RESUMEN
In high-performance liquid chromatography, the dependence of retention factor k on volumetric fraction Ï of organic phase is expressed by log k = F(Ï) with F(Ï) obtained by measuring log k at different Ï values. From F(Ï), a value kw is calculated by taking Ï = 0. The equation log k = F(Ï) is applied for predicting k, and kw is a descriptor of hydrophobic character of solutes and stationary phases. Calculated kw should not depend on the nature of organic component of mobile phase but extrapolation procedure leads to different kw for different organic components. The present study shows that the expression of F(Ï) changes depending on the range of Ï and the same function F(Ï) cannot be used for the full range of Ï from 0 to 1. Consequently, kw obtained by extrapolation of Ï to zero is not correct because the expression of F(Ï) was generated by fitting the data using Ï with higher values. The present study shows the proper way to obtain the value of kw .
RESUMEN
Few biosensors are reported for usage in combination with the organic solvent due to their negative impact on the enzymes. The usage of ternary water-organic solvent mixtures in combination with acetylcholinesterase biosensors allows to increase the useable total content of organic solvents with minimum negative effects to a higher content in comparison with a single organic solvent in water. The combination of acetonitrile/ethanol/water has a smaller negative effect on both enzyme activity and inhibition by insecticides in comparison with acetonitrile/methanol/water mixtures. The insecticides were eluted from solid-phase extraction (SPE) columns with a binary mixture of organic solvents acetonitrile/ethanol in 1/3 ratio and subsequently analysed with an acetylcholinesterase biosensor and the optimum total content of organic solvents of 12%. The analytical method allows the analysis of complex samples with improved selectivity and at improved limits of detection for chlorpyrifos-oxon and carbofuran analysis in river waters and soil samples. The usage of mixtures of organic solvents in combination with enzymes is an interesting approach that allows working with a higher total content of organic solvents than each individual solvent.
Asunto(s)
Acetilcolinesterasa/química , Técnicas Biosensibles , Insecticidas , Acetonitrilos/química , Técnicas Biosensibles/métodos , Etanol , Extracción en Fase Sólida/métodos , Solventes , AguaRESUMEN
Quality of the analytical data obtained for large-scale and long term bioanalytical studies based on liquid chromatography depends on a number of experimental factors including the choice of sample preparation method. This review discusses this tedious part of bioanalytical studies, applied to large-scale samples and using liquid chromatography coupled with different detector types as core analytical technique. The main sample preparation methods included in this paper are protein precipitation, liquid-liquid extraction, solid-phase extraction, derivatization and their versions. They are discussed by analytical performances, fields of applications, advantages and disadvantages. The cited literature covers mainly the analytical achievements during the last decade, although several previous papers became more valuable in time and they are included in this review.
Asunto(s)
Métodos Analíticos de la Preparación de la Muestra/métodos , Materiales Biocompatibles/química , Cromatografía Liquida/métodos , Animales , Precipitación Fraccionada/métodos , Humanos , Extracción Líquido-Líquido/métodos , Preparaciones Farmacéuticas/química , Extracción en Fase Sólida/métodosRESUMEN
The use of a large volume injection of hydrophobic solvents as diluents for less hydrophobic solutes has already been proven for C18 and C8 stationary phases in reversed-phase liquid chromatography. The same possibility is investigated for a phenyl-hexyl stationary phase using aromatic solvents (benzene, toluene, ethylbenzene and propylbenzene) as diluents for several model analytes also containing aromatic rings. Both hydrophobic interaction and π-π stacking account for the competitive interaction of both the diluent and model analytes with the phenyl-hexyl phase. A linear decrease in analyte retention factor was observed with an increase of injection volume in the range of 1-100 µL. A moderate peak efficiency decrease was also observed, but peaks of model analytes remained undistorted with minimum band broadening up to 100 µL injection volume. A very small retention decrease was observed when changing the sample diluent in the homologous series: benzene, toluene, ethylbenzene and propylbenzene. The critical conditions for a successful large volume injection of analytes dissolved in studied hydrophobic solvents are for the analyte to have lower hydrophobicity and for the specified solutes to have proper solubility.