ASTM D6445 Test Method for Sulfur in Gasoline
ASTM D6445 Standard Test Method for Sulfur in Gasoline by Energy-Dispersive X-ray Fluorescence Spectrometry
11. Procedure
11.1 Although sulfur radiation will penetrate through only a small distance in the sample, scatter from the sample cell and the sample may vary. As such, ensure that the sample cell is filled with sample above a minimum depth, at which point, further filling causes an insignificant change in the counting rate. Generally speaking, filling the sample cup to at least three quarters of the capacity of the sample cell will be sufficient. Prepare the sample cell, providing adequate head space. Provide a vent hole in the top to prevent bowing of the X-ray film during measurement of volatile samples.
NOTE 5 - Warning: Avoid spilling flammable liquids inside the analyzer.
11.2 Instrument Calibration - Calibrate the instrument with the standards listed in Table 3, following manufacturer's instructions. Typically, the calibration procedure involves setting up the instrument for recording of net sulfur X-ray intensity, followed by the measurement of known standards. Analyze each standard two times, using a freshly prepared cell for each analysis and an analysis time of 200 to 300 s. Once all the standards have been analyzed, follow manufacturer's instructions for generating the optimum calibration curve based on the net sulfur counts for each standard.
11.3 Analysis of Unknown Samples - Fill the cell with the sample to be measured, as described in 11.1. Ensure that no air bubbles are present between the cell window and the liquid sample. Analyze each sample two times, using a freshly prepared sample, and analyze each sample, using the same analysis time as in the calibration. Obtain the average of the readings for the sulfur content in the unknown sample.
12. Calculation
12.1 The concentration of sulfur in the sample is automatically calculated from the calibration curve.
