Air segmented amplitude modulated multiplexed flow analysis (air segmented AMMFA) has been applied to the simultaneous determination of ammonium ions in water samples by an Indophenol Blue spectrophotometry. The flow rates of sample solutions to be merged are periodically varied at different frequencies. The merged solution, comprised of the sample solutions, coloring reagent solutions and water (diluent), is segmented by air bubbles so as to prevent the axial dispersion and thus to enhance the sensitivity. Both liquid and air segments are introduced to the flow cell of a UV/Vis detector and analytical signals at 660 nm are obtained. The signals corresponding to the air phase are removed by an in-house software. Thus deaerated signals are smoothed by a moving average computation and then analyzed by fast Fourier transform. The concentration of ammonium ion in each sample is determined from the amplitude of the corresponding wave component. Through the introductions of the air segmentation and the software-based phase recognition approaches, the sensitivity is increased maximally by a factor of 5.8 and lower detection limit (〈 0.11 mg dm-3 as N) is obtained compared with the previous non-segmented AMMFA. The proposed method has successfully been applied to the simultaneous determination of ammonium ions in real water samples.
A simple lab-on-chip with reflective optical fiber system was developed for determination of sweetness in grape juice samples. The detection principle is based on the measurement of light scattering due to Schlieren effect that occurs when a sample solution containing sugar merges with another liquid (DI water) of different refractive indices. The degree of Schlieren effect and thus, the intensity of scattered light, relates to the concentration of sugar in the sample. The angle of the LOC at 65 with respect to the horizontal plane was found to be suitable to provide a well-defined response peak shape for easy peak area integration. The system was evaluated at detection wavelengths 700, 750, and 800 nm. The linear range of the sugar contents of 7-20 degree Brix (°Bx), and RSD of less than 5% (n=5), were achieved for the three detection wavelengths. The results obtained from the red and white grape juice samples agree well with the reading from the refractometer.
A simultaneous injection effective mixing flow analysis (SIEMA) system was proposed for the spectrophotometric determination of palladium. The determination of palladium was based on its complexation reaction with 2-(5-bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]aniline (5-Br-PSAA) to form a blue complex, which has an absorption maximum at 612 nm. The analytical performances of the proposed SIEMA method were superior to a conventional FIA method using 5-Br-PSAA in several parameters, such as reagent consumption, waste volume and analysis time. The SIEMA method was applied to the determination of palladium in dental alloy and hydrogenation catalyst.