Multi-wavelength deep-ultraviolet absorbance detector based upon program-controlled pulsing light-emitting diodes

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Instrumentation

Background:

• Traditional UV absorbance detection methods can be limited in speed and multiplexing capabilities.
• Deep-ultraviolet light-emitting diodes (DUV-LEDs) offer potential for compact and efficient absorbance measurements.
• Integrating advanced computing with optical detection is crucial for modern analytical instrumentation.

Purpose of the Study:

• To introduce a novel pulsed multi-wavelength ultraviolet absorbance detector (PMLAD) for enhanced analytical performance.
• To demonstrate the system's capability for simultaneous pharmaceutical analysis using liquid chromatography.
• To validate the detector's linearity, accuracy, and quantitation limits.

Main Methods:

• A single board computer (SBC) with a field-programmable gate array (FPGA) was used to generate synchronized micro-pulses for three DUV-LEDs (235, 250, 280 nm).
• Data acquisition and processing were performed using a custom-made program, with combined DUV-LED outputs transmitted via optical fiber to a flow cell.
• An ultra-fast photodiode recorded DUV pulse intensities, and the system was coupled with a standard liquid chromatograph.

Main Results:

• The PMLAD demonstrated excellent linearity with upper limits of linearity (A95%) ranging from 1768 to 2189 mAU and effective path lengths ≥98.0%.
• Stray light was measured to be ≤0.9%.
• Simultaneous determination of paracetamol, caffeine, and aspirin was achieved with high linearity (r² ≥ 0.99996) and low quantitation limits (LOQs) down to 0.10 µg/mL.

Conclusions:

• The developed pulsed multi-LEDs absorbance detector (PMLAD) offers a sensitive and selective method for pharmaceutical analysis.
• The use of absorbance ratios between wavelengths aids in compound identification.
• This novel approach provides a robust platform for multi-wavelength UV detection in chromatography.