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Analytica Chimica Acta (v.624, #2)

Editorial Board (pp. i).

Contents (pp. iii-iv).

Capillary electrophoresis-based methods for the determination of lipids—A review by Anthony C. Otieno; Simon M. Mwongela (pp. 163-174).

Capillary electrophoresis (CE) is a high-resolution technique for the separation of complex biological and chemical mixtures. CE continues to emerge as a powerful tool in the determination of lipids. Here we review the analytical potential of CE for the determination of a wide range of lipids. The different classes of lipids are introduced, and the different modes of CE and optimization methods for the separation of lipids are described. The advantages and disadvantages of the different modes of CE compared to traditional methods like gas chromatography (GC) and liquid chromatography (LC) in the determination of lipids are discussed. Finally, the potential of CE in the determination of lipids in the future is illustrated.

Keywords: Capillary electrophoresis; Capillary zone electrophoresis; Micellar electrokinetic chromatography; Microemulsion electrokinetic chromatography; Capillary electrochromatography; Microchip capillary electrophoresis; Lipid determination

Manganese(III) and manganese(IV) as chemiluminescence reagents: A review by Allyson J. Brown; Paul S. Francis; Jacqui L. Adcock; Kieran F. Lim; Neil W. Barnett (pp. 175-183).

Although potassium permanganate [Mn(VII)] has been used extensively as a chemiluminescence reagent for many decades, other manganese-based oxidants have only recently been explored for this purpose. There is strong evidence to suggest that, like permanganate, manganese(III) and manganese(IV) oxidants react with many molecules to produce an excited manganese(II) species that emits light. However, these reagents differ markedly in terms of selectivity, and possess characteristics that provide new avenues for detection, such as the immobilisation of solid manganese dioxide, the production of ‘soluble’ manganese(IV) nanoparticles, and the electrochemical generation of manganese(III). In this review we examine the emergence of these alternative manganese oxidants as chemiluminescence reagents.

Keywords: Chemiluminescence; Manganese(III); Manganese(IV); Manganese dioxide; Flow injection analysis; High-performance liquid chromatography

¹³C nuclear magnetic resonance spectroscopy for determining the different components of epicuticular waxes of olive fruit ( Olea europaea) Dritta cultivar by Giovanna Vlahov; Giuseppe Rinaldi; Paolo Del Re; Angela Alessia Giuliani (pp. 184-194).

¹³C nuclear magnetic resonance spectroscopy (NMR) was applied to determine the different components of apolar and polar fractions which were isolated by column chromatography from the crude chloroform-soluble waxes of olive fruits ( Olea europaea) Dritta cultivar.¹³C NMR enabled the determination in the wax apolar fraction, of aliphatic aldehydes, and of benzyl, alkyl and glyceryl esters. In particular, the fatty acid composition of alkyl esters, comprising saturated and unsaturated oleic and linoleic acids, was determined. Acyl chain composition and the chain composition of 1,3- and 2-glycerol positions were also determined for triacylglycerols of olive fruit waxes.Oleanolic and maslinic acids were confirmed to be the major components of wax polar fraction. Complete assignments of¹³C NMR chemical shifts of oleanolic and maslinic acids as a mixture were achieved by using homonuclear correlation spectroscopy with gradient (g-COSY), attached proton test (APT), inverse-detected heteronuclear single-quantum coherence with gradient (g-HSQC), high-resolution heteronuclear correlation spectroscopy (HETCOR) for C–H directly attached pairs and C–H long-range-coupled experiments.

Keywords: ¹³; C nuclear magnetic resonance spectroscopy; Apolar; Polar fractions; Epicuticular waxes; Olea europaea

Specific determination of selenoaminoacids in whole milk by 2D size-exclusion-ion-paring reversed phase high-performance liquid chromatography–inductively coupled plasma mass spectrometry (HPLC–ICP MS) by Katarzyna Bierla; Joanna Szpunar; Ryszard Lobinski (pp. 195-202).

