Calibration and standardization of Iatroscan (TLC-FID) using standards derived from crude oils

The TLC-FID technique, using the Iatroscan instrument, which constitutes separation and quantification of a complex mixture into various compound classes, has recently become a widely used and reliable method for characterisation of solvent extracts (particularly from reservoir rocks) and crude oils. However, there has been only limited reported research conducted aimed at calibration of the instrument and usage of standards which are relevant to the petroleum industry. This study is specifically aimed at identifying, separating, characterising, testing and developing standards, derived from natural crude oil(s), that are well suited and chromatographically pure for quantification purposes. A sample set comprising of over 30 crude oils from various basins of the world was used. The oils range widely in maturity, API gravity (8–46°), source rock type, degree of biodegradation, reservoir rock type and relative compositions. Whole oils, maltenes and asphaltenes were initially screened using Iatroscan. The process to identify suitable saturated hydrocarbons, aromatic hydrocarbons, polars and asphaltenes for the purpose of making the standard(s) included MPLC, gas chromatography, column chromatography and preparative thin-layer chromatography. Only about half the oils separate into 4 ‘clean’ fractions (saturated and aromatic hydrocarbons, resins and asphaltenes) resulting in 4 well defined peaks. Analysis of the maltenes and asphaltenes shows that neither of the fractions is free of the other fraction. Pure fractions of saturated and aromatic hydrocarbons, resins and asphaltene were isolated using a combination of various analytical techniques and standards prepared. Compositional variations between the different fractions was established using GC, Py-GC and GC-MS. Several synthetic standards were prepared and tested for comparison and the implication of their use discussed. The Iatroscan TLC-FID instrument was calibrated using data from naturally derived fractions/standard mixtures and a mathematical model developed that could be used as the basis for calibration.