Enriching columns

As another illustration, Eq. (22-48) becomes Eq. (22-50) for an enriching column which is concentrating a surfactant with a constant E ... 

Yin, H., Killeen, K., Brennen, R., Sobek, D., Werlich, M., and van de Goor, T., Microfluidic chip for peptide analysis with an integrated HRLC column, sample enrichment column, and nanoelectrospray tip, Analytical Chemistry 11(2), 527-533, 2005. 

A more detailed discussion from an economic and operability viewpoint can be found in Doherty and Malone [8]. Despite the apparent advantage, the two-column sequence seems not to be the most economical because of the large entrainer recycle and large number of stages. On the contrary, the two-column sequence plus enrichment column, in total three units, offers the best compromise between investment and solvent-recycle costs. 

Botazzi el al., 1985 Gibson el al., 1992 Lotti el al., 1980). In this study eight monounsaturated fatty acids were readily detected, with the major one being C18 1 with several minor ones, C14 l and C15 l, only detected in the enriched column fractions. The major Cl6 1 fatty acids identified in evening primrose were n-7 and n-9, which contrasted with borage oil that contained Cl6 1 (n-7) and 06 1 (n-5) (Wretensjo and Svensson, 1990). 

Figure 11.1 Concentration step river water pumped through trace enrichment column.

Figure 11.2 Back-flushing step organic compounds concentrated on trace enrichment column washed on to an analytical column.

H. Yin, K. Killeen, R. Breimen, D. Sobek, M. Werhch, T. van der Goor, Microfluidic chip for peptide analysis with an integrated HPLC column, sample enrichment column, andnano-ESI tip. Anal. Chem., 77 (2005) 527. 

Trace enrichment is the sample preparation procedure which is performed by passing a crude sample through a special collection column, but with a couple of added features. It is often done on-line, one at a time, just prior to the analytical procedure. It usually involves a minicolumn very similar to an off-line device, like a solid-phase extraction tube, but packed into a stainless-steel column and attached to the injection valve. This is called a trace enrichment column in many published procedures. Another name that is often given to this technique is column switching in the title or key words of published articles. This is because this technique involves valves that must be switched from one solvent flow stream to another. The valve, in its initial position, allows the crude sample... 

The crude sample is injected or pumped onto the TE column. [Note Even a crude sample requires membrane filtration and/or centrifugation to prevent shortened column life of the trace enrichment column.] The TE column will attract the components of interest, depending on the nature bonded phase in the TE column, the solvent in which the sample is dissolved, and the solvent in which the TE column has been equilibrated. The TE column, most likely, will remove more than just the components of interest and, thus, might need an additional solvent wash sequence to remove other collected impurities. 

Steam stripping is to be used to remove a solvent from contaminated soil. An enriching colunm will be used to recover the solvent from the stream. A vapor feed of 40 mol/hr with a composition of 20 mol% solvent and 80 mol% water enters an enriching column. The distillate stream is to have a flow rate of 5 mol/hr and a concentration of 90 mol% solvent. The internal reflux ratio is 0.875 and constant molar overflow (CMO) may be assumed. Graph the operating line to predict the number of equilibrium stages in this enriching column. 

Figure 4.4 Graphical solution of enriching column, Example 4.2.

Stripping columns also exist, just like the enriching, or rectifying, column in the previous example. The purpose of a stripping column would be to purify the least volatile component an enriching column would purify the most volatile component. 

The main reason for moving to low-flow LC/MS systems is to handle the analytes in the smallest possible volume. Thus, by using an enrichment column, the sample can be trapped and then eluted in the smallest possible volume, so as to reach maximum concentration levels. This approach has required the development of a nanopump. The related technology is nowadays available on the market, but the weak point of the nanopump-nanocolumn-nano-ESI system is mainly related to the connections among the three components, introducing dead volumes and the possibility of small, undetectable leaks. 

Recently, a new approach was proposed to overcome these problems, based on a microfluidic chip device (Agilent, 2007) (Fig. 1.11). This finding includes the enrichment column, the separation column, and the nanospray emitter. By use of a robotic system, the chip is automatically positioned in front of the entrance orifice of the mass spectrometer. 

The full LC-chip/MS system includes an autosampler and capillary LC pump for delivery of the sample to the enrichment column, which allows sample loading of larger volume samples in a short period of... 

The present microfluidic device differs slightly from similar systems previously reported by our group.34 36 The chip device integrates a 40 nL enrichment column, a 4.3 cm analytical column (75 x 50 pm cross-section channel) and a 10 pm i.d. nanoelectrospray emitter directly on a polymer surface which is itself encased into an aluminium holder for convenient manipulation (Figure 8.1a). An on-line filter (0.5 pm pore size) is positioned between the valve stator and the nanopump to prevent occlusion of the chip device. The chip is mounted in a... 

In a similar effort to combine preconcentration with electrophoretic separations, Fortier et al. [123] investigated the analytical performances of a microfluidic system comprised of an enrichment column, a reversed phase separation channel, and a nanoelectrospray emitter embedded together in polyimide layers. The authors demonstrated that the configuration minimized transfer lines and connections and reduced peak broadening and dead volumes, resulting in good reproducibility of retention time and peak intensity. The microchip was interfaced to both ion trap and TOF MS. Measurements were performed for a dilution series of protein digests spiked into rat plasma samples and provided an LOD of 1-5 fmol. 

In enriching columns, some of the collapsed fonmate is recycled back to lhe upper section of the column to increase the solute concentration in the fonmate as moch as possible. 

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