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Analytica Chimica Acta (v.778, #)

Editorial Board (pp. iii).

Enzyme activity measurement via spectral evolution profiling and PARAFAC by Andreas Baum; Anne S. Meyer; Javier Lopez Garcia; Max Egebo; Per Waaben Hansen; Jørn Dalgaard Mikkelsen (pp. 1-8).

•Enzyme activity determination using FTIR and PARAFAC.•Directly and universally applicable without the need of any external standards.•The method provides alternative solutions to the cumbersome reducing sugar analysis.•Enzymatic hydrolysis of plant polymers and sugar release can be determined.The recent advances in multi-way analysis provide new solutions to traditional enzyme activity assessment. In the present study enzyme activity has been determined by monitoring spectral changes of substrates and products in real time. The method relies on measurement of distinct spectral fingerprints of the reaction mixture at specific time points during the course of the whole enzyme catalyzed reaction and employs multi-way analysis to detect the spectral changes. The methodology is demonstrated by spectral evolution profiling of Fourier Transform Infrared (FTIR) spectral fingerprints using parallel factor analysis (PARAFAC) for pectin lyase, glucose oxidase, and a cellulase preparation.

Keywords: Chemometrics; Fourier transform infrared spectroscopy; Enzyme kinetics; Substrate evolution; Product evolution; Multiway

Simultaneous determination of aflatoxins B₂ and G₂ in peanuts using spectrofluorescence coupled with parallel factor analysis by A.S. Luna; R.A. Luiz; I.C.A. Lima; P.H. Março; P. Valderrama; R. Boqué; J. Ferré (pp. 9-14).

•A method was developed for the determination of aflatoxins B₂ and G₂ in peanuts.•This method uses EEM together with PARAFAC.•LOQs were 0.16 and 0.12μgkg⁻¹ for aflatoxins B₂ and G₂, respectively.In the present study a method for the simultaneous determination of aflatoxins B₂ and G₂ in peanuts has been developed. The method uses second order standard addition method and excitation–emission fluorescence data together with parallel factor analysis (PARAFAC). The aflatoxin analysis was based on extraction with methanol–water and carried out using immunoaffinity clean-up. The results of PARAFAC on a set of spiked and naturally contaminated peanuts indicated that the two aflatoxins could be successfully determined. The method was validated and analytical figures of merit were obtained for both analytes. The limits of detection (LOD) were 0.05 and 0.04μgkg⁻¹ for aflatoxins B₂ and G₂, respectively. The limits of quantification (LOQ) were 0.16 and 0.12μgkg⁻¹ for aflatoxins B₂ and G₂, respectively. Coupling of spectrofluorimetry with PARAFAC can be considered as an alternative method for quantification of aflatoxins in the presence of unknown interferences obtained through analysis of highly complex matrix of peanuts samples at a reduced cost per analysis.

Keywords: PARAFAC; Spectrofluorescence; Aflatoxins B2 and G2; Peanuts

Efficient use of pure component and interferent spectra in multivariate calibration by Sandeep Sharma; Mohammad Goodarzi; Laure Wynants; Herman Ramon; Wouter Saeys (pp. 15-23).

•Performance of calibration techniques using ‘a priori’ information is evaluated.•Calibration models are built using NAP, IDC, SBC, ACLS and PLSR.•Robustness of models is evaluated in presence of changing interferent structure.•Among all techniques, ACLS is found to result in robust model with lowest RMSEPPartial Least Squares (PLS) is by far the most popular regression method for building multivariate calibration models for spectroscopic data. However, the success of the conventional PLS approach depends on the availability of a ‘representative data set’ as the model needs to be trained for all expected variation at the prediction stage. When the concentration of the known interferents and their correlation with the analyte of interest change in a fashion which is not covered in the calibration set, the predictive performance of inverse calibration approaches such as conventional PLS can deteriorate. This underscores the need for calibration methods that are capable of building multivariate calibration models which can be robustified against the unexpected variation in the concentrations and the correlations of the known interferents in the test set. Several methods incorporating ‘a priori’ information such as pure component spectra of the analyte of interest and/or the known interferents have been proposed to build more robust calibration models. In the present study, four such calibration techniques have been benchmarked on two data sets with respect to their predictive ability and robustness: Net Analyte Preprocessing (NAP), Improved Direct Calibration (IDC), Science Based Calibration (SBC) and Augmented Classical Least Squares (ACLS) Calibration. For both data sets, the alternative calibration techniques were found to give good prediction performance even when the interferent structure in the test set was different from the one in the calibration set. The best results were obtained by the ACLS model incorporating both the pure component spectra of the analyte of interest and the interferents, resulting in a reduction of the RMSEP by a factor 3 compared to conventional PLS for the situation when the test set had a different interferent structure than the one in the calibration set.

