Determination of chlorophenols by micellar electrokinetic chromatography with electrochemical detection

Gas chromatography/mass spectrometry versus liquid chromatography/fluorescence detection in the analysis of phenols in mainstream cigarette smoke

A new gas chromatographic/mass spectrometric (GC/MS) technique for the analysis of hydroxybenzenes (phenols) in mainstream cigarette smoke has been developed. The technique allows the measurement of 24 individual compounds, and the sum of a few other alkyl-dihydroxybenzenes. A critical evaluation is done for the new technique and for an established high-performance liquid chromatographic (HPLC) technique reported in the literature for the analysis of hydroxybenzenes in cigarette smoke, which uses fluorescence detection. Compared with the HPLC procedure, the new technique has similar accuracy, precision, and robustness. However, the GC/MS procedure allows for a larger number of phenols to be analyzed simultaneously, and eliminates any potential interference that may appear in the HPLC method. Using the GC/MS analysis, it was found that besides the main phenols typically measured in mainstream cigarette smoke such as phenol, catechol, hydroquinone, and cresols, many other phenols that are present at lower levels can be quantitated in mainstream cigarette smoke.

In-capillary solid-phase extraction-capillary electrophoresis for the determination of chlorophenols in water

A novel CE method combined with SPE in a single capillary was developed for analysis of chlorophenols in water. A frit of 0.5 mm was first made by a sol-gel method, followed by packing a SPE sorbent in the inlet end of the capillary. Two phenol derivatives, 2,4-dichlorophenol and 2,4,5-trichlorophenol, were used as the model compounds. By loading sample solutions into the capillary, the two chlorophenols were extracted into the sorbent. They were desorbed by injecting only about 4 nL of methanol. Finally, the analytes were separated by conventional CE. The technique provided a concentration enhancement factor of over 4000-fold for both chlorophenols. The detection limits (S/N = 3) of 2,4-dichlorophenol and 2,4,5-trichlorophenol were determined to be 0.1 ng/mL and 0.07 ng/mL, respectively. For replicate analyses of 5 ng/mL of 2,4-dichlorophenol, within-day and between-day RSDs of migration time, peak height and peak area were in the range of 1.8-2.0%, 4.0-4.4% and 4.1-4.6%, respectively. The method shows wide linear range, acceptable reproducibility and excellent sensitivity, and it was applied to the analyses of spiked river water samples. The capillary packed with the SPE sorbents can be used for more than 400 runs without performance deterioration.

Direct Analysis of Trace Phenolics with a Microchip: In-Channel Sample Preconcentration, Separation, and Electrochemical Detection

A micrototal analytical method assembling in-channel preconcentration, separation, and electrochemical detection steps has been developed for trace phenolic compounds. A micellar electrokinetic chromatography separation technique was coupled with two preconcentration steps of field-amplified sample stacking (FASS) and field-amplified sample injection (FASI). An amperometric detection method with a cellulose-dsDNA-modified, screen-printed carbon electrode was applied to detect preconcentrated and separated species at the end of the channel. The microchip was composed of three parallel channels: first, two are for the sample preconcentration using FASS and FASI methods, and the third one is for the separation and electrochemical detection. The modification of the electrode surface improved the detection performance by enhancing the signal-to-noise characteristic without surface fouling of the electrode. The method was examined for the analysis of eight phenolic compounds. Experimental parameters affecting the analytical performance of the method were assessed and optimized. The preconcentration factor was increased by about 5200-fold as compared with a simple capillary zone electrophoretic analysis using the same channel. Reproducible response was observed during multiple injections of samples with a RSD of <8.0%. The calibration plots were shown to be linear (with the correlation coefficient between 0.9913 and 0.9982) over the range of 0.4-600 nM. The sensitivity was between 0.17 +/- 0.001 and 0.48 +/- 0.006 nA/nM, with the detection limit of approximately 100 to approximately 150 pM based on S/N = 3. The applicability of the method to the direct analysis of trace phenolic compounds in water samples was successfully demonstrated.

Chlorinated Phenol Analysis Using Off-Line Solid-Phase Extraction and Capillary Electrophoresis Coupled with Amperometric Detection and a Boron-Doped Diamond Microelectrode

The analysis of chlorinated phenols (2-chlorophenol, 3-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, pentachlorophenol) in river water was accomplished using off-line solid-phase extraction (SPE) and capillary electrophoresis coupled with electrochemical detection. A key to the sensitive, reproducible, and stable detection of these pollutants was the use of a boron-doped diamond microelectrode in the amperometric detection mode. An off-line SPE procedure was utilized to extract and preconcentrate the pollutants prior to separation and detection, with ENVI-Chrom P, a highly cross-linked styrene-divinylbenzene copolymer, being employed as the sorbent. Pollutant recoveries in the 95-100% range with relative standard deviations of 1-4% were achieved. The diamond microelectrode provided a low and stable background current with low peak-to-peak noise. The oxidative detection of the pollutants was accomplished at +1.05 V vs Ag/AgCl without the need for electrode pretreatment. The method was evaluated in terms of the linear dynamic range, sensitivity, limit of quantitation, response precision, and response stability. A reproducible electrode response was observed during multiple injections of the chlorinated phenol solutions with a relative standard deviation of < or =5.4%. Good electrode response stability was observed over many days of continuous use with no significant electrode deactivation or fouling. The separation efficiencies for all six pollutants were greater than 170,000 plates/m. The minimum concentration detectable for all six ranged from 0.02 to 0.2 ppb (S/N > or = 3) using a 250:1 preconcentration factor.

