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Mar del Plata, Argentina

Allen R.C.,Virginia Commonwealth University | John M.G.,Virginia Commonwealth University | Rutan S.C.,Virginia Commonwealth University | Filgueira M.R.,University of Minnesota | And 2 more authors.
Journal of Chromatography A

A singular value decomposition-based background correction (SVD-BC) technique is proposed for the reduction of background contributions in online comprehensive two-dimensional liquid chromatography (LC × LC) data. The SVD-BC technique was compared to simply subtracting a blank chromatogram from a sample chromatogram and to a previously reported background correction technique for one dimensional chromatography, which uses an asymmetric weighted least squares (AWLS) approach. AWLS was the only background correction technique to completely remove the background artifacts from the samples as evaluated by visual inspection. However, the SVD-BC technique greatly reduced or eliminated the background artifacts as well and preserved the peak intensity better than AWLS. The loss in peak intensity by AWLS resulted in lower peak counts at the detection thresholds established using standards samples. However, the SVD-BC technique was found to introduce noise which led to detection of false peaks at the lower detection thresholds. As a result, the AWLS technique gave more precise peak counts than the SVD-BC technique, particularly at the lower detection thresholds. While the AWLS technique resulted in more consistent percent residual standard deviation values, a statistical improvement in peak quantification after background correction was not found regardless of the background correction technique used. © 2012 Elsevier B.V. Source

Gu H.,University of Minnesota | Huang Y.,University of Minnesota | Filgueira M.,University of Minnesota | Filgueira M.,University Nacl La Plata | Carr P.W.,University of Minnesota
Journal of Chromatography A

In this study, we examined the effect of first dimension column selectivity in reversed phase (RP) online comprehensive two dimensional liquid chromatography (LC×LC). The second dimension was always a carbon clad metal oxide reversed phase material. The hydrophobic subtraction model (HSM) and the related phase selective triangles were used to guide the selection of six different RP first dimension columns. Various kinds of samples were investigated and thus two different elution conditions were needed to cause full elution from the first dimension columns. We compared LC×LC chromatograms, contours plots, and fcoverage plots by measuring peak capacities, peak numbers, relative spatial coverage, correlation values, etc. The major finding of this study is that the carbon phase due to its rather different selectivity from other reversed phases is reasonably orthogonal to a variety of common types of bonded reversed phases. Thus quite surprisingly the six different first dimension stationary phases all showed generally similar separation patterns when paired to the second dimension carbon phase. This result greatly simplifies the task of choosing the correct pair of phases for RP×RP. © 2011 Elsevier B.V. Source

Paek C.,University of Minnesota | Huang Y.,University of Minnesota | Filgueira M.R.,University of Minnesota | Filgueira M.R.,University Nacl La Plata | And 2 more authors.
Journal of Chromatography A

We recently introduced a new method [1] to deposit carbon on fully porous silicas (5μm) to address some of the shortcomings of carbon clad zirconia (C/ZrO 2), which has rather low retention due to its low surface area (20-30m 2/g). The method enables the introduction of a thin, homogeneous layer of Al(III) on silica to serve as catalytic sites for carbon deposition without damaging the silica's native pore structure. Subsequent carbon deposition by chemical vapor deposition resulted in chromatographically useful carbon phases as shown by good efficiencies and higher retentivity relative to C/ZrO 2. Herein, we use the above method to develop a novel carbon phase on superficially porous silica (2.7μm). This small, new form of silica offers better mass transfer properties and higher efficiency with lower column back pressures as compared to sub 2μm silica packings, which should make it attractive for use as the second dimension in fast two-dimensional LC (LC×LC). After carbon deposition, several studies were conducted to compare the new packing with C/ZrO 2. Consistent with work on 5μm fully porous silica, the metal cladding did not cause pore blockage. Subsequent carbon deposition maintained the good mass transfer properties as shown by the effect of velocity on HETP. The new packing exhibits efficiencies up to ∼5.6-fold higher than C/ZrO 2 for polar compounds. We observed similar chromatographic selectivity for all carbon phases tested. Consequently, the use of the new packing as the second dimension in fast LC×LC improved the peak capacity of fast LC×LC. The new material gave loading capacities similar to C/ZrO 2, which is rather as expected based on the surface areas of the two phases. © 2012 Elsevier B.V. Source

Huang Y.,University of Minnesota | Gu H.,University of Minnesota | Filgueira M.,University of Minnesota | Filgueira M.,University Nacl La Plata | Carr P.W.,University of Minnesota
Journal of Chromatography A

The experimental effects of sampling time on the resolving power of on-line LC×LC were investigated. The first dimension gradient time (1tg) and sampling time (ts) were systematically varied (1tg=5, 12, 24 and 49min; ts=6, 12, 21 and 40s). The resolving power of on-line LC×LC was evaluated in terms of two metrics namely the numbers of observed peaks and the effective 2D peak capacities obtained in separations of extracts of maize seeds. The maximum effective peak capacity and number of observed peaks of LC×LC were achieved at sampling times between 12 and 21s, at all first dimension gradient times. In addition, both metrics showed that the " crossover" time at which fully optimized 1DLC and LC×LC have equal resolving power varied somewhat with sampling time but is only about 5min for sampling times of 12 and 21s. The longest crossover time was obtained when the sampling time was 6s. Furthermore, increasing the first dimension gradient time gave large improvements in the resolving power of LC×LC relative to 1DLC. Finally, comparisons of the corrected and effective 2D peak capacities as well as the number of peaks observed showed that the impact of the coverage factor is quite significant. © 2011 Elsevier B.V. Source

Filgueira M.R.,University of Minnesota | Filgueira M.R.,University Nacl La Plata | Huang Y.,University of Minnesota | Witt K.,Hewlett - Packard | And 2 more authors.
Analytical Chemistry

The use of flow splitters between the two dimensions in online comprehensive two-dimensional (2D) liquid chromatography (LC × LC) has not received very much attention, in comparison with their use in 2D gas chromatography (GC × GC), where they are quite common. In principle, splitting the flow after the first dimension column and performing online 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 perform 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 through the 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, 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. © 2011 American Chemical Society. Source

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