On-the-Fly Fluorescence Lifetime Detection in Liquid Chromatography with Data Collected Simultaneously at Multiple Emission Wavelengths

Abstract

A novel liquid chromatography (LC) fluorescence detector simultaneously generates fluorescence decay curves at multiple emission wavelengths. The fourth harmonic (266 nm) excitation light from a pulsed Nd:YAG laser is focused into a standard LC flow cell. A small spectrograph disperses the fluorescence. Fiber-optic delay lines positioned in the exit focal plane time the arrival of photons at the photomultiplier tube detector. Four wavelength channels with 50 ns channel spacing were used in this study. The intensity-decay time waveform is averaged with a digital storage oscilloscope. Temporal overlap between adjacent wavelength channels is removed during the post-processing of the data. System performance was characterized for chromatographic elution of polycyclic aromatic hydrocarbons (PAHs). Detection limits are 1.6 ppb for naphthalene and 0.14 ppb for fluorene. Resolution of co-eluting 1,4-dimethyl-naphthalene and anthracene components on the basis of differences in their lifetimes and spectral distributions is demonstrated.