Similar Retention Characteristics Research Articles

Recycling HPLC for the Isolation of Styryl Lactone from Goniothalamus lanceolatus Miq

A unique plant from the rainforest of Sarawak, Malaysia, Goniothalamus lanceolatus Miq., was chosen for a phytochemical study based on its ethnomedicinal characteristics amongst the locals. Isolation and purification of a minor compound exhibiting similar retention characteristics was made possible by using preparative Recycling HPLC. Due to a recycle valve in the HPLC system, this method enables the unresolved peaks to recirculate into the column repeatedly until the peaks were successfully separated as pure entity. During the recycling process, solvent consumption is not needed. Recycling HPLC expediates the isolation and purification of complex mixtures in such a sustainable way. One styryl lactone was successfully isolated and identified as 6S,7S,8S-(-)-goniodiol.

2-Bit/Cell Operation of Hf0.5Zr0.5O2Based FeFET Memory Devices for NAND Applications

The multilevel memory performances of ferroelectric field effect transistor (FeFET) with Hf0.5Zr0.5O2 (HZO) ferroelectric thin film are investigated. First, similar retention characteristics are observed for intermediate and saturated polarization states of HZO ferroelectric thin film, which enables memories for multi-bit data storage. And then, 2-bit/cell operation of HZO-based FeFET is demonstrated utilizing two NAND architecture compatible write schemes of varying program pulse amplitude and width. Low cycle-to-cycle variability, long retention to extrapolation of 10 years at 85°C, and endurance of 500 cycles are achieved for the both schemes. Moreover, the mechanism for multilevel memory operations of the FeFET is illustrated based on the polarization switching dynamics of HZO ferroelectric thin film.

Comparative Study on Charge Trapping Induced <inline-formula> <tex-math notation="LaTeX">${V}_{\textsf{th}}$ </tex-math> </inline-formula> Shift for GaN-Based MOS-HEMTs With and Without Thermal Annealing Treatment

In this paper, threshold voltage ( ${V}_{{\textsf {th}}}$ ) shift in Al2O3/ AlGaN/GaN metal–oxide–semiconductor high-electron-mobility transistors (MOS-HEMTs) induced by charge trapping and the impacts of postmetallization annealing (PMA) were studied. In addition to the transient voltage shift caused by interface trapping effect, retentive voltage shift was also observed which was attributed to border traps with very large emission time constant ( $\tau _{e}$ ). PMA has little influence on the transient ${V}_{\textsf {th}}$ shift which is related to interface traps with $\textsf {18}~\textsf {s} s, while the total interface traps with $\textsf {4}~\textsf {s} s are reduced by PMA from $\textsf {4.03} \times \textsf {10}^{\textsf {12}}\,\,\textsf {cm}^{-\textsf {2}}$ to $\textsf {1.77} \times \textsf {10}^{\textsf {12}}\,\,\textsf {cm}^{-\textsf {2}}$ . Interface trapping dominates at low program voltage ( ${V}_{p}$ ), while border trapping becomes remarkable with ${V}_{p}$ above the critical level. Due to the cumulative border trapping effect, an increase in program voltage by per volt causes an additional retentive voltage shift by about $\textsf {1}$ V. PMA leads to an increase in critical ${V}_{p}$ from 5 to 7 V, which therefore results in a decrease in the density of total accessible border traps from $\textsf {1.99} \times \textsf {10}^{\textsf {13}}\,\,\textsf {cm}^{-\textsf {2}}$ to $9.25\times \textsf {10}^{\textsf {12}}$ cm−2 with ${V}_{p}$ up to 12 V. The border trapping for both devices with and without PMA shows similar retention characteristics, with ${V}_{{\textsf {th}}}$ recovery as small as 1.2 V after one week.

Recycle HPLC: A Powerful Tool for the Purification of Natural Products

Natural compounds occur as various isomeric or closely related structures in biological matrices. These compounds are difficult to separate from the complex mixtures, and hence, the need for effective and innovative separation techniques arises. Recycle HPLC allows the recycling of sample, in part or full, and increases the separation efficiency of the process while keeping the peak dispersion to a minimum. Recycling in an HPLC system has been used in the isolation and purification of different types of natural products including enantiomers, diastereomers, epimers, positional isomers, and structurally related or unrelated compounds having similar retention characteristics. The present paper overviews the development of instrumentation and setup of recycle HPLC and its applications in the separation of natural products.

