Dispersive liquid-liquid microextraction followed by sweeping micellar electrokinetic chromatography-tandem mass spectrometry for determination of six breast cancer drugs in human plasma.

Herein, we have developed a novel method of aqueous-sample dispersive liquid-liquid microextraction (AqS-DLLME) followed by sweeping micellar electrokinetic chromatography-tandem mass spectrometry (MEKC-MS/MS) for simultaneous determination of breast cancer drugs letrozole, anastrozole, palbociclib, ribociclib, abemaciclib, and fulvestrant in human plasma. Coupling of MEKC to MS was possible due to the use of ammonium perfluorooctanoate (APFO) as a volatile surfactant. The MEKC and MS conditions were optimized to achieve a fast, sensitive, selective, and green analysis enabling full separation of the analytes within 16 min. Electrophoretic buffer was 125 mM APFO at apparent pH 10.5 in 32 % MeOH, while sheath liquid was 70 % MeOH with 0.2 % formic acid, delivered at 10 µL/min. Excellent extraction recoveries from plasma ranging from 89.4 to 104.9 % were obtained with a combination of protein precipitation and DLLME. The developed method was validated according to the ICH guidelines. Remarkable selectivity, accuracy (bias < 6.7 %), precision (RSD < 15.8 %), and stability (bias < 10.4 %) with insignificant matrix effect (RSD < 14.0 %) and no carry-over were obtained over a wide range of concentrations. Linearity with inter-day slope RSD lower than 8.7 % was demonstrated. With this method, very low concentrations could be detected after the injection of only 68.7 nL of the sample. The method was applied to plasma samples from six women currently receiving breast cancer treatment. Determined concentrations of the drugs of interest agreed with concentrations found in clinical studies, thus proving the suitability of the developed method for therapeutic drug monitoring as a superior alternative to published LC-MS methods.

Rapid indirect separation of glutamine enantiomers by micellar electrokinetic chromatography. Analysis of dietary supplements.

Glutamine is the most abundant free proteinogenic α-amino acid. It is naturally produced in the organism and acts as a precursor for the synthesis of different biologically important molecules (such as proteins or nucleotides). However, under stressful conditions, the organism is unable to produce it in enough amounts to function properly. Thus, glutamine (Gln)-based supplements have become increasingly popular over the last decade. Since legal regulations establish that amino acid-based dietary supplements must contain only the L-enantiomer and not the racemate, adequate chiral methodologies are required to achieve their quality control. In this work, an analytical methodology based on the use of micellar electrokinetic chromatography is proposed for the rapid enantiomeric determination of DL-Gln in dietary supplements. Using (+)-1-(9-fluorenyl)-ethyl chloroformate as a derivatizing agent and ammonium perfluorooctanoate as separation medium, the Gln diastereoisomers formed under optimal conditions were separated in 8 min with a resolution of 2.8. The analytical characteristics of the method were evaluated in terms of linearity, precision, accuracy, and limits of detection/quantitation, and they were found appropriate for the analysis of L-Gln-based dietary supplements.

Rapid enantiomeric separation of indacaterol by electrokinetic chromatography.

The first chiral methodology enabling the separation of indacaterol enantiomers was developed in this work by cyclodextrin-electrokinetic chromatography. Indacaterol (IND) is a chiral drug marketed as a pure enantiomer. Then, the separation and quantification of each enantiomer is of great importance for the quality control of pharmaceutical formulations. After selecting the most suitable chiral selector and background electrolyte, two Box-Behnken designs were achieved to optimize the electrophoretic conditions using two different approaches to shorten analysis times: i) decreasing the capillary length, or ii) performing a short-end injection. Indacaterol enantiomers were separated in less than 5 min with a resolution value of 3.6 under the optimal separation conditions: 0.7% (m/v) carboxymethyl-α-cyclodextrin in 50 mM sodium formate buffer (pH 4.0) and using a short-end injection. Then, the analytical characteristics of the method were evaluated and LODs of 0.05 mg/L for S-IND and 0.04 mg/L for R-IND were achieved. Also, the method allowed the detection of a 0.1% enantiomeric impurity (S-IND) in the R-IND-based pharmaceutical formulations. The developed method was applied to the analysis of two pharmaceutical formulations. Percentages of 97 ± 3% and 103 ± 6% of R-IND with respect to the labeled amounts were found.

