Towards functional group-specific detection in high-performance liquid chromatography using mid-infrared quantum...

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Chromatography

Background:

• Mid-infrared (MIR) detection in liquid chromatography (LC) is crucial for analyzing various compounds.
• Traditional Fourier transform infrared (FTIR) detection has limitations in sensitivity and specificity for complex samples like wine.
• Developing sensitive and selective detection methods for carbohydrates in complex matrices remains a challenge.

Purpose of the Study:

• To introduce a distributed feedback quantum cascade laser (QCL) as a novel light source for MIR detection in LC.
• To evaluate the QCL's performance for the group-specific detection of carbohydrates (fructose and glucose) in red wine.
• To assess the potential for enhanced sensitivity compared to conventional FTIR detection.

Main Methods:

• An isocratic high-performance liquid chromatography (HPLC) system was coupled with a custom-made flow cell.
• The flow cell featured adjustable spacing between two diamond windows and hollow waveguides.
• Separation was performed on an ion-exchange column at 80°C using 0.04% formic acid as the mobile phase, with QCL emission at 1067 cm⁻¹.

Main Results:

• The distributed feedback quantum cascade laser enabled sensitive MIR detection of fructose and glucose in red wine.
• Group-specific detection was achieved as the laser's emission wavelength matched the absorption maxima of carbohydrates, while organic acids showed minimal absorption.
• The adjustable optical path length (25–125 µm) demonstrated potential for significantly enhanced sensitivity.

Conclusions:

• A distributed feedback quantum cascade laser is a viable and powerful light source for MIR detection in LC.
• This QCL-based method allows for group-specific detection of carbohydrates in complex samples like red wine.
• The system offers promising prospects for achieving higher sensitivity in chromatographic detection.