978 Electrophoresis 2014, 35, 978–985 Mei-Yu Su Yen-Yi Chen Jian-Ying Yang You-Sian Lin Yang-Wei Lin Mine-Yine Liu Department of Chemistry, National Changhua University of Education, Changhua, Taiwan Received August 1, 2013 Revised September 11, 2013 Accepted September 27, 2013 Research Article Separation of total lipids on human lipoproteins using surfactant-coated multiwalled carbon nanotubes as pseudostationary phase in capillary electrophoresis Surfactant-coated multiwalled carbon nanotubes (MWNTs) were used as pseudostationary phase (PSP) in CE to investigate the total lipids of high-density lipoproteins and low-density lipoproteins. To optimize the CE conditions, several experimental factors including carbon nanotube concentration, bile salt concentration, sodium phosphate (PB) concentration, or- ganic modifier concentration and buffer pH value have been examined. In addition, the CE capillary temperature and applied voltage have also been examined. The optimal sepa- ration buffer selected was a mixture of 3.2 mg/L MWNT, 50 mM bile salt, 10 mM PB, 20% 1-propanol, pH 9.5. The optimal capillary temperature and applied voltage selected were 50°C and 20 kV, respectively. Phosphatidyl choline (PC) has been used as a model analyte and investigated by the optimal CE method. The linear range for PC was 0.1–3 mg/mL with a correlation coefficient of 0.9934, and the concentration LOD was 0.055 mg/mL. The optimal CE method has been used to characterize the total lipids of high-density lipoprotein and low-density lipoprotein. At absorbance 200 nm, one major peak and two or three minor peaks showed for the total lipids of lipoproteins within 13 minutes. Res- olutions of the total lipids were enhanced using surfactant-coated MWNTs as PSPs in the CE separation buffer. However, resolutions of the total lipids were not enhanced using surfactant-coated single-walled carbon nanotubes as PSPs in the CE separation buffer. Keywords: Carbon nanotubes / CE / Lipids / Lipoproteins / Pseudostationary phase DOI 10.1002/elps.201300360 1 Introduction Lipoproteins are heterogeneous particles that have various sizes, densities, charges, and chemical compositions. Low- density lipoproteins (LDLs), especially oxidized LDLs, are known to be crucial in the development of cardiovascular diseases. In human blood, high levels of LDL are positively associated with atherosclerosis. During the pathogenic pro- cess, oxidized LDLs accumulate within the subendothelial Correspondence: Dr. Mine-Yine Liu, Department of Chemistry, National Changhua University of Education, Changhua, Taiwan 50058 E-mail: myliu@cc.ncue.edu.tw Fax: +886-4-7211190 Abbreviations: CNT, carbon nanotube; HDL, high-density lipoprotein; LDL, low-density lipoprotein; MWNT, multi- walled carbon nanotube; NP, nanoparticle; PB, sodium phosphate; PC, phosphatidyl choline; PSP, pseudostationary phase; SWNT, single-walled carbon nanotube; VLDL, Very low-density lipoprotein space, and are engulfed by macrophages. Then, LDL choles- terols accumulate within macrophages and finally foam cells and atherosclerotic plaques form. [1–6]. However, it is not understood yet how the structural modifications of the total lipids of LDLs relate to cardiovascular disease. High-density lipoproteins (HDLs) are known to be car- dioprotective because they are anti-inflammatory, antithrom- botic and capable of promoting cholesterol efflux. [7–10]. Recently, it has been found that HDLs might become pro-oxidant during the process of chronic disease such as atherosclerosis. Several studies have suggested that the pro- inflammatory properties of HDL might be resulted from the structural modification of HDLs. However, little is known about the relationship between structural modifications of the total lipids of HDL and their pro-inflammatory properties [11–13]. Previously, LC-MS analysis has been used to study phos- pholipids of human HDLs [14, 15]. LC-MS analysis has also been used to study phospholipids and other lipids of human LDLs [16–19]. Compared to the commonly used LC-MS anal- ysis, CE has the advantages of simplicity, high speed, and C  2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.electrophoresis-journal.com