A procedure was developed for the quantitative recovery of selenomethionine (SeMet) and selenocysteine (SeCys) from whole milk. It was based on the protein unfolding, carbamidomethylation of the aminoacid residues using iodoacetamide and proteolysis using Protease XIV. The selenoaminoacids were specifically determined by ion-paring reversed phase HPLC–ICP MS after their isolation from the post-reaction mixture by size-exclusion LC. Se(IV) present in the sample was derivatized as well and was determined along with the selenoaminoacids. The origin and identity of species were identified by the co-elution with the Se(IV), isotopically labelled selenomethionine, and with the synthetic standard of carbamidomethylated selenocysteine. The method development for SeCys was assisted by using glutathione peroxidise as the SeCys standard. SeMet, SeCys and Se(IV) were quantified by the method of standard additions. The mass balance provided a measure of the method validation. The method was applied to monitoring selenium speciation during supplementation of cows (dose–effect study) with Se-rich yeast containing feed and during milk processing.

Keywords: Milk; Selenium; Selenium speciation

Computational study of histamine H₃-receptor antagonist with support vector machines and three dimension quantitative structure activity relationship methods by Hai-Feng Chen (pp. 203-209).

Support vector machine (SVM) was used to derive QSAR models for 144 histamine H3 receptor antagonists. Several additional descriptors determined by SVM method, such as highest occupied molecular orbit (HOMO) and lowest unoccupied molecular orbit (LUMO), combined with conventional fields of CoMFA and CoMSIA were employed to construct 3D-QSAR model. The results show that inclusion of HOMO and LUMO is meaningful for 3D-QSAR model. The validation of this model was testified by some structural diverse compounds, which were not included in the CoMFA and CoMSIA models. Therefore, the non-linear SVM method can be applied to the selection of reasonable additional descriptors for 3D-QSAR investigations. The combination of these techniques could dramatically improve the statistical properties of model.

Keywords: Support vector machine; Additional descriptors; Highest occupied molecular orbit; Lowest unoccupied molecular orbit

Pareto-optimal front as a tool to study the behaviour of experimental factors in multi-response analytical procedures by C. Reguera; M.S. Sánchez; M.C. Ortiz; L.A. Sarabia (pp. 210-222).

This work presents a methodology to analyse the behaviour of an analytical procedure, above all when optimization of the procedure is needed. The methodology starts by the design of an experiment suitable to fit response surfaces to some analytical responses of interest in the problem being studied. Then, a pareto-optimal front is estimated that accounts for the optimal possibly trading-off solutions among the responses. The analysis of the behaviour of the optimal values of the response surfaces and the experimental conditions that provide these values allows going deeply into the analytical procedure.

Keywords: Experimental design; Response surface methodology; Optimization; Pareto-optimal front; Flow injection analysis; Amperometric detection; Malachite green; Leucomalachite green

Ni(II) selective sensors based on Schiff bases membranes in poly(vinyl chloride) by Vinod K. Gupta; Ashok K. Singh; Manoj K. Pal (pp. 223-231).

The two nickel chelates of Schiff bases, 3-hydroxy- N-{2-[(3-hydroxy- N-phenylbutyrimidoyl)-amino]-phenyl}- N′-phenylbutyramidine (M₁) and bis-4-(ethyliminomethyl)naphthalene-1-ol (M₂), have been synthesized and explored as ionophores for preparing PVC-based membrane sensors selective to nickel ion. The influences of membrane compositions on the potentiometric response of the electrodes have been found to substantially improve the performance characteristics. The best performance was obtained with the electrode having a membrane composition (w/w; mg) of (M₁): PVC:NaTPB:CN in the ratio 5:150:5:150. The sensor shows a linear potential response for Ni²⁺ over a wide concentration range 1.6×10⁻⁷ to 1.0×10⁻²M with Nernstian compliance (30.0±0.2mV/decade of activity) within pH range 2.5–9.5 and a fast response time of 10s. The sensor has been found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of methanol, ethanol, and acetonitrile and could be used for a period of 4 months. The analytical usefulness of the proposed electrode has been evaluated by its application in the determination of nickel in real samples. The practical utility of the membrane electrode has also been observed in the presence of surfactants.

Keywords: Ion selective electrodes; Ni(II); Schiff base; Sensors

Adsorptive stripping voltammetric determination of trace concentrations of molybdenum at an in situ plated lead film electrode by Katarzyna Tyszczuk; Mieczyslaw Korolczuk (pp. 232-237).

