FlipLCTM. A New Method for Measuring Charged Analytes in Complex Mixtures. Part III.

Significance of the Topic

Accurate determination of ascorbic acid in complex matrices such as fruits, vegetables and nutritional supplements is critical for nutritional quality control and research. Conventional HPLC analyses often suffer from matrix interferences, short column lifespan due to contaminant buildup, and lengthy sample preparation steps. The FlipLC method addresses these challenges by integrating orthogonal isolation and analytical columns in a single run, streamlining analysis and protecting the analytical column.

Objectives and Study Overview

This study presents the application of FlipLC™ for rapid isocratic measurement of ascorbic acid in various food matrices. Key aims include:

• Developing a robust dual-column chromatographic approach for charged analytes.
• Demonstrating reduction of interfering peaks without extensive sample cleanup.
• Assessing method performance across multiple plant-derived samples.

Methodology and Instrumentation

The FlipLC system employs two mixed-mode columns connected by a switching valve:

• Isolation column (Flip column): Primesep 100, 4.6 × 50 mm
• Analytical column: Primesep B, 4.6 × 150 mm
• Flow rate: 1.0 mL/min
• Valve switch time: 0.5 min
• Detection: UV at 270 nm
• Injection volume: 5 µL of filtered sample

The isolation column first retains charged components under normal flow, then reverses flow mid-run to divert contaminants away from the analytical column. This orthogonal retention enables a simplified, isocratic separation completed in under five minutes.

Main Results and Discussion

Application of FlipLC to strawberry juice yielded a dramatically simplified chromatogram with a well-resolved ascorbic acid peak, compared to a complex profile under conventional single-column operation. Column protection was markedly improved, extending the operational lifespan relative to traditional guard columns. Quantitative results for ascorbic acid in various plant sources ranged widely:

• Rosehips fruit: 7 200 ppm
• Red pepper: 2 300 ppm
• Blackcurrant: 1 800 ppm
• Lemon: 660 ppm
• Strawberry: 500 ppm
• Orange: 440 ppm
• Tangerine: 420 ppm
• Grapefruit: 330 ppm
• Cornelian cherry: 320 ppm
• Spinach: 220 ppm
• Horseradish: 190 ppm
• Cabbage: 70 ppm

These data confirm the method’s broad applicability across diverse sample matrices without specialized pretreatment.

Benefits and Practical Applications

The FlipLC approach offers multiple advantages:

• Elimination of extensive sample cleanup procedures
• Rapid, isocratic analysis in less than five minutes
• Enhanced protection and extended lifetime of the analytical column
• Simplified chromatograms with minimal interfering peaks

This makes the method particularly suitable for routine QA/QC in food, nutraceutical and environmental laboratories.

Future Trends and Potential Applications

Future developments may include:

• Extension to additional charged analytes such as organic acids and amino acids
• Integration with mass spectrometric detection for enhanced sensitivity and selectivity
• Automation of valve switching and data processing workflows
• Application to clinical and environmental samples requiring minimal sample handling

Scaling FlipLC to high-throughput platforms could further enhance laboratory efficiency.

Conclusion

The FlipLC™ dual-column technique provides a versatile, robust solution for measuring ascorbic acid in complex samples. By combining orthogonal retention mechanisms, the method reduces interferences, shortens analysis time and preserves column integrity, enabling reliable quantitation across diverse matrices with a single standardized protocol.

Reference

SIELC Technologies, Inc. FlipLC™: A New Method for Measuring Charged Analytes in Complex Mixtures. Part III. 2002–2018.