Capillary Electrophoretic Separation of Tricyclic Antidepressants Using 1‐Alkyl‐3‐Methylimidazolium‐Based Ionic Liquids as Background Electrolyte

A capillary electrophoretic (CE) method coupled with the use of 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (1E‐3MI‐TFB) ionic liquid as background electrolyte (BGE) has been developed for the simultaneous separation of nine tricyclic antidepressants, viz. amitriptyline (Ami), clomipramine (Clo), desipramine (Des), fluphenazine (Flu), imipramine (Imi), nortriptyline (Nor), promazine (Pro), thioridazine (Thi) and trimipramine (Tri). Resolution of TCAs with similar molecular structures and pK_a values was accomplished by minute manipulation of the electrophoretic velocities of TCAs via reversed electroosmotic flow (EOF) generated by adsorption of 1E‐3MI cations onto the capillary wall. The optimal separation was obtained with a 50 mM 1E‐3MI‐TFB as the sole BGE at pH 3. Symmetric peaks with efficiencies up to 2.4 × 10⁵ plates/m were achieved. RSD values on migration times and peak areas were in the ranges of 0.63–0.95% and 3.41–6.34% (n = 4), respectively. The role of different alkyl groups on the imidazolium cations was also investigated.     

Original paper application of cyclodextrins as modifiers in electrophoretic separation of metalloporphyrins

Several metallocomplexes of tetrakis-carboxyphenylporphyrin (TCPP) were separated on fused-silica capillary using CZE with UV-VIS detection. Metalloporphyrins of Co(II), Cu(II), Mn(II), Ni(II), and Zn(II) were formed directly in TCPP solution with addition of Cd(II) to increase the formation reaction rate. The composition of BGE, its concentration, and pH were optimized to ensure the stability of complexes and proper resolution. In particular, the problem of signals' shape was investigated and discussed. The presence of beta-CD in borate buffer significantly improved separation efficiency and signal shapes due to formation of inclusion complexes. Under the best separation conditions (50 mM borate running buffer at pH 9 with addition of 2 mM beta-CD, 30 kV applied voltage) a separation of metal complexes with TCPP was accomplished in 16 min.     

毛细管区带电泳法研究肾上腺素类药物的手性分离

使用β－环糊精（β－ＣＤ）及β－ＣＤ－羧甲基（ＣＭ－β－ＣＤ）作为手性选择剂,采用毛细管区带电泳法（ＣＺＥ）对去甲肾上腺素、肾上腺素和异丙肾上腺素的手性分离进行了研究。对影响这类药物手性分离的主要因素〔手性选择剂、背景电解质（ＢＧＥ）、分离体系的酸度和温度〕进行了讨论,并对手性识别机理进行了探讨。     

Determination of pharmaceuticals in drinking water by CD-modified MEKC: separation optimization using experimental design

A suite of 12 widely used pharmaceuticals (ibuprofen, diclofenac, naproxen, bezafibrate, gemfibrozil, ofloxacin, norfloxacin, carbamazepine, primidone, sulphamethazine, sulphadimethoxine and sulphamethoxazole) commonly found in environmental waters were separated by highly sulphated CD-modified MEKC (CD-MEKC) with UV detection. An experimental design method, face-centred composite design, was employed to minimize run time without sacrificing resolution. Using an optimized BGE composed of 10 mM ammonium hydrogen phosphate, pH 11.5, 69 mM SDS, 6 mg/mL sulphated beta-CD and 8.5% v/v isopropanol, a separation voltage of 30 kV and a 48.5 cm x 50 microm id bare silica capillary at 30 degrees C allowed baseline separation of the 12 analytes in a total analysis time of 6.7 min. Instrument LODs in the low milligram per litre range were obtained, and when combined with offline preconcentration by SPE, LODs were between 4 and 30 microg/L.     

