Matthias Pursch,¹ Andreas Schweizer-Theobaldt,¹ Hernan Cortes,² Angelika Gratzfeld-Huesgen,³ Helmut Schulenberg-Schell³ and Bernd-Walter Hoffmann,^{3 1}Dow Deutschland Anlagengesellschaft mbH, Analytical Sciences, Rheinmünster, Germany, ²The Dow Chemical Company, Analytical Sciences, Midland, USA, ³Agilent Technologies Deutschland GmbH, Waldbronn, Germany.

High-speed liquid chromatography is becoming important in many pharmaceutical and biochemical laboratories because of the demand to analyse complex samples quickly.¹ The availability of small-particle columns (less than 2 µm particle size) has paved the way for LC separations with short analysis times, while maintaining — or even increasing — high separation efficiencies.

There is a growing interest in this new generation of LC columns for a wide range of chemical applications, including small molecules, oligomers and polymers. The availability of high pressure liquid chromatography (HPLC) systems that operate at high pressures (> 400 bar) allows the use of long, small particle columns. Such columns are now available at lengths up to 150 mm. Thus, high resolution LC separations can be generated for difficult separations of complex mixtures. Recent experimental studies revealed that sub-2 µm particle columns show superior kinetic performance (peak capacity) compared with 3–3.5 µm particles, when operated at high-pressures and run times of less than 30 min.²

Fast LC columns of different lengths were evaluated in terms of column performance. It should be noted that some of these were prototype/experimental columns. Some columns were coupled to assess the maximum possible plate numbers for high-efficiency separations. Experiments were performed with the 1200 Series Rapid Resolution LC system (Agilent Technologies, Waldbronn, Germany), which operates at pressures up to 600 bar. A fast scanning diode array detector (DAD) with a maximum scan rate of 80 Hz was used.

Higher temperatures were recently applied to obtain high performance liquid phase separations with sets of coupled conventional columns.^3,4 This concept was also applied to our investigations which include the separation of epoxy resins. Examples of fast LC for the determination of copolymer composition and functionality type distributions are described. Finally, ultra-fast separations of inhibitors were used to assess system performance.

Figure 1

Figure 1 illustrates a typical high-resolution separation of SRM 869a (National Institute of Standards and Technology (NIST), Gaithersburg, Maryland, USA) — a shape selectivity and column test mixture,⁵ which is available from the National Institute of Standards and Technology (NIST). For this example, two small-particle columns were coupled for a total length of 150 mm. Excellent column efficiency was observed with plate numbers of N = 37000 for tetrabenzonaphthalene (TBN) or about 250000 plates/m. Figure 2 shows the performance of several individual and coupled columns. All columns were of 4.6 mm internal diameter (i.d.) with a 1.8 µm Zorbax SB-C18 silica (Agilent Technologies, Wilmington, Delaware, USA) as the packing material and some of these were prototypes.