Use Of Chemometric Approaches Research Articles

Methodological approach for the automatic discrimination of pictorial materials using fused hyperspectral imaging data from the visible to mid-infrared range coupled with machine learning methods

Hyperspectral imaging represents a powerful tool for the study of artwork’s materials since it permits to obtain simultaneously information about the spectral behavior of the materials and their spatial distribution. By combining hyperspectral images performed on several spectral intervals (visible, near infrared and mid-infrared ranges) through chemometric methods it is possible to clearly identify most of the materials used in painting (i.e., pigments, dyes, varnishes, and binders). Moreover, in the last decade, the development of machine learning algorithms coupled with comprehensive and continuously updated databases opens new perspective on the automatic recognition of pictorial materials.In this work, we propose a novel procedure to support the automatic discrimination of pictorial materials consisting in a mid-level data fusion on imaging datasets coming from two commercial hyperspectral cameras, in the 400–1000 nm and 1000–2500 nm spectral ranges, respectively, and a MAcroscopic Fourier Transform InfRared scanning in reflection mode (MA-rFTIR), in the 7000 to 350 cm-1 (1428 nm − 28 μm) spectral range. The automatic recognition of 102 pictorial mock-ups from the fused data is performed by testing the performance of ECOC-SVM (error-correcting output coding and support vector machine) model obtaining a good predictive result with only few pixels that are confused with other classes. The methodology described in this paper demonstrates that an accurate paint layer multiclass recognition is feasible, and the use of chemometric approaches solves some challenges involving the study of materials.

The differentiation of 2,5-dimethoxy-N-(N-methoxybenzyl)phenethylamine (NBOMe) isomers using GC retention indices and multivariate analysis of ion abundances in electron ionization mass spectra

Synthetic phenethylamine derivatives known as 2,5-dimethoxy-N-(N-methoxybenzyl)phenethylamines (NBOMes) are a common class of novel psychoactive substances (NPS) that are causing many accidental deaths across the United States. Many derivatives are now banned at the federal and state levels, but such control requires reliable identification of the different positional isomers. This manuscript helps establish retention indices and characteristic ion ratios that can be used to distinguish between the positional isomers of 25C-NBOMe and 25I-NBOMe. This manuscript also provides additional support for the ortho effect as a reliable, general, fragmentation mechanism to differentiate positional isomers of NBOMes in electron ionization (EI) mass spectra.The retention indices and fragment ion abundances of the positional isomers of 25C-NBOMe and 25I-NBOMe were measured on two instruments using three different GC columns and parameters. The measured retention indices for the six compounds on three different 5% diphenyl columns are as follows: ortho-25C-NBOMe = 2614 ± 15; meta-25C-NBOMe = 2666 ± 13; para-25C-NBOMe = 2692 ± 13; ortho-25I-NBOMe = 2821 ± 16; meta-25I-NBOMe = 2877 ± 15; and para-25I-NBOMe = 2904 ± 12, where the errors represent the 95% confidence interval of the measurements. Principal component analysis (PCA) and canonical discriminant analysis (CDA) were used, respectively, to assess the variance and classification of NBOMe isomers based on the 15 most abundant ions relative to the base peak. The CDA classification accuracy for the six NBOMe compounds was 99.5% when the data set included spectra from three instrumental setups and the widest range of concentrations. Isomer classification was greater than 99.9% within an instrument and excluding low abundance spectra. These results support the use of chemometric approaches for the classification of unknown compounds, even when non-ideal lower-abundance spectra are used for classification.

Планирование эксперимента в оптимизации синтеза ванкомицин-селективных "исскуственных рецепторов"

The work is focused on the use of chemometric approach to "design of experiment", implemented using MODDE 9.0 software package to optimize the synthesis of the vancomycin-selective nanoparticles ("artificial receptor" based on molecularly imprinted polymers) in an automatic reactor in order to obtain its maximum quantitative yield.

Chemometric approach to optimize the operational parameters of ESI for the determination of contaminants of emerging concern in aqueous matrices by LC-IT-TOF-HRMS

Contaminants of emerging concern are organic compounds used in large quantities by the society for various purposes. They have shown biological activity at low concentrations, which gives great environmental relevance. The difficulty to detect and quantify contaminants of emerging concern in the environment stimulates the development of appropriate analytical methods. In this work a chemometric approach to positive and negative electrospray ionization (ESI) optimization for the simultaneous determination of contaminants of emerging concern in water samples by liquid chromatography-ion trap-time of flight-high resolution mass spectrometry (LC-IT-TOF-HRMS) was applied. Three types of phase modifiers were used: formic acid, ammonium hydroxide and formic acid/ammonium formate. The effects of operational parameters such as mobile phase modifier concentrations, mobile phase flow rate, heating block temperature and drying gas flow rate were evaluated by the 24−1 fractional factorial experimental design, resolution IV, in the screening phase and by Doehlert experimental design. Initial factorial experimental design studies indicated that the phase modifier ammonium hydroxide was more efficient compared to the other evaluated modifiers. It provided higher ion intensities to the majority of analytes. Doehlert experimental design allowed finding a region indicative of the optimum experimental conditions for most analytes. The best experimental condition observed was 3.5mM ammonium hydroxide concentration; 0.0917mL/min of mobile phase; 300°C heating block temperature; and drying gas at 200kPa. These optimized parameters resulted in decreased detection limits of the method. The optimized method was applied to the evaluation of water samples coming from the Rio Doce basin — Minas Gerais/Brazil utilizing multivariate exploratory techniques such as principal component analysis and Kohonen neural network. In this way, the use of chemometric approach showed to be a promising way to optimize the simultaneous determination of twenty-one contaminants of emerging concern in aqueous matrices by LC-IT-TOF-HRMS using ESI.

