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Analytica Chimica Acta (v.594, #2)
Molecularly templated materials in chemical sensing by Ellen L. Holthoff; Frank V. Bright (pp. 147-161).
Biologically-based recognition elements (e.g., antibodies, aptamers, enzymes, etc.) are used as the recognition element within a wide variety of assays and sensor systems. There are, however, compelling reasons for researchers to develop inexpensive, robust, and reusable alternatives for these expensive and unstable biorecognition elements. This review summarizes recent research efforts on the development of molecularly templated (sometimes called molecularly imprinted) organic and inorganic polymers as possible replacements for expensive/labile biorecognition elements. The review begins with a briefing on biosensing and the pertinent issues and limitations. The focus then swings toward molecularly templating within organic and inorganic (xerogels) polymers to create materials with analyte binding characteristics akin to a biorecognition element. The review then describes several recent developments wherein analyte recognition and an analyte-dependent transduction methodology are simultaneously incorporated directly within the templated materials. The review ends by outlining the current state-of-the-art and the remaining issues and impediments.
Keywords: Sensors; Materials; Molecular imprinting
Development of a selective optical sensor for Cr(VI) monitoring in polluted waters by Raquel Güell; Clàudia Fontàs; Victòria Salvadó; Enriqueta Anticó (pp. 162-168).
An optical sensor is described for the sensitive and selective determination of the Cr(VI) ion in aqueous solutions. The optode membrane is prepared by incorporating Aliquat 336 as an ionophore and a chromoionophore (4′,5′-dibromofluorescein octadecyl ester) in a poly(vinyl chloride) (PVC) membrane containing ortho-nitrophenyloctyl ether ( o-NPOE) as a plasticizer. The response to Cr(VI) is indicated by co-extraction of the target species and of hydrogen ions into the bulk of the membrane yielding large absorbance changes which can easily be measured in the visible spectral range. The optode membrane shows a reversible response in the concentration range of 1.1×10−5–1.0×10−3M and has been shown to be more selective towards theHCrO4− ion than other anions with a selectivity pattern HCrO4−>SCN−≈ClO4−>NO3−≈I−≈NO2−≫H2PO4−≈Cl−≈SO42−. The sensing method developed has successfully been applied to the determination of Cr(VI) in spiked river water as well as in electroplating rinse waters.
Keywords: Cr(VI); Bulk optode; Aliquat 336; Polluted waters
Tris(2,2′-bipyridyl)ruthenium(II) electrochemiluminescence sensor based on carbon nanotube/organically modified silicate films by Ying Tao; Zhi-Jie Lin; Xiao-Mei Chen; Xi Chen; Xiao-Ru Wang (pp. 169-174).
In this paper, a novel electrochemiluminescence (ECL) sensor was constructed to determine herring sperm (HS) double-stranded (ds) DNA. Tetramethoxysilane and dimethyldimethoxysilane were selected as co-precursors to form an organically modified silicate (ORMOSIL) film for the immobilization of multiwall carbon nanotubes (MWNTs) wrapped by poly( p-styrenesulfonate) (PSS), and then Tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)32+) was successfully immobilized on a glassy carbon electrode via ion-association. PSS was employed to increase the conductivity of the ORMOSIL film and disperse the cut MWNTs, which were cut and shortened in a mixture of concentrated sulfuric and nitric acids, in the film. It was found that MWNTs could adsorb Ru(bpy)32+ and acted as conducting pathways to connect Ru(bpy)32+ sites to the electrode. MWNTs also played a key role as materials for the mechanical and thermal properties. The ECL performance of this modified electrode was evaluated in a flow injection analysis (FIA) system, and the detection limit ( S/ N=3) for HS ds-DNA was 2.0×10−7gmL−1 with a linear range from 1.34×10−6 to 6.67×10−4gmL−1 ( R2=0.9876). In addition, the ECL sensor presented excellent characteristics in terms of stability, reproducibility and application life.
