ASTM D4951 for additive elements in lubricating oils by ICP-AES
ASTM D4951 standard test method for determination of additive elements in lubricating oils by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES)
6. Apparatus
6.1 Inductively-Coupled Plasma Atomic Emission
Spectrometer - Either a sequential or simultaneous spectrometer is suitable, if equipped with a quartz ICP torch and r-f generator to form and sustain the plasma.
6.2 Analytical Balance, capable of weighing to 0.001 g or 0.0001 g, capacity of 150 g.
6.3 Peristaltic Pump, (Recommended) - A peristaltic pump is strongly recommended to provide a constant flow of solution. The pumping speed must be in the range 0.5 to 3 mL/min. The pump tubing must be able to withstand at least 6 h exposure to the dilution solvent. Fluoroelastomer copolymer tubing is recommended.
6.4 Solvent Dispenser, (Optional) - A solvent dispenser calibrated to deliver the required weight of diluent can be advantageous. Ensure that solvent drip does not affect accuracy.
6.5 Specimen Solution Containers, of appropriate size, glass or polyolefin vials or bottles, with screw caps.
6.6 Vortexer, (Optional) - Vortex the sample plus diluent mixture until the sample is completely dissolved.
6.7 Ultrasonic Homogenizer, Optional - A bath-type or probe-type ultrasonic homogenizer can be used to homogenizer the test specimen.
7. Reagents and Materials
7.1 Purity of Reagents - Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where such specifications are available.
7.2 Base Oil, U.S.P. white oil, or a lubricating base oil that is free of analytes, having a viscosity at room temperature as close as possible to that of the samples to be analyzed.
(Warning - Lubricating base oils can contain sulfur. For preparation of sulfur standards and blending of additive packages, white oil is recommended.)
7.3 Internal Standard, (Required) - An oil-soluble internal standard element is required. The following internal standards were successfully used in the interlaboratory study on precision: Ag, Be, Cd, Co (most common), La, Mn, Pb, Y.
7.4 Organometallic Standards - Multi-element standards, containing known concentrations (approximately 0.1 mass %) of each element, can be prepared from the individual metal concentrates. Refer to Practice D 4307 for a procedure for preparation of multicomponent liquid blends. When preparing multi-element standards, be certain that proper mixing is achieved. Commercially available multi-element blends (with known concentrations of each element at approximately 0.1 mass %) are also satisfactory.
7.4.1 More than one multi-element standard can be necessary to cover all elements, and the user of this test method can select the combination of elements and their concentrations in the multi-element standards. It can be advantageous to select concentrations that are typical of unused oils. However, it is imperative that concentrations are selected such that the emission intensities measured with the working standards can be measured precisely (that is, the emission intensities are significantly greater than background) and that these standards represent the linear region of the calibration curve. Frequently, the instrument manufacturer publishes guidelines for determining linear range.
7.4.2 Some commercially available organometallic standards are prepared from metal sulfonates and therefore contain sulfur. For sulfur determinations, a separate sulfur standard can be required. A sulfur standard can be prepared by blending NIST SRM 1622 with white oil.
7.4.3 Metal sulfonates can be used as a sulfur standard if the sulfur content is known or determined by an appropriate test method such as Test Method D1552.
7.4.4 Petroleum additives can also be used as organometallic standards if their use does not adversely affect precision nor introduce significant bias.
7.5 Dilution Solvent - Mixed xylenes, o-xylene, and kerosine were successfully used in the interlaboratory study on precision.
