Showing papers by "Purnendu K. Dasgupta published in 2018"
TL;DR: A low-bleed HILIC stationary phase, PVA-coated benzylthioethyl-silica, where the benzyl groups shield the silica from water erosion, while the thiol group provides sufficient local polarity for PVA to wet the material.
Abstract: Bleeding of hydrophilic interaction liquid chromatographic (HILIC) phases is a major problem. A hydrophobic silica surface exhibits low bleeding but does not behave as a HILIC phase. A hydrophilic coating, such as that of poly(vinyl alcohol) (PVA) on a hydrophobic particle should result in a low-bleed hydrophilic phase. However, a silica particle functionalized in a hydrophobic manner is not wetted by PVA and cannot be coated with it. Coating with PVA becomes possible if one region of the hydrophobic functionality is polar. We describe a low-bleed HILIC stationary phase, PVA-coated benzylthioethyl-silica. The benzyl groups shield the silica from water erosion, while the thiol group provides sufficient local polarity for PVA to wet the material. The new stationary phase demonstrated good chromatographic performance and typical HILIC retention behavior. The measured silica concentration in the effluent was ∼80-fold lower than that from a bare silica column. The new stationary phase exhibited a lower background level, lower background noise, and lower background drift under gradient conditions than benchmark commercial columns.
27 citations
TL;DR: The temporal peak variance (σt,obs2), which increases as the flow rate through the detector decreases, is found to be well-described as a quadratic function of 1/F.
Abstract: Following a brief overview of the emergence of absorbance detection in liquid chromatography, we focus on the dispersion caused by the absorbance measurement cell and its inlet. A simple experiment is proposed wherein chromatographic flow and conditions are held constant but a variable portion of the column effluent is directed into the detector. The temporal peak variance (σt,obs2), which increases as the flow rate (F) through the detector decreases, is found to be well-described as a quadratic function of 1/F. This allows the extrapolation of the results to zero residence time in the detector and thence the determination of the true variance of the peak prior to the detector (this includes contribution of all preceding components). This general approach should be equally applicable to detection systems other than absorbance. We also experiment where the inlet/outlet system remains the same but the path length is varied. This allows one to assess the individual contributions of the cell itself and the in...
12 citations
TL;DR: All such contact conductance results were linear with concentration, and initial results suggest that attainable LODs will be competitive with those from benchtop ICs.
Abstract: Admittance detection, more commonly called capacitively coupled contactless conductivity detection, is widely used. While the true conductance of a solution is linear with concentration up to ∼1 mequiv/L, the admittance signal is nonlinear. In small-bore capillaries and highly resistive solutions, such as in suppressed open tubular ion chromatography (SOTIC), the admittance signal is exponentially related to concentration. Solution contact conductivity detection is common in microfluidics, but no true conductivity measurement efforts have been made with conventional capillaries in the last two decades. We examine five solution contact cell geometries: (A) wire/disk electrodes perpendicular to the flow direction, (B) annular tubular electrodes facing the flow (that exits through the center tube), (C) ring-disk electrodes facing the flow that exits through the annulus, (D) coplanar parallel wire/disk electrodes facing the flow that exits around the electrodes, and (E) planar electrodes separated by a thin i...
10 citations
TL;DR: A parameter γiex is proposed, which is the ion exchange capacity of a column (packed or open tubular) per unit liquid volume present in the column (including accessible volume within pores) and it is shown that the retention factor for any given ion is directly related to γIEx.
9 citations
TL;DR: In a pooled standard deviation based t-test for the data on 8 columns, at the 95% confidence level, CEX capacity differed significantly between two halves of a column, but AEX capacity of AEX columns prepared by coating the same CEX columns with AEX latex did not.
7 citations
TL;DR: Comparing batch experiments in which samples were not photodigested at all or thermally digested off-line for an extended period indicated no statistically significant difference in the results, which agrees with early theoretical and experimental work.
5 citations
Patent•
08 Mar 2018TL;DR: An electrodialytic device for ion chromatography, including aspects functioning as an eluent suppressor and aspects serving as a generator, is described in this paper, where a monolithic block of ionomeric polymer material having (1) a first channel with an inlet port, an outlet port, and an active length of exposed polymer material disposed therebetween, (2) a second channel having inlet ports, outlet ports, and a long exposed polymer length disposed there between, and (3) the first and second at-least-partially exposed
Abstract: An electrodialytic device for ion chromatography, including aspects functioning as an eluent suppressor device and aspects functioning as an eluent generator device. In general, the device includes a monolithic block of ionomeric polymer material having (1) a first channel with an inlet port, an outlet port, and an active length of exposed polymer material disposed therebetween, (2) a second channel having an inlet port, an outlet port, and an active length of exposed polymer material disposed therebetween, (3) a first and second at-least-partially exposed electrodes positioned in electrical communication with the second channel, with the second electrode disposed, at least in part, across the second channel from the first electrode. A current flowing between the electrodes will drive an electrodialytic migration of ions between the active lengths, from an eluent stream in the case of a suppression device or into an eluent stream in the case of a generator device.
1 citations