Dansyl amino acid enantiomer separation on a teicoplanin chiral stationary phase: effect of eluent pH.

The retention and separation of a series of D,L dansyl amino acids (used as test solutes) on a teicoplanin stationary phase were investigated over a wide range of mobile phase (citrate buffer-methanol, 90:10, v/v) pH. An approach based on the development of various equilibria was carried out in order to describe the retention behavior of the solute in the chromatographic system. The equilibrium constants corresponding to the transfer of the anionic and zwitterionic forms of the dansyl amino acids from the mobile to the stationary phase were determined. These values allowed one to explain the decrease in the retention factor and the associated increase in the separation factor as the eluent pH was increased. Thermodynamic parameter variations were calculated so that the driving forces of the solute association with the teicoplanin phase were derived. This approach indicated that the chiral discrimination was principally controlled by the interaction between the anionic form of the solute and the stationary phase.

DNA migration regimes in hydrodynamic chromatography and slalom chromatography: evidence for a transition.

Recently, we hypothesized that DNA separation mechanisms in slalom chromatography (SC) and packed column hydrodynamic chromatography (HDC) could be connected and simultaneously observed 'J. Chromatogr. A 886 (2000) 1'. The present paper describes the migration of various circular and linear double-stranded DNAs in a chromatographic system using a C1 stationary phase and an acetonitrile-phosphate buffer mixture as a mobile phase. The migration dependence on the flow rate for the different species showed the relative contribution of both the SC and HDC separation mechanisms. A transition between the SC and HDC regimes was demonstrated for the first time. In addition, the data were analyzed in terms of polymer migration in a dense structure. Three different behaviors were distinguished in relation to the size and the compactness of the nucleic acid.

Column efficiency and separation of DNA fragments using slalom chromatography: hydrodynamic study and fractal considerations.

Novel equations (Guillaume Y. C.; et al. Anal. Chem. 2000, 72, 853) were developed to describe the large double-stranded DNA molecule retention in slalom chromatography (SC). These equations were applied for the first time to model both the "apparent selectivity" and the resolution between two eluted DNA fragments on a chromatogram. A study of the column efficiency corroborated the fact that slalom chromatography is not based on an adsorption or equilibrium phenomenon, but can be attributed to a hydrodynamic phenomenon. Using a combination of the dynamics of DNA fragment progression in the column and fractal considerations, it was shown that the apparent selectivity depends both on the DNA fragment sizes and mobile-phase flow rate and therefore a balance between two hydrodynamic regimes. A chromatographic response function was also used to obtain the most efficient separation conditions for a mixture of DNA fragments in a minimum analysis time. The chromatographic data confirmed that in SC the flow rate can increase or maintain the separation efficiency with an associated decrease in the analysis time. This constitutes an attractive outcome in relation to the classical chromatographic separation.

Mobile-phase-viscosity dependence on DNA separation in slalom chromatography.

Slalom chromatography (SC) is an alternative chromatographic procedure for the separation of relatively large double-stranded DNA molecules and is based on a new principle. The retardation of the DNA fragments from the cleavage of the Lambda DNA by the KpnI restriction enzyme was studied using an acetonitrile-phosphate buffer as a mobile phase with various concentrations of viscosity modifier (i.e. glycerol) and a C1 column as a stationary phase. The DNA molecule retention was accurately described over the glycerol concentration range using a model previously established. It was shown that the eluent viscosity increase enhanced the slalom chromatographic capacity to separate the DNA fragments. A connection between SC and 'hydrodynamic chromatography' processes was predicted to link the two processes in a global separation mechanism based on a non-equilibrium principle.

Mechanism of DNA hydrodynamic separation in chromatography.

An alternative chromatographic procedure for the separation of large double-stranded DNA molecules was discovered recently and called "slalom chromatography". This fractionation is based on a new hydrodynamic process that is determined by the progression of the mobile-phase flow through the interstitial spaces created between the highly packed particles inside the column. Here, the separation is treated as the result of a slowing down of the large double-stranded DNA fragments in relation to their size with the flow direction changing around the particles. A model, based on the concept derived from the reorientation time of macromolecules, was adequate to describe the hydrodynamic phenomenon. This model constitutes an attractive tool to enhance the expansion of this chromatographic procedure and provide valuable information on the dynamic behavior of biological polymers.

A novel approach to study the inclusion mechanism of imidazole derivatives in micellar chromatography.

A chromatographic approach was proposed to describe the existence of surfactant micelles in a surfactant/hydroorganic phosphate buffer mobile phase. Using this mixture as a mobile phase, a novel mathematical theory is presented to describe the inclusion mechanism of imidazole derivatives in surfactant micelles. Using this model, enthalpy, entropy and the Gibbs free energy were determined for two chromatographic chemical processes: (i) the transfer of the imidazole derivative from the mobile phase to the stationary phase; and (ii) the imidazole derivative inclusion in surfactant micelles. These thermodynamic data indicate that the main parameter determining chromatographic retention is distribution of the imidazole derivatives to micelles of surfactant while the interaction with the stationary phase play a minor role.

