Contribution of the recent HPTLC developments to the analysis of complex samples with broad polarity ranges: Lipidomics, petroleum products and biofuels

Talk delivered at the Eastern Analytical Symposium (EAS) meeting, held November 17-19, 2019, in Princeton, NJ, USA, organized by the International Association for the Advancement of High-Performance Thin-Layer Chromatography (HPTLC Association).High Performance Thin-Layer Chromatography (HPTLC) separation of broad-polarity, complex petroleum or lipid-related samples into compound classes was approached using gradient-based Automated Multiple Development (AMD), a technique that combines incremental multiple development and solvent gradient in short steps to obtain efficient separations. AMD is adequate for obtaining separations with different levels of complexity. The possibility of performing multiple detection in a planar format is a strong differential feature of HPTLC versus other techniques. Thus, Ultraviolet (UV) and Fluorescence(FL)-induced scanning densitometry (SD) was used to detect and quantify separated classes of compounds in the studied samples, including those that do not possess cromophores (i.e., saturated hydrocarbons in heavy petroleum). Likewise, in the case of lipids, the bands of interest separated on the plate were on-line transferred to an Electrospray Ionization-Mass Spectrometry (ESI-MS) instrument via an elution-based interface. In this way, ESI-MS spectrum allows the profile of lipids belonging to a given class to be obtained. In addition, the corresponding identification of molecular individual species was achieved by on-plate MS/MS or High Resolution-MS spectra. Lipid species determination will be discussed for different lipid classes in several matrices: (1) Mono-, di-acylglycerides and free fatty acids, as impurities in a fatty acid methyl ester-based biodiesel sample; (2) Sphingomyelins and globotriaosylceramides in human plasma; (3) Phospholipids associated to membrane proteins in the purified RC-LH1-PufX complex from Rbc. bogoriensis, a photosynthetic purple bacterium. UV/FL-SD with MS coupling makes possible to develop strategies for obtaining qualitative and different levels of quantitative information from lipid-based complex samples