Jinming Lin

Field‐amplified on‐line sample stacking for simultaneous enantioseparation and determination of some β‐blockers using capillary electrophoresis

A capillary electrophoresis method using carboxymethyl‐β‐cyclodextrin as the chiral selector and mixture of methanol and ethanol as the organic additive was successfully developed for the simultaneous enantioseparation and determination of six β‐blockers, namely, carteolol, atenolol, sotalol, metoprolol, esmolol and propranolol in this paper. The most suitable running buffer for enantioseparation was found to be the solution of 20 mmol/L NaH2PO4–Na2HOP4 (pH 5.5) containing 1.5% w/v carboxymethyl‐β‐cyclodextrin, 5% v/v methanol and 5% v/v ethanol. Furthermore, field‐amplified sample injection as an on‐line sample stacking method was developed in order to increase the detection sensitivity. The experimental conditions for both simultaneous enantioseparation and the field‐amplified sample injection method had been investigated in detail. Under the optimum conditions, the detection limits (defined as S/N=3) of this method were 0.01, 0.05, 0.05, 0.05, 0.05 and 0.5 μg/mL for (±) carteolol, (±) atenolol, (±) sotalol, (±) metoprolol, (±) esmolol and (±) propranolol, respectively, which were much lower than those of the conventional methods. The enhancement factors were greatly improved by 25‐fold for the enantiomers of the β‐blockers except five‐fold for (±) propranolol. Eventually, the proposed method has been applied for the analysis of human serum sample.

Improved simultaneous enantioseparation of β-agonists in CE using β-CD and ionic liquids

In this study, approaches to improve chiral resolutions in simultaneous enantioseparation of β‐agonists by CE via a CD inclusion complexation modified with ionic liquids (ILs) are described. Different types of ILs, including tetraalkylammonium‐based ILs, alkylimidazolium‐based ILs and alkylpyridinium‐based ILs, were examined and compared for controlling the EOF in order to improve resolutions of β‐agonists enantiomers. In this regard, tetraalkylammonium‐based ILs were more effective because they could be used at much higher concentrations than other types of ILs. N‐octylpyridinium hexafluorophosphate gave poor resolutions of β‐agonists enantiomers. In addition, when different ILs were mixed to use, they would present particular properties of their own. Moreover, the presence of ILs was essential in the chiral separations of (±) salbutamol, (±) cimaterol and (±) formoterol, which were reportedly not enantioseparated by using the buffer electrolytes containing only β‐CD as a chiral selector.

Microemulsion electrokinetic chromatography coupling with field amplified sample injection and electroosmotic flow suppressant for analysis of some quinolizidine alkaloids

A new rapid and reproducible method using microemulsion electrokinetic chromatography (MEEKC) combining field amplified sample injection and electroosmotic flow suppressant for the analysis of five quinolizidine alkaloids is developed in this paper. For the separation of five quinolizidine alkaloids, a running buffer composed of 1.2% (v/v) 1-butanol, 0.6% (v/v) ethyl acetate and 98.2% (v/v) 1 mM Na(2)B(4)O(7)-2 mM NaH(2)PO(4) buffer solution containing 21 mM sodium cholate (SC) (pH 6.5) was developed. The resolution of the analytes was improved significantly by adding a divalent cation (e.g., Mg(2+)) to the running buffer as an electroosmotic flow modification. In order to analyze trace quinolizidine alkaloids in traditional Chinese herbal medicines, field amplified sample injection (FASI) was applied to increase the detection sensitivity. The detection limits (defined as S/N=3) for the analytes could be as low as 0.0001 microg/mL. This method was applied for the determination of quinolizidine alkaloids in real samples with simple extraction procedures, and the assay results were satisfactory.

Separation and detection of isoquinoline alkaloids using MEEKC coupled with field-amplified sample injection induced by ACN

New methods based on MEEKC coupling with field‐amplified sample injection (FASI) induced by ACN were proposed for five isoquinoline alkaloids (berberine, palmatine, jatrorrhizine, sinomenine and homoharringtonine) in no salt and high salt sample solution (HS). For the separation of five isoquinoline alkaloids, a running buffer composed of 18 mM sodium cholate, 2.4% v/v butan‐1‐ol, 0.6% v/v ethyl acetate, 10% v/v (or 30% v/v) methanol and 87.0% v/v (or 67% v/v) 5 mM Na2B4O7∼10 mM NaH2PO4 buffer (pH 7.5) was developed. In order to improve the sensitivity, FASI induced by ACN was applied to increase the detection sensitivity. The detection limit was found to be as low as 0.0002 μg/mL in no salt sample solution and 0.062 μg/mL in HS. The method has been applied for the analysis of human urine spiked with analytes, and the assay results were proved to be satisfactory, and also the determination of berberine in urine sample after oral administration berberine.

