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Analytica Chimica Acta (v.693, #1-2)

Editorial Board (pp. iii).

Enzyme-linked immunosorbent assay for detection of organophosphorylated butyrylcholinesterase: A biomarker of exposure to organophosphate agents by Limin Wang; Dan Du; Donglai Lu; Chiann-Tso Lin; Jordan N. Smith; Charles Timchalk; Fengquan Liu; Jun Wang; Yuehe Lin (pp. 1-6).
A sandwich enzyme-linked immunosorbent assay (sELISA) has been developed for detection of organophosphorylated butyrylcholinesterase (OP-BChE), a potential biomarker for human exposure to organophosphate insecticides and nerve agents. A pair of antibodies specific to OP-BChE adduct were identified through systematic screening of several anti BChE antibodies (anti-BChE) and anti-phosphoserine antibodies (anti-Pser) from different sources. The selected anti-BChE (set as capture antibody) antibodies recognize both phosphorylated and nonphosphorylated BChE. These antibodies can therefore be used to capture both BChE and OP-BChE from the sample matrices. The anti-Pser (set as detecting antibody) was used to recognize the OP moiety of OP-BChE adducts. With the combination of the selected antibody pair, several key parameters (such as the concentration of anti-BChE and anti-Pser, and the blocking agent) were optimized to enhance the sensitivity and selectivity of the sELISA. Under the optimal conditions, the sELISA has shown a wide linear range from 0.03nM to 30nM, with a detection limit of 0.03nM. Furthermore, the sELISA was successfully applied to detect OP-BChE using in vitro biological samples such as rat plasma spiked with OP-BChE with excellent adduct recovery ( z>99%). These results demonstrate that this novel approach holds great promise to develop an ELISA kit and offers a simple and cost-effective tool for screening/evaluating exposure to organophosphate insecticides and nerve agents.

Keywords: Sandwich ELISA; Organophosphorylated butyrylcholinesterase; Butyrylcholinesterase; Organophosphate insecticides and nerve agents


A review on the fabrication of substrates for surface enhanced Raman spectroscopy and their applications in analytical chemistry by Meikun Fan; Gustavo F.S. Andrade; Alexandre G. Brolo (pp. 7-25).
This work reviews different types of substrates used for surface-enhanced Raman scattering (SERS) that have been developed in the last 10 years. The different techniques of self-assembly to immobilize metallic nanoparticles on solid support are covered. An overview of SERS platforms developed using nanolithography methods, including electron-beam (e-beam) lithography and focused ion beam (FIB) milling are also included, together with several examples of template-based methodologies to generate metallic nano-patterns. The potential of SERS to impact several aspects of analytical chemistry is demonstrated by selected examples of applications in electrochemistry, biosensing, environmental analysis, and remote sensing. This review shows that highly enhancing SERS substrates with a high degree of reliability and reproducibility can now be fabricated at relative low cost, indicating that SERS may finally realize its full potential as a very sensitive tool for routine analytical applications.

Keywords: Surface-enhanced Raman scattering; SERS; Plasmonics; Sensors; Nanolithography; Analytical spectroscopy


Rank annihilation factor analysis method for spectrophotometric study of second-order reaction kinetics by Hamid Abdollahi; Azadeh Golshan (pp. 26-34).
In this study several methods are described to determine the rate constant of a second-order reaction in the form of A+B→C. These approaches allow circumventing a rank deficiency inherent of a second-order reaction when the spectroscopic data is influenced by additional source of variance. Classically, to determine the unknown rate constant in this kind of systems, one needs to have extra knowledge about the system, including the spectra of the reactants or product and the exact kinetics. In the case of the presence of an unknown phenomenon in the data set that cannot be explained by the model, such as baseline drift, the estimated rate constant might be erroneous. Present work is a modification of the rank annihilation factor analysis (RAFA) algorithm by inclusion of I) pure spectra of reactants, or IIA) mean centering step, or IIB) mean spectrum. The proposed methods can interestingly be applied on a single kinetic run. The performances of the new methods have been evaluated by applying them to analysis of simulated and experimental data.

