Chemie und Prozesstechnik
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The high ionization potentials and low wavelength emission lines of halogens difficult the analysis of their organohalogen compounds by ICP-based methods [1]. Other techniques, such as combustion ion chromatography (CIC) or ion-selective electrodes have proven to be more reliable to determine these elements. However, these techniques are more time-consuming and/or have lower precision and accuracy.
High resolution continuum source graphite furnace molecular absorption spectrometry (HR CS GFMAS) allows the determination of solid and liquid samples by monitoring a molecule formed with the analyte and a molecule forming reagent. In the case of F, Cl and Br, several molecule forming agents have been studied for their determination. Among all of them, calcium can form a stable bond with the three elements and provides optimal analytical properties for trace analysis [2]. However, the spectral window of commercially available continuum source AAS instruments is not broad enough to cover the wavelength range necessary for a simultaneous determination. Thus, coupling it with a modular simultaneous echelle spectrograph (MOSES), which can register around 200 nm in a single measure, allows the simultaneous study of the three analytes [3].
This instrumentation is capable of register more than 200 nm of the spectra per measure keeping a high resolution. This spectral window is suitable for the monitorization of a variety of transitions of the three molecules. However, some of them are overlapped and the competitive mechanism of formation of the three molecules modify their sensitivity depending on the proportions in the sample.
In this study, a compromise in the conditions and modifiers were selected in order to maximize the sensitivity and signal to noise ratio for the three molecules. The determination was carried out by standard addition of CaF and Cl and Br were obtained from the PLS model.
References:
[1] X. Bu, T. Wang, G. Hall, J. Anal. At. Spectrom., 18, 1443–1451 (2003)
[2] M. Resano, E. García-Ruiz, M. Aramendía, M. A. Belarra, J. Anal. At. Spectrom., 34, 59–80 (2019)
[3] S. Geisler, M. Okruss, H. Becker-Ross, M. Dong Huang, N. Esser, S. Florek, Spectrochimica Acta PartB, 107, 11–16 (2015)
Simultaneous multielemental analysis of crude oils by high-resolutions absorption spectrometry
(2019)
When crude oil arrives at a refinery it needs a lot of processing before it is suitable for cracking into lighter fractions. Sulfur has to be extracted to meet ultra-low sulfur legislation for most of the fuel grades, and desalination is a crucial process as chlorine within salts is corrosive to refinery equipment. Measuring the amounts of sulfur and chlorine within crude oil is the first step in a complex clean-up process.
Heavy metals, such as vanadium, nickel and iron need to be removed too. These metals can poison the catalyst used to crack the oil into lighter fractions. This is costly as it reduces the useful life of the catalyst. Like chlorine, heavy metals also have a corrosive effect on the plant. There is some evidence that the presence of some metals in the final product can reduce performance.
A fast determination of elements and size of suspended particles is vital for diagnosis and safeguard of refinery equipment. However, sample preparation for current analytical methods consumes precious time and lost particle size information.
High-resolution continuum source graphite furnace absorption spectrometry (HR-CS-GFAS) is proposed as a fast analytical method for elemental determination in crude oils and potentially for simultaneous multielement and particle size analysis. This HR-CS-GFAS instrumentation is coupled to a modular simultaneous echelle spectrometer (MOSES) and provides a full optical window with high resolution (from 180 to 900 nm with bandwidth λ/170,000). By using this set-up, it is possible to generate a multiparameter 3D spectral image (atomic and molecular lines, isotopic shift, atomization delay, and intensities). The generated spectral images can be analyzed by multivariate regressions for the elemental and particle size analysis. Additionally, if several atomic and molecular lines are simultaneously measured, they may be used in multi-energy calibration (MEC), a method based on the use of many wavelengths of the same absorbing/emitting entity to improve the accuracy in analytical atomic spectrometry. This MEC approach combined with multivariate image analysis allows the quantification of selected elements (Si, Al, Ni, Fe, V, S, and Cl) and overcomes matrix effects.