Determination of ammonium on an integrated microchip with LED-induced fluorescence detection.
A simply fabricated microfluidic device integrated with a fluorescence detection system has been developed for on-line determination of ammonium in aqueous samples. A 365-nm light-emitting diode (LED) as an excitation source and a minor band pass filter were mounted into a polydimethylsiloxane (PDMS)-based microchip for the purpose of miniaturization of the entire analytical system. The ammonium sample reacted with o-phthaldialdehyde (OPA) on-chip with sodium sulfite as reducing reagent to produce a fluorescent isoindole derivative, which can emit fluorescence signal at about 425 nm when excited at 365 nm. Effects of pH, flow rate of solutions, concentrations of OPA-reagent, phosphate and sulfite salt were investigated. The calibration curve of ammonium in the range of 0.018-1.8 microg/mL showed a good linear relationship with R2 = 0.9985, and the detection limit was (S/N = 3) 3.6 x 10(-4) microg/mL. The relative standard deviation was 2.8% (n = 11) by calculating at 0.18 microg/mL ammonium for repeated detection. The system was applied to determine the ammonium concentration in rain and river waters, even extent to other analytes fluorescence detection by the presented device.
Department of Chemistry, Tsinghua University, Beijing 100084, China. henanxue@126.com
Shuhua
S
Xue
Katsumi
K
Uchiyama
Hai-Fang
HF
Li
D004784:Environmental Monitoring / Q000295:instrumentation / Q000379:methods; D005453:Fluorescence; D008027:Light; D046210:Microfluidic Analytical Techniques / Q000379:methods*; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry*
D000644:Quaternary Ammonium Compounds; D014874:Water Pollutants, Chemical