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Mitotane is a cytotoxic drug used in the treatment of inoperable adrenocortical carcinoma, it inhibits steroidogenesis as well, and therefore monitoring the level of steroid hormones in patients treated with mitotane is a crucial point of therapy. Hence, we have developed a simple, fast, and efficient electrophoretic method combined with reverse polarity sweeping as online preconcentration technique and dispersive liquid-liquid microextraction for the simultaneous determination of mitotane, its main metabolite DDA, and five steroid hormones (progesterone, testosterone, epitestosterone, cortisol, and corticosterone) in urine samples. In addition, a new sample matrix consisting of β-CD 2 SDS 1 complexes for a high hydrophobic compounds solubilization was developed. Approach based on the application of β-cyclodextrin and SDS complex of a ratio 2:1 allowed for hydrodynamic injection into the capillary of a solution containing both mitotane and other analytes. The detection limits of the analytes for the reverse polarity sweeping-dispersive liquid-liquid microextraction method were found to be in the range of 1.5-3 ng/mL, which were approximately 1000 times lower than in the conventional hydrodynamic injection (5 s, 0.5 psi) without any preconcentration procedure. All analytes were completely resolved in less than 13 min by uncoated silica capillary with an inner diameter of 75 μm (ID) × 60 cm. Electrophoretic separation was performed in reverse polarity with a voltage of -25 kV with a background electrolyte (BGE) consisting of 100 mM SDS, 25% ACN, 25 mM phosphate buffer (pH 2.5), and 7 mM β-cyclodextrin., (© 2021 Wiley-VCH GmbH.)

One of the most cited limitations of capillary and microchip electrophoresis is the poor sensitivity. This review continues to update this series of biannual reviews, first published in Electrophoresis in 2007, on developments in the field of online/in-line concentration methods in capillaries and microchips, covering the period July 2016-June 2018. It includes developments in the field of stacking, covering all methods from field-amplified sample stacking and large-volume sample stacking, through to isotachophoresis, dynamic pH junction, and sweeping. Attention is also given to online or in-line extraction methods that have been used for electrophoresis., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Conductivity detection is a universal detection technique often encountered in electrophoretic separation systems, especially in modern chip-electrophoresis based devices. On the other hand, it is sparsely combined with another contemporary trend of enhancing limits of detection by means of various preconcentration strategies. This can be attributed to the fact that a preconcentration experimental setup usually brings about disturbances in a conductivity baseline. Sweeping with a neutral sweeping agent seems a good candidate for overcoming this problem. A neutral sweeping agent does not hinder the conductivity detection while a charged analyte may preconcentrate on its boundary due to a decrease in its effective mobility. This study investigates such sweeping systems theoretically, by means of computer simulations, and experimentally. A formula is provided for the reliable estimation of the preconcentration factor. Additionally, it is demonstrated that the conductivity signal can significantly benefit from slowing down the analyte and thus the overall signal enhancement can easily overweight amplification caused solely by the sweeping process. The overall enhancement factor can be deduced a priori from the linearized theory of electrophoresis implemented in the PeakMaster freeware. Sweeping by neutral cyclodextrin is demonstrated on an amplification of a conductivity signal of flurbiprofen in a real drug sample. Finally, a possible formation of unexpected system peaks in systems with a neutral sweeping agent is revealed by the computer simulation and confirmed experimentally., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A new version of dispersive liquid-liquid microextraction, namely, cyclodextrin-assisted dispersive liquid-liquid microextraction, with subsequent sweeping micellar electrokinetic chromatography has been developed for the preconcentration and sensitive detection of carbamazepine and clobazam. α-Cyclodextrin and chloroform were used as the dispersive agent and extraction solvent, respectively. After the extraction, carbamazepine and clobazam were analyzed using micellar electrokinetic chromatography with ultraviolet detection. The detection sensitivity was further enhanced using the sweeping technique. Under optimal extraction and stacking conditions, the calibration curves of carbamazepine and clobazam were linear over a concentration range of 2.0-200.0 ng/mL. The method detection limits at a signal-to-noise ratio of 3 were 0.6 and 0.5 ng/mL with sensitivity enhancement factors of 3575 and 4675 for carbamazepine and clobazam, respectively. This developed method demonstrated high sensitivity enhancement factors and was successfully applied to the determination of carbamazepine and clobazam in human urine samples. The precision and accuracy for urine samples were less than 4.2 and 6.9%, respectively., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

