Abstract :
A compact, reliable and low cost flow injection chemiluminescence system is described. The flow system consists of a set of solenoid micropumps that can dispense reproductive microvolumes of solutions. The luminometer was based on a coiled cell constructed from polyethylene tubing that was sandwiched between two large area photodiodes. The whole equipment costs about US$ 750 and weights ca. 3 kg. Equipment performance was evaluated by measuring low concentrations of hydrogen peroxide by oxidation of luminol and for the determination of ammonium, based on its inhibition of the luminescence provided by the reaction of luminol and sodium hypochlorite. Linear responses were achieved within 1.080 (mu)mol L^-1 H2O2 and 0.6-60 (mu)mol L^-1 NH4+ with detection limits estimated as 400 nmol L^-1 H2O2 and 60 nmol L^-1 NH4+ at the 99.7% confidence level. Coefficients of variation were 1.0 and 1.8%, estimated for 20 (mu)mol L^-1 H2O2 and 15 (mu)mol L^-1 NH4+ (n = 20), respectively. Reagent consumption of 55 (mu)g luminol, effluent volume of 950 (mu)L per determination and sampling rate of 120 samples per hour were also achieved.
