Valeria A. Lozano

Standard addition analysis of fluoroquinolones in human serum in the presence of the interferent salicylate using lanthanide-sensitized excitation-time decay luminescence data and multivariate curve resolution

Three fluoroquinolone antibiotics (ciprofloxacin, norfloxacin and danofloxacin) have been determined in human serum in the presence of the potential interferent salicylate, by processing lanthanide-sensitized excitation-time decay matrix data for their terbium (III) complexes. The algorithm employed, multivariate curve resolution-alternating least-squares, is one of the few methodologies which permit the achievement of the second-order advantage in the presence of a high degree of overlapping between the time decay profiles for the analyte and the interferent complexes. Furthermore, the presence of analyte-background interactions makes it necessary to employ the standard addition method for successful quantitation. Both simulations and experiments showed that the modified standard addition method was suitable for this purpose, in which the test data matrix was subtracted from the standard addition matrices, and quantitation proceeded using classical external calibration procedure. The analyte concentration ranges were all within the therapeutic range, i.e., 0-6 mgL(-1) in serum, with final concentrations in the measuring cell in the order of 0.2 mgL(-1).

Three-way partial least-squares/residual bilinearization study of second-order lanthanide-sensitized luminescence excitation-time decay data: Analysis of benzoic acid in beverage samples

Lanthanide-sensitized luminescence excitation-time decay matrices were employed for achieving the second-order advantage using as chemometric algorithms parallel factor analysis (PARAFAC) and multidimensional partial least-squares with residual bilinearization (N-PLS/RBL). The second-order data were measured for a calibration set of samples containing the analyte benzoic acid in the concentration range from 0.00 to 5.00 mg L(-1), for a validation set containing the analyte and the potential interferent saccharin (in the range 0.00-6.00 mg L(-1)), and for real samples of beverages containing benzoic acid as preservant, saccharin, and other potentially interfering compounds. All samples were treated with terbium(III), trioctylphosphine oxide as a synergistic ligand, and contained a suitable imidazol buffer, in order to ensure maximum intensity of the luminescence signals. The results indicate a slightly better predictive ability of the newly introduced N-PLS/RBL procedure over standard PARAFAC, both in what concerns the comparison with nominal analyte concentrations in the validation sample set and with results provided by the reference high-performance liquid chromatographic technique for the real sample set.

Second-order advantage from kinetic-spectroscopic data matrices in the presence of extreme spectral overlapping: A multivariate curve resolution—Alternating least-squares approach

Multivariate curve resolution coupled to alternating least-squares (MCR-ALS) has been employed to model kinetic-spectroscopic second-order data, with focus on the achievement of the important second-order advantage, under conditions of extreme spectral overlapping among sample components. A series of simulated examples shows that MCR-ALS can conveniently handle the studied analytical problem unlike other second-order multivariate calibration algorithms, provided matrix augmentation is implemented in the spectral mode instead of in the usual kinetic mode. The approach has also been applied to three experimental examples, which involve the determination of: (1) the antiparkinsonian carbidopa (analyte) in the presence of levodopa as a potential interferent, both reacting with cerium (IV) to produce the fluorescent species cerium (III) with different kinetics; (2) Fe(II) (analyte) in the presence of the interferent Zn(II), both catalyzing the oxidation of methyl orange with potassium bromate; and (3) tartrazine (analyte) in the presence of the interferent brilliant blue, both oxidized with potassium bromate, with the interferent leading to a product with an absorption spectrum very similar to tartrazine. The results indicate good analytical performance towards the analytes, despite the intense spectral overlapping and the presence of unexpected constituents in the test samples.

A novel second-order standard addition analytical method based on data processing with multidimensional partial least-squares and residual bilinearization.

