Partial Least-squares Multivariate Calibration Research Articles

Multiple emission line analysis for improved isotopic determination of uranium — a computer simulation study

Forty-three atomic emission lines for 235U and 238U were compiled for computer simulation of isotopic analysis using laser induced breakdown spectroscopy (LIBS). The spectral line profile was assumed to be Lorentzian in shape and the magnitude of three common types of noises (detector-read, photon-shot and flicker) were experimentally determined and incorporated into the simulation. Precision and root mean square error of prediction (RMSEP) for isotopic analysis of a single U line were simulated, and it was found that analytical performance (precision) primarily depended on the signal-to-background ratio (SBR) and net intensity of the emission line, rather than on the magnitude of isotopic splitting (IS), when partial least squares (PLS) was used for calibration. This is because PLS multivariate calibration can be performed correctly even when the spectra are only partially resolved, which in turn relaxes the requirement on having IS larger than the spectral resolution. The analytical performance was found to improve with multiple-line analysis. Depending on the criteria (e.g., SBR, net intensity, magnitude of IS, or best single-line performance) used in sorting the spectral lines into the multiline pool, improvement factors ranging from 2× to 9× were obtained. The absolute uncertainty of isotopic analysis is practically constant and independent of isotopic abundance, which makes experimental estimation of the detection limit in isotopic analysis straightforward because one can experimentally measure this uncertainty with one arbitrary and conveniently chosen isotopic standard and then estimate the detection limit through simple extrapolation.

An integrated approach to the simultaneous selection of variables, mathematical pre-processing and calibration samples in partial least-squares multivariate calibration

A new optimization strategy for multivariate partial-least-squares (PLS) regression analysis is described. It was achieved by integrating three efficient strategies to improve PLS calibration models: (1) variable selection based on ant colony optimization, (2) mathematical pre-processing selection by a genetic algorithm, and (3) sample selection through a distance-based procedure. Outlier detection has also been included as part of the model optimization. All the above procedures have been combined into a single algorithm, whose aim is to find the best PLS calibration model within a Monte Carlo-type philosophy. Simulated and experimental examples are employed to illustrate the success of the proposed approach.

Arabica and Robusta Coffees: Identification of Major Polar Compounds and Quantification of Blends by Direct-Infusion Electrospray Ionization–Mass Spectrometry

Considering that illegal admixture of robusta coffee into high-quality arabica coffee is an important task in coffee analysis, we evaluated the use of direct-infusion electrospray ionization-mass spectrometry (ESI-MS) data combined with the partial least-squares (PLS) multivariate calibration technique as a fast way to detect and quantify arabica coffee adulterations by robusta coffee. A total of 16 PLS models were built using ESI± quadrupole time-of-flight (QTOF) and ESI± Fourier transform ion cyclotron resonance (FT-ICR) MS data from hot aqueous extracts of certified coffee samples. The model using the 30 more abundant ions detected by ES+ FT-ICR MS produced the most accurate coffee blend percentage prediction, and thus, it was later successfully employed to predict the blend composition of commercial robusta and arabica coffee. In addition, ESI± FT-ICR MS analysis allowed for the identification of 22 compounds in the arabica coffee and 20 compounds in the robusta coffee, mostly phenolics.

Potentiality of partial least-squares multivariate calibration in the spectrophotometric analysis of binary mixtures of purine bases

A partial least-squares (PLS) modeling was developed for the simultaneous spectrophotometric determination of adenine (AD) and guanine (GU). The determination of these analytes is pharmacologically necessary. Multivariate calibration is used because of spectral overlapping. The calibration set contained AD and GU in the concentration range of 1.4–20.3 and 1.5–25.7 μg cm−3, respectively. The absorption spectra were recorded from 200 to 300 nm. The predicted residual error sum-of-squares for AD and GU was 0.0500 and 0.4000 for number of principal components 3 and 2, respectively. The root mean square error of prediction for AD and GU was 0.0913 and 0.2582, respectively. The limits of detection were 0.02 and 0.03 μg cm−3 for AD and GU, respectively. The proposed method allows the simultaneous determination of AD and GU in spiked real matrixes of human urine, serum, and plasma.