Keywords: Rank annihilation factor analysis; Second-order kinetics; Rank deficiency; Hard-modeling


Effect of gold nanoparticle attached multi-walled carbon nanotube-layered indium tin oxide in monitoring the effect of paracetamol on the release of epinephrine by Rajendra N. Goyal; Anoop Raj Singh Rana; Md. Abdul Aziz; Munetaka Oyama (pp. 35-40).
A gold nanoparticle attached multi-walled carbon nanotube-layered indium tin oxide (AuNP/MWNT/ITO) electrode has been used for monitoring the effect of paracetamol (PAR) on the release of epinephrine (EPI) in human urine. The modified electrode shows an excellent electrocatalytic activity for the oxidation of EPI and PAR with acceleration of electron transfer rate as compared to MWNT/ITO and AuNP/ITO. An apparent shift of the oxidative potential towards less positive potential with a marked increase in peak currents is observed in square wave voltammetry at AuNP/MWNT/ITO electrode. The calibration curves for the simultaneous determination of PAR and EPI showed an excellent linear response, ranging from 5.0×10−9molL−1 to 80.0×10−9molL−1 for both the compounds. The detection limits for the simultaneous determination of PAR and EPI were found to be 46×10−10molL−1 and 42×10−10molL−1 respectively. The proposed method has been successfully applied for the simultaneous determination of PAR and EPI in human urine. It is observed that gold nanoparticles attached with multi-wall carbon nanotube catalyze the oxidation of EPI and PAR.

Keywords: Nanogold; Epinephrine; Paracetamol; Square wave voltammetry; Carbon nanotubes


Cooperative use of cytochrome cd1 nitrite reductase and its redox partner cytochrome c552 to improve the selectivity of nitrite biosensing by A.S. Serra; S.R. Jorge; C.M. Silveira; J.J.G. Moura; E. Jubete; E. Ochoteco; G. Cabañero; H. Grande; M.G. Almeida (pp. 41-46).
In this work, a novel enzymatic biosensor for determination of nitrites constructed on an electrochemical transducing platform is proposed. The sensor is based on cytochrome- cd1 (cyt- cd1) nitrite reductase from Marinobacter hydrocarbonoclasticus strain 617 as biological recognition element, and its putative physiological redox partner cytochrome- c552 (cyt- c552), as electron mediator. The proteins were co-immobilized using a photopolymerizable polyvinyl alcohol (PVA) derivative, onto carbon paste screen printed electrodes (CPSPEs); the optimal modification conditions were 100μM cyt- cd1/100μM cyt- c552 and 50% PVA, after a 48h polymerization time. Electrochemical characterization of the mediator was carried out by cyclic voltammetry. The one-electron exchange between cyt- c552 and the working electrode is a quasi-reversible process, without mass transport limitations. The formal potential of the mediator is 254±2mV vs NHE and the intermolecular electron transfer rate constant between cytochromes c552 and cd1 is 9.9×103M−1s−1. The analytical parameters of the biosensor response to nitrite as assessed by amperometric measurements were: linear range from 10 to 200μM; detection and quantification limits of 7 and 24μM, respectively; sensitivity of 2.49±0.08Amol−1cm2μM−1. Catalytic profiles in the presence of possible interfering species were also investigated. The interference from competitive enzymatic reduction of dissolved oxygen could be overcome by tuning the cyclic voltammograms for faster sweep rates.

Keywords: Nitrite biosensor; Cytochrome; cd; 1; Cytochrome; c; 552; Photopolymerizable PVA; Screen printed electrodes


Optimisation of pressurised liquid extraction for the ultra-trace quantification of 20 priority substances from the European Water Framework Directive in atmospheric particles by GC–MS and LC–FLD–MS/MS by Céline Becouze; Laure Wiest; Robert Baudot; Jean-Luc Bertrand-Krajewski; Cécile Cren-Olivé (pp. 47-53).
Atmospheric deposition plays an important role in environmental pollution and human health. However, very few information is available on the presence, in atmospheric particles, of organic priority substances in contrast to inorganic fraction. A method for the extraction and quantification of 20 priority organic substances listed in the European Water Framework Directive in atmospheric particles was developed. This method consists in a combination of gas chromatography coupled with mass spectrometry and ultra-high-pressure liquid chromatography coupled with tandem mass spectrometry and fluorescence. Optimized pressurized liquid extraction using a hexane/dichloromethane/isopropanol mixture was used as extraction procedure from atmospheric particulate matter. The influence of several extraction experimental factors related to the PLE was investigated. The optimized extraction method (80°C, 40bar, 10min, 1 cycle) exhibited average recoveries of target analytes higher than 62%. The method detection limits (MDL) were between 0.3ngg−1 and 83ngg−1. This extraction method, combined with sensitive analytical techniques, leads to satisfactory reliability, sensitivity, and accuracy. The method was applied to real samples, collected from two urban sites by an atmospheric sampling prototype developed in this study. The first results reveal a systematic presence of PAHs at high levels (ranging from 500ngg−1 to 10μgg−1) and a variable and lower presence of pesticides at concentrations below 50ngg−1 in the samples.

