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Capillary scale admittance detection


Zhang, M and Stamos, BN and Amornthammarong, N and Dasgupta, PK, Capillary scale admittance detection, Analytical Chemistry, 86, (23) pp. 11538-11546. ISSN 0003-2700 (2014) [Refereed Article]

Copyright Statement

2014 American Chemical Society

DOI: doi:10.1021/ac503245a


Techniques that have been variously termed oscillometric detection or (capacitively coupled) contactless conductivity detection (C4D) are known actually to respond to the admittance. It is not often appreciated that the frequency range (f) over which such systems respond (quasi)linearly with the cell conductance decreases acutely with increasing cell resistance. Guidance on optimum operating conditions for high cell resistance, such as for very small capillaries/channels and/or solutions of low specific conductance (σ), is scant. It is specially necessary in this case to take the capacitance of the solution into account. At high frequencies and low σ values, much of the current passes through the solution behaving as a capacitor and the capacitance is not very dependent on the exact solution specific conductance, resulting in poor, zero, or even negative response. We investigated, both theoretically and experimentally, capillaries with inner radii of 5160 μm and σ ≈ 11400 μS/cm, resulting in cell resistances of 51 GΩ to 176 kΩ. A 400-element discrete model was used to simulate the behavior. As model inputs, both the wall capacitance and the stray capacitance were measured. The solution and leakage capacitances were estimated from extant models. The model output was compared to the measured response of the detection system over broad ranges of f and σ. Other parameters studied include capillary material and wall thickness, electrode spacing and length, Faraday shield thickness, excitation wave forms, and amplitude. The simulations show good qualitative agreement with experimental results and correctly predict the negative response behavior observed under certain conditions. We provide optimum frequencies for different operating conditions.

Item Details

Item Type:Refereed Article
Keywords:admittance detection, contactless conductivity detection, capillary
Research Division:Chemical Sciences
Research Group:Analytical chemistry
Research Field:Instrumental methods (excl. immunological and bioassay methods)
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the chemical sciences
UTAS Author:Zhang, M (Dr Min Zhang)
ID Code:104669
Year Published:2014
Web of Science® Times Cited:37
Deposited By:Chemistry
Deposited On:2015-11-18
Last Modified:2017-10-29

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