This detector is designed and constructed to replace the commercial fluorescence detector. As a result the detector is small and provides high sensitivity (Detection Limit = 10 nM for ammonia measurement). The configuration and electronic circuit of the LED photodiode-based fluorescence detector (LPFD) and the components inside LPFD are shown in pictures below. A 1.7 mm bore hole was drilled straight through the center of one face of a 5 cm black plastic cube and a fluorinated ethylene propylene copolymer (FEP) Teflon tube (1.5 mm i.d., 7 cm length, 152 μm light weight wall, type AWG15) inserted through this hole. At each end the tube is fixed into place with a standard ¼-28 threaded male nut and ferrule. On one face perpendicular to the long axis of the tubular flow passage (SP), an InGaN LED (NSHU550B, Nichia USA, λpeak 365 nm, half bandwidth 10 nm) illuminated the FEP tubing through a 5.2 mm aperture. Perpendicular to the LED light source, a photodiode-operational amplifier (OPT301, Texas Instruments) was affixed in place with a blue plastic filter (OF) on its face (type 385-Royal Blue, Edmund Scientific, Gloucester, NJ) for filtering stray LED light. The light sensor OPT301 measured emitted fluorescence through a 2.4 x 6.6 mm rectangular aperture.
(a) The details of the LED-photodiode-based flow-through fluorescence cell and electronic circuit:
LED, light emitting diode; SP, solution pathway; OF, optical filter; OPT301, photodiode-operational amplifier.
(b) Photograph of inside of the developed detector.
(1) Amornthammarong, N.; Zhang, J.-Z.; Ortner, P.B.; Stamates, J.; Shoemaker, M.; Kindel, M.W. Environ. Sci.: Processes Impacts. 2013, 15, 579 - 584.
(2) Amornthammarong, N.; Jakmunee, J.; Li, J.; Dasgupta, P.K. Anal. Chem. 2006, 78, 1890-1896.