Improving Peak Capacity in Fast Online Comprehensive Two-Dimensional Liquid Chromatography with Post-First-Dimension Flow Splitting

Abstract

The use of flow splitters between the two dimensions in on-line comprehensive two dimensional liquid chromatography (LC×LC) has not received very much attention in comparison to their use in GC×GC where they are quite common. In principle, splitting the flow after the first dimension column and performing on-line LC×LC on this constant fraction of the first dimension effluent should allow the two dimensions to be optimized almost independently. When there is no flow splitting any change in the first dimension flow rate has an immediate impact on the second dimension. With a flow splitter one could for example double the flow rate into the first dimension column and do a 1:1 flow split without changing the sample loop size or the sampler’s collection time. Of course, the sensitivity would be diminished but this can be partially compensated by use of a larger injection; this will likely only amount to a small price to pay for this increased resolving power and system flexibility. Among other benefits, we found a 2-fold increase in the corrected 2D peak capacity and the number of observed peaks for a 15 min analysis time by using a post first dimension flow splitter. At a fixed analysis time this improvement results primarily from an increase in the gradient time resulting from the reduced system re-equilibration time and to a smaller extent it is due to the increased peak capacity achieved by full optimization of the first dimension.

Comprehensive two-dimensional liquid chromatographic analysis of anthocyanins

“…the product of the first dimension flow rate and the sampling time), splitting before the second dimension column may be used in on-line and stop-flow LC×LC [127,130,131]. [127].…”

“…On-line LC×LC separation is most commonly used in phenolic analysis, with various separation modes being coupled [130,132,137,144,145,158,159] Different column stationary phases and mobile phases have been used in the on-line LC×LC analysis of a range of phenolic compounds in various samples such as wine [144], plant extracts, apples [160], beer [145], grape seeds [137] and cocoa [130].…”

A Simple, Robust Orthogonal Background Correction Method for Two-Dimensional Liquid Chromatography

“…The gradient was 0–56 % B in 0–24.5 min, 0 % B at 24.51 min. The flow rate in the 1 D column was 0.5 mL/min and the flow rate in the splitting pump was 0.1 mL/min 10 . The column was maintained at a temperature of 40 °C.…”

Two dimensional assisted liquid chromatography – a chemometric approach to improve accuracy and precision of quantitation in liquid chromatography using 2D separation, dual detectors, and multivariate curve resolution

“…The 1 D effluent was split to 0.05 mL min À1 (see Ref. [8] for more details about splitting) and directed to a pair of 40 mL sample loops connected to an 8-port valve. The sample loops were alternatively filled with 1 D effluent and then the effluent was delivered to the 2 D column by switching the valve position.…”

“…In practice, the effective peak capacity is lower for several reasons, including the difficulty in choosing a pair of columns which maximize the use of the 2D separation space [3], partially due to the lack of orthogonality between commercially available columns [4], and the undersampling of the first dimension separation [5]. Despite these limitations Stoll, Wang, and Carr determined through both theoretical and experimental studies that when separation times are greater than 10 min and the 2 D separation is conducted sufficiently rapidly, LC Â LC has superior effective peak capacity as compared to 1D-LC [5][6][7][8]. While multi-dimensional chromatography has definite advantages in terms of peak capacity and peak capacity per unit time, the precision and accuracy of these methods compared to 1D chromatography often are not considered.…”