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Analytica Chimica Acta (v.612, #2)
An ensemble of Monte Carlo uninformative variable elimination for wavelength selection by Qing-Juan Han; Hai-Long Wu; Chen-Bo Cai; Lu Xu; Ru-Qin Yu (pp. 121-125).
An improved method based on an ensemble of Monte Carlo uninformative variable elimination (EMCUVE) is presented for wavelength selection in multivariate calibration of spectral data. The proposed algorithm introduces Monte Carlo (MC) strategy to uninformative variable elimination-PLS (UVE-PLS) instead of leave-one-out strategy for estimating the contributions of each wavelength variable in the PLS model. In EMCUVE wavelength variables are evaluated by different Monte Carlo uninformative variable elimination (MCUVE) models. Moreover, a fusion of MCUVE and the vote rule can obtain an improvement over the original uninformative variable elimination method. Results obtained from simulated data and real data sets demonstrate that EMCUVE can properly carry out wavelength selection in the course of data analysis and improve predictive ability for multivariate calibration model.
Keywords: Wavelength selection; Multivariate calibration; Monte Carlo; Uninformative variable elimination; Partial least squares
Quantitative structure–property relationship study for estimation of quantitative calibration factors of some organic compounds in gas chromatography by Feng Luan; Hui Tao Liu; Yingying Wen; Xiaoyun Zhang (pp. 126-135).
Quantitative structure–property relationship (QSPR) models have been used to predict and explain gas chromatographic data of quantitative calibration factors ( fM). This method allows for the prediction of quantitative calibration factors in a variety of organic compounds based on their structures alone. Stepwise multiple linear regression (MLR) and non-linear radial basis function neural network (RBFNN) were performed to build the models. The statistical characteristics provided by multiple linear model ( R2=0.927, RMS=0.073; AARD=6.34% for test set) indicated satisfactory stability and predictive ability, while the predictive ability of RBFNN model is somewhat superior ( R2=0.959; RMS=0.0648; AARD=4.85% for test set). This QSPR approach can contribute to a better understanding of structural factors of the compounds responsible for quantitative analysis by gas chromatography, and can be useful in predicting the quantitative calibration factors of other compounds.
Keywords: Quantitative calibration factors; Multiple linear regression; Radial basis function neural network; Quantitative structure–property relationship
Preparation of molecularly imprinted adsorptive resin for trapping of ligustrazine from the traditional Chinese herb Ligusticum chuanxiong Hort. by Zhi-Feng Guo; Ting-Ting Guo; Mufan Guo (pp. 136-143).
A highly selective molecularly imprinted adsorptive resin for ligustrazine was prepared by melamine–urea–formaldehyde (MUF) gel. In the experiments, two pieces of MUF gel were synthesized firstly; one was added ligustrazine hydrochloride as the template molecule in it to prepare the imprinted adsorptive resin, and the other was not. Scanning electron microscopy (SEM) revealed that both resins were the porous with a network structure whether or not it was added template molecule. The imprinted adsorptive resin had an absorbability of 85.22% measured by a 200mgL−1 solution of ligustrazine hydrochloride at room temperature. The resin of MUF without template, on the other hand, displayed an adsorption capacity of almost zero. It illuminated the imprinted adsorptive resin formed ligustrazine recognition sites when the template molecule had been eluted. In the present paper, ligustrazine was effectively separated and enriched from herbs by using a solid-phase adsorptive column filled with the imprinted adsorptive resin. Its eluate, obtained from three kinds of solvents, was analyzed by GC–MS, and the results indicated that the imprinted adsorptive resin showed a high selectivity for ligustrazine. This is believed to be beneficial for extracting natural and highly purified ligustrazine.
Keywords: Melamine–urea–formaldehyde gel; Solid-phase adsorptive resin; Ligustrazine; Molecularly imprinted polymers
On-line metals preconcentration and simultaneous determination using cloud point extraction and inductively coupled plasma optical emission spectrometry in water samples by Yadollah Yamini; Mohammad Faraji; Shahab Shariati; Rahim Hassani; Mahnaz Ghambarian (pp. 144-151).
