DETARCHI: A program for detection limits with specified assurance probabilities and characteristic curves of detection

Simultaneous determination of 4-ethylphenol and 4-ethylguaicol on C60 modified dual screen-printed electrochemical sensors

4-ethylphenol and 4-ethylguaicol levels in wine are associated to organoleptic defects that cause consumer rejection accompanied by significant economic losses for producers. Thus, electrochemical sensors based on screen-printed carbon electrodes (SPCEs) modified with activated fullerene C60 (AC60) have been developed for the analysis of both phenols by direct headspace amperometric measurements. Upon optimization of the experimental variables affecting the sensors performance, the AC60/SPCE sensors presented linearity ranges from 9.9 to 65.4 μg/L and from 19.6 to 107.1 μg/L for 4-ethylphenol and 4-ethylguaicol, respectively. The achieved detection capacities were 10.3 μg/L (4-ethylphenol) and 19.6 μg/L (4-ethylguaicol), with a reproducibility of 6.3 % and 9.1 % (n = 3), respectively. In addition, dual-working AC60/SPCE devices were developed for the simultaneous analysis of both phenols using different working potentials for each electrode. The dual systems were successfully applied in the analysis of different spiked wine samples, obtaining good recoveries ranging from 94 to 108 %.

Gel polymer electrolyte-based dual screen-printed electrodes for the headspace quantification of 4-ethylphenol and ethanethiol simultaneously in wines

The identification and correction of negative factors, such as 4-ethylphenol and ethanethiol, is important to comply with food safety regulations and avoid economic losses to wineries. A simple amperometric measurement procedure that facilitates the simultaneous quantification of both compounds in the gas phase has been developed using fullerene and cobalt (II) phthalocyanine-modified dual screen-printed electrodes coated with a room temperature ionic liquid-based gel polymer electrolyte. The replacement of the typical aqueous supporting electrolyte by low-volatility ones improves both operational and storage lifetime. Under the optimum conditions of the experimental variables, Britton Robinson buffer pH 5 and applied potentials of + 0.86 V and + 0.40 V for each working electrode (vs. Ag ref. electrode), reproducibility values of 7.6% (n = 3) for 4-ethylphenol and 6.6% (n = 3) for ethanethiol were obtained, as well as capability of detection values of 23.8 μg/L and decision limits of 1.3 μg/L and 9.2 μg/L (α = β = 0.05), respectively. These dual electrochemical devices have successfully been applied to the headspace detection of both compounds in white and red wines, showing their potential to be routinely used for rapid analysis control in wineries.

Model inversion and three-way decompositions in the analytical quality by design strategy for the determination of phthalates BY HS-SPME-GC-MS

In this work, strategies within Analytical Quality by Design (AQbD) with tools of the Process Analytical Technology (PAT) were used in the development of a head space-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) procedure for the multiresidue analysis of four phthalic acid esters, benzyl butyl phthalate, bis(2-ethylhexyl) phthalate, dibutyl phthalate and diethyl phthalate (regulated by Commission Regulation (EU) No 10/2011). The approach is based on the fact that the intended quality of the resulting chromatograms is defined in terms of the loadings on the sample mode of a Parallel Factor Analysis (PARAFAC2) decomposition. These loadings are the ones used for the inversion of a Partial Least Squares (PLS2) prediction model that has been previously fitted. The inversion gives the experimental conditions that represent a compromise solution in terms of the desired or target values of the responses (Critical Quality Attributes, CQAs), while guaranteeing that these experimental conditions are inside the experimental domain of the Control Method Parameters (CMPs). This strategy results in experimental conditions of extraction time and temperature that lead to a chromatogram of predefined quality for the four analytes together, with the subsquent saving of time and energy. The experimental conditions achieved have been experimentally verified and figures of merit of the analytical method have been determined. The method has been applied to a case study, bottled natural and flavoured mineral water. Concentrations around 0.3 μg L-1 of dibutyl phthalate have been found in 5 of the 22 bottles of water analysed.

