Analytical Response Research Articles

NiFe-based Prussian blue analogue nanopolygons hybridized with functionalized glyoxal polymer as a voltammetric platform for the determination of amisulpride in biological samples

A novel voltammetric platform based on pencil graphite electrode (PGE) modification has been proposed, containing bimetallic (NiFe) Prussian blue analogue nanopolygons decorated with electro-polymerized glyoxal polymer nanocomposites (p-DPG NCs@NiFe PBA Ns/PGE). Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and square wave voltammetry (SWV) were utilized to investigate the electrochemical performance of the proposed sensor. The analytical response of p-DPG NCs@NiFe PBA Ns/PGE was evaluated through the quantity of amisulpride (AMS), one of the most common antipsychotic drugs. Under the optimized experimental and instrumental conditions, the method showed linearity over the range from 0.5 to 15 × 10−8 mol L−1 with a good correlation coefficient (R = 0.9995) and a low detection limit (LOD) reached, 1.5 nmol L−1, with excellent relative standard deviation for human plasma and urine samples. The interference effect of some potentially interfering substances was negligible, and the sensing platform demonstrated an outstanding reproducibility, stability, and reusability. As a first trial, the proposed electrode aimed to shed light on the AMS oxidation mechanism, where the oxidation mechanism was monitored and elucidated using the FTIR technique. It was also found that the prepared p-DPG NCs@NiFe PBA Ns/PGE platform had promising applications for the simultaneous determination of AMS in the presence of some co-administered COVID-19 drugs, which could be attributed to the large active surface area, and high conductivity of bimetallic nanopolygons.Graphical

Gradient method for accurate affinity determinations

The value of the affinity constants (kd, ka, and KD) that are determined by label free interaction analysis methods are strongly affected by the ligand density at the sensor surface [1]. This paper outlines a new SPR-imaging method that applies a ligand density gradient enabling the analyte response to be extrapolated to Rmax = 0 μRIU. The mass transport limited region is used to determine the analyte concentration. Cumbersome optimization procedures for tuning the ligand density is prevented and surface dependent effects as rebinding, strong biphasic behavior etcetera are minimized. The method can be fully automated for e.g. accurate determination of the quality of antibodies from commercial sources.

Sensitive and selective impedimetric determination of TNT using RSM-CCD optimization

Detection of trace amounts of 2,4,6-Trinitrotoluene as a widely used explosive in the military and industrial sectors is of vital importance due to security and environmental concerns. The sensitive and selective measurement characteristics of the compound still is considered a challenge for analytical chemists. Unlike conventional optical and electrochemical methods, the electrochemical impedance spectroscopy technique (EIS), has a very high sensitivity, but it faces a significant challenge in that it requires complex and expensive steps to modify the electrode surface with selective agents. We reported the design and construction of an inexpensive, simple, sensitive, and selective impedimetric electrochemical TNT sensor based on the formation of a Meisenheimer complex between magnetic multiwalled carbon nanotubes modified with aminopropyl triethoxysilane (MMWCNTs @ APTES) and TNT. The formation of the mentioned charge transfer complex at the electrode-solution interface blocks the electrode surface and disrupts the charge transfer in [(Fe (CN) 6)] 3−/4- redox probe system. Charge transfer resistance changes (ΔRCT) were used as an analytical response that corresponded to TNT concentration. To investigate the influence of effective parameters on the electrode response, such as pH, contact time, and modifier percentage, the response surface methodology based on central composite design (RSM-CCD) was used. The calibration curve was achieved in the range of 1–500 nM with a detection limit of 0.15 nM under optimal conditions, which included pH of 8.29, contact time of 479 s, and modifier percentage of 12.38% (w/w). The selectivity of the constructed electrode towards several nitroaromatic species was investigated, and no significant interference was found. Finally, the proposed sensor was able to successfully measure TNT in various water samples with satisfactory recovery percentages.

