Flow Modulation-based Flow Analyses - Flow Ratiometry and Amplitude Modulated Multiplexed Flow Analysis -

This paper provides a comprehensive description of the flow modulation-based flow analyses proposed by the author and coworkers. Flow ratiometry merges multiple solutions at various flow ratios. Information of interest is obtained by analyzing the relationship between the flow ratio and the detection signal obtained downstream. In the application to flow titration, an unprecedented high throughput titration of up to 46.9 titrations/min was achieved by combining feedback control and fixed triangular wave control. A novel concept for detecting color transition by the inner product of RGB unit vectors obtained by digital image-based colorimetry was developed. Flow ratiometry was also applied to determine the electrolytic dissociation constant and distribution coefficient. Amplitude modulated multiplexed flow analysis is a flow analysis that introduces frequency analysis. Multiple samples (or sample and reagent) are merged while their flow rates are varied at respective frequencies. The detection signal obtained downstream is analyzed by a fast Fourier transform in real time. The method enabled simultaneous analysis/determination of multiple samples/analytes from a single kind of signal with a simple system. Air segmentation and internal standard methods were introduced to improve sensitivity and robustness. It was shown that saturated signals can be analyzed by controlling the sample flow rate with a triangular wave. Analytical processes, including controlling the system, acquiring/analyzing the data, and displaying the results, were fully automated by using in-house software.