Hans Borén

Direct liquid chromatographic separation of enantiomers on immobilized protein stationary phases : III. Optical resolution of a series of N-aroyl d,l-amino acids by high-performance liquid chromatography on bovine serum albumin covalently bound to silica

A series of N-aroyl d,l-amino acids was investigated with respect to direct optical resolution by high-performance liquid affinity chromatography on a stationary phase consisting of bovine serum albumin covalently bound to a 10-μm silica support. In all instances the k′ values increased with decreasing pH of the mobile phase. Many of the compounds, such as the N-benzoyl and N-naphthoyl derivatives of d,l-alanine and ,d,l-phenylalanine, could be completely resolved into the optical antipodes. The 2-substituent of the amino acid was found to exert a great influence not only on the degree of resolution but also on the elution order of the enantiomers. A change in the N-aroyl substituent from a benzoyl to a 2-naphthoyl group caused a large increase in the retention of both enantiomers of a d,l-alanine derivative.

Degradation of humic substances by UV irradiation

Abstract Aqueous solutions of humic substances (humic and fulvic acids) were irradiated with light at λ = 254 nm followed by analyses of total organic carbon (TOC), ultraviolet (UV) absorbance and molecular weight distribution. A degradation of the dissolved humic compounds by up to 50% after 6 h was observed. The average molecular weight decreased (from 1800 to approx. 300) as well as the UV absorbance of the remaining organic fraction. Low molecular weight organic acids were formed during the irradiation and tentatively identified by capillary electrophoresis (formic, acetic, succinic, and oxalic acids). The low molecular organic acids continued to degrade by further irradiation; the loss of TOC is assumed to be due to CO 2 formation. Indications of a large-scale photo degradation process in nature was observed as a seasonal variation of the ratio humic substances/TOC related to the length of the day. Weekly sampling and analysis of UV absorbance and TOC in the Kalix River in northern Sweden indicate a higher humic fraction of the TOC during winter (dark period) than during summer.

Direct liquid chromatographic separation of enantiomers on immobilized protein stationary phases : IV. Molecular interaction forces and retention behaviour in chromatography on bovine serum albumin as a stationary phase☆

Chromatography with the use of immobilized bovine serum albumin as a stationary phase and aqueous buffer systems as eluents has proved to be a highly selective method, capable of separating structurally very closely related compounds. Retention can be effectively regulated by changes in at least three independent parameters of the mobile phase, which may be used for an optimization of separation factors. Particularly, the enantioselective properties of the chiral stationary phase have been demonstrated to be useful for the analytical resolution of a variety of racemates into enantiomers. From the variation of the retention behaviour with substituent effects, as well as the mobile phase composition, some indications regarding the molecular interaction forces regulating the substrate-protein equilibria have been obtained.

Analysis of mono- and diesters of o-phthalic acid by solid-phase extractions with polystyrene–divinylbenzene-based polymers

Retention mechanisms of an unmodified and a hydroxylated polystyrene-divinylbenzene polymer were studied by solid-phase extraction of o-phthalic acid and some of its mono- and diesters from purified water and then analysing by GC-MS. The monoesters and phthalic acid were retained only when protonated (i.e. acidified with HCI to pH 0.9). Of all elution solvents tested, ethyl acetate gave the best overall recoveries (61-89%) with both polymers. Applicability to complex matrixes (e.g. acidogenic landfill leachates) was examined by introducing a washing step with acetone in acidified water (pH 0.9) to eliminate volatile fatty acids (C2-C6) from the cartridge. Finally, the method was tested on real samples.

Analysis of bacterial vaginosis-related amines in vaginal fluid by gas chromatography and mass spectrometry

ABSTRACT The presence of various amines in vaginal fluid from women with malodorous vaginal discharge has been reported before. The investigations have used several techniques to identify the amines. However, an optimized quantification, together with a sensitive analysis method in connection with a diagnostic procedure for vaginal discharge, including the syndrome of bacterial vaginosis, as defined by the accepted “gold standard,” has not been done before. We now report a sensitive gas chromatographic and mass spectrometric method for identifying the amines isobutylamine, phenethylamine, putrescine, cadaverine, and tyramine in vaginal fluid. We used weighted samples of vaginal fluid to obtain a correct quantification. In addition, a proper diagnosis was obtained using Gram-stained smears of the vaginal fluid that were Nugent scored according to the method of Nugent et al. (R. P. Nugent et al., J. Clin. Microbiol., 29:297–301, 1991). We found that putrescine, cadaverine, and tyramine occurred in high concentrations in vaginal fluid from 24 women with Nugent scores between 7 and 10. These amines either were not found or were found only in very low concentrations in vaginal fluid from women with Nugent scores of 0 to 3. There is a strong correlation between bacterial vaginosis and the presence of putrescine, cadaverine, and tyramine in high concentrations in vaginal fluid.

