Microbore packed columns

SFC-APCI-MS using methanol-water-modified carbon dioxide as the mobile phase has been applied to the analysis of PACs. A direct fluid introduction interface with flow splitting removed two thirds of the SEC effluent transferred to the APCI-MS system. PACs were separated on a Cjg packed column at 45°C and LCDs were similar to those obtained with HPLC-UV. SFC-APCI-MS-MS using microbore packed columns applied to the analysis of PACs in coal tar was able to provide structural information for isomer differentiation. LODs in the low ng range were obtained by SIM. 

Liu, Y. Yang, F.Y. Unified high-pressure gas and supercritical fluid chromatography with microbore packed columns. Anal. Chem. 1991,63,926. 

Figure 12. Schematic drawing of the connection between the microbore column and the capillary tubing. 1 = Modified Swagelock union (1/16 in.) 2 = microbore-packed column (1/16 in. O.D., 1 mm I.D.) 3 = Vespel ferrule 4 = 0.5- m porosity filter 5 = PTFE tubing (1/16 in. O.D., 0.2 mm I.D., length 5 mm) 6 = 1/16 in. Vespel ferrule 7 = capillary tid>ing (0.3 mm O.D., 50 I.D.).

Liu, Y., F. Yang, C. Pohl, Microbore packed column SFC using a polymer stationary phase, J. Microcol. Sep., 1990, 2, 245-254. 

The packed GC column has a value for (og) of about 55 pi, whereas the high efficiency microbore LC column only 0.23 pi. It is clear that problems of extracolumn dispersion with packed GC columns are not very severe. However, shorter GC capillary columns with small diameters will have a very poor tolerance to extracolumn dispersion. In the same way, short microbore LC columns packed with small... 

Jedrzejewski and Taylor [408] have evaluated microbore pSFC-PB-MS. Microbore separations can take full advantage of the simple DFI design, and are still being pursued. Packed-column SFC-MS was recently reviewed [13]. The two techniques, cSFC and pSFC, are complementary compounds in complex mixtures may be more easily identified with cSFC-MS, while pSFC-MS may be more suitable for target component analysis. 

Utilizing the difference in selectivity between a monolithic silica-C18 column (2nd-D) and another particle-packed column of C18 phase (lst-D), 2D HPLC separation was shown mainly for basic compounds and other species (Venkatramani and Zelechonok, 2003). The authors also reported other examples of reversed-phase 2D HPLC, using amino- and cyano-derivatized particle-packed columns for 2nd-D separation. The combination of normal-phase separation for the 1 st-D and reversed-phase separation on monolithic Ci g column for the 2nd-D was reported (Dugo et al., 2004). The use of a microbore column and weak mobile phase for the lst-D and a monolithic column for the 2nd-D was essential for successful operation. Improvement in the 2D separation of complex mixtures of Chinese medicines was also reported (Hu et al., 2005). Following are practical examples of comprehensive 2D HPLC using monolithic silica columns that have been reported. 

J.D. Henion, A comparison of direct liquid introduction LC/MS techniques employing microbore and conventional packed columns, J. Chromatogr. Sci., 18 (1980) 101-115. 

Figure 10.3. Examples of chromatograms. (a) The separation of 20 essential amino acids (in derivatized form) by RPLC using 1 mm inside diameter by 150 mm long microbore column packed with 4 ft m silica support (with C18 CBP) particles and a water/ acetonitrile mobile phase gradient. (6) The fractionation of gasoline using SFC with C02 mobile phase (temperature and pressure programmed) in 0.25 mm x 50 cm packed column with 5 fim polymeric support particles. (Courtesy of Frank J. Yang.)...

Finally, several attempts have been made to develop an absolute molar mass detector based on osmotic pressure measurements. Commercially available membrane osmometers are designed for static measurements, and the cell design with a flat membrane is not suited for continuous flow operation. Different from the conventional design, Yau developed a detector which measures the flow resistance of a column caused by osmotic swelling and deswelling of soft gel particles used for the packing (see Fig. 12) [65,78]. With a microbore gel column, a... 

In the same way, short microbore LC columns packed with small particles will make very stringent demands on dispersion control in LC detecting systems. 

Column-liquid chromatography (CLC) can be conveniently divided into those systems which use packed columns and those which use open tubes (Figure 3.1). Capillary tubes (<4 < 350 pm) are used in open-tubular chromatography and the stationary phase is coated on the internal surface. Packed-column systems can be sub-divided arbitrarily into capillary columns, microbore columns, analytical columns and preparative columns according to the internal diameter of the column (Figure 3.1). 

Among the works of supercritical fluid separations of PCBs, UV has been the most popular detector. A Microbore Cig column was used to separate individual PCB congeners in Aroclor mixtures. Density and temperature programming was also utilized for separation of PCBs. Both packed (with phenyl and Cig) and capillary (Sphery-5 cyanopropyl) columns were used in this work. Carbon dioxide, nitrous oxide, and sulfur hexafluoride were tested as mobile phases for the separation of PCBs. 

For analytical LC, standard packed columns (4-8 mm I.D.), capillary packed colunms (50-100 pm I.D.), and microbore packed colunms (0.5-1.5 mm I.D.) are used widely. Colunm sizes depend on the application, e.g., analytical, preparative, or commercial separations. Special configurations also exist, including membrane chromatography modules (stacks and hollow fibers) that offer lower pressure drops and easier scale-up than packed beds. 

The flame-based detector was reported to accept in excess of 20 ui/mln of 10-25Z aqueous methanol without extinction of the flame Optimum response was obtained at flow rates below 5 iii/min. Compatible solvent systems were aqueous methanol (up to 50%), acetone and ethanol (up to 40%) The minimum detectable quantity (at 5 times noise) measured for the FPD was 2 pg P. The dual-flame TSD can also be directly Interfaced with mlcrocaplllary packed columns The TSD was reported to be compatible with 75 to 100% aqueous methanol The utilization of microbore column LC-TSD for the analyls of nitrogen, phosphorous, and halogen containing compounds is particularly Important in studies of biomolecules, and drugs and their metabolites in physiological fluids ... 

Laser excitation for fluorescence detection has received much research interest, but as of yet there is no commercially available instrument. Fluorescence intensity increases with excitation intensity, and it is generally assumed that laser excitation would then offer improved limits of detection. However, as Yeung and Synovec have shown, various types of light scattering, luminescence from the flow cell walls, and emission from impurities in the solvent all increase with source intensity as well, yielding no net improvement in signal-to-noise ratio (53). Where laser excited fluorescence may prove useful is for the design of fluorescence detectors for microbore packed and open tubular LC columns, where the laser source can be focused to a small illuminated volume for on-column detection. 

Where solvent costs are an important consideration the reduced solvent consumption of microbore columns will allow the use of more exotic solvents. For the other column technologies there is no substantial applications literature as the investigative work has been carried out on individually prepared columns. The following chromatograms illustrate the potential of small bore packed and microcapillary packed columns, respectively. Shown below. Figure 6.56 is an example of a highly efficient separation of... 

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