An in situ plated lead film electrode has been applied for adsorptive stripping voltammetric determination of trace concentrations of molybdenum in the presence of Alizarin S. The procedure is based on the preconcentration of the molybdenum–Alizarin S complex at an in situ plated lead film electrode held at −0.6V (versus Ag/AgCl), followed by a negatively sweeping square wave voltammetric scan. The peak current is proportional to the concentration of molybdenum over the range 2×10⁻⁹ to 5×10⁻⁸molL⁻¹, with a 3 σ detection limit of 9×10⁻¹⁰molL⁻¹ with an accumulation time of 60s. The measurements were carried out from underaerated solutions. The proposed procedure was validated in the course of Mo(VI) determination in water certified reference materials.

Keywords: Lead film electrode; Stripping voltammetry; Determination of molybdenum

Optimization of the thickness of a conducting polymer, polyaniline, deposited on the surface of poly(vinyl chloride) membranes: A new way to improve their potentiometric response by T.V. Shishkanova; P. Matějka; V. Král; I. Šeděnková; M. Trchová; J. Stejskal (pp. 238-246).

Repeated depositions of polyaniline (PANI) have been used to control the thickness of the polymeric film deposited on poly(vinyl chloride) (PVC) membrane surface. The oxidation of aniline was carried out in a dispersion mode, i.e. in the presence of poly( N-vinylpyrrolidone) (PVP). Two kinds of PVC were used for this purpose: a non-plasticized PVC for the study of PANI deposition and PVC, plasticized with nitrophenyl octyl ether (NPOE), as a prototype of a liquid membrane electrode. The results of UV-visible and FTIR spectroscopies and electron microscopy showed that (1) the film thickness increased by about equal increments of ∼40nm after each polymerization, and (2) the interface with PVC was constituted by PANI film and adhering PANI–PVP colloidal particles.The various thicknesses of the deposited PANI films affected the potentiometric response of the NPOE/PVC membrane with and without an anion-exchanger. The potentiometric anionic response was observed with a minimal thickness of PANI film on the blank NPOE/PVC membrane. Sensitivity of the PANI film to pH occurred only with a blank NPOE/PVC membrane coated with a thick polymeric film, while it was strongly suppressed by the presence of a lipophilic anion-exchanger, tridodecylmethylammonium chloride (TDDMACl), in the membrane, regardless of the thickness of the polymer film. The thickness of the PANI film did not affect the anionic selectivity pattern of TDDMACl-based membranes to any great extent, but its presence improved and stabilized their potentiometric characteristics (sensitivity, linear-response range).

Keywords: Potentiometry; Membrane electrode; Polyaniline; Anion response; Conducting polymer

Solid phase microextraction procedure for the determination of alkylphenols in water by on-fiber derivatization with N- tert-butyl-dimethylsilyl- N-methyltrifluoroacetamide by Yi-Ping Pan; Shih-Wei Tsai (pp. 247-252).

The solid phase microextraction (SPME) technique with on-fiber derivatization was evaluated for the analysis of alkylphenols (APs), including 4- tert-octylphenol (4- t-OP), technical nonylphenol isomers (t-NPs) and 4-nonylphenol (4-NP), in water. The 85μm polyacrylate (PA) fiber was used and a two-step sample preparation procedure was established. In the first step, water sample of 2mL was placed in a 4mL PTFE-capped glass vial. Headspace extraction of APs in water was then performed under 65°C for 30min with 800rpm magnetic stirring and the addition of 5% of sodium chloride. In the second step, the SPME fiber was placed in another 4mL vial, which contained 100μL of N- tert-butyl-dimethylsilyl- N-methyltrifluoroacetamide (MTBSTFA) with 1% tert-butyl-dimethylchlorosilane (TBDMCS). Headspace extraction of MTBSTFA and on-fiber derivatization with APs were performed at 45°C for 10min. Gas chromatography/mass spectrometry (GC/MS) was used for the analysis of derivatives formed on-fiber. The adsorption-time profiles were also examined. The precision, accuracy and method detection limits (MDLs) for the analysis of all the APs were evaluated with spiked water samples, including detergent water, chlorinated tap water, and lake water. The relative standard deviations were all less than 10% and the accuracies were 100±15%. With 2mL of water sample, MDLs were in the range of 1.58–3.85ngL⁻¹. Compared with other techniques, the study described here provided a simple, fast and reliable method for the analysis of APs in water.

