María Eugenia Centurión

Determination of phenol, resorcinol and hydroquinone in air samples by synchronous fluorescence using partial least-squares (PLS)

The determination of phenolic compounds is of great importance owing to their high toxicity. Some of them are present in tobacco smoke and it is important for their monitoring in air of closed room. A simple, rapid and sensitive method was developed for simultaneous determination of hydroquinone, resorcinol and phenol in this kind of samples. Synchronous fluorescence technique was used and the data were processed by using the partial least-squares (PLS) chemometric algorithm. The concentrations for experimental calibration matrix were varied between 0.02 and 0.2 mg L(-1) for hydroquinone, between 0.05 and 0.6 mg L(-1) for resorcinol and between 0.05 and 0.4 mg L(-1) for phenol in accordance with the national legislation. The cross-validation method was used to select the number of factors. To check the accuracy of the proposed method a recovery study on real samples was carried out.

Flow-batch technique for the simultaneous enzymatic determination of levodopa and carbidopa in pharmaceuticals using PLS and successive projections algorithm.

An enzymatic flow-batch system with spectrophotometric detection was developed for simultaneous determination of levodopa [(S)-2 amino-3-(3,4-dihydroxyphenyl)propionic acid] and carbidopa [(S)-3-(3,4-dihydroxyphenyl)-2-hydrazino-2-methylpropionic acid] in pharmaceutical preparations. The data were analysed by univariate method, partial least squares (PLS) and a novel variable selection for multiple lineal regression (MLR), the successive projections algorithm (SPA). The enzyme polyphenol oxidase (PPO; EC 1.14.18.1) obtained from Ipomoea batatas (L.) Lam. was used to oxidize both analytes to their respective dopaquinones, which presented a strong absorption between 295 and 540 nm. The statistical parameters (RMSE and correlation coefficient) calculated after the PLS in the spectral region between 295 and 540 nm and MLR-SPA application were appropriate for levodopa and carbidopa. A comparative study of univariate, PLS, in different ranges, and MLR-SPA chemometrics models, was carried out by applying the elliptical joint confidence region (EJCR) test. The results were satisfactory for PLS in the spectral region between 295 and 540 nm and for MLR-SPA. Tablets of commercial samples were analysed and the results obtained are in close agreement with both, spectrophotometric and HPLC pharmacopeia methods. The sample throughput was 18 h(-1).

Simultaneous determination of hydroquinone, resorcinol, phenol, m-cresol and p-cresol in untreated air samples using spectrofluorimetry and a custom multiple linear regression-successive projection algorithm

In this study, a novel, simple, and efficient spectrofluorimetric method to determine directly and simultaneously five phenolic compounds (hydroquinone, resorcinol, phenol, m-cresol and p-cresol) in air samples is presented. For this purpose, variable selection by the successive projections algorithm (SPA) is used in order to obtain simple multiple linear regression (MLR) models based on a small subset of wavelengths. For comparison, partial least square (PLS) regression is also employed in full-spectrum. The concentrations of the calibration matrix ranged from 0.02 to 0.2 mg L(-1) for hydroquinone, from 0.05 to 0.6 mg L(-1) for resorcinol, and from 0.05 to 0.4 mg L(-1) for phenol, m-cresol and p-cresol; incidentally, such ranges are in accordance with the Argentinean environmental legislation. To verify the accuracy of the proposed method a recovery study on real air samples of smoking environment was carried out with satisfactory results (94-104%). The advantage of the proposed method is that it requires only spectrofluorimetric measurements of samples and chemometric modeling for simultaneous determination of five phenols. With it, air is simply sampled and no pre-treatment sample is needed (i.e., separation steps and derivatization reagents are avoided) that means a great saving of time.

Flow-Batch Analyzer for the Chemiluminescence Determination of Catecholamines in Pharmaceutical Preparations

A novel, simple, cheap, flexible, versatile, and highly sensitivity flow-batch analyzer (FBA) with chemiluminescence detection was developed for determination of dopamine, norepinephrine, and epinephrine in pharmaceutical preparations. The method was based on the inhibitory effect of the mentioned catecholamines on a luminol-potassium hexacyanoferrate (III) chemiluminescence system in alkaline medium. The optimization of the chemical variables affecting this chemiluminescence inhibition effect has been carried out using a Box-Behnken experimental design. The sample throughput was 28 h−1. The system allowed the automatic preparation of standard solutions and analytical process can be accomplished just by changing the operational parameters in FBA control software.

Automatic Flow-Batch System for Cold Vapor Atomic Absorption Spectroscopy Determination of Mercury in Honey from Argentina Using Online Sample Treatment

An automatic flow-batch system that includes two borosilicate glass chambers to perform sample digestion and cold vapor atomic absorption spectroscopy determination of mercury in honey samples was designed. The sample digestion was performed by using a low-cost halogen lamp to obtain the optimum temperature. Optimization of the digestion procedure was done using a Box-Behnken experimental design. A linear response was observed from 2.30 to 11.20 μg Hg L(-1). The relative standard deviation was 3.20% (n = 11, 6.81 μg Hg L(-1)), the sample throughput was 4 sample h(-1), and the detection limit was 0.68 μg Hg L(-1). The obtained results with the flow-batch method are in good agreement with those obtained with the reference method. The flow-batch system is simple, allows the use of both chambers simultaneously, is seen as a promising methodology for achieving green chemistry goals, and is a good proposal to improving the quality control of honey.