On-Site Multisample Determination of Chlorogenic Acid in Green Coffee by Chemiluminiscent Imaging

The potential of antioxidants in preventing several diseases has attracted great attention in recent years. Indeed, these products are part of a multi-billion industry. However, there is a lack of scientific information about safety, quality, doses, and changes over time. In the present work, a simple multisample methodology based on chemiluminiscent imaging to determine chlorogenic acid (CHLA) in green coffee samples has been proposed. The multi-chemiluminiscent response was obtained after a luminol-persulfate reaction at pH 10.8 in a multiplate followed by image capture with a charge-coupled device (CCD) camera as a readout system. The chemiluminiscent image was used as an analytical response by measuring the luminescent intensity at 0 °C with the CCD camera. Under the optimal conditions, the detection limit was 20 µM and precision was also adequate with RSD < 12%. The accuracy of the proposed system was evaluated by studying the matrix effect, using a standard addition method. Recoveries of chlorogenic acid ranged from 93-94%. The use of the CCD camera demonstrated advantages such as analysis by image inspection, portability, and easy-handling which is of particular relevance in the application for quality control in industries. Furthermore, multisample analysis was allowed by one single image saving time, energy, and cost. The proposed methodology is a promising sustainable analytical tool for quality control to ensure green coffee safety through dosage control and proper labelling preventing potential frauds.

Linear Fitting of Time-Varying Signals in Static Noble Gas Mass Spectrometry Should Be Avoided.

This Perspective highlights a malpractice during data processing in static noble gas mass spectrometry, viz. retrodicting the noble gas signals at "time zero" based on the linear fitting results of the time-varying analytical responses. Linear fitting is the most commonly used by noble gas analysts mainly on the consideration of high coefficient of determination (R2), while it poses risks of inaccurate estimation of required information. Here, we appeal to re-examining the signal variation mechanisms before deciding the way of fitting instead of merely choosing one with good R2. The primary processes during the static mass spectrometry measurement are considered, and a mechanism-based exponential fitting is recommended for the relevant data processing. For the same given data set, exponential fitting is a more robust processing strategy than linear fitting because not only does the former show perfect goodness of fitting but also it contributes to better consistence of retrodicted signals. For the sake of maintaining a high level of data quality in analytical science, we propose to apply the mechanism-based exponential fitting to retrodict the "time zero" signal in static noble gas mass spectrometry, and the commonly used linear fitting should be avoided.

Microbial nanowires with genetically modified peptide ligands to sustainably fabricate electronic sensing devices

Nanowires have substantial potential as the sensor component in electronic sensing devices. However, surface functionalization of traditional nanowire and nanotube materials with short peptides that increase sensor selectivity and sensitivity requires complex chemistries with toxic reagents. In contrast, microorganisms can assemble pilin monomers into protein nanowires with intrinsic conductivity from renewable feedstocks, yielding an electronic material that is robust and stable in applications, but also biodegradable. Here we report that the sensitivity and selectivity of protein nanowire-based sensors can be modified with a simple plug and play genetic approach in which a short peptide sequence, designed to bind the analyte of interest, is incorporated into the pilin protein that is microbially assembled into nanowires. We employed a scalable Escherichia coli chassis to fabricate protein nanowires that displayed either a peptide previously demonstrated to effectively bind ammonia, or a peptide known to bind acetic acid. Sensors comprised of thin films of the nanowires amended with the ammonia-specific peptide had a ca. 100-fold greater response to ammonia than sensors made with unmodified protein nanowires. Protein nanowires with the peptide that binds acetic acid yielded a 4-fold higher response than nanowires without the peptide. The protein nanowire-based sensors had greater responses than previously reported sensors fabricated with other nanomaterials. The results demonstrate that protein nanowires with enhanced sensor response for analytes of interest can be fabricated with a flexible genetic strategy that sustainably eliminates the energy, environmental, and health concerns associated with other common nanomaterials.

