Showing papers by "Purnendu K. Dasgupta published in 2021"

Gradient nanopump based suppressed ion chromatography using PEEK open tubular columns

Abstract: The progress of open tubular suppressed ion chromatography is reviewed from a broad perspective Then a suppressed open tubular ion chromatography system, composed mostly of commercial components, is described: A splitless gradient-capable nanopump providing eluent delivery in the 10–1000 nL/min regime, a 7-nL injector integral to the pump, an anion exchange column based on a 25 µm id poly(ether ether ketone) (PEEK) capillary, and an on-column admittance detector The membrane suppressor was custom fabricated Good gradient separation of seven common anions in 9 min is demonstrated using a manually prepared hydroxide eluent

Automated Programmable Generation of Broad pH Range Volatile Ionic Eluents for Liquid Chromatography.

Abstract: Many of the universal detectors in liquid chromatography, including mass spectrometry, must completely volatilize the chromatographic eluent first before further processing and detection of the analytes. A basic requirement is that the eluent does not contain a nonvolatile dissolved component. However, separation of biomolecules must be conducted in mostly aqueous media of compatible pH and ionic strength if their biological activity must survive the separation process. Combinations of ammonia with acetic and formic acids are commonly used as eluent for this purpose but generally maximum concentrations that can be tolerated are relatively low. Further, buffering is good only over a limited pH range. We describe a system where the eluent is generated in an automated pressure-programmed manner from high-purity gaseous NH3 and CO2 through gas-permeable membrane devices. This can be aided by the prior presence of formic/acetic acids in the mobile phase to extend the attainable low pH limit. We outline the fundamental pH, ionic strength, and buffer intensity considerations and demonstrate the application of such eluents in the separation of amino acids, proteins, and monoclonal antibodies. We also demonstrate the use of dissolved CO2 as an ion-pairing agent in the separation of chiral amines.

Moldable capillary suppressor for open tubular ion chromatography based on a polymeric ion exchanger.

Abstract: We successfully fabricated 45 μm bore microchannels in PVA-Poly(styrenesulfonate) cation exchange polymers. by casting aqueous prepolymer mixtures around fine tungsten wire mandrels, curing, crosslinking by thermal annealing, and subsequently removing the microwire. This was then used as a chemically regenerated microsuppressor (with a cleaner MS background than its commercial macro counterparts) for open tubular ion chromatography, with an integrated tubular conductivity cell, tested to backpressures up to 600 psi. The overall system permits detection limits for common inorganic ions in the low μg/L levels with a 4-nL injection, isocratic elution and regeneration with poly(styrene sulfonic acid).

Shape-Based Peak Identity Confirmation in Liquid Chromatography.

Abstract: Chromatography is used to separate analytes in a mixture. In the absence of a detector providing analyte-specific information, the retention time is used to identify the analyte, typically by comparing the retention time of the unknown with that of a standard. This is the simplest of identification routines, but it remains the most widely used. The challenge is that analyte retention times can and do shift; sole reliance on retention time for identification is not prudent. Retention time is influenced by the total sample concentration, elution of components near the peak of interest, aging of a column, and so on, complicating time window-based identification. We propose a sameness threshold (ST) that is based on numerical comparison of shapes of chromatographic peaks for identification confirmation. We demonstrate shape-based identification confirmation or lack thereof of an unconfirmed peak by comparison with a shape library of standards. In numerous cases we look at, only one analyte in the shape library fits the putative identity. ST can be based on r2, the commonly used coefficient of determination used in regression analysis, or on an "index of width mismatch" that compares the widths of the peaks throughout the available height range.