Amplitude modulated multiplexed flow analysis

We propose a new concept, amplitude modulated multiplexed flow analysis, for the simultaneous determination of multiple analytes from a single continuous analytical signal. The flow rates (FS1 and FS2) of two sample solutions are independently varied in response to trigonometric voltage signals each at a different anharmonic frequency. With the total flow rate FT held constant, the solutions are merged with a reagent solution that is aspirated to the confluence point at the flow rate of FT − FS1 − FS2. Downstream, the analytical signal due to the mixed reacted solution, Vd, is monitored. Vd will show a complicated profile resulting from the trigonometrically varying flow rates of the sample solutions. The signal contains information on the multiple analytes. The signal can be demodulated to the contribution of each sample solution through fast Fourier transform (FFT). The amplitudes of the separated wave components are related to the concentration of the analytes in the sample solutions. By moving a window for FFT analysis with time, temporal profile of amplitudes can be obtained in real-time. We demonstrate the concept by applying it to the simultaneous determination of food dyes and to that of ferrous ions in two sample solutions.