Applied voltage, MECC

Figure 5.8 Separation of eleven water-soluble vitamins by MECC. Peaks 1, pyridoxamine 2, nicotinamide 3 pyridoxal 4, vitamin B6 5, vitamin B2 6, vitamin B12 7, vitamin B2 phosphate 8, pyridoxamine 5 -phosphate 9, niacin 10, vitamin Bi 11, pyridoxal 5 -phosphate. Conditions buffer, 50 mM SDS in 20 mAf phosphate-borate buffer, pH 9.0 applied voltage, 20 kV detection, UV absorbance at 210 nm. (Reprinted from Ref. 20 with permission.)...

Under the proper conditions, column efficiency in MECC is outstanding. In one separation of purine compounds we obtained over 600,000 plates/m for theophylline. However, the effects of parameters such as column dimensions, applied voltage, and the concentration of the buffer and surfactant on efficiency can be very dramatic. A brief discussion of how these parameters influence efficiency follows. 

Despite the improved mass transfer characteristics of the "plug-like" flow profiles observed in MECC, "intra-column" resistance to mass transfer is significant at higher flow velocities (i.e., at high applied voltages). Although not as dramatic as in our work with hydrostatically-pumped open capillary LC, we have observed improvements in efficiency with the MECC technique when column diameter is reduced. This is illustrated in Figure 6. 

Figure 33-1 5 Typical separation by MECC. (a) Some test compounds 1 = methanol, 2 = resorcinol, 3 = phenol, 4 = p-nitroaniline, 5 = nitrobenzene, 6 = toluene, 7 = 2-naphthol, 8 = Sudan III capillary, 50-p.m inside diameter, 500 mm to the detector applied voltage, ca. 15 kV detection UV absorption at 210 nm. (b) Analysis of a cold medicine 1 = acetaminophen, 2 = caffeine, 3 = sulpyrine, 4 = naproxen, 5 = guaiphenesin, 10 = noscapine, 11 = chloropheniramine and tipepidine applied voltage, 20 kV capillary, as in (a) detection UV absorption at 220 nm. (From S. Terabe, Trends Anal. Client., 1989,8, 129.)...

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