Keywords: Solid phase microextraction; N; -; tert; -butyl-dimethylsilyl-; N; -methyltrifluoroacetamide; Alkylphenols; Gas chromatography

Environmental and bioanalytical applications of hollow fiber membrane liquid-phase microextraction: A review by Jingyi Lee; Hian Kee Lee; Knut E. Rasmussen; Stig Pedersen-Bjergaard (pp. 253-268).

In hollow fiber membrane liquid-phase microextraction (LPME), target analytes are extracted from aqueous samples and into a supported liquid membrane (SLM) sustained in the pores in the wall of a small porous hollow fiber, and further into an acceptor phase present inside the lumen of the hollow fiber. The acceptor phase can be organic, providing a two-phase extraction system compatible with capillary gas chromatography, or the acceptor phase can be aqueous resulting in a three-phase system compatible with high-performance liquid chromatography or capillary electrophoresis. Due to high enrichment, efficient sample clean-up, and the low consumption of organic solvent, substantial interest has been devoted to LPME in recent years. This paper reviews important applications of LPME with special focus on bioanalytical and environmental chemistry, and also covers a new possible direction for LPME namely electromembrane extraction, where analytes are extracted through the SLM and into the acceptor phase by the application of electrical potentials.

Keywords: Sample preparation; Liquid-phase microextraction; Hollow fiber membranes; Bioanalytical applications; Environmental applications

Metabonomic profiling of renal cell carcinoma: High-resolution proton nuclear magnetic resonance spectroscopy of human serum with multivariate data analysis by Hongchang Gao; Baijun Dong; Xia Liu; Hanqing Xuan; Yiran Huang; Donghai Lin (pp. 269-277).

Metabonomic profiling using proton nuclear magnetic resonance (¹H NMR) spectroscopy and multivariate data analysis of human serum samples was used to characterize metabolic profiles in renal cell carcinoma (RCC). We found distinct, easily detectable differences between (a) RCC patients and healthy humans, (b) RCC patients with metastases and without metastases, and (c) RCC patients before and after nephrectomy. Compared to healthy human serum, RCC serum had higher levels of lipid (mainly very low-density lipoproteins), isoleucine, leucine, lactate, alanine, N-acetylglycoproteins, pyruvate, glycerol, and unsaturated lipid, together with lower levels of acetoacetate, glutamine, phosphatidylcholine/choline, trimethylamine- N-oxide, and glucose. This pattern was somewhat reversed after nephrectomy. Altered metabolite concentrations are most likely the result of the cells switching to glycolysis to maintain energy homeostasis following the loss of ATP caused by impaired TCA cycle in RCC. Serum NMR spectra combined with principal component analysis techniques offer an efficient, convenient way of depicting tumour biochemistry and stratifying tumours under different pathophysiological conditions. It may be able to assist early diagnosis and postoperative surveillance of human malignant diseases using single blood samples.

Keywords: Proton nuclear magnetic resonance; Metabonomics; Pattern recognition; Carcinoma; Renal cell

Determination of critical eluent composition for polyethylenglycols using on-line liquid chromatography—Fourier transform infrared spectrometry by J. Kuligowski; G. Quintás; S. Garrigues; M. de la Guardia (pp. 278-285).

In this work, it has been extended to methanol:water mobile phases, the use of a background correction method for on-line LC–FTIR measurements named Univariate background correction based on the use of a reference spectra matrix (UBC-RSM) and absorbance ratios. It permits to overcome the problem related to spectral changes occurring during the gradient elution, which in the past limited the on-line coupling of LC and FTIR to isocratic elutions. The combined use of the aforementioned background correction technique in on-line isocratic and gradient LC–FTIR, and partial least squares (PLS) has been applied for the search of the critical conditions for polymers. Polyethylenglycol (PEG) has been used as a model example and results found fitted well with previously published ones.