Simultaneous Spectrophotometric Determination of Iron, Cobalt and Copper by Partial Least-Squares Calibration Method in Micellar Medium

Iron, cobalt and copper are metals, which appear together in many real samples, both natural and artificial. Recently a classical univariate micellar colorimetric method has been developed for determination of these metal ions. The organized molecular assemblies such as micelles are used in spectroscopic measurements due to their possible effects on the systems of interest. The ability of micellar systems to solublize slightly insoluble or even very insoluble complexes and/or ligands has been used to enhance the analytical merit of the given methods. The ability of micelles to solublize complexes in aqueous solutions can eliminate the need for non-aqueous extraction step in a given analysis. The simultaneous determination of Fe, Co and Cu was carried out as 1-nitroso-2-naphtol complexes in presence of aqueous solution of nonionic surfactant of Triton-X100. A partial least-squares multivariate calibration method for the analysis of ternary mixtures of Fe, Co and Cu was developed. For individual determinations, molar absorptivities and the limit of detection were obtained, respectively. The total relative standard error for applying the method on synthetic samples was 2.02%. The proposed method was also successfully when applied to the determination of Fe, Co and Cu in several synthetic alloy solutions

Spectrophotometric multicomponent analysis of a mixture of chlorhexidine hydrochloride and lidocaine hydrochloride in pharmaceutical formulation using derivative spectrophotometry and partial least-squares multivariate calibration

Two spectrophotometric methods were applied to the simultaneous assay of chlorhexidine hydrochloride (CHL) and lidocaine hydrochloride (LIH) in pharmaceutical formulations. Using derivative spectrophotometry, CHL was determined by measurement of its first derivative signal at 290 nm (peak to zero amplitude) in the concentration range 5–9 μg/mL, and LIH was analysed by measurement of its second derivative signals at 272 and 276 nm (peak to peak amplitude) in the concentration range 160–480 μg/mL. With the partial least-squares (PLS-2), the experimental calibration matrix was constructed using 9 samples. The concentration ranges considered were 5–7 μg/mL for CHL and 220, 240, 260 μg/mL for LIH. The absorbances were recorded between 240 and 310 nm at every 5 nm.

Determination of octane numbers for clean gasoline using dielectric spectroscopy

In the present work, dielectric spectroscopy (DES) in association with partial least squares (PLS) multivariate calibration method was employed to determine octane numbers (research octane number or RON and motor octane number or MON) of clean gasoline samples. The factor number included in PLS model was obtained according to the lowest sum of squares of predicted residual error (PRESS) in calibration set. The performance of the final model was evaluated according to PRESS and correlation coefficient ( R). The optimal factor numbers are 9 in both RON and MON PLS calibration models, which were achieved with PRESS = 2.74 and R = 0.9598 in RON calibration set and the lowest PRESS = 2.72 and R = 0.8983 in MON calibration set. In validation set, PRESS = 1.00 and R = 0.9552 for RON and PRESS = 0.47 and R = 0.9105 for MON were obtained. Results indicated that PLS multivariate calibration models based on DES data were proven suitable as a practical analytical method for predicting octane numbers of clean gasoline.

Individual and simultaneous determinations of phenothiazine drugs using PCR, PLS and (OSC)-PLS multivariate calibration methods

Individual and simultaneous determinations of some phenothiazine drugs are described. The individual determination method is based on the reaction of chlorpromazine hydrochloride (CPH), promethazine hydrochloride (PH), trifluoperazine hydrochloride (TFPH), trimipramine maleate (TPM) and thioridazine hydrochloride (TRDH) with complex of [Fe(Bpy)3]3+. In the presence of phenothiazine derivatives, [Fe(Bpy)3]3+ is reduced easily to the colored complex [Fe(Bpy)3]2+, which shows an absorption maximum at 525 nm. The individual method is highly sensitive and suitable for 0.3-190 ?g ml-1 concentrations, with detection limits in the range 0.18-2.46 ?g ml-1. Simultaneous kinetic-spectrophotometric determination of ternary mixture of CPH, PH and TPM using principal component regression (PCR), partial least squares (PLS) and orthogonal signal correction (OSC)-PLS multivariate calibration methods is also described. The simultaneous methods are based on the difference observed in the reduction rate of the [Fe(Bpy)3]3+ complex with CPH, PH and TPM in acidic media. The results showed that the simultaneous determination of CPH, PH and TPM can be performed in the concentration ranges of 0.5-120.0, 0.3-80.0 and 5.0-100.0 ?g ml-1, respectively, for three methods (PCR, PLS and OSC-PLS). The root mean square errors of prediction (RMSEP) of CPH, PH and TPM were 0.346, 0.663 and 0.820 (for PCR) 0.317, 0.659 and 0.830 (for PLS) and 0.087, 0.124 and 0.085 (for OSC-PLS), respectively. The proposed methods were successfully applied to the individual and simultaneous determination of phenothiazine derivatives in pharmaceutical preparations, the results of which compared well with those obtained by the official method, and several synthetic (spiked) samples, whereby satisfactory results were obtained.

