ASTM D7740 Standard Practice for Optimization, Calibration, and Validation of Atomic Absorption Spectrometry for Metal Analysis of Petroleum Products and Lubricants
15. Report
15.1 For each element determined, report the concentration in m% or mg/kg units as required in the product specifications. State that the results were obtained by using the specific test method utilized for that analysis.
15.2 If a concentration is determined to be below the detection limit (BDL) of the instrument, it should be identified as such (BDL) or less than (<) value along with the determined detection limit for that element.
16. Optimum Performance
16.1 In Table 5, suggestions to improve the precision and accuracy of metal analysis in petroleum products and lubricants using AAS are listed. These suggestions are based on practical laboratory experience and they should be a useful guide for the practitioners of this technique.
17. Quality Control
17.1 Confirm the performance of the instrument or the test procedure by analyzing a quality control (QC) sample that is, if possible, representative of the samples typically analyzed.
17.2 Prior to monitoring the measurement process, the user of the method needs to determine the average value and control limits of the QC sample (see Practice D6299 and MNL7).
17.2.1 Where possible, the C sample should not be the same as the one used for calibrating the instrument.
17.3 Record the QC results and analyze by control charts or other statistically equivalent techniques to ascertain the statistical control status of the total test process (see Practice D6299, Guide D6792, and MNL7). Any out-of-control data should trigger investigation for root cause(s). The results of this investigation may, but not necessarily, result in instrument recalibration.
17.4 In the absence of explicit requirements given in the test method, the frequency of QC testing is dependent on the criticality of the quality being measured, the demonstrated stability of the testing process, and customer requirements. Generally, a QC sample should be analyzed each testing day with routine samples. The QC frequency should be increased if a large number of samples is routinely analyzed. However, when it is demonstrated that the testing is under statistical control, the QC testing frequency may be reduced. The QC sample precision should be periodically checked against the ASTM method precision to ensure data quality.
17.5 It is recommended that, if possible, the type of QC sample that is regularly tested be representative of the sample routinely analyzed. An ample supply of QC sample material should be available for the intended period of use, and must be homogeneous and stable under the anticipated storage conditions.
17.6 It may be useful to confirm the optimum performance of the instrument system by analyzing certified reference materials such as available from NIST or other sources, if such materials are available.
17.7 Refer to relevant documents (see Practice D6299, Guide D6792, and MNL7) for further guidance on QC and control charting technique.
18. Precision and Bias
18.1 Typical precision and bias obtained in the ASTM Standard Test Methods for petroleum products and lubricants are listed in Table 6. For most of these methods no bias can be calculated because of the lack of availability of standard reference materials.
19. Keywords
19.1 atomic absorption spectrometry; elemental analysis; fuels analysis; lubricant analysis
