Determination of nitrophenols by capillary zone electrophoresis in a hydrodynamically closed separation compartment

Abstract

The use of β-cyclodextrin (β-CD) and polyvinylpyrrolidone (PVP) as complexing agents to capillary zone electrophoretic (CZE) separations of a group of ten nitrophenols was investigated. The analytes were baseline resolved in one CZE run when PVP was present in the carrier electrolyte at a 2.5% (w/v) concentration. β-CD was less effective as it did not baseline resolve a complete group of the studied nitrophenols within an applicable concentration range (0–10 mmol/l). The separations were carried out in a 300-μm I.D. capillary tube made of fluorinated ethylene–propylene copolymer to enhance the load capacity of the separation system. Under these working conditions, a 100-nl sample injection volume resulted in 20–80 ppb concentration limits of detection for nitrophenols, using a photometric absorbance detector operating at a wavelength of 254 nm. The separation efficiencies for the analytes spanned from 1.6–2·105 theoretical plates per meter. Their migration times were reproducible not only in a within day but also in a day-to-day time frame (1% or less for a period of several weeks). This was achieved for a hydrodynamically closed separation compartment while minimizing fluctuations in the concentration of CO2 in the carrier electrolyte. Reproducibility in the determination of nitrophenols was in the range of 1–5% for 1–6 ppm concentrations. Rain, drinking and process water samples served as matrices to assess the practical applicability of the elaborated CZE procedure. This procedure can be combined with isotachophoretic sample pretreatment to make its use possible in situations when nitrophenols are present in the samples at low ppb concentrations.