Resolution of Ofloxacin–Ciprofloxacin and Ofloxacin–Norfloxacin Binary Mixtures by Flow-Injection Chemiluminescence in Combination with Partial Least Squares Multivariate Calibration

A flow-injection chemiluminescence (CL) method is described for the determination of ciprofloxacin (CIP), norfloxacin (NOR) and ofloxacin (OFL), commonly used antibiotics of the fluoroquinolones family. The method is based on the CL reaction of the fluoroquinolones with tris(2,2'-bipyridyl) ruthenium(II) and Ce (IV), in sulfuric acid medium. The maximum CL emission, given at 0.45 min for CIP, at 0.35 min for NOR and at 0.04 min for OFL, respectively, were measured, allowing the simple application of the proposed method to the routine analysis of the antibiotics. The methods were applied to the determination of CIP, NOR and OFL, in several pharmaceutical preparations, with very satisfactory results, and validated by a previously reported HPLC method. The time-resolved equipment allowed the measurement of the kinetic evolution of the chemiluminescence signals. In base to the differences in the kinetic behaviour of ofloxacin with respect to ciprofloxacin and norfloxacin, binary mixtures of the drugs were resolved by using the time-resolved chemiluminescence signals, in combination with first-order partial least-squares (PLS) multivariate calibration.

Kinetics of the electrochemical oxidation of 2-nitrophenol and 4-nitrophenol studied by in situ UV spectroscopy and chemometrics

Here we report on the elimination of 4-nitrophenol (4-NPh) and 2-nitrophenol (2-NPh) from aqueous solutions by electrochemical oxidation at the dimensionally stable anodes (DSA) Ti/IrO 2–SnO 2–Sb 2O 5. The ternary oxide electrodes show high catalytic activity for the electrochemical oxidation of nitrophenolic compounds. UV–vis spectroscopy was employed to in situ monitor time-dependent concentration changes during the electrochemical oxidation of the 2-NPh and 4-NPh. A kinetic analysis of the electrochemical oxidation of 2-NPh, 4-NPh and a mixture of the two has been carried out. The electrochemical oxidation of 4-NPh and 2-NPh is governed by the hydroxyl radical reaction and obeys the first-order kinetics with the overall apparent activation energy of 8.3 and 9.2 kJ mol −1, respectively. Partial least squares (PLS) regression was performed to resolve the highly overlapping spectrophotometric signals measured from the mixture of 4-NPh and 2-NPh. In situ UV–vis spectroscopic measurements in combination with PLS multivariate calibration enabled us to determine the competitive effects during the electrochemical treatment of variety of mixtures of 2-NPh and 4-NPh, showing that the presence of 2-NPh inhibits the electrochemical oxidation of 4-NPh.

Determination of Ternary Mixtures of Dextromethorphan Hydrobromide, Pseudoephedrine Hydrochloride and Triprolidine Hydrochloride in Syrups by Partial Least-Squares Multivariate Calibration

Determination of Ternary Mixtures of Dextromethorphan Hydrobromide, Pseudoephedrine Hydrochloride and Triprolidine Hydrochloride in Syrups by Partial Least-Squares Multivariate Calibration

Rapid and Simple Method for Simultaneous Determination of Escin and Diethylamine Salicylate in Pharmaceutical Preparations by Partial Least-Squares Multivariate Calibration

A partial least-squares calibration (PLS) method has been developed for simultaneous quantitative determination of escin (ES) and diethylamine salicylate (DAS) in pharmaceutical preparations. The resolution of these mixtures has been accomplished without prior separation or derivatisation, by using partial least-squares (PLS-2) regression analysis of electronic absorption spectral data. The experimental calibration matrix was constructed with 9 samples. The concentration ranges considered were 10, 20, 30 (ES) and 40, 50, 60 (DAS) μg cm−3. The absorbances were recorded between 200 and 325 nm every 5 nm. Proposed method was compared with conventional spectrophotometric method. The results show that PLS-2 is a simple, rapid, and accurate method applied to the determination of these compounds in pharmaceuticals.