Chiral separation of propranolol by electrokinetic chromatography using nanodiamonds and human serum albumin as a pseudo-stationary phase in river water.

Propranolol is currently considered as an emerging contaminant in water bodies. In this study, R- and S-propranolol were determined in river samples by electrokinetic chromatography (EKC) using nanodiamonds (NDs) and human serum albumin (HSA) as a pseudo-stationary phase in order to achieve enantioseparation. Previously, river samples were preconcentrated using a column filled with Amberlite® IR-120 and Dowex® 50WX8 resins. The setting up of influential factors such as temperature, voltage, pH, and HSA and NDs concentration is accurately described along this manuscript. A multivariate study and optimization was carried out to obtain the enantioseparation of propranolol (Rs = 2.91), which was reached under the following experimental conditions: voltage of 16 kV, temperature of 16°C, phosphate buffer pH 9.5, NDs of 0.20%, and HSA of 15 µmol l-1 . The recoveries of analytes under optimal conditions were higher than 98%. The limits of detection were 0.85 µg l-1 for R- and S-propranolol. The method was applied to real samples, and the obtained results in three different water sources studied were 1.02, 0.59, and 0.30 µg l-1 for the R-enantiomer and 0.99, 0.54, and 0.28 µg l-1 for the S-enantiomer. The accuracy of the proposed methodology (including bias and precision) has allowed us to propose it as a successful tool for the control of water quality.

On-line concentration and separation of multiple derivatized monosaccharides from edible fruit with cyclodextrin-encapsulated sweeping by micellar electrokinetic chromatography.

An on-line enrichment and separation of multiple derivatized monosaccharides with cyclodextrin-encapsulated sweeping (CDES) by micellar electrokinetic chromatography (MEKC) was presented. Five monosaccharides (L-(-)-Mannose, D-(+)-Glucose, D-(-)-Ribose, D-(+)-Xylose, and L-(+)-Rhamnose) were derivatized with 1-phenyl-3-methyl-5-pyrazolone, subsequently concentrated and separated by MEKC. The optimized conditions were as follows: 50 mM phosphoric acid (PA), 100 mM sodium dodecyl sulfate (SDS), and 30 % (v/v) methanol in background solution; 140 s injection of sample solution containing 50 mM CD and 100 mM PA, followed by 90 s injection of 40 mM SDS solution. Under the optimized conditions, the correlation coefficients ≥ 0.9953, and the limits of detection ranged from 4.2 to 7.4 ng/mL. Relative standard deviation values ranged from 0.24-4.23 %, and sensitivity enrichment factors were in the range of 53-82 compared with typical injection (50 mbar, 3 s). The CDES-MEKC method was successfully applied to Jujube with good recoveries of 84.22-104.33 %. The method provides new ideas for the on-line enrichment and detection of trace monosaccharides and even other target analytes in foods with complex matrices.

Determination of ticagrelol in rat plasma and tablets by micellar electrokinetic chromatography coupled with large volume sample stacking: Application to a pharmacokinetic study.

A method using micellar electrokinetic chromatography coupled with large-volume sample stacking for the determination of ticagrelol was developed and validated. The analysis was performed in a fused silica capillary (41.5 cm effective length, 50 µm diameter) with ultraviolet detection at 195 nm. The background electrolytes were 30 mM phosphate buffer of pH 3.0 with 120 mM sodium dodecylsulfate and 10 % (v/v) acetonitrile (120 s X 50 mbar; 20°C; -18 kV) and 30 mM borate buffer of pH 8.5 with 75 mM sodium dodecylsulfate (120 s X 50 mbar; 20°C; 25 kV); under acidic and alkaline conditions, respectively. The method was found to be reliable with respect to specificity, linearity of the calibration line (R2  > 0.99), repeatability (relative standard deviation 2.56%-3.34%), and accuracy (recovery in the range 101.21%-102.67%). The limits of detection and quantitation were 0.032, 0.071, and 0.087, 0.188 µg/mL, respectively. The method was successfully applied for the determination of ticagrelol concentrations in rat plasma and tablets with good recoveries and reproducibility. The presented method proved to be suitable for monitoring ticagrelor in rat plasma.

