ASTM D7041 Standard Test Method for Determination of Total Sulfur in Liquid Hydrocarbons and Hydrocarbon-Oxygenate Blends by Gas Chromatography with Flame Photometric Detection
8. Sampling
8.1 General Requirements:
8.1.1 Collect samples in accordance with Practice D4057 or D4177.
8.1.2 To prevent the loss of volatile components, which may be present in some samples, protect samples from excess temperatures prior to testing. This can be done by storage in an ice bath or refrigerator.
8.1.3 Analyze samples as soon as possible to prevent loss of sulfur components or contamination.
8.1.4 Do not store samples in plastic containers, since volatile materials may diffuse through the walls of the container.
8.1.5 Do not test samples stored in leaky containers. Discard and obtain a new sample if leaks in the containers are detected.
9. Preparation of Apparatus
9.1 Place in service in accordance with the manufacturer's instructions. Typical instrument parameters are listed in Table 1.
9.2 Set gas flows and temperatures to the desired operating conditions, in accordance with the manufacturer's instructions.
9.3 Ignite the flame photometric detector according to the manufacturer's procedure.
9.4 Prepare the sample introduction accessories, if required, according to the manufacturer's instructions.
9.5 Load a sulfur standard (see 6.5) into the injection valve or auto injector and inject into the gas chromatograph. Determine the retention time of the SO2 peak.
9.6 Set-up a chromatographic analysis method according to the manufacturer's instructions.
10. Calibration
10.1 Choose which type of calibration method is required (mass/volume or mass/mass) and prepare a calibration standard from the stock solution (see 6.5.1 or 6.5.2) by volumetric dilution or mass dilution (see Note 3). The concentration of the calibration standard should be approximately 50 % of the full-scale concentration range of the test samples to be analyzed.
10.1.1 Load calibration standard into injection valve or auto injector.
10.1.2 Inject the calibration standard into the gas chromatograph. See Table 2 for recommended injection volumes.
10.1.3 Analyze the calibration standard and obtain a chromatogram. Calculate the relative response factor for the SO2 peak:
RFS = (Cn/AS)
where:
RFS = relative response factor of SO2,
Cn = sulfur concentration (mgS/kg) ofthe compound in the calibration mixture, and
AS = peak area of the SO2 component.
