High performance liquid chromatography with mid-infrared detection based on a broadly tunable quantum cascade laser

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Laser Technology

Background:

• Traditional detectors in liquid chromatography often lack specificity.
• Mid-infrared (mid-IR) spectroscopy provides molecular fingerprint information.
• External cavity quantum cascade lasers (EC-QCLs) offer tunable mid-IR light sources.

Purpose of the Study:

• To introduce and evaluate a tunable mid-IR EC-QCL as a molecular-specific detector for liquid chromatography.
• To demonstrate the capability of EC-QCL detection for the separation and quantification of sugars.
• To explore the potential for identifying other analytes based on their IR spectra.

Main Methods:

• Coupling a tunable EC-QCL (200 cm⁻¹, 1030–1230 cm⁻¹) to isocratic high-performance liquid chromatography (HPLC).
• Utilizing a cation exchange column with distilled water as the mobile phase for sugar separation.
• Performing on-line transmission measurements using a 165 μm flow cell.

Main Results:

• Successful separation and quantification of glucose, fructose, and sucrose in beverages (5–100 mg mL⁻¹).
• EC-QCL detector results showed good agreement with a differential refractive index (DRI) detector.
• Method standard deviation for calibration was <5 mg mL⁻¹, with a minimum of 1.9 mg mL⁻¹.
• Identification of other analytes like taurine, ethanol, and sorbitol based on IR spectra.

Conclusions:

• A tunable mid-IR EC-QCL is a viable molecular-specific detector for liquid chromatography.
• The EC-QCL detector enables accurate quantification of sugars and identification of other compounds.
• This technology advances analytical capabilities in complex sample matrices like beverages.