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Analytica Chimica Acta (v.674, #1)

Editorial Board (pp. iii).

Investigation of SPR and electrochemical detection of antigen with polypyrrole functionalized by biotinylated single-chain antibody: A review by H.Q.A. Lê; H. Sauriat-Dorizon; H. Korri-Youssoufi (pp. 1-8).

An electrochemical label-free immunosensor based on a biotinylated single-chain variable fragment (Sc-Fv) antibody immobilized on copolypyrrole film is described. An efficient immunosensor device formed by immobilization of a biotinylated single-chain antibody on an electropolymerized copolymer film of polypyrrole using biotin/streptavidin system has been demonstrated for the first time. The response of the biosensor toward antigen detection was monitored by surface plasmon resonance (SPR) and electrochemical analysis of the polypyrrole response by differential pulse voltammetry (DPV). The composition of the copolymer formed from a mixture of pyrrole (py) as spacer and a pyrrole bearing a N-hydroxyphthalimidyl ester group on its 3-position (pyNHP), acting as agent linker for biomolecule immobilization, was optimized for an efficient immunosensor device. The ratio of py:pyNHP for copolymer formation was studied with respect to the antibody immobilization and antigen detection. SPR was employed to monitor in real time the electropolymerization process as well as the step-by-step construction of the biosensor. FT-IR demonstrates the chemical copolymer composition and the efficiency of the covalent attachment of biomolecules. The film morphology was analyzed by electron scanning microscopy (SEM).Results show that a well organized layer is obtained after Sc-Fv antibody immobilization thanks to the copolymer composition defined with optimized pyrrole and functionalized pyrrole leading to high and intense redox signal of the polypyrrole layer obtained by the DPV method. Detection of specific antigen was demonstrated by both SPR and DPV, and a low concentration of 1pgmL⁻¹ was detected by measuring the variation of the redox signal of polypyrrole.

Keywords: Immunosensor; Biotinylated single-chain antibody; Surface plasmon resonance; Electrochemical detection; Copolymer; Polypyrrole

Multivariate analysis of nutritional information of foodstuff of plant origin for the selection of representative matrices for the analysis of pesticide residues by Ricardo Jorge Neves Bettencourt da Silva; Maria Filomena Gomes Ferreira Crujo Camões (pp. 9-19).

Testing safety of foodstuffs of plant origin involves the analysis of hundreds of pesticide residues. This control is only cost-effective through the use of methods validated for the analysis of many thousands of analyte/matrix combinations. Several documents propose representative matrices of groups of matrices from which the validity of the analytical method can be extrapolated to the represented matrices after summarised experimental check of within group method performance homogeneity. Those groups are based on an evolved expert consensus based on the empirical knowledge on the current analytical procedures; they are not exhaustive, they are not objectively defined and they propose a large list of representative matrices which makes their application difficult. This work proposes grouping 240 matrices, based on the nutritional composition pattern equivalence of the analytical portion right after hydration and before solvent extraction, aiming at defining groups that observe method performance homogeneity. This grouping was based on the combined outcome of three multivariate tools, namely: Principal Component Analysis, Hierarchical Cluster Analysis and K-Mean Cluster Analysis. These tools allowed the selection of eight groups for which representative matrices with average characteristics and objective criteria to test inclusion of new matrices were established. The proposed matrices groups are homogeneous to nutritional data not considered in their definition but correlated with the studied multivariate nutritional pattern. The developed grouping that must be checked with experimental test before use was tested against small deviations in food composition and for the integration of new matrices.

Keywords: Foodstuffs; Nutritional composition; Multivariate analysis; Method validation; Pesticide residues

A highly sensitive hydrogen peroxide amperometric sensor based on MnO₂-modified vertically aligned multiwalled carbon nanotubes by Bin Xu; Min-Ling Ye; Yu-Xiang Yu; Wei-De Zhang (pp. 20-26).