Keywords: Electrochemiluminescence sensor; Carbon nanotubes; Tris(2,2′-bipyridyl)ruthenium(II); Nucleic acid
Selective and sensitive electrochemical detection of glucose in neutral solution using platinum–lead alloy nanoparticle/carbon nanotube nanocomposites by Hui-Fang Cui; Jian-Shan Ye; Wei-De Zhang; Chang-Ming Li; John H.T. Luong; Fwu-Shan Sheu (pp. 175-183).
Electrodeposition of Pt–Pb nanoparticles (PtPbNPs) to multi-walled carbon nanotubes (MWCNTs) resulted in a stable PtPbNP/MWCNT nanocomposite with high electrocatalytic activity to glucose oxidation in either neutral or alkaline medium. More importantly, the nanocomposite electrode with a slight modification exhibited high sensitivity, high selectivity, and low detection limit in amperometric glucose sensing at physiological neutral pH (poised at a negative potential). At +0.30V in neutral solution, the nanocomposite electrode exhibited linearity up to 11mM of glucose with a sensitivity of 17.8μAcm−2mM−1 and a detection limit of 1.8μM (S/N=3). Electroactive ascorbic acid (0.1mM), uric acid (0.1mM) and fructose (0.3mM) invoked only 23%, 14% and 9%, respectively, of the current response obtained for 3mM glucose. At −0.15V in neutral solution, the electrode responded linearly to glucose up to 5mM with a detection limit of 0.16mM (S/N=3) and detection sensitivity of ∼18μAcm−2mM−1. At this negative potential, ascorbic acid, uric acid, and fructose were not electroactive, therefore, not interfering with glucose sensing. Modification of the nanocomposite electrode with Nafion coating followed by electrodeposition of a second layer of PtPbNPs on the Nafion coated PtPbNP/MWCNT nanocomposite produced a glucose sensor (poised at −0.15V) with a lower detection limit (7.0μM at S/N=3) and comparable sensitivity, selectivity and linearity compared to the PtPbNP/MWCNT nanocomposite. The Nafion coating lowered the detection limit by reducing the background noise, while the second layer of PtPbNPs restored the sensitivity to the level before Nafion coating.
Keywords: Glucose detection; Platinum–lead nanoparticle; Carbon nanotube; Amperometry; Nafion; Interferences
Electrocatalytic detection of estradiol at a carbon nanotube|Ni(Cyclam) composite electrode fabricated based on a two-factorial design by Xiaoqiang Liu; Danny K.Y. Wong (pp. 184-191).
In this work, we have developed a carbon nanotube|Ni(cyclam)-coated glassy carbon electrode to achieve minimal fouling effects and to catalyse the oxidation of the oestrogen, estradiol, during voltammetric detection. This electrode was fabricated by initially applying a Nafion–carbon nanotube mixture, and then electropolymerising Ni(cyclam) complexes on the electrode. During this process, a two-level factorial design was used to optimise experimental parameters including the amount of carbon nanotubes, the concentration of Nafion and the surface coverage of Ni(cyclam). A linear calibration plot between 0.5 and 40μM estradiol was then obtained in synthetic laboratory standard solutions. Based on a signal-to-noise ratio of 3, a detection limit of 60nM was estimated, which is below the typical estradiol level measured in a normal menstrual cycle. The electrodes were subsequently applied to the detection of estradiol in protein-free human serum samples. Comparable sensitivity between synthetic laboratory standard solutions and serum samples was obtained, indicating minimal interference effects from the serum matrix.
Keywords: Electrocatalytic oxidation; Estradiol; Carbon nanotubes; Ni(cyclam) complexes
Optimization and validation of an automated voltammetric stripping technique for ultratrace metal analysis by D. Monticelli; E. Ciceri; C. Dossi (pp. 192-198).