Assay of bradykinin-related peptides in human body fluids using capillary electrophoresis with laser-induced fluorescence detection

A CE with LIF detection was developed for separation and determination of bradykinin (BK)‐related peptides, such as BK, kallidin (Kal), and neurokinin A (NKA). BK‐related peptides were derivatized with FITC prior to CE‐LIF analysis. Sodium borate 10 mmol/L at pH 9.5 was selected as derivatization media in order to get the high efficiency. Three peptides were baseline‐separated within 10 min by using 110 mmol/L sodium borate–sodium hydroxide solution at pH 10.0 as the running buffer. Concentration detection limits (S/N = 3) for BK, Kal, and NKA were 0.08, 0.5, and 0.2 nmol/L, respectively. Meanwhile we have also developed a simple, quick, and sensitive large‐volume sample stacking (LVSS) technique for CE‐LIF detection of BK, Kal, and NKA. By using this stacking technique, the detection limits (S/N = 3) for BK, Kal, and NKA were 0.02, 0.05, and 0.04 nmol/L, respectively. This method has been applied to the assay of human saliva and cerebrospinal fluid with satisfactory results.

Capillary electrophoresis chemiluminescent detection system equipped with a two‐step postcolumn flow interface for detection of some enkephalin‐related peptides labeled with acridinium ester

Despite its low equipment cost and simple design, as one of the sensitive detectors for CE, the chemiluminescence (CL) detector was less developed compared to the detectors of MS and LIF. The main reasons were the limitation of CL reagents, the repeatability problems and the relatively low sensitivity compared to LIF. In this paper, a highly sensitive CE‐CL detection system was developed for detection of some enkephalin‐related peptides labeled with acridinium ester. A new detection interface was designed for CE with CL detection of acridinium ester and its labeled analytes. The interface included two sections: one was used to acidify the capillary outflow so that the corresponding acridinium pseudo‐base form can be changed into acridinium ester form by adding excess acid to the system; the other was designed to provide a suitable solution to produce the CL from acridinium ester. The effect factors, such as pH, the concentration of reaction reagents and the flow rates of the reagents, were investigated. The results showed that acridinium ester had similar CL properties in this interface when pH values of CE BGE were changed from 2.0 to 10.8. The interface was used to detect acridinium ester and three acridinium ester‐labeled enkephalin‐related peptides, the corresponding LODs were found to be in the attomole range. This CL detection system proved to be of high sensitivity, good repeatability, and relatively low cost.

Assay of bradykinin metabolites in human body fluids by CE-LIF coupled with transient ITP preconcentration

A CE with LIF detection was developed for the separation and determination of three bradykinin (BK) metabolites: BK2‐9, BK1‐7 and BK1‐5. BK fragments were derivatized with 5‐(4, 6‐dichloro‐s‐triazin‐2‐ylamino) fluorescein before CE‐LIF analysis. Eighty millimolar of Tris‐H3PO4 (pH 9.0) was selected as the derivatization media. Three BK fragments were baseline separated within 10 min by using 0.2 M TAPS‐Tris buffer (pH 8.5) as the running buffer. Meanwhile we have also developed a simple, quick, and sensitive on‐column transient ITP preconcentration for CE‐LIF detection of three BK fragments. Ten millimolar of Tris‐HCl (pH 9.0) was chosen as the leading electrolyte and 0.2 M TAPS‐Tris (pH 8.5) containing 10 mM 1‐butyl‐3‐methylimidazolium tetrafluoroborate as the terminating electrolyte and also served as the running buffer during CZE separation. By using this transient ITP coupled with CE‐LIF, concentration detection limits (S/N=3) for BK2‐9, BK1‐7 and BK1‐5 were 0.3, 0.1 and 0.1 pmol/L, respectively. This method has been applied to the assay of human saliva and plasma samples with satisfactory results.

Filmy channel microchip with amperometric detection

In this article, a new type of microchip with filmy channels and a sample‐injection fracture is introduced. Unlike commercial microchip, new microchip possessed filmy channel with width 2–3 mm. The effective cooling ability made filmy channel microchip restrain the generation of Joule heat even under electric field of 588 V/cm. Moreover, wider channel could be more easily modified to prevent the absorption of samples, load more samples and result in a higher sensitivity. Sample‐injection fracture was first applied to match the filmy channel in microchip. Equipped with an amperometric detector, the characteristics of the newly designed filmy channel microchip had been studied and the results showed that it had good reproducibility, higher sensitivity and excellent separation ability. The microchip was also applied to separate L‐tryptophans metabolites, namely 5‐hydroxy‐L‐tryptophan, 5‐hydroxytryptamine and 5‐hydroxy‐indole‐3‐acetic acid.