Profiling Alkyl Phosphates in Industrial Petroleum Samples by Comprehensive Two-Dimensional Gas Chromatography with Nitrogen Phosphorus Detection (GC × GC–NPD), Post-column Deans Switching, and Concurrent Backflushing

Abstract

Several refinery fouling incidents in North America have been due to the presence of alkyl phosphates in the crude oil feed. These phosphates originate in some cases from their use as gellants (viscosity builders) for fracturing fluids used in the process of hydraulic fracturing in water-sensitive geologies. Industry responded with an inductively coupled plasma–optical emission spectroscopy (ICP–OES) method for the analysis of total volatile phosphorus. Applied to distillate fractions of crude oil, this method is plagued with limited precision and a high limit of detection (0.5 ± 1 μg of phosphorus mL–1). This approach provides only total P with no speciation information; thus, it cannot be used to develop an understanding of alkyl phosphate fouling at a molecular level. Our group previously presented an approach using comprehensive two-dimensional gas chromatography with nitrogen phosphorus detection (GC × GC–NPD) and post-column Deans switching that provided qualitative and quantitative profiles of alkyl phosphates in industrial petroleum samples with increased precision and at levels comparable to or below those achievable by ICP–OES. Here, we present a refinement to this method that incorporates splitless injection and concurrent backflushing. Using this technique, it is possible to quantify alkyl phosphates to levels 2 orders of magnitude lower than those achieved with our previous approach and 2–3 orders of magnitude lower than what is possible by ICP–OES while still maintaining an increased precision over ICP–OES. The addition of concurrent backflushing provided column protection, reducing instrument maintenance and improving the reproducibility of retention times when analyzing heavier industrial petroleum fractions. A recovery study performed in two different industrial petroleum samples demonstrated the reliability of calibrations performed in solvent when used for quantification of alkyl phosphates in real samples. Finally, a profiling study of alkyl phosphates in 14 different industrial petroleum samples (crude oil and mixtures of crude oil and fracture fluid) is also presented.

Complete Group-Type Quantification of Petroleum Middle Distillates Based on Comprehensive Two-Dimensional Gas Chromatography Time-of-Flight Mass Spectrometry (GC×GC-TOFMS) and Visual Basic Scripting

“…The nonpolar × semipolar (or polar) column combination used for the method development is a very common combination for the analysis of petroleum fractions, and its application is described in the literature. − ,− In most cases, columns with 5% phenyl-substitution, being more temperature stable than pure dimethylpolysiloxane, and 30 m length are used for the first dimension, often in combination with 50% phenyl-substituted columns in the second dimension with varying length. First dimension columns with a length of more than 30 m are more common nowadays, due to the advantageous separation of complex samples with enormous numbers of isomers.…”

“…All these individual analytical methods can be replaced by a comprehensive two-dimensional GC×GC analysis. In numerous previous works, different petrochemical products of fossil and renewable sources have been analyzed using GC×GC with a variety of detection methods, − above all TOFMS and flame ionization detection. − With GC×GC-TOFMS it is possible to get a deeper insight into the chemical composition of complex mixtures, as is the case for petrochemical products, for example concerning biomarkers such as hopanes. , Nevertheless, the analysis of common middle distillates with this method is still an analytical challenge despite modern technology and software. The whole composition of middle distillates can be categorized in more than a dozen substance classes, each containing up to several hundred single compounds.…”

Comprehensive Two-Dimensional Gas Chromatography: A Universal Method for Composition-Based Prediction of Emission Characteristics of Complex Fuels

“…Starting from the chemical composition, application of the molecular knowledge enables the determination of numerous fuel properties such as density, freezing point, flash point, heat of combustion, surface tension, and viscosity. , As a consequence, a very detailed understanding of the composition of complex fuel mixtures becomes the crucial factor in linking molecules to combustion processes. Detailed compositional determination can be achieved by comprehensive two-dimensional gas chromatography (GCxGC), playing an important role in the analysis of petroleum-derived products, fossil fuels, and increasingly synthetic fuels and fuels from bio-based sources. − …”

Unique ion filter—A data reduction tool for chemometric analysis of raw comprehensive two‐dimensional gas chromatography‐mass spectrometry data

“…When coupled with a mass spectrometer, the separation potential of GC × GC is further enhanced by the rich data generated from the detector. GC × GC‐MS has been widely applied in various areas of analysis such as petroleum [5–14], environmental [15–22], metabolomics [23–29], etc. Recent reviews have highlighted several areas where GC × GC‐MS has been applied [30–35].…”