A new automated batch method for the determination of ultratrace metals (nanogram per liter level) was developed and validated. Instrumental and chemical parameters affecting the performance of the method were carefully assessed and optimized. A wide range of voltammetric methods under different chemical conditions were tested. Cadmium, lead and copper were determined by anodic stripping voltammetry (ASV), while nickel, cobalt, rhodium and uranium by adsorptive cathodic stripping voltammetry (AdCSV). The figures of merit of all of these methods were determined: very good precision and accuracy were achieved, e.g. relative percentage standard deviation in the 4–13% for ASV and 2–5% for AdCSV.The stripping methods were applied to the determination of cadmium, lead, copper, nickel, cobalt, rhodium and uranium in lake water samples and the results were found to be comparable with ICP-MS data.
Keywords: Automation; Validation; Ultratrace metal determination; Anodic stripping voltammetry; Cathodic stripping voltammetry; Inductively coupled plasma-mass spectrometry
Potentiometry of effective concentration of polyacrylate as scale inhibitor by Akio Yuchi; Yasumasa Gotoh; Shinsuke Itoh (pp. 199-203).
The concentration of polyacrylate (PA) used as a scale inhibitor was potentiometrically determined with a solid state copper ion-selective electrode after addition of Cu2+ as a probe. While the conventional methods monitor only the total concentration of PA, the proposed method measures the free, “effective” concentration of PA in equilibrium with species like Ca2+ and CaCO3. The slope of a potential response to PA was −40mVdecade−1 and the limit of detection was 10−6.3M (= moldm−3) at a probe concentration of 10−6M. The system could be used to control the PA concentration just enough to prevent the scale formation in various circulating water systems.
Keywords: Polyacrylate; Scale inhibitor; Calcium carbonate; Copper(II) ion-selective electrode; Complexation equilibria
Galvanic cell without liquid junction for potentiometric determination of copper by Jan Migdalski; Teresa Błaż; Barbara Źrałka; Andrzej Lewenstam (pp. 204-210).
This paper describes potentiometric measurements in an integrated galvanic cell with both indicator and reference electrodes. Both electrodes are conducting polymer-based. The copper-sensitive indicator electrode is made by using poly(3,4-ethylenedioxythiophene) (PEDOT) doped with 2-( o-arsenophenylazo)-1,8-dihydroxynaphthalene-3,6-disulphonic sodium salt (Arsenazo-I) as the electroactive substance in the film, while the reference electrode is based on PEDOT doped by 2-morpholineoethanesulfonic acid (MES). It is shown that the galvanic cell can be used for determination of copper both in non-aqueous media (where all PVC-based membranes failed) and in the presence of chloride ions, which disturb the signal of conventional copper ion-selective electrodes with solid-state membranes. It is further shown that the titration of copper ions can be successfully monitored using the described electrochemical cell.
Keywords: Conducting polymers; Metal complexing ligands; Membrane potential; Ion-selective electrode; Junctionless reference electrode; Potentiometric titration
Synthesis of haptens and development of a sensitive immunoassay for tetracycline residues by Nuria Pastor-Navarro; Sergi Morais; Ángel Maquieira; Rosa Puchades (pp. 211-218).
A new synthesis way of haptens for tetracyclines (tetracycline, chlortetracycline and oxytetracycline) based on the formation of their carboxamido and diazo derivatives that maintain the tetracyclic nucleus and possess an aromatic or aliphatic spacer arm – in order to create a degree of heterology in the chemical structure – is described. The haptens were used to successfully raise polyclonal antibodies and a reliable and sensitive indirect competitive enzyme-linked immunosorbent assay (ELISA) for tetracycline was set up. After the optimization of physical and chemical parameters (pH, salt, detergent concentration, and time), a detection limit of 0.4ngmL−1 for tetracycline was reached. The optimized ELISA showed cross-reactivity to rolitetracycline (91%), oxytetracycline (30%), methacycline (14%), and chlortetracycline (10%). The analytical potential of the immunoassay was demonstrated by the excellent recoveries obtained (mean value ranging between 79% and 108%) when determining tetracycline residues in honey samples with a simple preparation procedure. The obtained results confirmed the suitability of the assay as screening method for either food monitoring or laboratory quantification of tetracycline residues.
