GB/T 3208-2009Standard test method for the total sulfur content in benzene -- Type products by oxidative microcoulometry (English PDF)

7.1 Preparation of test equipment

7.1.1 Before carrying out the test, first confirm the combustion tube and gas duct as shown below.

7.1.1.1 Combustion tube. Check the combustion tube and quartz fiber for quartz aging and dirt, if not very clean, it needs to be cleaned or perform a sufficient air-burning after replacement.

7.1.1.2 Gas duct. Check the gas duct for aging or dirt, and clean it sufficiently.

7.1.2 After cleaning the inside of the titration cell with the electrolyte, add the electrolyte to it until the electrodes are completely submerged.

7.1.3 Indicating electrode. connect the respective terminals of the reference electrode and the generating electrode to the circuit of the microcoulomb counter.

Note. If a vertical test instrument is used, the end point potential needs to be set at this stage.

7.1.4 Connect the gas conduit of the titration cell to the top position of the outlet of the combustion tube, and energize the strip heater to make the gas conduit of the titration cell.

The temperature is kept above 100°C.

7.1.5 Set the flow rate of oxygen and inert gas, the temperature of the combustion furnace, and the microcoulomb counter to meet the measurement conditions. Typical Conditions for Assays shown in Table 2.

7.2 Calibration

7.2.1 According to the range of sulfur content, select the appropriate sulfur standard solution or standard material.

7.2.2 Select the injection volume of the sulfur standard solution from Table 3, then use a micro-syringe to inject the sample, and inject the fuel according to the following method.

Burn the tube.

7.2.2.1 When using the vertical instrument. insert the needle tip of the microinjector into the instrument through the sample filling port until it reaches the entrance of the combustion tube, then Then inject the sulfur standard solution into it at a speed of 1.0 µL/s ~ 1.2 µL/s, accurately read the injected amount or weigh its mass (accurate to 0.1 mg).

7.2.2.2 When using the horizontal instrument. insert the needle tip of the micro syringe into the test instrument through the sample filling port, and then insert the needle into the sample bolt.

Sulfur standard solution was injected into it, and the injected amount was accurately read or its mass was weighed (accurate to 0.1 mg). Move the sample bolt to the entrance of the combustion tube, After holding for 20s to 60s, push it into the inlet of the combustion tube.

Note. (1) In order to inject the sample at a certain speed, a blender or an automatic injector can be used.

(2) Before and after injecting the sulfur standard solution, it is necessary to inhale the same volume of air into the micro syringe, and calculate the original injection volume of the solution according to the volume difference, so that Errors due to evaporation of the solution from the tip are avoided, ensuring accurate values can be obtained.

(3) Failure to stop for a short time before pushing the specimen bolt into the inlet of the combustion tube will result in insufficient combustion of the specimen and failure to obtain the correct measured value.

(4) If a horizontal instrument is used, the filling rate is 0.2 µL/s to 0.3 µL/s.

7.2.3 Check the shape of the sulfur peak.

7.2.3.1 The correct sulphur peak must be maintained (Figure 2B).

7.2.3.2 If the peak is tailed (Figure 2A), slightly increase the gain or perform bias control to keep the peak in the correct shape.

GB/T 3208-2009

7.2.3.3 If the peaks appear sharp (Fig. 2C), reduce the gain slightly or perform bias control to keep the peaks in the correct shape.

7.2.4 Calculate the recovery coefficient according to the following formula (2). If the recovery factor is not within the range of 0.65 to 0.95, the test sample If there is a problem in itself, it is necessary to check the device parameters and re-prepare the sulfur standard solution and perform the measurement again.

7.2.5 Read and record the sulfur content value of the sulfur standard solution displayed on the sulfur content recorder. Repeat the operation three times to calculate the standard solution of each sulfur the average sulphur content of the liquid.

7.2.6 Using the sulfur mass (µg) and the average sulfur content value of each sulfur standard solution read by the sulfur content recorder, draw a diagram of each sulfur standard solution.

liquid curve.

When the sulfur content of the sample is similar to that of the sulfur standard, single-point calibration can be used, but the determination should be repeated at least three times.

7.2.7 Check the calibration line every day or every 10 samples to confirm whether the operating conditions have changed.

7.2.8 In order to confirm whether the test operation and the test equipment are normal, measure the sulfur standard solution (5.9) according to the sample measurement procedure, confirm and standardize it.

value deviation.

7.2.8.1 When the test is carried out for the first time, the deviation between the test result and the standard value of the standard solution must be ensured within the calculation tolerance of formula (3).

within the allowable error range.

7.2.8.2 When the first test is carried out, the deviation between the average value of the test results and the standard value of the standard solution must be ensured within Formula (4) is calculated within the allowable error range.

GB/T 3208-2009

7.2.8.3 Confirm whether the test results are within the allowable error range. If it is not within the allowable error range, check the test instrument and repeat New test.

7.3 Determination of samples

7.3.1 For direct measurement. use a micro-syringe to draw an appropriate amount of sample, inject it into the combustion tube according to the operation in 7.2.2, and read the maximum surface area.

accumulated value. Repeat the measurement twice and take the average value.

Note. According to the estimated concentration of the sample, draw an appropriate amount of sample to make it roughly in the middle of the calibration line range.

7.3.2 When measuring by dilution. Weigh the sample correctly to the nearest 1 mg, dilute it to 50 mg/kg with isooctane or toluene, and obtain the test sample.

required dilution of the sample solution. Determine the sulfur content of the diluted test solution according to the procedure of 7.3.1.

Note. For samples whose sulfur content does not exceed.200mg/kg, direct measurement can be carried out, while for samples with sulfur content exceeding.200mg/kg, it is better to carry out Dilution assay.