Online transient micellar phase concentration of anions using CTAB in CE

A transient micellar phase extractor using CTAB was described for the online sample concentration of various anionic analytes (drugs and herbicides) in CE. Stacking and separation was performed at neutral pH in coelectroosmotic flow in a hexadimethrine bromide coated fused‐silica capillary. A micellar plug (e.g. 10 mM CTAB) was injected prior to hydrodynamic injection of the analytes prepared in aqueous organic solvent (e.g. with 30% ACN). In the presence of an electric field, the micelles interacted with the anions inside the capillary. This was followed by selective analyte focusing via the mechanism of micelle to solvent stacking. The micelles acted as transient extractor because the stacking ends when the injected micelles completely migrated through the boundary between the sample and micellar plug. Fundamental studies were performed (effect of surfactant concentration, etc.) and the technique yielded 13‐ to 30‐fold improvements in peak height. A stacking CE method in conjunction with liquid–liquid extraction was also tested for the detection of the herbicides fenoprop and mecoprop in fortified drinking water at analyte concentration levels relevant to Australian Drinking Water Guidelines.     

Sweeping and new on-line sample preconcentration techniques in capillary electrophoresis

Sweeping is a powerful on-line sample preconcentration technique that improves the concentration sensitivity of capillary electrophoresis (CE). This approach is designed to focus the analyte into narrow bands within the capillary, thereby increasing the sample volume that can be injected, without any loss of CE efficiency. It utilizes the interactions between an additive [i.e., a pseudostationary phase (PS) or complexing agent] in the separation buffer and the sample in a matrix that is devoid of the additive used. The accumulation occurs due to chromatographic partitioning, complexation or any interaction between analytes and the additive through electrophoresis. The extent of the preconcentration is dependent on the strength of interaction involved. Both charged and neutral analytes can be preconcentrated. Remarkable improvements—up to several thousandfold—in detection sensitivity have been achieved. This suggests that sweeping is a superior and general approach to on-line sample preconcentration in CE. The focusing mechanism of sweeping under different experimental conditions and its combination with other on-line preconcentration techniques are discussed in this review. The recently introduced techniques of transient trapping (tr-trapping) and analyte focusing by micelle collapse (AFMC) as well as other novel approaches to on-line sample preconcentration are also described.

Identification of a novel series of alkylitaconic acids in wood cultures of Ceriporiopsis subvermispora by gas chromatography/mass spectrometry.

A novel series of long-chain unsaturated dicarboxylic acids consisting of a long aliphatic chain attached to the C-3 position of itaconic acid has been identified by gas chromatography/mass spectrometry during in vitro decay of eucalypt wood by the white-rot basidiomycete Ceriporiopsis subvermispora. The major compounds were identified as tetradecyl-, 7-hexadecenyl- and hexadecylitaconic acids by their mass fragmentation patterns. Other members of the same compound series, identified as dodecanyl-, tridecanyl-, tetradecenyl-, pentadecanyl-, octadecenyl- and octadecanylitaconic acids, were present in very minor amounts or traces. Whereas hexadecenylitaconic acid has already been reported in cultures of C. subvermispora, to our knowledge this is the first report of the presence of the other alkylitaconic acids in fungal cultures. These new alkylitaconic-type metabolites may constitute a source for peroxidizable lipids involved in lignin degradation during wood decay by C. subvermispora and other white-rot basidiomycetes.     

On-line sample concentration via micelle to solvent stacking of cations prepared with aqueous organic solvents in capillary electrophoresis

In this paper, by injecting a SDS micellar plug before the sample prepared in aqueous organic solvents, we show the on-line sample preconcentration of cations via micelle to solvent stacking (MSS) using solvents of as low as 30%. This extends the choice of stacking techniques to include moderate amounts of organic solvent in the sample. The approach is akin to in-line solid phase extraction where the micellar plug acted as a transient micellar phase extractor. Basic studies were conducted (e.g. type and amount of organic solvent in the sample). The calculated sensitivity enhancement factors based on LOD obtained for the six test antipsychotic drugs were from 41 to 68. The peak signals were linear (R2 > 0.99) from 0.2 to 10.0 μg/mL. The intraday and interday reproducibility (n = 10) for migration time, peak height, and corrected peak area were from 0.2 to 13.6%. The technique was also tested on spiked wastewater sample with minimal sample treatment (i.e. dilution and centrifugation).     

