Quantification of nitrogen markers in crude oils using gas chromatography-triple quadrupole mass spectrometry

This study presents optimization and validation of a novel gas chromatography-triple quadrupole mass spectrometry (GC-MS/MS) method for the determination of nitrogen-containing heterocyclic aromatic compounds assumed to be geochemistry markers in crude oils. Parameters for the operation of tandem mode MS/MS, i.e., precursor and product ions and collision energy (CE), were optimized, and an MS/MS instrument was used to provide multiple reaction monitoring (MRM) data. Matrix effects were evaluated, and matrix-matched calibration was used for quantification. The method was validated under optimal conditions, and all analytical parameters demonstrated satisfactory results. Indeed, the linearity (R2) in the tested calibration range was >= 0.99 for all compounds. Limits of detection ranged from 0.0014 to 0.0383 mu g mL-1, and the limits of quantitation of the target compounds were in the range 0.0042 to 0.1275 mu g mL-1. Average recoveries of the analytes were between 78.6% and 117%, with intraday and interday precisions lower than 9.4% and 19.5%, respectively, for all N-markers at spiking levels of 0.01, 0.1 and 0.5 mu g mL-1. The method was successfully applied to eight crude oil samples for geochemical evaluation of maturity, migration and depositional ambient conditions without preliminary fractionation steps. The results indicated that the GC-MS/MS method is promising for fast, easy and efficient quantitative analysis of N-markers in crude oils, and it minimizes sample preparation time and solvent consumption.