An on-chip chemical micro-determination device, integrating the FIA system, was applied to L-ascorbic acid (AA) and dehydroascorbic acid (DHAA) determination. Microchannels having a 250×100 µm cross-section were fabricated in a quarts glass chip as a component in an integrated FIA system. They were put to use for flow, mixing, reaction, and detection. The reaction system was a coupled redox-complexation reaction between AA and a 1,10-phenantroline-Fe(III) mixture. Sample solutions were introduced into micro-channels by micro-syringes, the flow rate was controlled by a micro-syringe pump, and the reagents, were mixed by molecular diffusion. A photothermal microscope was used for the ultra-sensitive detection of the non-fluorescent reaction product (ferroin). For DHAA determination, dithiothreithol was used as a reducing agent and the total AA was determined. The DHAA quantity was calculated by subtraction. This method allows for the determination of AA with a linear range of up to 40 µM. The RSD for 25 µM AA (n=5) is 1%, and the limit of detection (LOD) is 0.1 µM. The procedure was successfully applied to determining the AA and DHAA content of urine and AA in vitamin C tablets. The results agree well with those obtained by reference methods.

A new method for determination for catecholamines (CA) utilizing microchip technology and a thermal lens microscope has been developed. Microchannels with a 250 microm x 10 microm cross section were used for mixing, reaction, and detection. Epinephrine (EP), nor-epinephrine (NE), dopamine (DA), and L-dopa (LD) were determined by using coloring oxidization to aminochromes by sodium metaperiodate. A thermal lens microscope (TLM) was used for detection of the product. The sensitivity of the system was comparable for the four CA and required only 15 s for mixing of sample and reagent. The calibration lines indicated excellent linearity for concentrations of 5-20 microg mL(-1). The relative standard deviations for 10 microg mL(-1) solution were 1.08, 2.18, 2.2, and 2.5% for EP, NE, DA, and LD, respectively. CA in pharmaceutical injections were also determined by use of the system and the results correlated very well with nominal values. Results obtained by use of the integrated system suggested there was a sufficient possibility to realize high-throughput medical diagnosis systems.