NMR characterization of the host-guest inclusion complex between beta-cyclodextrin and doxepin

The interaction between doxepin, a member of the tricyclic antidepressant (TCA) class of drugs, with beta-cyclodextrin (beta-CD) was investigated using NMR. Several TCAs have been reported to form a complex with beta-CD having 1:1 stoichiometry. Previous results from UV-visible spectroscopy, fluorescence measurements, and molecular modeling indicated that for imipramine, desipramine, and amitriptyline, the TCA aliphatic tail is included in the cyclodextrin cavity with apparently no interaction of the tricyclic ring. An alternative view of the doxepin-beta-CD complex is presented in this work using analysis of complexation-induced chemical shifts (CICSs), the method of continuous variation (Job's analysis), and analysis of ROESY spectra. The Job's plot derived from the NMR spectral data confirms that the complex formed has 1:1 stoichiometry. The largest changes in the CICS data were observed for the aromatic protons of one of the doxepin rings, with much smaller chemical shift changes observed for the protons of the other aromatic ring and the doxepin tail. Perhaps the most significant evidence for inclusion of the doxepin tricyclic ring is the strong ROESY cross peaks between the doxepin aromatic resonances and the protons located inside the beta-CD cavity. Changes in the doxepin (1)H NMR spectrum and the behavior of ROESY exchange cross peaks suggest that inclusion complex formation decreases the rate of internal motions of doxepin.     

Enantiomeric separation of citalopram and its metabolites by capillary electrophoresis

A simple and fast capillary electrophoretic method has been developed for the enantioselective separation of citalopram and its main metabolites, namely N-desmethylcitalopram and N,N-didesmethylcitalopram, using beta-cyclodextrin (beta-CD) sulfate as the chiral selector. For method optimisation several parameters were investigated, such as CD and buffer concentration, buffer pH, and capillary temperature. Baseline enantioseparation of the racemic compounds was achieved in less than 6 min using a fused-silica capillary, filled with a background electrolyte consisting of a 35 mM phosphate buffer at pH 2.5 supplemented with 1% w/v beta-CD sulfate and 0.05% w/v beta-CD at 25 degrees C and applying a voltage of -20 kV. A fast separation method for citalopram was also optimized and applied to the analysis of pharmaceutical formulations. Racemic citalopram was resolved in its enantiomers in less than 1.5 min using short-end injection (8.5 cm, effective length) running the experiments in a background electrolyte composed of a 25 mM citrate buffer at pH 5.5 and 0.04% w/v beta-CD sulfate at a temperature of 10 degrees C.     

Analysis of neutral nitromusks in incenses by capillary electrophoresis in organic solvents and gas chromatography-mass spectrometry

Nitromusks used as fragrances in a variety of personal-care products, cleansers, and domestic deodorants, including incense sticks, are neutral nitro aromatic compounds; some of these have been reported as photosensitizers. In this work, their analysis was performed by capillary electrophoresis (CE) in a methanol-based background electrolyte (BGE). In particular, a 10 mM solution of citric acid in methanol was used; under these conditions the strong suppression of the electroosmotic flow favored the use of negatively charged surfactants as additives for the anodic migration of the studied analytes. To this end, sodium taurodeoxycholate (TDC) was supplemented at high concentration (190 mM) to the organic background electrolyte (BGE), showing strong indication of the ability to give micelle-like aggregates. Since nitromusks are characterized by the presence of a nitroaromatic ring with low charge density, their association with TDC aggregates can be ascribed to donor-acceptor interactions. Separation of musk xylene, musk ketone, and the banned musk moskene and musk ambrette was obtained under full nonaqueous BGE; the addition of relatively small water percentages (15% v/v) was found to be useful in improving the separation of pairs of adjacent peaks. Under optimized conditions (190 mM sodium TDC in methanol-water, 85-15 v/v containing citric acid 10 mM) the system was applied to the analysis of nitromusks in incense sticks extracted with methanol. The results were compared with those obtained by the analysis of the same samples using gas chromatography with mass detector. The expected different selectivity of separation obtained using the two techniques can be useful in the unambiguous determination of the analytes; furthermore, a substantial accord of the preliminary quantitative results achieved with the two methods was assumed as the confirmation of the potential reliability of CE performed with high percentage of organic solvent.     

