Potentiometric Titrations in a Poly(dimethylsiloxane)-Based Microfluidic Device

Analytical Chemistry

Volumn 76, Issue 8, 2004, Pages 2273-2280

  Ferrigno, Rosaria ^a,b   Lee, Jessamine Ng ^a   Jiang, Xingyu ^a   Whitesides, George M ^a  

^a HARVARD UNIVERSITY   (United States)

^b UNIVERSITÉ LYON 1   (France)

Author keywords

[No Author keywords available]

Indexed keywords

FLUIDIC DEVICES; MICROELECTRODES; MICROPROCESSOR CHIPS; POTENTIOMETRIC SENSORS; REDOX REACTIONS; TITRATION;

MICROCHANNELS; MICROFLUIDIC DEVICES; REDOX POTENTIALS;

SILICONES;

DIMETICONE;

ARTICLE; DEVICE; MICROELECTRODE; OXIDATION REDUCTION POTENTIAL; POTENTIOMETRIC TITRATION; REACTION ANALYSIS;

DIMETHYLPOLYSILOXANES; ELECTRODES; MICROFLUIDICS; PLATINUM; POTENTIOMETRY; SILICONES;

EID: 1942423035     PISSN: 00032700     EISSN: None     Source Type: Journal    
DOI: 10.1021/ac035281i     Document Type: Article

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23. We tried plotting the potential as a function of the ratio of the volume of Fe(II) to Cr(IV), but this plot does not give a sigmoidal curve. A sigmoidal curve was not obtained, due to the superimposition of two phenomena that cause the depletion of the sample in this titration: (i) dilution of the titrant and (ii) reaction between the titrant and the sample at each junction (i.e., during each dilution). The case presented in this paper is more complex than that of a classical batch titration experiment. In the case of a classical batch titration experiment, the potential can be plotted against the ratio of the volume of Fe(II) to Cr(IV) to give a sigmoidal curve, since this ratio is directly proportional to the volume of titrant, and the depletion of the sample in the beaker depends only on the reaction with the titrant. Our case, however, is more complicated, because the concentration of titrant is different at each junction (due to dilution and reaction of the titrant). The volume of titrant (or a ratio using this volume), thus cannot be used to follow the progress of the reaction. We therefore plotted the potential against φ, a function that gives a sigmoidal relationship between the points (here, the potential vs channel number) and "adjusts" the points in order to fit them in the form of a curve. The end point can then be determined graphically by finding the inflexion point of the sigmoid, where φ = 0.
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