Mixtures Of Analytes Research Articles

Determination of cochineal and erythrosine in cherries in syrup in the presence of quenching effect by means of excitation-emission fluorescence data and three-way PARAFAC decomposition

The simultaneous determination of two food colorants (cochineal (E-120) and erythrosine (E-127)) was achieved by means of excitation-emission fluorescence matrices and three-way PARAFAC decomposition together with the use of a calibration set that contained binary mixtures of both analytes. In the measured conditions, the amount of cochineal present in the sample affected the fluorescence signal of erythrosine since cochineal caused a quenching effect in the fluorescence of the other food additive. However, the signal of cochineal was not affected by the presence of erythrosine.A calibration line for erythrosine was built for each different concentration level of cochineal. The slopes of these regressions were different depending on the amount of quencher, whereas the intercepts were statistically equal to 0 at a 95% confidence level. The quantification of erythrosine was possible using the regression “amount of cochineal” versus “the slope of the calibration line for erythrosine”. Using this procedure, the mean of the absolute values of the relative errors in prediction for mixtures of both colorants were 5.86% (n = 10) for cochineal and 4.17% (n = 10) for erythrosine. Both analytes were unequivocally identified by the correlation between the pure spectra and the PARAFAC excitation and emission spectral loadings.Pitted cherries in syrup were analyzed. Cochineal and erythrosine were detected in those cherries at a concentration of 185.05 mg kg−1 and 10.76 mg kg−1, respectively. These concentration values were statistically equal to the ones obtained with a HPLC/DAD method.

Recognition of Model Analyte Mixtures in the Presence of Blood Plasma Using a Mixture of Fluorophores (“Fluorescent Tongue”)

The paper is devoted to the development of a version of the fingerprint method based on the effect of analytes on the shape of the fluorescence spectrum of a fluorophore mixture. The model analytes were medicinal substances (amikacin, sulfamethoxazole, pyracetam, and chloramphenicol) and binary to quaternary mixtures of these substances in equal concentrations. The mixtures were recognized using a fluorophore whose fluorescence was quenched to different extent by different model analytes (CdSe/CdS/ZnS quantum dots, Schiff base prepared from o-phthalic dialdehyde and polyethyleneimine, and also rhodamine B and fluorescein immobilized on silica nanoparticles to increase the degree of quenching – Rhod/SiO2 and Fluor/SiO2). The fluorophores were used as mixtures (“fluorescent reagents”) containing from one to four fluorophores. The classes of analytes were distinguished by calculating Mahalanobis distances on score plots of the principal component analysis method. It was found that it was more difficult to distinguish analyte mixtures in the presence of blood plasma than in a buffer solution and that the best fluorescent reagent was the mixture of all four fluorophores, which ensured the subdivision of 15 mixtures of 2–4 model analytes into seven classes. An alternative fingerprint method based on the use of UV absorption spectra allowed distinguishing of only five classes.

Micellar Electrokinetic Chromatography.

Micellar electrokinetic chromatography (MEKC) is a mode of capillary electrophoresis that allows for the separation of neutral molecules in an electric field. Typically, neutral molecules move with electroosmotic flow (EOF) or bulk flow during electrophoretic separations resulting in no temporal resolution between mixtures of neutral analytes. Inclusion of surfactant micelles in the separation buffer allows for the separation of neutral analytes from one another through association with the micelle. Here we outline the implementation of MEKC for the separation of neutral molecules using a mixture of nitroaromatic explosives and their degradation products serving as a test analyte mixture.

Rapid quantification of quinine by multi-stacking in a portable microchip electrophoresis system.