Two-step pressure injection-assisted online enrichment of herbicides from foods with affinity micelle sweeping by micellar electrokinetic chromatography.

A novel online two-step pressure injection-assisted stacking preconcentration method, which involves sweeping and affinity micelles in micellar electrokinetic chromatography was developed to simultaneously measure various organic anions. The micellar solution was a mixed solution that contained 0.3 mM didodecyldimethylammonium bromide and 20 mM borax. After the micellar solution was injected for 60 s, the tested analytes prepared in 20 mM borax were introduced into the capillary for 150 s. The key experimental factors that influenced the separation and sensitivity were investigated and optimized, including the concentration and injection time of the micellar solution, the concentration of borax in the sample solution, the concentration of sodium dodecyl sulfate and borax in the background electrolyte (BGE), the content of acetonitrile in the BGE and the injection time of the sample solution. Compared with typical injection methods, this method achieved sensitivity enhancement factors ranging from 85 to 97 under optimized conditions. Good linearity for matrix-matched calibration was established for all analytes with R2 values of 0.9986-0.9996. The intraday (n = 6) and interday (n = 6) precisions of the method were less than 2.85% when expressed as relative standard deviations. When the method was applied to analyze rice and dried ginger samples, analyte recoveries ranged from 85.81% to 106.59%. Through sweeping and affinity micelles, stacking preconcentration method was successfully employed to analyze trace amounts of fenoprop and 2,4-dichlorophenoxyacetic acid in rice and dried ginger samples.

Reverse-Polarization High-Performance Layer Electrochromatography-A New Approach to Anion Separation.

High-performance layer electrochromatography (HPLEC) combines the advantages of overpressured-layer chromatography (OPLC) and pressurized planar electrochromatography (PPEC) while overcoming some of their limitations. HPLEC equipment can work in various HPLEC, OPLC, and PPEC modes. The equipment enables HPLEC analysis also with an electroosmotic effect directed against the hydrodynamic flow of the mobile phase. The change in the electric field direction in the separation system does not result in a change in either the direction of the mobile phase flow or the direction of solute migration. The hydrodynamic flow generated by the pump dominates the electroosmotic effect and enables separation against the direction of the latter. Reversed-polarization HPLEC may be advantageous for the analysis of anionic compounds, as it facilitates faster and more selective separation than OPLC performed in similar conditions. This separation mode provides a new possibility to develop and optimize separation methods by performing separation against the electroosmotic effect and without need of any modification of the adsorbent surface. A drawback of this separation mode is the increase in the backpressure at the mobile phase inlet and the limitation of the mobile phase flow rate. Currently, contrary to the single-channel mode, multi-channel reverse-polarity HPLEC still requires some technical and methodological improvements.

Analytical Quality by Design-Compliant Development of a Cyclodextrin-Modified Micellar ElectroKinetic Chromatography Method for the Determination of Trimecaine and Its Impurities.