Keywords: Tetracyclines; Hapten synthesis; Immunoassay; Honey analysis
Ultra-sensitive Flow Injection Analysis (FIA) determination of calcium in ice cores at ppt level by R. Traversi; S. Becagli; E. Castellano; V. Maggi; A. Morganti; M. Severi; R. Udisti (pp. 219-225).
A Flow Injection Analysis (FIA) spectrofluorimetric method for calcium determination in ice cores was optimised in order to achieve better analytical performances which would make it suitable for reliable calcium measurements at ppt level.The method here optimised is based on the formation of a fluorescent compound between Ca and Quin-2 in buffered environment. A careful evaluation of operative parameters (reagent concentration, buffer composition and concentration, pH), influence of interfering species possibly present in real samples and potential favourable effect of surfactant addition was carried out. The obtained detection limit is around 15ppt, which is one order of magnitude lower than the most sensitive Flow Analysis method for Ca determination currently available in literature and reproducibility is better than 4% for Ca concentrations of 0.2ppb.The method was validated through measurements performed in parallel with Ion Chromatography on 200 samples from an alpine ice core (Lys Glacier) revealing an excellent fit between the two chemical series. Calcium stratigraphy in Lys ice core was discussed in terms of seasonal pattern and occurrence of Saharan dust events.
Keywords: Flow injection analysis; Calcium; Ice cores; Alps; Antarctica
Simultaneous determination of antioxidants, preservatives and sweetener additives in food and cosmetics by flow injection analysis coupled to a monolithic column by J.F. García-Jiménez; M.C. Valencia; L.F. Capitán-Vallvey (pp. 226-233).
Today it is common to find samples with various additives from several families. This is the case of sweeteners, preservatives and antioxidants. We have selected a set of additives broadly used in foods and cosmetics with an ample variety of polarities, namely: aspartame (AS), acesulfame (AK)/saccharin (SA), metylparaben (MP), ethylparaben (EP), propylparaben (PP), butylparaben (BP), propylgallate (PG) and butylhydroxyanysole (BA). The monolithic column used as separative system is a 5mm commercial precolumn of silica C18 coupled to a flow injection manifold working with a peristaltic pump. The mixture was separated in only 400s with resolution factors greater than 1.1 in all cases. To achieve the separation in the FIA system we used two carriers: first, a mixture of ACN/water buffered with 10mM pH 6.0 phosphate buffer and second, a methanol:water mixture to improve the carrier strength and speed up the more apolar analytes at 3.5mLmin−1. Detection is accomplished by means of a diode array spectrometer at the respective wavelength of each compound. The comparison of the analytical parameters obtained for this procedure with a standard HPLC method validates our new method, obtaining a method that is quick, with high repeatability and reproducibility and with good resolution between analytes. We have successfully applied the method to real food and cosmetics samples.
Keywords: Food and cosmetics analysis; Antioxidants; Preservatives; Intense sweeteners; Flow injection procedure; Monolithic minicolumn
Flow injection determination of choline in milk hydrolysates by an immobilized enzyme reactor coupled to a selective hydrogen peroxide amperometric sensor by Sandra Pati; Maurizio Quinto; Francesco Palmisano (pp. 234-239).
A choline oxidase (ChO) immobilized enzyme reactor (IMER) prepared by glutaraldehyde coupling of the enzyme on aminopropyl modified controlled pore glass beads is described. The ChO–IMER was coupled, in a flow injection configuration system, to an interference free hydrogen peroxide amperometric sensor based on a Pt surface modified by an overoxidized polypyrrole film. The resulting analytical device responds selectively to choline and displays a sensitivity of 46.9±0.2μCmM−1 and a limit of detection, calculated at a signal-to-noise ratio equal to 3, of 7μM. Sensitivity remains constant for about 20 days and then starts to slowly deteriorate and after 2 months a 70% of the initial sensitivity was still retained. The application to choline determination in milk hydrolysates is demonstrated. Short- and long-term drift observed in the analytical response can be corrected by a bracketing technique.