Use of disposable GRC electrodes for the detection of phenol and chlorophenols in liquid chromatography

In this study, a wall-jet flow cell with a GRC (graphite reinforced by carbon) electrode was designed for the amperometric detection of phenol and chlorophenols in liquid chromatography. The voltammetric responses of these analytes at the GRC electrodes are very similar to those at conventional glassy carbon electrodes. As the GRC electrodes were made of the same materials as commercially available mechanical pencil leads, they exhibit the advantages of low cost, simple surface renewability, lower residual current, and good electrode-to-electrode reproducibility, and thus can be used as disposable-type electrodes. Chromatographic separations of phenol, o-chlorophenol (o-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), and pentachlorophenol (PCP) were achieved with an ODS column using a mobile phase containing a mixture of CH3CN and H20 (40:60) containing 25 mM L-(+)tartaric acid (pH = 4.5). Amperometric detections were based on the electrochemical oxidation of these compounds around +0.9 V vs. Ag/AgCl. Under the optimized conditions, linear calibrations were obtained in a range up to 100 microM for phenol, o-CP, 2,4-DCP, 2,4,6-TCP, and 200 microM for PCP, with the correlation coefficients r2 of 0.9992, 0.9997, 0.9986, 0.9992, and 0.9968, respectively. The chromatographic detection limits for the tested analytes were obtained at pmol levels.

Solid-phase extraction coupling to capillary electrophoresis with emphasis on environmental analysis

This article reviews the status of solid-phase extraction (SPE) coupled with capillary electrophoresis (CE). It focuses on some of the organic pollutants which have captured the interest of analytical chemists--phenols, surfactants, dyes, polynuclear aromatic hydrocarbons (PAHs), aromatic and aliphatic amines, aromatic acids and aromatic sulfonic acids--and, in particular, on monitoring pesticides from different sources. It shows that the coupling of SPE to CE has considerable potential in the analysis of environmental pollutants.

Determination of aromatic amines in water samples by capillary electrophoresis with electrochemical and fluorescence detection

Two capillary electrophoresis methods have been compared for the determination of aniline derivatives in environmental water samples. With the first method the anilines were separated as cations by free zone electrophoresis at low pH, and detected by amperometry. For this, the separation capillary was connected through a palladium field decoupler to an electrochemical detection cell which had been modified to match the volume scale of the separation. Most anilines tested, except chlorinated compounds, could be detected with full sensitivity at a detection potential of +0.7 V. Detection limits with this detection scheme were on a low microg/l level. The alternative method involved the derivatization of the anilines with fluorescamine, the separation of the derivatives formed by micellar electrokinetic chromatography, and fluorescence detection. For detection a lamp-based, fibre optics instrument was used. Detection limits with fluorimetry were comparable with those obtained with amperometric detection (in the order of 1 microg/l). Still, this method was preferred since it gave a higher separation efficiency and shorter analysis times (approximately 4 min). The most important argument, however, was its higher reliability and ease-of-handling. Preliminary experiments with water samples collected in areas where pollution with anilines may be expected showed that the method is highly specific, with few interferences showing up in the electropherograms.

Solid-phase extraction of phenols

Sample preparation for phenol analysis using solid-phase extraction (SPE) is reviewed. The scope of the review has been restricted to the literature dealing with the analysis of phenols as the main objective. The use, advantages and disadvantages of silica sorbents, polymeric, functionalized, carbon-based and mixed available sorbents, when applied to the separation and preconcentration of phenols, as well as the available experimental devices, are discussed. Other aspects such as phenol derivatisation prior to SPE, solid-phase microextraction, matrix effects and the storage of phenols in SPE cartridges, have been also discussed.

Approaching a million-fold sensitivity increase in capillary electrophoresis with direct ultraviolet detection: cation-selective exhaustive injection and sweeping

A novel method that combines two on-line concentration techniques in capillary electrophoresis (CE), namely, sample stacking with electrokinetic injection (field-enhanced sample injection, FESI) and sweeping, afforded the detection of positively chargeable analytes in parts per trillion (ppt) levels. The main idea is to selectively introduce by FESI as many molecules of cationic analytes as possible from a very dilute sample solution and focus the resulting zone by sweeping. Limit of detection values (signal-to-noise ratio 3) of 4.1 and 8.0 ppt-the lowest concentration reported by direct UV detection in CE-with average plate numbers of 3.6 x 10(5) and 4.4 x 10(5) are obtained for laudanosine and naphthylamine (standard solutions), respectively. This translates to improvements in peak heights compared with usual injection approaching a million-fold. Optimization schemes and application to quantitative and qualitative analyses are also investigated.

Electrokinetic chromatography

The important features of electrokinetic chromatography are critically reviewed. Special emphasis is given to systems using micelles as pseudostationary phase. Short and comprehensive overviews are given on the subjects of separation, comparison with capillary electrochromatography, on-line coupling with mass spectrometry, and developments that are expected in the future. A greater coverage on the subject of improvement of detection sensitivity, specifically by on-line concentration was also contributed.

Capillary electrophoresis in the determination of pollutants

The applications of capillary electrophoresis to the analysis of environmental pollutants have been carefully revised from the literature compiled in the Current Contents and focused on the description of methods developed since 1994. The literature is reported according to the pollutant type. Groups of compounds which have received much attention include phenols, polynuclear hydrocarbons, amines, carbonyl compounds, surfactants, dyes and inorganic pollutants. Easy-to-read table provides useful information about the state-of-the-art and possibilities offered by capillary electrophoresis (CE) in environmental analysis.