Simplified Pressure-Controlled Sample Introduction into Separation Capillary in Laboratory-Made Electrophoretic Apparatus
Abstract
Standard and most frequently used method of introducing sample into the separation capillary in laboratory electrophoretic apparatus is based on elevation of the vessel with the sample solution sufficiently to generate gravity flow of solution into the sampling end of the capillary which is immersed in the sample vessel. The sample vessel is held in certain elevated position for a defined period of time and then returned to the basic position and replaced with the vessel containing separation buffer.
The other modes of hydrodynamic injection require the application of positive pressure to the sample vessel or a negative pressure to the outlet vessel; these methods are common in commercial apparatus. A simplified pressure-controlled method usable in laboratory apparatus is described.
It markedly accelerates sample introduction into a separation capillary. Without moving the capillary, sample is introduced by a pressure applied for a defined time-period into a vessel with the sample solution.
The pressure is generated by a membrane pump. Except for the manual replacement of the vessel with separation electrolyte for the vessel with sample solution, all other sampling steps are controlled by a computer.
The results were compared with those obtained by a standard sampling method utilizing an elevation of the capillary sampling end. Repeatability of the sampling expressed as RSD is for a peak area about one half of that obtained for the standard method.
The basic analytical and separation parameters are quite comparable for both methods under identical sampling parameters, 50 mbar/4 s and 10 cm/20 s. The method was tested on the separation of 0.5 mM K+, Na+ and tyramine mixture.