Influence of pH on formation and stability of phosphatidylcholine/phosphatidylserine coatings in fused-silica capillaries

The effect of pH on the formation and stability of phospholipid coatings in fused-silica capillaries in electrophoresis was investigated. A liposome solution consisting of 3 mM of 80:20 mol% phosphatidylcholine/phosphatidylserine (PC/PS) in N-(2-hydroxyethyl)piperazine-N'-(2-ethanesulfonic acid) (HEPES) buffer was used as coating material. The coating was prepared by a method described earlier and five steroids were used as neutral model analytes. First, the effect of pH of the coating solution on the formation and stability of phospholipid coatings was studied at pH 6.5-8.5. The pH of the background electrolyte (BGE) solution (HEPES) was either kept constant at pH 7.4 or made similar to the pH of the liposome coating solution. Results showed that attachment of the coating on the fused-silica wall mostly depends on the protonation of amines of the phospholipids and HEPES. The ability of the phospholipid coating to withstand changes in pH was then investigated by coating at pH 7.5 and separating steroids with acetic acid, 3-(cyclohexylamino)-1-propanesulfonic acid (CAPS), HEPES, or glycine BGE, adjusted to pH between 4.5 and 10.8. The results showed that with use of BGE solution at pH 10.8, the separation of steroids was not successful and the electroosmotic flow was high because of leakage of the phospholipid coating during preconditioning of the capillary with BGE solution. There was no phospholipid leakage with a BGE solution of pH 4.5, indicating that the protonated form of the functional groups of PS and HEPES participating in the attachment of the phospholipid coating to the capillary play an essential role in the success of the coating.     

Chiral capillary electrophoretic determination of the enantiomeric purity of homocamptothecin derivatives, promising antitumor topoisomerase I inhibitors, using highly sulfated CDs and fluorescence detection

EKC methods for the enantiomeric resolution of homocamptothecin derivatives, potent anticancer agents targeting DNA topoisomerase I selected for clinical trials, were developed using highly sulfated beta-CD as chiral selectors at acidic pH. Optimal electrophoretic conditions, with migration times under 15 min, were as follows: for the neutral homocamptothecin analog 1, a BGE of 75 mM phosphate buffer pH 2.5 (H(3)PO(4) + triethanolamine)/ACN - 95/5 v/v, with 7.5% w/v highly S-beta-CD, an applied field of 0.2 kV/cm and a fused capillary temperature control of 30 +/- 0.1 degrees C (typical current approximately 175 microA); for the cationic homocamptothecin 2, a BGE of 25 mM phosphate buffer pH 2.5 (H(3)PO(4) + TEA)/ACN - 90/10 v/v, with 2.5% w/v highly S-beta-CD, an applied field of 0.15 kV/cm and a fused capillary temperature control of 25 +/- 0.1 degrees C (typical current approximately 45 muA), and both are validated. The best results in terms of LOQ were obtained by EC with fluorescence detection: 10 ng/mL and 20 ng/mL for 1 and 2, respectively (LOQ divided by 150 for 1 and 5 for 2 with respect to UV), thus making this method particularly convenient for enantiomeric purity determination of galenic forms. UV detection appears to be an alternative to fluorescence for the analysis of the main component either for the control of galenic forms or for therapeutic adaptation. Moreover, this method exhibits better performances than HPLC.     

Separation of monomethyl-benz[a]anthracene isomers using cyclodextrin-modified electrokinetic chromatography

Cyclodextrin-modified electrokinetic chromatography (CD-EKC) was investigated for the separation of 12 monomethylbenz[a]anthracene (MBA) isomers. Combined use of a polymeric surfactant, poly(sodium 10-undecenyl sulfate) (poly-SUS), with various types of neutral cyclodextrins (CDs) [beta-CD, gamma-CD, dimethyl-beta-CD (DM-beta-CD), trimethyl-beta-CD (TM-beta-CD) and hydroxypropyl-beta-CD (HP-beta-CD)] were successful in CD-EKC separation of the MBA isomers. Baseline resolution of 10 of the 12 isomers, except for 9-MBA and 2-MBA, was achieved with gamma-CD at pH 9.75. The beta-CD, gamma-CD, and beta-CD derivatives (DM-beta-CD, TM-beta-CD, HP-beta-CD) were found to have different resolution and selectivity. Additionally, the tR/t0 values of isomers were found to be dependent on the type and concentration of the CD additives. In general, tR/t0 values of MBA isomers decrease with an increase in the concentration of beta-CD derivatives, whereas the reversed was true when the concentrations of native beta-CD and gamma-CD were varied. The combination of 5 mM gamma-CD, 0.5% (w/v) poly-SUS, 35% (v/v) acetonitrile at a pH of 9.75 provided the best selectivity and resolution of the MBA isomers with a separation time of 110 min. However, the use of 30 mM DM-beta-CD under similar EKC conditions resulted in much faster separation (ca. 16 min) of 10 MBA isomers.     