In this report, a highly sensitive amperometric sensor based on MnO₂-modified vertically aligned multiwalled carbon nanotubes (MnO₂/VACNTs) for determination of hydrogen peroxide (H₂O₂) was fabricated by electrodeposition. The morphology of the nanocomposite was characterized by scanning electron microscopy, energy-dispersive X-ray spectrometer and X-ray diffraction. Cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy were applied to investigate the electrochemical properties of the MnO₂/VACNTs nanocomposite electrode. The mechanism for the electrochemical reaction of H₂O₂ at the MnO₂/VACNTs nanocomposite electrode was also discussed. In borate buffer (pH 7.8, 0.20M), the MnO₂/VACNTs nanocomposite electrode exhibits a linear dependence ( R=0.998) on the concentration of H₂O₂ from 1.2×10⁻⁶M to 1.8×10⁻³M, a high sensitivity of 1.08×10⁶μAM⁻¹cm⁻² and a detection limit of 8.0×10⁻⁷M (signal/noise=3). Meanwhile, the MnO₂/VACNTs nanocomposite electrode is also highly resistant towards typical inorganic salts and some biomolecules such as acetic acid, citric acid, uric acid andd-(+)-glucose, etc. In addition, the sensor based on the MnO₂/VACNTs nanocomposite electrode was applied for the determination of trace of H₂O₂ in milk with high accuracy, demonstrating its potential for practical application.

Keywords: Carbon nanotubes; Hydrogen peroxide; Sensor; Manganese dioxide; Amperometry

Highly sensitive electrochemical stripping detection of hepatitis B surface antigen based on copper-enhanced gold nanoparticle tags and magnetic nanoparticles by Guangyu Shen; Yun Zhang (pp. 27-31).

On the basis of copper-enhanced gold nanoparticle tags as an amplification approach, we introduced, in this paper, magnetic nanoparticles for further improving performance of electrochemical immunoassay by anodic stripping voltammetry (ASV) at a glassy-carbon electrode. Due to the use of antibody-immobilized magnetic nanoparticles, the immunoreaction between antibody and antigen takes place in a homogeneous bulk solution phase. Compared with traditional solid interface reaction, the proposed strategy can provide some advantages such as easy of separation, shorter analytical time, wider linear range, and lower detection limit. It was also successfully applied to HBsAg determination in a linear range of 0.1–1500ngmL⁻¹ with a detection limit of 87pgmL⁻¹. The proposed analytical strategy holds good selectivity, sensitivity and repeatability and also great promise for the extended application in the fields of clinical diagnosis, bio-affinity assay and environmental monitoring.

Keywords: Copper-enhanced gold nanoparticle tags; Magnetic nanoparticles; Metal immunoassay; Hepatitis B surface antigen

Screening of transformation products in soils contaminated with unsymmetrical dimethylhydrazine using headspace SPME and GC–MS by Bulat N. Kenessov; Jacek A. Koziel; Tim Grotenhuis; Lars Carlsen (pp. 32-39).

The paper describes a novel SPME-based approach for sampling and analysis of transformation products of highly reactive and toxic unsymmetrical dimethylhydrazine (UDMH) which is used as a fuel in many Russian, European, Indian, and Chinese heavy cargo carrier rockets. The effects of several parameters were studied to optimize analyte recovery. It was found that the 85μm Carboxen/polydimethylsiloxane fiber coating provides the highest selectivity for selected UDMH transformation products. Optimal sampling/sample preparation parameters were determined to be 1-h soil headspace sampling time at 40°C. The GC inlet temperature was optimized to 170°C held for 0.1min, then 1°Cs⁻¹ ramp to 250°C where it was held for 40min. Temperature programing resulted in a fast desorption along with minimal chemical transformation in the GC inlet. SPME was very effective extracting UDMH transformation products from soil samples contaminated with rocket fuel. The use of SPME resulted in high sensitivity, speed, small labor consumption due to an automation and simplicity of use. It was shown that water addition to soil leads to a significant decrease of recovery of almost all target transformation products of UDMH. The use of SPME for sampling and sample preparation resulted in detection of the total of 21 new compounds that are relevant to the UDMH transformation in soils. In addition, the number of confirmed transformation products of UDMH increased from 15 to 27. This sampling/sample preparation approach can be recommended for environmental assessment of soil samples from areas affected by space rocket activity.

