Comparison of UV derivative-spectrophotometry and partial least-squares (PLS-1) calibration for determination of methotrexate and leucovorin in biological fluids

Binary mixtures of methotrexate (MTX) and leucovorin (LV) have been resolved by application of first-derivative spectrophotometry and partial least squares calibration (PLS-1). By measuring the first-derivative signals of MTX and LV at 354 and 300 nm, respectively, simultaneous determination was possible. The mean recoveries for urine samples were 91 and 96% for MTX and LV, respectively. Partial least squares (PLS-1) multivariate calibration has been applied to the determination of these compounds in serum and in urine without pretreatment of the samples. The absorption spectra of serum or urine samples spiked with methotrexate and/or leucovorin, were used to optimize the calibration matrixes by the PLS-1 method. The sensitivity and selectivity of the proposed procedures were calculated. Mean recoveries were 101 and 97% for MTX and LV, respectively, for serum samples, and 101 and 98% for MTX and LV, respectively, for urine samples.     

Multicomponent determination of the pesticide naptalam and its metabolites in river water, by applying partial least squares calibration to the derivative spectrophotometric signals

A multivariate calibration method, partial least squares (types PLS-1 and PLS-2), was applied to the simultaneous determination of naptalam (N-(1-naphthyl) phthalamic acid) and its metabolites N-(1-naphthyl) phthalimide and 1-naphthylamine in mixtures by UV-visible absorption spectrophotometry. The absorption and first-derivative absorption spectra of mixtures were used to perform the optimization of the calibration matrices by the PLS method. Two different experimental designs for the three-component mixtures are assayed and the results are discussed. The proposed method with the derivative spectra was applied to the determination of these analytes in river water at the ppb level.     

Simultaneous Determination of Timolol Maleate and Pilocarpine Hydrochloride in Ophthalmic Solutions by First Derivative UV Spectrophotometry and PLS-1 Multivariate Calibration

ABSTRACT

The use of UV spectrophotometry (first-derivative/zero-crossing and zero-order spectra/multivariate calibration) is reported for the analysis of two miotic agents in ophthalmic solutions. The resolution of these mixtures has been accomplished without prior separation or derivatisation by using: 1) first-derivative measurements at two appropriate zero-crossing points: λ₁ = 222 nm, where the absorption corresponding to excipients is negligible, and λ₂ = 307 nm, where the contribution of pilocarpine and excipients to the overall absorption is negligible, and 2) partial least squares (PLS-1) regression analysis of zero-order spectral data. Although the components show an important degree of spectral overlap, they have been simultaneously determined with high accuracy, and with no interference from ophthalmic solution excipients.     

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

Summary. 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.     

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 Dispersive Liquid�CLiquid Microextraction for the Analysis of Six Fungicides in Fruit Samples by GC�CECD

A novel approach for the determination of six fungicides (triadimefon, procymidone, hexaconazole, myclobutanil, diniconazole and iprodione) in fruit samples is presented. Analytes were extracted using the dispersive liquid?Cliquid microextraction technique and determined by GC?CECD. Parameters affecting the dispersive liquid?Cliquid microextraction performance, such as the kind and volume of extraction and dispersive solvents, extraction time and salt concentration, were studied and optimized. Under the optimum extraction conditions, the linearities of the method were obtained in the range of 0.5?C20.0 ??g kg^?1 for triadimefon, hexaconazole, diniconazole and procymidone, and 1.0?C40.0 ??g kg^?1 for myclobutanil and iprodione, with the correlation coefficients ranging from 0.9902 to 0.9995. The enrichment factors ranged from 685 to 820 and the extraction recoveries ranged from 81.3 to 98.4%. The relative standard deviations varied from 3.1 to 7.8%. The limits of detection of the method were in the range of 0.02?C0.12 ??g kg^?1. Results showed that the method we proposed can meet the requirements for the determination of target fungicides in fruit samples. Several compounds considered in this study were found in fruit samples.     