Keywords: Robust calibration; Glucose; Net Analyte Preprocessing; Improved Direct Calibration; Science Based Calibration; Augmented Classical Least Squares

Flow electrochemical biosensors based on enzymatic porous reactor and tubular detector of silver solid amalgam by Bohdan Josypčuk; Jiří Barek; Oksana Josypčuk (pp. 24-30).

•Flow amperometric enzymatic biosensor was constructed.•The biosensor is based on a reactor of a novel material – porous silver solid amalgam.•Tubular amalgam detector was used for determination of decrease of O₂ concentration.•Covalent bonds amalgam−thiol−enzyme contributed to the sensor long-term stability.•LOD of glucose was 0.01mmolL⁻¹ with RSD=1.3% ( n=11).A flow amperometric enzymatic biosensor for the determination of glucose was constructed. The biosensor consists of a flow reactor based on porous silver solid amalgam (AgSA) and a flow tubular detector based on compact AgSA. The preparation of the sensor and the determination of glucose occurred in three steps. First, a self-assembled monolayer of 11-mercaptoundecanoic acid (MUA) was formed at the porous surface of the reactor. Second, enzyme glucose oxidase (GOx) was covalently immobilized at MUA-layer using N-ethyl-N′-(3-dimethylaminopropyl) carboimide and N-hydroxysuccinimide chemistry. Finally, a decrease of oxygen concentration (directly proportional to the concentration of glucose) during enzymatic reaction was amperometrically measured on the tubular detector under flow injection conditions. The following parameters of glucose determination were optimized with respect to amperometric response: composition of the mobile phase, its concentration, the potential of detection and the flow rate. The calibration curve of glucose was linear in the concentration range of 0.02–0.80mmolL⁻¹ with detection limit of 0.01mmolL⁻¹. The content of glucose in the sample of honey was determined as 35.5±1.0mass % (number of the repeated measurements n=7; standard deviation SD=1.2%; relative standard deviation RSD=3.2%) which corresponds well with the declared values. The tested biosensor proved good long-term stability (77% of the current response of glucose was retained after 35 days).

Keywords: Key words; Flow analysis; Amperometry; Silver solid amalgam; Porous reactor; Electrochemical biosensors; Glucose

Single-step extraction and cleanup of bisphenol A in soft drinks by hemimicellar magnetic solid phase extraction prior to liquid chromatography/tandem mass spectrometry by Samaneh Raouf Yazdinezhad; Ana Ballesteros-Gómez; Loreto Lunar; Soledad Rubio (pp. 31-37).

•A single-step extraction and cleanup process is proposed for bisphenol A in soft drinks.•Hemimicelles of tetradecanoate adsorbed onto magnetic nanoparticles are used as a sorbent.•Magnetic SPE/LC–MS/MS provides a reliable method for evaluation of human BPA intake from drinks.Hemimicelles of tetradecanoate chemisorbed onto magnetic nanoparticles (MNPs) are here proposed as a sorbent for the single-step extraction and cleanup of bisphenol A (BPA) in soft drinks. The purpose of this work was to develop a simple, rapid and low-cost sample treatment suitable to assess the human exposure to BPA from this type of high consumption food. The nanoparticles were easily coated by mixing commercially available magnetite of 20–30nm mean particle diameter with tetradecanoate at 85°C for 30min. The extraction/cleanup procedure involved stirring the samples (3mL) with 200mg of tetradecanoate-coated MNPs for 20min, isolating the sorbent with a Nd–Fe–B magnet and eluting BPA with methanol. The extraction efficiency was not influenced by salt concentrations up to 1M and pH values over the range 4–9. No cleanup of the extracts was needed, and the method proved matrix-independent. The extracts were analyzed by liquid chromatography, electrospray ionization tandem mass spectrometry. Quantitation was performed by internal standard calibration using BPA-¹³C₁₂. The limit of quantitation obtained for the method, 0.03ngmL⁻¹, was below the usual range of concentrations reported for BPA in soft drinks (0.1–3.4ngmL⁻¹). The proposed method was successfully applied to the determination of BPA in different samples acquired from various supermarkets in southern Spain; the concentrations found ranged from 0.066 to 1.08ngmL⁻¹. Recoveries from samples spiked with 0.33ngmL⁻¹ of BPA ranged from 91% to 105% with relative standard deviations from 3% to 8%.