Keywords: Unsymmetrical dimethylhydrazine; Solid phase microextraction; Soil; Rocket fuel; Sampling; Sample preparation

Evaluation of a new method for chemical coating of aluminum wire with molecularly imprinted polymer layer. Application for the fabrication of triazines selective solid-phase microextraction fiber by Djavanshir Djozan; Bahram Ebrahimi; Mehrdad Mahkam; Mir Ali Farajzadeh (pp. 40-48).

A new solid-phase microextraction (SPME) fiber is fabricated through ultra violet irradiation polymerization of ametryn-molecularly imprinted polymer on the surface of anodized–silylated aluminum wire. The prepared fiber is durable with very good chemical and thermal stability which can be coupled to GC and GC/MS. The effective parameters on the fabrication and application procedures such as spraying mode, ultra violet irradiation (polymerization) time, number of sprayings and polymerizations, pH and ionic strength of sample and extraction time were optimized. This fiber shows high selectivity with great extraction capacity toward triazines. SPME and GC analysis of ametryn, prometryn, terbutryn, atrazine, simazine, propazine and cyanazine using the fabricated fiber result in the detection limits of 9, 32, 27, 43, 51, 74 and 85ngmL⁻¹, respectively. The reliability of the prepared fiber in real samples has been investigated and proved by using spiked tap water, rice, maize and onion samples.

Keywords: Gas chromatography; Solid-Phase microextraction; Molecularly imprinted polymer; Anodized aluminum; Coated fiber; Triazine herbicides

Green procedure using limonene in the Dean–Stark apparatus for moisture determination in food products by Sébastien Veillet; Valérie Tomao; Karine Ruiz; Farid Chemat (pp. 49-52).

In the past 10 years, trends in analytical chemistry have turned toward the green chemistry which endeavours to develop new techniques that reduce the influence of chemicals on the environment. The challenge of the green analytical chemistry is to develop techniques that meet the request for information output while reducing the environmental impact of the analyses. For this purpose petroleum-based solvents have to be avoided. Therefore, increasing interest was given to new green solvents such as limonene and their potential as alternative solvents in analytical chemistry. In this work limonene was used instead of toluene in the Dean–Stark procedure. Moisture determination on wide range of food matrices was performed either using toluene or limonene. Both solvents gave similar water percentages in food materials, i.e. 89.3±0.5 and 89.5±0.7 for carrot, 68.0±0.7 and 68.6±1.9 for garlic, 64.1±0.5 and 64.0±0.3 for minced meat with toluene and limonene, respectively. Consequently limonene could be used as a good alternative solvent in the Dean–Stark procedure.

Keywords: Dean–Stark distillation; Limonene; Alternative solvent; Green analytical chemistry

Preparation and evaluation of molecularly imprinted solid-phase micro-extraction fibers for selective extraction of phthalates in an aqueous sample by Juan He; Ruihe Lv; Haijun Zhan; Huizhi Wang; Jie Cheng; Kui Lu; Fengcheng Wang (pp. 53-58).

A novel molecularly imprinted polymer (MIP) that was applied to a solid-phase micro-extraction (SPME) device, which could be coupled directly to gas chromatograph and mass spectrometer (GC/MS), was prepared using dibutyl phthalate (DBP) as the template molecule. The characteristics and application of this fiber were investigated. Electron microscope images indicated that the MIP-coated solid-phase micro-extraction (MI-SPME) fibers were homogeneous and porous. The extraction yield of DBP with the MI-SPME fibers was higher than that of the non-imprinted polymer (NIP)-coated SPME (NI-SPME) fibers. The MI-SPME fibers had a higher selectivity to other phthalates that had similar structures as DBP. A method was developed for the determination of phthalates using MI-SPME fibers coupled with GC/MS. The extraction conditions were optimized. Detection limits for the phthalate samples were within the range of 2.17–20.84ngL⁻¹. The method was applied to five kinds of phthalates dissolved in spiked aqueous samples and resulted in recoveries of up to 94.54–105.34%, respectively. Thus, the MI-SPME fibers are suitable for the extraction of trace phthalates in complicated samples.