In 2022, the International Council for Harmonisation released draft guidelines Q2(R2) and Q14, intending to specify the development and validation activities that should be carried out during the lifespan of an analytical technique addressed to assess the quality of medicinal products. In the present study, these recommendations were implemented in Capillary Electrophoresis method development for the quality control of a drug product containing trimecaine, by applying Analytical Quality by Design. According to the Analytical Target Profile, the procedure should be able to simultaneously quantify trimecaine and its four impurities, with specified analytical performances. The selected operative mode was Micellar ElectroKinetic Chromatography employing sodium dodecyl sulfate micelles supplemented with dimethyl-ß-cyclodextrin, in a phosphate-borate buffer. The Knowledge Space was investigated through a screening matrix encompassing the composition of the background electrolyte and the instrumental settings. The Critical Method Attributes were identified as analysis time, efficiency, and critical resolution values. Response Surface Methodology and Monte Carlo Simulations allowed the definition of the Method Operable Design Region: 21-26 mM phosphate-borate buffer pH 9.50-9.77; 65.0 mM sodium dodecyl sulfate; 0.25-1.29% v/v n-butanol; 21-26 mM dimethyl-ß-cyclodextrin; temperature, 22 °C; voltage, 23-29 kV. The method was validated and applied to ampoules drug products.

In-capillary screening and quantifying the antioxidants of Yangxinshi Tablet using field-enhanced sample injection-micellar electrokinetic chromatography.

An in-capillary 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulphonate) as oxyradicals combining field-enhanced sample injection with micellar electrokinetic chromatography was developed for screening and determination of the major antioxidants in Yangxinshi Tablet. To obtain simultaneous separation and detection of radicals and analytes, relevant factors were optimized separately. Under the optimum conditions, four compounds including salvianolic acid B, hyperoside, puerarin, and caffeic acid were identified as the major antioxidants. All validation results covering recovery, precision, and stability demonstrated good applicability of the method. On this basis, the total antioxidant activity was successfully evaluated in terms of the decreased peak area of radicals. There was a correlation coefficient of 0.8974 between the total contents of major antioxidants and the total antioxidative activity of the sample. Therefore, these four compounds were selected as combinatorial markers for the quality evaluation of Yangxinshi Tablet. It was concluded that the established method presented a powerful potential to screen and quantify active ingredients in the complex preparation of Chinese medicine.

Efficient determination of non-steroidal anti-inflammatory drugs by micellar electrokinetic chromatography in wastewater.

Recently, non-steroidal anti-inflammatory drugs (NSAIDs) have been increasingly used in humans and animals. Despite being effective against a wide variety of diseases, they pose a threat to aquatic environments. In the current work, a highly efficient, selective, and sensitive micellar electrokinetic chromatography (MEKC) method was developed for the determination of five NSAIDs in environmental water samples. The optimal separation BGE was 15 mM borate buffer (pH 9), 90 mM SDS, and 10% methanol at a separation voltage of 15 kV and a hydrodynamic injection of 10 mbar for 5 s. The results presented in this study provide a higher number of theoretical plates N > 780 000 with excellent RSDs of 0.1-1.5% and great sensitivity (3-15 µg L-1) for NSAIDs. To validate this method, the solid phase extraction method was optimized using two different cartridges (C18 and Oasis HLB); the results showed excellent recoveries (73-111.6%) for all the analytes in wastewater samples.

Separation of unsaturated C18 fatty acids using perfluorinated-micellar electrokinetic chromatography: I. Optimization and separation process.

Ammonium perfluorooctanoate (APFOA) was used as a surfactant for the separation of free unsaturated C18 fatty acids by micellar electrokinetic chromatography. A simple background electrolyte of 50 mM APFOA water/methanol (90:10, v/v) at pH = 10 enabled the repeatable separation of oleic acid, elaidic acid, linoleic acid, and alpha-linolenic acid in less than 20 min. Separation conditions were optimized regarding various parameters (organic solvent, counterion, APFOA concentration, and pH). Because the repulsive interactions between fluorocarbon chains and hydrogenated chains are known to lead to segregation and phase separation, the choice of perfluorinated micelles to separate such perhydrogenated long-chain acids could appear astonishing. Therefore, the critical micelle concentration, the charge density, and the mobility of the micelles have been determined, resulting in a first description of the separation process.

Induced sample via transient isotachophoresis mediated with sweeping in micellar electrokinetic chromatography for the dual-stacking strategy of non-steroidal anti-inflammatory drugs in environmental water samples.

