Investigations in HPLC System Containing Silica Dynamically Modified by Camphorsulfonic Acid

Abstract

The adsorption of camphorsulfonic acid (CSA) by silica was followed by the break-through method using methanol-water-CSA and acetonitril-water-CSA mixture as mobile phases. The break-through curves comprise two distinct waves, indicating the formation of CSA-double layer on the silica surface. The amount of CSA bound in the 1. and 2. layer is a function of the methanol-, acetonitril- and CSA-content of the eluent. Following the retention of a model substance along the break-through curve from methanol-water-CSA eluent, the different sorptional feature of the two CSA layers was revealed: retention increase followed by the depression of     

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.     

Capillary Column Inlet System for the Gas Chromatography of Biological Samples

Abstract

A glass injection system consisting of a packed precolumn and gasphase splitter has been developed for the introduction of derivatized biological samples on glass capillary columns. The precolumn provides complete sample evaporation before the splitter zone, traps contaminating nonvolatiles, and prevents decomposition or adsorption of components. In addition, a carrier gas control system is described that permits stable and repeatable adjustment of split ratio and capillary inlet pressure.

The linearity of the splitter has been established using a hydrocarbon mixture covering the range of methylene unit (MU) values in which the steroid derivatives are eluted.     

Ligand Exchange Chromatography Separations of Some Phenolic Compounds on Zinc Silicate in Fe(III) Form

Abstract

The high sorption capacity of zinc silicato for Fe(III) has been utilized for the separation of phenolic compounds on the basis of ligand exchange. The coordination of ligands with the central metal ion occurs through oxygen. Ligand sorption capacity, rate of sorption and break-through capacity have been studied. The distribution coefficients (Kd values) of 21 phenols have been determined in five different systems. Selectivity has been determined on the basis of Kd values of these phenols. On the basis of differences in Kd values various analytically important quantitative binary and ternary separations on columns of zinc silicate in Fe(III) form have been achieved.     

Effects of Counter Ions in Ion-Pair Liquid Chromatography of Hydrophobic Amines on Non-Polar Bonded Phases

Abstract

The retention behaviour of alprenolol and related hydrophobic amines in ion-pair adsorption systems has been examined with particular emphasis on the influence of different mono-and divalent counter ions (dihydrogenphosphate, bromide, perchlorate, dimethylcyclohexyl sulphate, sulphate and ethylenediaminetetraacetate). N,N-dimethyloctylamine (DMOA) and 1-pentanol were used as modifiers in the aqueous eluent and LiChrosorb RP-8 as stationary phase.

The retention is evaluated according to a two-site adsorption model and equilibrium constants are given for ion pair adsorption of DMOA. The retention of alprenolol has been evaluated in terms of ion exchange with DMOA and the ion-exchange constants are shown to be of the same magnitude and independent of the nature of the counter ion used. The ion-pair adsorption and the ion-exchange approaches are analogous expressions for the distribution process governing the retention.     

Comportement Polarographique d'Un Nouvel Agent Cytostatique: La Carminomycine

Abstract

Carminomycin, a new cytostatic agent related to the anthracyclin group, has been investigated using D.C., A.C., D.P. polarography and cyclic voltammetric techniques. Two reduction waves have been reported, one concerning the quinonic function, the other being devoted to the carbonyl group located in C₁₃. Some important adsorption phenomena may interfere in a large pH range. The detection limit is 8. 10^?6 M (D.P.P.).     

The Comparative Study of “Adsorbed Co” Oxidation On the Rough and Smooth Pt Electrodes

Abstract

The oxidation of carbon monoxide adsorption products from rough and smooth platinum electrodes has been studied by cyclic voltammetry. It was found that the roughness of the electrode surface has strong influence on the composition and/or structure of the final adsorption products.     

Simultaneous Determination of Seven Toxic Trace and/or Ultratrace Metals in Environmental Plants by Differential Pulse Voltammetry Without Change of Solution and Electrode

Abstract

A simple and reliable procedure simultaneously to determine seven trace and/or ultratrace toxic metals in a single sample of environmental plants has been presented. The procedure is based on the simultaneous determination of Cu, Pb and Cd by differential pulse anodic stripping voltammetry, of Zn and Mn by differential pulse voltammetry and of Ni and Co by differential pulse adsorption voltammetry at the hanging mercury drop electrode. The details of sampling, washing and drying of samples and the approach of digestion and preparation of samples for voltammetric determination have been investigated. The method has been applied to determination of the seven metals in grass and hucerne from different environments.     