Keywords: Bisphenol A; Soft drinks; Magnetic SPE; Chemisorbed hemimicelles; Liquid chromatography; Tandem mass spectrometry

Sequential injection methodology for carbon speciation in bathing waters by Inês C. Santos; Raquel B.R. Mesquita; Ana Machado; Adriano A. Bordalo; António O.S.S. Rangel (pp. 38-47).

•Carbon speciation using a sequential injection methodology with a gas diffusion unit and in-line UV photo-oxidation.•Multiparametric determination of dissolved inorganic carbon, total carbon, dissolved carbon dioxide and alkalinity.•Application to complex environmental samples, namely inland bathing waters.A sequential injection method (SIA) for carbon speciation in inland bathing waters was developed comprising, in a single manifold, the determination of dissolved inorganic carbon (DIC), free dissolved carbon dioxide (CO₂), total carbon (TC), dissolved organic carbon and alkalinity. The determination of DIC, CO₂ and TC was based on colour change of bromothymol blue (660nm) after CO₂ diffusion through a hydrophobic membrane placed in a gas diffusion unit (GDU). For the DIC determination, an in-line acidification prior to the GDU was performed and, for the TC determination, an in-line UV photo-oxidation of the sample prior to GDU ensured the conversion of all carbon forms into CO₂. Dissolved organic carbon (DOC) was determined by subtracting the obtained DIC value from the TC obtained value. The determination of alkalinity was based on the spectrophotometric measurement of bromocresol green colour change (611nm) after reaction with acetic acid. The developed SIA method enabled the determination of DIC (0.24–3.5mgCL⁻¹), CO₂ (1.0–10mgCL⁻¹), TC (0.50–4.0mgCL⁻¹) and alkalinity (1.2–4.7mgCL⁻¹ and 4.7–19mgCL⁻¹) with limits of detection of: 9.5μgCL⁻¹, 20μgCL⁻¹, 0.21mgCL⁻¹, 0.32mgCL⁻¹, respectively. The SIA system was effectively applied to inland bathing waters and the results showed good agreement with reference procedures.

Keywords: Carbon speciation; Gas diffusion unit; In-line UV photo-oxidation; Sequential injection analysis; Multi-parametric determination

Selective fluorimetric method for the determination of histamine in seafood samples based on the concept of zone fluidics by Paraskevas D. Tzanavaras; Olga Deda; Theano D. Karakosta; Demetrius G. Themelis (pp. 48-53).

•Automated analysis of histamine.•Selective determination in seafood.•No complicated sample preparation.•Zone fluidics single channel configuration.In the present article we report our results on the development of a selective automated method for the determination of histamine in seafood using the concept of zone fluidics. The method is based on the sequential on-line reaction of the analyte with o-phthalaldehyde in the absence of a nucleophilic reagent, followed by acidification. The careful selection of the chemical and instrumental variables enabled the determination of the analyte with adequate sensitivity at the low micromolar level and with specificity against other biogenic amines and amino acids such as histidine. The LOD was 0.05μmolL⁻¹ (0.6mgkg⁻¹) and linearity was obeyed in the range of 0.5–15μmolL⁻¹ (5.5–170mgkg⁻¹). The proposed method offers a satisfactory sampling rate of 15h⁻¹ and adequate accuracy and precision for the analysis of seafood products after minimum sample preparation and without employing a separation technique.

Keywords: Zone fluidics; Histamine; o-Phthalaldehyde; Seafood; Automation

Rapid automatic identification and quantification of compounds in complex matrices using comprehensive two-dimensional gas chromatography coupled to high resolution time-of-flight mass spectrometry with a peak sentinel tool by Yasuyuki Zushi; Shunji Hashimoto; Akihiro Fushimi; Yoshikatsu Takazawa; Kiyoshi Tanabe; Yasuyuki Shibata (pp. 54-62).

