Feasibility of Rare Earth Element Determination in Low Concentration in Crude Oil: Direct Sampling Electrothermal Vaporization-Inductively Coupled Plasma Mass Spectrometry

Abstract

A comprehensive study was developed showing the feasibility of determination of rare earth elements (REE) in low concentration in crude oil by using direct sampling electrothermal vaporization system coupled to inductively coupled plasma mass spectrometry (ETV-ICP-MS). The effect of organic modifier on the REE signal was evaluated and the use of 6 mg of citric acid allowed calibration using aqueous reference solutions (selected pyrolysis and vaporization temperatures were 700 and 2200 °C, respectively). Because of the facility of REE in forming refractory compounds inside the graphite furnace during the heating step, the use of a modifier gas (Freon R-12, 3.0 mL min) was necessary to allow quantitative vaporization of these elements. A flow rate of 0.40 L min was selected for both bypass and carrier gases. Under optimized conditions, the influence of sample mass was evaluated, and even using a relatively high mass of crude oil (up to 18 mg), accurate results were obtained. The accuracy was evaluated by the comparison of results by ETV-ICP-MS with those obtained by ICP-MS with ultrasonic nebulizer (USN) after high-pressure microwave-assisted wet digestion (MAWD) and microwave-induced combustion (MIC) and no statistical difference was observed between the results. The limits of quantification for REE by ETV-ICP-MS were lower (0.02-0.8 ng g) than those obtained by USN-ICP-MS after MAWD and MIC (0.6-5.1 ng g). Negligible blank values and relative standard deviations lower than 12% show the feasibility of the proposed ETV-ICP-MS method for routine analysis of crude oil.

Mercury determination in bioresorbable calcium phosphate using a new electrothermal vaporization system coupled to ICP-MS

“…This advantage related to the high sample throughput was also reported in other research studies involving the ETV-ICP-MS technique. 33,39,40 On using the reference method, determination by NEB-ICP-MS aer acid extraction, it was possible to make only four replicates per hour because the method has several steps which involve weighing, transferring the samples, and acid mixing in the vessels, and dilution with water, followed by centrifugation, since solid residues remained in the solution aer acid extraction, although the standing time (12 h) of the acid extraction procedure was not considered for the sample throughput estimation. Another important advantage of the ETV-ICP-MS method is the minimum sample manipulation, reducing the time of analysis.…”

“…22 To minimize analyte losses and memory effects, using a bypass gas (Ar) and establishing a proper heating program are essential. 22,33 However, sometimes it is difficult to overcome these limitations, making it unfeasible to use the system to analyze high-purity materials. The relatively high cost of acquisition and replacement materials is another negative aspect of this system for routine analysis.…”

Microsampling of biological fluids for elemental and isotopic analysis by ICP-MS: strategies and applications for disease diagnosis

“…The vapour is subsequently transported into the ICP by a carrier gas (Ar) through an inert tube. ETV-ICP-MS is specially well suited for the direct analysis of solids (0.1–5 mg) and slurries, 51 as well as for liquid samples (5 to 50 μL) such as oil or petroleum products, 52 because the organic matrix is easily removed. ETV-ICP-MS can offer lower detection limits and less risk of interferences as compared with sample nebulization.…”