Application of partial least-squares spectrophotometric-multivariate calibration to the determination of 2- sec-butyl-4,6-dinitrophenol (dinoseb) and 2,6-dinitro- p-cresol in industrial and water samples containing hydrocarbons

The present report describes the spectrophotometric determination of 2- sec-butyl-4,6-dinitrophenol (dinoseb) and 2,6-dinitro- p-cresol, two inhibitors of the styrene polimerization, in two very different types of matrices. One of them is present in an industrial distillation tower, and contains styrene and more than 60 hydrocarbons. Partial least-squares (PLS) multivariate calibration enabled us to determine both analytes without the necessity of applying extraction processes, as well as significantly reducing the time involved in the currently applied analytical method. The limit of detection for both compounds, referred to the industrial sample, was 1.0 μg ml −1, for concentration ranges of 0–261 μg ml −1 (dinoseb) and 0–448 μg ml −1 (2,6-dinitro- p-cresol). The method was successfully applied to real samples. In addition, dinoseb was simultaneously determined with 2,6-dinitro- p-cresol in hydrocarbon–water mixtures by PLS calibration. In this type of samples, the concentrations are significantly lower and thus a pre-concentration step through solid-phase extraction preceded the spectrophotometric measurements. The limits of detection for the simultaneous determination of dinoseb and 2,6-dinitro- p-cresol were 1.2 and 1.0 ng ml −1, respectively.

Simultaneous spectrophotometric determination of Fe(III), Al(III) and Cu(II) by partial least-squares calibration method

A spectrophotometric method for simultaneous determination of Fe(III), Al(III) and Cu(II) using Alizarin Red S as a chelating agent was developed. The parameters controlling behavior of the system were investigated and optimum conditions were selected. A partial least-squares multivariate calibration method was used for the analysis of ternary mixtures of Fe(III), Al(III) and Cu(II) over the range of 450–6000, 140–4000 and 450–15000ngml−1, respectively. Absorbance data were taken between 400 and 800nm. Applying this method to simultaneous determination of these metal ions in several synthetic alloy solutions with total relative standard error of less than 5% validated the proposed method.

Solid-phase spectrofluorimetric determination of acetylsalicylic acid and caffeine in pharmaceutical preparations using partial least-squares multivariate calibration

PLS-1, a variant of the partial least-squares algorithm was used for the solid-phase spectrofluorimetric determination of acetylsalicylic acid (ASA) and caffeine (CF) in pharmaceutical formulations. The method allows the simultaneous quantification of the analytes, as the closely overlapping spectral bands are efficiently solved. Sample preparation prior to analysis is not required. The calibration set consisted of 83 samples with 50–170 mg g −1 ASA plus 5–20 mg g −1 CF; another set of 25 samples was used for external validation. Agreement between predicted and experimental concentrations was fair ( r = 0.987 and 0.974 for ASA and CF models). For both models, the prediction performance was evaluated in terms of the coefficient of variability (CV), relative predictive determination (RPD), and ratio error range (RER). The final PLS-1 models were used for the determination of ASA and CF in pharmaceutical formulations.

Measurements and quality assessments of near-infrared plasma glucose spectra in the combination band region using a scanning filter spectrometer

Near-infrared measurements of glucose in human plasma are performed using a custom, rapid, high-throughput filter-based spectrometer covering a spectral range between 2080 and 2315 nm. Quality of the measured glucose signals is quantified through the use of two figures of merit: selectivity and limit of detection. Selectivity measures the uniqueness of the glucose spectrum from among the interfering spectra. Limit of detection measures the smallest glucose concentration change detectable. The proposed system, which includes the spectroscopic hardware and a spectral preprocessing algorithm, is shown to produce a selectivity value of 0.57, with zero being nonselective and one being fully selective, and a limit of detection value of 2.2 mM. Prediction of an independent dataset is also performed using net analyte signal-based and partial least-squares multivariate calibration techniques, which produce standard error of prediction values of 1.14 and 1.45 mM, respectively.

