Microcolumns packed capillary

Microcolumns use less solvent and, because the sample is diluted to a lesser extent, produce larger signals at the detector. These columns are made from fused silica capillaries with internal diameters of 44—200 pm and lengths of up to several meters. Microcolumns packed with 3-5-pm particles have been prepared with column efficiencies of up to 250,000 theoretical plates. 

Monolithic columns are comparatively easy to prepare. This is particularly true for capillary columns, which are known to be tedious to pack with particles. Furthermore, the reproducibility of microcolumn packing is low. 

Figure 8.1 Different types of microcolumns (a) open tubular capillary column (1-50 fim I.D.), (b) dry packed capillary column ( 200 jim I.D.), and (c) microbore column (0.5-1 mm I.D.), narrow-bore column (1-2 mm I.D.), and slurry packed capillary column ( 500 /xm I.D.). (Adapted from Ref. 2 with permission.)...

Fig. 3.4. Effect of mobile phase selectivity on the CEC separation of barbiturates (1-6). Electrochromatography was performed at 15°C with an applied voltage of 30 kV on a 25 cm, 100 pm i.d., 3 pm Hypersil Phenyl packed capillary. Sample concentration was 170 pg ml"1 of each component with a 15 kV/5s injection. Detection was at 210 nm. a) ACN-50 mM phosphate buffer, pH 4.5-water (4 2 4 v/v/v), b) MeOH-50 mM phosphate buffer, pH 4.5-water (5 2 3 v/v/v). From Euerby et al [26], Journal of Microcolumn Separations, 1999. Reproduced with permission of John Wiley Sons, Inc.

Amperometric detectors are easily miniaturized with preservation of performance, since their operation is based on reactions at the electrode surface. Using a single carbon fiber or microelectrode as a working electrode allows detector cells of very small volume and in-column detectors to be constructed for use in open tubular and packed capillary column liquid chromatography [189-192]. These microcolumn separation techniques combined with amperometric detection are exploited for the quantitative analysis of volume-limited samples such as the contents of single cells [193,194]. 

Tong, D., Bartle, K. D., Clifford, A. A., and Edge, A. M., Theoretical studies of the preparation of packed capillary columns for chromatography. Journal of Microcolumn Separations 1995, 7, 265-278. 

A multidimensional system using capillary SEC-GC-MS was used for the rapid identification of various polymer additives, including antioxidants, plasticizers, lubricants, flame retardants, waxes and UV stabilizers (12). This technique could be used for additives having broad functionalities and wide volatility ranges. The determination of the additives in polymers was carried out without performing any extensive manual sample pretreatment. In the first step, microcolumn SEC excludes the polymer matrix from the smaller-molecular-size additives. There is a minimal introduction of the polymer into the capillary GC column. Optimization of the pore sizes of the SEC packings was used to enhance the resolution between the polymer and its additives, and smaller pore sizes could be used to exclude more of the polymer... 

Figure 12.7 Cliromatograms of a polycarbonate sample (a) microcolumn SEC ti ace (b) capillary GC ti ace of inti oduced fractions. SEC conditions fused-silica (30 cm X 250 mm i.d.) packed with PL-GEL (50 A pore size, 5 mm particle diameter) eluent, THE at aElow rate of 2.0ml/min injection size, 200 NL UV detection at 254 nm x represents the polymer additive fraction ti ansfeired to EC system (ca. 6 p-L). GC conditions DB-1 column (15m X 0.25 mm i.d., 0.25 pm film thickness) deactivated fused-silica uncoated inlet (5 m X 0.32 mm i.d.) temperature program, 100 °C for 8 min, rising to 350 °C at a rate of 12°C/min flame ionization detection. Peak identification is as follows 1, 2,4-rert-butylphenol 2, nonylphenol isomers 3, di(4-tert-butylphenyl) carbonate 4, Tinuvin 329 5, solvent impurity 6, Ii gaphos 168 (oxidized). Reprinted with permission from Ref. (14).

The ability to prepare monoliths within a mold of any shape was used by Lee et al. [128] who prepared monolithic ST-DVB microbeads within pulled fused silica needles and used them for the reversed-phase separation and on-line electrospray ionization mass spectrometry (ESI-MS) detection of proteins and peptides. As illustrated by Fig. 18, these monolithic microcolumns separated proteins far better than capillaries packed with commercial C18 silica or polymeric beads. 

M. Konishi, Y. Mori, and T. Amano, High-performance packed glass-lined stainless steel capillary column for microcolumn liquid chromatography, Anal. Chem., 57 2235-2239 (1985). 

In a study presented by Jinno et al. [124], packed column capillary electrochromatography, open-tubular CEC, and microcolumn liquid chromatography using a cholesteryl silica bonded phase have been studied to compare the retention behavior for benzodiazepines. The results indicated that CEC was a promising method, as it yielded better resolution and faster analysis than microcolumn LC for benzodiazepines. Similar selectivity to HPLC was noted, except for a few solutes that were charged under the separation conditions. Columns packed with the ODS and cholesteryl phases were compared and showed totally different migration orders of the analytes. The retention on the cholesteryl silica sta-... 

Profile LC Packings is a privately held company based in San Francisco, Amsterdam and Zurich. It was founded in Zurich in 1987 with the goal to develop, manufacture, and commercialize packed microcolumns for use in HPLC. The company offers a complete range of products for use in microseparation techniques such as micro, capillary and nano LC, including electrochromatography, capillary electrophoresis, and LC-MS. 

Higher pressures are required for pressure-assisted separations in packed columns used for capillary electrochromatography [235,376,464-466]. These columns require a high-pressure pump to provide the supplementary mobile phase flow. Conventional rotary injection valves and autosamplers can be used for sample introduction with this arrangement if a special inlet tee housing the electrode and split line with a restrictor is installed [422]. Microcolumn pumps are also useful for conditioning columns before initial use in capillary electrochromatography (section 8.4.2). There are no com-... 

Pack a silica capillary-scale microcolumn (150pm i.d.) 7.5cm of C18 reverse phase packing material (Zorbax eclipse XDB-Cis resin). 

Clearly, the capabilities of modem chromatographic techniques have been vastly improved. Packed column GC has been replaced by capillary column GC. Similarly, the large columns of normal-phase liquid chromatography (LC) are replaced by microcolumn reverse phase LC columns. Capillary electrophoresis (CE) is an entirely new means of separating small amounts of more complex, and charged sample molecules, and has evolved into several distinct forms with unique capabilities. Mass spectrometry coupled with different forms of chromatography is now applied to the analysis of many mixtures, of higher complexity, and more disparate sample types. 

LC-DAD, IT-SPME-capillary LC-DAD and IT-SPME-LC with a monolithic column-FLD. Such methods are clearly advantageous over a classical procedure based on SPE with disposable cartridges for a number of reasons (i) the minimum off-line sample manipulation, as the samples only needed to be filtered (ii) the rapidity, as on-line analyte enrichment is accomplished in a few min, (Hi) the minimum consumption of extractive phases, as the extractive columns used (a Cis packed microcolumn or a segment of a capillary GC coliunn) can be reutilized for several hundred samples and (iv) the total elimination of organic solvents in sample preparation. 

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