Eof

In CEC, the EOF is harnessed to propel the mobile phase through the column unlike the pressure-driven flow in LC. EOF results from electrophoretic movement of the diffuse

Separation Mechanisms

Two basic mechanisms influence the migration velocity of analytes:[15,18] a partition between solid and liquid phases as in LC in the case of neutral analytes (characterized by capacity factor k) and electrophoretic migration as in CE for charged analytes (characterized by effective mobility meph,eff). Other separation mechanisms (e.g., ion exchange, size exclusion, chiral recognition, and molecular imprinting) can also participate.1-14-1

Figure 1 can be used to compare some separation characteristics of LC, CE, and the hybrid of both CEC: 1) the expected higher separation efficiency of CEC in comparison with LC is clearly visible in Fig. 1; 2) the higher selectivity of CEC compared with CE—originating from the broad range of partition coefficients, on one hand, and relatively small difference in solutes mobilities, on the other hand—is also obvious from Fig. 1; 3) in CEC, the separation window is wider (— 1<k< 1) than in LC (0< k< i) because of the increased velocity of charged solutes comigrating with EOF; and 4) the combination of two orthogonal separation mechanisms, viz. partition and

Fig. 1 Comparison of separation of drug mix by capillary electrochromatography (CEC), microliquid chromatography (|LC), and CE. Column (CEC and |LC): Spherisorb ODS-I, 3 |m, 250 (335) x 0.1 mm, (CE) uncoated fused silica capillary 250 (335) x 0.075 mm. Eluent: ACN 25 mM phosphate, 0.2% hexylamine, pH 2.5 (80:20), voltage (CEC and CE): 25 kV, pressure (|LC): 200 bar, temperature: 20°C. Peaks: 1=procaine, 2=timolol, 3=ambroxol, 4=metoclopramide, 5=thiourea, 6=nap-roxene, 7=antipyrine. (From Ref. [19].)

Fig. 1 Comparison of separation of drug mix by capillary electrochromatography (CEC), microliquid chromatography (|LC), and CE. Column (CEC and |LC): Spherisorb ODS-I, 3 |m, 250 (335) x 0.1 mm, (CE) uncoated fused silica capillary 250 (335) x 0.075 mm. Eluent: ACN 25 mM phosphate, 0.2% hexylamine, pH 2.5 (80:20), voltage (CEC and CE): 25 kV, pressure (|LC): 200 bar, temperature: 20°C. Peaks: 1=procaine, 2=timolol, 3=ambroxol, 4=metoclopramide, 5=thiourea, 6=nap-roxene, 7=antipyrine. (From Ref. [19].)

migration, gives rise to a much larger potential to manipulate selectivity.

Column Technology

A typical CEC column[1'5'6'10'20] is a fused silica capillary (50-100 mm ID, 200-500 mm long), filled either by particulate or monolithic[21] stationary phase. The small column internal diameter is dictated by the necessity of heat dissipation. Open-tube CEC columns (10-25 mm ID)

were also used, but these suffer from smaller detection sensitivity. The basic problem of particle packed column is frit, which is unavoidable to keep the tiny sorbent particles (1.5-10 mm in diameter) in the original position. The ultimate solution here is the use of silica or organopolymeric monolithic columns.[17]

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

Get My Free Ebook


Post a comment