A new multi-stacking pre-concentration procedure based on field-enhanced sample injection (FESI), field-amplified sample stacking, and transient isotachophoresis was developed and implemented in a compact microchip electrophoresis (MCE) with a double T-junction glass chip, coupled with an on-chip capacitively coupled contactless conductivity detection (C4 D) system. A mixture of the cationic target analyte and the terminating electrolyte (TE) from the two sample reservoirs was injected under FESI conditions within the two sample-loading channels. At the double T-junction, the stacked analyte zones were further concentrated under field-amplified stacking conditions and then subsequently focused by transient-isotachophoresis and separated along the separation channels. The proposed multi-stacking strategy was verified under a Universal Serial Bus (USB) fluorescence microscope employing Rhodamine 6G as the model analyte. This developed approach was subsequently used to monitor the target quinine present in human plasma samples. The total analysis time for quinine was approximately 200s with a sensitivity enhancement factor of approximately 61 when compared to the typical gated injection. The detection and quantification limits of the developed approach for quinine were 3.0μg/mL and 10μg/mL, respectively, with intraday and interday repeatability (%RSDs, n = 5) of 3.6 and 4.4%. Recoveries in spiked human plasma were 98.1-99.8%.

Modeling of the Functionalized Gold Nanoparticle Aggregation in the Presence of Dopamine: A Joint MD/QM Study

The investigation of gold nanoparticle (AuNP) aggregation at the atomic level is a great challenge from the experimental view, while theoretical methods facilitate our understanding of the AuNP aggregation process. In this article, by applying full atomistic molecular dynamics simulations, the aggregation process and the stability of the functionalized AuNPs with 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (AT) was investigated. Moreover, the ability of AT–AuNPs toward selective detection of dopamine was analyzed. Theoretical results showed that AT groups on the surface of the AuNPs increase the resistance of nanoparticles against the aggregation. Also, AT–AuNPs are only accumulated in the presence of dopamine in a mixture of different analytes. In this process, dopamine acts as a molecular bridge between the AT–AuNPs, which facilitates nanoparticle aggregation through hydrogen bond interactions. Quantum chemistry calculations confirmed that the structural feature of dopamine is a more effective factor ...

Separation performance of a star-shaped truxene-based stationary phase functionalized with peripheral 3,4-ethylenedioxythiophene moieties for capillary gas chromatography

This work describes the separation performance of a star-shaped truxene-based material (denoted as EDOTT) as the stationary phase for capillary gas chromatography (GC). The EDOTT capillary column achieved the column efficiency of 5920 plates/m by n-dodecane, 4890 plates/m by naphthalene and 3960 plates/m by 1-octanol at 120 ℃. Its selectivity and retention behaviour were investigated by a number of mixtures of diverse analytes and their isomers. As a result, it showed advantageous performance for separations of apolar to polar analytes, especially phenols and alcohols, over its analogous TTT, TDT and TFT stationary phases. In addition, the EDOTT capillary column was investigated for its column loadability, repeatability and thermal stability, and was finally applied for the determination of isomer impurities in real samples. This work provides an alternative truxene-based stationary phase with high selectivity for polar analytes and demonstrates the key role of structural modification in developing a family of stationary phases with specific selectivity for targeted analytes.

Absolute Amounts of Analytes: When Gravimetric Methods Are Insufficient.

Tandem mass spectrometry (MS/MS)2, often combined with liquid chromatography (LC-MS/MS), has emerged as an extremely versatile platform for quantification of analytes in complex biological samples. The method is rendered highly quantitative by use of a chemically identical but isotopically differentiated internal standard. Such an internal standard corrects for losses of analyte signal in the assay owing to sample handing or MS/MS signal loss because of suppression of analyte ionization in the electrospray source. At a minimum, the true concentration of the analyte in a stock solution should be known as accurately as possible. One can then inject an absolute number of moles of analyte into the instrument (the true moles), together with an aliquot of a solution of internal standard, and determine the ratio of analyte to internal standard MS/MS response (response ratio). It is not required that the true moles of internal standard in the stock solution be accurately known. Even if a truly equimole mixture of analyte and internal standard is analyzed, the response ratio may not be 1 because of biases in the tuning of the quadrupole mass filters and/or an isotope effect on the fragmentation of the parent ion to give the product ions (no isotope effect is expected if a bond to the heavy isotope does not break in the fragmentation reaction). Thus, the measured response ratio will reflect the true difference in absolute moles of analyte and internal standard analyzed, tuning bias, and any isotope effects on fragmentation. For example, if one injected truly 1 nmol of analyte and nominally 1 nmol of internal standard in the MS/MS instrument and observed a response ratio of 1.2, one can obtain the true moles of analyte in a new sample via the following equation: ![Formula][1] The above equation is valid even if the absolute moles … [1]: /embed/mml-math-1.gif