Keywords: Atmospheric particle; European Water Framework Directive; Pesticide; PAH; Alkylphenol; PLE; GC–MS; LC–MS/MS; LC–FLD; Multiresidue analysis


Preparation, characterization and application of octadecyl modified magnesium oxide microspheres by Jing Jin; Zhiping Zhang; Yun Li; Xianbo Lu; Lidong Wu; Jiping Chen (pp. 54-61).
A new solid-phase extraction sorbent, octadecyl modified magnesium oxide (C18-MgO) microspheres, was successfully prepared in the present work. Its composition, morphology and structure were studied by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), N2 adsorption–desorption technique, and solid-state nuclear magnetic resonance (NMR). The as-synthesized C18-MgO was employed as a solid-phase extraction sorbent for the enrichment of polycyclic aromatic hydrocarbons (PAHs) in aqueous solutions. Several factors affecting the extraction efficiency of PAHs, including the type and concentration of organic modifiers, flow rate, sample volume, and the types of rinsing solvents and eluting solvents, were investigated systematically. The results demonstrated that C18-MgO was superior to MgO in terms of large volume in loading samples. In comparison with MgO and Sep-Pak C18, C18-MgO exhibited excellent extraction efficiency (>91% except for naphthalene) in respect of high recoveries under the optimized conditions. The limits of detection varied from 0.001 to 0.603ngmL−1 for 15 PAHs using high-performance liquid chromatography coupled with a fluorescence detector, indicating that the analytical method was highly sensitive. The proposed method was applied to enrich PAHs in tap water and acceptable recoveries (18–96%) were obtained.

Keywords: Octadecyl; Modification; Magnesium oxide; Preparation; Characterization; Solid-phase extraction


Comprehensive analysis of polycyclic aromatic hydrocarbons in wastewater using stir bar sorptive extraction and gas chromatography coupled to tandem mass spectrometry by Nieves Barco-Bonilla; Roberto Romero-González; Patricia Plaza-Bolaños; José Luis Fernández-Moreno; Antonia Garrido Frenich; José Luis Martínez Vidal (pp. 62-71).
The objective of this study was the optimization and comparison of two extraction methods for the determination of polycyclic aromatic hydrocarbons (PAHs) in wastewater (WW). A distribution study of the target compounds between the aqueous phase and the suspended particulate matter (SPM) has been performed in order to establish whether the analysis of both phases is necessary. In this sense, the feasibility of stir bar sorptive extraction (SBSE) and solid-phase extraction (SPE) for the determination of 24 PAHs in WW samples has been evaluated. The results demonstrated the suitability of SBSE to perform a comprehensive analysis of liquid samples containing high amounts of SPM, such as in the determination of PAHs in WWs. A gas chromatography triple quadrupole mass spectrometry (GC–QqQ-MS/MS) method has been also optimized for the separation and detection of the target compounds, avoiding the co-elution of some groups of isomers, such as benzo[ b], [ j] and [ k] fluoranthenes and indene[1,2,3- cd]pyrene/dibenz[ a, h]anthracene. For that purpose, a specific capillary column developed for PAH determination was used. The SBSE procedure was validated and adequate parameters (such as recovery, linearity, precision, limits of detection and quantification) were obtained. Finally, the validated method was applied to the analysis of real samples collected from an experimental WW treatment plant, detecting some PAHs at concentrations in the range 0.007–0.022μgL−1.

