ASTM D7691 Standard Test Method for Multielement Analysis of Crude Oils Using Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES)
7. Apparatus
7.1 Balance - Top loading or analytical, with automatic tare, capable of weighing to 0.001 or 0.0001 g, with sufficient capacity to weigh prepared solutions.
7.2 Inductively-Coupled Plasma Atomic Emission Spectrometer - Either a sequential or simultaneous spectrometer is suitable, if equipped with a quartz ICP torch and RF generator to form and sustain the plasma. Suggested wavelengths for the determination of the elements in crude oils are given in Table 1. For the analysis of sulfur, the spectrometer shall be capable of operating in the wavelength region of 180 nm.
7.3 Nebulizer - A Babington-type high-solids nebulizer is strongly recommended. This type of nebulizer reduces the possibility of clogging and minimizes aerosol particle effects.
7.4 Peristaltic Pump - A peristaltic pump is strongly recommended to provide a constant flow of solution. The pumping speed shall be in the range 0.5 mL/min to 3 mL/min. The pump tubing shall be able to withstand at least 6 h exposure to the dilution solvent. Viton tubing is typically used with hydrocarbon solvents, and polyvinyl chloride tubing is typically used with methyl isobutyl ketone.
7.5 Solvent Dispenser, (Optional) - Asolvent dispenser calibrated to deliver the required weight of dilution solvent for a tenfold dilution of test specimen is very useful.
7.6 Specimen Solution Containers - Of appropriate size, glass or plastic vials or bottles, with screw caps.
7.7 Ultrasonic Homogenizer, (Recommended) - A bath-type or probe-type ultrasonic homogenizer to homogenize the sample.
7.8 Vortexer, (Optional) - Vortexing the sample is an alternative to ultrasonic homogenization.
7.9 High Speed Homogenizer, (Optional).
8. Reagents and Materials
8.1 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. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.
8.2 Internal Standard - Oil-soluble cadmium, cobalt, lanthanum, scandium, or yttrium (or other suitable metal) is required for internal standardization.
8.3 Organometallic Standards - Multi-element standards, containing 0.0500 mass % of each element, can be prepared from the individual concentrates. Refer to Practice D4307 for a procedure for preparation of multi-component liquid blends. When preparing multi-element standards, be certain that proper mixing is achieved. An ultrasonic bath is recommended. Standard multi-element concentrates, containing 0.0500 mass % of each element, are also satisfactory. (Warning - Some commercially available organometallic standards are prepared from metal sulfonates and therefore contain sulfur. For sulfur determinations, a separate sulfur standard would be required.)
8.3.1 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 crude oils. However, it is imperative that the 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.
8.4 Sulfur Standard - To use a metal sulfonate as a sulfur standard, analyze the sulfonate by Test Method D1552. Alternatively, prepare a sulfur standard by diluting NIST SRM 1622c in white oil. If sulfur is to be determined, the internal standard compound should not contain sulfur. Use metal napthenate or similar compounds rather than metal sulfonates. Non-sulfonate oil based sulfur standards are available commercially and can be used.
8.5 Dilution Solvent - A solvent that is free of analytes and is capable of completely dissolving all standards and samples. Mixed xylenes, kerosine, toluene, and ortho-xylene were successfully used as dilution solvents in the interlaboratory study on precision.
8.6 Base Oil or White Oil.
