Optimizing separations in online comprehensive two‐dimensional liquid chromatography

Abstract

Online comprehensive two‐dimensional liquid chromatography has become an attractive option for the analysis of complex nonvolatile samples found in various fields (e.g. environmental studies, food, life, and polymer sciences). Two‐dimensional liquid chromatography complements the highly popular hyphenated systems that combine liquid chromatography with mass spectrometry. Two‐dimensional liquid chromatography is also applied to the analysis of samples that are not compatible with mass spectrometry (e.g. high‐molecular‐weight polymers), providing important information on the distribution of the sample components along chemical dimensions (molecular weight, charge, lipophilicity, stereochemistry, etc.). Also, in comparison with conventional one‐dimensional liquid chromatography, two‐dimensional liquid chromatography provides a greater separation power (peak capacity). Because of the additional selectivity and higher peak capacity, the combination of two‐dimensional liquid chromatography with mass spectrometry allows for simpler mixtures of compounds to be introduced in the ion source at any given time, improving quantitative analysis by reducing matrix effects. In this review, we summarize the rationale and principles of two‐dimensional liquid chromatography experiments, describe advantages and disadvantages of combining different selectivities and discuss strategies to improve the quality of two‐dimensional liquid chromatography separations.

Chemical profiling of bioactive constituents in hop cones and pellets extracts by online comprehensive two‐dimensional liquid chromatography with tandem mass spectrometry and direct infusion Fourier transform ion cyclotron resonance mass spectrometry

“…After this correction a peak capacity of 1478 was calculated. Moreover, the degree of dissimilarity between the two separation dimensions, or the orthogonality ( A 0 ) of the system, must be considered . Finally, the value of 756 was obtained, which is similar to previous RP × RP approaches detailed calculation are reported in supporting material.…”

Dynamic extraction coupled on-line to liquid chromatography with a parallel sampling interface—a proof of concept for monitoring extraction kinetics

“…It is obvious that for these relatively less polar compounds, the retention was stronger on the C18 column than on the P-H column. Thus, the usage of the C18 column would require longer analysis time in order to avoid un-eluted compounds interfere with the analysis of the next collected extract fraction, which is similar to the wrap-around issues in two-dimensional liquid chromatography [23]. The P-H column was therefore chosen for optimization as shorter analysis time allows higher sampling frequency, which adds more details into the final extraction profiles generated.…”

Recent applications of chemometrics in one‐ and two‐dimensional chromatography

“…The second dimension complies to the LSS (log-linear) model for reversed-phase LC. Reproduced with permission from [6] is provided. These characteristics and trends are then used to make predictions under new circumstances.…”

“…The quest for more separation power led to the development of comprehensive 2D chromatography where the entire first-dimension ( 1 D) effluent is divided into many fractions, each of which is subjected to a second-dimension ( 2 D) separation [5,6]. The result is illustrated for a comprehensive 2D LC (LC×LC) separation in Figure 1, where a mixed-mode ion-exchange LC separation (A) is combined with a reversedphase LC separation (B) leading to a 2D chromatogram (C) [7].…”

“…Target optimization can be seen as a special (usually simpler) case of the general optimization strategy. Readers interested in a more detailed discussion of the rationale behind the different forms of optimization are referred to an earlier work [6].…”