Keywords: Bioreactor; Choline; Flow injection analysis; Milk; Overoxidized polypyrrole; Amperometric detection
Extracting syringe for extraction of phthalate esters in aqueous environmental samples by Staffan Bergström; Thaer Barri; Jan Norberg; Jan Åke Jönsson; Lennart Mathiasson (pp. 240-247).
The use of the extracting syringe (ESy), a fully automated membrane-based extraction technique, for analysis of phthalate esters in complex aqueous samples has been investigated. The ESy, working as an autosampler that combines the extraction process and injection into the gas chromatograph (GC) in one single step, is placed on top of the GC equipped with a flame ionisation detector. The aqueous samples are loaded in a tray and automatically extracted by employing microporous membrane liquid–liquid extraction principle. After the extraction, the extract is directly injected into the GC's programmable temperature vaporisation injector. Six different phthalate esters were used as model compounds. Four extraction solvents were tested and the addition of sample organic modifier was examined.Toluene was the optimal solvent to use for extraction. Due to the large variation in polarity of phthalate esters, 50% methanol as organic modifier had to be added to the samples so as to extract the most nonpolar phthalate esters; di-2-ethylhexylphthalate and di- n-octylphthalate, whereas the other four relatively polar phthalate esters were extracted from unmodified samples. No significant difference between extraction of river water, leachate water from a landfill and reagent water was noted, except for minor deviations. The extraction time was 20min for extraction of a 1-mL sample, resulting in a good linearity for all aqueous media investigated, good enrichment factors (54–110 folds) and low LOD values (0.2–10ngmL−1) and relative standard deviation (%R.S.D.; 0.9–3.7%).
Keywords: Extracting syringe; Membrane extraction; Microporous membrane liquid–liquid extraction; Phthalate esters; Environmental analysis; Leachate water; Gas chromatography
Development and validation of a reversed-phase liquid chromatographic method with fluorescence detection for the study of Saquinavir pharmacokinetics in rat plasma by Shriram M. Pathak; A. Ranjith Kumar; G. Subramanian; N. Udupa (pp. 248-256).
This research work aims to exploit the high selectivity and sensitivity of fluorescence detector to develop and validate a high performance liquid chromatography (HPLC) method having very small sampling volume, much better mass-sensitive detection limit and lower operating cost for the determination of Saquinavir (SQV), known to have low oral bioavailability, in rat plasma. Unlike the traditional methods that require at least 0.25mL of plasma for each measurement, the present method requires only a 0.1mL sample volume. This is very useful in reducing the blood collection from study rats, offering the possibility to make sufficient number of samples for pharmacokinetic study and minimizing the amount of blood-derived biological waste. After liquid–liquid extraction, the compounds were separated on a Vydac C18 monomeric column (250mm×4.6mm i.d.×5μm particle size) using a mobile phase composed of acetonitrile and potassium dihydrogen phosphate buffer (45:55, v/v). Fluorescence detection was performed at 237nm (excitation) and 380nm (emission). Validity of the method was studied and the method was found to be precise and accurate with a linearity range from 0.005 to 1.000μgmL−1 ( r>0.9980). The limit of detection (LOD) was found to be 0.001μgmL−1. The intra-day and inter-day precision studies showed good reproducibility with coefficients of variation (C.V.) less than 11.4%. The developed method was applied successfully to monitor the pharmacokinetic profile following oral administration of SQV to rats.
Keywords: Saquinavir; Fluorescence; Rat plasma; Validation; Pharmacokinetics
Validation according to European Commission Decision 2002/657/EC of a confirmatory method for aflatoxin M1 in milk based on immunoaffinity columns and high performance liquid chromatography with fluorescence detection by Marilena Muscarella; Sonia Lo Magro; Carmen Palermo; Diego Centonze (pp. 257-264).
