Column switching devices

Column switching devices fitted to existing HPLC systems can offer significant improvements in method development time in LC [147, 148]. They offer 

Controller/data processor Photo diode array Columns Parallel switching valve 

Other applications where the use of column switching devices have offered significant benefits include the direct analysis of the drug indomethacin in rat plasma [154]. 

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As well as the methods discussed above headspace samplers, pyrolyzers, thermal desorbers, and column switching devices could be considered as specialized sample inlet systems. These are treated separately in Chapter 8. 

Boppana V, Miller-Stein C, Schaefer WH (1996) Direct plasma liquid chromatographic-tandem mass spectrometric analysis of granisetron and its 7-hydroxy metabolite utilizing internal surface reversed-phase guard columns and automated column switching devices. J Chromatogr B 678 227-236... 

If no rational starting point for the separation of a racemate can be found, a random screening procedure has to be applied. In most cases 250 X 4 or 4.6 mm columns are used for this purpose. Modern HPLC systems often include a column switching device with up to 12 columns. Most systems have programmable software options for the set of different mobile phase compositions. Combination of UV and polarimetric detection allows even very small selectivities to be found and used as a starting point for further optimization. Commercial systems with deconvolution and optimization options are available, together with a given set of 12 different chiral stationary phases (www.pdr-chiral.com). After an initial detection of selectivity on a CSP, the mobile phase composition and additives as well as temperature have to be varied either manually or by means of an automated system. 

Boppana, V.K. Miller-Stein, C. Schaefer, W.H. Direct Plasma Liquid Chromatographic-Tandem Mass Spectrometric Analysis of Ganisetron and its 7-Hydroxy Metabolite Utilizing Internal Surface Reversed-Phase Guard Columns and Automated Column-switching Devices, J. Chromatogr. B. 678, 227-236 (1996). 

A schematic diagram of a six-vessel UOP Cyclesorb process is shown in Figure 15. The UOP Cyclesorb process has four external streams feed and desorbent enter the process, and extract and raffinate leave the process. In addition, the process has four internal recycles dilute raffinate, impure raffinate, impure extract, and dilute extract. Feed and desorbent are fed to the top of each column, and the extract and raffinate are withdrawn from the bottom of each column in a predeterrnined sequence estabUshed by a switching device, the UOP rotary valve. The flow of the internal recycle streams is from the bottom of a column to the top of the same column in the case of dilute extract and impure raffinate and to the top of the next column in the case of dilute raffinate and impure extract. 

An LC-LC coupling experiment system can be performed by employing a commercially available HPLC apparatus and involving various combinations of HPLC columns, eluents, additives, switching devices and detectors. 

Figure 10.4 shows a schematic representation of the multidimensional GC-IRMS System developed by Nitz et al. (27). The performance of this system is demonstrated with an application from the field of flavour analysis. A Siemens SiChromat 2-8 double-oven gas chromatograph equipped with two FIDs, a live-T switching device and two capillary columns was coupled on-line with a triple-collector (masses 44,45 and 46) isotope ratio mass spectrometer via a high efficiency combustion furnace. The column eluate could be directed either to FID3 or to the MS by means of a modified Deans switching system . 

Inoue K, Higuchi T, Okada F, Iguchi H, Yoshimura Y, Sato A, Nakazawa H (2003) The validation of column-switching LC/MS as a high-throughput approach for direct analysis pf di(2-ethylhexyl) phthalate released from PVC medical devices in intravenous solution. J Pharm Biomed Anal 31 1145-1152... 

Fig. 17.12 MDGC-pyrolysis-IRMS precolumn and main column are connected via the multi-column switching system MCS2 (GERSTEL). Cutting is realised by different gas flows through the MCS2 device [71]...

Tuned output control signals to peripheral and ancillary devices such as sample valves, column switching valves, and other external functions which are part of the automated procedure. 

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