Check out our New Publishers' Select for Free Articles

Analytica Chimica Acta (v.663, #2)

Editorial Board (pp. i).

Modeling of combined electroosmotic and capillary flow in microchannels by Prashant R. Waghmare; Sushanta K. Mitra (pp. 117-126).

In the present study, theoretical model for the transient response of a capillary flow under the combined effects of electroosmotic and capillary forces at low Reynolds number is presented. The governing equation is derived based on the balance among the electrokinetic, surface, viscous and gravity forces. A non-dimensional transient governing equation for the penetration depth as a function of time is obtained by normalizing the viscous, gravity and electroosmotic forces with surface tension force. A new non-dimensional group for the electroosmotic force,Eo, is obtained through the non-dimensional analysis. This new non-dimensional group is a representation of combined electroosmosis and surface tension, i.e., capillarity. The numerical solution of governing equation is obtained to study the effect of different operating parameters on the flow front transport. In a combined flow, it is observed that the flow with positive and low negative magnitudeEo numbers, the attainment of equilibrium penetration depth is similar to a capillary flow. In case of high negative magnitudeEo numbers, complete filling of the channel is observed. The electrolyte with lower permittivity delays the progress of the flow front whereas a large EDL transports the electrolyte quickly. Higher viscous and gravity forces also delay the transport process in the combined flow. This model suggests that in combined flow the electrokinetic parameters also play an important role on the capillary flow and experiments are required to confirm this electrokinetic effect on capillary transport.

Keywords: Capillary flow; Electroosmotic flow; Electroosmotic number; Microchannels; Microfluidics

Methods for the determination and speciation of mercury in natural waters—A review by Kerstin Leopold; Michael Foulkes; Paul Worsfold (pp. 127-138).

This review summarises current knowledge on Hg species and their distribution in the hydrosphere and gives typical concentration ranges in open ocean, coastal and estuarine waters, as well as in rivers, lakes, rain and ground waters. The importance of reliable methods for the determination of Hg species in natural waters and the analytical challenges associated with them are discussed. Approaches for sample collection and storage, pre-concentration, separation, and detection are critically compared. The review covers well established methods for total mercury determination and identifies new approaches that offer advantages such as ease of use and reduced risk of contamination. Pre-concentration and separation techniques for Hg speciation are divided into chromatographic and non-chromatographic methods. Derivatisation methods and the coupling of pre-concentration and/or separation methods to suitable detection techniques are also discussed. Techniques for sample pre-treatment, pre-concentration, separation, and quantification of Hg species, together with examples of total Hg determination and Hg speciation analysis in different natural (non-spiked) waters are summarised in tables, with a focus on applications from the last decade.

Keywords: Mercury analysis; Speciation; Natural waters; Sample storage; Pre-concentration; Separation

Spectrometric study of the interaction between Alpinetin and bovine serum albumin using chemometrics approaches by Yongnian Ni; Shuangshuang Wang; Serge Kokot (pp. 139-146).

The binding interaction of Alpinetin (APT) with bovine serum albumin (BSA) was studied by fluorescence, UV–visible and synchronous fluorescence spectroscopy (SFS) under simulated physiological conditions. The measured complex spectra were resolved by multivariate curve resolution-alternating least squares (MCR-ALS), yielding a host of data and information, which otherwise would have been impossible to obtain. The extracted profiles corresponded to the spectra of the single species in the APT/BSA mixture. In addition, the presence of the APT–BSA complex was demonstrated, and it was shown that the associated quenching of the fluorescence from the BSA protein resulted from the formation of APT–BSA complex via a static mechanism. The binding constant ( K_a(ave)=2.34×10⁶Lmol⁻¹) and the number of sites ( n=1) were obtained by fluorescence methods as were the thermodynamic parameters (Δ H⁰, Δ S⁰ and Δ G⁰). This work suggested that the principal binding between APT to BSA was facilitated by hydrophobic interactions. The thermodynamic parameters for APT were compared to those from the structurally similar Chrysin and Wogonin molecules. It appeared that the entropy parameters were relatively more affected by the small structural changes. SFS from the interaction of BSA and APT showed that the ligand affected the conformation of BSA. The competitive interaction of APT and site makers with BSA indicated site I as the binding area of APT in BSA.

Keywords: Alpinetin; Bovine serum albumin; Fluorescence and UV–visible spectroscopy; Chemometrics; Ligand comparison

An electrochemical immunosensor based on enzyme-encapsulated liposomes and biocatalytic metal deposition by Bo Qu; Lei Guo; Xia Chu; Dan-Hong Wu; Guo-Li Shen; Ru-Qin Yu (pp. 147-152).