Headspace detection of ethanethiol in wine by cobalt phthalocyanine modified screen-printed carbon electrodes

The formation of thiols has a notable and detrimental sensory impact, especially in the aroma of bottled wines. Their detection in wine is of great interest to avoid important economic and image losses for wineries. This work reports the study of different cobalt phthalocyanine/nanomaterials-based sensors for the headspace detection of volatile thiols. The amperometric procedure based on the use of carbon sensors simply modified with cobalt phthalocyanine showed the best performance. Under the optimum conditions of applied potential, +0.8 V, and pH of the supporting electrolyte, 2.6, this procedure shows a reproducibility of 7% (n = 5) in terms of relative standard deviation of the slopes of calibration curves built in the concentration range from 9.9 to 82.6 μg/L, a capability of detection of 12.5 μg/L and a decision limit of 6.5 μg/L (α = β = 0.05). The use of this electrocatalytic material and the headspace measurements reduce interferents, increasing the selectivity of the procedure, which allows the easy and successful quantification of ethanethiol in white and red wines.

Electrochemical sensors for the determination of 4-ethylguaiacol in wine

The development of an electrochemical procedure for the determination of 4-ethylguaiacol and its application to wine analysis is described. Modified screen-printed carbon electrodes (SPCEs) with fullerene C₆₀ (C₆₀) have been shown to be efficient in this kind of analysis. The developed activated C₆₀/SPCEs (AC₆₀/SPCEs) were adequate for the determination of 4-ethylguaicol, showing a linear range from 200 to 1000 µg/L, a reproducibility of 7.6% and a capability of detection (CC_β) value of 200 µg/L, under optimized conditions. The selectivity of the AC₆₀/SPCE sensors was evaluated in the presence of possibly interfering compounds, and their practical applicability was demonstrated  in the analysis of different wine samples obtaining recoveries ranging from 96 to 106%.

Molecularly imprinted polypyrrole based electrochemical sensor for selective determination of ethanethiol

This work describes a molecularly imprinted (MIP) sensor, based on the electropolymerization of pyrrole on a glassy carbon electrode (GCE), for the determination of ethanethiol. Ethanethiol was used as a template molecule for the formation of cavities in the imprinted polymer. The effect of molar ratios template molecules/functional monomers and time needed to remove the template were optimized. The developed MIP/GCE sensor presented a linear range from 6.1 to 32.4 mg L^-1 with capability detection and reproducibility values of 7.2 mg L^-1 and 10.4%, respectively. The sensitivity of the developed sensor was enhanced by the incorporation of gold nanoparticles (AuNPs). The AuNPs/MIP/GCE showed a capability of detection and reproducibility values of 0.4 mg L^-1 and 4.1%, respectively (calibration range from 0.3 to 3.1 mg L^-1). The sensor was successfully applied to the determination of ethanethiol in spiked wine samples with recoveries ranging from 99% to 107%.

Procedure to explore a ternary mixture diagram to find the appropriate gradient profile in liquid chromatography with fluorescence detector. Application to determine four primary aromatic amines in napkins

The purpose of this work is to develop a tool to search for a gradient profile with ternary or binary mixtures in liquid chromatography, that can provide well-resolved chromatograms in the shortest time for multianalyte analysis. This approach is based exclusively on experimental data and does not require a retention time model of the compounds to be separated. The methodology has been applied for the quantification of four primary aromatic amines (PAAs) using HPLC with fluorescence detector (FLD). Aniline (ANL), 2,4-diaminotoluene (TDA), 4,4'-methylenedianiline (MDA) and 2-aminobiphenyl (ABP) have been selected since their importance in food contact materials (FCM). In order to achieve that, partial least squares (PLS) models have been fitted to relate CMP (control method parameters) and CQA (critical quality attributes). Specifically, PLS models have been fitted using 30 experiments for each one of the four CQA (resolution between peaks and total elution time), considering 33 predictor variables (the composition of the methanol and acetonitrile in the mobile phase and the time of each one of the 11 isocratic segments of the gradient). These models have been used to predict new candidate gradients, and then, some of those predictions (the ones with resolutions above 1.5, in absolute value, and final time lower than 20 min) have been experimentally validated. Detection capability of the method has been evaluated obtaining 1.8, 189.4, 28.8 and 3.0 µg L^-1 for ANL, TDA, MDA and ABP, respectively. Finally, the application of chemometric tools like PARAFAC2 allowed the accurate quantification of ANL, TDA, MDA and ABP in paper napkins in the presence of other interfering substances coextracted in the sample preparation process. ANL has been detected in the three napkins analysed in quantities between 33.5 and 619.3 µg L^-1, while TDA is present in only two napkins in quantities between 725.9 and 1908 µg L^-1. In every case, the amount of PAAs found, exceeded the migration limits established in European regulations.