In the presence of analyte-background interactions and a significant background signal, both second-order multivariate calibration and standard addition are required for successful analyte quantitation achieving the second-order advantage. This report discusses a modified second-order standard addition method, in which the test data matrix is subtracted from the standard addition matrices, and quantitation proceeds via the classical external calibration procedure. It is shown that this novel data processing method allows one to apply not only parallel factor analysis (PARAFAC) and multivariate curve resolution-alternating least-squares (MCR-ALS), but also the recently introduced and more flexible partial least-squares (PLS) models coupled to residual bilinearization (RBL). In particular, the multidimensional variant N-PLS/RBL is shown to produce the best analytical results. The comparison is carried out with the aid of a set of simulated data, as well as two experimental data sets: one aimed at the determination of salicylate in human serum in the presence of naproxen as an additional interferent, and the second one devoted to the analysis of danofloxacin in human serum in the presence of salicylate.

Second-Order Analyte Quantitation under Identical Profiles in One Data Dimension. A Dependency-Adapted Partial Least-Squares/Residual Bilinearization Method

Analyte quantitation can be achieved from second-order data in the presence of uncalibrated components using multivariate calibration methods such as partial least-squares with residual bilinearization. However, the latter fails under conditions of identical profiles for interfering agents and calibrated components in one of the data dimensions. To overcome this problem, a new residual bilinearization procedure for linear dependency is here introduced. Simulated data show that the new model can conveniently handle the studied analytical problem, with a success comparable to multivariate curve resolution-alternating least-squares and also comparable to a version of parallel factor analysis adapted to cope with linear dependencies. The new approach has also been applied to two experimental examples involving the determination of the antibiotic ciprofloxacin in (1) urine samples from lanthanide-sensitized excitation-time decay matrixes and (2) serum samples from a novel second-order signal based on the time evolution of chemiluminescence emission. The results indicate good analytical performance of the new procedure toward the analyte in comparison with the classical approaches.

Green analytical determination of emerging pollutants in environmental waters using excitation-emission photoinduced fluorescence data and multivariate calibration.

An eco-friendly strategy for the simultaneous quantification of three emerging pharmaceutical contaminants is presented. The proposed analytical method, which involves photochemically induced fluorescence matrix data combined with second-order chemometric analysis, was used for the determination of carbamazepine, ofloxacin and piroxicam in water samples of different complexity without the need of chromatographic separation. Excitation-emission photoinduced fluorescence matrices were obtained after UV irradiation, and processed with second-order algorithms. Only one of the tested algorithms was able to overcome the strong spectral overlapping among the studied pollutants and allowed their successful quantitation in very interferent media. The method sensitivity in superficial and underground water samples was enhanced by a simple solid-phase extraction with C18 membranes, which was successful for the extraction/preconcentration of the pollutants at trace levels. Detection limits in preconcentrated (1:125) real water samples ranged from 0.04 to 0.3 ng mL(-1). Relative prediction errors around 10% were achieved. The proposed strategy is significantly simpler and greener than liquid chromatography-mass spectrometry methods, without compromising the analytical quality of the results.

Characterization of sildenafil citrate tablets of different sources by near infrared chemical imaging and chemometric tools

The chemical imaging technique by near infrared spectroscopy was applied for characterization of formulations in tablets of sildenafil citrate of six different sources. Five formulations were provided by Brazilian Federal Police and correspond to several trademarks of prohibited marketing and one was an authentic sample of Viagra. In a first step of the study, multivariate curve resolution was properly chosen for the estimation of the distribution map of concentration of the active ingredient in tablets of different sources, where the chemical composition of all excipients constituents was not truly known. In such cases, it is very difficult to establish an appropriate calibration technique, so that only the information of sildenafil is considered independently of the excipients. This determination was possible only by reaching the second-order advantage, where the analyte quantification can be performed in the presence of unknown interferences. In a second step, the normalized histograms of images from active ingredient were grouped according to their similarities by hierarchical cluster analysis. Finally it was possible to recognize the patterns of distribution maps of concentration of sildenafil citrate, distinguishing the true formulation of Viagra. This concept can be used to improve the knowledge of industrial products and processes, as well as, for characterization of counterfeit drugs.