A new on-line cloud point extraction (CPE) system coupled to ICP-OES was designed for simultaneous extraction, preconcentration and determination of Cd2+, Co2+, Cr3+, Cu2+, Fe3+ and Mn2+ ions in water samples. This is based on the complexation of the metal ions with 1-(2-thenoyl)-3,3,3-trifluoraceton reagent (TTA) at pH 6.0 in the presence of non-ionic surfactant of Triton X-114. The micellar solution was heated above 60°C and loaded through a column packed with cotton, which acts as a filter for retaining the analyte-entrapped surfactant-rich phase. Then the surfactant-rich phase was eluted using propanol:0.5molL−1 nitric acid solution (75:25, v/v) at a flow rate of 3.0mLmin−1 and directly introduced into the nebulizer of the ICP-OES. Several factors influencing the instrumental conditions and extraction were evaluated and optimized. Under the optimum conditions, the enhancement factors of the proposed method for target ions were between 42 and 97, the detection limits (DLs) were in the range of 0.1–2.2μgL−1. The relative standard deviations (R.S.D.s) at 100μgL−1 concentration levels of each ion were found to be less than 4.6%. Also, the calibration graphs were linear in the range of 0.5–100μgL−1 with the correlation coefficients within the range of 0.9948–0.9994.Finally, the developed method was successfully applied to the extraction and determination of the mentioned metal ions in the tap, well, sea and mineral water samples and satisfactory results were obtained.
Keywords: Metal ions; On-line cloud point extraction; Inductively coupled plasma-optical emission spectrometry; Triton X-114; Water samples
Development of a simultaneous pressurised-liquid extraction and clean-up procedure for the determination of UV filters in sediments by Rosario Rodil; Monika Moeder (pp. 152-159).
A useful tool for the determination of eight UV filters in sediments which combines extraction and clean-up in a single-step has been developed. To this end, the protocol incorporates silica gel and copper powder placed directly in the pressurised-liquid extraction (PLE) cell. After extract evaporation, salicylate- and benzophenone-type UV filters are derivatised with N, O-bis-trimethylsilyltrifluoroacetamide (BSTFA). Trimethylsilylation increases the sensitivity of these UV filters about 4–10-fold when they are finally analysed by gas chromatography–mass spectrometry (GC–MS). Derivatisation conditions (temperature, time and volume of BSTFA) and PLE parameters (temperature, time, number of cycles and solvent composition) were optimised using multivariate experimental designs. Under optimal conditions, the developed procedure provides an excellent linearity, detection limits (1–5ngg−1) and recoveries above 73% for all the compounds. Compared to the few existing methods, this analytical approach affords optimal throughput and method automation. Finally, the proposed method was applied to the analysis of three sediment samples.
Keywords: Pressurised-liquid extraction; Gas chromatography–mass spectrometry; Ultraviolet filters; Sunscreen agents; Sediments
Application of non-ionic surfactant in the microwave-assisted extraction of alkaloids from Rhizoma Coptidis by Chen Sun; Huizhou Liu (pp. 160-164).
The feasibility of employing non-ionic surfactant oligoethylene glycol monoalkyl ether (Genapol X-080) as an alternative and effective solvent for the microwave-assisted extraction of alkaloids from Rhizoma Coptidis was demonstrated. When compared with commonly used solvents, 5% Genapol X-080 enhanced the extraction efficiency. Under optimal conditions, i.e. 5% acidified Genapol X-080 (v/v), microwave-assisted extraction for 10min at 100°C, the extraction recovery of alkaloids reached 92.8% in a one-step extraction. The efficiency of cloud-point preconcentration of three alkaloids was in the range 93.6–94.7% with relative standard deviation lower than 3.3% by the proposed procedure. Furthermore, the combination of microwave-assisted extraction and cloud-point extraction was shown to be a green, rapid and effective approach for alkaloids preconcentration of Rhizoma Coptidis samples.