Online concentration by field-amplified sample injection in acidic buffer for analysis of fangchinoline and tetrandrine in herbal medicine by flow injection-micellar electrokinetic capillary chromatography

A novel, rapid, and continuous online concentration approach based on field-amplified sample injection for the analysis of fangchinoline and tetrandrine was developed in this paper by combination of flow injection-MEKC. The BGE used was a solution composed of 75 mM H3PO4-triethylamine-2.5% v/v polyoxyethylene sorbitan monolaurate-20% v/v methanol buffer (pH* 5.0). The analytes prepared in 50% v/v aqueous ethanol were used as the test analytes. Sample was injected electrokinetically between plugs of water. When the cations reached the boundary between the water plug and BGE, they slowed down and became concentrated. Thereafter, MEKC was initiated for the separation. This results in 6.8-8.9-fold improvement in concentration sensitivity relative to conventional CE methods. The separation could be achieved within 10 min and sample throughput rate can reach up to 50/h. The repeatability (defined as RSD) was 4.8, 4.4% with peak height evaluation and 3.6, 0.94% with peak area evaluation for TET and FAN, respectively.     

Determination of strobilurin fungicide residues in fruits and vegetables by nonaqueous micellar electrokinetic capillary chromatography with indirect laser‐induced fluorescence

A nonaqueous micellar electrokinetic capillary chromatography method with indirect LIF was developed for the determination of strobilurin fungicide residues in fruits and vegetables. Hydrophobic CdTe quantum dots (QDs) synthesized in aqueous phase were used as background fluorescent substance. The BGE solution, QD concentration, and separation voltage were optimized to obtain the best separation efficiency and the highest signal intensity. The optimal BGE solution consists of 40 mM phosphate, 120 mM sodium dodecyl sulfate, 15% v/v water and 15% v/v hydrophobic CdTe QDs in formamide, of which apparent pH is 9.5. The optimized separation voltage is controlled as 25 kV. The resultant detection limits of azoxystrobin, kresoxim‐methyl, and pyraclostrobin are all 0.001 mg/kg, their linear dynamic ranges are 0.005–2.5 mg/kg, and the recoveries of the spiked samples are 81.7–96.1%, 86.5–95.7%, and 87.3–97.4%, respectively. This method has been proved to be sensitive enough to detect the aforementioned fungicides in fruits and vegetables at the maximum residue limits.     

Enantioseparation of chiral tropa alkaloids by means of cyclodextrin-modified microemulsion electrokinetic chromatography

CD-modified microemulsion EKC as a CE technique has been applied to the chiral separation of atropine, scopolamine, ipratropium and homatropine. Enantioseparations of these tropa alkaloids were optimized by using a standard oil-in-water (O/W) microemulsion and varying the nature and concentration of CD additives as well as of the organic modifier (methanol, 2-propanol or ACN) whilst keeping the applied voltage of 15 kV and capillary temperature of 30 degrees C constant. The standard (O/W) microemulsion BGE solution consisted of 0.8% w/w octane, 6.6% w/w 1-butanol, 2.0% w/w SDS and 90.6% w/w 10 mM sodium tetraborate buffer (pH 9.2). Enantioseparations with high resolution and short migration times of all tropa alkaloids were achieved by using heptakis(2,3-di-O-methyl-6-O-sulfo)-beta-CD and sulfated beta-CD in the microemulsion BGE and were superior to corresponding CD-modified CE methods.     

