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Admittance detector for high impedance systems: design and applications


Zhang, M and Stamos, BN and Dasgupta, PK, Admittance detector for high impedance systems: design and applications, Analytical Chemistry, 86, (23) pp. 11547-11553. ISSN 0003-2700 (2014) [Refereed Article]

Copyright Statement

© 2014 American Chemical Society

DOI: doi:10.1021/ac503247g


We describe an admittance detector for high impedance systems (small capillary bore and/or low solution specific conductance). Operation in the low frequency range (≤1 kHz, much lower than most relevant publications) provides optimum response to conductance changes in capillaries ≤20 μm in bore. The detector design was based on studies described in a preceding companion paper (Zhang, M.; Stamos, B. N.; Amornthammarong, N.; Dasgupta, P. K. Anal. Chem. 2014, 86, DOI 10.1021/ac503245a.). The highest S/N for detecting 100 μM KCl (5.5 μM peak concentration, ∼0.8 μS/cm) injected into water flowing through a capillary of 7.5 μm inner radius (r) was observed at 500–750 Hz. A low bias current operational amplifier in the transimpedance configuration permitted high gain (1 V/nA) to measure pA–nA level currents in the detection cell. Aside from an oscillator, an offset-capable RMS-DC converter formed the complete detection circuitry. Limits of detection (LODs) of KCl scaled inversely with the capillary cross section and were 2.1 and 0.32 μM injected KCl for r = 1 and 2.5 μm capillaries, respectively. When used as a detector on an r = 8 μm bore poly(methyl methacrylate) capillary in a split effluent stream from a suppressed ion chromatograph, the LOD was 27 nM bromide (Vex 22 V p-p), compared to 14 nM observed with a commercial bipolar pulse macroscale conductivity detector with an actively thermostated cell. We also show applications of the detector in electrophoresis in capillaries with r = 1 and 2.5 μm. Efficient heat dissipation permits high concentrations of the background electrolyte and sensitive detection because of efficient electrostacking.

Item Details

Item Type:Refereed Article
Keywords:admittance detector, capillary electrophoresis, contactless conductivity detection
Research Division:Chemical Sciences
Research Group:Analytical chemistry
Research Field:Separation science
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:104671
Year Published:2014
Web of Science® Times Cited:38
Deposited By:Chemistry
Deposited On:2015-11-18
Last Modified:2017-10-29

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