Keywords: Molecularly imprinted polymer; Solid-phase micro-extraction; Fiber; Dibutyl phthalate

Ultrasound-assisted emulsification microextraction with simultaneous derivatization coupled to fibre optics-based cuvetteless UV–vis micro-spectrophotometry for formaldehyde determination in cosmetic samples by Isela Lavilla; Noelia Cabaleiro; Francisco Pena; Inmaculada de la Calle; Carlos Bendicho (pp. 59-63).

In this work, ultrasound-assisted emulsification microextraction in combination with fibre optics-based cuvetteless UV–vis micro-spectrophotometry has been proposed as a novel method for the determination of formaldehyde in water-based cosmetics such as shampoo, conditioner and shower gel. The use of a powerful cup-horn sonoreactor allows simultaneous extraction and derivatization of the samples without any pre-treatment. The type and volume of organic extractant solvent, need for a disperser solvent, sonication conditions (sonication time and amplitude), ionic strength and centrifuging time have been carefully studied. Matrix effects were also evaluated. The European official method for quantification of formaldehyde in cosmetic products was used for comparison purposes. An important improvement in sensitivity and sample throughput as well as miniaturization was achieved. A limit of detection of 0.02μgg⁻¹ of formaldehyde and a repeatability expressed as relative standard deviation of 5.9% were obtained.

Keywords: Ultrasound-assisted emulsification microextraction; Cosmetics; Formaldehyde; Fibre optics-based cuvetteless UV–vis micro-spectrophotometry

Simultaneous determination of phoxim and its photo-transformation metabolite residues in eggs using liquid chromatography coupled with electrospray ionization tandem mass spectrometry by Jung Han Lee; Semin Park; Won Young Jeong; Hyung Jin Park; Hae Gyeong Kim; Soo-Jung Lee; Jae-Han Shim; Soo Taek Kim; A.M. Abd El-Aty; Moo Hyeog Im; Ok Ja Choi; Sung Chul Shin (pp. 64-70).

The principal objective of this study was to develop an appropriate, sensitive, and selective method for the simultaneous quantitative determination of phoxim and its photo-transformation product, O, O-diethyl α-cyanobenzylideneamino-thiophosphonate (DCTP) in both chicken and quail eggs. Eggs (1g) were blended with anhydrous magnesium sulfate (1g) for sample pretreatment and extracted with acetonitrile. The extracts were then further purified with SPE silica gel tubes deactivated with trimethylamine. Residues were analyzed via a reversed phase-liquid chromatography–tandem mass spectrometry (RP-LC–MS/MS) in positive-ion electrospray ionization (ESI) mode. Tebufenozide was utilized as an internal standard for the quantification of phoxim and its metabolite residues. The identification and quantification of analytes were based on ion transitions monitored by multiple reaction monitoring (MRM). LC–MS/MS analysis was performed from 0.02 to 1mgkg⁻¹ and correlation coefficients ( r²) ranging from 0.998 to 0.999 were obtained for both analytes in blank egg extracts. The relative standard deviations (RSDs) of intra- and inter-day variations ranged from 2.1% to 6.7% and from 2.8% to 6.4% for phoxim and DCTP in chicken and quail eggs. At all levels of fortification (0.02, 0.05, and 0.125mgkg⁻¹), the recoveries fell within a range of 81.3% to 93.6% for phoxim and 83.3% to 90.1% for DCTP. The matrix effect was <2%, due to the partial dilution of the sample. Decision limits (CC α) and detection capabilities (CC β) were in the range of 0.0005–0.0044 and 0.0054–0.0224mgkg⁻¹, respectively. The method was evaluated further by analyzing real samples purchased from markets. All chicken and quail egg samples were free from residues of the target compounds.

Keywords: Phoxim; Degradation product; Tandem mass; Eggs; Chicken; Quail

Simultaneous determination of four tobacco-specific N-nitrosamines in mainstream smoke for Chinese Virginia cigarettes by liquid chromatography–tandem mass spectrometry and validation under ISO and “Canadian intense” machine smoking regimes by Wei Xiong; Hongwei Hou; Xingyi Jiang; Gangling Tang; Qingyuan Hu (pp. 71-78).

