The Effect of Silanol Masking on the Recovery of Picloram and Other Solutes from a Hydrocarbonaceous Pre-analysis Extraction Column

Abstract

The recoveries of picloram, picloram-methylester, hexazinone, benzene, and acetophenone from aqueous samples were studied using a commercially available hydrocarbonaceous pre-analysis extraction cartridge, both with and without tetrabutylammonium hydrogen sulfate (TBAHS) in the eluent. Extraction efficiency was found to be dependent on sample loading volume. The results suggest a mixed mechanism of retention involving both “silanophilic” and “hydrophobic” interactions in the absence of tetrabutylammonium ion. The ability of TBAHS to mask surface silanol groups and/or ion-pair with counterionic solutes is invoked to explain the observations. Chromatograms of the solutes obtained on a C₁₈ bonded analytical column in both the presence and absence of TBAHS are also presented.     

Silanophilic Interaction in the Retention Mechanism of Pharmaceutical Drugs on a Cyanopropyl Bonded Silica Column

Abstract

The mechanism of retention of several pharmaceutical drugs with basic, neutral and acidic properties have been examined on a cyano bonded silica stationary phases (Ultrasphere cyano). Clenbuterol, bromhexine, terphenadine, pirenzepine, astemizol, betamethasone, acetaminophen, indomethacin, diclofenac and nimesulide were chosen for this study. Methanol-phosphate buffer mixtures with low water levels were used as mobile phases. Different pH values and ionic strengths were considered. Under experimental conditions, the chromatographic behavior of basic drugs is more complex than the behavior of acidic and neutral ones. The predominant silanophilic interactions observed for drugs of basic characteristics may become quite useful in optimizing selectivity.     

Analysis of Group Retention Contributions for Peptides Separated by Reversed Phase High Performance Liquid Chromatography

Abstract

Within the framework provided by solvophobic theory, selectivities for unprotected peptides separated on fully porous, microparticulate, chemically bonded alkylsilicas can be ascribed to differences between the effective hydrophobic contact areas of the solutes. Furthermore, this theoretical treatment predicts that retention behaviour differences can be evaluated from topological parameters which accomodate the influence of amino acid side chain and end group contributions in the retention process. With data obtained for 57 peptides, including a variety of peptide hormones, eluted under the same conditions from a μBondapak C₁₈ column, these predictions have been rigorously tested using two methods of numerical analysis. The results provide further evidence that the hydrophobic group retention contributions of the amino acid residues in small peptides have an essentially additive effect on peptide retention with alkylsilicas. Divergences in retention behaviour are interpreted in terms of specific silanophilic and solvation interactions.     

Calibration of Separation and Instrumental Peak Broadening in Sec Coupled with Light Scattering of Simple Polymers

Abstract

A recently developed procedure for calibration of separation and instrumental peak broadening in SEC was used for a comparative study of separation and axial dispersion of polystyrene, poly(methyl methacrylate) and poly(vinylchloride). The influence of the uncertainty in the volume lag between the concentration and LALLS detectors upon peak broadening was investigated and a new procedure for the determination of the lag was proposed. The applicability of the universal calibration concept was tested; all the polymers have been found to match a single universal calibration function. Polystyrene and poly(methyl methacrylate) also coincided very well with respect to the instrumental spreading, but for poly(vinylchloride) spreading was found to be a function of polymer concentration.     

Characterization of Nonionic Polyacrylamides by Aqueous Size Exclusion Chromatography Using a DRI/LALLSP Detector System

Abstract

Herein is reported an experimental investigation of the molecular weight characterization of nonionic polyacrylamides by aqueous SEC with a DRI/LALLSP detector system. Methodology for the use of the DRI/LALLSP detector responses to determine the molecular weight calibration curve and the peak broadening parameter, [sgrave]² (variance of a Gaussian instrumental spreading function) over a wide molecular weight range has been developed. The method is based on the use of a broad MWD standard made by blending Polysciences broad MWD standards and a generalized analytical solution of Tung's integral equation for the detector response corrected for peak broadening. Molecular weight averages measured by SEC/DRI/LALLSP are in excellent agreement with those measured offline by LALLSP.     