Keywords: Alkaloids; Rhizoma Coptidis; Genapol X-080; Microwave-assisted extraction; High-performance liquid chromatography
Development of novel detection reagent for simple and sensitive determination of trace amounts of formaldehyde and its application to flow injection spectrophotometric analysis by Qiong Li; Piyanete Sritharathikhum; Mitsuko Oshima; Shoji Motomizu (pp. 165-172).
In this paper, a novel detection reagent for formaldehyde determination is proposed, and is applied to a simple and highly sensitive flow injection method for the spectrophotometric determination of formaldehyde. The method is based on the reaction of formaldehyde with methyl acetoacetate in the presence of ammonia. The increase in the absorbance of the reaction product was measured at 375nm. An inexpensive light emitting diode (LED)-based UV detector (375nm) was, for the first time, used. Under the optimized experimental conditions, formaldehyde in an aqueous solution was determined over the concentration range from 0.25 to 20.0×10−6M with a liner calibration graph; the limit of detection (LOD) of 5×10−8M (1.5μgL−1) was possible. The relative standard deviation of 12 replicate measurements of 5×10−6M formaldehyde was 1.2%. Maximum sampling throughput was about 21samples/h. The effect of potential interferences such as metals, organic compounds and other aldehyde was also examined. The analytical performance for formaldehyde determination was compared with those obtained by the conventional acetylacetone method, which uses visible absorption spectrophotometry. Finally, the proposed method was successfully applied to the determination of formaldehyde in natural water samples.
Keywords: Flow injection; Formaldehyde determination; Spectrophotometry; Methyl acetoacetate; UV-light emitting diode (LED)
Improving CMC-derivatization of pseudouridine in RNA for mass spectrometric detection by Anita Durairaj; Patrick A. Limbach (pp. 173-181).
A protocol that utilizes matrix-assisted laser desorption/ionization mass spectrometry (MALDI–MS) and N-cyclohexyl- N′-β-(4-methylmorpholinium)ethylcarbodiimide (CMC) derivatization to detect the post-transcriptionally modified nucleoside, pseudouridine, in RNA has been optimized for RNase digests. Because pseudouridine is mass-silent (i.e., the mass of pseudouridine is the same as the mass of uridine), after CMC-derivatization and alkaline treatment, all pseudouridine residues exhibit a mass shift of 252Da that allows its presence to be easily detected by mass spectrometry. This protocol is illustrated by the direct MALDI–MS identification of pseudouridines within Escherichia coli tRNATyrII starting from microgram amounts of sample. During this optimization study, it was discovered that the post-transcriptionally modified nucleoside 2-methylthio- N6-isopentenyladenosine, which is present in bacterial tRNAs, also retains a CMC unit after derivatization and incubation with base. Thus, care must be exercised when applying this MALDI-based CMC-derivatization approach for pseudouridine detection to samples containing transfer RNAs to minimize the misidentification of pseudouridine.
Keywords: N; -cyclohexyl-; N; ′-β-(4-methylmorpholinium)ethylcarbodiimide; p; -tosylate derivatization; Endonucleases; RNase T1; Pseudouridine; 2-Methylthio-; N; 6; -isopentenyladenosine; Transfer ribonucleic acid; Matrix-assisted laser desorption/ionization mass spectrometry; Ribonucleic acid signature products
Immobilization of trypsin in polyaniline-coated nano-Fe3O4/carbon nanotube composite for protein digestion by Sheng Wang; Huimin Bao; Pengyuan Yang; Gang Chen (pp. 182-189).
In this report, a four-component nanocomposite, trypsin-immobilized polyaniline-coated Fe3O4/carbon nanotube composite, was synthesized for highly efficient protein digestion. Fe3O4 was deposited by the chemical coprecipitation of Fe2+ and Fe3+ in an alkaline solution containing carbon nanotubes (CNTs) to prepare nano-Fe3O4/CNT composite. Subsequently, polyaniline (PA) was assembled on the Fe3O4/CNT composite by the in situ polymerization of aniline in the presence of trypsin to obtain trypsin-immobilized PA/Fe3O4/CNT nanocomposite. The novel 1D superparamagnetic biomaterial has been characterized by TEM, SEM, XRD, and magnetometric analysis. The feasibility and performance of the unique magnetic biomaterial have been demonstrated by the tryptic digestion of bovine serum albumin, myoglobin, and lysozyme within 5min. The digests were identified by MALDI-TOF MS with sequence coverages that were comparable to those obtained from the conventional in-solution tryptic digestion. The present biocomposite offers considerable promise for protein analysis due to its high magnetic responsivity and excellent dispersibility. It can be easily isolated from the digests with the aid of an external magnetic field. Because the enzyme-immobilized nanocomposite can be prepared by a simple two-step deposition approach at low cost, it may find a wide range of biological applications including proteome research.