A novel electrochemical immunosensor based on double signal amplification of enzyme-encapsulated liposomes and biocatalytic metal deposition was developed for the detection of human prostate specific antigen (PSA). Alkaline phosphatase (ALP)-encapsulated and detection antibody-functionalized liposomes were first prepared and used as the detection reagent. In the sandwich immunoassay, the model analyte PSA was first captured by anti-PSA capture antibody immobilized on the electrode and then sandwiched with the functionalized liposomes. The bound liposomes were then lysed with surfactant to release the encapsulated ALP, which served as secondary signal amplification means. ALP on the electrode surface initiated the hydrolysis of ascorbic acid 2-phosphate (AA-p) to produce ascorbic acid. The latter, in turn, reduced silver ions on the electrode surface, leading to deposition of the metal silver on the electrode surface. Linear sweep voltammetry (LSV) was chosen to detect the amount of the deposited silver. The results showed that the anodic stripping peak current was linearly dependent on the PSA concentration in the range of 0.01–100ngmL⁻¹, and a detection limit as low as 0.007ngmL⁻¹ can be obtained. Since the cut-off value of human PSA is 4ngmL⁻¹, the proposed electrochemical immunosensor would be expected to gain widespread applications for the detection of PSA in clinical diagnosis.

Keywords: Liposome; Alkaline phosphatase; Biocatalytic deposition; Prostate specific antigen; Electrochemical immunosensor

Enzyme-free ethanol sensor based on electrospun nickel nanoparticle-loaded carbon fiber paste electrode by Yang Liu; Lei Zhang; Qiaohui Guo; Haoqing Hou; Tianyan You (pp. 153-157).

We have developed a novel nickel nanoparticle-loaded carbon fiber paste (NiCFP) electrode for enzyme-free determination of ethanol. An electrospinning technique was used to prepare the NiCF composite with large amounts of spherical nanoparticles firmly embedded in carbon fibers (CF). In application to electroanalysis of ethanol, the NiCFP electrode exhibited high amperometric response and good operational stability. The calibration curve was linear up to 87.5mM with a detection limit of 0.25mM, which is superior to that obtained with other transition metal based electrodes. For detection of ethanol present in liquor samples, the values obtained with the NiCFP electrode were in agreement with the ones declared on the label. The attractive analytical performance and simple preparation method make this novel material promising for the development of effective enzyme-free sensors.

Keywords: Ethanol; Enzyme-free sensor; Electrospinning technique; Nickel nanoparticle-loaded carbon fibers

Highly sensitive determination of hydroxylamine using fused gold nanoparticles immobilized on sol–gel film modified gold electrode by P. Kannan; S. Abraham John (pp. 158-164).

We are reporting the highly sensitive determination of hydroxylamine (HA) using 2-mercapto-4-methyl-5-thiazoleacetic acid (TAA) capped fused spherical gold nanoparticles (AuNPs) modified Au electrode. The fused TAA-AuNPs were immobilized on (3-mercaptopropyl)-trimethoxysilane (MPTS) sol–gel film, which was pre-assembled on Au electrode. The immobilization of fused TAA-AuNPs on MPTS sol–gel film was confirmed by UV–vis absorption spectroscopy and atomic force microscopy (AFM). The AFM image showed that the AuNPs retained the fused spherical morphology after immobilized on sol–gel film. The fused TAA-AuNPs on MPTS modified Au electrode were used for the determination of HA in phosphate buffer (PB) solution (pH=7.2). When compared to bare Au electrode, the fused AuNPs modified electrode not only shifted the oxidation potential of HA towards less positive potential but also enhanced its oxidation peak current. Further, the oxidation of HA was highly stable at fused AuNPs modified electrode. Using amperometric method, determination of 17.5nM HA was achieved for the first time. Further, the current response of HA increases linearly while increasing its concentration from 17.5nM to 22mM and a detection limit was found to be 0.39nM ( S/ N=3). The present modified electrode was also successfully used for the determination of 17.5nM HA in the presence of 200-fold excess of common interferents such as urea, NO₂⁻, NH₄⁺, oxalate, Mn²⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Ba²⁺ and Cu²⁺. The practical application of the present modified electrode was demonstrated by measuring the concentration of HA in ground water samples.

Keywords: Fused AuNPs; (3-mercaptopropyl)-trimethoxysilane sol–gel film; 2-Mercapto-4-methyl-5-thiazoleacetic acid; Hydroxylamine; Amperometry

Trace analysis of endectocides in milk by high performance liquid chromatography with fluorescence detection by Vesna Cerkvenik-Flajs; Luka Milčinski; Adica Süssinger; Lena Hodošček; Martin Danaher; Jan Antonić (pp. 165-171).