Multiway analysis through direct excitation-emission matrix imaging

In this work, a direct in-flow methodology for the acquisition of excitation-emission fluorescence matrices is presented. The system is particularly suited for measurements in the order of tens of milliseconds. A light source operated in continuous mode is dispersed through a grating and focused onto a square-section capillary. Under the spatially resolved excitation, the emission is collected, dispersed through a second grating and further focused onto a CCD array sensor. To allow the wavelength accuracy, a spectral calibration was performed registering the scattering signal of a dispersive element using interference filters ranging from 340 nm to 740 nm. The theoretical performance of the method was analyzed and second-order data obtained for different analyte mixtures are presented and discussed. PARAFAC was applied to evaluate the trilinearity of the obtained data. Mathematical evaluation by means of the criterion of similarity corroborates the agreement between experimental pure spectra and spectral profiles retrieved from PARAFAC. Moreover, the feasibility of the spectrometer to obtain second-order data for analyses with quantitative aims was demonstrated. Finally, fast data acquisition was proved by monitoring a chromatographic analysis of dye mixtures for the generation of third-order LC-EEM data. Here, an improvement in the resolution of the different instrumental modes was demonstrated.

Finger-Based Printed Sensors Integrated on a Glove for On-Site Screening Of Pseudomonas aeruginosa Virulence Factors.

Early screening of clinically relevant pathogens in the environment is a highly desirable goal in clinical care, providing precious information that will improve patient-care outcomes. In this work, a glove-based electrochemical sensor has been designed for point-of-use screening of Pseudomonas aeruginosa's virulence factors. The methodology used for the elaboration of the fabric platform relied on printing the conductive inks on the index and middle fingers of the glove, with the goal of screening pyocyanin and pyoverdine targets. The analytical signatures of the analytes were recorded in about 4 min, via the rapid and selective square-wave-voltammetry technique. Finger-based sensors display good performance and discrimination between the targets and potential interferences, along with good reproducibility. The sensors featured linearity over the 0.01-0.1 μM range for pyocyanin and 5-50 μM range for pyoverdine, with sensitivities of 2.51 μA/μM for pyocyanin and 1.09 nA/μM for pyoverdine ( R2 = 0.990 and 0.995, respectively) and detection limits of 3.33 nM for pyocyanin and 1.66 μM for pyoverdine. Moreover, the sensors were tested in binary mixtures of analytes, with successful outcomes. In order to gain information from the surrounding environment, the active electronic areas of the printed fingers were coated with a conductive hydrogel matrix, and relevant target surfaces were "swiped for notification" of contaminants. The simple fabrication, low-cost, and reusability of the proposed glove are likely to underpin the progressive drive of wearable sensors toward decentralized environmental and healthcare applications.

High-throughput chemometrically assisted flow-injection method for the simultaneous determination of multi-antiretrovirals in water