Isolation of Ligands of Trace Metals from Plant Samples by Immobilized Metal Affinity Chromatography

Abstract

Isolation of ligands of trace elements from plants by affinity chromatography with a metal immobilised on iminodiacetate resin has been investigated. To simulate various types of bioligands the following compounds were tested: phytic acid, peptides containing Cys and peptides containing Asp. Optimal conditions allowing isolation of the peptides with good efficiency comprise the use of Ga³⁺ ion, sample adsorption at pH = 4 and elution of the compounds by 0.3 mol/l NH₃. Phytic acid was bound too tightly and was not eluted. The procedure was used for purification of extracts of rye flour. The purified sample is suitable for analysis by MALDI-MS.     

The Comparative Study of Co Adsorption on Smooth and Rough Rhodium Electrodes

Abstract

The adsorption of carbon monoxide on smooth and Rh/Rh rhodium electrodes has been studied by potentiodynamic and radiochemical techniques. It was shown that there are marked differences between CO adsorption products on these two kinds of electrodes. The results were compared with the data of CO₂ adsorption studies on rhodium electrodes.     

Donnan Exclusion Chromatography with Nonionic Adsorption

Abstract

The Donnan exclusion chromatography associated with nonionic adsorption has been studied on nucleotides (AMP, ADP and ATP) and aromatic acids (phthalic acid, benzole acid, salicylic acid and phenol) using crosslinked dextran cation-exchangers, SP-Sephadex and CM-Sephadex. It has been clarified experimentally based on a theoretical prediction that the combination of ionic exclusion and adsorption effects can make the separation in the Donnan exclusion range more effective in some cases.     

Desorption Potentials of Alkyl Alcohols and Specific Adsorption of Anions

Abstract

The potentials of desorption of various alkyl alcohols have been studied as a function of concentration of alcohol and of the nature and concentration of various electrolytes. Specific adsorption of the electrolyte ions is reflected in shifts of the desorption peaks of the alcohols. At anodic potentials, the order of specific adsorption appears to be chloride > sulfate >perchlorate > fluoride, and at cathodic potentials (vs. S. C. E.), chloride > perchlorate > sulfate > fluoride.     

A Kinetic and Quantitative Approach to Peak Splitting Phenomena When Using 2-Propanol as Modifier in Adsorption HPLC

Abstract

When using 2-propanol as a modifier in adsorption chromatography, a “satellite” peak is observed if a shight excess of a polar chlorinated hydrocarbon, such as CH₂Cl₂, is injected.

This satellite peak whose appearance is related to the presence of 2-propanol, has been identified as a part of the CH₂Cl₂ injected. The satellite peak behaves chromatographically mainly as a normal solute peak and its area is proportional to both the amount of CH₂Cl₂ injected and the concentration of 2-propanol in the mobile phase and on the other hand inversely related to the flow-rate and the concentration of CH₂Cl₂ in the mobile phase.

A physico-chemical model is proposed based on the perturbance of the dynamic equilibrium when the sample enters the column. The model is compatible with the experimental results and explains the origin of the satellite peak as well as its chromatographic behaviour. It also allows a better understanding of the role of a modifier related to its adsorption-desorption process.     

Electrosorption of CO and CO2 on Pt-Rh Alloy Electrodes

Abstract

The adsorption of carbon monoxide and carbon dioxide on smooth Pt-Rh alloy has been studied by potentiodynamic technique. It is shown that the main products of CO and CO² adsorption on Pt-Rh alloys (15% Rh and below) are similar to products obtained on Pt electrodes.     

Sources of Errors Associated with the Determination of PAH and PCB Analytes in Water Samples

Abstract

This work describes the problems occurring in routine determination of polyaromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in water. On the basis of experiments carried out, sources of analyte losses in a particular step of the analytical procedure were identified and assessed. Primary attention has been paid to evaluation of the?following:

• degree of adsorption of analytes from the group of PCBs and PAHs on the walls of glass vessels used during sample pretreatment and storage

• influence of excess of solvent evaporation from extracts on analyte recoveries

• influence of material of extraction column (glass, polyethylene) on analyte recovery during the solid extraction process.

     

Spectrofluorometric Determination of Thiamin and Riboflavin in Vegetable Foods

Abstract

Modifications of the AOAC thiamin and riboflavin methods allow effective and simple determination of both vitamins from aliquots of the digested sample of vegetable foods. Study of the minimum amount required for a complete hydrolysis of the vitamers corresponding to each vitamin have been carried out. A critical study of thiocrome formation which was later used in the spectrofluorimetric determination of thiamin was done. In order to separate riboflavin from the digested sample, a new liquid chromatographic method based on adsorption in florisil is proposed. The aforementionated methods were applied to different samples of several vegetable foods.     

