Fraction-collecting device

Another approach to fraction collection is the use of an on-column frit structure or capillary fracture that depends on the electroosmotic flow to deposit the eluent in a continuous manner on a moving surface. Although this approach circumvents the dilution problem, the collection structures are complex and can result in the loss of some of the analyte. One commercially available fraction collection device couples CE with membrane fraction collection, without the need for frits or capillary fractures. The outlet vial holder can be removed and replaced with a wetted circular polyvinylidene difluoride (PVDF) disk, which enables the collection of eluted analytes and subsequent manipulations such as immunoblotting and microsequencing. Figure 6.13 shows a schematic diagram of the CE membrane fraction collector interface.74... 

The components separated by FFF are washed out of the channel and into a detector and/or fraction collection device. The detectors are mainly those used in liquid chromatography where light absorption, refractive index changes, and so on, are measured as components flush through a small flow cell following their elution. 

Setting up a 2D chromatographic separation system is actually not as difficult as one might first think. As long as well-known separation methods exist for each dimension [8], the experimental aspects can be handled quite easily in most cases. Off-line systems just require a fraction collection device and something or someone who reinjects the fractions into the next chromatographic dimension. In on-line 2D systems, the transfer of fractions is preferentially done by automated injection valves, as was proposed by Kilz et al. [9]. 

Fraction collectors are especially useful in apphcations involving unattended, overnight, and automated chromatographic purification schemes. If only several fractions are to be collected from the liquid chromatograph and only a few samples are to be purified, then the eluent from the column can sometimes be collected manually. However, a fraction collection device is recommended if the analyst has many samples to process and/or if there are many fractions to collect. 

The functional requirements of fraction collectors have changed as liquid chromatography evolved from low-pressure (low-resolution) to high-pressure (high-resolution) techniques. This evolution was led by developments in column technologies and packing materials, and followed by adaptations to pumps, detectors, injectors, and fraction collectors. The following subsections briefly describe some of the key operational considerations of fraction collection devices. 

R. Caputto, C. E. Cardini, R. Trucco, and A. C. Paladini from everyday objects. For instance, a fraction-collecting device for column chromatography was built with a Meccano set (a toy from Leloir s childhood that was similar to an erector set) its collection bottles moved about with a toy railroad train. 

Fraction collection. For single-run separations, manual fraction collection or known fraction collection devices will suffice, but for cyclic operation collectors such as those described in the next section are advantageous. 

Semipreparative HPLC is the most popular method for purifying combinatorial libraries. This is largely due to the relatively high resolution of HPLC, the ease with which HPLC instruments can be interfaced with automatic sampling and fraction collecting devices for unattended operation, and the possibility to develop a generic method for a whole library or even many libraries. 

OfF-hne systems just require a fraction collection device with manual transfer and reinjection of the first dimension fractions into the second instrument. In on-line 2D systems, the fraction transfer is preferentially done by automatic transfer. Figure 2a shows the general layout and Fig. 2b shows a picture of an automated two-dimensional chromatography instrument as used by the author. 

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