ASTM D2622 for sulfur in petroleum products
ASTM D2622 standard test method for sulfur in petroleum products by wavelength dispersive X-ray fluorescence spectrometry
3. Summary of Test Method
3.1 The sample is placed in the X-ray beam, and the peak intensity of the sulfur Ka line at 0.5373 nm is measured. The background intensity, measured at a recommended wavelength of 0.5190 nm (0.5437 nm for a Rh target tube) is subtracted from the peak intensity. The resultant net counting rate is then compared to a previously prepared calibration curve or equation to obtain the concentration of sulfur in mg/kg or mass % (see Section 12).
4. Significance and Use
4.1 This test method provides rapid and precise measurement of total sulfur in petroleum and petroleum products with a minimum of sample preparation. A typical analysis time is 1 to 2 minutes per sample.
4.2 The quality of many petroleum products is related to the amount of sulfur present. Knowledge of sulfur concentration is necessary for processing purposes. There are also regulations promulgated in federal, state, and local agencies that restrict the amount of sulfur present in some fuels.
4.3 This test method provides a means of determining whether the sulfur content of petroleum or a petroleum product meets specification or regulatory limits.
4.4 When this test method is applied to petroleum materials with matrices significantly different from the white oil calibration materials specified in this test method, the cautions and recommendations in Section 5 should be observed when interpreting results.
NOTE 1 - The equipment specified for Test Method D2622 tends to be more expensive than that required for alternative test methods, such as Test Method D4294. Consult the Index to ASTM Standards for alternative test methods.
5. Interferences
5.1 When the elemental composition (excluding sulfur) of samples differs significantly from the standards, errors in the sulfur determination can result. For example, differences in the carbon-hydrogen ratio of sample and calibration standards introduce errors in the determination. Some other interferences and action levels are listed in Table 1. If a sample is known from its history or another analysis to contain any of the species listed in Table 1 at or above the values listed there, that sample should be diluted with blank sulfur solvent to reduce the interferent concentration below the value to mitigate the effect of this interference.
NOTE 2 - The concentrations of substances in Table 1 were determined by the calculation of the sum of the mass absorption coefficients times mass fraction of each element present. This calculation was made for dilutions of representative samples containing approximately 3 % of interfering substances and 0.5 % sulfur.
5.2 Fuels containing large quantities of ethanol or methanol (see Table 1) have a high oxygen content leading to significant absorption of sulfur Ka radiation and low sulfur results. Such fuels can, however, be analyzed using this test method provided either that correction factors are applied to the results (when calibrating with white oils) or that the calibration standards are prepared to match the matrix of the sample. See 11.5.
5.3 In general, petroleum materials with compositions that vary from white oils as specified in 9.1 can be analyzed with standards made from base materials that are of the same or similar composition. Thus a gasoline may be simulated by mixing isooctane and toluene in a ratio that approximates the expected aromatic content of the samples to be analyzed. Standards made from this simulated gasoline can produce results that are more accurate than results obtained using white oil standards.
5.4 Test Method D4927 is the recommended test method for the determination of sulfur >100 mg/kg in lubricating oils and lubricating oil additives because method D4927 implements inter-element correction factors. Method D2622 is not suitable because it does not encompass the measurement of the additional elements present in lubricating oils and their additives making matrix correction impossible.
