Electrochemical Separation and Detection of Chemical Species in Flow Cell: Examination of a Microfluidic Device
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Park, Sean
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Abstract
The development of microscale devices or “Lab-on-a-Chip” has intrigued widespread interest due to its possible analytical applications in the field of medical, environmental, and material science. For example, microscale flow cells exhibit great surface-to-volume ratio and therefore provide a high sensitivity even from a weak surface interaction. Furthermore, different configurations of flow cells deliver their specific electrochemical properties used for analyzing the electroactive species. The detection of redox species is commonly practiced and comprehended however, the separation by electrochemical field is not well understood. In order to better understand the separation phenomenon with the microfluidic channel, a simple wall jet flow cell has been tested. Then, the results obtained from these experiments were used to design experiments where separation and detection can be done on the same platform. The electrochemical potential modulated microchannel (EPMM) is the device capable of separating and detecting electroactive species on the same platform. Both EPMM and wall jet flow cell were used in this research to determine the area of the electrodes, diffusion properties, time constant, and other electrochemical analysis with K3Fe(CN)6 and metal ions. Various analytical parameters such as scan rate, flow rate, and concentrations also helped on characterizing the system. As a result, 2.5mM K3Fe(CN)6 flowing at 4μL/min to the system and scanned at different rates determined the area of an electrode and the diffusion coefficient to be (1.00±0.05) x 10-3cm2 and (8.05±0.3) x 10-6cm2/s, respectively. Several plots were constructed with the observed electrochemical parameters and confirmed the system is quasireversible. The plots also determined the detection limits as 0.1mM for concentration and 0.14nA for current. Furthermore, the electron transfer rate constant was found to be (5.52±0.04) x 10-3cm/s. Besides the basic voltammetric properties of the cell and the redox couple, the detection of metal ions was attempted at a ppb level using the EPMM device in addition with the AC modulation voltage and frequency. In effect of electrolysis on detecting the metal ions with AC modulation of 1.0V and 1.0MHz, there were at least seven distinctive peaks correspondent to the metal ions with respect to their retention order. The detection limit of 0.20 - 1.15ppb and the sensitivity level of 50 - 250nA/ppb showed possibilities of enhancement.
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Separation, Detection, Microfluidics, Electrochemistry