Capillary inner diameter

McKillop and associates have examined the electrophoretic separation of alkylpyridines by CZE. Separations were carried out using either 50-pm or 75-pm inner diameter capillaries, with a total length of 57 cm and a length of 50 cm from the point of injection to the detector. The run buffer was a pH 2.5 lithium phosphate buffer. Separations were achieved using an applied voltage of 15 kV. The electroosmotic flow velocity, as measured using a neutral marker, was found to be 6.398 X 10 cm s k The diffusion coefficient,... 

Our initial experiments required about 8 h to complete the two-dimensional separation. This long period results in drift due to temperature changes and buffer evaporation. We have modified the instrument to generate faster separations (Kraly et al., 2006). Shorter and narrower inner-diameter capillaries are now employed, which allow operation at 1000 V/cm, and dramatically improves the separation time. We employ a 10 s second-dimension separation period, and the separation is now complete in 40 min. 

FIGURE 14.3 Fast analysis of control drugs and metabolites using a 15 cm x 300 fim inner diameter capillary column packed with 3 /tin C18 particles (Micro-Tech Scientific MC-15-C18SS-320-EU) operated at 10 /tL/min gradient flow rate. UV at 278 nm. (Source Drug Enforcement Administration, Southwest Laboratory, Vista, California and S. DiPari.)... 

The conductivity of the buffer solution is, however, also of great relevance in this context (Eq. 10) and capillaries of very small diameter with very efficient heat dissipation are commercially available. Using well designed buffer solutions and conventional 50 pm capillaries, fast protein separations at 2000 V/cm have been described by Hjerten et al. [47]. Using a laser photolysis based gating technique, the group of Jorgenson has reported extremely fast CE separations on a subsecond timescale at up to 2500 V/cm in a 6 pm and at 3300 V/cm in a 10 pm inner diameter capillary respectively [48,49]. 

Many of the detectors used in HPLC have been adapted for use in CE. This has been a major challenge, as the highly efficient separations afforded by CZE are a direct result of employing extremely narrow separation columns. Narrow inner diameter capillaries are required to provide effective dissipation of the heat generated by the passage of electrical... 

K. Mayrhofer, A. J. Zemann, E. Schnell, and G. K. Bonn, Capillary electrophoresis and contactless conductivity detection of ions in narrow inner diameter capillaries. Anal. Chem., 71, 3828, 1999. 

Fig. 13 Fluorescence images of 50 and 10 glm inner diameter capillaries patterned with alternating segments of poly(bis-SorbPC) and 1 50 (mol/mol) Rhodamine-capped DPPE DOPC. Reprinted with permission from [96]. Copyright 2007, American Chemical Society...

Only a few microliters of sample are required for CE because usually only 1-50 nanoliters of sample are injected into a capillary. For example, a 50-pm inner diameter capillary 50 cm long has a volume of only ca. 1 pL [9]. Samples are injected... 

Woods, L.A., Gandhi, P.U., and Ewing, A.G, Electrically assisted sampling across membranes with electrophoresis in nanometer inner diameter capillaries. Anal. Chem., 77, 1819, 2005. 

Woods, L. A. and Ewing, A. G, Etched electrochemical detection for electrophoresis in nanometer inner diameter capillaries, Chemphyschem, 4, 207-211, 2003. 

In addition, a scanning microvoitammelric detector for open tubular liquid chromatography has been described [61 ]. This detector consists of a 9-pm (outer diameter) carbon fiber as electrode, inserted into the end of a 15-pm (inner diameter) capillary column. The potential can be scanned at rates up to 1 V/s over a range of 0.0 to -hl.5 V. A... 

A limitation with operation of ESTMS at high flow rates is the requirement that the spray capillary be placed far back from the inlet aperture, which means that only a fraction of the spray is transferred into the mass spectrometer, and the detection limit of the technique suffers. This limitation can be overcome with the use of microspray or nanospray, provided that smaller inner-diameter capillaries are employed. The smaller inner-diameter capillaries and lower flow rates employed with nanospray and microspray result in the production of smaller droplets, which allows the capillary to be placed closer to the inlet aperture than is possible with high-flow operation. Consequently, a larger fraction of the analyte may enter the mass spectrometer, and the mass detection limit may improve. Another advantage of low-flow electrospray is that it often eliminates the need for nebulizing gas. 

Fig. 9.3 Supercritical fluid chromatography of a nonionic fluorinated surfactant RfCH2CH20(CH2CH20) H. A 50-/xm-inner diameter capillary column, 10 m long, coated with a 0.25- im dimethylpolysiloxane film. (Courtesy of J. J. Kozlowski, Du Pont.)...

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