Hypoxia-Responsive Molecular Probe Lighted up by Peptide Self-Assembly for Cancer Cell Imaging

Hypoxia is a characteristic feature of most solid tumors, which promotes the proliferation, metastasis, and invasion of tumors and stimulates the resistance of cancer treatments, leading to the serious consequences of tumor recurrence. The exploration of hypoxia detection technology will aid tumor diagnosis and treatment. Fluorescence imaging technology is an accurate and efficient hypoxia detection technology. It has attracted significant research interest, but designing novel fluorescence probes, especially stimuli-responsive probes with high sensitivity and low toxicity is still challenging. In this work, we report a hypoxia-responsive molecular bioprobe lighted up by peptide self-assembly, which contains aggregationinduced emission (AIE) fluorescent molecule TPE, hypoxia-responsive azo group (-N═N-), the self-assembling peptide GFFY, and targeting ligand RGD. The resulting peptide derivative TPE-GFFY-N═N-EERGD forms supramolecular nanofibers but emit weak fluorescence because the azobenzene moiety can effectively quench the fluorescence of the TPE dye. However, the fluorescence-quenched nanofibers could be lighted up dramatically when the azo group is reduced. More importantly, this "turn-on" supramolecular fluorescence bioprobe enables effective detecting tumor hypoxia due to the overexpressed azoreductase in the tumor microenvironment. This work affords a paradigm of designing environmentsensitive fluorescent molecular probes for tumor hypoxia imaging.

Nitroreductase-Induced Aggregation of Gold Nanoparticles for "Off-On" Photoacoustic Imaging of Tumor Hypoxia

Hypoxia is an important phenomenon due to insufficient oxygen supply in tumor tissue, and nitroreductase (NTR) is a characteristic enzyme used for evaluating hypoxia level in tumors. In this work, we designed a smart gold nanoparticle (AuNPs), modified by 16-mercaptoundecanoic acid (MHDA) and hypoxia-responsive 11-(2-nitro-1H-imidazol-1-yl)undecane-1-thiol (NI) ligand, that responds to the hypoxic environment in tumor sites. With proper surface ligand composition, the responsive nanoprobe exhibited aggregation through the bioreduction of the nitro group on NI ligands under hypoxic conditions and the UV-vis absorption peak maximum would shift to 630 nm from 530 nm, which acts as an "off-on" contrast agent for tumor hypoxic photoacoustic (PA) imaging. In vitro and in vivo experiments revealed that AuNPs@MHDA/NO₂ exhibited an enhanced PA signal in hypoxic conditions. This study demonstrates the potential of hypoxia-responsive AuNPs as novel and sensitive diagnostic agents, which lays a firm foundation for precise cancer treatment in the future.

A new approach based on inversion of a partial least squares model searching for a preset analytical target profile. Application to the determination of five bisphenols by liquid chromatography with diode array detector