Keywords: Composite; Fe; 3; O; 4; Polyaniline; Carbon nanotube; Proteomics; Trypsin
A novel procedure for rapid surface functionalisation and mediator loading of screen-printed carbon electrodes by Nikolay A. Pchelintsev; Paul A. Millner (pp. 190-197).
We report a simple and rapid procedure that leads to incorporation of mediator and introduction of amine functionality onto the surface of screen-printed carbon electrodes (SPCE). The electrodes were doped with cobalt phthalocyanine (CoPc) by enhanced adsorption in a process that uses minimal amounts of this redox mediator as compared with CoPc loaded inks. The CoPc-doped SPCE showed a substantially increased sensitivity to hydrogen peroxide and thiocholine as compared to unmodified electrodes. This greatly facilitated their use as transducers for the construction of amperometric biosensors based on enzymes producing oxidizable products such as hydrogen peroxide or thiols. Immobilisation of enzymes including glucose oxidase, acetylcholinesterase and choline oxidase was achieved through their multi-contact electrostatic interaction with polyethyleneimine (PEI) which was electrodeposited on the surface of CoPc-doped electrodes in one step from ethanolic solution. The efficiency of enzyme immobilisation was shown to depend on the molecular weight of the PEI used, reaching a maximum for 25kDa PEI. The biosensors shown sensitivity to glucose at 130nAmM−1 (LOD 0.15mM) and to acetylcholine at 70nAmM−1 (LOD 0.10mM) under +0.6V. Detection of glucose has been demonstrated at +0.4V with the sensitivity of 60nAmM−1 and LOD of 0.33mM. Possibility of the inhibition analysis of pesticides has been shown for acetylcholinesterase-based sensors.
Keywords: Screen-printed carbon electrodes (SPCE); Amperometric biosensor; Cobalt phthalocyanine (CoPc); Enzymes immobilisation; Polyethyleneimine (PEI)
Phenol biosensor based on Sonogel-Carbon transducer with tyrosinase alumina sol–gel immobilization by H. Zejli; J.L. Hidalgo-Hidalgo de Cisneros; I. Naranjo-Rodriguez; Baohong Liu; K.R. Temsamani; J.L. Marty (pp. 198-203).
A new biosensor for detection of phenols, based on tyrosinase immobilization with alumina sol–gel on Sonogel-Carbon transducer, has been developed. The electrode was prepared using high energy ultrasounds directly applied to the precursors. The alumina sol–gel provided a microenvironment for retaining the native structure and activity of the entrapped enzyme and a very low mass transport barrier to the enzyme substrates. Phenols are oxidized by tyrosinase biosensor to form a detectable product, which was determined at −300mV vs. Ag/AgCl reference electrode. For phenol, the sensor exhibited a fast response which resulted from the porous structure and high enzyme loading of the sol–gel matrix. The linear range was from 5×10−7M to 3×10−5M, with a detection limit of 3×10−7M. The stability of the biosensor was also evaluated.
Keywords: Biosensors; Sonogel-Carbon electrode; Tyrosinase; Alumina sol–gel; Phenolic compounds
Analysis of the recent antipsychotic aripiprazole in human plasma by capillary electrophoresis and high-performance liquid chromatography with diode array detection by Alessandro Musenga; Maria Addolorata Saracino; Domenico Spinelli; Egon Rizzato; Giancarlo Boncompagni; Ernst Kenndler; Maria Augusta Raggi (pp. 204-211).