Fast spectrophotometric determination of fluoride in ground waters by flow injection using partial least-squares calibration

The presence of sulphate constitutes a serious interference in the usual zirconium lake-based spectrophotometric method for the determination of fluoride in water. In this report, full spectral data have been recorded for the zirconium lake of 2-(parasulfophenylazo)-1,8-dihydroxy-3,6-naphthalene-disulfonate (SPADNS) in the simultaneous presence of fluoride and sulphate, as obtained with a flow injection system with a diode-array detector. The information has been processed with partial least-squares (PLS) multivariate calibration. Adequate modeling using a sixteen-sample calibration set allows fluoride to be determined in ground waters by the automated flow injection method, even in the presence of sulphate in concentrations up to 1000 mg l −1. In the calibration range 0–1.50 mg l −1 for fluoride, the limit of detection is 0.1 mg l −1. The fluoride contents in real samples, as determined with the present method, were satisfactorily compared with those provided by ion selective potentiometry.

Simultaneous fluorometric determination of chlorophylls a and B and pheophytins a and B in olive oil by partial least-squares calibration.

The resolution of quaternary mixtures of chlorophylls a and b and pheophytins a and b has been accomplished by partial least-squares (PLS) multivariate calibration, applied to the fluorescence signals of these pigments. The total luminescence information of the compounds has been used to optimize the spectral data set to perform the calibration. After preliminary studies, a method is described in acetone media, to avoid emulsions with the olive oil samples. Different scanning paths have been selected for each method. For the simultaneous determination of the pigments in olive oil samples, a comparative study of the results found by using excitation, emission, and synchronous spectral data, as analytical signal, was performed. The excitation spectra were selected as the better analytical signals for the determination of the pigments in olive oil samples. The optimum wavelength range to record the excitation spectra (lambda(em) = 662 nm) was selected to minimize the contribution of pheophytin a and to maximize the contribution of the other pigments, which are the minor constituents in olive oil. Determination of these pigments in olive oil samples was effected from the excitation spectra of dissolutions o suitable aliquots in acetone. Recovery values from olive oil, spiked with chlorophylls a and b and pheophytins a and b, were in the ranges of 70-112, 71-111, 76-105, and 82-109%, respectively.

Two derivative spectrophotometric methods for the simultaneous determination of lovastatin combined with three antioxidants

A zero crossing and an algorithm bivariate calibration derivative method for the simultaneous determination of lovastatin combined separately with three antioxidants (ascorbic acid, quercetin and gallic acid) in synthetic mixtures are described. The aqueous or methanolic solutions obeyed Beer's law in the concentration ranges of 3.20–17.36 μg/ml for lovastatin, 1.76–8.80 μg/ml for ascorbic acid, 1.41–7.04 μg/ml for gallic acid and 1.84–9.20 μg/ml for quercetin, for both methods, respectively. In the second derivative ( 2D) zero crossing method measurements were carried out at 238.4 nm for lovastatin and 265.6 nm for ascorbic acid, 247.7 nm for lovastatin and 281.1 nm for quercetin, 251.8 nm for lovastatin and 267.6 nm for gallic acid. In the first derivative ( 1D) bivariate spectrophotometric method an optimum pair of wavelengths was chosen for the determination of different binary mixtures. The proposed procedures were successfully applied to the simultaneous determination of lovastatin and different antioxidants in mixtures with high percentage of recovery, 98.3–100.4% for lovastatin, 98.3–98.6% for ascorbic acid, 99.0–99.8% for quercetin and 100.5–101.1% for gallic acid and good precision. In addition, the results from the above procedures were verified by using partial least-squares (PLS) multivariate calibration method.

Comparison between different data pre-treatment methods in the analysis of forage samples using near-infrared diffuse reflectance spectroscopy and partial least-squares multivariate calibration method

Moisture and protein content of alfalfa samples from Catalonia (Spain) have been analyzed by near-infrared (NIR) diffuse reflectance spectroscopy and multivariate calibration methods. In order to remove systematic variation in experimental data, such as base-line and multiplicative scatter effects, the evaluation of different data pre-processing methods is performed. Different figures of merit are used for quality assessment and comparison of these pre-treatment methods.