Realising the need to devise a simple, sensitive, and reliable detection method, this study investigated the development of a dual-stacking transient isotachophoresis (t-ITP) and sweeping in micellar electrokinetic chromatography with diode array detector (t-ITP/sweeping-MEKC-DAD) for the determination of selected non-steroidal anti-inflammatory drugs (NSAIDs); ketoprofen, diclofenac and naproxen from aqueous matrices. Prior to the system setup, various parameters were optimised to assess the potential use of the t-ITP paired with the sweeping stacking technique in micellar background electrolyte for dual preconcentration and separation of trace amounts of NSAIDs. Once the optimum conditions have been established, the method performance was validated and applied to 17 environmental water samples. Based on the results, the combined t-ITP and sweeping approach significantly improved the stacking and separation sensitivity. A large volume of samples could also be introduced and subsequently separated by MEKC with greater focusing effects due to the sweeping. Under optimised conditions, the developed method exhibited excellent linearity at a high range (0.1-500 ng/mL, r2 ≥ 0.998), low limits of detection (LODs) of 0.01-0.07 ng/mL, and a remarkable relative recovery (RR) of 99.6-101.9% with a relative standard deviation (RSD) of 1.4-8.6% (n = 9). Ultimately, the sensitivity enhancement factors improved up to 666-fold using the optimised method. Therefore, the proposed method presents a simplified yet effective and suitable for the determination of NSAIDs from aqueous matrices.

Development of the Microemulsion Electrokinetic Capillary Chromatography Method for the Analysis of Disperse Dyes Extracted from Polyester Fibers.

The study aimed to develop a method for the separation of dispersed dyes extracted from polyester fibers. Nine commercially available disperse dyes, which were used to dye three polyester fabrics, were tested. Extraction of dyes from 1 cm long threads was carried out in chlorobenzene at 100 °C for 6 h. The separation was performed using microemulsion electrokinetic capillary chromatography (MEEKC) with photodiode array detection. Microemulsion based on a borate buffer with an organic phase of n-octane and butanol and a mixture of surfactants, sodium dodecyl sulphate and sodium cholate, were used. The addition of isopropanol and cyclodextrins to microemulsion resulted in a notable improvement in resolution and selectivity. The content of additives was optimized by using the Doehlert experimental design. Values of the coefficient of variance obtained in the validation process, illustrating the repeatability and intermediate precision of the migration times fit in the range of 0.11-1.24% and 0.58-3.21%, respectively. The developed method was also successfully applied to the differentiation of 28 real samples-polyester threads collected from clothing. The obtained results confirmed that proposed method may be used in the discriminant analysis of polyesters dying by disperse dyes and is promisingly employable in forensic practice.

Comparison of the Performance of Different Bile Salts in Enantioselective Separation of Palonosetron Stereoisomers by Micellar Electrokinetic Chromatography.

Bile salts are a category of natural chiral surfactants which have ever been used as the surfactant and chiral selector for the separation of many chiral compounds by micellar electrokinetic chromatography (MEKC). In our previous works, the application of sodium cholate (SC) in the separation of four stereoisomers of palonosetron (PALO) by MEKC has been studied systematically. In this work, the parameters of other bile salts, including sodium taurocholate (STC), sodium deoxycholate (SDC), and sodium taurodeoxycholate (STDC) in the separation of PALO stereoisomers by MEKC were measured and compared with SC. It was found that all of four bile salts provide chiral recognition for both pairs of enantiomers, as well as achiral selectivity for diastereomers of different degrees. The structure of steroidal ring of bile salts has a greater impact on the separation than the structure of the side chain. The varying separation results by different bile salts were elucidated based on the measured parameters. A model to describe the contributions of the mobility difference of solutes in the aqueous phase and the selectivity of micelles to the chiral and achiral separation of stereoisomers was introduced. Additionally, a new approach to measure the mobility of micelles without enough solubility for hydrophobic markers was proposed, which is necessary for the calculation of separation parameters in MEKC. Under the guidance of derived equations, the separation by SDC and STDC was significantly improved by using lower surfactant concentrations. The complete separation of four stereoisomers was achieved in less than 3.5 min by using 4.0 mM of SDC. In addition, 30.0 mM of STC also provided the complete resolution of four stereoisomers due to the balance of different separation mechanisms. Its applicability for the analysis of a small amount of enantiomeric impurities in the presence of a high concentration of the effective ingredient was validated by a real sample.