Simultaneous kinetic spectrophotometric determination of cyanide and thiocyanate using the partial least squares (PLS) regression

The partial least squares (PLS-1) calibration model based on spectrophotometric measurement, for the simultaneous determination of CN⁻ and SCN⁻ ions is described. The method is based on the difference in the rate of the reaction between CN⁻ and SCN⁻ ions with chloramine-T in a pH 4.0 buffer solution and at 30 °C. The produced cyanogen chloride (CNCl) reacts with pyridine and the product condenses with barbituric acid and forms a final colored product. The absorption kinetic profiles of the solutions were monitored by measuring absorbance at 578 nm in the time range 20-180 s after initiation of the reaction with 2 s intervals. The experimental calibration matrix for partial least squares (PLS-1) calibration was designed with 31 samples. The cross-validation method was used for selecting the number of factors. The results showed that simultaneous determination could be performed in the range 10.0-900.0 and 50.0-1200.0 ng mL⁻¹ for CN⁻ and SCN⁻ ions, respectively. The proposed method was successfully applied to the simultaneous determination of cyanide and thiocyanate in water samples.     

Multicomponent Chemometric Determination of Colorant Mixtures by Voltammetry

Abstract

A quantitative chemometric approach, iterative target transformation factor analysis (ITTFA), was applied to the simultaneous determination of mixtures of four food colorants (Amaranth, Sunset Yellow. Tartrazine and Ponceau 4R) by adsorptive voltammetry. The conventional and first-derivative voltammograms of the quaternary mixtures were used to perform the optimization of the calibration procedure by the ITTFA models. The proposed method was applied satisfactorily to the determination of a set of synthetic quaternary mixtures of colorant in phosphate/citric acid buffers (pH 5.7) and acceptable results were obtained. No significant advantages were found with the application of derivative technique in this voltammetric work.     

Simultaneous determination of iron, cobalt, nickel and copper by UV-visible spectrophotometry with multivariate calibration

A method for the simultaneous spectrophotometric determination of the divalent ions of iron, cobalt, nickel and copper based on the formation of their complexes with 1,5-bis(di-2-pyridylmethylene) thiocarbonohydrazide (DPTH) is proposed. The resolution of quaternary mixtures of these metallic ions was accomplished by several chemometric approaches. A comparative study of the results obtained for simultaneous determinations in mixture by using principal component regression (PCR) and partial least-squares regression (PLS-1 and PLS-2) for absorbance, first-derivative and second-derivative data is presented. In general, the best recovery values are obtained by the PLS-2 method for absorbance data. This procedure allows the simultaneous determination of the cited ions in alloys and biological materials Good reliability of the determination was proved.     

Trace determination of carbendazim, fuberidazole and thiabendazole in water by application of multivariate calibration to cross-sections of three-dimensional excitation-emission matrix fluorescence

The simultaneous determination of carbendazim, fuberidazole and thiabendazole was accomplished by cross-section (CS) fluorimetry in combination with multivariate calibration algorithms. The total luminescence information of the compounds was used to optimise the linear trajectories of the CS. A comparison between principal component regression (PCR) and two partial least squares (PLS) algorithms, PLS-1 and PLS-2, with different pre-processing methodologies was made. The final model, which applied the PLS-1 method, built using pesticide standard and emission spectra, was successfully used for the determination of these compounds in synthetic mixtures. However, a different PLS-1 multivariate calibration model, based on CS through the total luminescence spectroscopic data, was necessary for determining the cited pesticides in water samples. Mean centring was the best pre-processing technique in both PLS-1 models. This later calibration model was built from ultra-pure water samples spiked with known carbendazim, fuberidazole and thiabendazole concentrations, after solid-phase extraction (SPE). The method, which had a precision better than 5%, was shown to be suitable for carbendazim, fuberidazole and thiabendazole monitoring in water samples at trace levels.     

Simultaneous fluorimetric determination of glyphosate and its metabolite, aminomethylphosphonic acid, in water, previous derivatization with NBD-Cl and by partial least squares calibration (PLS)

