Anal. Chem. 1909, 61, 2747-2750
2747
Separation of Cations by Open-Tubular Column Liquid Chromatography Stephan R. Muller and Wilhelm Simon* Department of Organic Chemistry, Swiss Federal Institute of Technology (ETH), CH-8092 Zurich, Switzerland
H. Michael Widmer and Karl Grolimund Central Function Research, Ciba-Geigy AG, CH-4002 Basel, Switzerland
Gerhard Schomburg and Peter Kolla Chromatography Department, Max-Planck-Institut fur Kohlenforschung, 0-4300 Mulheim-Ruhr, FRG
The band broadenlng In open-tubular column liquid chromatography with caplllarles of 9.5, 5.4, and 4.6 pm inner dlameter coated wlth poly(butadlenesulfon1c acid) or poly(butadlene-maleic acid) Is measured and compared wlth results from the Golay equatlon. For a caplllary column of 9.5 pm l.dJ0.58 m length, coated wlth the strong catlon exchanger, ' = 210 000 and 47 100 theoretlcal plates for k' = 0 and k 1.65, respectlvely, at the optimal flow rates were obtained. These values correspond to about 99% and 67%, respectively, of the theoretkal ones. For the caplllary column of 4.6 pm l.d./0.90 m length, coated with the weak cation exchan' = 0 and k' ger, 680 000 and 246 000 theoretlcal plates for k = 0.16, respectively, were obtained at the optimal flow rates. these values correspond to about 100 % and 89 YO,respectively, of the theoretlcal ones. For both caplllary columns about 91-100% of the theoretlcal plate numbers were obtalned at higher flow rates ( 3 . ~ ~ Separatlons ). of alkallmetaVammonIum Ions withln 6 min and of the alkall-metal mol Ions within 3 mln wlth detected quantities in the range (9.5 pm 1.d. caplllary), as well as of ammonium, alkali, and alkaline-earth metal Ions In 4 min (4.6 pm i.d. caplllary) wlth quantltles of 0.2 to 20 X mol were achleved.
INTRO DUCT1 0N T o realize acceptable analysis times in high-resolution open-tubular column liquid chromatography, column diameters 110 pm have to be used (1-3). For such separation systems, both the injection and detection processes frequently are limiting factors to the resolution power of the chromatographic system ( 4 ) . On-column electrochemical detectors are of special interest to obtain small detection volumes and fast response (5-13). Utilizing a pressure pulse-driven stopped-flow injection system (8)and an on-column potentiometric detector (7), lo8 theoretical plates were obtained for nonretained components in 220 s with a column of 1.30 m length and 3.5 pm inner diameter (i.d.1 (7). This corresponds to a loss of 25% in the theoretically possible number of theoretical plates (7). There are very few reports quantitating the loss of resolution in realistic liquid chromatographic separations in open-tubular columns of a diameter 110 pm (13-21). Here we report on the chromatographic resolution observed in the separation of cations utilizing capillaries of 9.5, 5.4, and 4.6 pm i.d. taking theoretically care of the diffusion of components in the stationary phase (14-16). EXPERIMENTAL SECTION Chromatographic System. The chromatographicsystem used has been described previously (5-8). It consists of the components shown in Figure 1: A constant flow high precision pump, Model
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CYLINDER 5 2 0 0 bar
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PRESSURE GaUGE
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VOLTMETER RECORDER
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Figure 1. Schematic diagram of the open-tubular column liquid
chromatograph. P-500 (140 bar, Pharmacia Fine Chemicals AG, Uppsala, Sweden), for the pressure pulse and rinsing procedure, a helium cylinder (1200 bar, PanGas, Zurich, Switzerland) and a high-pressure autoclave equipped with a Teflon h e r (1200bar, 0.75 L, Berghof GmbH, Eningen, FRG) for the elution process, a titanium tube (1m, Pharmacia Fine ChemicalsAG, Uppsala, Sweden) and three VICI switching valves, Model C6W, with electric actuators (switching time