Nanoemulsion supported microemulsion electrokinetic chromatography coupled with selected preconcentration techniques as an approach for analysis of highly hydrophobic compounds.

In this paper, an oil-in-water (O/W) nanoemulsion (NE) prepared by water cold dilution of an O/W microemulsion (ME) was introduced as a sample matrix in microemulsion electrokinetic capillary chromatography (MEEKC) for the highly hydrophobic compounds analysis. Several model compounds with log PO/W values in the 4.1-10.9 range, from different chemical groups, including retinol, α-tocopherol, cholecalciferol, phylloquinone, menaquinone-7, dichlorodiphenyltrichloroethane, ivermectin have been tested. As a proof of the concept of NE formation, a dynamic light scattering technique was employed to determine the size distribution profile of NE particles. Moreover, due to relatively low conductivity of the NE matrix (50-100 times lower in comparison to the separation buffer) and a negative electric charge provided to hydrophobic compounds through NE dispersed phase, NE matrices have been combined with preconcentration techniques based on electrokinetic dosing, namely field amplified sample injection (FASI) and pressure assisted electrokinetic injection (PAEKI). The detection limits for vitamin K1 and K2-MK7 in the NE matrix in combination with FASI (NE-MEEKC-FASI) as well as PAEKI (NE-MEEKC-PAEKI) were up to 42.9 and 12.1 ng mL-1, respectively. In comparison to standard hydrodynamic injection for microemulsion sample matrix NE-MEEKC-PAEKI grant 45-fold improvement in signal sensitivity. The study presents an innovative approach, as it enables the use of preconcentration techniques for highly hydrophobic compounds (log PO/W > 4), which was not previously possible for implementation in the electromigration techniques. Likewise, the use of organic solvents has been reduced by using ME as a solvent for stock solutions and diluting with water prior to the analysis. The application to real samples was investigated using a dietary supplement containing vitamin K2-MK7 obtained from the fermentation product of soybeans.

Understanding nonlinear composition dependency of enantioselectivity in chiral separation using mixed micelle.

HYPOTHESIS: Mixtures of chiral and achiral building blocks of supramolecules exhibit interesting cooperative phenomena, indicated by the nonlinear composition dependence of the chiral properties. However, the nonlinear composition dependence of the enantioselectivity of mixed micelles is not well understood. It was hypothesized that in-depth understanding can be achieved by carefully investigating the composition dependence of the properties. EXPERIMENTS: In this work, the nonlinear composition dependence of the enantioselectivity was found for the mixed micelle of achiral and chiralN-acyl amino acids by micellar electrokinetic chromatography (MEKC). Capillary electrophoresis, circular dichroism (CD) spectroscopy, surface tension measurement, and fluorescence spectroscopy were used to investigate the mechanisms. FINDINGS: Four mechanisms that could be causing the nonlinearity were investigated: (i) synergistic and antagonistic interactions of the surfactants; (ii) the chiral transfer from chiral to achiral surfactant; (iii) differences in the retention factor; and (iv) cooperative chiral recognition of the chiral and achiral surfactant. The investigation of the composition dependency of critical micelle concentration (CMC) and molar circular dichroism revealed that the effect of (i) and (ii) was negligibly small. The newly derived equations for (iii) and (iv) revealed that (iii) and (iv) have a major or medium effect on the nonlinear enantioselectivity.

Capillary Electrophoresis Mass Spectrometry: Developments and Applications for Enantioselective Analysis from 2011-2020.