An analytical method has been developed for the simultaneous determination of the following endectocide drugs in milk: ivermectin, abamectin, doramectin, moxidectin, eprinomectin, emamectin and nemadectin. Samples were extracted with acetonitrile, purified with solid-phase extraction on a reversed phase C₈, derivatised with N-methylimidazole, trifluoroacetic anhydride and acetic acid to a stable fluorescent derivative, and were further analysed by gradient high performance liquid chromatography (HPLC) on an endcapped reversed phase Supelcosil LC-8-DB. The derivatisation step was mathematically optimised and the method was validated according to the requirements of Commission Decision 2002/657/EC, using fortified raw bovine milk. Mean recovery was between 78 and 98%. The repeatability (CV_r) and within-laboratory reproducibility (CV_W) ranged from 4.6 to 13.4% and from 6.6 to 14.5%, respectively. Decision limits (CCα) for analytes with MRL values, namely eprinomectin and moxidectin, were determined to be 24.8 and 50.6μgkg⁻¹, respectively. CCα values for unauthorised endectocides ranged from 0.1 to 0.2μgkg⁻¹. Due to high acceptability regarding the required criteria and applicability to ovine and caprine milk, giving similar results, this multi-analyte method has been successfully implemented in pharmacokinetic research studies as well as statutory residue monitoring in Slovenia.

Keywords: Endectocides; Avermectins; Milk; Analysis; HPLC-fluorescence

Determination of ferrous and ferric iron in aqueous biological solutions by S.E. Pepper; M. Borkowski; M.K. Richmann; D.T. Reed (pp. 172-177).

A solvent extraction method was employed to determine ferrous and ferric iron in aqueous samples. Fe³⁺ is selectively extracted into the organic phase ( n-heptane) using HDEHP (bis(2-ethylhexyl) hydrogen phosphate) and is then stripped using a strong acid. After separation, both oxidation states and the total iron content were determined directly by ICP-MS analysis. This extraction method was refined to allow determination of both iron oxidation states in the presence of strong complexing ligands, such as citrate, NTA and EDTA. The accuracy of the method was verified by crosschecking using a refinement of the ferrozine assay. Presented results demonstrate the ability of the extraction method to work in a microbiological system in the presence of strong chelating agents following the bioreduction of Fe³⁺ by the Shewanella alga BrY. Based on the results we report, a robust approach was defined to separately analyze Fe³⁺ and Fe²⁺ under a wide range of potential scenarios in subsurface environments where radionuclide/metal contamination may coexist with strongly complexing organic contaminants.

Keywords: Fe; ²⁺; determination; Fe; ³⁺; determination; HDEHP extraction; Ferrozine method; Shewanella alga BrY

Mathematical modeling of dispersion in single interface flow analysis by S. Sofia M. Rodrigues; Karine L. Marques; João A. Lopes; João L.M. Santos; José L.F.C. Lima (pp. 178-183).

This work describes the optimization of the recently proposed fluid management methodology single interface flow analysis (SIFA) using chemometrics modelling. The influence of the most important physical and hydrodynamic flow parameters of SIFA systems on the axial dispersion coefficients estimated with the axially dispersed plug-flow model, was evaluated with chemometrics linear (multivariate linear regression) and non-linear (simple multiplicative and feed-forward neural networks) models. A D-optimal experimental design built with three reaction coil properties (length, configuration and internal diameter), flow-cell volume and flow rate, was adopted to generate the experimental data. Bromocresol green was used as the dye solution and the analytical signals were monitored by spectrophotometric detection at 614nm. Results demonstrate that, independent of the model type, the statistically relevant parameters were the reactor coil length and internal diameter and the flow rate. The linear and non-linear multiplicative models were able to estimate the axial dispersion coefficient with validation r²=0.86. Artificial neural networks estimated the same parameter with an increased accuracy ( r²=0.93), demonstrating that relations between the physical parameters and the dispersion phenomena are highly non-linear. The analysis of the response surface control charts simulated with the developed models allowed the interpretation of the relationships between the physical parameters and the dispersion processes.

Keywords: Single interface flow analysis; Optimization; Experimental design; Multivariate linear regression; Feed-forward neural networks

8-Quinolineboronic acid as a potential phosphorescent molecular switch for the determination of alpha-fetoprotein variant for the prediction of primary hepatocellular carcinoma by Jia-Ming Liu; Fei-Ming Li; Zhen-Bo Liu; Chang-Qing Lin; Shao-Qin Lin; Li-Ping Lin; Xin-Xing Wang; Zhi-Ming Li (pp. 184-189).