Development and validation of an ion chromatography‐ultraviolet method for determination of uric acid in the delactosed permeate

AbstractIn this study, we developed and validated a new analytical method for the quantitative evaluation of uric acid in delactosed permeate using ion chromatography coupled with an ultraviolet detector. Uric acid was extracted from delactosed permeate samples by diluted hydroxide solution at room temperature. The separation was carried out on a high‐capacity anion‐exchange column by isocratic elution with 50 mM potassium hydroxide. Uric acid was detected at 295 nm. The results from this study demonstrate that the new ion chromatography‐ultraviolet method facilitates both the resolution and the detection of uric acid and provides a highly accurate and sensitive determination of uric acid in delactosed permeate samples with minimal sample preparation effort. The new method provided an excellent range of analyte response linearity in the 2.5–255.6 ng range with R2 &gt; 0.99. The limit of detection for uric acid obtained was 0.04 mg/kg in 1 mM sodium hydroxide. Intraday and interday variabilities were less than 3%, and the mean recoveries (%) of the uric acid spiked in two types of delactosed permeate were between 100.4% and 103.9%. This method was successfully applied to determine uric acid amounts in ten delactosed permeate samples.

P737 Intensification with intravenous ustekinumab in refractory Crohn′s disease

Abstract Background There is little scientific evidence available about the results in terms of clinical and biochemical response after intensification with intravenous (IV) ustekinumab (UST) as a therapeutic strategy to be used in patients with refractory Crohn’s disease (CD) who are receiving subcutaneous (SC) treatment with said drug. Methods Patients with CD in stable follow-up at Hospital Universitario La Paz (Madrid), who were undergoing intensified treatment with IV UST, were recruited. The objective of the study was to assess the clinical and analytical response and drug levels 12 weeks after the change from subcutaneous to intravenous UST. Results 27 patients were retrospectively included, all of them with previous treatment with UST SC. In Table 1 baseline characteristics are collected. Out of the 27 patients included, 4/27 were under treatment with UST in first line, 10/27 in second line, 9/27 in third line and 4/27 had failed to three biologics. The reason for intensification with IV UST was the lack of response to treatment in the 27 patients, 7 of them (25.93%) being found in the context of post-surgical recurrence. On the other hand, 10 patients (37.03%) were already under treatment with intensified SC UST, while the remaining 17 patients (62.96%) were under treatment with a standard schedule of SC UST every 8 weeks. At the baseline visit, prior to the change to IV UST, differences in levels were observed between intensified and non-intensified patients (7216 vs 2842, p=0,00005). However, no significant differences were appreciated between these two groups 12 weeks after IV intensification (7949 vs 7937; p=0,99). In patients with intensified UST SC was observed a decrease in fecal calprotectin 12 weeks after starting IV intensification, going from a mean of 1463 to 751, although the differences were not significant (p=0,14). In Figure 1 is shown improvement in fecal calprotectin levels and in Figure 2 improvement in UST levels in blood is reflected, both parameters quantified 12 weeks after intravenous intensification of the drug. In Table 2 data derived from the analysis of the clinical activity and determinations of CRP and calprotectin are collected, before performing the intensification with UST IV and 12 weeks after it. Conclusion In our experience, change to intravenous ustekinumab in maintenance led to an improvement in the clinical and biochemical response in patients with Crohn’s disease (even in patients already intensified). Likewise, an increase in drug levels was observed 12 weeks after the change from subcutaneous to intravenous treatment.

Composite material immobilized in 3D-printed support, an economical approach for electrochemical sensing of nimesulide

This work aimed to build a disposable electrode, cheap, and robust, with a maximum manufacturing value of US$ 0.02 per sensor, whose basic structure is a composite material (CM) immobilized on 3D support of acrylonitrile butadiene styrene (ABS), to the determination of Nimesulide (NIM) in different samples. The surface characterization of the electrodes was made by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). The electrochemical response for NIM obtained was compared with a commercial Glassy Carbon electrode (GCE), where a 70 % increase in the analytical response was observed. The sensor was applied for the quantification of NIM by the square wave voltammetry (SWV) method in pharmaceutical formulations, tap water, synthetic urine, and breast milk. The optimized method presented a satisfactory linear range of 10 to 50 µmol/L, with a simple sample treatment, good precision (RSD < 3.38 %), and excellent detectability (limit of detection 0.018 µmol/L). Samples were spiked at three concentration levels to evaluate the accuracy of the method, obtaining recovery values from 96.2 to 112.8 %. Thus, the disposable proposed device proves to be a promising analytical tool for routine analysis of NIM in different samples with a minimum sample preparation step (simple dilution).