Size Exclusion Chromatography (SEC) of Complex Polymers-Methods of Correction for Imperfect Resolution

Abstract

Herein is reported a review and extension of recently published methods of correction for imperfect resolution (inadequate peak separation and or excessive peak broadening) for the SEC of linear homo and uniform copolymers and complex polymers such as polymers with long chain branching and nonuniform copolymers. Emphasis Is placed on analytical correction methods and absolute detector systems such as the low angle laser light scattering photometer and viscometer in series with a mass detector. Analytical correction methods and absolute detector systems play a vital role in the SEC characterization of complex polymers.     

Effects of aliphatic amines on capillary electrochromatographic performance of tricyclic antidepressants on octadecylsilica

Adding aliphatic amines to the mobile phase improves peak symmetry and efficiency in capillary electrochromatography of tricyclic antidepressants on octadecylsilica. The most hydrophobic aliphatic amine studied, dimethyloctylamine (DMOA), was the most efficient. Despite the fact that the amine additives substantially reduced the electroosmotic flow, the retention of the analytes decreased indicating a strong competitive effect of the additives. DMOA gave the largest retention decrease, and simultaneously reduced the resolution, indicating that silanophilic interaction is significant to the separation. Highest efficiencies were obtained at the lowest pH (2.8). Acetonitrile influenced both efficiency and peak symmetry, and best results were obtained at 60%.     

High Performance Size Exclusion Chromatography with Microparticulate Porous Silica Spheres. Influence of Flow Rate,Salute Mass Transfer and Polydispersity of Samples

Abstract

The contributions to peak broadening in Size Exclusion Chromatography with microparticles of porous silica spheres having narrow size distributions have been determined by measuring the plate height dependence on flow rate for toluene and for polystyrene standards covering a wide range of molecular weights. From these contributions, the diffusion coefficients of the macromolecules in the pore matrix and the polydispersities of the samples could be evaluated. It is shown that for permeating polymers the band broadening is determined by the eddy diffusion in the mobile phase, by the slow mass transfer of the solute in the stationary phase and by the polydispersity of the standards. In properly packed columns the eddy diffusion term is of minor importance compared to the other effects, whereas the solute mass transfer, which is a velocity dependent process, can be minimized only at extremely low flow rates.     

Chromatography on Papers Impregnated with Zinc Silicate: A New Adsorbent for Qualitative and Quantitative Separation of Amines

Abstract

Papers impregnated with zinc silicate have been used for the chromatographic studies of amines taken in the form of their hydrochlorides. R_f values of various amines have been determined and compared with its behaviour on plain papers. Quantitative separations of dimethylamine from methylamine, α-naphthylamine, o-toluidine and o-nitroaniline; o-phenylenediamine from m-phenylenediamine; diphenylamine from piperidine have also been achieved on columns loaded with zinc silicate exchanger.     

Retention in Reversed-Phase Ion-Pair Chromatography of Amines On Alkyl-Bonded Phases

Abstract

Reversed phase ion-pair chromatography of phenethylamine derivatives (noradrenaline, adrenaline, dopamine, synephrine, tyramine and pholedrine) and lower alkylamines has been performed with octyl sulfate as counter ion in an aqueous eluent with a low content of 1-pentanol. LiChrosorb RP-18 was used as the solid phase. The retention of lithium and potassium in the system has also been studied.

On the basis of adsorption and retention studies a model for the chromatographic behaviour of the amines is proposed that includes interaction with two sites with different binding ability in the stationary phase. The adsorption capacity of the sites has been calculated as well as adsorption constants for the octyl sulfate ion pairs.     