This work is focused on the simultaneous determination of different nucleosides (lamivudine, abacavir, zidovudine) and non-nucleoside (nevirapine, efavirenz) reverse transcriptase inhibitors (antiretrovirals) in river, tap and well water by pH-gradient flow-injection analysis with diode-array detection (FIA-DAD) and further multivariate curve resolution-alternating least square (MCR-ALS) processing. Previous to the development of the analytical method with quantitative purpose, the acid-base characterization was conducted for all the analytes by determination of the experimental pKa. The pKa values, obtained by UV spectrometric titration coupled to MCR-ALS data modeling, were in agreement with those found in the literature, and, interestingly, a non-reported pKa of 12.27 was identified for nevirapine. Eventually, the analytical method was developed and its performance on the quantitation of the antiretrovirals was evaluated through its application to validation and environmental samples. The recovery studies showed values between 85 and 115% with relative errors of prediction below 10%. The figures of merit were satisfactory for all the studied drugs, with limits of detection between 25 and 40 μg L−1. Therefore, the proposed method, which is based on the generation of high-throughput data, is a simple and suitable alternative to determine the concentration of antiretroviral drugs in complex matrices, without pre-concentration or extraction steps. Additionally, MCR-ALS demonstrated to be a useful tool for solving mixtures of analytes with high spectral overlapping, in the presence of unknown interferences.

Chirality Sensing, Halochromism and Solvatochromism in a Conjugated Calix[4]Pyrrole

The conjugated calix[4]pyrrole tetrakis(3,5-di-t-butyl-4-oxocyclohexadien-2,5-yl)porphyrinogen (OxP) is a highly coloured macrocycle with excellent potential as a sensing element in various applications. The first of these is chiral sensing where guest binding at the macrocyclic NH groups allows for estimation of enantiomeric excesses in non-racemic mixtures of chiral analytes. This feature is permitted by the relatively weak binding of the guest resulting in its rapid exchange so that the molecule essentially acts as a probe of average solution chirality. Chirality sensing in OxP is complicated by tautomeric processes when an acid analyte is used. This has allowed us also to develop an acidity sensor for use in non-polar media. More recently, we have designed a series of OxP type molecules that undergo modulation of halochromic (sensitivity to acid) properties and the development of colour scales based on the blocking of OxP binding sites and involving allied protic tautomerization of the OxP chromophore. We will discuss the sensing properties of OxP in relation to chirality, tautomeric processes and the complicating factor of solvatochromism.

Analysis of Multiplexed Nanosensor Arrays Based on Near-Infrared Fluorescent Single-Walled Carbon Nanotubes.

The high-throughput, label-free detection of biomolecules remains an important challenge in analytical chemistry with the potential of nanosensors to significantly increase the ability to multiplex such assays. In this work, we develop an optical sensor array, printable from a single-walled carbon nanotube/chitosan ink and functionalized to enable a divalent ion-based proximity quenching mechanism for transducing binding between a capture protein or an antibody with the target analyte. Arrays of 5 × 6, 200 μm near-infrared (nIR) spots at a density of ≈300 spots/cm2 are conjugated with immunoglobulin-binding proteins (proteins A, G, and L) for the detection of human IgG, mouse IgM, rat IgG2a, and human IgD. Binding kinetics are measured in a parallel, multiplexed fashion from each sensor spot using a custom laser scanning imaging configuration with an nIR photomultiplier tube detector. These arrays are used to examine cross-reactivity, competitive and nonspecific binding of analyte mixtures. We find that protein G and protein L functionalized sensors report selective responses to mouse IgM on the latter, as anticipated. Optically addressable platforms such as the one examined in this work have potential to significantly advance the real-time, multiplexed biomolecular detection of complex mixtures.

Recognition mechanism of aromatic derivatives resolved by argentation chromatography: The driving role played by substituent groups

Argentation chromatography is widely used nowadays as a powerful tool to separate complex mixtures of analytes containing unsaturated and/or aromatic fragments. Here we present the results of chromatographic and computational studies on a silver-thiolate stationary phase, in which the silver metal is covalently bonded to mercaptopropyl silica particles. The exceptionally high selectivity displayed by this organometallic moiety prompted us to deeply investigate its molecular recognition properties. The interactions of the silver atom with a series of benzene derivatives was investigated to gain information on the mechanism by which the different ring substituents modulate retention factors and selectivity. The experimental trend was fully rationalized by means of quantum-mechanical Density Functional Theory (DFT) calculations, which allowed us to elucidate the chromatographic results in the light of unusual and unexpected substituent effects.

