Profiling of Polycyclic Aromatic Hydrocarbons in Crude Oil with the Agilent 1290 Infinity 2D-LC Solution

Significance of the Topic

• Polycyclic aromatic hydrocarbons (PAHs) are toxic contaminants present in crude oil and related products.
• Conventional one-dimensional LC or GC approaches lack the resolution needed to separate complex mixtures of substituted and heterocyclic PAHs.
• Advanced profiling techniques support risk assessment, quality control and regulatory compliance in environmental and industrial contexts.

Objectives and Study Overview

• Demonstrate the use of the Agilent 1290 Infinity 2D-LC solution for comprehensive two-dimensional liquid chromatography (LC×LC) of the PAH fraction in crude oil.
• Assess the orthogonality and peak capacity improvements over one-dimensional methods.
• Evaluate detection using parallel diode-array and fluorescence detectors.

Instrumentation Used

• Agilent 1290 Infinity 2D-LC Solution including two binary pumps, autosampler, thermostat, column compartment, valve drive and 2D valve for comprehensive LC.
• Detectors: Agilent diode-array detector (DAD) and fluorescence detector (FLD).
• Software: Agilent OpenLAB CDS ChemStation with 2D-LC module; GC Image LC×LC Edition for data analysis.

Methodology and Sample Preparation

• Sample extraction: Liquid–liquid partitioning of crude oil between hexane and nitromethane to isolate the aromatic fraction.
• First dimension: ZORBAX SB-CN column (2.1 × 150 mm, 5 μm) with water/methanol gradient (40% to 100% MeOH over 80 min) at 100 μL/min, 40 °C.
• Second dimension: ZORBAX RRHD Eclipse PAH column (3.0 × 50 mm, 1.8 μm) with water/acetonitrile gradient and 0.5 min modulation using two 60 μL loops in cocurrent configuration.
• Injection: 1 μL sample with a 1 μL water plug; needle wash in methanol/acetone.
• Detection: Parallel DAD at 220 nm and FLD in multi-emission modes (Ex 260 nm with Em 350, 430, 500 nm).

Key Results and Discussion

• One-dimensional CN-phase LC separated standard PAH mix but failed to resolve the complex crude oil extract due to numerous alkyl-substituted and heterocyclic PAHs.
• LC×LC contour plots revealed enhanced orthogonality and peak capacity, resolving isomeric pairs such as phenanthrene/anthracene and benzo(a)anthracene/chrysene.
• FLD at different emission wavelengths identified additional series of substituted PAHs eluting outside the standard PAH regions.
• High complexity of crude oil’s PAH fraction underscores the need for two-dimensional separation and selective detection.

Benefits and Practical Applications

• Improved qualitative and quantitative profiling of PAHs in petroleum matrices.
• Supports environmental monitoring, food safety, and industrial quality control by providing detailed PAH composition data.
• Complementary to GC×GC and GC–MS techniques, especially for higher molecular weight or polar PAHs.

Future Trends and Potential Applications

• Integration with mass spectrometry (e.g., APPI-MS) for compound identification and structural elucidation.
• Implementation of UHPLC columns and faster gradients to further increase throughput and resolution.
• Automation and advanced data processing to handle complex LC×LC datasets for routine laboratory use.

Conclusion

• The Agilent 1290 Infinity 2D-LC solution effectively profiles the complex PAH fraction in crude oil using orthogonal CN and PAH columns with DAD and FLD detection.
• This approach enhances separation power and detection sensitivity, offering a valuable tool for research and industrial laboratories.

Reference

• EFSA Journal 2012;10(6):2704.