title: Monitoring gradient profile on-line in micro- and nano-high performance liquid chromatography using conductivity detection.
abstract: In micro- or nano-flow high performance liquid chromatography (HPLC), flow-splitters and gradient elutions are commonly used for reverse phase HPLC separations. When a flow splitter was used at a high split-ratio (e.g., 1000:1 or higher), the actual gradient may deviate away from the programmed gradient. Sometimes, mobile phase concentrations can deviate by as much as 5%. In this work, we noticed that the conductivity (σ) of a gradient decreased with the increasing organic-solvent fraction (φ). Based on the relationship between σ and φ, a method was developed for monitoring gradient profile on-line to record any deviations in these HPLC systems. The conductivity could be measured by a traditional conductivity detector or a capacitively coupled contactless conductivity detector (C(4)D). The method was applied for assessing the performance of an electroosmotic pump (EOP) based nano-HPLC. We also observed that σ value of the gradient changed with system pressure; a=0.0175ΔP (R(2)=0.964), where a is the percentage of the conductivity increase and ΔP is the system pressure in bar. This effect was also investigated.
authors.affiliation: Department of Chemistry and Biochemistry, University of Oklahoma, 101 Stephenson Parkway, Norman, OK 73019, United States; Australian Centre for Research on Separation Science, School of Physical Sciences - Chemistry, University of Tasmania, Private Bag 75, Hobart, Tasmania, 7001, Australia.
authors.forename: Min
authors.initials: M
authors.lastname: Zhang
authors.affiliation: Department of Chemistry and Biochemistry, University of Oklahoma, 101 Stephenson Parkway, Norman, OK 73019, United States.
authors.forename: Apeng
authors.initials: A
authors.lastname: Chen
authors.affiliation: Department of Chemistry and Biochemistry, University of Oklahoma, 101 Stephenson Parkway, Norman, OK 73019, United States.
authors.forename: Joann J
authors.initials: JJ
authors.lastname: Lu
authors.affiliation: Laboratory of Analytical Biochemistry and Bio-separation, State Key Laboratory of Microbial Metabolism, School of Life Science and Biotechnology, Shanghai Jiao Tong University, Shanghai, 200240, People's Republic of China. Electronic address: cxcao@sjtu.edu.cn.
authors.forename: Chengxi
authors.initials: C
authors.lastname: Cao
authors.affiliation: Department of Chemistry and Biochemistry, University of Oklahoma, 101 Stephenson Parkway, Norman, OK 73019, United States. Electronic address: Shaorong.liu@ou.edu.
authors.forename: Shaorong
authors.initials: S
authors.lastname: Liu
mesh_terms: D002623:Chemistry Techniques, Analytical / Q000295:instrumentation*; D002851:Chromatography, High Pressure Liquid / Q000592:standards; D004553:Electric Conductivity; D053841:Electroosmosis; D011312:Pressure
keywords: Capacitively coupled contactless conductivity detector; Electroosmotic pump; Gradient profile monitoring; Nano-flow high performance liquid chromatography