Keywords: Polycyclic aromatic hydrocarbons (PAHs); Wastewater analysis; Stir bar sorptive extraction (SBSE); Solid-phase extraction (SPE); Gas chromatography–tandem mass spectrometry (GC–MS/MS)


Determination of 40 currently used pesticides in airborne particulate matter (PM 10) by microwave-assisted extraction and gas chromatography coupled to triple quadrupole mass spectrometry by Clara Coscollà; Mercedes Castillo; Agustin Pastor; Vicent Yusà (pp. 72-81).
A confirmatory and sensitive procedure has been developed for the determination of 40 currently used pesticides (CUPs) in airborne particulate matter (PM 10) at trace level. The proposed method includes extraction of PM 10-bound pesticides by microwave-assisted extraction (MAE) followed by a gel permeation chromatography (GPC) clean-up and determination by GC–MS/MS. The injection mode and the main parameters in MS/MS were optimized. The matrix effect was also evaluated. Recoveries ranged from 70 to 120% except for pyrimethanil and pirimicarb. The limit of quantification (LOQ) ranged from 1.32 to 39.47pgm−3, when air volumes of 760m3 were collected. The method was applied to 38 samples collected from a rural station belonging to the atmospheric monitoring network of the Regional Valencia Government (Spain) during April–June 2010. Eighteen out of 40 pesticides investigated were found in at least one sample (bifenthrin, chlorothalonil, chlorpyriphos-e, chlorpyriphos-m, clorpropham, diazinon, dicofol, diphenylamine, fipronil, fludioxonil, folpet, malathion, metalaxyl, penconazole, quinoxyfen, triadimefon, trifluralin, and vinclozoline), with concentrations ranging from 1.32 to 625.80pgm−3.

Keywords: Pesticides; Ambient air; PM 10; Microwave-assisted extraction; Gas chromatography–mass spectrometry


Quantification in MALDI-TOF mass spectrometry of modified polymers by Zuzana Walterová; Jiří Horský (pp. 82-88).
MALDI-TOF mass spectrometry quantification is hampered by the poor reproducibility of the signal intensity and by molecular-mass and compositional discrimination. The addition of a suitable compound as an internal standard increases reproducibility and allows a calibration curve to be constructed. The concept was also verified with synthetic polymers but no instructions for practical implementation were given [H. Chen, M. He, J. Pei, H. He, Anal. Chem. 75 (2003) 6531–6535.], even though synthetic polymers are generally non-uniform with respect to molecular mass and composition and access to the polymer of the same molecular mass distribution and composition as that of the quantified one is thus the exception rather than rule. On the other hand, relative quantification of polymers e.g., the content of the precursor polymer in a batch of a modified polymer, is usually sought. In this particular case, the pure precursor is usually available and the modified polymer can serve as an internal standard. However, the calibration curve still cannot be constructed and the use of the internal standard has to be combined with the method of standard addition in which the precursor polymer is added directly to the analyzed sample. The experiments with simulated modified polymers, mixtures of poly(ethylene glycol) (PEG) and poly(ethylene glycol) monomethyl ether (MPEG) of similar molecular-mass distribution, revealed a power dependence of the PEG/MPEG signal-intensity ratio (MS ratio) on the PEG/MPEG concentrations ratio in the mixture (gravimetric ratio). The result was obtained using standard procedures and instrumentation, which means that the basic assumption of the standard-addition method, i.e., the proportionality of the MS and gravimetric ratios, generally cannot be taken for granted. Therefore, the multi-point combined internal-standard standard-addition method was developed and experimentally verified for the quantification of the precursor in modified polymers. In this method, the two parameters of the power-type calibration curve – the proportionality constant and the exponent–are assumed. If the exponent strongly deviates from unity the minority component can be significantly underrepresented in the spectrum. Therefore, the absence of the precursor polymer signals in the MALDI-TOF mass spectrum of a modified polymer sample does not prove the absence of the precursor in the sample. Such a conclusion has to be corroborated by the standard-addition method.