Free Energy Peturbation and Molecular Dynamics Simulation Studies on the Enantiomeric Discrimination of Amines by Dimethyldiketopyridino-18-Crown-6

Abstract

Discrimination of chiral amines by dimethyldiketopyridino-18-crown-6 (1) is studied by free energy peturbation (FEP) and molecular dynamics (MD) methods. 1 has two (S)-chiral centers and discriminates chiral amines through host-guest interactions. The optically active amines in this study are α-(1-naphthyl)ethylamine, methylbenzylamine, cyclohexylethylamine, and sec-butylamine. The trends in binding free energy differences obtained from FEP calculations were in excellent agreement with experimental results obtained in the gas phase. In order to explain the enantioselectivity of the host in terms of the host-guest interactions at the molecular level, we analyzed the structures generated by 10-ns MD simulations of host-guest complexes. The suggested chiral discrimination mechanism, the π-π interaction and the steric repulsion between the guest and the host, was verified by our MD simulation analysis.     

Studies on Fluorescamine. Part II - Thin-Layer Chromatographic Mobilities of Fluorescamine Positive Drugs

Abstract

Fluorescamine reacts with primary amines, it does not react with secondary or tertiary amines, to yield bright acquamarine fluorescent products. This reaction has been developed into a spot test useful for differentiation of amphetamine from methamphetamine; previous spot tests did not have this degree of specificity. The fluorescent products of several primary amines have been demonstrated to have sufficient stability to permit thin-layer chromatography comparisons with authentic materials. The fluorescent derivative of amphetamine has been demonstrated to be capable of differentiation from other fluorescent products formed from fluorescamine based on its unique migration in three different TLC systems.     

Optimization of Peak Separation and Broadening in Aqueous Gel Permeation Chromatography (GPC) -Poly (Sodium Styrene Sulfonates)

Abstract

An experimental study of the gel permeation chromatography of a series of poly (sodium styrene sulfonates) in aqueous media has been undertaken. The objective of this study was to develop a set of operating conditions that would maximize peak separation and minimize peak broadening. Using CPG-10 porous glass packing, it has been found optimal to work at pH near 6 and ionic strength near 0.05. Under those conditions, ion exclusion is eliminated and the optimum balance between resolution and reproducibility is obtained. Addition of a few ppm neutral surfactant to the mobile phase prevents adsorption to the packing surface, and improves resolution.     

Retention of Ionized Solutes in Reversed-Phase High Performance Liquid Chromatography

Abstract

The mechanism of retention in reversed-phase high performance liquid chromatography is affected by both solute-eluent interactions and the nature of the stationary phase. The hydrophobic expulsion of ionized solutes plays a major role in affecting solute behavior in the water-rich range of hydroorganic eluents. In the water-lean range of eluent composition, there is little hydrophobic expulsion, and specific interactions between the solute and surface can be observed. The nature of the surface affects the retention of a variety of ionized species, both large cations and anions. Octadecylsilane (ODS) bonded phases can exhibit two different binding sites: one exhibiting a weak interaction and the second a strong specific interaction with a solute. Styrenedivinylbenzene polymeric surfaces exhibit the potential for weak dispersion interactions, and in addition pi-bonding interactions with a solute. A variety of solutes have been injected in a water: methanol eluent system in order to assess solute-surface effects on reversed-phase supports.     