One of the most cited limitations of capillary (and microchip) electrophoresis is the poor sensitivity. This review continues to update this series of biennial reviews, first published in Electrophoresis in 2007, on developments in the field of on-line/in-line concentration methods in capillaries and microchips, covering the period July 2014-June 2016. It includes developments in the field of stacking, covering all methods from field amplified sample stacking and large volume sample stacking, through to isotachophoresis, dynamic pH junction, and sweeping. Attention is also given to on-line or in-line extraction methods that have been used for electrophoresis., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A novel and simple method that combines an online concentration technique with an enantioseparation technique for capillary electrophoresis-namely, cation-selective exhaustive injection and sweeping cyclodextrin-modified micellar electrokinetic chromatography (CSEI-sweeping CD-modified MEKC)-realizes the effective enantioseparation of cationic analytes while keeping a significant increase of detection sensitivity. This technique consists of a slight modification of the basic CSEI-sweeping MEKC. The main idea is to simply add an anionic CD as a chiral selector into the micellar buffer including sodium dodecyl sulfate, but not to change any other buffers in order to preserve the online concentration mechanism. When applied to analysis of the street drug, methamphetamine, the method achieved not only a baseline enantioseparation but also limits of detection (LODs; S/N = 3) of 70-90 pg/mL (ppt) for each isomer. This translates to a more than 10 000-fold improvement compared to the LODs by the usual injection method. The present technique, which was made from a slight modification of CSEI-sweeping MEKC, would give an attractive approach that is applicable to almost any analytes for which CSEI-sweeping MEKC is applicable; all that is required is the selection of an appropriate anionic CD to be added to the micellar buffer., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Simultaneous electrophoretic concentration and separation (SECS) was used as a simple and environmental friendly sample preparation strategy for herbicides in beer samples. An electric field was used to facilitate the separation and concentration of the analytes based on their charge from a 20 mL sample of diluted beer into two separate 20 μL aliquots of an acceptor electrolyte housed inside a micropipette. The anionic organophosphonate and cationic quaternary ammonium herbicides were concentrated in the anodic and cathodic pipette, respectively. Under optimized conditions, SECS was completed in 30 min at an applied voltage of 150 V, which provided analyte concentration factors of up to 90. After sample preparation, the SECS concentrate of cationic and anionic herbicides was analyzed by stacking CE with UV detection and also by LC-MS, respectively. The method detection limit for the diluted and undiluted sample was as low as 3 and 15 ng/mL, respectively. The method was linear over two orders of concentration with repeatability and intermediate precision of better than 5.8 and 7.0%RSD, respectively. Accuracy values were between 91.0-115.1%., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A new method for determination of thiosulfate in human urine has been developed and validated. Analytical procedure is very simple and consists of only few steps: derivatization of thiosulfate with 2-chloro-1-methylquinolinium tetrafluoroborate, centrifugation of a mixture, separation of so-formed derivative by micellar electrokinetic chromatography with sweeping and UV detection at 375 nm. A fused-silica capillary with an inlet to detector length of 51.5 cm and a total length of 60 cm (75 μm id) was served as a separation column. The separation voltage of 20.5 kV (∼160 mA) and buffer solution consisting of 0.055 mol/L sodium phosphate (pH 8), 25% acetonitrile, and 0.035 mol/L sodium dodecyl sulfate were found to be the most suitable conditions for the effective separation. The limit of quantification for thiosulfate was 4 μmol/L urine. The method was validated and calibrated for thiosulfate in the range of 4-64 μmol/L (R(2) = 0.9997). The relative standard deviation of the points of the calibration curve varied from 1.2 to 4.8% RSD., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A new method for the determination of hydrogen sulfide in hen tissues has been developed and validated. For estimation of hydrogen sulfide content, a sample (0.1 g) of hen tissue was treated according to the procedure consisted of some essential steps: simultaneous homogenization of a tissue and derivatization of hydrogen sulfide to its S-quinolinium derivative with 2-chloro-1-methylquinolinium tetrafluoroborate, separation of so-formed derivative by micellar electrokinetic chromatography with sweeping, and detection and quantitation with the use of UV detector set to measure analytical signals at 375 nm. Effective electrophoretic separation was achieved using fused silica capillary (effective length 41.5 cm, 75 μm id) and 0.05 mol/L, pH 8 phosphate buffer with the addition of 0.04 mol/L SDS and 26% ACN. The lower limit of quantification was 0.12 μmol hydrogen sulfide in 1 g of tissue. The calibration curve prepared in tissue homogenate for hydrogen sulfide showed linearity in the range from 0.15 to 2.0 μmol/g, with the coefficient of correlation 0.9978. The relative standard deviation of the points of the calibration curve varied from 8.3 to 3.2% RSD., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