Exploiting microdistillation and smartphone-based digital-image colorimetry for determination of protein in foods

Because of their nutritional importance and industrial interest, determination of proteins is usual in food quality control. The Kjeldahl method, the most usual for protein determination and a reference to other indirect methods, is time-consuming and generates significant amounts of waste. Aiming to circumvent these drawbacks, this work proposes a simple, cost-effective, and more environmental friendly procedure based on microdistillation of the ammonium from Kjeldahl digests, absorption on an acid-base indicator solution, and digital-image colorimetry for protein determination in food. Microdistillation was carried out in a simple and inexpensive lab-made apparatus. The digital images were acquired by a smartphone camera under controlled illumination and the intensity of the reflected radiation was converted to the RGB color system using a free app (PhotoMetrix®). Measurements were based on the color change of phenol red from yellow to pink and the G channel (corresponding to the complementary color of the dissociated indicator) was taken as analytical response. A linear response was achieved within 5.0–50.0 mg/L ammonium, equivalent to 0.003–0.03 % protein (r = 0.996), as confirmed by the lack-of-fit test at the 95 % confidence level. Coefficient of variation (n = 10) and limit of detection (99.7 % confidence level) were estimated at 2.3 % and 2 mg kg−1 protein, respectively. A sample throughput of 12 h−1 was achieved with simultaneous sample processing. Protein amounts determined in foods of animal (milk) and vegetal (beans and lentils) origin yielded results in agreement with the micro-Kjeldahl reference procedure at the 95 % confidence level.

Gas Adsorption Response of Piezoelectrically Driven Microcantilever Beam Gas Sensors: Analytical, Numerical, and Experimental Characterizations.

This work presents an approach for the estimation of the adsorbed mass of 1,5-diaminopentane (cadaverine) on a functionalized piezoelectrically driven microcantilever (PD-MC) sensor, using a polynomial developed from the characterization of the resonance frequency response to the known added mass. This work supplements the previous studies we carried out on the development of an electronic nose for the measurement of cadaverine in meat and fish, as a determinant of its freshness. An analytical transverse vibration analysis of a chosen microcantilever beam with given dimensions and desired resonance frequency (>10 kHz) was conducted. Since the beam is considered stepped with both geometrical and material non-uniformity, a modal solution for stepped beams, extendable to clamped-free beams of any shape and structure, is derived and used for free and forced vibration analyses of the beam. The forced vibration analysis is then used for transformation to an equivalent electrical model, to address the fact that the microcantilever is both electronically actuated and read. An analytical resonance frequency response to the mass added is obtained by adding simulated masses to the free end of the beam. Experimental verification of the resonance frequency response is carried out, by applying known masses to the microcantilever while measuring the resonance frequency response using an impedance analyzer. The obtained response is then transformed into a resonance frequency to the added mass response polynomial using a polynomial fit. The resulting polynomial is then verified for performance using different masses of cantilever functionalization solution. The functionalized cantilever is then exposed to different concentrations of cadaverine while measuring the resonance frequency and mass of cadaverine adsorbed estimated using the previously obtained polynomial. The result is that there is the possibility of using this approach to estimate the mass of cadaverine gas adsorbed on a functionalized microcantilever, but the effectiveness of this approach is highly dependent on the known masses used for the development of the response polynomial model.

Determination of thiomersal and mercurial residues by photo-degradation and flow injection analysis with luminescence probing using carbon quantum dots prepared from thiourea

Thiomersal is an organomercurial compound but, despite that, it is widely used in vaccines formulations to inactivate organisms and toxins and to prevent microbial growth during storage and use. In this work, thiomersal (along with traces of mercurial residues) was determined after photo-degradation (using UV and H2O2) to produce Hg2+ that was determined by flow injection analysis using luminescence probing with carbon quantum dots (prepared from citric acid and thiourea). Linear analytical response was observed in the concentration range of 25 to 900 µg L−1 and the method was efficiently applied to the determination of thiomersal in vaccines against hepatitis B and diphtheria-tetanus with recoveries ranging from 93 to 94%.