Keywords: MALDI-TOF mass spectrometry; Modified polymers; Quantification; Internal standard; Standard-addition method


Determination of osteocalcin in meat and bone meal of bovine and porcine origin using matrix-assisted laser desorption ionization/time-of-flight mass spectrometry and high-resolution hybrid mass spectrometry by Gabor Balizs; Christoph Weise; Christel Rozycki; Tobias Opialla; Stefanie Sawada; Jutta Zagon; Alfonso Lampen (pp. 89-99).
A method has been developed for determining the origin of meat and bone meal (MBM) by detecting species-specific osteocalcin (OC) using matrix-assisted laser desorption ionization/time-of-flight (MALDI/TOF) and high-resolution hybrid mass spectrometry (HR-Q/TOF MS). The analysis is based on the detection of typical species-specific OC and its tryptic peptide fragments which differ in mass due to differences in the amino-acid sequences between species.After dissolving the MBM samples in EDTA buffer, purification after ultrafiltration was performed using two methods: solid-phase extraction using Zip-Tip C18 or size exclusion coupled with reverse-phase chromatography. Fractions containing partially purified intact OC were analyzed using LC-Q/TOF and MALDI/TOF mass spectrometry. Species-specific OC was detected at the typical protonated and doubly protonated molecular ions. Furthermore, typical porcine- and bovine-derived tryptic fragments from MBM were detected after enzymatic digestion. In order to determine the underlying amino-acid sequences and to confirm the assignment to OC-derived peptides, MS/MS analysis was carried out. In conclusion, we were able to detect OC in bovine and porcine MBM with high sensitivity and the MS-based method described here by which total OC mass and marker peptides of digested OC are recorded can be used as an alternative approach to detect genus-specific differences in MBM and can be applied as a confirmatory method to mainly immunological osteocalcin screening methods.

Keywords: Abbreviations; AA; amino acid; amu; atomic mass unit; BSE; bovine spongiform encephalopathy; ESI; electrospray ionization; HCCA; α-cyano-4-hydroxycinnamic acid; HR; high resolution; HR-MS; high-resolution MS; MALDI/TOF-MS; matrix-assisted laser desorption ionization/time of flight mass spectrometry; MBM; meat and bone meal; OC; osteocalcin; PMF; peptide mass fingerprint; Q/TOF; tandem-quadrupol/time of flight-mass spectrometer; SEC; size exclusion chromatography; PCR; polymerase chain reaction; TOF/TOF; tandem time-of-flight mass spectrometry; ELISA; enzyme-linked immunosorbent assayOsteocalcin; Meat and bone meal; Identification; Mass spectrometry


A new approach to study cadmium complexes with oxalic acid in soil solution by Jana Jaklová Dytrtová; Michal Jakl; Ivana Šestáková; Emilie-Laure Zins; Detlef Schröder; Tomáš Navrátil (pp. 100-105).
This study presents a new analytical approach for the determination of heavy metals complexed to low-molecular-weight-organic acids in soil solutions, which combines the sensitivity of differential pulse anodic stripping voltammetry (DPASV) with the molecular insight gained by electrospray ionization mass spectrometry (ESI–MS). The combination of these analytical methods allows the investigation of such complexes in complex matrixes. On the voltammograms of the soil solutions, in addition to the expected complexes of oxalic acid with cadmium and lead, respectively, also peaks belonging to mixed complexes of cadmium, lead, and oxalic acid (OAH2) were observed. In order to verify the possible formation of complexes with OAH2, aqueous solutions of OAH2 with traces of Cd(II) were investigated as model systems. Signals corresponding to several distinct molecular complexes between cadmium and oxalic acid were detected in the model solutions using negative-ion ESI–MS, which follow the general formula [Cd n( X, Y)(2 n+1)]−, where n is the number of cadmium atoms, X=Cl−, and Y=OAH−. Some of these complexes were also identified in the ESI mass spectra taken from the soil solutions.