8-Quinolineboronic acid phosphorescent molecular switch (8-QBA-PMS) in the “off” state emitted weak room temperature phosphorescence (RTP) of 8-QBA on the acetylcellulose membrane (ACM) with the perturbation of Pb²⁺. When 8-QBA-PMS was used to label concanavalin agglutinin (Con A) to form 8-QBA-PMS-Con A based on the reaction between –OH of 8-QBA-PMS and –COOH of Con A, 8-QBA-PMS turned “on” automatically due to its structure change, and RTP of the system increased 2.7 times. Besides, –NH₂ of 8-QBA-PMS-Con A could carry out affinity adsorption (AA) reaction with the –COOH of alpha-fetoprotein variant (AFP-V) to form the product Con A-AFP-V-Con A-8-QBA-PMS containing –NH–CO– bond, causing the RTP of the system to further increase. Moreover, the amount of AFP-V was linear to the Δ I_p of the system in the range of 0.012–2.40 (fgspot⁻¹). Thus, a new affinity sensitive adsorption solid substrate room temperature phosphorimetry using 8-QBA-PMS as labelling reagent (8-QBA-PMS-AASSRTP) for the determination of AFP-V was proposed with the detection limit (LD) of 9×10⁻¹⁵gmL⁻¹. It had been used to determine AFP-V in human serum with the results agreeing with enzyme-link immunoassay (ELISA), showing promise for the prediction of PHC due to the intimate association between AFP-V and primary hepatocellular carcinoma (PHC). The mechanism of the promethod was also discussed.

Keywords: 8-Quinolineboronic acid phosphorescent molecular switch; Phosphorescent labelling reagent; Alpha-fetoprotein variant; Concanavalin agglutinin; Affinity adsorption solid substrate room temperature phosphorimetry

Capillary electrophoresis procedure for the simultaneous analysis and stoichiometry determination of a drug and its counter-ion by using dual-opposite end injection and contactless conductivity detection: Application to labetalol hydrochloride by Reine Nehmé; Adrien Lascaux; Raphaël Delépée; Bérengère Claude; Philippe Morin (pp. 190-197).

In this work, a capillary electrophoresis (CE) procedure was developed for the simultaneous determination of a pharmaceutical drug and its counter-ion, namely labetalol hydrochloride. For this purpose, an uncoated fused-silica capillary, a low conductivity background electrolyte (BGE) and a capacitively coupled contactless conductivity detector (C⁴D) were employed. This detection system is highly sensitive and enables detection of inorganic as well as organic ions unlike with direct UV detection. Moreover, to be able to simultaneously analyze the cationic drug (labetalol⁺) and its anionic counter-ion (Cl⁻) in the same electrophoretic run without the need of a coated capillary, a dual-opposite end injection was performed. In this technique, the sample is hydrodynamically injected into both ends of the capillary. This method is simple and easy to perform since the different injection steps are automated by the CE software.This novel CE-C⁴D procedure with dual-opposite end injection has been successfully validated and applied for the analysis of chloride content in an adrenergic antagonist (labetalol hydrochloride). Thus, the hereby developed method has been shown to enable fast (analysis time<10min), precise (repeatability of migration times<0.7% and of corrected-peak areas<3.3%; n=6) and rugged analyses for the simultaneous determination of a pharmaceutical drug and its counter-ion.

Keywords: Abbreviations; AcOH; acetic acid, CH; ₃; CO; ₂; H; BGE; background electrolyte; C; ⁴; D; capacitively coupled contactless conductivity detection; His; l; -histidine, C; ₆; H; ₉; N; ₃; O; ₂; labetalol-HCl; labetalol hydrochloride, C; ₁₉; H; ₂₄; N; ₂; O; ₃; ·HClCapillary electrophoresis; Contactless conductivity detection; Stoichiometry; Counter-ion; Pharmaceutical drug

Immobilization of trypsin onto 1,4-diisothiocyanatobenzene-activated porous glass for microreactor-based peptide mapping by capillary electrophoresis: Effect of calcium ions on the immobilization procedure by Catherine Dartiguenave; Hussein Hamad; Karen C. Waldron (pp. 198-205).