Prostate Cell Membrane Chromatography–LC/MS Method for Screening α1A-Adrenoceptor Antagonists from Lotus Plumule

The α1A-adrenoceptor (α1A-AR) plays an important role in drug discovery and development. An online analytical method coupling prostate cell membrane chromatography (CMC) with high-performance liquid chromatography/mass spectrometry (LC/MS) was established to screen α1A-AR antagonists in traditional Chinese medicines (TCMs). The prostate cell membrane stationary phase (CMSP) was prepared by immobilizing the prostate cell membrane onto the surface of the silica carrier. The surface and chromatographic characteristics of the prostate CMSP were studied using tamsulosin as a model molecule. The retained fractions from the prostate CMC were analyzed by transferring them to an LC/MS system through a 10-port switch valve. The active component, which could act on the prostate cell membrane and receptor on it (such as α1A-AR), was determined using a displacement experiment. The results indicated that liensinine, isoliensine, and neferine from Lotus Plumule exhibited similar retention characteristics to the control drug tamsulosin when utilizing the prostate CMC model. This new prostate CMC–LC/MS method is applicable for screening α1A-AR antagonists from TCMs such as Lotus Plumule and could be employed as a drug discovery tool for natural medicinal herbs.

Separation of Dietary Folates by Gradient Reversed-Phase HPLC: Comparison of Alternative and Conventional Silica-Based Stationary Phases

A study of ten silica-based stationary phases and gradient elution conditions to separate dietary folates by reversed-phase HPLC was performed. Alkyl-bonded stationary phases (both conventional and alternative) were found to be the most promising for the separation of different folate monoglutamates in terms of selectivity and peak shape. These phases were better than phenyl-bonded phases which lacked selectivity when separating 10-formyl-folic acid and 5-formyl-tetrahydrofolate. Polar-bonded (cyano) stationary phase showed similar retention characteristics as the conventional alkyl-bonded phases, but ranked below those in terms of peak shape. Overall, alternative stationary phases exhibited slightly higher retention of late-eluted folates and greater retention variability for early-eluting tetrahydrofolate and 5-methyl-tetrahydrofolate. Best selectivity was achieved on alternative polar endcapped Aquasil C18 followed by conventional Synergy MAX C12 and Genesis C18 stationary phases.

Comparison of commercial membranes in nanofiltration of sweet whey

The performance of commercial nanofiltration membranes was studied during concentra- tion and demineralization of sweet whey. The tested membranes were Desal-5 DK, NF45 and Koch SR1. Two different generations of the NF45 membranes were studied. Concentration of whey was made both with a flat-sheet module and in a pilot plant equipped with one spiral wound element. The new generation of the NF45 membrane has comparable retention characteristics with the Desal-5 DK. The Koch SR1 membrane has lower salt and lactose retention than the Desal-5 DK and similar retention characteristics to the older generation of the NF45, which is no longer commercially avail- able. When using the new generation of the NF45 membrane one can expect lower permeate flux and higher retention of salts and lactose than before with the older generation of the NF45 membrane. The highest permeate fluxes of the tested membranes were reached with the Koch SR1 membrane. Con- centration of sweet whey with a flat-sheet module and a spiral wound element resulted in similar con- centrate composition. Therefore, the flat-sheet module may be used when information on product composition is being investigated. The permeate flux was higher with the flat-sheet module than with the spiral wound element. Thus, either the spiral wound module is more prone to concentration polar- ization than the flat-sheet module or one can assume that the whole membrane area of the spiral wound module is not used effectively. Nanofiltration / spiral wound module / flat-sheet module / sweet whey / concentration

Chromatographic behaviour of basic amino compounds on silica and ods-silica using aqueous methanol mobile phases

Summary The effects of the variation of pH, methanol concentration, ionic strength and nature of the ions in aqueous methanol mobile phases on the capacity ratios of amprolium (INN), amylocaine, benzocaine, butacaine (INN) and cocaine using both silica and silica surface-modified by treatment with trichloro(octadecyl)silane (ODS-silica) have been investigated. The differences in retention of the solutes on the two columns are related to the partition coefficients between 2,2,4-trimethylpentane and the mobile phase over the pH range studied. Amprolium, a quaternary ammonium salt, had similar retention characteristics on both silica and ODS-silica when a mobile phase containing 0.05 M ammonium formate was used. The retention mechanisms of the species are complex and involve ion exchange with the proton of a surface silanol site, particularly with amprolium, partition of ion pairs and salting-out effects. Applications of these observations to the analysis of erythromycin (INN) and various toxic diamines are given.