ASTM D 7691 : 2016

1.1This test method covers the determination of several elements (including iron, nickel, sulfur, and vanadium) occurring in crude oils.

1.2For analysis of any element using wavelengths below 190 nm, a vacuum or inert gas optical path is required.

1.3Analysis for elements such as arsenic, selenium, or sulfur in whole crude oil may be difficult by this test method due to the presence of their volatile compounds of these elements in crude oil; but this test method should work for resid samples.

1.4Because of the particulates present in crude oil samples, if they do not dissolve in the organic solvents used or if they do not get aspirated in the nebulizer, low elemental values may result, particularly for iron and sodium. This can also occur if the elements are associated with water which can drop out of the solution when diluted with solvent.

1.5This test method uses oil-soluble metals for calibration and does not purport to quantitatively determine insoluble particulates. Analytical results are particle size dependent and low results may be obtained for particles larger than a few micrometers.

1.6The precision in Section 18 defines the concentration ranges covered in the interlaboratory study. However, lower and particularly higher concentrations can be determined by this test method. The low concentration limits are dependent on the sensitivity of the ICP instrument and the dilution factor used. The high concentration limits are determined by the product of the maximum concentration defined by the calibration curve and the sample dilution factor.

1.7Elements present at concentrations above the upper limit of the calibration curves can be determined with additional appropriate dilutions and with no degradation of precision.

1.8As a generality based on this interlaboratory study (see 18.1), the trace elements identifiable in crude oils can be divided into three categories:

1.9The detection limits for elements not determined by this test method follow. This information should serve as an indication as to what elements are not present above the detection limits typically obtainable by ICP-AES instruments.

1.10This test method determines all possible elements simultaneously and is a simpler alternative to Test Methods D5184, D5708, or D5863.

1.11The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.12This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.