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At least 631 records · Page 35Linked to original sources
PubMed1981

Determination of the relative amounts of the B and C components of neomycin by ion-exclusion chromatography using refractometric detection.

Refractometric detection can be used as a convenient alternative to ninhydrin colorimetric or polarimetric detection in ion-exclusion chromatography of neomycinn. The determination of the relative amounts of neomyci B and C using different detection methods is examined. The use of a resin of smaller granulometry and a medium-pressure chromatographic apparatus reduces the analysis time to less than 25 min.

Chromatography, Gel↗
PubMed1989

Microbore liquid chromatography and refractive index gradient detection of low-nanogram and low-ppm quantities of carbohydrates.

A refractive index gradient detector is presented as a universal detector in the microbore high-performance liquid chromatography analysis of carbohydrates. Simultaneously, low-ng and low-ppm injected quantities of carbohydrates were detected at the 3 x root-mean-square baseline noise level. A typical microbore high-performance liquid chromatography chromatogram separating fructose from sucrose followed by refractive index gradient (RIG) detection is reported. Use of a position sensitive detector (PSD) in the RIG detector design is reported and experimental considerations discussed. Optimization of the PSD-based RIG detector is addressed. Potential for the device in industrial and clinical applications is considered.

Carbohydrates↗
PubMed2001

Liquid exclusion-adsorption chromatography, a new technique for isocratic separation of nonionic surfactants. II. Quantitation in the analysis of fatty alcohol ethoxylates.

A new technique of liquid chromatography, which allows baseline separation of fatty alcohol ethoxylates with up to 15-20 ethylene oxide units under isocratic conditions allows an accurate quantitative analysis of single hydrophobic chain surfactants. Using density and refractive index detection, the accurate weight fractions of the individual oligomers are obtained. Moreover, the contribution of preferential solvation can be determined. With refractive index detection alone, good accuracy can also be achieved.

Adsorption↗
PubMed2001

Characterization of starch polysaccharides by flow field-flow fractionation-multi-angle laser light scattering-differential refractometer index.

The coupling between flow field-flow fractionation (FFF), multi-angle laser light scattering and differential refractometer index provides a promising technique for fractionation of starch polysaccharides in aqueous conditions. Native starches with different amylose/amylopectin levels (0-70%) as well as a pure amylose sample were characterized. By applying a sudden drop in the cross-flow-rate, clear separation was achieved between amylose (which elutes first) and amylopectin. Flow FFF produced correct relationships between the molecular mass or the gyration radius versus elution volume for the fractionated amylopectin population. The results are also considered in terms of the macromolecular composition of starches.

Amylopectin↗
PubMed2001

Liquid chromatographic determination of total and beta-N-oxalyl-L-alpha,beta-diaminopropionic acid in lathyrus sativus seeds using both refractive index and bioelectrochemical detection.

A further improved chromatographic method for the simultaneous determination of the total amount of ODAP, selectively the amount of its neurotoxic form, beta-ODAP, and free L-glutamate in raw Lathyrus sativus (grass pea) seed samples is described using post-column refractive index in combination with bioelectrochemical detection. The biosensor is based on crosslinking horseradish peroxidase (HRP) and an Os-containing mediating polymer with poly(ethyleneglycol)(400) diglycidyl ether (PEGDGE), forming an inner hydrogel layer and then immobilising L-glutamate oxidase (GlOx) as an outer layer on top of a graphite electrode. Addition of polyethylenimine (PEI) to the hydrogel is believed to have sensitivity and stability enhancing effect on the biosensor. The double-layer approach in the biosensor construction avoided direct electrical wiring of GlOx and resulted in a higher sensitivity of 4.6 mA/M cm2 with respect to beta-ODAP and a wider linear range (1-250 microM) for both L-glutamate and beta-ODAP when compared with a single-layer approach where GlOx, HRP, and Os-polymer are crosslinked together. The limit of detection for the chromatographic-biosensor system was found to be 2 microM with respect to beta-ODAP and 0.7 microM with respect to L-glutamate. The refractive index detection on-line with the biosensor enabled full control of the chromatographic system for the determination of the total amount of ODAP, selectively the amount of beta-ODAP and L-glutamate. Ten grass pea samples have been collected from Lathyrism prone areas of Ethiopia to test the applicability of the presently developed analytical system for real sample analysis. The toxin levels of grass pea collections were determined in an aqueous extracts and ranged from 0.52 to 0.76%, dry mass basis. Comparison of results of an established spectrophotometric assay and that of the present system has shown an extraordinary degree of agreement as revealed by parallel "t" test (90% confidence limit). The present system has operational stability of more than 50 h. Analysis time per sample is 10 min after extraction for 90 min.

Amino Acids, Diamino↗
PubMed2002

Scale-up potential of ion-pair high-performance liquid chromatography method to produce biologically active inositol phosphates.