Two methods, based on the use of capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC), respectively, were developed for the analysis of the atypical antipsychotic aripiprazole in plasma of schizophrenic patients for therapeutic drug monitoring purposes. Good analytical performances were obtained with the CE method, using uncoated fused silica capillaries and a background electrolyte composed of 50mM phosphate buffer at pH 2.5. With 20kV voltage, aripiprazole was detectable at 214nm within 5min. The second analytical method, based on HPLC with diode array detection, employed a C8 reversed-phase column and a mixture of a 12.5mM phosphate buffer, pH 3.5, containing triethylamine and acetonitrile as the mobile phase. Aripiprazole was detected at 254nm and a complete chromatographic run lasted about 10min. For both analytical methods loxapine was used as the internal standard and the same plasma sample pre-treatment by means of solid-phase extraction on cyano cartridges was carried out, with extraction yield values always higher than 91.3%. Linear responses for aripiprazole were obtained between 70 and 700ngmL−1 and precision assays (expressed as relative standard deviation values) were lower than 7.0%. After validation, both methods were successfully applied to human plasma samples drawn from schizophrenic patients undergoing therapy with Abilify® tablets. Accuracy was satisfactory, with recovery value higher than 91.0%.
Keywords: Abbreviations; ARP; aripiprazole; IS; internal standard; DAD; diode array detection; TDM; therapeutic drug monitoringAripiprazole; Capillary electrophoresis; High-performance liquid chromatography; Human plasma; Therapeutic drug monitoring; Solid-phase extraction
Glutaraldehyde activated eggshell membrane for immobilization of tyrosinase from Amorphophallus companulatus: Application in construction of electrochemical biosensor for dopamine by Sanket Tembe; B.S. Kubal; Meena Karve; S.F. D'Souza (pp. 212-217).
Tyrosinase from a plant source Amorphophallus companulatus was immobilized on eggshell membrane using glutaraldehyde. Among the three different approaches used for immobilization, activation of eggshell membrane by glutaraldehyde followed by enzyme adsorption on activated support could stabilize the enzyme tyrosinase and was found to be effective. Km and Vmax values for dopamine hydrochloride calculated from Lineweaver-Burk plot were 0.67mM and 0.08mMmin−1, respectively. Studies on effect of pH showed retention of more than 90% activity over a pH range 5.0–6.5. Membrane bound enzyme exhibited consistent activity in the temperature range 20–45°C. Shelf life of immobilized tyrosinase system was found to be more than 6 months when stored in phosphate buffer at 4°C. An electrochemical biosensor for dopamine was developed by mounting the tyrosinase immobilized eggshell membrane on the surface of glassy carbon electrode. Dopamine concentrations were determined by the direct reduction of biocatalytically liberated quinone species at −0.19V versus Ag/AgCl (3M KCl). Linearity was observed within the range of 50–250μM with a detection limit of 25μM.
Keywords: Eggshell membrane; Tyrosinase; Glutaraldehyde; Biopolymers; Electrochemical biosensor
Control of aqueous droplets using magnetic and electrostatic forces by Tetsuo Ohashi; Hiroki Kuyama; Koichi Suzuki; Shin Nakamura (pp. 218-225).
Basic control operations were successfully performed on an aqueous droplet using both magnetic and electrostatic forces. In our droplet-based microfluidics, magnetic beads were incorporated in an aqueous droplet as a force mediator. This report describes droplet anchoring and separation of the beads from the droplet using a combination of magnetic and electrostatic forces. When an aqueous droplet is placed in an oil-filled reservoir, the droplet sinks to the bottom, under which an electrode had been placed. The droplet was adsorbed (or anchored) to the bottom surface on the electrode when a DC voltage was applied to the electrode. The magnetic beads were removed with magnetic force after the droplet had been anchored. Surfactant addition into droplet solution was very effective for the elimination of electric charge, which resulted in the stable adsorption of a droplet to hydrophobic substrate under an applied voltage of DC 0.5–3kV. In a sequential process, small volume of aqueous liquid was successfully transferred using both magnetic and electrostatic forces.
Keywords: Magnetic beads; Electrostatic force; Surfactant; Droplet-based microfluidics