Adaptable 3D printed detector for absorbance monitoring of column chromatography separations using deep-UV LED at 280 nm

Column chromatography has been extensively used in the field of chemistry for a variety of applications, from the purification of synthesized compounds for pharmaceutical products to the isolation of natural products. Typically, the separated compounds are collected at the end of the column based on elution time, mobile phase volume, or colored markers. However, many target substances exhibit absorption in the ultraviolet range, making it challenging to monitor the elution process without an expensive instrumental detection system. In this study, we describe a flow-through absorbance-based detector for column chromatography using a deep-UV light-emitting diode with peak emission centered at 280 nm as light source for the first time. A 3D-printed holder was designed to house the LED and a UV-sensitive photodiode, positioned at 180° to measure radiation through a quartz tube with a diameter of 5 mm. The current generated by the photodiode was converted to absorbance using a log-ratio amplifier circuit and monitored via a USB data recorder. A noise level of 2.1 mAU was achieved, suitable for qualitative analysis. As a proof of concept, this detector was coupled with column chromatography to monitor the elution of (i) caffeine, (ii) a caffeine-hesperetin mixture, and a (iii) coffee extract sample. Absorbance spectra and thin-layer chromatography (TLC) experiments were performed to confirm the detector's capability to evaluate the efficiency of identifying UV-absorbing compounds. With this approach and the potential use of various deep-UV LEDs, we anticipate a cost-effective and efficient solution for monitoring the elution of non-colored compounds in column chromatography.