ASTM D2622 for sulfur in petroleum products
ASTM D2622 standard test method for sulfur in petroleum products by wavelength dispersive X-ray fluorescence spectrometry
13. Quality Control
13.1 It is recommended that each laboratory establish a program to ensure that the measurement system described in this test method is in statistical control. One part of such a program might be the regular use and charting5 of quality control samples (see 7.11). It is recommended that at least one type of quality control sample be analyzed that is representative of typical laboratory samples as defined in Practice D6299.
13.2 In addition to running a quality control sample (7.11), it is strongly recommended that the calibration blank (for example, diluent oil) be analyzed on a daily basis.
13.2.1 The measured concentration for the blank should be less than 2 mg/kg (0.0002 mass %) sulfur. If the measured concentration for the blank is greater than 2 mg/kg (0.0002 mass %), re-standardize the instrument and repeat the measurement of the blank (use a fresh sample and fresh cell). If the result falls outside the acceptable range, carry out a full calibration. If the sample loading port becomes contaminated, especially when analyzing <20 mg/kg sulfur level samples, it is necessary to open and clean it according to manufacturer's recommendations before further use.
13.2.2 It should be noted that in order to obtain a good fit for the calibration at low concentrations, it may be necessary to change the weighting factor in the regression. It may also be beneficial to change the weighting method used. Many software packages default to square root error weighting but have the possibility of using linear error weighting or no error weighting.
13.3 Results Validation - Once a standard or sample has been measured, a procedure should be carried out to validate that measurement. This requires the operator to check for obvious signs of damage to the sample such as leaking sample cells, crinkled sample cell window and inspection of any secondary film.
13.4 Observation of the Resultant Analysis. If a result is considered outside normal thresholds, a repeat of the analysis should be carried out to confirm anomalous results.
13.5 Regular checks should be carried out to ensure that purging gas performance is within the instrument manufacture's specification.
13.6 Drift and quality control standards/monitors shall be run on a regular basis. The tolerance levels of the checks made using these monitors should be such that a protocol of either drift correction or total recalibration is carried out if the results fall outside these levels. All measurements should be repeated between the last accepted monitor result and point of non-compliance should a current monitor measurement prove to be outside acceptable levels.