It is now more than 25 years since the first report of enantioselective analysis by capillary electrophoresis-mass spectrometry (CE-MS) appeared. This article reviews the power of chiral CE-MS in resolving issues on the use of chiral selector incompatibility with MS and poor detectability encountered for chiral compounds by UV detection. The review begins with the general principles, requirements, and critical aspects of chiral CE-MS instrumentation. Next, the review provides a survey of MS-compatible chiral selectors (CSs) reported during the past decade, and the key achievements encountered in the time period using these CSs. Within the context of the strategies used to combine CE and MS, special attention is paid to the approaches that feature partial filling technique, counter-migration techniques, and direct use of CS, such as molecular micelles. In particular, the development and application of moving and fixed CS for EKC-MS, MEKC-MS, and CEC-MS demonstrate how various chiral compounds analyses were solved in a simple and elegant way during the 2010-2020 review period. The most noteworthy applications in the determination of chiral compounds are critically examined. The operating analytical conditions are detailed in the Tables, and the authors provide commentary on future trends of chiral separations by CE-MS.

The two-phase amphiphilic preconcentration based on surfactants to enrich phenolic compounds from diluted plant extracts and rat urine by micellar electrokinetic chromatography.

A novel technology by two-phase amphiphilic preconcentration based on surfactants was established for enriching phenolic compounds by micellar electrokinetic chromatography (MEKC). The cationic surfactant cetyltrimethylammonium chloride (CTAC) was combined with the anionic analytes that existed in the sample solution before injection. The boundary was formed between CTAC and sodium dodecyl sulfate (SDS) in the background solution when the sample solution was injected into the capillary, where the analytes bound inside micelles were released due to the stronger electrostatic force between SDS and CTAC. This procedure accelerated the separation of analytes from CTAC and greatly improved the enrichment efficiency. The optimal conditions were obtained after a series of optimizations, and the sensitivity enrichment factors of the four analytes were in the range of 39-93 compared to typical injections in capillary zone electrophoresis. Good linearity for matrix-matched calibrations was established for all analytes with R2 values of 0.9993-0.9997. The limits of detection (S/N = 3) for kaempferol, quercetin, salvianolic acid C, and salvianolic acid B were 0.0166, 0.0292, 0.0215, and 0.0195 µg/ml, respectively. The intracapillary RSDs of the analytes ranged from 0.8% to 1.3% for migration time and from 0.4% to 1.8% for peak areas. The developed method was successfully applied to the determination of phenolic compounds, the main compounds of Salvia miltiorrhiza Bge., and had been validated for the determination of spiked recoveries in rat urine.

Development of transient trapping micellar electrokinetic chromatography coupled with mass spectrometry for steroids analysis.

An on-line sample preconcentration technique based on transient trapping (tr-trapping) in micellar electrokinetic chromatography (MEKC) was applied for steroid detection with UV (tr-trapping-UV) and electrospray ionization mass spectrometry detection (tr-trapping-ESI-MS). ESI-MS was used to improve the sensitivity in MEKC. The MEKC separation was carried out using volatile ammonium formate as a background solution to facilitate the coupling with ESI-MS. The partial introduction of a sodium dodecyl sulfate (SDS) micellar solution before the introduction of a sample solution to the capillary provided the effective preconcentration of analytes. At the same time, the SDS micelle would not enter the ESI-MS system, so its interference in ESI-MS detection was suppressed under the optimal condition, then five steroids can be separated by the developed method. In tr-trapping-ESI-MS, an acidic condition of pH 3.5 was employed to suppress the electroosmotic flow, which can avoid micellar solution migrating to the MS instrument. The developed method showed that the micellar solution requires a twofold slower time than the sample to migrate along the column, which can prohibit the cause of the problem with the MS instrument and interference signal of SDS in the steroid's detection. The tr-trapping-ESI-MS protocol showed up to 540-fold enhancements of the peak intensity and 50-fold improvement of the limit of detection compared with capillary zone electrophoresis using androsterone as a model sample.