Reverse-High Performance Liquid Chromatography Mechanism Explained by Polarization of Stationary Phase

Abstract

Original results and conclusions on Reverse Phase High Performance Liquid Chromatography (RPLC) mechanism are here presented. So far, none of the theoretical approaches applied to the RPLC mechanism can explain the retention and elution mechanisms of most of the analytes by RPLC, especially neutral organic compounds. Our experiences allowed us to state that RPLC retention mechanism most likely occurs through polarization of stationary phase (usually dielectric surfaces) submerged into solvents with huge dielectric constant and high dipole moment (i.e. water and/or acetonitrile) at high pressures as those applied in RPLC systems. The surface polarized interacts with polarizable target analytes (i.e. naphthalene, pyrene or benzo(ghi)perylene) in such a way that the retention depends on the medium polarizability of the target compound. The higher is the medium polarizability of the compound retained the higher is its retention time.By using Polycyclic Aromatic Hydro-carbons (PAHs) and 6-nitrochrysene as probes, we found that although the dependence of retention times on pressure is not evident in most cases, the interaction between pressure and the mobile phase dipole moment is evidenced at the light of the constructed mathematical models. Two very different cases can be distinguished:1. On one hand, when low dipole moment mobile phases are used, high pressure means big work developed by the system in such a way that high pressures inside the system reduce retention times compared to low pressures.2. On the another one, when high dipole moment solvents are used as mobile phase, high pressure entails an outstanding increase of the retention times compared to low dipole moment mobile phases. This is most likely due to high pressures that entail closer alignment of mobile phase dipoles and lesser tilt of them, originating an outstanding electric field inside the analytical column.In addition to this, reduced retention times for dipole solutes (6-nitrochrysene, dipole molecule) compared to non-polar solutes (PAHs) were observed when pressure drops. This conclusions would allow to extend the model to basic/acid molecules at different pH. In this case, electrostatic repulsions among analyte molecules should be considered.

Polar Aromatic Compounds in Soot from Premixed Flames of Kerosene, Synthetic Paraffinic Kerosene, and Kerosene–Synthetic Biofuels

“…PACs account for most of the toxic potential and atmospheric reactivity of soot. , A detailed list of the polar compounds identified is given in Tables – The PAC families determined were (a) oxa-AHs (xanthenes, benzoxanthene, methoxy-AHs, furan, ethers...), (b) hydroxy-AHs; (c) aldehydes-AHs; (d) ketones-AH; (e) quinones-AHs; (f) aromatic monocarboxylic acids/aromatic hydroxy acids/aromatic dicarboxylic diacids; (g) nitrated-AHs (including amines, acridines, cinnoline derivatives, carbazoles...); and (h) nitro-AHs. In this paper, no quantitative data are presented (except for the nitro-AH group) due to the high cost and/or the unavailability of most of the standards.…”

“…The formation of nitro-AHs is much concerning because of their potential mutagenicity and atmospheric reactivity . These compounds may be emitted from incomplete combustion processes such as fossil fuel and biomass burning − or produced by heterogeneous or homogeneous reactions of AHs with atmospheric oxidants such as the hydroxyl radical, the nitrate radical, or ozone. , On the other hand, some oxy-PAHs have been reported to transform into nitro-PAHs via atmospheric reaction. , …”

“…63 These compounds may be emitted from incomplete combustion processes such as fossil fuel and biomass burning [63][64][65] or produced by heterogeneous or homogeneous reactions of AHs with atmospheric oxidants such as the hydroxyl radical, the nitrate radical, or ozone. 25,26 On the other hand, some oxy-PAHs have been reported to transform into nitro-PAHs via atmospheric reaction. 67,68 Due to heating occurring in most of the extraction methodologies in the literature (Soxhlet, microwave-assisted extraction or supercritical fluid extraction) and/or dichloromethane for extracting nitro-PAHs [69][70][71] , most nitro-PAHs in soot samples can be lost.…”

“…Byproducts of fuel and biofuel combustion, such as aromatic compounds [AHs (aromatic hydrocarbons) and PACs (made up of AHs containing oxygen and/or nitrogen heteroatoms)], are known to be soot precursors , and account for most of the toxic potential and atmospheric reactivity of soot. , In spite of the importance of these compounds, data on their analytical profile and concentration in fossil fuel and biofuel soot are scarce in the literature. Moreover, efficient, reliable, and simple analytical methodologies for determining these highly toxic compounds in soot samples are lacking. , …”

Kütle Spektrometresinden Glikan Mikrodizilerine: Glikomikte Analitik Tekniklere Genel Bir Bakış

“…HPLC, sıvı fazda bulunan bileşenlerin mobil fazda taşınması ve ayrılması prensibine dayanır [39]. HPLC'nin en yaygın kullanılan türü, aşamalı olarak değişen polariteye sahip bir sabit faz üzerindeki mobil fazın hareketiyle ayrım sağlayan ters fazlı kromatografidir (Reverse-phase chromatography / RPC) [40]. RPC'de, hidrofobik bir malzeme olan C18-bağlanmış silika gibi bir sabit faz kullanılır ve glikanlar gibi hidrofilik biyomolekülleri hidrofobisitelerine göre ayırmak için mobil fazda organik bir çözücü kullanılır [41].…”