Liquid Chromatography: Applications for the Oil and Gas Industry

This chapter focuses on the liquid chromatography (LC) techniques used in the petroleum industry. It provides a brief introduction into the basic principles of LC, LC hyphenated with mass spectrometry (LC‐MS), and two‐dimensional liquid chromatography (2D‐LC). The chapter provides an overview of contemporary LC techniques for samples related to oil, refining, and wastewater encountered in the oil and petrochemical industries. Group‐type separation is commonly used to analyze quantitatively or to preparatively obtain specific fractions of oil or refined products, such as fractions containing aromatics, resins, or saturates. Besides separating petroleum samples into different hydrocarbon groups, molecular‐weight distributions of petroleum samples or fractions can be determined. This can be achieved with size‐exclusion chromatography, which separates compounds based on the hydrodynamic volume. The chapter also describes how LC can be used as a pre‐separation technique for gas chromatography analysis

Investigation of the effects of solvent-mismatch and immiscibility in normal-phase × aqueous reversed-phase liquid chromatography

Comprehensive two-dimensional liquid chromatography (LC × LC) is an attractive separation technique that allows achieving high peak capacities and information on chemical correlations. Unfortunately, its application in industrial practice is still not widespread due to limiting factors such as complex method development, tedious method optimization and solvent-incompatibility (such as solvent-strength mismatch or immiscibility experienced during fraction transfer). A severe case of solvent-incompatibility is encountered in the comprehensive coupling of normal-phase LC and reversed-phase LC (NPLC × RPLC). NPLC × RPLC is considered a desirable LC × LC system, especially for the characterization of synthetic polymers, due to the high orthogonality of the two retention mechanisms. However, its experimental realization often suffers from solvent-injection effects in the RPLC dimension, such as peak-deformation, peak-splitting, or even unretained elution (“breakthrough”) of sample components. Such a decrease in performance or loss of retention is highly dependent on the types of solvents used. To explore the boundaries of solvent compatibility, we applied large-volume injections (LVI) of reference analytes (e.g. alkyl benzenes; ethoxylate and propoxylate polymers) dissolved in water-immiscible sample solvents, such as dichloromethane, n-hexane, and isooctane in fast water-based gradient RPLC separations (using methanol or acetonitrile as eluent). It was found that, when using highly aqueous initial gradient conditions, hydrophobic sample diluents were retained and eluted during the applied gradient. Depending on the relative retention of the retained diluent and the sample analytes, good chromatograms for LVI of immiscible solvents were obtained, comparable with injections under ideal conditions. The conclusions from injection experiments in aqueous RPLC were verified by coupling an NPLC system with a gradient from isooctane to tetrahydrofuran and an RPLC system with a gradient from water to acetonitrile in an online comprehensive NPLC × RPLC separation of a mixture of propoxylate polymers. The separation provided separation of the polymers based on their number of hydroxyl end-groups (NPLC) and oligomer chain-length (RPLC), without suffering from significant band-broadening effects due to solvent-mismatch upon injection in the second-dimension RPLC system

Characterization of complex polyether polyols using comprehensive two-dimensional liquid chromatography hyphenated to high-resolution mass spectrometry

Polyether polyols are often used in formulated systems, but their complete characterization is challenging, because of simultaneous heterogeneities in chemical composition, molecular weight and functionality. One-dimensional liquid chromatography–mass spectrometry is commonly used to characterize polyether polyols. However, the separation power of this technique is not sufficient to resolve the complexity of such samples entirely. In this study, comprehensive two-dimensional liquid chromatography hyphenated with high-resolution mass spectrometry (LC × LC-HRMS) was used for the characterization of (i) castor oil ethoxylates (COEs) reacted with different mole equivalents of ethylene oxide and (ii) a blended formulation consisting of glycerol ethoxylate, glycerol propoxylate and glycerol ethoxylate-random-propoxylate copolymers. Retention in the first (hydrophilic-interaction-chromatography) dimension was mainly governed by degree of ethoxylation, while the second reversed-phase dimension resolved the samples based on degree of propoxylation (blended formulation) or alkyl chain length (COEs). For different COE samples, we observed the separation of isomer distributions of various di-, tri- and tetra-esters, and such positional isomers were studied by tandem mass spectrometry (LC–MS/MS). This revealed characteristic fragmentation patterns, which allowed discrimination of the isomers based on terminal or internal positioning of the fatty-acid moieties and provided insight in the LC × LC retention behavior of such species