The reactions of 4-chloro-7-nitrobenzofurazan (NBD-Cl) with glyphosate (GLY) and with its main metabolite, aminomethylphosphonic acid (AMPA), have been studied. The resolution of binary mixtures of glyphosate and aminomethylphosphonic acid has been accomplished by partial least squares (PLS) multivariate calibration. The method of determination is based on the fluorescence emission of the derivatives formed in presence of NBD-Cl at 90 °C, in methanol and in basic medium. The dynamic ranges of the methods were comprised between 10 and 150 μg l⁻¹ for GLY and between 10 and 200 μg l⁻¹ for AMPA, being the detection limits 2 and 5.4 μg l⁻¹ for GLY and AMPA, respectively. The total luminiscence information of the derivatives has been used to optimize the spectral data set to perform the calibration, by analysis of the three-dimensional excitation-emission matrices. A comparison between the predictive ability of the multivariate calibration method, partial least squares type 1 (PLS-1), on two spectral data sets, emission and synchronous spectra, has been performed. The PLS-1 method, applied to the emission spectra, has been selected as optimum. The proposed method has been applied to the simultaneous determination of GLY and AMPA in river water. For concentrations ranging from 100 to 600 μg l⁻¹ of each compound in the samples, analytical recoveries range from 83 to 94% for GLY and from 104 to 120% for AMPA.     

Cross-sections of spectrochromatograms for the resolution of overlapping peaks in diode-array high-performance liquid-chromatography

Multi-wavelength detectors offer improved detection capabilities for liquid chromatographic methods, but require multivariate approaches to utilise all the available information. The photodiode-array detector in high-performance liquid chromatography (HPLC) generates a three-dimensional data matrix, which is conventionally presented as an isometric projection or a contour plot. In this work, a new graphical technique is described for improving the quantitative results obtained from HPLC, using the available spectrochromatographic information in both the time and wavelength domains. The technique consists of performing cross-sections through the data matrix to obtain the maximum analytical information for each of the analytes. Hence, the resolution of overlapping peaks and the sensitivity in the determination are optimised. In order to demonstrate the validity and simplicity of the approach, the method has been applied to the resolution of synthetic mixtures of iprodione, procymidone and chlorothalonil. Also, the method has been satisfactorily applied to the simultaneous determination of the pesticides in environmental groundwater samples.     

Simultaneous First-Derivative Spectrophotometric Determination of Nickel and Manganese Complexes with 2-(2-Pyridylmethyleneamino)phenol

Abstract

A method is proposed for the simultaneous determination of nickel and manganese by first-derivative spectrophotometry based on their reactions with 2-(2-pyridylmethyleneamino)phenol (PMAP) Schiff base. The method allows the determination of Ni and Mn in the concentration range 0.3–3.0 μg ml^?1 in mixtures with their ten-fold concentration ratio. The method has been applied for Ni and Mn determination in bronzes. To optimize the experimental conditions for spectrophotometric determination of Mn with PMAP stability constants at different pH values have been determined. A critical evaluation of the proposed method was performed by statistical analysis of the experimental data.     

Multicomponent determination of pesticides in vegetables by gas chromatography with mass spectrometric detection and multivariate calibration

Three multivariate calibration methods, partial least squares (PLS-1 and PLS-2) and principal component regression (PCR), were applied for the first time to the simultaneous determination of a mixture of six pesticides in vegetables samples by gas chromatography with mass spectrometric detection (GC-MS). PLS-1 method showed better prediction ability than PLS-2 and PCR methods. The GC-MS chromatograms obtained of vegetable samples spiked with the target pesticides were used to build the calibration matrix. The PLS-1 models were evaluated by predicting the concentrations of independent test samples. Also, the proposed models were successfully applied for the determination of these pesticides in vegetable samples after an extraction step with dichloromethane. By using the first derivative signals in PLS-1 models, simultaneous determination of the compounds was not improved.     

Multivariate analysis of chlorophenols by diode array spectrophotometry

A multivariate-multicomponent analysis method for the determination of chlorophenols by diode array derivative spectrophotometry is proposed. The method is based on extraction of chlorophenols directly or as ion pairs with tetrabutylammonium as the counterion in chloroform at pH 9.1. Prediction and quantitative determinations (within the concentration range 3.0–15.0 mg liter⁻¹) of two-, three-, and four component mixtures were possible using multivariate calibration of first-derivative spectra and a multicomponent analysis computer program based on least-squares regression.     

Determination of the fungicide dichlone by normal and first-derivative spectrofluorimetry

The influence of solvents on the sensitivity of the spectrofluorimetric determination of dichlone (2,3-dichloro-1,4-naphthoquinone) is discussed. Linear normal and first-derivative calibration graphs are established for 10–50 μg ml^?1 dichlone; relative standard deviations are 3.8 and 2.2%, respectively. Application to synthetic mixtures is described.     