The immobilization conditions and kinetic behaviour of trypsin, covalently immobilized via the 1,4-diisothiocyanatobenzene (DITC) linker onto aminopropylated controlled pore glass (CPG) particles, have been evaluated to establish a rapid and efficient protocol for fabrication of an immobilized enzyme microreactor (IMER) for protein hydrolysis and subsequent peptide mapping. Addition of calcium ions to either the immobilization reaction solution or hydrolysis assay was studied for a synthetic substrate. Activity was slightly higher when immobilization was carried out in the presence of Ca²⁺ whereas more enzyme could be immobilized in its absence. A protocol requiring less than 3h was devised to obtain maximal enzymatic activity with the lowest ratio of soluble trypsin to DITC–CPG particles. The resulting immobilized enzyme was found to retain an acceptable percentage ( ca. 35%) of its activity after immobilization. The particles were dry-packed into a capillary to make a microscale IMER. Repeatability, reusability and digestion efficiency of the μIMER were investigated for the substrate β-casein using capillary electrophoretic-based peptide mapping. In initial tests, a single device showed reproducible peptide maps for 21 digestions lasting 2h each, carried out over a period of 2 months. Complete digestion of β-casein could be achieved in a few minutes (86s residence time in the μIMER followed by a wash step).

Keywords: Trypsin; Immobilized enzyme reactor; Controlled pore glass; Peptide mapping; β-Casein; Capillary electrophoresis

Development of a fast and simple immunochromatographic method to purify alpha 1-acid glycoprotein from serum for analysis of its isoforms by capillary electrophoresis by Sara Ongay; Izaskun Lacunza; Jose Carlos Díez-Masa; Jesús Sanz; Mercedes de Frutos (pp. 206-212).

Alpha 1-acid glycoprotein (AGP) is a very heterogeneous glycoprotein presenting several isoforms due to variations in its polypeptidic and glycosidic moieties. Differences in AGP isoforms between healthy and diseased individuals have been related to different pathological situations such as cancer or cardiovascular diseases, among others. Capillary electrophoresis study of the role of AGP isoforms as biomarkers requires prior purification of AGP from biological samples. Current AGP purification methods are time- and labour-consuming, and generally they have not been proven to be compatible with capillary electrophoresis analysis. In this work, different methods for AGP purification from human serum are developed and compared. The applicability of acidic precipitation and immunoaffinity chromatographic methods for AGP purification are studied. Two different immunoaffinity approaches are employed; in the first one, interferents present in the AGP sample are captured and removed, and in the second one, AGP is retained in a house-made anti-AGP column, being in this way isolated from the rest of interferents of the sample. Best results in AGP purification from human serum to be analyzed by capillary zone electrophoresis (CZE) were obtained when acidic purification was combined with immunoaffinity chromatography (IAC) employing the house-made anti-AGP column. The method was shown not to alter the proportion of AGP peaks due to isoforms existing in AGP samples. The applicability of this fast and easy purification method developed for analyzing by CZE isoforms of AGP from natural serum samples by CZE is demonstrated.

Keywords: Serum purification; Albumin depletion; Biomarker; Glycoprotein; Isoforms; AGP isolation

Chemically modified attapulgite with asparagine for selective solid-phase extraction and preconcentration of Fe(III) from environmental samples by Zhipeng Zang; Zhenhua Li; Li Zhang; Ruijun Li; Zheng Hu; Xijun Chang; Yuemei Cui (pp. 213-217).

A new method that utilizes asparagine modified attapulgite as a solid phase extractant has been developed for preconcentration of trace Fe(III) prior to the measurement by inductively coupled plasma optical emission spectrometry. Characterization of the surface modification was performed on the basis of Fourier transform infrared spectra. The separation/preconcentration conditions of the analyte were investigated, including the pH value, the shaking time, the sample ﬂow rate and volume, the elution condition and the interfering ions. At pH 4, the new adsorbent had relatively high capacity and enrichment factor compared to other methods reported so far. The adsorbed Fe(III) was quantitatively eluted by 2mL of 0.5molL⁻¹ HCl. Common coexisting ions did not interfere with the separation. The detection limit of the method was 0.19μgL⁻¹. The relative standard deviation was 3.4% ( n=8) which indicated that the method had good precision for the analysis of trace Fe(III) in solution samples. The method was validated using two certified reference materials and has been applied for the determination of trace Fe(III) in biological and natural water samples with satisfactory results.

Keywords: Modified attapulgite; Asparagine; Iron determination; Solid-phase extraction; Inductively coupled plasma optical emission spectrometry

Sections

Personal tools

Analytica Chimica Acta (v.663, #2)

Sections

Personal tools

Local resources

Analytica Chimica Acta (v.663, #2)