Number Of Stationary Phases Research Articles

Competition for resources in an exclusion model with biased lane-changing mechanism.

The motivation for the proposed work is drawn from the attachment-detachment observed in biological and physical transport processes that entail finite resources. We investigate the influence of limited particle availability on particle dynamics within two parallel totally asymmetric simple exclusion lanes, with one lane incorporating only particle detachment and the other considering particle attachment. We establish a theoretical framework by employing vertical mean-field theory in conjunction with singular perturbation technique. The analytical findings are supported by numerical and stochastic validation using a finite-difference scheme and the Gillespie algorithm. By utilizing these approaches, we scrutinize various stationary properties, including particle densities, phase boundaries, and particle currents for both lanes. Our analysis reveals that the complexity of the phase diagram exhibits a nonmonotonic trend in the number of stationary phases as the particle count increases. Each phase diagram is constructed with respect to the intrinsic boundary parameters, illustrating both bulk and surface transitions occurring within the lanes. The interplay between finite resources and coupling mechanisms gives rise to two phases involving upward shock in one of the lanes, while two phases exhibit synchronized downward shock in both lanes. Finally, we delve into shock dynamics to comprehend critical phase transitions occurring in the system.

Improving the chromatographic selectivity of β-lactam residue analysis in milk using phenyl-column chemistry prior to detection by tandem mass spectrometry.

Analyte isobaric interferences can limit the development of a comprehensive analytical method for the quantitative liquid chromatography-tandem mass spectrometry profiling of an important cohort of veterinary drugs. In this work, a selective chromatographic separation was developed for the analysis of 32 β-lactam antibiotic residues (12 penicillins, 14 cephalosporins, five carbapenems and faropenem) in milk samples. A range of analytical columns with different stationary phases and mobile phases were evaluated for retention and separation of the β-lactam compounds. Results showed that, among the columns tested, only phenyl-hexyl could adequately separate ampicillin from cephalexin and amoxicillin from cefadroxil, which had shown isobaric interferences on a number of stationary phases. Chromatography was performed using a water/acetonitrile binary gradient with formic acid and ammonium acetate. The β-lactam residues were extracted from the milk samples using a water:acetonitrile solution and purified by C18 dispersive solid-phase extraction (d-SPE) clean-up, followed by concentration under nitrogen and ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) determination. Analytes were monitored in positive electrospray ionisation mode (ESI(+)). Possible interfering matrix effects were overcome by using 13 internal standards. The method was fully validated according to 2002/657/EC guidelines, showing satisfactory performance characteristics. Under within-laboratory reproducibility conditions, trueness and precision ranged from 91 to 130% and from 1.4 to 38.6%, respectively. Decision limits (CCα) were in the range 2.1-133μgkg-1. Limits of detection (LODs) and quantitation (LOQs) ranged between 0.0090 and 1.5μgkg-1 and from 0.030 to 5.0μgkg-1, respectively.

Effect of interactions for one-dimensional asymmetric exclusion processes under periodic and bath-adapted coupling environment

Stimulated by the effect of the nearest neighbor interactions in vehicular traffic and motor proteins, we study a 1D driven lattice gas model, in which the nearest neighbor particle interactions are taken in accordance with the thermodynamic concepts. The non-equilibrium steady-state properties of the system are analyzed under both open and periodic boundary conditions using a combination of cluster mean-field analysis and Monte Carlo simulations. Interestingly, the fundamental diagram of current versus density shows a complex behavior with a unimodal dependence for attractions and weak repulsions that turns into the bimodal behavior for stronger repulsive interactions. Specific details of system-reservoir coupling for the open system have a strong effect on the stationary phases. We produce the steady-state phase diagrams for the bulk-adapted coupling to the reservoir using the minimum and maximum current principles. The strength and nature of interaction energy has a striking influence on the number of stationary phases. We observe that interactions lead to correlations having a strong impact on the system dynamical properties. The correlation between any two sites decays exponentially as the distance between the sites increases. Moreover, they are found to be short-range for repulsions and long-range for attractions. Our results also suggest that repulsions and attractions asymmetrically modify the dynamics of interacting particles in exclusion processes.