Gold nanomaterials based pseudostationary phases in capillary electrophoresis: A brand‐new attempt at chondroitin sulfate isomers separation

In this work, a CE method with bare gold nanorods (GNRs) based pseudostationary phase was developed and applied for the separation of chondroitin sulfate (CS) isomers, CS, and dermatan sulfate (DS). The separation efficiency was investigated by varying the experimental parameters such as concentration and pH of the BGE, separation voltage, internal diameter of capillary, different size, and morphology of gold nanomaterials. Results showed that different size and morphology of gold nanomaterials had different effects on the separation of CS and DS. The best separation of CS and DS was achieved in the BGE composed of aqueous 150 mmol/L (mM) ethylenediamine + 20 mM sodium dihydrogen phosphate + 30% v/v GNRs, pH 4.5, at the separation voltage of ?10 kV. Capillary was 59.2 cm in length (effective length 49 cm), 50 μm id capillary thermostated at 25°C. CE with bare GNRs used as pseudostationary phase was shown to be a suitable technique for the separation of CS and DS mixtures with wider peaks. RSD of migration time and peak area of CS and DS were 0.13, 0.14 and 0.86, 1.07%, respectively.     

Analysis of drying oils used as binding media for objects of art by capillary electrophoresis with indirect UV and conductivity detection

Capillary electrophoresis (CE) was applied to analyse the long-chain fatty acid composition of vegetable oils, and their degradation products formed upon ageing when drying oils are used as binding media. The analytes were detected with contactless conductivity detection (CCD) and indirect UV absorption, both detectors positioned on-line at the separation capillary. The long-chain fatty acids were resolved in a background electrolyte (BGE) consisting of phosphate buffer (pH = 6.86, 15 mM) containing 4 mM sodium dodecylbenzensulfonate, 10 mM Brij 35, 2% (v/v) 1-octanol and 45% (v/v) acetonitrile. As in this system dicarboxylic analytes, the products of oxidative degradation of unsaturated fatty acids, cannot be determined, a suitable background electrolyte was developed by the aid of computer simulation program PeakMaster. It makes use of a 10 mM salicylic acid, 20 mM histidine buffer, pH 5.85, which combines buffering ability with the optical properties obligatory for indirect UV detection. This buffer avoids system eigenpeaks, which are often impairing the separation efficiency of the system. Separation of the dicarboxylic analytes was further improved by a counter-directed electroosmotic flow (EOF), obtained by dynamically coating the capillary wall with 0.2 mM cetyltrimethylammonium bromide. Long-chain fatty acids and their decomposition products could be determined in recent and aged samples of drying oils, respectively, and in samples taken from two paintings of the 19th century.     

Determination of anthracycline antibiotics doxorubicin and daunorubicin by capillary electrophoresis with UV absorption detection.

Sweeping preconcentration and electrokinetic injection was used for the capillary electrophoretic analysis of trace amounts of biologically active anthracyclines with UV absorption detection. Phosphate buffer (100 mM), pH 2.5, with addition of 40% v/v methanol was used as background electrolyte (BGE). Sodium dodecyl sulfate (150 mM) was added to BGE in the inlet vial as the sweeping agent. The system enables effective separation of anthracyclines as well as cleanup from matrix impurities. Sweeping preconcentration of sample provides an excellent detection limit (1 x 10(-9) mol L(-1)). The method was applied for the determination of therapeutic levels of doxorubicin in real plasma samples.     

Enantioseparation of phenothiazines in cyclodextrin-modified micellar electrokinetic chromatography

In this study, enantioseparations of five phenothiazines in cyclodextrin (CD)-modified micellar electrokinetic chromatography (MEKC) were investigated using a citrate buffer containing tetradecyltrimethylammonium bromide (TTAB) as a cationic surfactant at low pH. Beta-cyclodextrin (beta-CD) and hydroxylpropyl-beta-CD (HP-beta-CD) were selected as chiral selectors. The results indicate that the separation window is greatly enlarged by beta-CD concentration and that the separability and selectivity of phenothiazines are remarkably influenced by the concentrations of both beta-CD and TTAB, as well as buffer pH. The interaction of thioridazine with beta-CDs is considerably reduced in the presence of TTAB micelles due to competitive complexation of thioridazine with TTAB micelles, which is pH-dependent. As a result, effective enantioseparation of thioridazine is simultaneously achievable with that of trimeprazine and promethazine or ethopropazine in MEKC with addition of either beta-CD or HP-beta-CD, respectively, to a micellar citrate buffer containing TTAB at pH 3.5. Better enantioresolution of thioridazine in MEKC than in capillary zone electrophoresis can be obtained.     

