Electric Resistance Variation of Packing Materials in Capillary Electrochromatography by Using Fluorinated-Bonded Silica and Octadecylsilane Phases

Abstract

The alternation of the nature of the stationary phase due to the application of the electric field was observed in electrochromatography. [1][2][3][4][5][6][7] In electrochromatography, the retention time and peak height of a solute depended on the period from the beginning of the voltage application.2,3 The capacity factor in electrochromatography was found to depend to some degree on the value of the applied voltage. [4][5][6] The application of the electric field on the ion exchange packing supports in electrochromatography induced the release of the sample solutes from the stationary phase 5 and the variation of distribution coefficient. 6 During the application of electric voltage, the surface charges of the fluorinated-bonded silica phase altered. 7 These phenomena indicated the alternation of the nature of the stationary phase due to the application of electro voltage which was also evidenced in the dependence of the electric resistance of the column on applied voltage as was discovered in the cation exchange resin support. 4 In this article, the relationship between the electric resistance variation and the surface charges of some packing materials in electrochromatography was studied. This provides additional evidence of the alternation of the nature of the stationary phase caused by the electro voltage application. Experimental Apparatus, column and materialsThe same instrument for pressurized flow driven electrochromatography as described in the former reports 3,4,7,8 was used with different types of columns. A high-voltage power supply (dc ± 30 kV, type HCZE-30P, Matsusada Precision, Kusano, Shiga) was used. The expression "applied + X kV" means that +X kV is applied to the column outlet and the split injector is grounded. Fluorinated-bonded silica (type Fluofix 120E, 80421, particle diameter 5 µm, pore size 120 Å, surface area 300 m 2 /g, Neos Co., Ltd., Kobe) in the capillary column (150 µm i.d., 18.6 cm packed part, 28.6 cm total capillary length)

Alternating Voltage Capillary Electrochromatography

“…When the applied V peak increased, all variation ratios of the three sample solutes decreased; i.e., the higher voltage accelerated the reduction of the capacity factor. In the case of the application of a direct voltage, the variation of capacity factors was also determined by the magnitude of the applied voltage. − The effect of V peak on the variation ratio was specified by the species of sample solute. Salicylic acid is the sample solute that is most susceptible to an applied electric field.…”

“…Thus, we have found interesting phenomena induced by the applied electric field. Those phenomena are variations of the capacity factor, − , conductivity of a column, ,, and electroosmotic mobility . The phenomena suggest that the applied electric field affects the properties of a stationary phase or an interface between stationary and mobile phases.…”