Improved Sample Pretreatment Using Offine Supercritical Fluid Extraction

Importance of the Topic

Efficient pretreatment of solid samples is vital for reliable separation analyses by HPLC, SFC, or GC. Traditional methods such as solvent dissolution or Soxhlet extraction face challenges including solvent optimization, long processing times, high labor demands, and limited throughput. Supercritical fluid extraction (SFE) addresses these limitations by leveraging the unique properties of supercritical CO2—high diffusivity, low viscosity, tunable solvating power with modifiers, easy solvent removal, low cost, and compatibility with automation.

Objectives and Study Overview

This report presents the offline Nexera UC SFE pretreatment system designed to automate and streamline the extraction of target analytes from solid matrices. Two application examples illustrate the system’s performance: extraction of d-​α-​tocopherol from a soft capsule nutritional supplement, and simultaneous extraction of 301 residual pesticides from brown rice, followed by SFC or GC/MS/MS analysis.

Methodology and Instrumentation

The Nexera UC SFE system combines precise temperature and pressure control with automated sample handling. Key components include:

• Extraction vessels (0.2 mL and 5 mL volumes) mounted on a 48-position rack changer.
• CO2 pump and solvent delivery pump with LabSolutions control for modifier addition.
• SFE unit performing static and dynamic extraction at controlled temperatures (40–80 °C) and pressures (up to 15 MPa).
• Back pressure regulator and trap column (e.g., ODS) for collection of extracted material at near-atmospheric pressure.
• Fraction collector to elute analytes with an organic solvent (hexane or acetone/hexane) for downstream analyses.
• Integration with analytical platforms: SFC/UV-VIS, GC/MS/MS, LC/MS, and NMR for comprehensive sample characterization.

Main Results and Discussion

Case Study 1: Vitamin E Extraction

• A d-α-tocopherol supplement mixed with a dehydrating agent underwent SFE (CO2, 5 mL/min; 40 °C; 15 MPa; 15 min). Hexane was used for elution.
• Six replicates yielded an average recovery of 104 % and RSD of 1.55 %, demonstrating high accuracy and precision.

Case Study 2: Pesticide Residue Analysis in Brown Rice

• Ground rice was combined with dehydrating agent, extracted with CO2 + methanol (5 mL/min; 40 °C; 15 MPa; 8 min), and eluated with acetone/hexane.
• GC/MS/MS analysis of 301 pesticides in six replicates achieved recoveries of 70–120 % and RSDs below 10 %, confirming robust performance across diverse analytes.

Benefits and Practical Applications

• Automation of up to 48 samples reduces hands-on time and human error.
• Lower organic solvent consumption enhances cost-effectiveness and sustainability.
• Wide polarity range via modifier addition expands analyte scope from nonpolar lipids to moderately polar and ionic compounds.
• Compatibility with multiple detection techniques enables integrated workflows for food safety, pharmaceuticals, environmental monitoring, and QA/QC laboratories.

Future Trends and Potential Applications

• Development of online SFE–chromatography interfaces for real-time analysis and reduced dead volume.
• New modifier systems and vessel designs to improve extraction of highly polar or ionic species.
• Miniaturized and high-throughput SFE modules for clinical and metabolomic applications.
• Integration with high-resolution mass spectrometry and ambient ionization techniques for rapid screening.
• Expansion into green analytical chemistry initiatives to minimize environmental footprint.

Conclusion

The Nexera UC SFE pretreatment system delivers a versatile, high-efficiency solution for automated solid sample extraction. Demonstrated by vitamin E and pesticide studies, it achieves excellent recoveries, repeatabilities, and low solvent usage. Its modular design and compatibility with various analytical detectors make it a powerful tool for modern laboratories focusing on throughput, sustainability, and data quality.

Reference

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