Improving sensitivity by large-volume sample stacking combined with sweeping without polarity switching by capillary electrophoresis coupled to photodiode array ultraviolet detection

An easy, simple, and highly efficient on-line preconcentration method for polyphenolic compounds in CE was developed. It combined two on-line concentration techniques, large-volume sample stacking (LVSS) and sweeping. The analytes preconcentration technique was carried out by pressure injection of large-volume sample followed by the EOF as a pump pushing the bulk of low-conductivity sample matrix out of the outlet of the capillary without the electrode polarity switching technique using five polyphenols as the model analytes. Identification and quantification of the analytes were performed by photodiode array UV (PDA) detection. The optimal BGE used for separation and preconcentration was a solution composed of 10 mM borate-90 mM sodium cholate (SC)-40% v/v ethylene glycol, without pH adjustment, the applied voltage was 27.5 kV. Under optimal preconcentration conditions (sample injection 99 s at 0.5 psi), the enhancement in the detection sensitivities of the peak height and peak area of the analytes using the on-line concentration technique was in the range of 18-26- and 23-44-fold comparing with the conventional injection mode (3 s). The detection limits for (-)-epigallocatechin (EGC), (-)-epicatechin (EC), (+)-catechin (C), (-)-epigallocatechin gallate (EGCG), and (-)-epicatechin gallate (ECG) were 4.3, 2.4, 2.2, 2.0, and 1.6 ng/mL, respectively. The five analytes were baseline-separated under the optimum conditions and the experimental results showed that preconcentration was well achieved.     

Analysis of red inks by micellar electrokinetic capillary chromatography with laser‐induced fluorescence detection

A combination of MEKC with a—highly sensitive but not commonly used—LIF detector was tested regarding the possibility of differentiation of red inks. The separation process was conducted in a fused silica capillary (id 50 μm, 60/50 cm total/effective length) in BGE consisting of 40 mM sodium borate, 20 mM SDS and 10% v/v ACN with 30 kV applied. The optimized temperature of storage and capillary was 10 and 25°C, respectively. The samples were prepared using 20 dots (ø 0.5 mm), extracted in 35 μL BGE and diluted with 30 μL of water. The proposed method showed excellent repeatability and reproducibility (RSD (t_m) < 0.8 and < 2.5%, respectively). It was applied to group identification and differentiation of different brands, models, and batches of red printing, stamp, and pen inks. It was demonstrated that differentiation can be performed effectively on the basis of migration times and ratios of peak areas. The high efficiency of the developed method was indicated by discriminating power ranging from 87.3 to 98.8%, for stamp and pen inks, respectively. The results showed that the proposed procedure can be valuable for an objective examination of the red parts of questioned documents.     

Chiral capillary electrophoretic separation of amino acids derivatized with 9-fluorenylmethylchloroformate using mixed chiral selectors of beta-cyclodextrin and sodium taurodeoxycholate

Chiral separation of 19 pairs of amino acid (AA) enantiomers derivatized with 9-fluorenylmethylchloroformate (FMOC) was successfully conducted by capillary electrophoresis using the mixture of beta-CD and sodium taurodeoxycholate (STDC) as selectors. Resolution was considerably superior to that obtained by using either beta-CD or STDC alone. After a systematic inspection, a buffer composed of 150 mM borate and 18% v/v isopropanol at pH 8.0, dissolved with 30 mM beta-CD and 30 mM STDC, was adopted and able to generate baseline resolution (>1.50) for 17 pairs of FMOC-AA enantiomers and somewhat lower resolution for arginine (1.36) and alanine (1.18), respectively. Experimental data revealed that the addition of the second selector did not increase the mobility difference between a pair of enantiomers (Delta mu = mu(D) - mu(L) and the number of theoretical plates (N), but decreased the summed apparent mobility of a pair of enantiomers (Sigma mu = mu(D) - mu(L)), which was mainly due to the decrease of the electroosmotic flow. The variation of Sigma mu was thus the major reason responsible for the improvement of chiral resolution in this study. The result demonstrated that not only the intrinsic selectivity of the selectors was the basis of the chiral separation, but also the non-chiral effect of the selectors, the change of the electroosmotic flow, was an important factor in enhancing the enantioseparation resolution. This study could probably help to explain the reasons for resolution improvement in some dual selectors systems, which are not very clear at present.