One of the most cited limitations of capillary (and microchip) electrophoresis is the poor sensitivity. This review continues to update this series of biannual reviews, first published in Electrophoresis in 2007, on developments in the field of on-line/in-line concentration methods, covering the period July 2012-July 2014. It includes developments in the field of stacking, covering all methods from field-amplified sample stacking and large-volume sample stacking, through to ITP, dynamic pH junction, and sweeping. Attention is also given to on-line or in-line extraction methods that have been used for electrophoresis., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A simple method that consumes low organic solvent is proposed for the analysis of phthalic acid esters in Chinese white spirit using dispersive liquid-liquid microextraction coupled with sweeping-micellar electrokinetic chromatography. Tetrachloromethane and white-spirit-containing ethanol were used as the extraction and dispersing solvents, respectively. The electrophoresis separation buffer was composed of 5 mM β-cyclodextrin, 50 mM sodium dodecyl sulfate and 25 mM borate buffer (pH 9.2) with 9% acetonitrile, enabling the baseline resolution of the analytes within 13 min. Under the optimum conditions, satisfactory linearities (5-1000 ng/mL, r ≥ 0.9909), good reproducibility (RSD ≤ 6.7% for peak area, and RSD ≤ 2.8% for migration time), low detection limits (0.4-0.8 ng/mL) and acceptable recovery rates (89.6-105.7%) were obtained. The proposed method was successfully applied to 22 Chinese white spirits, and the content of dibutyl phthalate in 55% of the samples exceeded the Specific Migration Limit of 0.3 mg/kg established by the domestic and international regulations., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Methotrexate (MTX) is widely used for the treatment of many types of cancer. Folinic acid (FNA) and folic acid (FA) were usually simultaneously supplemented with MTX to reduce the side effects of a folate deficiency. This study, for the first time, included on-line sample preconcentration by stacking and sweeping techniques under reduced or enhanced electric conductivity in the sample region using short chain alkyl imidazolium ionic liquids (ILs) as micelle forming agents for analyte focusing. Both analyte focusing by micelle collapse (AFMC) and sweeping-MEKC had been investigated for the comparison of their effectiveness to examine simultaneously MTX, FNA and FA in plasma and urine under physiological conditions. In sweeping-MEKC, the sample solution without micelles was hydrodynamically injected as a long plug into a fused-silica capillary pre-filled with phosphate buffer containing 3.0 mol/L of 1-butyl-3-methylimidazolium bromide (BMIMBr). Using AFMC, the analytes were prepared in BMIMBr micellar matrix and hydrodynamically injected into the phosphate buffer without IL micelles. The conductivity ratio between BGE and sample (γ, BGE/sample) was optimized to be 3.0 in sweeping-MEKC and 0.33 in AFMC resulting the adequate separation of analytes within 4.0 min. To reduce the possibility of BMIMBr adsorption, an appropriate rinsing protocol was used. The limits of detection were calculated as 0.1 ng/mL MTX, 0.05 ng/mL FNA and 0.05 ng/mL FA by sweeping-MEKC and 0.5 ng/mL MTX, 0.3 ng/mL FNA and 0.3 ng/mL FA by AFMC. The accuracy was tested by recovery in plasma and urine matrices giving values ranging between 90 and 110%. Both stacking and sweeping by BMIMBr could be successfully used for the rapid, selective and sensitive determination of pharmaceuticals in complex matrices due to its fascinating properties, including high conductivity, good thermal stability and ability to form different types of interactions by electrostatic, hydrophobic, hydrogen bonding and π-π interactions. In sweeping-MEKC, the using of BMIMBr enhanced the γ factor, k retention factor and the injected amount of sample. Consequently, this technique offers particular potential for higher sensitivity by giving 22- and 5-fold sensitivity enhancement factors (SEFs) of MTX compared to CZE and AFMC, respectively., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Sweeping is an enrichment method in MEKC, which includes following steps: stacking/destacking of the micelles, sweeping of analyte by the stacked/destacked micelles, destacking/stacking of the swept analyte zone and additional focusing/defocusing due to the retention factor gradient effect (RFGE). In this study, we investigate additional processes, regarding online focusing in cyclodextrin-modified MEKC (CD-MEKC) of hydrophobic basic analytes: dynamic pH junction (sample with pH different from that of BGE) and adsorption of analyte onto the capillary wall within the sample zone. It is demonstrated that the developed method for the assessment of the sweeping efficiency is also applicable to CD-MEKC taking ethylparaben as an example of acidic analytes and desloratadine as an example of basic analytes using different types of β-cyclodextrin. Our previous results regarding RFGE as an additional focusing/defocusing effect in sweeping-MEKC are confirmed for the case that the apparent distribution coefficient differs for the sample and the BGE due to a different content of the complex-forming agent cyclodextrin and due to a pH difference between the sample and the BGE. Despite being significantly more hydrophobic than ethylparaben, desloratadine shows an unexpectedly low enrichment factor. This enrichment factor is nearly unaffected by the addition of CD to the BGE. This unexpected behavior is attributed to wall adsorption of the protonated hydrophobic basic analyte within the sample zone, which significantly counteracts the sweeping process. This assumption is corroborated by an improvement in the enrichment factor achieved via addition of a dynamic coating agent (triethylamine) to the sample solution., (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)