Hm. Sorouraddin et al., Integrated FIA for the determination of ascorbic acid and dehydroascorbic acid in a microfabricated glass-channel by thermal-lens microscopy, ANAL SCI, 16(10), 2000, pp. 1033-1037
An on-chip chemical micro-determination device, integrating the FIA system,
was applied to L-ascorbic acid (AA) and dehydroascorbic acid (DHAA) determ
ination. Microchannels having a 250x100 mum cross-section were fabricated i
n 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-phenantroli
ne-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 re
ducing agent and the total AA was determined. The DHAA quantity was calcula
ted by subtraction. This method allows for the determination of AA with a l
inear range of up to 40 muM. The RSD for 25 muM AA (n=5) is 1%, and the lim
it of detection (LOD) is 0.1 muM. 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.