This study was undertaken to evaluate the possibility that an analytical ion-pair HPLC procedure used to determine phytic acid (IP6) and its degradation products (IP3-IP5) can be transformed to a preparative purification method. A commercial phytic acid (CPA) preparation was separated into its component fractions of IP3, IP4, IPS, and IP6 on two C18 columns (1.8 and 4.2 ml) using 51% methanol containing 0.6-1% tetrabutylammonium hydroxide as ion-pair reagent and 0-0.025 M formic acid (pH 4.3) as eluent at 1.7 and 3.0 cm/min linear velocity, respectively, and 40 degrees C. Elution was monitored at 40 degrees C by a refractive index detector. Reproducible separation of CPA into four well-resolved peaks on these columns was possible after optimizing method variables, particularly the concentration of ion-pair reagent in the injected sample (>1.5%). The same separations were obtained after CPA loads were scaled up 25 times on a steel column (15 cm x 19 mm I.D.), packed with Ethyl C2 sorbent (10 microm) and on a 25 cm x 21.2 mm I.D. C18 column, but at a reduced linear velocity to increase the resolution. Therefore, this optimization of separation not only is useful for analysis of phytic acid and its degradation products but also it provides key parameters for scale up for further fractionation and characterization.

Chromatography, High Pressure Liquid↗
PubMed2002

Temperature-dependent refractive index issues using a UV-visible detector in high-performance liquid chromatography.

While studying the properties of some potential, UV-detection compatible, mobile phase modifiers for reversed-phase liquid chromatography (RPLC) we encountered serious detector baseline problems. The most severe problem was a periodic saw-tooth-shaped drift. This drift was most noticeable when using water-THF and water-dioxolane mobile phases. We demonstrate that the baseline problems are related to temperature fluctuation in a water bath used to maintain a constant column temperature. The temperature fluctuations change the refractive index (RI) of the mobile phase, which in turn affects the amount of light reaching the detector. Our results show that the magnitude of the baseline drift is related to the RI value of the mobile phases. The baseline problems can be alleviated using a different temperature controller whose feedback mechanism assures smoother operation. Since there is no single and complete source of information in the literature concerning the RI values of typical mobile phases in RPLC, we decided to measure them as a function of the % modifier (between 0 and 100%) and the temperature (between 25 degrees C and 50 degrees C). Knowing the RI values allows us to calculate the excess volume of a binary liquid system.

Chromatography, High Pressure Liquid↗
PubMed2002

Molecular weight determination of lignosulfonates by size-exclusion chromatography and multi-angle laser light scattering.

A lignosulfonate sample was fractionated according to the solubility in ethanol-water. The fractions were analysed by aqueous size exclusion chromatography (SEC) combined with in-line multi-angle laser light scattering (MALLS), and by static MALLS. Satisfactory SEC results were obtained with aqueous phosphate buffer containing DMSO and SDS. The refractive index increment (dn/dc) varied from 0.186 to 0.205 ml/g, depending on Mw and the degree of sulfonation. The second viral coefficient (A2) was 7 x 10(-3) ml mol/g2. The weight-average molecular weight (Mw) of the fractions varied from 4600 up to 398 000 g/mol. and the polydispersity (Mw/Mn) varied between 1.3 and 3.5.

Chromatography, Gel↗
PubMed2002

Monitoring of azo dye degradation processes in a bioreactor by on-line high-performance liquid chromatography.

A technical solution and development of a method for on-line HPLC monitoring of bioreactor processes in a membrane reactor system are presented. Experiences in system design for the continuous coupling of a bioreactor system with capillary by-pass circuits using membrane flow cells and a dual HPLC system are reported. A continuously working integrated sample purification step by ultrafiltration with the membrane cell coupling is established. Using electrical switching valves and separated pumping and eluent systems, the dual HPLC system allows diode array detection as well as measurement of the refractive index. The application of the on-line HPLC monitoring system is demonstrated by measuring the anaerobic H-acid degradation kinetics. H-acid, 1-amino-8-hydroxynaphthalene-3,6-disulfonic acid, is one of the most important coupling components for a variety of direct, mordant, reactive dyes which remains in the process water and the textile dyeing effluents in high concentration.

Azo Compounds↗
PubMed2002

Molecular mass distribution analysis of ethyl(hydroxyethyl)cellulose by size-exclusion chromatography with dual light-scattering and refractometric detection.

