Rapid fluorometric determination of ammonium in exhaled breath condensate based on digital image of a windowless falling drop cell via a low-cost digital microscope

Abstract

Measurement of ammonia in exhaled breath is of interest in medical and health sciences. The fluorometric determination of NH3 in exhaled breath condensate (EBC) was developed based on a digital image of a windowless falling drop (WFD) cell at the end of tube via a sensitive and selective reaction of NH3-OPA-sulfite in flow injection analysis system (FIA). A low-cost USB microscope as a facile instrumentation without expensive optical parts, an amplifier circuit, and a data acquisition unit, was used as a fluorescence light detector for the WFD cell via instant reporting temporal profile of digital value. A linear calibration graph of NH4+ in the range of 0.5–10 µmol L−1 can be obtained with a limit of detection of 0.5 µmol L−1 NH4+, and repeatability of 5.5% RSD (n = 11). The fluorescence (FL) signal obtained from the low-cost USB microscope was not different from that using the photodiode detector via a cross-shape flow cell. The proposed device was successfully applied for NH4+ determination in EBC and air absorbing solution samples with the recovery of 98–110%. The approach for instant reporting of a temporal profile of digital image value from a camera shows a potential to be applied for rapid chemical analysis in other microfluidics systems.