Low-Cost Multiwavelength Absorbance Detection Using Pulsed-DUV-LEDs

Speaking on behalf of his PhD student, Ibraam Mikhail, at HPLC 2023, Brett Paull of the University of Tasmania in Australia presented research into a low-cost multiwavelength absorbance detector that utilizes pulsed deep ultraviolet light-emitting diodes (DUV-LEDs) (1). This enables simultaneous monitoring of pharmaceuticals at different wavelengths, expanding the capabilities of liquid chromatographic (LC) applications.

LEDs have been widely used in miniaturized absorbance detection due to their numerous advantages, including fast warmup times, stable output, compact size, and long lifespan. However, the narrow bandwidth of an individual LED restricts its ability to provide multiwavelength detection. Previous attempts at achieving multiwavelength detection using multiple LEDs resulted in high-cost devices due to the need for complex optics and portable spectrometers.

The novel approach presented by Paull employs a microcontroller with a field programmable gate array (FPGA) to generate short and separated micropulses for three DUV-LEDs. The team combined this with data acquisition and processing through a custom-made program and an appropriate algorithm. The microcontroller enabled simultaneous pulse signal generation and data processing without any delay.

The low-cost multiwavelength absorbance detector was constructed using easily accessible components. Three DUV-LEDs emitting at wavelengths of 235 nm, 250 nm, and 280 nm were connected to a solarization-resistant trifurcated optical fibre, which led to a 12-μL flow cell. A high-speed photodiode with a spectral response in the DUV region was connected to the fibre-compatible flow cell.

The newly developed detection system was successfully integrated with a standard liquid chromatograph and demonstrated simultaneous monitoring of pharmaceuticals at different wavelengths without compromising sensitivity. Paracetamol, caffeine, and aspirin were simultaneously determined at 250 nm, 280 nm, and 235 nm, respectively, using a chromatographic system consisting of a C18 column and a methanol–50 mM potassium dihydrogen phosphate solution adjusted to pH 3.3 (43:57) as the mobile phase.

The method utilizing the novel detection system exhibited excellent linearity and sensitivity. Regression equations with high correlation coefficients (r) of 0.9999 were obtained for paracetamol, caffeine, and aspirin. The quantitation limits (LOQs) were determined as 0.10 μg/mL, 0.38 μg/mL, and 0.66 μg/mL for paracetamol, caffeine, and aspirin, respectively. Furthermore, the repeatability of the multiwavelength determination showed a relative standard deviation of less than 3% for all drugs tested.

This opens new possibilities for cost-effective analytical instruments in various fields, including pharmaceutical analysis, environmental monitoring, and chemical research. The simplicity, affordability, and reliable performance of this novel detection system have the potential to enhance analytical capabilities and advance scientific research in diverse applications.

Reference

(1) Paull, B. Low Cost Multiwavelength Absorbance Detector Based Upon Pulsed DUV LEDs. Presented at: HPLC 2023. June 18–22, 2023. Duesseldorf, Germany. OR67.