Advances in Trace Element Analysis of Petroleum Samples PDF Download

Author: Nopparat Vorapalawut
Publisher:
ISBN:
Category :
Languages : en
Pages : 18

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Book Description
The advent of inductively coupled plasma quadrupole mass spectrometry (ICP MS) largely contributed to reliable and fast multielement trace analysis of petroleum samples but the inherent problems related to plasma instability, carbon deposition on the sampler and skimmer cones and carbon-related polyatomic interferences are omnipresent. The goal of this work was to address several analytical tasks impossible to be successfully handled by ICP quadrupole ICP MS. They include the determination of non-metals, such as sulphur and silicon, simultaneous multielement trace analysis at the low ng g-1 levels, and insight into the molecular binding of the trace elements present. The method developed for the sulphur determination in gasoline was based on the formation of microemulsion introduced directly into the ICP. Quantification was carried out by ICP AES using external calibration which allowed high throughput analysis. The developed method was applied for total sulphur analysis in diesel samples from various gas stations in Thailand. Problems related to spectral interferences were alleviated by the use of a double-focusing sector field ICP MS optimized for the direct simultaneous determination of Ag, Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Pb, Sn, Ti, and V. Polyatomic interferences originating from the carbon-rich matrix were completely eliminated at a resolution of 4000 allowing the detection limits at the low pg g-1 level to be obtained (typically one order of magnitude lower than using a quadrupole ICP MS). A method for the routine comprehensive trace element analysis of xylene solutions of oil samples using external calibration was developed, validated by the analysis of CRMs and applied to the analysis of gas condensate and oil samples. Another method based on the micro-flow injection total consumption sample introduction was developed for the silicon determination allowing the detection limits down to 1 ng g-1. The effects of the sample matrix and of the chemical form of silicon on the sensitivity were investigated and alleviated when necessary by heating the spray chamber and sample dilution. Laser ablation-ICP-SF MS was developed for direct multielement analysis in crude oils and asphaltenes. A silica gel plate was impregnated for 30 min with a sample solution and analyzed by laser ablation-ICP MS. Carbon-related polyatomic interferences and matrix suppression effects were absent enabling quantitation by external calibration. The detection limits were in the low ng g-1 range. The method was validated by the analysis of NIST 1084a and 1085b certified reference materials (wear metals in lubricating oils) and applied to the analysis of crude oil and asphaltene samples. An insight into the chemical forms of Co, Cr, Fe, Ni, S, Si, V and Zn present in crude oil and oil vacuum distillation residue was gained by the coupling of microchromatography using permeation through gels with the increasing exclusion limit (5000, 400 000 and 20 000 000 Da) with high resolution (R = 4000) ICP MS. The method allowed the acquisition of chromatograms with high sensitivity competitive to the existing methods, showing element- and sample origin-dependent morphology. Normal phase HPLC-ICP MS and size-exclusion ICP MS were proposed to evaluate the purity of the silicon standard compounds, their reactivity with different petroleum-related matrices and speciation of silicon.