Parts-per-billion Limits of Detection via Absorbance Spectroscopy: An Ultraviolet (254 nm) Absorbance Detector for Liquid Chromatography using a Light Emitting Diode (LED)

Abstract

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 3σ 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.