Keywords: Liquid chromatography; Fourier transform infrared spectrometry; On-line background correction; Gradient elution

Functionalization of Ag nanoparticles with the bis-acridinium lucigenin as a chemical assembler in the detection of persistent organic pollutants by surface-enhanced Raman scattering by L. Guerrini; A.E. Aliaga; J. Cárcamo; J.S. Gómez-Jeria; S. Sanchez-Cortes; M.M. Campos-Vallette; J.V. García-Ramos (pp. 286-293).

Organochlorine pesticide endosulfan has been detected for the first time by using surface-enhanced Raman scattering (SERS) at trace concentrations. The bis-acridinium dication lucigenine was successfully used as a molecular assembler in the functionalization of metal nanoparticles to facilitate the approach of the pesticide to the metal surface. From the SERS spectra valuable information about the interaction mechanism between the pesticide and lucigenin can be deduced. In fact, endosulfan undergoes an isomerization upon adsorption onto the metal, while the viologen undergoes a rotation of the acridinium planes to better accommodate the pesticide molecule. An interaction between the N atom of the central acridinium ring and the pesticide Cl–CC–Cl fragment is verified through a charge-transfer complex. The present study affords important information which can be applied to the design of chemical sensor systems of persistent organic pollutants based on the optical detection on functionalized metal nanoparticle.

Keywords: Metal functionalization; Viologen; Lucigenin; Molecular recognition; Surface-enhanced Raman scattering; Nanosensors; Organochlorine pesticides

Improvement of surface plasmon resonance biosensor with magnetic beads via assembled polyelectrolyte layers by Ying Sun; Daqian Song; Yuping Bai; Liying Wang; Yuan Tian; Hanqi Zhang (pp. 294-300).

The conjugates of magnetic beads coupled with an antibody can be trapped on the Au film firmly due to the magnetic force for the immunoassay of a surface plasmon resonance (SPR) biosensor. However, this approach exhibits significant limitations in robustness and sensitivity due to incomplete dissociation of magnetic beads from the Au film. The incorporation of a polyelectrolyte film on the Au surface can prevent the magnetic beads from the direct contact with the Au film. The layer-by-layer assembly of polyelectrolyte was used as spacer between the gold surface and the magnetic bead. Different layers of polyelectrolyte can be assembled onto the Au film based on an electrostatic force between polycations and polyanions. After the polyelectrolyte film was fabricated on the Au film, the deposition of the magnetic beads was maintained effectively on the film, which favors the sensitivity of the biosensor and the regeneration of the sensing membrane. When the polyelectrolyte layers of (PAH/PSS)₃ were constructed on the Au film, the SPR biosensor with magnetic beads exhibited a satisfactory response to human IgG in the concentration range from 0.25 to 30.00μgmL⁻¹, and the determination limit obtained is eight times lower than that obtained with (PAH/PSS)₁ layer.

Keywords: Surface plasmon resonance; Conjugates; Magnetic microbeads; Layer-by-layer

Development of an impedimetric immunosensor based on electropolymerized polytyramine films for the direct detection of Salmonella typhimurium in pure cultures of type strains and inoculated real samples by Antonios V. Pournaras; Theodora Koraki; Mamas I. Prodromidis (pp. 301-307).

The development of a faradic impedimetric immunosensor based on electropolymerized polytyramine (Ptyr) films for the detection of S. typhimurium in milk is described for the first time. Polyclonal anti- Salmonella was cross-linked, in the presence of glutaraldehyde vapors, on Ptyr-modified gold electrodes. The dielectric behaviour of Ptyr films was evaluated with capacitance measurements, while their stability in neutral aqueous solutions was examined with impedimetric measurements. The effect of the concentration of tyramine in the forming solution on both the sensitivity and the dynamic range of the resulted immunosensors was also investigated. The alteration of the interfacial features of the electrodes due to different modification or recognition steps, was measured by faradic electrochemical impedance spectroscopy in the presence of a hexacyanoferrate(II)/(III) redox couple. At samples containing a low initial concentration of 10cfumL⁻¹ S. typhimurium, that actually defines the LOD of the immunosensors, signal changes of 33% and 88% were achieved after 3 and 10h incubation, respectively. To achieve the working simplicity expected by a biosensor, immunoreaction was performed directly in cultures. This resulted in the elimination of various centrifugation and washing steps, which are used for the isolation of bacteria cells from the culture, thus making the proposed immunosensors promising candidates for on-site applications. Finally, the proposed immunosensors were successfully used for the detection of S. typhimurium in experimentally inoculated milk samples.