A liquid chromatography–tandem mass spectrometry (LC–MS/MS) method for determining four tobacco-specific N-nitrosamines (TSNAs) in mainstream smoke from Chinese Virginia cigarettes was developed. Mainstream cigarette smoke particulate matter was collected on a Cambridge filter pad, further extracted using 100mM ammonium acetate after 100μL internal standard addition, and subsequently analyzed with LC–MS/MS. The limit of detection for NNN, NNK, NAT and NAB were 0.006, 0.013, 0.003 and 0.021ngmL⁻¹ respectively, with a linear calibration range spanning 1–200ngmL⁻¹. Intra- and inter-day precision for four TSNAs ranged from 3.3% to 8.5% and 2.3% to 10.1%; recovery was between 89.1% and 104.9% for Chinese Virginia cigarettes. The proposed method was applied to evaluate TSNAs yields for 39 commercially available cigarettes in Chinese market under ISO and “Canadian intense” machine smoking regimes, on the ground that it comes closest to representing smoke deliveries from human smoking. Total TSNAs emissions are more than double under the Canadian regime. TSNAs:nicotine ratios were used in our assay to show any differences in yield from different brands. TSNAs:nicotine levels show more than a 10-fold difference across brands and types (Chinese Virginia cigarettes and blended cigarettes) in the Chinese market.

Keywords: Tobacco-specific N-nitrosamines; Liquid chromatography–tandem mass spectrometry; Canadian intense; Chinese Virginia cigarettes

Determination of antioxidants by a novel on-line HPLC-cupric reducing antioxidant capacity (CUPRAC) assay with post-column detection by Saliha Esin Çelik; Mustafa Özyürek; Kubilay Güçlü; Reşat Apak (pp. 79-88).

A novel on-line HPLC-cupric reducing antioxidant capacity (CUPRAC) method was developed for the selective determination of polyphenols (flavonoids, simple phenolic and hydroxycinnamic acids) in complex plant matrices. The method combines chromatographic separation, constituent analysis, and post-column identification of antioxidants in plant extracts. The separation of polyphenols was performed on a C18 column using gradient elution with two different mobile phase solutions, i.e., MeOH and 0.2% o-phosphoric acid. The HPLC-separated antioxidant polyphenols in the extracts react with copper(II)-neocuproine (Cu(II)-Nc) reagent in a post-column reaction coil to form a derivative. The reagent is reduced by antioxidants to the copper(I)-neocuproine (Cu(I)-Nc) chelate having maximum absorption at 450nm. The negative peaks of antioxidant constituents were monitored by measuring the increase in absorbance due to Cu(I)-Nc. The detection limits of polyphenols at 450nm (in the range of 0.17–3.46μM) after post-column derivatization were comparable to those at 280nm UV detection without derivatization. The developed method was successfully applied to the identification of antioxidant compounds in crude extracts of Camellia sinensis, Origanum marjorana and Mentha. The method is rapid, inexpensive, versatile, non-laborious, uses stable reagents, and enables the on-line qualitative and quantitative estimation of antioxidant constituents of complex plant samples.

Keywords: On-line HPLC-cupric reducing antioxidant capacity (CUPRAC); Post-column detection; Spectrophotometric cupric reducing antioxidant capacity assay; Polyphenols

An amperometric penicillin biosensor with enhanced sensitivity based on co-immobilization of carbon nanotubes, hematein, and β-lactamase on glassy carbon electrode by Bi Chen; Ming Ma; Xiaoli Su (pp. 89-95).

An amperometric penicillin biosensor with enhanced sensitivity was successfully developed by co-immobilization of multi-walled carbon nanotubes (MWCNTs), hematein, and β-lactamase on glassy carbon electrode using a layer-by-layer assembly technique. Under catalysis of the immobilized enzyme, penicillin was hydrolyzed, decreasing the local pH. The pH change was monitored amperometrically with hematein as a pH-sensitive redox probe. MWCNTs were used as an electron transfer enhancer as well as an efficient immobilization matrix for the sensitivity enhancement. The effects of immobilization procedure, working potential, enzyme quantity, buffer concentration, and sample matrix were investigated. The biosensor offered a minimum detection limit of 50nM (19μgL⁻¹) for penicillin V, lower than those of the conventional pH change-based biosensors by more than two orders of magnitude. The electrode-to-electrode variation of the response sensitivity was 7.0% RSD.

