid in the syringe. After the sample is injected, pull the syringe back to make the lowest liquid level drop to 10% of the mark.

Record the volume of liquid in the syringe, and the difference between the two volume readings is the volume of the sample. You can also use a fully automatic sampler for sample injection.

b) Gravimetric method. Use a syringe to extract the sample to the required volume according to the method described in 7.2.2, and weigh the mass of the syringe before and after the sample is injected.

The difference is the quality of the sample.

7.2.4 Establishment of the standard curve

After sampling, use a direct sampling system or a boat sampling system to inject the standard solution in the syringe into the combustion tube

Or in the sample boat, record the response value of sulfide, each sample should be repeated three times, and the relative standard deviation of three repeated determinations should not exceed 5% (Except blank), and deduct reagent blank. The average value of the response of each standard solution minus the average value of the reagent blank is the average value of the net response.

The sulfur mass (ng) of each standard solution is the abscissa, and the corresponding average value of the net response is the ordinate. Draw a standard curve, which should be linear

Yes, the linear correlation coefficient should be greater than 0.99.Before using the boat sampling system to analyze samples, push the empty boat into the combustion furnace to ensure that the sample boat is

Clean; and the sample can be injected again after the boat is completely cooled.

7.3 Determination of samples

Use a syringe to inject the sample, clean the syringe with the sample to be tested 3 to 5 times, according to the operation method of 7.2.2 to 7.2.4, under the same conditions

Inject the sample into the combustion tube or the sample boat, measure twice in parallel, record the response value of sulfur, and select the standard curve of the appropriate concentration range to calculate

The mass of sulfur in the sample. The sample injection method used for sample determination should be consistent with the sample injection method when the standard curve is established.

8.1 Calculation

8.1.1

When the volumetric method is used for sampling, the sulfur content c1 in the sample, in milligrams per liter (mg/L), is calculated according to formula (2).

8.1.2

When the volumetric method is used for sample injection, the sulfur content w in the sample, in milligrams per kilogram (mg/kg), is calculated according to formula (3).

8.1.3

When sampling by gravimetric method, the sulfur content w in the sample, in milligrams per kilogram (mg/kg), is calculated according to formula (4).

8.2 Presentation of results

Take the arithmetic average of two parallel determinations as the analysis result, and round off the value according to GB/T 8170 to the nearest 0.1mg/kg (Or 0.1mg/L).

9.1 Repeatability

In the same laboratory, the same operator uses the same equipment, according to the same test method, and compares the same test object in a short time.

The absolute difference between the two independent test results obtained by independent testing is not greater than the repeatability limit (r) specified in Table 2 to be greater than the repeatability limit

The condition of (r) does not exceed 5%.

9.2 Reproducibility

In different laboratories, different operators operate different equipment, and according to the same test method, the same test object is independently processed.

The absolute difference between the two independent test results obtained by the test is not greater than the reproducibility limit (R) specified in Table 2, to be greater than the reproducibility limit (R)

The condition does not exceed 5% as a prerequisite.

10.1

Quality control (QC) sample analysis is required before daily sample analysis. This sample can be a certified sulfur standard solution or

Therefore, it is a self-prepared standard solution, or the property is stable, and the actual average value is determined by repeated analysis and mathematical statistics.

sample.

10.2

If a self-prepared standard solution is used to make the standard curve, another quality control sample different from this standard solution should be used to compare the curve.

Line for analysis and verification.

10.3

Quality control samples are required to check the performance of the system every day. If the deviation of the measurement results of the quality control samples is greater than 10%, the system should be checked according to 7.2.

Draw a new standard curve.