Effect of temperature on DNA fractionation in slalom chromatography.

Slalom chromatography is an alternative chromatographic procedure for the analysis of relatively large double-stranded DNA molecules and is based on a hydrodynamic principle. The retardation of the DNA fragments from the cleavage of the Lambda DNA by the KpnI restriction enzyme was studied using an acetonitrile-phosphate buffer as a mobile phase (flow rate equal to 0.3 ml/min) and a C1 column as a stationary phase at various temperatures. It was shown that the temperature constituted an important parameter for the separation of the DNA fragments in slalom chromatography. The DNA hydrodynamic behavior with the temperature was related to the variation in the fluid viscosity and the modification of the elastic properties of the biopolyrner.

Fatty acid nutriture in hospitalized elderly women.

OBJECTIVE: The aim of this study was to measure the fatty acid (FA) dietary intakes and the FA composition of plasma total lipids in a selected group of hospitalized elderly patients. METHODS: Twenty-three women aged 76 to 99 years were recruited. FA were analyzed in 5-day duplicate portions and in plasma by gas liquid chromatography. RESULTS: The hospitalized elderly women ingested an average of 5.22 megajoules (MJ) and 45.9 g of lipids per day. Polyunsaturated fatty acids (PUFA) represented 11.0% and saturated fatty acids (SFA) 53.6% of the lipid intake. Minimal recommendations for linoleic acid intake were reached in average, but 32% of the patients ingested less than 3 g of linoleic acid/d. Eighty-six percent received less than 0.5% of energy for alpha-linolenic acid and 64% had low intakes in very long-chain n-3 FA. In parallel, these patients presented several biochemical signs of essential fatty acids (EFA) insufficiency (decrease in linoleic acid, increase in monounsaturated fatty acids (MUFA), in n-7 FA and in indexes of delta-6 and delta-9 desaturase activities). CONCLUSIONS: Hospitalized elderly patients have low PUFA intakes and show biochemical indices of EFA insufficiency. These patients might benefit from a nutritional supplementation providing both EFA and antioxidant micronutrients to limit the risk of skin troubles, immune system impairment and vascular disease often observed in institutionalized elderly subjects.

Fish oil effects on tissular fatty acids and plasma lipid peroxidation in zinc deficient rats.

Zinc has been reported to play a key role in lipid metabolism as well as in defences against oxidative stress. The aim of this work was to investigate the fatty acid distribution (plasma, heart, kidney, liver) and peroxidation (plasma) in zinc-deficient rats fed with n-6 fatty acids (10% corn oil) or n3 fatty acid fish oil (10% Maxepa). Zinc deficiency led to a decreased tissular and plasma n-6/n-3 ratio both in triglycerides and phospholipids. This effect was more marked in the Maxepa group than in the corn oil group. In plasma, the TBARs/TG + PL ratio was significantly enhanced in zinc-deficient animals, especially in rats receiving Maxepa. With regard to these results, zinc deficiency could appear as an aggravating factor of oxidative risk when associated with a n-3 fatty acid-rich diet. This work draws attention to the harmful oxidative risk associated with patients' intake of fish oil concentrate, without taking into account their antioxidant dietary intakes and status.

HPLC analysis of antioxidants.

Qualitative and quantitative HPLC methods are described for the analysis of mixtures of twelve antioxidants. For identification of the components present, gradient elution with a convex profile from 35:65 v/v water-methanol to pure methanol is used, on a Waters 5 mum C(18) Resolve column, with an ultraviolet detector. Propyl gallate and methyl p-hydroxybenzoate cannot be separated, however. For quantitative analysis, with ultraviolet and electrochemical detectors in series, the 35:65 water-methanol mixture or pure methanol is used as the eluent, under isocratic conditions, with lithium perchlorate as supporting electrolyte. An applied potential ranging from +0.8 to + 1.7 V allows detection of all the antioxidants tested. Both modes of detection are very sensitive, with limits of detection as low as 61 pg (UV, methyl p-hydroxybenzoate) and 360 pg (electrochemistry, butylhydroxyanisole).

[Not Available]. / Separation chromatographique des azepines Nanochromatographie sur couche mince et chromatographie en phase liquide sous pression.

Two chromatographic methods are proposed for separation, identification and determination of dibenzoazepines and benzodiazepines. A micro thin-layer method has been developed and transposed to give an HPLC system, which requires a slight modilfication of the solvent. Retention data are given, and two quantitative applications arc described.