The paper shows a procedure for selecting the control method parameters (factors) to obtain a preset 'analytical target profile' when a liquid chromatographic technique is going to be carried out for the simultaneous determination of five bisphenols (bisphenol-A, bisphenol-S, bisphenol-F, bisphenol-Z and bisphenol-AF), some of them regulated by the European Union. The procedure has three steps. The first consists of building a D-optimal combined design (mixture-process design) for the control method parameters, which are the composition of the ternary mobile phase and its flow rate. The second step is to fit a PLS2 model to predict six analytical responses (namely, the resolution between each pair of consecutive peaks, and the initial and final chromatographic time) as a function of the control method parameters. The third final step is the inversion of the PLS2 model to obtain the conditions needed for attaining a preset analytical target profile. The computational inversion of the PLS2 prediction model looking for the Pareto front of these six responses provides a set of experimental conditions to conduct the chromatographic determination, specifically 22% of water, mixed with 58% methanol and 20% of acetonitrile, keeping the flow rate at 0.66 mL min^-1. These conditions give a chromatogram with retention times of 2.180, 2.452, 2.764, 3.249 and 3.775 min for BPS, BPF, BPA, BPAF and BPZ, respectively, and excellent resolution among all the chromatographic peaks. Finally, the analytical method is validated under the selected experimental conditions, in terms of trueness and precision. In addition, the detection capability for the five bisphenols were: 596, 334, 424, 458 and 1156 μg L^-1, with probabilities of false positive and of false negative equal to 0.05.

New strategy for determination of anthocyanins, polyphenols and antioxidant capacity of Brassica oleracea liquid extract using infrared spectroscopies and multivariate regression

A new method was developed to determine the antioxidant properties of red cabbage extract (Brassica oleracea) by mid (MID) and near (NIR) infrared spectroscopies and partial least squares (PLS) regression. A 70% (v/v) ethanolic extract of red cabbage was concentrated to 9° Brix and further diluted (12 to 100%) in water. The dilutions were used as external standards for the building of PLS models. For the first time, this strategy was applied for building multivariate regression models. Reference analyses and spectral data were obtained from diluted extracts. The determinate properties were total and monomeric anthocyanins, total polyphenols and antioxidant capacity by ABTS (2,2-azino-bis(3-ethyl-benzothiazoline-6-sulfonate)) and DPPH (2,2-diphenyl-1-picrylhydrazyl) methods. Ordered predictors selection (OPS) and genetic algorithm (GA) were used for feature selection before PLS regression (PLS-1). In addition, a PLS-2 regression was applied to all properties simultaneously. PLS-1 models provided more predictive models than did PLS-2 regression. PLS-OPS and PLS-GA models presented excellent prediction results with a correlation coefficient higher than 0.98. However, the best models were obtained using PLS and variable selection with the OPS algorithm and the models based on NIR spectra were considered more predictive for all properties. Then, these models provided a simple, rapid and accurate method for determination of red cabbage extract antioxidant properties and its suitability for use in the food industry.

Standard addition method based on four-way PARAFAC decomposition to solve the matrix interferences in the determination of carbamate pesticides in lettuce using excitation-emission fluorescence data

The simultaneous determination of two carbamate pesticides (carbaryl and carbendazim) and of the degradation product of carbaryl (1-naphthol) in iceberg lettuce was achieved by means of PARAFAC decomposition and excitation-emission fluorescence matrices. A standard addition method for a calibration based on four-way data was applied using different dilutions of the extract from iceberg lettuce as a fourth way that provided the enough variation of the matrix to carry out the four-way analysis. A high fluorescent overlapping existed between the three analytes and the fluorophores of the matrix. The identification of two fluorescent matrix constituents through the four-way model enabled to know the matrix contribution in each dilution of the extract. This contribution was subtracted from the previous signals and a subsequent three-way analysis was carried out with the tensors corresponding to each dilution. The PARAFAC decomposition of these resulting tensors showed a CORCONDIA index equal to 99%. For the identification of the analytes, the correlation between the PARAFAC spectral loadings and the reference spectra has been used. The trueness of the method, in the concentration range studied, was guaranteed because there was neither constant nor proportional bias according to the appropriate hypothesis tests. The best recovery percentages were obtained with the data from the most diluted extract, being the results: 127.6% for carbaryl, 125.55% for carbendazim and 87.6% for 1-naphthol. When the solvent calibration was performed, the decision limit (CCα) and the capability of detection (CCβ) values, in x0=0, were 2.21 and 4.38 μg L(-1) for carbaryl, 4.87 and 9.64 μg L(-1) for carbendazim; and 3.22 and 6.38 μg L(-1) for 1-naphthol, respectively, for probabilities of false positive and false negative fixed at 0.05. However, these values were 5.30 and 10.49 μg L(-1) for carbaryl, 18.05 and 35.73 μg L(-1) for carbendazim; and 1.92 and 3.79 μg L(-1) for 1-naphthol, respectively, when the matrix-matched calibration using the most diluted extract was carried out in the recovery study.

