Preparative-scale Liquid Chromatography Research Articles

Characterization of the impact of chlorogenic acids on tactile perception in coffee through an inverse effect on mouthcoating sensation

Coffee “body” is acknowledged by coffee industry professionals to be an attribute which contributes meaningfully to overall coffee quality and is defined as the collective tactile sensation imparted by the beverage. Currently, there is limited knowledge of the chemical compounds that contribute to tactile attributes in coffee. In the present work, coffee body was determined to be comprised of 4 sub-attributes including mouthcoating, astringency, chalkiness, and thickness and the specific constituents contributing to the tactile sensation of mouthcoating were further pursued using sensory-guided fractionation via preparative-scale liquid chromatography. Signal detection-based sensory methodologies were employed to characterize the sensory effects elicited by selected compounds in water and coffee matrices. Two chlorogenic acids, 3-O-caffeoylquinic acid (3-CQA) and 4-O-caffeoylquinic acid (4-CQA), were observed to impart subtle but significantly perceptible mouthcoating effects in water and/or coffee. Counterintuitively, sensory perception was inversely related to compound concentration. Complex receptor-ligand interactions or salivary lubrication dynamics are discussed as two potential mechanisms to explain this inverse relationship. Taken together, the outcomes of the present study (1) provide new targets for coffee tactile sensation optimization and modulation, (2) identify a novel dimension of sensory impact for two compounds of the chlorogenic acid family, and (3) present a need for deeper investigation into 3-CQA and 4-CQA mechanisms of sensation.

Chromatographic separation of saccharide mixtures on zeolites

The separation of glucose and fructose by preparative scale liquid chromatography has been accomplished on granulated pellets of a hydrophobic, dealuminated Y-zeolite without Ca++ ion complexation. The separation efficiency is similar to that of a hydrophilic Ca++ exchanged Y-zeolite and also comparable with the common separation on Ca++ loaded ion-exchange resins. In contrast to the hydrophilic zeolites the hydrophobic ones are shown to separate disaccharides. The isolation of isomaltose from a mixture of isomalto-oligosaccharides, and the isolation of inulobiose from fructo-oligosaccharides are presented, also the separation of an industrial molasses of the crystallization of isomaltulose. The addition of small amounts of ethanol to the aqueous eluent not only shortens the retention time but results in more favorable sharpness of the peaks.

Chromatography of mono- and disaccharides on granulated pellets of hydrophobic zeolites

The chromatographic response of sugars at granulated zeolite pellets in preparative scale liquid chromatography is analyzed with respect to the distribution equilibrium and mass transfer. In contrast to hydrophilic FAU type zeolites their hydrophobic dealuminated counterpart, used here, can separate disaccharides the retention of which can strongly exceed those of the monosugars. The retention is correlated with data of batch adsorption studies from the literature. Whereas the retention decreases with increasing temperature, the peak sharpness shows the opposite trend. The effective mass resistance is calculated for a series of mono- and disaccharides. It increases with the capacity factor. The diffusion coefficient of the trehalulose disaccharide is restricted by a factor of about 2 in the macropores and by a factor of more than 104 in the micropores.

Identification of Unknown Compound in Apocynum cannabinum by High Resolution Mass Spectrometry (HRMS) and 600 MHz NMR

High resolution mass spectrometry (HRMS) was able to determine that the m/z of the [M+H]+ ion formed by an unknown compound that was purified by preparative scale liquid chromatography (LC) was 137.05966. This was done rapidly and easily by direct infusion. Neither a column nor chromatography was needed. This is within 0.4 ppm of the mass calculated by ThermoFisher’s exact mass calculator for the protonated version of C8H8O2. Based on this, the compound could have been 2’-, 3’- or 4’-hydroxyacetophenone or 2’-, 3’- or 4’-methoxybenzaldehyde. However, 1H- and 13C-NMR spectra of the isolated compound showed that it was 4’-hydroxyacetophenone, without needing a standard. Neither mass spectrometry (MS) nor NMR could have identified this compound by itself. Finally, HRMS was also able to verify that another peak isolated by preparative scale LC was apocynin, or 4’-hydroxy-3’-methoxyacetophenone.https://doi.org/10.21423/jrs-v04n03p014 (DOI assigned 5/31/2019)

Preparative-Scale Liquid Chromatography and Characterization of Large Fullerenes Generated in Low-Pressure Benzene Flames

Soot generated in a premixed benzene/oxygen/argon low-pressure flame was extracted sequentially with dichloromethane, toluene, CS2 and 1,2-dichlorobenzene. Quantifications by HPLC were performed for C60, C70, C76, C78, and C84 by means of external standards using a monomeric octadecylsilica (ODS) bonded stationary phase and acetonitrile/toluene (55:45) as a mobile phase. Toluene was found to be the most suitable solvent for all the cases studied here. After the partial removal of smaller fullerenes with preparative HPLC, the presence of fullerenes up to C104 was shown by means of HPLC−APCI−MS using a heated nebulizer interface. The macroscopic isolation of C86, C90, C92, C94, and C96 was performed using a two-step HPLC separation with a 2-(1-pyrenyl)ethylsilica stationary phase and toluene as eluent preceded by the partial removal of C60 and C70 with a poly(divinylbenzene) HPLC column. UV−vis spectra were measured, and the presence of a C90 adduct could be discerned. Based on the results of this work, the...

