Determination of Pollutant Phenols by Capillary High-Performance Liquid Chromatography with UV Detection

Effect of temperature on the separation of chlorophenoxy acids and carbamates by capillary high-performance liquid chromatography and UV (or diode array) detection

In this work, the effect of temperature in isothermal and programmed modes on several chromatographic parameters such as retention factor, selectivity, resolution and plate number has been discussed. A critical comparison of isocratic/isothermal, gradient/isothermal and isocratic/program temperature modes has been made. Two representative families of pesticides have been selected for this study. One includes ionisable chlorophenoxy acids and two of their esters, some of which show similar polarities. The other one contains several weakly polar carbamates. Analysis was carried out using a reversed-phase capillary high-performance liquid chromatography (HPLC) system and focusing technique with UV or diode array detection (DAD).

Simple method for the quantitative examination of extra column band broadening in microchromatographic systems

In recent years capillary chromatography has gained popularity for trace analyses. Most often UV or electrochemical detection is employed because the small peak volumes make post-column derivatization challenging. We have developed a simple method based on flow injection for determining contributions to peak broadening from post-column reactors. The only requirement for application of our methodology is that diffusion be in the Taylor regime so that radial concentration gradients are relaxed enabling mixing purely by diffusion.

Determination of phenols in water using liquid phase microextraction with back extraction combined with high-performance liquid chromatography

Liquid phase microextraction with back extraction (LPME/BE) combined with high-performance liquid chromatography (HPLC) was studied for the determination of a variety of phenols in water samples. The target compounds were extracted from 2-ml aqueous sample adjusted to pH 1 (donor solution) through a microliter-size organic solvent phase (400-microl n-hexane), confined inside a small PTFE ring, and finally into a 1-microl basic aqueous acceptor microdrop suspended inthe aforementioned solvent phase from the tip of a microsyringe needle. After extracting for a prescribed time, the microdrop was taken back into the syringe and directly injected into an HPLC for detection. Factors relevant to the extraction procedure were studied. At the optimized extraction conditions, a large enrichment factor (more than 100-fold) can be achieved for most of the phenols within 35 min. The detection limit range was 0.5-2.5 microg/l for different analytes in aqueous samples. The results demonstrate the suitability of the LPME/BE approach to the analysis of polar compounds in aqueous samples.

Liquid-liquid-liquid microextraction of nitrophenols with a hollow fiber membrane prior to capillary liquid chromatography

A simple liquid-liquid-liquid microextraction device utilizing a 2 cm x 0.6 mm I.D. hollow fiber membrane was used to preconcentrate nitrophenols from water sample prior to capillary liquid chromatography (cLC) analysis. The extraction procedure was induced by the pH difference inside and outside the hollow fiber. The donor phase outside the hollow fiber was adjusted to pH approximately 1 with HCl; the acceptor phase was NaOH solution used at various concentrations. Organic solvent was immobilized into the pores of the hollow fiber. With stirring, the neutral nitrophenols outside the fiber were extracted into the organic solvent, then back extracted into 2 microl of basic acceptor solution inside the fiber. The acceptor phase was then withdrawn into a microsyringe and injected into the cLC system directly. This technique used a low-cost disposable extraction "device" and is very convenient to operate. Up to 380-fold enrichment of analytes could be achieved. This procedure could also serve as a sample clean-up step because large molecules and basic compounds were not extracted into the acceptor phase. The RSD (n=6) was less than 6.2%, while the linear calibration range was from 1 to 200 microg/ml with r>0.998. The procedure was applied to the analysis of seawater.