Compensation for matrix effects in gas chromatography–tandem mass spectrometry using a single point standard addition

One of the major problems in quantitative analysis of pesticide residues in food samples by gas chromatography–tandem mass spectrometry (GC–MS/MS) is the enhancement or the suppression, of the target analyte signals in matrix extracts. Potentially positive samples, which had previously been identified by a rapid screening method, were quantified using standard addition to compensate matrix effects. As example we performed a systematic study on the application of the standard addition calibration (SAC) method for the determination of 12 pesticides (acephate, bromopropylate, chlorpyrifos, cypermethrin, diazinon, etrimfos, heptenophos, iprodione, methamidophos, procymidone, tetradifon, and triadimefon) in two matrices (cucumber and orange) in the range of initial concentrations of 10–200 μg kg⁻¹. The influence of some factors, such as the minimum number of standard additions used (single, two, three or four points calibration), as well as the known amount of analyte added to the sample, is evaluated in order to obtain reliable results. Accurate quantification is achieved when a single point SAC at 200 μg kg⁻¹ was used, obtaining for all the cases recoveries between 70 and 120%. The proposed analytical approach only needs two injections per sample (blank and spiked extracted sample) to determine the final concentration of pesticide in positive samples.     

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.     

Resolution of Ternary and Quaternary Mixtures of Drugs in Pharmaceutical Preparations by Use of Spectrophotometric Data in Conjunction with PLS-1 and PLS-2 Data Processing Methods

Abstract

Two variants of partial least-squares methodology (PLS-1 and PLS-2) have been used for the analysis of ternary and quaternary mixtures of acetaminophen-acetylsalicylic acid-codeine and caffeine, respectively. This methodology permits the simultaneous quantification of the aforementioned drugs even with closely overlapping spectral bands without any separation step. The concentration ranges are 4.0–12.0, 0.2–1.0 and 4.0–12.0 μg·ml^?1 for acetaminophen-acetylsalicylic acid-codeine and 10.0–20.0, 6.0–16.0, 1.0–5.0 and 0.2–1.0 μg·ml^?1 for acetaminophen-acetylsalicylic acid-caffeine and codeine, respectively. A systematic study of the experimental data by applying an exhaustive statistical analysis to demostrate the validity of the proposed methods is presented. The results of the determination of these drugs in pharmaceutical preparations are also presented. The analytical results were quite good in all cases.     

Multiresidue method using SPME for the determination of various pesticides with different volatility in confined atmospheres

An analytical method is described for assessing the vapour concentration of 11 pesticides (bioallethrin, chlorpyriphos methyl, folpet, malathion, procymidone, quintozene, chlorothalonil, fonofos, penconazole and trimethacarb) in confined atmospheres (e.g. a greenhouse after pesticide application). This study is a successful extension of a method previously developed by the authors for dichlorvos to much less volatile pesticides. Sampling was performed by using polydimethylsiloxane–solid phase micro-extraction (PDMS–SPME) fibres immersed in a 250-mL sampling flask through which air samples were dynamically pumped from the analysed atmosphere. After a 40-min sampling duration, samples were analysed by GC/MS.Calibration was performed from a vapour-saturated air sample. The linearity of the observed signal versus pesticide concentration in the vapour phase was proved from spiked liquid samples whose headspace concentrations were measured by using the proposed method. This procedure gave calibration curves with regression coefficients (R²) greater than 0.98, and the repeatability of these measurements was found with RSDs of 1.9–7.6%. As a field application test, this analysis procedure was used for the determination of gaseous procymidone concentrations as a function of time in the atmosphere of an experimental 8-m² and 20-m³ greenhouse. The pesticide was sprayed according to real cultivation conditions, and measurements were made for 80 h after application (8 measurements). The observed concentrations found ranged from 200 to 500 µg m^–3, thus indicating the level of contamination of the air breathed by people in such working conditions.Abbreviations GC/MS gas chromatography/mass spectrometry - SIM selective ion monitoring - FC43 perfluorotributylamine - RSD relative standard deviation - LOD limit of detection - LOQ limit of quantification