Algebraic conditions, in terms of the solvent partition constants, for the separation of chemical classes by gas–liquid chromatography

ABSTRACTThe interdependence between the solvation Gibbs energy of several functional groups and the solvent partition coefficients was studied, starting from gas chromatographic data. Single-parameter relationships were derived for the –OH, -CHO, -CO, -O-,-COO (acetate), -COO (methyl ester)-, and -CN group increments. The obtained equations were found to be temperature independent, and could be successfully used for the evaluation of 19 stationary phases with respect to certain separation questions. The selectivity problem was converted into an inequality system. The graphical solution of such a system provides an image of the separation abilities of a sorbent material with respect to a given pair of solutes, and allows an efficient comparison of a great number of stationary phases. The graphs are also illustrative for the temperature effect on the selectivity features.

Dispersed Mobile-Phase Countercurrent Chromatography

Countercurrent distribution based on liquid–liquid partition is a powerful separation method with minimal incurrence of loss of solutes, but its industrial application has been limited by cumbersome shifting of immiscible solvents. Although centrifugation has been employed to facilitate equilibration between phases, process scaling-up remains difficult. In this study, a dispersed mobile-phase countercurrent chromatography (DMCC) method has been developed to adapt the countercurrent distribution principle to a continuous column chromatography format. Continuous solute exchange between two immiscible phases within a series of separation columns is achieved by mechanical dispersion of an influx of mobile phase into an upward stream of small droplets travelling through the columns filled with stationary phase. The diameter, length, and number of columns, and the number of stationary phases employed in the different columns can be varied to match the requisite scale and resolution of operation. Illustrations of DMCC were provided by examples of solute separations where the fractionated solutes could be collected either from the eluate of the series of columns, or from drainage of the stationary phases in the individual columns at the end of a chromatographic run.

Orthogonal screening system of columns for supercritical fluid chromatography

The application of supercritical fluid chromatography is expanding nowadays, particularly in the pharmaceutical industry and for natural extracts. In order to select appropriate columns from the continuously increasing number of potentially suitable ones, a test that evaluates stationary phases properties, based on the solvation parameter model, was performed earlier. In this study, it is investigated whether the number of stationary phases can be reduced to an optimized set with only highly orthogonal systems. Such a set of orthogonal chromatographic systems having different selectivities may provide the initial separation for method development. Moreover, it was considered important to include systems with good overall separation performance in our final set. Thus the columns are also selected based on their ability to provide sharp and symmetric peaks. An example application based on the analysis of seven sunscreen molecules is presented as a validation of the suggested column set.

Reversed-phase liquid chromatography column testing and classification: Physicochemical interpretation based on a wide set of stationary phases

The high number of stationary phases commercially available for liquid chromatography makes the choice of the analyst a real headache. In order to provide a tool to carry out this choice on objective basis, the present work proposes interpretations of the column classifications obtained, thanks to a previously described testing procedure. The meaning of principal components was attributed to crossing over information carried by loading plots and groups revealed by hierarchical cluster analysis (HCA) on the corresponding score plots. At high solvent ratio, the retention seemed to be governed by enthalpy, whereas at low solvent ratio, entropic phenomena were predominating. Finally, the behavior of known families of RPLC columns was studied giving rise either to homogeneous groups like polar embedded grafts columns or to scattered families like Aqua type columns.

Immobilized metal-ion affinity chromatography.

Immobilized metal-ion affinity chromatography (IMAC) (1–4) is also referred to as metal chelate chromatography, metal-ion interaction chromatography, and ligand-exchange chromatography. We view this affinity-separation technique as an intermediate between highly specific, high-affinity bioaffinity separation methods, and wider-spectrum, low-specificity adsorption methods, such as ion exchange. The IMAC stationary phases are designed to chelate certain metal ions that have selectivity for specific groups (e.g., His residues) in peptides (e.g., refs. 5–9) and on protein surfaces (10–15). The number of stationary phases that can be synthesized for efficient chelation of metal ions is unlimited, but the critical consideration is that there must be enough exposure of the metal ion to interact with the proteins, preferably in a biospecific manner. Several examples are presented in Fig. 1. The challenge to produce new immobilized chelating groups, including protein surface metal-binding domains (17,18) is being explored continuously 19). A common fusion protein is the hexahistidine tag for purification (20). Table 1 presents a list of published procedures for the synthesis and use of stationary phases with immobilized chelating groups. This is by no means exhaustive and is intended only to give an idea of the scope and versatility of IMAC.