•Analytical method by GC×GC–HRTOFMS with automatic peak sentinel tool was developed.•PCDD/Fs and PCBs in crude lake sediment were automatically and accurately analyzed.•False positives/negatives were not observed except for when co-elution occurred.•GC×GC–HRTOFMS with the tool “T-SEN” is useful for rapid and accurate screening.Comprehensive two-dimensional gas chromatography coupled to mass spectrometry (GC×GC–MS) is a powerful tool for comprehensive analysis of organic pollutants. In this study, we developed a powerful analytical method using GC×GC for rapid and accurate identification and quantification of compounds in environmental samples with complex matrices. Specifically, we have developed an automatic peak sentinel tool, T-SEN, with free programming software, R. The tool, which consists of a simple algorithm for on peak finding and peak shape identification, allows rapid screening of target compounds, even for large data sets from GC×GC coupled to high resolution time of flight mass spectrometry (HRTOFMS). The software tool automatically assigns and quantifies compounds that are listed in user databases. T-SEN works on a typical 64 bit workstation, and the reference calculation speed is 10–20min for approximately 170 compounds for peak finding (five ion count setting) and integration from 1–2GB of sample data acquired by GC×GC–HRTOFMS. We analyzed and quantified 17 PCDD/F congeners and 24 PCB congeners in a crude lake sediment extract by both GC×GC coupled to quadrupole mass spectrometry (qMS) and GC×GC–HRTOFMS with T-SEN. While GC×GC–qMS with T-SEN resulted in false identification and inaccurate quantification, GC×GC–HRTOFMS with T-SEN provided correct identification and accurate quantification of compounds without sample pre-treatment. The differences between the values measured by GC×GC–HRTOFMS with T-SEN and the certified values for the certified reference material ranged from 7.3 to 36.9% for compounds with concentrations above the limit of quantification. False positives/negatives were not observed, except for when co-elution occurred. The technique of GC×GC–HRTOFMS in combination with T-SEN provides rapid and accurate screening and represents a powerful new approach for comprehensive analysis.

Keywords: Abbreviations; GC×GC–MS; comprehensive two-dimensional gas chromatography coupled to mass spectrometry; T-SEN; two-dimensional peak sentinel tool; HRTOFMS; high resolution time of flight mass spectrometry; AMDIS; automated mass spectral deconvolution and identification system; AIQS-DB; automatic identification and quantification system with database; CRM; certified reference materialTwo-dimensional peak sentinel; Automatic screening; GC; ×; GC–HRTOFMS; Comprehensive analysis; Sediment analysis; Organic micropollutants

Highly sensitive and selective colorimetric sensing of antibiotics in milk by Xiaofang Zhang; Yang Zhang; Hong Zhao; Yujian He; Xiangjun Li; Zhuobin Yuan (pp. 63-69).

The presence of antibiotic substrates kanamycin mono sulfate, neomycin sulfate, streptomycin sulfate and bleomycin sulfate influence the synthesis of AuNPs, including the color and state of AuNPs, which could be used to detect antibiotic substrates with the naked eye or a UV–vis spectrophotometer.•A colorimetric strategy for sensing four antibiotics was proposed.•Hydrogen bond between pyrocatechol violet and antibiotics played an important role.•This strategy can be applied in the pretreated liquid milk products.Antibiotics residues in foods are very harmful to human beings. Determination of antibiotics residues relies largely on the availability of adequate analytical techniques. Currently, there is an urgent need for on site and real time detection of antibiotics in food. In this work, a novel one step synthesis of gold nanoparticles (AuNPs) was proposed using pyrocatechol violet (PCV) as a reducer agent. Highly sensitive and selective colorimetric detection of four antibiotics kanamycin mono sulfate (KA), neomycin sulfate (NE), streptomycin sulfate (ST) and bleomycin sulfate (BL) was realized during the formation of AuNPs. PCV hasOH groups and these antibiotics haveOH,NH₂,NH groups, so there may be some special hydrogen-bonding interactions between PCV and these antibiotics. Therefore, the presence of KA, NE, ST and BL would influence the synthesis of AuNPs, then the color and state of AuNPs would change, which could be observed with the naked eye or a UV–vis spectrophotometer. Results showed that A₆₇₀ was linear with the logarithm of KA concentration in the range from 1.0×10⁻⁸ to 5.0×10⁻⁷M and 5.0×10⁻⁷ to 5.5×10⁻⁵M. The detection limit of KA was 1.0×10⁻⁹M (S/N=3). The coexisting substances including 1.0×10⁻⁵M phenylalanine, alanine, glycerol, glucose, Mg²⁺, Ca²⁺, Na⁺, K⁺, CO₃²⁻, SO₄²⁻, NO₃⁻, Cl⁻ and Br⁻ did not affect the determination of 1.0×10⁻⁷M antibiotics. In particular, the proposed method could be applied successfully to the detection of antibiotics in the pretreated liquid milk products.

Keywords: Abbreviations; AuNPs; gold nanoparticles; PCV; pyrocatechol violet; KA; kanamycin mono sulfate; NE; neomycin sulfate; ST; streptomycin sulfate; BL; bleomycin sulfateGold nanoparticles; Pyrocatechol violet; Antibiotics; Colorimetric; Hydrogen-bonding

Multiple approaches for enhancing all-organic electronics photoluminescent sensors: Simultaneous oxygen and pH monitoring by Rui Liu; Teng Xiao; Weipan Cui; Joseph Shinar; Ruth Shinar (pp. 70-78).

