Chromatography backflush

Ceglarek et al.45 reported the rapid simultaneous quantification of immmunosuppressants (cyclosporine A, tacrolimus, and sirolimus) in transplant patients by turbulent flow chromatography (TFC) coupled with HPLC-MS/MS. TFC is an online extraction technique involving the direct application of human plasma onto a turbulent flow column where protein is washed from the samples before the retained drug is backflushed onto an analytical column. 

Fig. 7 Representative chromatography of a proprietary assay. The lyso-PLs were resolved from the analytes and the late elution PLs were washed out of the column via backflush and switching...

Chromatographic System (See Chromatography, Appendix HA.) Chromatographic conditions may vary depending on the type of headspace unit used. Use a gas chromatograph equipped with a headspace sampler, flame ionization detector, backflush valve, 1-mL gas sample loop, and a 1-m x 3.2-mm (id) nickel precolumn and a 6-m x 3.2-mm (id) nickel analytical column, or equivalent, containing 60- to 80-mesh... 

Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form widiout the express written permission of Marcel Dekker, Inc. Purge-Backflushing Techniques in Gas Chromatography 3... 

The hardware employed in preparative liquid chromatography typically has the capability for feedback control of the pumps, automatic column switching, column backflushing, recycling, gradient mixing, online pressure, flow rate, UV-absorbance, and temperature monitoring, and automatic pneumatic actuation of fraction collection valves based on time, volume, or UV-absorbance thresholds. These capabilities are afforded by computer control. 

The first of the separation techniques to be used in process measurement was gas chromatography (GC) in 1954. The GC has always been a robust instrument and this aided its transfer to the process environment. The differences between laboratory GC and process GC instruments are important. With process GC, the sample is transferred directly from the process stream to the instrument. Instead of an inlet septum, process GC has a valve, which is critical for repetitively and reproducibly transferring a precise volume of sample into the volatiliser and thence into the carrier gas. This valve is also used to intermittently introduce a reference sample for calibration purposes. Instead of one column and a temperature ramp, the set up involves many columns under isothermal conditions. The more usual column types are open tubular, as these are efficient and analysis is more rapid than with packed columns. A pre-column is often used to trap unwanted contaminants, e.g. water, and it is backflushed while the rest of the sample is sent on to the analysis column. The universal detector - thermal conductivity detector (TCD)-is most often used in process GC but also popular are the FID, PID, ECD, FPD and of course MS. Process GC is used extensively in the petroleum industry, in environmental analysis of air and water samples" and in the chemical industry with the incorporation of sample extraction or preparation on-line. It is also applied for on-line monitoring of volatile products during fermentation processes" ... 

Rock samples were extracted using methylene chloride and a Soxhlet apparatus and the resulting extract was further fractionated by a semi-quantitative SARA separation. After asphaltenes were removed from the concentrated extract by precipitation with excess pentane, the pentane soluble portion of the sample was separated by medium-pressure liquid chromatography (MPLC) using a deactivated silica gel precolumn and an activated silica gel main column by eluting the saturate and aromatic hydrocarbon fractions from the activated silica column with hexane in the forward and back-flush modes respectively. Polar nonhydrocarbons were backflushed from the precolumn with methylene chloride-methanol. Carbon isotopes were done on a subset of hydrocarbon fractions at Coastal Sciences Labs, Austin, TX (Table 3). 

Figure 39. Arrangements for column switching technique A) Heart-, front-, and end-cut techniques B) Backflush technique C) Multidimensional chromatography a)-0 Column 1 -6 g) Detector h) Injection valve...

Skaar, H., Norli, H.R., Lundanes, E., and Greibrokk, T. (1990) Group separation of crude oil by supercritical fluid chromatography using packed narrow bore columns, column switching, and backflushing. Journal of Microcolumn Separations, 2,222. 

Sample preparation Condition a 3 mL 200 mg Bond Elut C18 SPE cartridge with two 3 mL portions of MeOH and two 3 mL portions of 5% acetic acid. Mix 500 p,L serum with 500 p.L 10% acetic acid, add to the SPE cartridge, wash with 3 mL water, elute with four 500 p.L portions of MeOHiwater 60 40. Evaporate the combined eluates to dryness under a stream of nitrogen, reconstitute the residue with 250 p,L water, filter (0.22 p.m). Inject a 100 p,L aliquot onto column A and elute to waste with mobile phase A. After an unspecified time, backflush the contents of column A onto column B using mobile phase B. Monitor the effluent from column B. (Sato,K. Kobayashi,K. Moore,C.M. Mizuno,Y. Katsumata,Y. Semi-quantitative analysis of cefaclor in human serum by capillary high performance liquid chromatography/fast atom bombardment mass spectrometry. Forensic Sci.Int. 1993, 59, 71-77.)... 

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