Turbulent-flow chromatography columns

Asperger A. et al., 2002. Trace determination of priority pesticide in water by means of high-speed online solid-phase extraction-liquid chromatography-tandem mass spectrometry using turbulent-flow chromatography columns for enrichment and a short monolithic column for fast liquid chromatographic separation. J Chromatogr A 960 109. 

Direct injection of pretreated biological samples (also called online sample cleanup) greatly simplified sample preparation for LC/MS/MS analysis. The normal process involves sample aliquot steps, internal standard addition, and centrifugation. Compared to traditional off-line LLE and SPE sample preparation procedures, online methods are easier and faster. Two types of online SPE columns are commercially available. One is the restricted access media (RAM) column. The other is the turbulent flow chromatography (TFC) column. 

In some cases, so called direct plasma injection techniques may be used23 83 104 108 instead of protein precipitation for loading plasma samples onto an HPLC/MS/MS system. Some direct plasma injection systems use a column switching technique in which the plasma is loaded onto an extraction column that retains the small molecules. The other plasma components are sent to waste and the flow is switched so that the small molecules are eluted onto an analytical column that connects to the MS/MS.23 83 108 One variation of the column switching method is turbulent flow chromatography commercialized by Cohesive Technologies (now part of Thermo, San Jose, CA).23... 

Turbulent flow chromatography uses large particle packing materials and high flow rates to separate small molecules from proteins and other matrix components in plasma. In one example, Herman et al.109 reported that turbulent flow chromatography was useful for a series of discovery compounds as the online extraction step in LC/MS/MS analysis. As an alternative, Hsieh et al.89-104 107 described the use of a single mixed function column as a simpler process for direct plasma injection applications. 

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. 

High flow rate is generally the basis for the high-throughput efficiency of several Turbulent Flow Chromatography (TFC), Restricted Access Material (RAM), and monolithic columns methodologies. 

In most common turbulent-flow chromatography experiments, a second conventional high-performance liquid chromatography (HPLC) column is employed. The conventional HPLC column, usually referred to as the analytical column, is used for peak sharpening and additional separation prior to MS detection. This approach requires an additional valve and pump to control the final HPLC separation. A typical dual-column methodology is shown in Fig. 10.5. 

Solid-phase extraction (SPE), which can be done off-hne or on-line by means of cartridges, cartridge columns, or extraction disks (Ch. 11.6.4), and eventually by using special packing materials, such as restricted access materials (RAM) or turbulent-flow chromatography (TFC) (Ch. 11.6.5). 

Turbulent flow chromatography is a direct-inject sample-preparation technique that is accomplished on a special chromatography column. The technique has some applicability toward plasma and serum. The special column combines large particle (50 lm) and frit size (20 lm) with high flow rate (5 to 10 mL/ min) to achieve eddies and nonlaminar flow. Under this arrangement, improved... 

As long ago as 1966 (Pretorius 1966) it was shown that operation of an open-tubular HPLC column under turbulent flow conditions permitted much shorter elution times than those observed using the conventional laminar (low speed) elution conditions considered by the van Deemter theory (Equation [3.39]). Extension of the turbulent flow condition to packed columns had to wait for development of HPLC pumps capable of generating sufficient pressure to drive the fast flows required. Although the approach is still referred to as turbulent flow chromatography, some doubt has been expressed (A5nton 1998) concerning... 

There are two different modes in which on-line extraction/clean-up by turbulent flow chromatography is performed (Zhou 2005). In the simpler mode, single column extraction, the analytical sample or primary extract is injected directly onto the extraction column and extracted directly onto the analytical column by the turbulent flow mobile phase that has high eluent strength (Section 4.4.2a), i.e., high organic content in the case of analytes to be analyzed by reverse phase HPLC. This... 

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