Immobilized metal ion affinity chromatography.

Immobilized metal ion affinity chromatography (IMAC) (1,2) is also referred to as metal chelate chromatography, metal ion interaction chromatography, and ligand-exchange chromatography. We view this affinity separation technique as an intermediate between highly specific, high-affinity bioaffinity separation methods, and wider spectrum, low-specificity adsorption methods, such as ion exchange. The IMAC stationary phases are designed to chelate certain metal ions that have selectivity for specific groups (e.g., His residues) in peptides (e.g., 3-7) and on protein surfaces (8-13). The number of stationary phases that can be synthesized for efficient chelation of metal ions is unlimited, but the critical consideration is that there must be enough exposure of the metal ion to interact with the proteins, preferably in a biospecific manner. Several examples are presented in Fig. 1. The challenge to produce new immobilized chelating groups, including protein surface metal-binding domains (14,15) is being explored continuously. Table 1 presents a list of published procedures for the synthesis and use of stationary phases with immobilized chelating groups. This is by no means exhaustive, and is intended only to give an idea of the scope and versatility of IMAC. Fig. 1 Schematic illustration of several types of immobilized metal-chelating groups, including, iminodiacetate (IDA), tris(carboxymethyl) ethylenediamine (TED), and the metal-binding peptides (GHHPH)(n)G (where n = 1,2,3, and 5) (14,15). Table 1 Immobilized Chelating Groups and Metal Ions Used for Immobilized Metal Ion Affinity Chromatography Chelating group Suitable metal ions Reference Commercial source Immodiacetate Transitional1,2 Pharmacia LKB Pierce Sigma Boehringer Mannheim TosoHaas 2-Hydroxy-3[N-(2- pyrtdylmethyl) glycme]propyl Transitional3 Not available ?-Alky1 mtrilo triacetic acid Transitional4 Not available Carboxymethylated asparhc acid Ca(II)13 Not available Tris (carboxy- methyl) ethylene Diamme Transitional2 Not available (GHHPH)(n)G* Transitional14,15 Not available *Letters represent standard l-letter amino acid codes (C = glycine, H = histidine, P = proline) The number of internal repeat units is given by n(n= 1, 2, 3, and 5).

Immobilized metal ion affinity chromatography.

This article describes the technique of immobilized metal ion affinity chromatography (IMAC). The IMAC stationary phases are designed to chelate certain metal ions that have selectivity for specific groups in peptides and on protein surfaces. The number of stationary phases that can be synthesized for efficient chelation of metal ions is unlimited, but the critical consideration is that there is enough exposure of the metal ion to interact with the proteins, preferably in a biospecific manner. The versatility of IMAC is one of its greatest assets. An important contribution to the correct use of IMAC for protein purification is a simplified presentation of the various sample elution procedures.

Computer method for the selection of a suitable stationary phase in gas chromatography

A selection of stationary phases is carried out for a gas chromatographic separation of certain hydrocarbon mixtures with help of a computer. For this purpose a suitable catalogue including the relative retention data of substances investigated on a large number of stationary phases and an algorithm of sequence of operations are proposed. The program written in ALGOL algorithmic language points out three stationary phases being the best for the separation of a certain n-component mixture by the criterion Rr, k. Besides the three suitable phases the conditions for a given separation are also pointed out.

A satisfactory glc column for the determination of epoxyoleic acid in seed oils

AbstractA number of stationary phases were evaluated for their suitability for the analysis of methyl epoxyoleate. Ethylene glycol succinate polyester, Carbowax 20M and Apiezon 舠L螇 all showed evidence of decomposition or alteration of the compound and also a loss of area on the chromatogram. A silicone rubber (SE‐30) column did not exhibit this tendency and was found satisfactory for the determination of methyl epoxyoleate.A limitation of the use of an SE‐30 column in the analysis of mixed esters is its inability to separate effectively fatty acid esters of the same chain length. However, by chromatographing the sample on a polyester column as well as on an SE‐30 column, all of the fatty acid components of the oil can be determined quantitatively.