Keywords: Faradic electrochemical impedance spectroscopy; Immunosensors; Salmonella typhimurium; Electropolymerized polytyramine films; On-site detection of pathogens

Determination of selected phenothiazines in human plasma by solid-phase extraction and liquid chromatography with coulometric detection by Maria Addolorata Saracino; Mario Amore; Elena Baioni; Carmine Petio; Maria Augusta Raggi (pp. 308-316).

A new analytical method, based on liquid chromatography with coulometric detection, has been developed and applied to the determination of selected phenothiazines (chlorpromazine, promazine, fluphenazine and levomepromazine) in human plasma. The drugs were separated on a Discovery pentafluorophenylpropyl column, using a mobile phase composed of acetonitrile (32%) and a pH 1.9 phosphate buffer (68%). Promethazine was used as the internal standard. Detection was carried out at an oxidation potential of +0.500V. A novel clean-up procedure was developed by means of solid-phase extraction, using cyanopropyl cartridges, which gave good extraction yield for all the analytes, with absolute recovery values higher than 91.0%. The detector response was linear over a plasma concentration range of 0.5–250.0ngmL⁻¹ for chlorpromazine, promazine and levomepromazine and of 0.2–4.0ngmL⁻¹ for fluphenazine. Precision results, expressed by the intra-day and the inter-day relative standard deviation values, were good, being lower than 3.9%. Accuracy data were satisfactory as well.The method has been successfully applied to the analysis of drug plasma levels of psychiatric patients undergoing therapy with selected phenothiazines.

Keywords: Abbreviations; CPZ; chlorpromazine; PMZ; promazine; FPZ; fluphenazine; LMP; levomepromazine; IS; internal standard; TDM; therapeutic drug monitoringLiquid chromatography; Coulometric detection; Selected phenothiazines; Human plasma; Solid-phase extraction

Development of a group selective molecularly imprinted polymers based solid phase extraction of malachite green from fish water and fish feed samples by Ya-hui Li; Tao Yang; Xiao-ling Qi; Yu-wei Qiao; An-ping Deng (pp. 317-325).

A group selective molecularly imprinted solid phase extraction (MISPE) for malachite green (MG) from fish water and fish feed samples was developed. Using MG as template molecule, methacrylic acid as functional monomer, ethylene glycoldimethacrylate as linking agent and bulk polymerization as synthetic method, the molecularly imprinted polymers (MIPs) were synthesized and characterized with rebinding experiment. The Scatchard polt's analysis revealed that the template–polymer system showed the two-site binding behavior with dissociation constants of 0.3194μmolL⁻¹ and 15.70μmolL⁻¹, respectively. MG and two structurally related compounds, leucomalachite green (LMG) and crystal violet (CV) were employed for selectivity test. The MIPs exhibited the highest selective rebinding to MG, but also displayed 83.0% and 87.5% of cross-reactivity with LMG and CV, demonstrating that MIPs could be used as group recognition sorbents in solid phase extraction. The extraction conditions of MISPE column for MG were optimized. Tap water samples spiked with MG at concentration of 0.5–10ngmL⁻¹ were extracted by MISPE column and analyzed by high performance liquid chromatography. The recoveries of MISPE column for MG extraction were found to be 76.8–93.7% with the relative standard deviations of 2.12–10.09%, indicating the feasibility of the prepared MIPs for MG extraction. No detectable MG was observed in one fish farming water sample and two fish feed samples; while the MG concentrations in two pet fishpond water samples were found at 1.50ngmL⁻¹ and 0.67ngmL⁻¹, respectively.

Keywords: Molecularly imprinted polymers; Malachite green; Solid phase extraction; High performance liquid chromatography; Fish farming water samples

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Analytica Chimica Acta (v.624, #2)