Understanding the transient large amplitude oscillatory shear behavior of yield stress fluids

A full understanding of the sequence of processes exhibited by yield stress fluids under large amplitude oscillatory shearing is developed using multiple experimental and analytical approaches. A novel component rate Lissajous curve, where the rates at which strain is acquired unrecoverably and recoverably are plotted against each other, is introduced and its utility is demonstrated by application to the analytical responses of four simple viscoelastic models. Using the component rate space, yielding and unyielding are identified by changes in the way strain is acquired, from recoverably to unrecoverably and back again. The behaviors are investigated by comparing the experimental results with predictions from the elastic Bingham model that is constructed using the Oldroyd–Prager formalism and the recently proposed continuous model by Kamani, Donley, and Rogers in which yielding is enhanced by rapid acquisition of elastic strain. The physical interpretation gained from the transient large amplitude oscillatory shear (LAOS) data is compared to the results from the analytical sequence of physical processes framework and a novel time-resolved Pipkin space. The component rate figures, therefore, provide an independent test of the interpretations of the sequence of physical processes analysis that can also be applied to other LAOS analysis frameworks. Each of these methods, the component rates, the sequence of physical processes analysis, and the time-resolved Pipkin diagrams, unambigiously identifies the same material physics, showing that yield stress fluids go through a sequence of physical processes that includes elastic deformation, gradual yielding, plastic flow, and gradual unyielding.

Layer-by-Layer Deposited Multi-Modal PDAC/rGO Composite-Based Sensors.

Different environmental parameters, such as temperature and humidity, aggravate food spoilage, and different volatile organic compounds (VOCs) are released based on the extent of spoilage. In addition, a lack of efficient monitoring of the dosage of pesticides leads to crop failure. This could lead to the loss of food resources and food production with harmful contaminants and a short lifetime. For this reason, precise monitoring of different environmental parameters and contaminations during food processing and storage is a key factor for maintaining its safety and nutritional value. Thus, developing reliable, efficient, cost-effective sensor devices for these purposes is of utmost importance. This paper shows that Poly-(diallyl-dimethyl ammonium chloride)/reduced Graphene oxide (PDAC/rGO) films produced by a simple Layer-by-Layer deposition can be effectively used to monitor temperature, relative humidity, and the presence of volatile organic compounds as indicators for spoilage odors. At the same time, they show potential for electrochemical detection of organophosphate pesticide dimethoate. By monitoring the resistance/impedance changes during temperature and relative humidity variations or upon the exposure of PDAC/rGO films to methanol, good linear responses were obtained in the temperature range of 10-100 °C, 15-95% relative humidity, and 35 ppm-55 ppm of methanol. Moreover, linearity in the electrochemical detection of dimethoate is shown for the concentrations in the order of 102 µmol dm-3. The analytical response to different external stimuli and analytes depends on the number of layers deposited, affecting sensors' sensitivity, response and recovery time, and long-term stability. The presented results could serve as a starting point for developing advanced multi-modal sensors and sensor arrays with high potential for analytical applications in food safety and quality monitoring.

Parametric resonance and bifurcation analysis of thin-walled asymmetric gyroscopic composite shafts: An asymptotic study

Nonlinear geometries and cross-sectional asymmetry can be among the most critical contributing factors affecting the performance and stability of composite shafts. The influence of these factors, which should be devoted to particular attention in the design of these systems and have not been investigated yet, are evaluated analytically in this study. The shaft is simply supported, made of orthotropic multi-layers, and spinning at a constant speed. To express the nonlinear system’s behavior, which is due to the large amplitude of the vibrations, it is assumed that the shaft is under the stretching assumption. Moreover, a rectangular cross-section is used to model the asymmetry that results in parametric excitation in the system. To accurately investigate the behavior of composite material, an optimal lay-up is employed. The gyroscopic coupling is included because of Rayleigh beam theory, and Euler’s angles are employed to achieve the angular velocities. The analytical study of the parametrically excited system, obtained by the method of multiple scales, is performed in two categories of resonant and nonresonant cases. In the nonresonant case, the analytical investigation suggests that the asymmetric shaft behaves like a symmetric one therefore, the parametric excitations do not have a significant impact. This claim is confirmed by numerical results. Also, the presence of the gyroscopic coupling and hollowness of the shaft causes the beating phenomenon in the system. However, in the resonant case, the presence of parametric excitation plays a pivotal role. The results also show that under certain conditions and despite the presence of damping, asymmetric balanced rotors can have a nontrivial stable amplitude. This response exists as long as the parametric excitation effects dominate the damping effects. Although damping reduces the vibrations’ amplitude, it can improve the stability of the system and eliminates unstable responses. Furthermore, the time response and frequency response curve of the system is carefully evaluated for various geometric design parameters and operation speed. Depending on the operating speed, the system can experience supercritical or subcritical pitchfork bifurcation. In addition, a detailed description of the system’s Campbell’s diagram, damping effect, and bifurcation is provided. Furthermore, it is proved that internal resonance cannot occur in the system. The accuracy of the analytical responses of the resonant case is compared with numerical ones. Stability of trivial and nontrivial responses is discussed in the time response and phase portrait of the system simultaneously. Finally, in the undamped system, multi-frequency responses are appeared as homoclinic and heteroclinic closed orbits.

