Ultra high flow rate liquid chromatography

9 Ultra High Flow Rate Liquid Chromatography 

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 

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Ayrton J. et al., 1998. Optimisation and routine use of generic ultra-high flow-rate liquid chromatography with mass spectrometric detection for the direct online analysis of pharmaceuticals in plasma. J Chromatogr A 8282 199. 

Bayliss, M.K. Little, D. Mallett, D.N. Plumb, R.S. Parallel Ultra-High Flow Rate Liquid Chromatography with Mass Spectrometric Detection Using aMulti-plex Electrospray Source for Direct, Sensitive Determination of Pharmaceuticals in Plasma at Extremely High Throughput, Rapid Commun. Mass Spectrom. 14, 2039-2045 (2000). 

Also, new-generation HPLC instrument which can exceed the pressure limitation of conventional equipment has been developed. This technique is ultra performance liquid chromatography (UPLC), where small particle size columns with 1.7 pm particle size in combination with high flow rates offers increased speed, resolution, and sensitivity [15]. Ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) has shown to be well suited for support of PK studies [16-19], Often, there is a need to improve the sensitivity of the assay for the determination of PK parameters, especially for very potent compounds, since lower amount is administrated, and also for compounds with low bioavailability. UPLC-MS/MS has shown decreased ion suppression and superior sensitivity, and has been successfully applied to PK studies for compounds with low bioavailability [20-22]. 

The penalty for using fine particles is resistance to solvent flow. Until recently, HPLC operated at pressures of 70-4(X) bar to attain flow rates of 0.5-5 mL/min. In 2004, equipment became available to employ 1.5- to 2-p.m-diameter particles at pressures up to 1 000 bar. These instruments provide increased resolution or decreased run time. Chromatography with 1.5- to 2-p,m-diameter particles at high pressure is commonly called UPLC (Ultra-Performance Liquid Chromatography). 

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