A high performance liquid chromatographic method with fluorimetric detection for the determination of aflatoxin M1 (AFM1) in milk has been optimized and validated according to Commission Decision 2002/657/EC by using the conventional validation approach. The procedure for determining selectivity, recovery, precision, decision limit (CC α), detection capability (CC β) and ruggedness of the method has been reported. The results of the validation process demonstrate the agreement of the method with the provisions of Commission Regulation 401/2006/EC. The mean recovery calculated at three levels of fortification (0.5, 1.0, and 1.5-fold the MRL) was 91% and the maximum relative standard deviation value for the within-laboratory reproducibility was 15%. Limit of detection (LOD) and limit of quantitation (LOQ) values were 0.006μgkg−1 and 0.015μgkg−1 while the CC α and CC β values were 0.058μgkg−1 and 0.065μgkg−1, respectively. The relative expanded measurement uncertainty of the method was 7%. The method was not affected by slight variations of some critical factors (ruggedness minor changes) as pre-treatment and clean-up of milk samples, thermal treatment and different storage conditions, as well as by major changes valued in terms of milk produced by different species (buffalo, goat and sheep). The method allowed accurate confirmation analyses of milk samples, resulted positive by the screening method. In fact, the Z-score values attained in a proficiency test round were well below the reference value of 1, proving the excellent laboratory performances.
Keywords: Aflatoxin M; 1; Milk; Validation; High performance liquid chromatography; Fluorescence detection; 2002/657/EC
Simultaneous determination of 17 ginsenosides in rat urine by ultra performance liquid chromatography–mass spectrometry with solid-phase extraction by Xiaoyan Wang; Tie Zhao; Xianfu Gao; Mo Dan; Mingmei Zhou; Wei Jia (pp. 265-273).
A rapid analytical method for quantifying 17 ginsenosides in rat urine by ultra performance liquid chromatography (UPLC) coupled to electrospray ionization mass spectrometry (ESI-MS) is described. All analytes were extracted by solid-phase extraction optimized to obtain good recovery and quantified using digoxin as an internal standard. ESI-MS was optimized for different cone voltages at positive ionization mode to allow simultaneous analysis of all analytes in a relatively short time. Qualitative methodological considerations, including the linear range, precision, limit of quantification, limit of detection, recovery and sensitivity are also provided.
Keywords: Saponin; Ginsenoside; Solid-phase extraction; Rat urine; Ultra performance liquid chromatography–mass spectrometry
Determination of anethole trithione in human plasma using high performance liquid chromatography coupled with tandem mass spectrometric detection by Tianmin Li; Zunjian Zhang; Haoyan Jiao; Lu Zhang; Yuan Tian; Yun Chen; Xiaoyang Pang; Jie Zhuang (pp. 274-278).
A rapid, sensitive and reliable high performance liquid chromatographic method coupled with tandem mass spectrometry via electrospray ionization (ESI) source (HPLC–MS/MS) has been developed and validated for the determination of anethole trithione (ATT) in human plasma. Diazepam was employed as the internal standard (IS). Sample extracts following liquid–liquid extraction were injected into the HPLC–MS/MS system. The analyte and IS were eluted isocratically on a C18 column, with a mobile phase consisting of methanol and aqueous ammonium acetate solution (5mM) (80:20, v/v) .The ions were detected by a triple quadrupole mass spectrometric detector in the positive mode. Quantification was performed using selected reaction monitoring (SRM) of the transitions m/ z 240.88→197.91 and m/ z 285.01→193.02 for ATT and for the IS, respectively. The analysis time for each run was 5.0min. The calibration curve fitted well over the concentration range of 0.02–5ngmL−1, with the regression equation y=1.1014 x+0.0003631, r=0.9992. The intra-batch and inter-batch R.S.D.% were less than 15% at all concentration levels within the calibration range. The recoveries were more than 80%. The present method provides a modern, rapid and robust procedure for the pharmacokinetic study of ATT. Some important pharmacokinetic parameters of ATT in healthy Chinese volunteers are also given for the first time.
