Characterization and use of a Raman liquid-core waveguide sensor using preconcentration principles.

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Optical Sensing

Background:

• Developing sensitive and selective methods for detecting volatile organic compounds (VOCs) is crucial for environmental monitoring.
• Traditional analytical techniques often require complex sample preparation or expensive instrumentation.
• Optical waveguide sensors offer potential for miniaturization and cost-effective analysis.

Purpose of the Study:

• To report a novel Raman sensor based on a liquid-core optical waveguide (LCW).
• To demonstrate the sensor's capability for preconcentrating and detecting an aqueous mixture of benzene, toluene, and p-xylene.
• To evaluate the analytical performance, including preconcentration factor, limit of detection, and precision.

Main Methods:

• A Teflon-AF 2400 tube filled with water was used as the liquid-core waveguide.
• Aqueous analytes (benzene, toluene, p-xylene) were introduced and preconcentrated on the waveguide surface.
• Analytes were eluted using an acetonitrile-water mixture, and Raman spectra were acquired.
• Preconcentration factors, relative standard deviation, and limits of detection were determined.

Main Results:

• A preconcentration factor of 14-fold was experimentally determined.
• Analytically useful Raman signals were obtained at specific wavenumbers for each analyte.
• The relative standard deviation for replicate measurements was 3%.
• A limit of detection of 730 ppb (parts per billion by volume) for benzene was achieved without surface enhancement.

Conclusions:

• The developed LCW Raman sensor is effective for preconcentrating and detecting benzene, toluene, and p-xylene.
• The method offers good precision and a low limit of detection for these analytes.
• This approach represents a promising, non-enhanced Raman technique for trace organic compound analysis.