•Novel simply-fabricated all-organic electronics pH and oxygen optical monitor.•Excitation sources: directionally emitting, narrowed multicolor microcavity OLEDs.•Photodetectors: small molecule- or polymer-based with selective spectral responses.•Sensor film: structured high molecular weight polystyrene:polyethylene glycol blend.•×1.9 sensitivity enhancement and ×2.7 increase in the photoluminescence for oxygen.Key issues in using organic light emitting diodes (OLEDs) as excitation sources in structurally integrated photoluminescence (PL)-based sensors are the low forward light outcoupling, the OLEDs’ broad electroluminescence (EL) bands, and the long-lived remnant EL that follows an EL pulse. The outcoupling issue limits the detection sensitivity ( S) as only ~20% of the light generated within standard OLEDs can be forward outcoupled and used for sensor probe excitation. The EL broad band interferes with the analyte-sensitive PL, leading to a background that reduces S and dynamic range. In particular, these issues hinder designing compact sensors, potentially miniaturizable, that are devoid of optical filters and couplers. We address these shortcomings by introducing easy-to-employ multiple approaches for outcoupling improvement, PL enhancement, and background EL reduction leading to novel, compact all-organic device architectures demonstrated for simultaneous monitoring of oxygen and pH. The sensor comprises simply-fabricated, directionally-emitting, narrower-band, multicolor microcavity OLED excitation and small molecule- and polymer-based organic photodetectors (OPDs) with a more selective spectral response. Additionally, S and PL intensity for oxygen are enhanced by using polystyrene (PS):polyethylene glycol (PEG) blends as the sensing film matrix. By utilizing higher molecular weight PS, the ratio τ₀/ τ₁₀₀ (PL decay time τ at 0% O₂/ τ at 100% O₂) that is often used to express S increases ×1.9 to 20.7 relative to the lower molecular weight PS, where this ratio is 11.0. This increase reduces to ×1.7 when the PEG is added ( τ₀/ τ₁₀₀=18.2), but the latter results in an increase ×2.7 in the PL intensity. The sensor's response time is <10s in all cases. The microporous structure of these blended films, with PEG decorating PS pores, serves a dual purpose. It results in light scattering that reduces the EL that is waveguided in the substrate of the OLEDs and consequently enhances light outcoupling from the OLEDs by ~60%, and it increases the PL directed toward the OPD. The multiple functional structures of multicolor microcavity OLED pixels/microporous scattering films/OPDs enable generation of enhanced individually addressable sensor arrays, devoid of interfering issues, for O₂ and pH as well as for other analytes and biochemical parameters.

Keywords: Microcavity OLED; Photoluminescence; Microporous sensing films; Oxygen and pH sensor; Organic photodetector

Multi-signalling cation sensing behaviour of a bis(pyridin-2-yl methyl)aniline based hetarylazo dye by Paramjit Kaur; Divya Sareen; Mandeep Kaur; Kamaljit Singh (pp. 79-86).

The chromogenic and electrochemical behaviour of bis(pyridine-2-yl methyl)aniline based hetarylazo dye gets perturbed in the presence of cations, most effective being Cu²⁺. The conversion of ICT to ICT/MLCT is witnessed by TD-DFT calculations.•Cation sensing of hetarylazo dye based upon visual, absorption and electrochemical changes is described.•Sensing mechanism is based upon perturbation in intramolecular charge-transfer upon interaction with cations.•Sensing protocol is supported by¹H NMR studies as well as theoretical calculations.•Hetarylazo dye acts as a multichannel sensor.•Response of the dye towards various cations has also been explored in acidic pH window.We investigated the cation sensing behaviour of a bis(pyridin-2-yl methyl)aniline appended hetarylazo dye via chromogenic and electrochemical transduction channels. The binding pocket constituting both the pyridyl as well as aniline nitrogen atoms acts as recognition site for the cations and consequent perturbation in the intramolecular charge-transfer prevailing in the dye results in the chromogenic response manifested in the form of hypsochromic shift in the intramolecular charge-transfer band and the attendant naked-eye color changes. The dye exhibits significant changes in its electrochemical behaviour in the presence of cations. The experimental results are also rationalized by time-dependent density functional theory (TD-DFT) calculations.

Keywords: Hetarylazo; Bis(pyridin-2-yl methyl)aniline; Naked-eye; Chemosensor; Multi-channel sensing; Density-functional calculation

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Analytica Chimica Acta (v.778, #)