Proposed Instrumental Spreading Shape Function (ISF) as Applied to Size Exclusion Chromatography (SEC)

Abstract

Herein is proposed a new statistical ISF. This function which is gaussian and symmetric in shape, is an infinite series. The series is described by two parameters, instrument peak dispersion coefficient, σ², and a new coefficient, a polyplatykurtic coefficient A_k. The two parameters combine to form a peak broadening parameter, X. This new shape function seems to fall within the expectation of several authors in the past (1–11). This series was obtained during studies involving aqueous SEC with series of dextran standards. This paper is a continuation of a series of papers on these investigations (12,13)     

Corrections for Instrumental and Secondary Broadening in the Chromatographic Analysis of Linear Copolymers

Abstract

The effects of instrumental broadening and of polymer/solvent/packing interactions (secondary broadening) are separately investigated in the context of chromatography experiments, for the characterization of linear copolymers with two types of repeating units. The problems associated to the estimation of: a) the joint molecular weight distribution - chemical composition distribution (MWD-CCD) through orthogonal chromatography; and of b) the average MWD - average CCD through standard size exclusion chromatography (SEC) with dual detection are considered. The main difficulty with the secondary broadening correction, is the calibration for this effect. In the case of standard SEC with dual detection, a simple solution was found to the instrumental broadening problem, that involves a direct extension of the calibration and deconvolution techniques developed for linear homopolymers and mass detectors.     

THE STUDY OF 2-CHLORO-5,5-DIMETHYL-2-OXO-1,3,2-DIOXAPHOSPHORINANE IN SOLUTIONS BY MOLECULAR DYNAMICS METHODS USING IR AND RAMAN SPECTROSCOPY

Abstract

2-Chloro-5,5-dimethyl-2-oxo-1,3,2-dioxaphosphorinane has been studied in CCl₄, CHCl₃ and CD₃CN solutions by IR and Raman line shape analysis. Equilibrium process of dimerization and ring conversion in CCl₄ solutions have been considered. On the contrary to the commonly expected dominance of the conformer with the equatorial oriented P[dbnd]O bond for 2-halo-2-oxo-1,3,2-dioxaphosphorinanes, it was found that for the 2-chloro derivative both conformers are nearly equally distributed. It has been shown that the interactions induced absorption is an important mechanism of relaxation in the studied compound and this mechanism gives significant contribution to the total IR band broadening, while the interaction induced light scattering is negligible. The obtained results show that the molecular dynamics method can be useful in studying cyclic compounds in solutions.     

Atlas of Fluorescence Spectra and Lifetimes of Dyes Attached to Protein

Abstract

Fluorescence spectra and lifetimes of ovalbumin labeled with a variety of fluorescent reagents have been measured. The peak positions of the emission spectrum and the long wavelength band of the excitation spectrum as well as the fluorescence lifetimes, are tabulated. Heterogeneity of binding sites is shown by the broadness of some emisison spectra and the presence of multiexponential decay. The atlas may serve as a guide to the properties of these dyes attached to proteins in general.     

Experimental Studies with a Bonded N-acetylaminopropylsilica Stationary Phase for the Aqueous High Performance Exclusion Chromatogrpahy of Polypeptides and Proteins

Abstract

The potential of the micoparticulate, chemically bonded N-acetylaminopropylsilica stationary phase of nominal pore diameter of 100 angstroms in the high speed gel permeation chromatography of polypeptides and small proteins has been further investigated. The influence of ionic strength on the elution behaviour of a selected group of polypeptides and proteins on this bonded hydrophilic support has been examined. The results obtained with this porous, microparticulate bonded ‘amide’ phase silica support, packed into standard analytical-size stainless steel HPLC columns, indicate that milligram quantities of polypeptides and protein swith molecular mass up to 45,000-50,000 daltons can be efficiently fractionated with excellent recoveries of biological activities. The role of silica-based sorbents in the gel permeation fractionation of polypeptide and protein hormones, including those of pituitary and hypothalamic origin, is discussed.     

Nucleophilic Ring Enlargement of 2-Substituted-3-isothiazolones to 1,3-Thiazin-4-ones

Abstract

1,3-Thiazin-4-ones 9 and 10 have been prepared from the corresponding isothiazolones 7 and 8 by a clean and smooth reaction with tertiary amines at room temperature. This rearrangement is attributed to the abstraction of a methine proton from the 2-position isothiazolone substituent, followed by ring enlargement through cleavage of the S-N bond.