PLS Regression in the Spectrophotometric Data for the Simultaneous Determination of Levodopa and Carbidopa in Pharmaceutical Preparations by Using an Enzymatic Stopped‐Flow FIA Technique

Abstract An enzymatic stopped‐flow‐injection analysis is proposed for simultaneous determination of levodopa and carbidopa in pharmaceutical preparations. The dopaquinones obtained after the oxidation catalized by the enzyme were measured by spectrophotometric method. A reduced calibration matrix based on a central composite experimental design was built and Partial Least Squares (PLS) was applied on the spectral data after reaction with the enzyme. The LOD was 0.015 and 0.0028 mg ml−1, respectively and the sample throughput was 22.5 h−1. The proposed method was applied to pharmaceutical preparations and the results are in close agreement with pharmacopeial method. The recovery study and results were satisfactory.

Automatic flow-batch system for the sample treatment and determination of hydroxyproline in sausages

In this study an automatic method for sample treatment and spectrophotometric determination of hydroxyproline in commercial sausages was developed. A flow-batch system that includes the steps of sample hydrolysis and determination of the analyte was designed. The method presents a linear range between 0.60 and 3.60 μg mL(-1) of hydroxyproline. A relative standard deviation of 1.68% was obtained from hydroxyproline standard solution (n=6, 1.20 μg mL(-1)) and the detection limit was 0.12 μg mL(-1). The sample throughput was 1 sample h(-1) while the reference method (AOAC) was carried out in about 17 h. This method employs 16 h of hydrolysis while in the proposed method the hydrolysis time was 15 min. For this purpose a pressure hydrolysis chamber with a low cost halogen lamp was used. The flow-batch system is simple and allows the use of both chambers (hydrolysis and detection) simultaneously. The obtained results with the flow-batch method are in good agreement with that obtained with the reference method. Moreover, it is good alternative to the quality control of meat products.

Kinetic approach for the enzymatic determination of levodopa and carbidopa assisted by multivariate curve resolution-alternating least squares

A combination of kinetic spectroscopic monitoring and multivariate curve resolution-alternating least squares (MCR-ALS) was proposed for the enzymatic determination of levodopa (LVD) and carbidopa (CBD) in pharmaceuticals. The enzymatic reaction process was carried out in a reverse stopped-flow injection system and monitored by UV-vis spectroscopy. The spectra (292-600 nm) were recorded throughout the reaction and were analyzed by multivariate curve resolution-alternating least squares. A small calibration matrix containing nine mixtures was used in the model construction. Additionally, to evaluate the prediction ability of the model, a set with six validation mixtures was used. The lack of fit obtained was 4.3%, the explained variance 99.8% and the overall prediction error 5.5%. Tablets of commercial samples were analyzed and the results were validated by pharmacopeia method (high performance liquid chromatography). No significant differences were found (alpha=0.05) between the reference values and the ones obtained with the proposed method. It is important to note that a unique chemometric model made it possible to determine both analytes simultaneously.

Determination of fat content in chicken hamburgers using NIR spectroscopy and the Successive Projections Algorithm for interval selection in PLS regression (iSPA-PLS)

Determining fat content in hamburgers is very important to minimize or control the negative effects of fat on human health, effects such as cardiovascular diseases and obesity, which are caused by the high consumption of saturated fatty acids and cholesterol. This study proposed an alternative analytical method based on Near Infrared Spectroscopy (NIR) and Successive Projections Algorithm for interval selection in Partial Least Squares regression (iSPA-PLS) for fat content determination in commercial chicken hamburgers. For this, 70 hamburger samples with a fat content ranging from 14.27 to 32.12mgkg-1 were prepared based on the upper limit recommended by the Argentinean Food Codex, which is 20% (ww-1). NIR spectra were then recorded and then preprocessed by applying different approaches: base line correction, SNV, MSC, and Savitzky-Golay smoothing. For comparison, full-spectrum PLS and the Interval PLS are also used. The best performance for the prediction set was obtained for the first derivative Savitzky-Golay smoothing with a second-order polynomial and window size of 19 points, achieving a coefficient of correlation of 0.94, RMSEP of 1.59mgkg-1, REP of 7.69% and RPD of 3.02. The proposed methodology represents an excellent alternative to the conventional Soxhlet extraction method, since waste generation is avoided, yet without the use of either chemical reagents or solvents, which follows the primary principles of Green Chemistry. The new method was successfully applied to chicken hamburger analysis, and the results agreed with those with reference values at a 95% confidence level, making it very attractive for routine analysis.

Determination of cadmium residues in bee products using a ‘lab-made’ bismuth bulk electrode

ABSTRACT Raw propolis and bee pollen has been widely used in different areas such as medicine, food and apitherapy because they have biological and medicinal properties. The beneficial effects of both bee products for human health include antibacterial, antiviral, antimicrobial and anti-inflammatory properties. However, hives exposure to heavy metals, due beekeeping practices and environment, is one of the problems facing beekeepers. The presence of cadmium in bee products should be controlled, because of its high toxicity. A lab-made Bismuth Bulk Electrode (BiBE) was developed for cadmium residue determination in Argentinean bee products such as raw propolis and bee pollen employing square wave anodic stripping voltammetry (SWASV) as electrochemical technique. The SWASV parameters were optimised based on a 2 5 factorial design. The method presents a linear range from 2.00 to 100.0 µg L−1 of Cd (II) with a limit of detection (LOD) and a limit of quantitation (LOQ) of 0.78 µg L−1 and 2.61 µg L−1, respectively. The repeatability was 8.03%, calculated as the relative standard deviation. Recovery experiments were performed using spiked raw propolis and bee pollen samples with standard deviation values from 1.16% to 7.20%. The BiBE is easy and fast to elaborate and the propose method is environmentally friendly and low cost. Then, it can be considered as a good alternative to the quality control of bee products due to its importance in the beekeeping industry.