Keywords: Anethole trithione; High performance liquid chromatographic method coupled with tandem mass spectrometry; Human plasma; Pharmacokinetics
Theoretical prediction of the Kovat's retention index for oxygen-containing organic compounds using novel topological indices by Fengping Liu; Yizeng Liang; Chenzhong Cao; Neng Zhou (pp. 279-289).
For the retention index of polar compounds, polar groups in molecules would participate in polar interactions between eluents and stationary phases and thus would be expected to make large and separate contributions to the total retention index (RI). The characterization of the structural feature will help to elucidate the quantitative structure–retention relationship (QSRR). In this paper, on the basis of the PEI index previously developed by Cao, two novel molecular polarizability effect index, modified molecular polarizability index (MPEIm) and modified inner molecular polarizability index (IMPEIm) were proposed to predict the GC retention of a variety of oxygen-containing organic compounds with diverse chemical structures on OV-1 and SE-54 stationary phases. The sets of molecular descriptors were derived directly from the structure of the compounds based on graph theory. Simple linear regression equations between the RI and the topological indices were established for each stationary phase separately ( R>0.99). Statistical analysis showed that the QSRR models have high internal stability and good predictive ability for external groups. The molecular properties known to be relevant for GC retention data, such as molecular size, branching and polar functional groups were well covered by the generated descriptors. The models with topological indices were compared with those based on quantum–chemical descriptors. It is observed that topological indices produce better correlations with Kovat's retention index. The results indicate the efficiency of presented indices in the structure–retention index correlations of complex compounds with polar multi-functional groups.
Keywords: Gas chromatographic retention index; Topological indices; Oxygen-containing organic compounds; Quantitative structure–retention relationships
Sensitive quantitative determination of oxymatrine and matrine in rat plasma by capillary electrophoresis with stacking induced by moving reaction boundary by Xing Wang; Wei Zhang; Liu-Yin Fan; Bing Hao; Ai-Niu Ma; Cheng-Xi Cao; Yong-Xiang Wang (pp. 290-296).
A quantitative method of capillary electrophoresis with sample stacking induced by moving reaction boundary (MRB) was developed for sensitive determination of oxymatrine (OMT) and matrine (MT) in rat plasma. The experimental conditions were optimized firstly. Below are the optimized experimental conditions: 20mM sodium formate solution (HCOONa, adjusted to pH 10.70 by ammonia) as sample solution, 3min 14mbar sample injection, 40mM formic buffer (HCOOH–HCOONa, pH 2.60) as stacking buffer, 7min 14mbar injection of stacking buffer, 100mM HCOOH–HCOONa (pH 4.80) as separation buffer, 73cm capillary (effective length 64cm), 21kV voltage, 210nm wavelength. Under the optimized conditions, higher than 60-fold sensitivity improvement of the stacking was simply achieved as compared with capillary zone electrophoresis, and the detectable limits obtained for OMT and MT were 0.26 and 0.19μgmL−1, respectively. Then, numerous demonstrations were carefully performed for the methodological validations of OMT and MT in rate plasma, including high specificity of method, good linearity ( r=0.9993 for OMT, r=0.9991 for MT), fair wide linear concentration range (1.30–65.00μgmL−1 for OMT, 0.84–42.00μgmL−1 for MT), low limit of detection (1.03μgmL−1 for OMT, 0.38μgmL−1 for MT), less than 5% intra- and inter-day variance value, and higher than 96% recovery of OMT and MT in plasma. The developed method could be used for the trace analyses of OMT and MT in plasma and was finally used for the investigation on pharmacokinetic study of OMT in rat plasma.
Keywords: Capillary electrophoresis; Matrine; Moving reaction boundary; Oxymatrine; Pharmacokinetics; Plasma; Stacking