Keywords: Penicillin biosensor; Amperometric biosensor; Carbon nanotubes; β-Lactam antibiotics; β-Lactamase

Synthesis, characterization and enhanced photoconductivity from a mesoporous titania on dye doping by Nabanita Pal; Manidipa Paul; Ashoke Bera; Durga Basak; Asim Bhaumik (pp. 96-101).

New wormhole-like mesoporous TiO₂ material has been synthesized through a convenient sol–gel method in the presence of a Schiff base secondary amine hexadecyl-2-pyrrole-methylamine (HPMA) containing chelating donor sites as template or structure directing agent (SDA). SDA molecules can be easily removed from the composite to generate mesoporosity and upon removal of the SDA molecule, this mesoporous TiO₂ material showed very high surface area (480±10m²/g) with an average pore diameter of 2.57±0.05nm. When Rose Bengal dye is entrapped inside the nanopores of this material, it showed a drastic enhancement ( ca. 40-folds) in the photoconductivity vis-à-vis mesoporous TiO₂ alone under white light illumination.

Keywords: Dye encapsulation; Mesoporous materials; Photoconductivity; Templated synthesis; Titania nanostructures

Non-orthogonal micro-free flow electrophoresis: From theory to design concept by Christopher J. Evenhuis; Victor Okhonin; Sergey N. Krylov (pp. 102-109).

Micro-free flow electrophoresis (μFFE) is a technique that facilitates continuous separation of molecules in a shallow channel with a hydrodynamic flow and an electric field at an angle to the flow. We recently developed a general theory of μFFE that suggested that an electric field non-orthogonal to the flow could improve resolution. Here, we used computer modeling to study resolution as a function of the electric field strength and the angle between the electric field and the hydrodynamic flow. In addition we used our general theory of μFFE to investigate other important influences on resolution, which include the velocity of the hydrodynamic flow, the height of the separation channel, and the magnitude and direction of the electroosmotic flow. Finally, we propose four designs that could be used to generate non-orthogonal electric fields and discuss their relative merits.

Keywords: Resolution; Electric field strength; Hydrodynamic flow velocity; Electroosmotic mobility; Channel height

A microfluidic device integrated with multichamber polymerase chain reaction and multichannel separation for genetic analysis by Xiaoyan Pan; Lei Jiang; Kaiying Liu; Bingcheng Lin; Jianhua Qin (pp. 110-115).

This work describes a microfluidic device integrated with multichamber polymerase chain reaction (PCR) and multichannel separation for parallel genetic analysis. The microdevice consists of three functional units: temperature control, multiple PCR (four chambers PCR), and multiple channel separation (four separation channels, each channel connected to a PCR chamber). Platinum (Pt)/titanium (Ti) microheater was used to ensure homogeneous temperature field, and Pt-chip sensor was used for temperature monitoring. The interface between chip-PCR and chip separation was simplified by connecting the PCR chamber with separation channel directly. After chip-PCR, PCR products were introduced into parallel separation channels for subsequent separation/detection by applying an electric field automatically. This microdevice was successfully applied for detection of pathogens including hepatitis B virus (HBV) and Mycobacterium tuberculosis (MTB), and genotyping of human leucocyte antigen (HLA)-B27 as well, demonstrating the feasibility of the integrated microdevice for parallel genetic analysis.

Keywords: Abbreviations; PCR; polymerase chain reaction; HBV; hepatitis B virus; MTB; Mycobacterium tuberculosis; TB; tuberculosis; HLA; human leucocyte antigen; R; –; T; resistance–temperature; CE; chip electrophoresis; DNA; deoxyribonucleic acid; AS; ankylosing sporidylitisMicrofluidic; Parallel analysis; Multichamber polymerase chain reaction; Pathogen detection; Genotyping

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Analytica Chimica Acta (v.674, #1)