A hand-held fluorescent sensor platform for selectively estimating green algae and cyanobacteria biomass

This paper reports a portable fluorescent sensor platform containing multiple excitation light illumination for quantification and differentiation of multiple analytes. The fluorescent sensor platform utilizes: (i) three different wavelengths of light emitting diodes (LEDs) for selectively stimulating target analytes; (ii) a sensitive photodetector for corresponding fluorescence measurements; (iii) a custom-built electronic system for data measurement and storage; and (iv) a compact three-dimensional printed housing for the developed sensor platform. Based on the fluorescent emission pattern obtained from each target analyte, multivariate analytical methods were applied to differentiate one analyte from the other in a mixture of multiple analytes. The fluorescent sensor platform was tested to selectively detect two target phytoplankton species: Chlorella vulgaris and Spirulina. Fluorescent emission of phytoplankton is caused by stimulation of photosynthetic pigments and is widely utilized to quantify and classify phytoplankton groups. Biomass estimation was therefore conducted by measuring chlorophyll a fluorescence emission for green algae (Chlorella vulgaris) using blue LED excitation and phycocyanin fluorescence emission for cyanobacteria (Spirulina) using amber LED excitation. The results demonstrated the viability of the developed device as a portable generic fluorescence sensor platform for simultaneously detecting various biochemical analytes.

Technological concentration sensor for ethanolamines based on an optical sensor

The most important parameters necessary for the precise control of the separation of monoethanolamine, diethanolamine, and triethanolamine on column distillation apparatus are their initial concentrations in the mixtures fed to the columns. Currently, the use of a solid-state optical sensor, which makes it possible to determine the desired ratio in a mode close to the real-time regime. The technical parameters for the sensitivity and speed achieved by the sensor are determined in the determination of monoethanolamine, diethanolamine, and triethanolamine, as well as the sensor parameters and conditions of use, which enable the sensor to effectively solve the tasks. In particular, the concentration of the mixture of analytes in the sensor chamber is 500 mg / m3, the thickness of the sensitive coating is about 0.5 μm, the operating temperature is 45÷50 ° C, the time for one cycle of measuring the diethanolamine/triethanolamine ratio is 150 ÷ 180 seconds.

Portable combination of Fourier transform infrared spectroscopy and differential mobility spectrometry for advanced vapor phase analysis.

Designing mobile devices for the analysis of complex sample mixtures containing a variety of analytes at different concentrations across a large dynamic range remains a challenging task in many analytical scenarios. To meet this challenge, a compact hybrid analytical platform has been developed combining Fourier transform infrared spectroscopy based on substrate-integrated hollow waveguides (iHWG-FTIR) with gas chromatography coupled differential mobility spectrometry (GC-DMS). Due to the complementarity of these techniques regarding analyte type and concentration, their combination provides a promising tool for the detection of complex samples containing a broad range of molecules at different concentrations. To date, the combination of infrared spectroscopy and ion mobility techniques remains expensive and bound to a laboratory utilizing e.g. IMS as prefilter or IR as ionization source. In the present study, a cost-efficient and portable solution has been developed and characterized representing the first truly hyphenated IR-DMS system. As a model analyte mixture, 5 ppm isopropylmercaptan (IPM) in methane (CH4) were diluted, and the concentration-dependent DMS signal of IPM along with the concentration-dependent IR signal of CH4 were recorded for all three hybrid IR-DMS systems. While guiding the sample through the iHWG-FTIR or the GC-DMS first did not affect the obtained signals, optimizing the IR data acquisition parameters did benefit the analytical results.

