Recent Advances in HPLC Optical Detection

Abstract

HPLC optical detector advances are reviewed in the field of absorbance, fluorescence, phosphorescence, and elemental emission detection. The development of UV-doped silicon photodiodes having excellent response throughout the UV, miniature gas discharge lamps (Hg, Zn, Cd) with high output UV lines, and high throughput UV interference filters allow optical systems with shot noise levels below 10⁻⁵ au. However, the fundamental noise limitations in such systems are now thermal changes in the optoelectronic components and flow cells. Future absorbance detectors may require thermostatting to achieve the minimal noise and drift performance inherent in the optical design. The emerging development of UV-doped photodiode arrays at reasonable cost offers multichannel absorbance detection and on-the-fly spectral information. Data system design for processing the multichannel data is critical in this field. On-column absorbance detection using packed microbore fused silica columns has been demonstrated, allowing a flow cell volume of <10 nanoliters, compatible with micro HPLC. In a similar development, on column fluorescence detection using an open tubular glass capillary column has been demonstrated in zone electrophoresis. A significant amount of research in fluorescence detection using laser sources is now underway. Sensitivity advantages of approximately 10-fold have been demonstrated due to high laser output and another 10-fold improvement for detecting long radiative lifetime molecules due to pulsed laser/temporal discrimination. Dual photon excited fluorescence, offering unique selectivities, has been demonstrated. This technique requires the high output power of the laser source. Room temperature phosphorescence HPLC detection has been demonstrated, utilizing triplet → triplet energy transfer from a donor solute molecule to a mobile phase acceptor additive (e.g., biacetyl). This energy transfer technique offers the expansion of the emission technique to phosphorescent molecules at nanogram sensitivities. Finally, the development of micro HPLC columns operating at 1–10 μl/min offers potential compatibility with element specific GC detectors such as the flame photometric detector (S, P specific).