ASTM D5708 Method for Nickel, Vanadium, and Iron in Crude Oils and Residual Fuels
ASTM D5708 Standard Test Methods for Determination of Nickel, Vanadium, and Iron in Crude Oils and Residual Fuels by Inductively Coupled Plasma (ICP) Atomic Emission Spectrometry
20.1 Report concentrations in mg/kg to three significant figures.
21. Precision and Bias
21.1 Precision - The precision of these test methods was determined by statistical analysis of interlaboratory test results. For Test Method A, eleven cooperators participated in the interlaboratory study. Mixed xylenes, o-xylene, and tetralin were successfully used as dilution solvents. One cooperator noted that when kerosine was used, a precipitate developed in several minutes. All cooperators used a peristaltic pump. Approximately half of the cooperators used a high-solids nebulizer. Approximately half of the cooperators used background correction. For Test Method B, eight cooperators participated in the interlaboratory study. All labs but one used a peristaltic pump. Most labs did not use a high-solids nebulizer. Approximately half of the labs used background correction. Seven samples (four residual oils and three crude oils) comprised the test set. One residual oil was NIST SRM 1618, and one crude oil was NIST RM 8505.
21.1.1 Repeatability - The difference between two test results, obtained by the same operator with the same apparatus under constant operating conditions on identical test materials would, in the long run, in the normal and correct operation of the test method, exceed the values in Table 2 and Table 3 only in one case in twenty.
21.1.2 Reproducibility - The difference between two single and independent results, obtained by different operators working in different laboratories on identical test materials would, in the long run, in the normal and correct operation of the test method, exceed the values in Table 4 and Table 5 only in one case in twenty.
21.2 Bias - Bias was evaluated from results obtained on two NIST samples. For Test Methods A and B, the means of the reported values for V and Ni do not differ from the corresponding expected values by more than the repeatability of the test method. Standard reference materials for Fe are not available, so bias was not determined.
22.1 emission spectrometry; ICP; inductively coupled plasma atomic emission spectrometry; iron; nickel; vanadium