Identification of Small-Molecule Noncovalent Binders Utilizing SAMDI Technology

In recent years, the ability to unambiguously identify complex mixtures of analytes with high accuracy and resolving power in a label-free format continues to expand the application of mass spectrometry (MS) in the drug discovery process. This advantage combined with improved instrumentation makes MS suitable for targets with limited alternative assays for high-throughput screening (HTS). We describe a novel screening format using Self-Assembled Monolayers and matrix-assisted laser Desorption Ionization (SAMDI) technology. SAMDI enables affinity capture of a target protein for use in a small-molecule–binding assay format. Subsequent ionization enables the inferred identification of noncovalent compound interactions. SAMDI technology overcomes shot-to-shot variability by uniformly saturating the surface with captured protein, thereby minimizing matrix crystallization “hot spots.” Furthermore, the combination with high-resolution matrix-assisted laser desorption/ionization time of flight significantly reduces interference of small-molecule detection from salt, detergent, and matrix. By using a pooled library format, the SAMDI assay can significantly improve the throughput of MS-based screening irrespective of enzyme activity. Finally, we demonstrate binding affinity rank ordering from a pool of compounds that correlates with potency data from a biochemical assay.

Compressive Detection of Highly Overlapped Spectra Using Walsh-Hadamard-Based Filter Functions.

In the chemometric context in which spectral loadings of the analytes are already known, spectral filter functions may be constructed which allow the scores of mixtures of analytes to be determined in on-the-fly fashion directly, by applying a compressive detection strategy. Rather than collecting the entire spectrum over the relevant region for the mixture, a filter function may be applied within the spectrometer itself so that only the scores are recorded. Consequently, compressive detection shrinks data sets tremendously. The Walsh functions, the binary basis used in Walsh-Hadamard transform spectroscopy, form a complete orthonormal set well suited to compressive detection. A method for constructing filter functions using binary fourfold linear combinations of Walsh functions is detailed using mathematics borrowed from genetic algorithm work, as a means of optimizing said functions for a specific set of analytes. These filter functions can be constructed to automatically strip the baseline from analysis. Monte Carlo simulations were performed with a mixture of four highly overlapped Raman loadings and with ten excitation-emission matrix loadings; both sets showed a very high degree of spectral overlap. Reasonable estimates of the true scores were obtained in both simulations using noisy data sets, proving the linearity of the method.

Number of theoretical plates achievable by a toroidal capillary electrophoresis system.

The ability of a method and instrument to separate very similar compounds is related to the "plate number," a number indicating performance. The resolution between two neighboring peaks is proportional to the square root of the plate number. Currently available commercial capillary electrophoresis instruments easily reach plate numbers of a few million. In the present work, a capillary electrophoresis system with a toroidal platform is proposed and theoretically studied with the goal of extending the achievable plate number. In this new system, electrophoresis occurs in a nonstop continuous circulating mode within a closed loop capillary (toroid). Plate numbers upwards of one billion are theoretically predicted. This could resolve hundreds of unseparated mixtures of stereoisomers and other analytes that remain without a method for their analysis.

Discrimination of 2-3-component mixtures of organic analytes by a “fluorescent tongue”: A pilot study

We suggest a new strategy for obtaining fluorescent fingerprints of samples for their recognition using chemometric treatment. The technique is based on the use of a blend of fluorophores of various nature emitting over a wide range of spectrum and changing the emission intensity to a different extent in the presence of different analytes. In this feasibility study we prepared a blend of up to 5 fluorophores covering the emission range of 360–800nm: quantum dots CdSe/CdS/ZnS and PbS, a Schiff base produced from o-phthalic dialdehyde and polyethyleneimine, and fluorescein and rhodamine B attached to silica nanoparticles. We showed that the attachment of the fluorescent dyes to a nanoadsorbent appreciably increased their responsiveness to quenching/dequenching by organic compounds. As model analytes, we used amikacin, sulfamethoxazole, piracetam and chloramphenicol and their mixtures in equal concentrations. To evaluate the discrimination ability of the fluorophore blends, their fluorescence spectra obtained in the presence of the model analytes were treated by principal component analysis (PCA). All the individual analytes and their 2- and 3-component mixtures were fully discriminated by using a blend of 4 fluorophores. When necessary, the efficiency of discrimination was quantified as Mahalanobis distances. A UV–vis fingerprint method applied to the same synthetic mixtures was found to provide poorer discrimination.