Keywords: Differential pulse anodic stripping voltammetry; Electrospray ionization; Low-molecular-weight organic acids; Mass spectrometry; Willow


Competitive immunochromatographic assay for the detection of the organophosphorus pesticide chlorpyrifos by Young Ah Kim; Eun-Hye Lee; Kwang-Ok Kim; Yong Tae Lee; Bruce D. Hammock; Hye-Sung Lee (pp. 106-113).
An immunochromatographic assay (ICA) based on competitive antigen-coated format using colloidal gold as the label was developed for the detection of the organophosphorus insecticide chlorpyrifos. The ICA test strip consisted of a membrane with a detection zone, a sample pad and an absorbent pad. The membrane was separately coated with chlorpyrifos Hapten–OVA conjugate (test line) and anti-mouse IgG (control line). Based on the fact that the competition is between the migrating analyte in the sample and the analyte hapten immobilized on the test strip for the binding sites of the antibody–colloidal gold (Ab–CG) conjugate migrating on the test strip, this study suggests that the relative migration speed between the two migrating substances is a critically important factor for the sensitive detection by competitive ICA. This criterion was utilized for the confirmation of appropriateness of a nitrocellulose (NC) membrane for chlorpyrifos ICA. The detection limit of the ICA for chlorpyrifos standard and chlorpyrifos spiked into agricultural samples were 10 and 50ngmL−1, respectively. The assay time for the ICA test was less than 10min, suitable for rapid on-site testing of chlorpyrifos.

Keywords: Organophosphorus pesticide; Chlorpyrifos; Immunochromatographic assay


A novel biosensing mechanism based on a poly( N-butyl benzimidazole)-modified gold electrode for the detection of hydrogen peroxide by Mu-Yi Hua; Hsiao-Chien Chen; Rung-Ywan Tsai; Yu-Chen Lin; Leeyih Wang (pp. 114-120).
A novel mechanism to detect hydrogen peroxide (H2O2) using a poly( N-butyl benzimidazole) (PBBI)-modified gold (PBBI/Au) electrode is proposed. Synthetic PBBI was oxidized using a mixture of acetic acid (AcOH) and H2O2 to form PBBI N-oxide (PBBINO). The structure of PBBINO was verified by Fourier transform infrared spectroscopy (FT-IR) and the degree of oxidation was measured by X-ray photoelectron spectroscopy (XPS). Moreover, the oxide could be reduced electrochemically back to PBBI. Based on this reaction, a novel enzyme-free PBBI/Au electrode was developed to detect H2O2 in the presence of AcOH electrochemically. The biosensor detected H2O2 linearly over concentrations ranging from 25μM to 10mM with a detection limit of 6.25μM in phosphate buffer solution (PBS) mixed with AcOH at pH 6.4. In addition, at an applied potential of −0.5V, the sensor characteristics could be tuned using AcOH over a pH range of 3.7–6.4. The sensitivity of the probe could be enhanced from 35.1 to 419.4μAmM−1cm−2 by modifying the surface morphology of the PBBI/Au electrode from a smooth plane to a granular, three-dimensional configuration. Furthermore, it was not influenced by interfering compounds and showed high thermal stability.

Keywords: Biosensor; Hydrogen peroxide; Peracetic acid; Poly(; N; -butyl benzimidazole); Poly(; N; -butyl benzimidazole); N; -oxide


A computational model for selectivity evaluation of 2-(3,4-dimethoxyphenyl)ethylamine (homoveratrylamine) imprinted polymers towards biogenic compounds by Teresa Żołek; Piotr Luliński; Dorota Maciejewska (pp. 121-129).
A computational model was proposed to evaluate the affinity and selectivity of 2-(3,4-dimethoxyphenyl)ethylamine (homoveratrylamine) imprinted polymers. Four functional monomers: methacrylic acid, 1-vinylimidazole, 4-vinylpyridine, and allylamine were taken into account. Two dielectric constants were used for solvent simulations: a value of ɛ=2.38 r ij for toluene was used in the analysis of prepolymerization complexes, and a value of ɛ=36 r ij for methanol–water was used in the investigations of adsorption. Theoretical analysis predicted the highest affinity for the polymer synthesized from methacrylic acid. Experimental results confirmed the finding. The prepolymerization complex formed by homoveratrylamine and four methacrylic acid molecules was used to design the polymer cavity. The selectivity of the polymer was analyzed as a simulation of adsorption of six compounds in the cavity by docking procedure. Selected compounds are structurally related to the template or can be present in biological samples. The designed polymer has high selectivity towards homoveratrylamine. The proposed computational procedure could be used for successful evaluation of the imprinted polymers.

Keywords: Molecular modeling; Molecularly imprinted polymers; Homoveratrylamine; Catecholamines
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