405 nm Absorption Detection in Nanoliter Volumes

摘要

Analytical UV absorption detection for microfluidic devices, capillary electrophoresis, and even high-performance liquid chromatography is hampered by the small detection volumes, short absorption paths, and the need to sample at a high rate with a stable background and low noise. Fiber-loop ring-down spectroscopy (FLRDS) permits absorption detection of dilute liquid samples in volumes as small as a few nanoliters, while being insensitive to light source fluctuations and permitting a millisecond temporal resolution. We demonstrate a FLRDS based detection scheme that is compatible in dimensions (<200 (mu)m absorption path, 6.0 nL detection volume) and optical design (405 nm detection wavelength, fiber coupled) with existing separation systems. An optical/fluidic interface has been built that allows injection of laser light into the loop while also permitting delivery of the sample. The detection limit of tartrazine was determined to be 5 (mu)M (30 fmol) corresponding to an absorption of 0.11 cm~(-1). Equivalent results were obtained when detecting myoglobin, a heterocyclic pharmaceutical ingredient, and 5.17 (mu)m diameter polystyrene beads.