ASTM D7623 Standard Test Method for Total Mercury in Crude Oil Using Combustion-Gold Amalgamation and Cold Vapor Atomic Absorption Method
14. Report
14.1 Report results from the mercury determination on ng/g (or mass-ppb) basis.
15. Precision and Bias
15.1 Precision:
15.1.1 Repeatability Limit (r) - The value below which the absolute difference between two test results of separate and consecutive test determinations, carried out on the same sample in the same laboratory by the same operator using the same apparatus on samples taken at random from a single quantity of homogeneous material, may be expected to occur with a probability of approximately 95 %.
15.1.1.1 The repeatability limit in the 5 to 400 ng Hg/g range in crude oil is 0.4396 X(0.5864) where X is the average mercury concentration in ng/g.
15.1.2 Reproducibility Limit (R) - The value below which the absolute difference between two test results, carried out in different laboratories using samples taken at random from a single quantity of material that is as homogeneous as possible, may be expected to occur with a probability of approximately 95 %.
15.1.2.1 The reproducibility limit is not known at present but will be obtained within 5 years after completing a new interlaboratory study. At that point the standard will be revised.
15.2 Bias - At present time the bias of this test method could not be determined since Standard Reference Materials in concentrations of interest are not yet available from NIST.
NOTE 4 - Whenever possible, the analysis of several reference materials, spanning the concentration range of interest, is the most meaningful way to investigate measurement bias. When a matrix match is possible the uncertainty in sample measurements can be equated to that observed in measurement of the Certified Reference Material (CRM). When such a match is not possible, but a CRM with a related matrix is available, the test sample uncertainty may be related to those observed when measuring the CRM. Different methods of measurement of a property may not be capable of equal repeatability. Accordingly, instances could arise where the method of measurement has greater variability than that or those used in certification of the CRM.
15.3 An interlaboratory study, designed consistent with Practice D6300, was conducted in 2009. Nine laboratories participated using 8 samples of crude oils. The details of the study and supporting data are given in ASTM Research Report RR:D02-1692 filed at ASTM headquarters.