Use of an electronic tongue to analyze mold growth in liquid media.

The feasibility of employing an electronic tongue to measure the growth of mold in a liquid medium was studied. We used the electronic tongue developed at Linköping University, which is based on pulsed voltammetry and consists of an array of different metal electrodes. Instead of focusing on a single parameter, this device provides information about the condition or quality of a sample or process. Accordingly, the data obtained are complex, and multivariate methods such as principal component analysis (PCA) or projection to latent structures (PLS) are required to extract relevant information. A gas chromatographic technique was developed to measure ergosterol content in mold biomass and was subsequently used as a reference method to investigate the ability of the electronic tongue to measure the growth of mold in liquid media. The result shows that the electronic tongue can monitor mold growth in liquids. In PLS analysis, the electronic tongue signals correlate well with the amount of ergosterol in the mold biomass as well as the microbially induced changes in the pH of the medium.

Alkaline Degradation of Cellulose: Mechanisms and Kinetics

Cellulose powder and softwood sawdust were subjected to alkaline degradation under conditions representative of a cementitious environment for periods of 7 and 3 years, respectively. During the first 3 years, sampling was frequent, and data on the degradation of cellulose and production of isosaccharinic acid was used for establishing long-term prediction models. Samples after an additional period of 4 years were compared to the predicted values. The total rate of degradation was measured as the increase in total organic carbon (TOC) in corresponding solutions. A previously published theoretical model of degradation kinetics gave a good approximation of the present experimental data. Peeling-off, stopping, and alkaline hydrolysis reaction rate constants were obtained as model parameters, and the results suggested that the transformation of the glucose end group is the rate-limiting step in the cellulose peeling-off reaction and also determines the pH dependence of that reaction. After 3 years, isosaccharinic (ISA) acid represented 70–85% of all degradation products as quantified by capillary zone electrophoresis. The long-term prediction model indicated that all of the cellulose would be degraded after only 150–550 years. The control sampling after 7 years points toward a lower degradation of cellulose and production of ISA than predicted by the model, reflecting either a degradation of ISA that was faster than the production or a termination of the ISA production.

Modified stripping technique for the analysis of trace organics in water

Abstract A modification of closed loop stripping analysis that considerably reduces the problem of contamination of the standard system is reported. This modification also makes the system more flexible in regard to stripping temperature and flow-rate of the purging gas. This modification, designated the straight and open system, allows the stripping technique to be utilized without sacrificing sensitivity or capacity, but gives very few blank peaks in the subsequent high resolution gas chromatogram. A case study of trace organics in the Motala river is presented. This river is a raw water source for water works and is a recipient for industries and sewage plants.

Direct optical resolution of a series of pharmacologically active racemic sulfoxides by high-performance liquid affinity chromatography

A series of pharmacologically active racemic sulfoxides was investigated with respect to optical resolution by an affinity chromatographic technique based on enantioselective interactions with immobilized bovine serum albumin. The results show that very small changes in the molecular structure of a drug, at a large distance from the asymmetric center, can drastically alter not only its affinity for the albumin molecule but also the enantioselectivity in the reversible binding process. Apart from being an excellent, rapid method for studies of drug binding to and transport by serum albumins, it has a large potential application as a chromatographic technique for the determination of enantiomeric purity as well as stereoselective uptake processes of drugs.

Properties of fulvic acids from deep groundwaters

Abstract Fulvic acids have been recovered from three deep groundwaters and one surface water and characterized with respect to elemental composition, molecular weight, acid capacity and 14 C-age. The corresponding waters are also characterized in detail. All of the fulvic acids, with ages varying from 0 to 5250 years, are very similar. The onlu significant difference between fresh and old materials are lower content of oxygen and nitrogen and higher COOH/OH-ratios for the materials from the old waters. Dating of the water using 14 C-analysis of the dissolved organic material is probably better than using the carbonate as the 14 C-source.