ASTM D7622 Standard Test Method for Total Mercury in Crude Oil Using Combustion and Direct Cold Vapor Atomic Absorption Method with Zeeman Background Correction
14. Report
14.1 Report results from the mercury determination on a ng/g (or mass-ppb) basis.
15. Precision and Bias
15.1 Precision - The precision of this test method for the determination of mercury in crude oil based on an interlaboratory study, designed consistent with Practice D6300, was conducted in 2009. Eleven laboratories participated in analyzing eight crude oil samples. Details of this study and the supporting data are given in the ASTM Research Report RR:D02-1692 filed at ASTM Headquarters.
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 350 ng Hg/mL range in crude oil is 0.7147 X(0.60), where X is the average mercury concentration in ng/mL.
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 five years after completing a new interlaboratory study.
15.2 Bias - Certified Reference Materials from NIST are not available in the concentration range applicable for this test method; hence, at present bias of this test method could not be determined.
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.