Determination of the Thickness of Silazane-Based SiOx Coatings in the Submicrometer Range by Near-Infrared Reflection Spectroscopy

The thickness of thin silica layers in the submicrometer range, i.e., between about 150 and 700 nm, was determined by near-infrared (NIR) reflection spectroscopy. Silica layers were prepared by spin-coating of perhydropolysilazane (PHPS) on silicon wafers or poly(ethylene terephthalate) (PET) foil and subsequent conversion of the PHPS into SiO(x) by vacuum ultraviolet (VUV) irradiation at 172 nm. Since the NIR spectra of the inorganic layers do not show overtone and combination bands, analysis is based on tiny differences in reflectance of samples provided with layers of different thicknesses. Quantitative investigations were carried out by use of chemometric approaches on the basis of the partial least squares (PLS) algorithm. Optimization of the chemometric models was achieved by systematic variation of the preprocessing of the spectra before application of the PLS regression. The root mean square error of prediction (RMSEP) and the coefficient of determination R(2) were used for the evaluation of the various pretreatment strategies. Reference data for the calibration procedures were obtained by means of gravimetry. The maximum error for the determination of the thickness was estimated to be on the order of 20%. The method was used to monitor the homogeneity of the thickness of silica layers made by use of a pilot scale coating machine. Thickness profiles recorded by NIR spectroscopy showed clear differences between layers with uniform or non-uniform quality of the application. Moreover, a close correlation of the profiles with the average coating weights determined by gravimetry was found.

Simultaneous determination of Fe(II) and Fe(III) in pharmaceutical formulations with chromogenic mixed reagent by using principal component artificial neural network and multivariate calibration

The use of chemometric approaches for the simultaneous determination of Fe(II) and Fe(III) ions has been explored by means of a two component reagent. Mixed reagents of 1,10-phenanthroline and thiocyanate were used as a selective chromogenic system for speciation of Fe(II) and Fe(III). Although the complexes of Fe(II) and Fe(III) with mixed reagent show a spectral overlap, they have been simultaneously determined with chemometric approaches, such as principal component artificial neural network (PC-ANN), principal component regression (PCR) and partial least squares (PLS). A set of synthetic mixtures of Fe(II) and Fe(III) was evaluated and the results obtained by the applications of these chemometric approaches were discussed and compared. It was found that the PC-ANN and PLS methods afforded better precision relatively than its of PCR. PC-ANN and PLS methods were also applied satisfactorily in determination of Fe(II) and Fe(III) in pharmaceutical samples.

Direct screening and confirmation of benzene, toluene, ethylbenzene and xylenes in water

A novel, straightforward sample screening method for benzene, toluene, ethylbenzene and xylene isomers (BTEX) in water is proposed. The method is based on the direct coupling of a headspace (HS) sampler with a mass spectrometer by using a chromatographic column heated to 200 °C as an interface. Samples are acidified and subjected to the headspace generation process, the resulting volatile fraction being directly introduced into the source of the mass spectrometer. The large number of samples to be analyzed and the wide range of m/ z ratios scanned (75–110) suggest the use of chemometric approaches based on pattern recognition techniques (PRT). For sample classification purposes, the detection limit of the method (overall response 4.0 ng/ml BTEX) was selected as the cut-off level. The method proved highly reliable as no false negatives were obtained at the legally established concentration levels. Positive water samples were confirmed by using the same instrumental setup as in the screening method, but by heating the chromatographic column at 40–200 °C to separate the analytes.

Voltammetric determination of butylated hydroxyanisole, butylated hydroxytoluene, propyl gallate and tert-butylhydroquinone by use of chemometric approaches

The voltammetric behavior of synthetic food antioxidants, such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate (PG) and tert-butylhydroquinone (TBHQ), at a glassy carbon electrode in solution of 0.1 mol l −1 perchloric acid containing 1% methanol has been investigated. The obtained linear sweep voltammograms (LSV) showed that all these four compounds have well-defined oxidation waves with peak potentials of 629, 818, 599 and 501 mV for BHA, BHT, PG and TBHQ, respectively. Linear calibration graphs were also obtained in the concentration ranges of 0.5–15.0, 0.5–8.0, 1.0–15.0 and 1.0–15.0 mg l −1 for BHA, BHT, PG and TBHQ, respectively. However, the voltammetric peaks of these antioxidants seriously overlap and it is difficult to determine them individually from a mixture without prior separation. In this work, a method for simultaneous determination of these antioxidants, based on their oxidation at the glassy carbon electrode, with the aid of chemometric approaches, such as classical least squares (CLS), principal component regression (PCR) and partial least squares (PLS), has been developed. The method was applied to determine the four antioxidants in a set of synthetic mixtures and several commercial food samples; in general, satisfactory results were obtained.