The Isolation of Proteins from Whey with a New Strongly Acidic Silica-Based Ion Exchanger

Abstract

A new type of strongly acidic ion exchanger based on macroporous silica coated with a thin layer of hydrophilic copolymer with sulphonic acid groups has been evaluated. The coating is crosslinked and covalently linked to the silica surface via diol groups.

The performance for isolation of proteins from whey of the new ion exchanger and Spherosil S were compared using both batchwise adsorption and column operations with reconstituted whey. Higher breakthrough capacities were observed for the new ion exchanger than for Spherosil S. Excellent column operational lifetimes were found for the new product.

A procedure is described to restore the original adsorption capacity of fouled columns.     

Preconcentration of Volatile Hydrocarbons as Air Pollutants by C-18 Bonded Silica used for Solid Phase Extraction

ABSTRACT

C₁₈-Silica used for Solid-Phase Extraction exhibits the same degree of adsorption of volatile hydrocarbons as compared to conventional Tenax adsorbent. The vapor pressure of the hydrocarbons and the velocity of the air sample through the sorbent are dominants of the preconcentration. Recovery of 80% for n-hexane and 98% for p-xylene at a concentration of 10 mg.m^?3 was obtained at 10 ml.g^?.min^? velocity.

C₁₈Bond Elut cartridges have been successfully used for quantitative determination of hydrocarbons as air pollutants by gas chromatography. The detection limit for p-xylene using preconcentration from 1 L air sample and a S/N ratio of 5 was 0.1 mg.m^?3. After regeneration of C₁₈Bond Elut cartridges by washing with acetonitrile and diethyl ether and drying at 85°C/15 min, their preconcentration potential remain acceptable upon reusing at least three times.     

Modern Analytical Methods for Monitoring Workplace Atmospheres

Abstract

Since measurements of exposure to hazardous substances were made obligatory in Germany under the Hazardous Material Regulation and Regulations for Accident Prevention there has been a need for widely-applicable, economic methods for determining airborne organic substance concentrations at workplaces. The relevant limits, which are based on toxicological and industrial hygiene data, are drawn up annually by the German Science Foundation and published as “Technische Regel für gefährliche Arbeitsstoffe” (TRgA 900) by the Ministry of Employment and Welfare.

Most organic substances, that have been assigned limits can be determined by gas liquid chromatography. The system described here is based on multicomponent GLC analysis. It has been used at BASF, the chemical-manufacturing company, where since 1979 approximately fifteen thousand workplaces have been evaluated. Hazardous substances have been detected at levels down to a few micrograms per cubic meter.

The standard system encompasses:

–-personal air samplers operating for 8 h;

–-adsorption by a solid sorbent;

–-desorption by solvent;

–-simultaneous GLC-separation on two different capillary columns;

–-computer correlation of the qualitative and quantitative data of the two chromatograms (plausibility check);

–-automatic print-out of the analytical report;

–-transfer of the results to a data bank for documentation.

Details are given of the method involving adsorption on activated charcoal and desorption with carbon disulfide. Benefits, cost advantages, and limitations are discussed.

Special sampling by means of other adsorbents (e.g. silica gel) in conjunction with special desorption, formation of derivatives, headspace analysis, and adsorption by liquids are techniques used to supplement the standard method of organic trace analysis in the field of industrial hygiene.     

THE FORMATION AND STABILITY OF MICROSCOPIC EMULSION FILMS OF AQUEOUS SOLUTIONS OF POLY (ACRYLIC ACID) AND ACRYLIC ACTD-VINYLACETATE COPOLYMERS

ABSTRACT

The effect of polymer volume concentration C, pH and ionic strength (NaCl concentration, CNal) of solution, polymer molecular mass, acetate groups' content in a polymer chain, and ethanol concentration on the stability of microscopic emulsion films (MEF) stabilized with the adsorption layers of poly(acrylic acid) (PAA) and acrylic acid-vinylacetate copolymers (PAA-VA) has been studied.

The kinetics of MEF thinning under the conditions when two heptane drops in a polymer solution are brought into contact and pressed with a permanent force has been studied.

The free energy ? F of interaction in the film has been evaluated on the basis of measuring the film thickness Hf by photometry and determining the film profile in the Plateau region.