NIR sensor for aqueous urea solution film thickness and concentration measurement using a broadband light source

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Chemical Sensing

Background:

• Accurate monitoring of urea concentration and layer thickness is crucial in various industrial and environmental applications.
• Existing methods may lack the simultaneous measurement capability or require complex sample preparation.
• Near-infrared (NIR) spectroscopy offers a non-destructive approach for analyzing aqueous solutions.

Purpose of the Study:

• To develop and validate a multi-wavelength NIR broadband absorption sensor.
• To achieve simultaneous determination of layer thickness and urea concentration in aqueous solutions.
• To explore the sensitivity of NIR absorption spectra to temperature and solute concentration.

Main Methods:

• Utilized thin-layer quartz transmission cells for sample preparation.
• Employed narrowband filters to select characteristic wavelength bands for transmittance ratio measurements.
• Converted transmittance ratios to absorbance ratios for quantitative analysis.
• Recorded Fourier transform infrared (FTIR) spectra across the 1250-2500 nm range.
• Designed a prototype sensor with a tungsten lamp, intensity modulation, and lock-in detection.

Main Results:

• Successfully demonstrated simultaneous monitoring of layer thickness and urea concentration.
• Identified optimal wavelength bands sensitive to temperature and urea concentration.
• Validated the sensor concept using a calibration cell with variable liquid layer thicknesses (7-1000 μm).
• Characterized spectral behavior across a wide range of urea concentrations (0-40 wt.%) and temperatures (298-338 K).

Conclusions:

• The developed multi-wavelength NIR sensor provides a robust method for simultaneous layer thickness and urea concentration analysis.
• This technology has potential applications in process monitoring and quality control where real-time data is essential.
• The sensor's design and methodology offer a promising advancement in quantitative spectroscopic analysis of aqueous solutions.