Optimum pH for the determination of bisphenols and their corresponding diglycidyl ethers by gas chromatography-mass spectrometry. Migration kinetics of bisphenol A from polycarbonate glasses

This paper presents, on the one hand, the study of the influence of the pH of the medium on the determination of bisphenol F (BPF), bisphenol A (BPA) and their corresponding diglycidyl ethers (BFDGE and BADGE, respectively) by GC-MS after a solid-phase extraction step, using BPA-d16 as internal standard and Parallel Factor Analysis (PARAFAC) decomposition as a multi-way tool for the unequivocal identification and quantification of the four analytes. As the structure of both BFDGE and BADGE has two 2,3-epoxypropoxy groups that can undergo an acid- or base-catalyzed ring-opening via nucleophilic substitution reactions, several samples spiked with the four analytes were set to different pH values between 2 and 12. The best results were obtained in the pH region 8-10, being 9 the most suitable value. Coelution of interferents was overcome using the PARAFAC decomposition; otherwise, the presence of some analytes could not have been ensured according to the regulations currently in force. Secondly, the release of BPA from polycarbonate glasses into food simulant D1 (ethanol 50% (v/v)) over time was studied through seven migration tests and the differences found in this migration process with the incubation temperature (50 and 70°C) were evaluated. A nonlinear regression was used to fit the experimental data following an exponential relation between the concentration of BPA transferred from every glass and the respective migration test. None of the quantities of BPA released exceeded the specific migration limit of 0.6mgkg(-1) laid down for this compound in the Commission Regulation (EU) No 10/2011, so the compliance of the glasses evaluated was ensured. The average recovery percentages of the four analytes at a fortification level of 800ngL(-1) ranged from 50.14 to 92.75%. The detection capability (CCβ) of the method for BPA was 2.60μgL(-1) for n=2 replicates, with probabilities of false positive and false negative fixed at 0.05.

Screen-printed acetylcholinesterase-based biosensors for inhibitive determination of permethrin

An amperometric assay based on acetylcholinesterase (AChE) inactivation has been developed for the monitoring of permethrin using a screen-printed three-electrode system. The enzyme AChE catalyzes the hydrolysis of acetylthiocholine to thiocholine, which can be electrochemically oxidized. The presence of permethrin inhibits the AChE activity, resulting in a lower thiocholine production and thus, a decrease in the amperometric oxidation current. Immobilization of AChE was performed by cross-linking giving a capability of detection of 8.1±0.4 μM. Repeatability and reproducibility of the developed AChE biosensor were also calculated, yielding values of 9.6% (n=4) and 5.4% (n=5), respectively related to the slopes of the calibration curves performed in the range from 6.2 up to 41 μM. The method was successfully applied to the determination of permethrin content in a commercial lice gel.

Sensitive enzyme-biosensor based on screen-printed electrodes for Ochratoxin A

Horseradish peroxidase has been successfully immobilized in a polypyrrole matrix onto disposable screen-printed carbon electrodes for the selective detection of Ochratoxin A. The chronoamperometric determination of this mycotoxin has been optimized by experimental design methodology, which implied the join evaluation of pH of the buffer solution, applied potential and concentration of H(2)O(2). The slopes of the calibration curves built under the optimum conditions of the experimental variables have been used to estimate the reproducibility and the repeatability of the developed biosensor for Ochratoxin A. Relative standard deviation values of 1.9% (n=5 and alpha=0.05) and 7.1% (n=4 and alpha=0.05) were obtained for reproducibility and repeatability, respectively. The capability of detection for this method was 0.1 ng mL(-1) (alpha=0.05 and beta<0.05). The viability of the developed biosensor in the determination of Ochratoxin A in spiked beer and in roasted coffee has been shown, yielding average recoveries of 103% and 99%, in that order, with relative standard deviation values less than 5% (n=3 and alpha=0.05) in both cases.