Micelle to solvent stacking of organic cations in micellar electrokinetic chromatography with sodium dodecyl sulfate

The on-line sample concentration technique, micelle to solvent stacking (MSS), was studied for small organic cations (quaternary ammonium herbicides, β-blocker drugs, and tricyclic antidepressant drugs) in reversed migration micellar electrokinetic chromatography. Electrokinetic chromatography was carried out in fused silica capillaries with a background solution of sodium dodecyl sulfate (SDS) in a low pH phosphate buffer. MSS was performed using anionic SDS micelles in the sample solution for analyte transport and methanol or acetonitrile as organic solvent in the background solution for analyte effective electrophoretic mobility reversal. The solvent also allowed for the separation of the analyte test mixtures. A model for focusing and separation was developed and the mobility reversal that involved micelle collapse was experimentally verified. The effect of analyte retention factor was observed by changing the % organic solvent in the background solution or the concentration of SDS in the sample matrix. With an injection length of 31.9 cm (77% of effective capillary length) for the 7 test drugs, the LODs (S/N=3) of 5-14 ng/mL were 101-346-fold better when compared to typical injection. The linearity (R(2), range=0.025-0.8 μg/mL), intraday and interday repeatability (%RSD, n=10) were ≥0.988, <6.0% and <8.5%, respectively. In addition, analysis of spiked urine samples after 10-fold dilution with the sample matrix yielded LODs=0.02-0.10 μg/mL. These LODs are comparable to published electrophoretic methods that required off-line sample concentration. However, the practicality of the technique for more complex samples will rely on dedicated sample preparation schemes.     

Simultaneous electrokinetic and hydrodynamic injection with on-line sample concentration via micelle to solvent stacking in micellar electrokinetic chromatography

Simultaneous electrokinetic and hydrodynamic injection (SEHI) of organic cations (tricyclic antidepressant and beta blocker drugs) with on-line sample concentration using micelle to solvent stacking (MSS) was studied in micellar electrokinetic chromatography. Compared to conventional injection, >300-fold improvements in signals were obtained by hydrodynamic injection. However, with SEHI the amount of sample ions introduced into the capillary was increased which afforded a higher gain of up to 4000-fold without compromise to separation efficiency. The electrokinetic injection at negative polarity (anode at the detector end) introduced the micelle bound analytes. The hydrodynamic injection also maintained the MSS boundary inside the capillary. The stability of the MSS boundary affected SEHI where mild conditions that were low voltage as well as pressure injection were desired. The limits of detection were in the range from 0.6–4.2 ng mL⁻¹. A strategy for optimization was described and the method was applied to the ng mL⁻¹ analysis of spiked wastewater after simple dilution and centrifugation.     

Sweeping-micellar electrokinetic chromatography for the simultaneous analysis of tricyclic antidepressant and β-blocker drugs in wastewater

The simultaneous analysis of tricyclic antidepressant (amitriptyline, clomipramine, doxepin and nortriptyline) and β-blocker (alprenolol, labetalol and propranolol) drugs in wastewater was developed via sweeping-micellar electrokinetic chromatography (MEKC) together with a simple liquid-liquid extraction step. For sweeping-MEKC, the amount of organic modifier in the separation electrolyte, the concentration of phosphoric acid in the sample matrix and the injection time of the sample were optimized. Sensitivity enhancements of up to 305-fold were achieved via sweeping. This allowed limits of detection (LOD) from 7 to 27 ng/mL. The relative standard deviations of migration time, corrected peak area and peak height were less than 3.2%, 7.8% and 4.5%, respectively. Liquid-liquid extraction using dichloromethane as solvent afforded up to 21-fold enrichment of the drugs from spiked wastewater. No interference of the sample matrix was observed and recoveries were obtained in the range of 77-113% for all analytes except labetalol at three spiking levels of 16, 80 and 160 ng/mL. Detection at the ng/mL level makes this simple, environmentally friendly and cost effective method competitive against recently reported methods using advanced liquid-phase separation techniques for monitoring similar drugs in wastewater.