Unusual ‘Turn-on’ Ratiometric Response of Fluorescent Porphyrin-Pyrene Dyads to the Nitroaromatic Compounds

Detection of nitroaromatic compounds (NAC) is an important task since these substances are hazardous to both the biosphere and the society. Fluorescent sensors developed for NAC detection usually demonstrate a ‘turn-off’ response to the analyte, while ‘turn-on’ sensors are rarely reported. Here, we present a showcase report on new pyrene-imidazoporphyrin dyads that demonstrate an unusual analytic response to NAC with clear ‘turn-on’ behavior followed by an unexpected appearance of a new band, which can be ascribed to exciplex emission. The porphyrin backbone of the dyad also allows registration of its own fluorescence, providing an internal reference signal for ratiometric detection. The association constants in the order of 104 M−1 are reported.

A novel approach for lactose determination in cow's milk exploiting smartphone-based digital-image photometry.

Lactose, the main carbohydrate in cow's milk, may cause health problems for consumers with intolerance. Lactose determination in milk is hindered by the matrix complexity and lack of chromophore groups. Chromatography, volumetric, and spectrophotometric approaches involving chemical derivatization are time-consuming and require laborious sample preparation, which is incompatible with the high analytical demand. In this context, a novel approach is presented for lactose determination in milk exploiting smartphone-based digital-image photometry. It was based on a modification of the Benedict's method, involving formation of the violet Cu(I)/2,2'-biquinoline-4,4'-dicarboxylate (BCA) complex instead of the copper(I) oxide precipitate, aiming at improvement of sensitivity and precision. Sample pretreatment and analyte derivatization were performed in Eppendorf tubes with minimal reagent amounts and a smartphone camera was used for image acquisition under controlled conditions. Measurements were based on the RGB color system, taking channel G as the analytical response because of the complementarity with the color of the complex. Under the optimized conditions, the proposed procedure yielded a linear response up to 20 mg L-1 (r = 0.999), with a limit of detection of 1.5 mg L-1, which is compatible with determination of lactose in milk and dairy products categorized with low content of the sugar. The procedure takes less than 10 min, with a coefficient of variation of 3.0% (n = 12) and consumes as low as 160 μg Cu and 430 μg BCA per determination, thus being a more practical, fast, cost-effective, and environmental friendly analytical method.

Development of multiple analytical labels for volatile organic compounds based on the results of sorption on CdS quantum dots in chitosan without and with modification with Rhodamine 6G