Bias and nonlinearity of ultraviolet calibration curves measured using diode-array detectors

Models for the dependence of diode-array UV chromatographic detector response on bandpass and on the shape of the absorbing sample's spectrum are presented. The equations derived comprise terms describing two sources of non-ideal response due to the polychromatic nature of the detected radiation. The bias, or deviation at low concentrations of the measured absorbance from the ideal, zero-bandwidth value, increases roughly as the product of the spectrum's local second derivative and the square of the bandwidth. Calibration curve nonlinearity at higher concentrations, present for monochromator-based detectors and transmittance-averaging diode-array detectors, is described quantitatively. These equations confirm that the calibration curves always bend downward when the sample's absorption spectrum varies at all within the bandpass. A distinction is drawn between transmittance-averaging and absorbance-averaging diode-array detectors. Experimental results illustrate the types of bias and nonlinearity seen in each class at the high concentrations of interest to preparative-scale liquid chromatography and quality-control applications.

Computer simulation of the separation of a two-component mixture in preparative-scale liquid chromatography

A model describing the propagation of a binary mixture at finite concentration in nonlinear liquid chromatography is discussed. This model consists of two mass balance equations, one for each solute. A finite difference method is used to derive numerical solutions of this set of nonlinear partial differential equation with boundary conditions corresponding to the elution of large concentration bands. These solutions describe the shape of the elution profiles of partially resolved compounds. Although the model used corresponds to ideal chromatography (constant equilibrium between the mobile and stationary phase, i.e., infinite column efficiency), it is possible to simulate the smoothing effect of a finite column efficiency by properly selecting the differential space element in the numerical integration. The numerical solutions appear to converge satisfactorily toward a stable solution of the system of equations provided the Courant-Friedrichs-Lewy (CFL) criterion is met in the choice of the integration parameters. The profiles obtained are very realistic and fare quite well with experimental results retrieved from the literature. Some of the results obtained are discussed in detail.

Simple Considerations on Column Design in Preparative-Scale Liquid Chromatography

Abstract This paper discusses some simple considerations on the design of preparative columns (particle size and column length and diameter). It is shown that the loadability of a column does not depend on the size of the particles for a given efficiency. In order to obtain the maximum efficacity from the pumping system, the design of the column must take into account the characteristics of the pumping system, particularly the flow rate. It is shown that a convenient particle size is in the range 10 to 20 μm. Small particles are associated with shorter and bulkier columns than large particles, while at the same time giving less back pressure (in order to generate a given plate number at a given flow rate). The larger the flow rate generated by the pumping system, the smaller must be the particles.

Effects of large sample loads on column lifetime in preparative-scale liquid chromatography

In preparative-scale liquid chromatography of proteins, the use of high sample concentration and large sample mass may result in irreversible adsorption to the support surface. This can change the stationary phase characteristics, reduce the capacity, shorten the column lifetime and diminish the economic viability of a particular separation method. Column recycling and regeneration can influence the throughput (mass purified per time unit) and selectivity, and affect the reproducibility. The effects of large sample loads on column lifetime and performance were evaluated for three strong anion-exchange columns: (1) a silica support with a quaternized polyethyleneimine (PEI) coating, (2) a polymeric support with an adsorbed PEI coating which also was quaternized, and (3) a polymeric support with a proprietary quaternary amine stationary phase. The column capacity for proteins was measured by frontal chromatography and monitored as a function of cycle number. The column lifetime was determined by examining chromatographic properties subsequent to the frontal chromatography. The change in protein binding capacity was then compared to the change in nitrate binding capacity. The column performance was evaluated under analytical conditions by measuring the change in resolution of standard protein mixtures.

1H NMR and 13C NMR spectra of stereoisomers of the methyl methacrylate “dimer”: Dimethyl 2‐methoxymethyl‐2,4‐dimethylglutarate

AbstractMethyl methacrylate oligomers were prepared through anionic oligomerization initiated with sodium methoxide. The pure dimer, isolated by careful fractional distillation, was subjected further to a preparativescale liquid chromatography and separated into its constituent stereoisomers. 1H NMR and 13C NMR spectra of the stereoisomers were studied in various organic solvents at different temperatures. An a priori assignment of the resonance patterns was attained successfully and the fine structures of the spectra were characterized with respect to the stereospecific features of the chemical structure of the stereoisomers.

Some aspects of preparative-scale liquid chromatography

The various factors that affect the loading capacity of a column are considered and it is shown that large-scale separations can only be achieved at the individual or combined expense of speed, scope and solvent consumption. An equation that predicts the maximum sample volume that can be placed on a column without impairing resolution is derived and experimentally verified. It is shown that, when the sample volume is progressively increased, the fronts of all peaks remain at constant retention while the retention of the rears of the peaks progressively increases. Conversely, under circumstances of mass overload the rears and fronts of all peaks tend to move toward positions of less retention, the maximum effect occurring with the major component in the mixture.

Tricarbonylchromium complexes of some substituted 9,10-dihydro-9,10-o-benzenoanthracenes

Tricarbonylchromium complexes of 9,10-dihydro-l,4-dimethoxy-9,10-o-benzenoanthracene and 9,10-dihydro-l,4-dimethyl-9,10-o-benzenoanthracene have been prepared and characterized. Under the given experimental conditions, the dimethoxy ligand forms two isomeric complexes. These have been separated by both analytical and preparative scale liquid chromatography. Structures have been tentatively assigned on the basis of experiments with the NMR shift reagent EuFod3. The methyl substituted ligand forms three isomeric complexes.