Dual low-angle light scattering and refractometric detection coupled to size-exclusion chromatography provided proof for the presence of a low amount of stable aggregates/particles in ethyl(hydroxyethyl)cellulose. Unlike the correct size-exclusion chromatographic behavior of the parent polysaccharide itself, the aggregates exhibit variable size-dependent weak retention as a function of flow-rate and of ionic strength of the aqueous mobile phase. Therefore, determination of the molecular mass of non-aggregated polymer is possible in aqueous mobile phase containing 0.1 M NaCl under conditions at which aggregates are completely adsorbed on the column packing irrespective of the flow-rate used. Flow-rate and ionic strength-dependent variations of aggregate behavior as well as model size-exclusion experiments with latex particles indicate that they partly carry a minute charge and have a compact structure. Their weak retention under the separation conditions used suggests a difference in their surface chemistry when compared with the dissolved polymer coils which exhibit a correct size-exclusion behavior.

Cellulose↗
PubMed1988

Optical errors in a liquid chromatography absorbance cell.

The shadowgraph method is used to visualize mobile phase flow through a liquid chromatography absorbance cell with "Z" flow geometry. It is shown that mixing is incomplete in the cell. Composition gradients persist throughout the elution of any sample. The gradients systematically change as the sample flows through the cell. Additionally, window wedge angles are measured in several cells. The implications for low noise absorbance detectors are discussed.

Azo Compounds↗
PubMed1989

Displacement chromatography on cyclodextrin-silicas. I. Separation of positional and geometrical isomers in the reversed-phase mode.

The retention behaviour of several charged and uncharged solutes on beta-cyclodextrin-silica was studied as a function of the methanol concentration, ionic strength and pH of the eluent in order to develop efficient displacement chromatographic separations for positional and geometric isomers. These retention curves were used to predict the eluent (carrier solvent) compositions that result in solute retentions in excess of k' = 10. The adsorption isotherms of several cationic detergents were determined in these carrier solutions and were found to be convex. The adsorption isotherms of several positional isomers used as test solutes were also determined in these carrier solutions. The adsorption isotherms permitted the development of efficient displacement chromatographic separations for the isomers tested. Column loadings as high as 58 mg were achieved on a regular 4.6 mm I.D. analytical-scale cyclodextrin silica columns.

Chromatography, Liquid↗
PubMed1989

Displacement chromatography on cyclodextrin-silicas. II. Separation of cis-trans isomers in the reversed-phase mode on alpha-cyclodextrin-silica.

The feasibility of preparative separations of cis-trans isomers by displacement chromatography on analytical-scale alpha-cyclodextrin-silica columns operated in the reversed-phase mode is demonstrated by using the isomers of 3-hexen-1-ol as model substrates and n-alkanols as displacers. The importance of matching the size of the cyclodextrin cavity and the solutes is shown. The crucial role of the displacer (both type and concentration) in the success of the displacement chromatographic separation is demonstrated.

Chromatography, Liquid↗
PubMed1989

Rapid analysis of triacylglycerols using high-performance liquid chromatography with light scattering detection.

This paper details a high-performance liquid chromatography (HPLC) method for the separation of triacylglycerols, using a 3-micron, 15 cm x 4.6 mm I.D. Spherisorb ODS column and gradient elution with dichloromethane and acetonitrile. The triacylglycerols are detected using a light scattering detector (mass detector). Separations of a number of different edible oils and fats are reported. The procedure offers a possible method for determining cocoa butter equivalents and the adulteration of edible oils and fats by other non-generic fats and oils.

Chromatography, High Pressure Liquid↗
PubMed1989

High-performance liquid chromatographic method for isolating coprostanol from sediment extracts.

We report a rapid, largely automated high-performance liquid chromatographic (HPLC) method, which uses an HPLC column packed with alkylnitrile-substituted secondary alkylamine (aminocyano) bonded phase, to isolate coprostanol from interfering compounds in sediment extracts. Coprostanol is then quantitated, as the trimethylsilyl ether, by gas chromatography with flame ionization detection. Results from using the HPLC method to analyze a sediment reference material for coprostanol were statistically comparable to a previously used gravity-flow column method. We also report the coprostanol concentrations in several sediment samples from the California coast which reflect a range of sewage contamination (62-15,000 ng/g).

Cholestanol↗
PubMed2003

Quantitation and test of enantiomeric purity of the L-ketohexoses by liquid chromatography with dual refractive index and laser-based chiroptical detection.

Experimental data for the synthetic methods of preparation of the L-ketohexoses have been lacking an analytical method for monitoring the chemical or enzymatic reactions described. Dual refractive index and laser-based chiroptical detection provides an ideal method for following the reactions, since the refractive index detector quantifies the amount of analyte, while the ratio of optical rotation to refractive index response allows the enantiomer mole fraction to be determined. Sulfonated polystyrenedivinylbenzene resin in the Ca form as the stationary phase with H2O at 80 degrees C as the eluent gives base-line separation of sorbose, fructose, tagatose, and psicose. Dependent on the complexity of the reaction mixture, analysis times range from 20 to 60 min.

Calibration↗