Second-order advantage with excitation-emission photoinduced fluorimetry for the determination of the antiepileptic carbamazepine in environmental waters

A photochemically induced fluorescence system combined with second-order chemometric analysis for the determination of the anticonvulsant carbamazepine (CBZ) is presented. CBZ is a widely used drug for the treatment of epilepsy and is included in the group of emerging contaminant present in the aquatic environment. CBZ is not fluorescent in solution but can be converted into a fluorescent compound through a photochemical reaction in a strong acid medium. The determination is carried out by measuring excitation-emission photoinduced fluorescence matrices of the products formed upon ultraviolet light irradiation in a laboratory-constructed reactor constituted by two simple 4 W germicidal tubes. Working conditions related to both the reaction medium and the photoreactor geometry are optimized by an experimental design. The developed approach enabled the determination of CBZ at trace levels without the necessity of applying separation steps, and in the presence of uncalibrated interferences which also display photoinduced fluorescence and may be potentially present in the investigated samples. Different second-order algorithms were tested and successful resolution was achieved using multivariate curve resolution-alternating least-squares (MCR-ALS). The study is employed for the discussion of the scopes and yields of each of the applied second-order chemometric tools. The quality of the proposed method is probed through the determination of the studied emerging pollutant in both environmental and drinking water samples. After a pre-concentration step on a C18 membrane using 50.0 mL of real water samples, a prediction relative error of 2% and limits of detection and quantification of 0.2 and 0.6 ng mL(-1) were respectively obtained.

Simultaneous determination of urea herbicides in water and soil samples based on second-order photoinduced fluorescence data

This work presents an innovative strategy for the simultaneous determination of four widely employed urea-derivative herbicides, namely isoproturon, linuron, monuron and rimsulfuron, in interfering environments, combining second-order photoinduced fluorescence (PIF) signals, obtained upon UV irradiation in micellar aqueous solutions, and multivariate calibration. The method is simple and fast and complies with the green analytical chemistry principles because it avoids the consumption of high amounts of organic solvents. Successful results were obtained by measuring excitation–emission photoinduced fluorescence matrices processed with unfolded partial least-squares/residual bilinearization (U-PLS/RBL) algorithm. Indeed, this algorithm allowed us to achieve selectivity even in a system which shows a significant spectral overlapping among the formed photoproducts. The quality of the proposed method was evidenced on the basis of the analytical recoveries from water and soil samples spiked with analytes. After solid-phase extraction, reaching a pre-concentration factor of 250, detection limits ranging from 0.006 to 0.026 ng mL−1 were obtained in water samples. In soil samples, the detection limits ranged from 1.1 to 3.3 ng g−1 without a pre-concentration step. The relative prediction errors were lower than 7% in both cases.

A second-order fluorimetric approach based on a boron dipyrromethene tetraamide derivative for Hg(II) chemosensing in water and fish samples

A new fluorimetric method is described for the determination of Hg(II), based on the selectivity of a boron dipyrromethene tetraamide derivative (BODIPYTD) towards this ion, in combination with second-order chemometric analysis, to deal with matrix interferents. This is the first time that the selectivity of a mercury chemosensor regarding other metal ions is reinforced with the selectivity offered by second-order calibration, which is able to overcome the potential interference produced by organic constituents of natural or bio-samples. After the BODIPYTD–Hg(II) complex was formed, the excitation–emission fluorescence matrix was recorded and parallel factor analysis (PARAFAC) was applied for data processing. This algorithm achieves the second-order advantage and was able to overcome the problem of the presence of unexpected interferents. This method was applied to the direct determination of Hg(II) ions in environmental waters and fish muscle tissues, with minimal pretreatment steps and without the need for organic solvents. The results were successfully evaluated through a spiking recovery study in both types of real samples, which have constituents displaying fluorescence signals potentially able to interfere in the analysis. The latter fact demonstrates the excellent selectivity of the proposed method. The studied concentration range in water samples was 10–30 ng mL−1, while in fish samples it was 0.12–0.30 μg g−1. The limits of detection for water and fish samples were 2 ng mL−1 and 4 × 10−3 μg g−1, respectively, with relative prediction errors below 5%, and a sample throughput of about 8 samples per hour.