Luminescence Detection with a Liquid Core Waveguide

Abstract

A new fluoropolymer tube is proposed as the basis of a novel class of liquid core waveguide-based luminescence detectors. Both chemiluminescence and photoluminescence detectors are possible. In the latter case, illumination is transverse to the main axis of the tube. With such a geometry, it is even possible to operate without monochromators, although limits of detection do improve with the incorporation of monochromators. The nature of the design is such that it is particularly simple to fabricate detectors in a flow-through configuration and where the light from the cell is coupled to a photodetector by an optical fiber. No focusing optics are necessary. A number of applications are illustrated. Attainable limits (LODs, S/N = 3) of detection include 150 pM fluorescein with a 254-nm excitation source, 200 amol of fluorescein in a capillary electrophoresis setup with excitation by two blue light-emitting diodes, 35 nM NH(3) as the isoindole derivative in a flow injection analysis system using a photodiode detector, 50 nM methylene blue and 1 nM Rhodamine 560 using respectively red and green LED arrays and an avalanche photodiode and a PMT in a FIA configuration, 100 parts per trillion by volume gaseous formaldehyde as the Hantzsch reaction product with cyclohexanedione using a diffusion scrubber, 2.7 μM and 17 nM hypochlorite based on its chemiluminescence reaction with luminol with photodiode and PMT detectors, respectively, and 1 ppm SO(4)(2)(-) based on nephelometric detection at 470 nm. The approach described herein leads to particularly simple and inexpensive luminescence detectors with excellent sensitivity.

A collinear light-emitting diode-induced fluorescence detector for capillary electrophoresis

“…The use of light emitting diodes (LED) as excitation source may provide a simple alternative [3][4][5][6]. The combination of extremely high stability, reasonably high intensity, small size, low cost, and very long lifetime makes LED an attractive excitation source for spectroscopic detectors [7,8].…”

“…Bruno et al [3] presented LEDinduced fluorescence detector (LED-FD) in CE using named pigtailing approach, in which the optical components used for in this detector were assembled into a compact unit using refractive-index matching materials to minimize losses and generation of stray light at the various optical interfaces. Dasgupta and coworkers [4,8] described the use of LED-FD combined with liquid-core waveguide technique in CE, achieving in 200 amole fluorescein of mass detection limit. Recently, Hillebrand et al [9] reported a LED-FD in CE using a pulsed mode-operating ultraviolet LED.…”

“…In addition, Wang and Morris [11] have demonstrated a continuous mode-operating UV LED in an analyte velocity modulation device applied for microfluidic devices. In previous reports, the optical scheme of LED-FD is usually based on orthogonal configuration for eliminating the interference of excitation beam [3,4]. Some reports described the use of confocal configuration of LED-FD [11,12], but details were not given.…”

Trends in Atmospheric Trace Gas Measurement Instruments with Membrane-based Gas Diffusion Scrubbers

“…This detector has been used for fluorometry 67,68 and chemiluminescence measurements 69 of H2O2 and hydroxymethyl hydroperoxide, and fluorometry of HCHO. 70,71 LODs of 10 -30 pptv have been obtained for continuous or near real-time measurements.…”

Atmospheric methanol measurement using selective catalytic methanol to formaldehyde conversion

“…Intercomparisons among various formaldehyde detection methods have also been carried out in Gilpin et al (1997) and Cárdenas et al (2000). Although formaldehyde can also be a challenge to analyse, over the last 20 years high quality measurements of formaldehyde have been established using wet-chemical techniques Dasgupta, 1986, 1987;Fan and Dasgupta, 1994;Heikes et al, 1996;Dasgupta et al, 1988Dasgupta et al, , 1998Dasgupta et al, , 1999Li et al, 2001). Such instruments are relatively inexpensive, have a detection limit in the mid-ppt (parts per trillion) range, are commercially available, run essentially continuously, and are highly selective for formaldehyde.…”