Development of high-performance liquid chromatography and nonaqueous capillary electrophoresis methods for the separation of calixarene derivatives Original Research Article

In the present work, the separations of calixarene derivatives have been investigated using both high-performance liquid chromatography (HPLC) and nonaqueous capillary electrophoresis (NACE) techniques. HPLC-1 method with LC-318 (pore size = 300 Å) column and MeCN mobile phase was optimized for the separation of calixarenes. At the flow-rate of 1 ml/min p-nitrocalix[6]arene, calix[4]arene and calix[6]arene could be well baseline and symmetrically separated within 5 min. For the separation of p-tert-butylcalix[n]arenes (n = 4, 6, 8), HPLC-2 and NACE methods have been optimized. The optimal conditions in HPLC-2 method included NH2 column and MeCN mobile phase, and p-tert-butylcalix[n]arenes (n = 4, 6, 8) were baseline separated within 10 min at 0.8 min/min. The optimal conditions for NACE method employed MeCN–H2O (8:2, v/v) as the nonaqueous medium and 120 mM Tris/HCl (pH 9.0) as the buffer, and p-tert-butylcalix[n]arenes (n = 4, 6, 8) were successfully baseline resolved within 16 min. With the detection at 280 nm, the calibration lines were linear in the ranges of 1–200 μg/ml for calixarene derivatives by HPLC-1 and HPLC-2 methods, and of 2.5–200 μg/ml for p-tert-butylcalix[n]arenes (n = 4, 6, 8) by NACE method, respectively. The detection limits (S/N = 3) and recoveries ranged from 0.5 to 1.4 μg/ml and from 98.1 to 102.4% by both HPLC-1 and HPLC-2 methods, and from 1.3 to 2.0 μg/ml and from 97.9 to 105.1% by NACE method, respectively. The intra-day reproducibility of the methods was determined with satisfactory results. The proposed HPLC and NACE methods were accurate and reproducible, and could be utilized to separate and determine calixarene derivatives.