Analytical solutions using the luminescent labels for the analysis of gaseous media and the detection of volatile organic compounds are discussed. Such solutions can potentially be applied for the development of optical, sorption gas sensors, smart label fillers, test systems with various carriers for the detection of chemical biomarkers in living systems. To solve the problem it is proposed to develop and study the properties of modifiers based on cadmium sulfide quantum dots. The aim of the work is studying the sorption properties of CdS quantum dots prepared using a method improved in the direction of "green chemistry", with stabilizing chitosan shells (pure and modified with Rhodamine 6G). Sorption properties of various phases based on quantum dots were studied at a temperature of 22±1 °C by a highly sensitive direct piezo-quartz microweighting method with a resolution of up to 10–9 g by the mass of the sorbent in vapors of volatile compounds. The selectivity of phases based on cadmium sulfide quantum dots in low-mass chitosan (5–10 micrograms) with respect to volatile organic compounds of different classes was evaluated. The relative selectivity and sensitivity of vapor weighing on different phases were evaluated using the parameters A(i/j), showing how many times the sorption properties of CdS phases in chitosan differ without and with the addition of Rhodamine 6G. The method of direct weighing allows to estimate the rate of sorption and desorption, and the capacity of the sorbent phases. It was established that substances belonging to the same selectivity group in terms of A(i/j) values, for example, water and ethanol, have different sorption rates. This feature can be applied for solving the problems of separate detection of vapors, they can be identified at different moments of exposure of piezo balances with phases based on CdS quantum dots in chitosan without and with the addition of Rhodamine 6G. The use of cadmium sulfide quantum dots in chitosan as a sorbent of organic compound vapors significantly affects the kinetics and sorption efficiency. Modification of chitosan with Rhodamine 6G changes the sorption properties of quantum dots in chitosan, which can be used for engineering new sorbents for sensor systems. Simple algorithms are proposed for solving problems of vapor recognition of volatile compounds according to calculated parameters even for non-selective sorption systems. Programming the approach can significantly increase the expressiveness of decision-making in integrated analytical systems, for example, "electronic noses" based on sensors, including those with studied phases. It was found that the mass of the phase based on cadmium sulfide quantum dots in chitosan does not affect the sorption properties in the micromass range, which is traditional for nanostructures. Changes in the luminescent properties of phases based on cadmium sulfide, as a possible visually detectable analytical response, will be discussed in the next paper.

Simple multi-residue analysis of persistent organic pollutants and molecular tracers in atmospheric samples

We present a simple, selective and sensitive analytical method to quantitatively determine a wide range of halogenated persistent organic pollutants and molecular tracers in atmospheric samples. Identification and quantification was carried out by high-resolution gas chromatography, hyphenated with low-resolution mass spectrometry operating in electron impact (EI) and electron capture negative ionization (ECNI) mode. Optimization on a number of instrumental parameters was conducted to obtain ultra-trace detection limits, in the range of few fg/m3 for organohalogen compounds. Repeatability and reproducibility of the method was thoroughly evaluated. The analysis was validated with standard reference materials and successfully applied to actual atmospheric samples. The proposed multi-residue method provides a precise, affordable and practical procedure of sample analysis for environmental research laboratories with conventional instrumentation on a routine basis.•A simple combination of alumina, florisil and silica gel adsorbents was applied to sufficiently isolate polychlorinated biphenyls, organochlorine pesticides, polycyclic aromatic hydrocarbons, long chain n-alkanes, hopanes and steranes.•Full elution was achieved in two successive fractions, using small volumes of n-hexane and n-hexane/dichloromethane to recover all target substances.•To maximize analytical response, optimization was applied for three operating parameters in ECNI mode: i) ion source temperature; ii) emission current; and iii) electron energy.

Microbial diversity in artisanal cheese produced and commercialized in Vale do Taquari in southern Brazil

Researchers have been utilizing matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) to identify bacteria and fungi directly from isolates obtained on culture plates; the resulting mass spectrum is then compared with spectra stored in the instrument software. Hence, a fast analytical response is obtained, and the more spectra are known to compare, the safer and more reliable the interpretation of the method will be. Thus, this study sought to identify the diversity of strains found in 10 samples of artisan cheese produced and commercialized in Vale do Taquari (Rio Grande do Sul State, Brazil) using MALDI-TOF MS. From the analyzed cheese, 22 strains were identified at the species level; one sample presented the pathogen Staphylococcus aureus, two showed the presence of lactic acid bacteria (Lactococcus lactis), and the vast majority (68.18%) of strains were composed of species of the Enterobacteriaceae family, with the prevalence of the genera Escherichia, Enterobacter, and Klebsiella. Escherichia coli was present in 50% of the samples analyzed. This demonstrates the need for greater control during all stages of artisanal cheese production and evaluation of the raw material, including safe practices during milking, so that the product meets the identity and quality parameters suitable for human consumption.