Micro titration device and its application to rice freshness measurement

A plug-based on-chip titration device, constructed with a glass substrate and a poly (dimethylsiloxane) (PDMS) substrate, was used for acid-base titration. The device features a volume-regulation unit to produce plugs of a uniform volume used for titration. Although the volume of plugs formed by only injecting a solution and air simultaneously from a T-junction distributed in a wide range, the plug volume became markedly uniform using the volume-regulation unit. Acid-base titration could be conducted using this device. Furthermore, freshness of rice was evaluated by titrating fatty acid in a rice grain with a KOH solution using phenolphthalein as a pH-indicator. Rice samples harvested in different years and from different areas as well as of different species were analyzed using this device. Difference was observed clearly in the titration curves. New rice showed a color change at an early stage, whereas the color change delayed with aged rice.