Parts-per-billion limits of detection via absorbance spectroscopy: An ultraviolet (254 nm) absorbance detector for liquid chromatography using a light emitting diode (LED)

An absorbance detector for high-performance liquid chromatography (HPLC) was developed using a commercially available light emitting diode (LED) at 254 nm. Use of the LED was investigated due to its low output power fluctuation, which should minimize noise and maximize performance. This detector has been characterized and used to perform several separations of relevance to the atmospheric chemistry of airborne particulate matter, specifically, brown carbon (BrC) or humic-like substances (HULIS). The study of atmospheric BrC can be aided by sensitive and general detection schemes, such as absorbance detection. Owing to the exceptional output stability of the LED, the absorbance detector exhibited 3s detection limits of 130 nmol/L (18 ppb) for the chromatography of 4-hydroxybenzoic acid and the detector itself demonstrated noise-equivalent absorption of approx. 180 μAU. The detector was applied to the separation of products resulting from the photo-Fenton reaction of guaiacol. No fewer than 15 individual peaks are noted in the resulting chromatogram. The sensitivity provided is a valuable tool for the chemical analysis of complex samples requiring chromatography.