Journal of Chromatography A, 1351 (2014) 56–60 Contents lists available at ScienceDirect Journal of Chromatography A jo ur nal ho me pag e: www.elsevier.com/locate/chroma Assessing the performance of curtain flow first generation silica monoliths Arianne Soliven a , Dominic Foley b , Luisa Pereira b , Gary R. Dennis a , R. Andrew Shalliker a , Karin Cabrera c , Harald Ritchie b , Tony Edge b,∗ a Australian Centre for Research on Separation Science (ACROSS), School of Science and Health, University of Western Sydney, Parramatta, NSW, Australia b Thermo Fisher Scientific, Manor Park, Tudor Road, Runcorn, UK c R&D Analytical Chromatography, Merck Millipore, Merck KGaA, Germany a r t i c l e i n f o Article history: Received 18 December 2013 Received in revised form 28 April 2014 Accepted 8 May 2014 Available online 17 May 2014 Keywords: Active flow technology Silica monolith Parallel segmented flow Curtain flow a b s t r a c t Analytical scale active flow technology first generation silica monolithic columns kitted out in curtain flow mode of operation were studied for the first time. A series of tests were undertaken assessing the column efficiency, peak asymmetry and detection sensitivity. Two curtain flow columns were tested, one with a fixed outlet ratio of 10% through the central exit port, the other with 30%. Tests were carried out using a wide range in inlet flow segmentation ratios. The performance of the curtain flow columns were compared to a conventional monolithic column. The gain in theoretical plates achieved in the curtain flow mode of operation was as much as 130%, with almost Gaussian bands being obtained. Detection sensitivity increased by as much as 250% under optimal detection conditions. The permeability advantage of the monolithic structure together with the active flow technology makes it a priceless tool for high throughput, sensitive, low detection volume analyses. Crown Copyright © 2014 Published by Elsevier B.V. All rights reserved. 1. Introduction active flow technology (AFT) [1] was largely designed to over- come the problems caused by wall effects and radial packing heterogeneity that limit the performance of current HPLC column technology [2–5]. In addition to improving the efficiency of chro- matography columns other advantages in this column technology also transpired, for example, when AFT columns were coupled to flow limiting detectors, i.e., the mass spectrometer, through-put could be dramatically increased since the volume load to the detec- tor could be reduced [6]. In addition, AFT columns kitted out in the curtain flow mode of operation provided for a substantially higher level of sensitivity in detection, since the analyte was constricted in the central region of the column [6–11]. Parallel segmented flow columns enabled multiplexed detection processes to be employed, which expanded the amount of information that could be collected on the sample within a single analysis [12–17]. To date, the performance of AFT columns has been tested on particle packed column formats only, but in scales that range from the preparative scale (21 mm internal diameter (i.d.)) down to narrow bore columns (2.1 mm i.d.) [18]. The gain in separation ∗ Corresponding author. Tel.: +49 44 1928543448; fax: +49 44192588106. E-mail address: tony.edge@thermo.com (T. Edge). performance across this range of operation was reviewed recently [1] and thus, details relating to specific aspects of the performance of AFT columns need not be repeated here. It is the aim of the current study, to demonstrate the benefits AFT when applied to first gener- ation silica based monolithic columns. These columns are perhaps the ideal candidate for the active flow technology, since the bed structure is such that peak tailing is substantial, and this has limited the performance of the monolithic column. Much of this tailing has been ascribed to the column wall effects and radial heterogeneity of the stationary phase bed [19,20]. Even though peak tailing has limited to some extent the per- formance of the first generation monolith, which was the driver towards the development of the second generation silica mono- lith, the first generation monolith has proven to be a useful tool for chromatographer’s who require high throughput separations since these beds offer a high degree of permeability and yield efficiency approaching 5-m particle packed columns when the number of theoretical plates (N) is measured at half height, although sub- stantially less efficiency is apparent when tailing is considered. Monolithic columns have been the focus of two independent and extensive reviews by Cabrera [21] and Guiochon [22]. Both high- lighted their main advantage; high permeability and fast mass transfer kinetics (reduced c-term) [21,22]. The benefits of through- put are substantial for the first generation silica monolith, and it is this additional factor that promotes the potential of utilising http://dx.doi.org/10.1016/j.chroma.2014.05.025 0021-9673/Crown Copyright © 2014 Published by Elsevier B.V. All rights reserved.