AVANÇOS ANALÍTICOS BASEADOS EM MODELOS DE CALIBRAÇÃO DE PRIMEIRA ORDEM E ESPECTROSCOPIA UV-VIS PARA AVALIAÇÃO DA QUALIDADE DA ÁGUA: UMA REVISÃO - PARTE 1

ANALYTICAL ADVANCES BASED ON FIRST-ORDER CALIBRATION MODELS AND UV-VIS SPECTROSCOPY FOR THE ASSESSMENT OF WATER QUALITY: A REVIEW – PART 1. This work aimed to infer about the scientific progress of the use of ultraviolet-visible (UV-Vis) spectrophotometry for evaluations of water quality. The research started in the 60s, when the imminence of obtaining characteristics of the UV-Vis spectrum that estimated the water quality. From a temporal perspective, the 1990s began using first order multivariate calibration models, focus of this work, to predict water quality parameters utilizing the UV-Vis spectra. During the period evaluated, numerous studies used spectrophotometry to quantify analytes using univariate calibration. However, many works also report the fact that the determined substances absorb at the same wavelengths and describe how to resolve these interferences. But gaps such as low concentration determinations are still a bottleneck as the best results, for example, are related to high amounts of organic matter, fact also related to instrumental aspects. One of the gains was the introduction of chemometric approaches which allows quantification without the need of analytical curve construction during the prediction step. However, although they are already used techniques, the survey carried out here verified the applications are considered incipient, where, for example, dissolved organic carbon and nitrate predictions using first order multivariate calibration represent less than 30% of the determinations.

IDENTIFICATION AND QUANTIFICATION OF WHEAT ROOTS FLAVONOIDS INOCULATED WITH NATIVE RHIZOBACTERIA

In this study, we identified the presence and quantity of flavonoids produced in wheat roots inoculated with rhizobacteria. Our goal is to confirm the efficiency of standard isolates and show new strains with biotechnological potential to promote plant growth. The experiment was carried out with different isolates under inoculation in the following situations: T1-Azospirillum brasiliense; T2-Herbaspirillum seropedicae; T3-Azospirillum brasiliense and Herbaspirillum seropedicae co-inoculation; T4-native Enterobacter sp. nº 203; T5- native Enterobacter sp. nº 208; T6-native Enterobacter sp. nº 493; T7-Control only under nitrogen fertilization (N+); T8-Control without nitrogen (N-) and bacterial inoculation. Agronomic characteristics were assessed after 42 days of inoculation. Identification and quantification of flavonoids were carried out through HPLC, using an analytical curve with four standards based on Coumarin, Quercetin, Isoflavone and Rutin. Regarding the production of total flavonoids, two (203 and 493) out of the three native strains we tested were statistically significant, exceeding the values obtained from the inoculation of standard strains, which presented association with grasses (Azopirilum e Herbaspirillum). Standard bacteria, when inoculated in isolation, presented, along with those that received N+ treatment, the highest values for length and root and aerial part dry mass. New studies need to be carried out in order to confirm the technological use of these native strains as inoculant, as these bacteria may contribute to Biological Nitrogen Fixation (BNF) in wheat culture, either by competition or synergism.

Sensitive Voltammetric Detection of Chloroquine Drug by Applying a Boron-Doped Diamond Electrode

In this research, a boron-doped diamond (BDD) electrode has been explored to detect the chloroquine drug. The electrochemical performance of BDD electrode towards the irreversible anodic response of chloroquine was investigated by subjecting this electrode to the cathodic (−0.5 A cm−2 by 180 s, generating a predominantly hydrogen-terminated surface) and anodic (+0.5 A cm−2 by 30 s, oxygen-terminated surface) pretreatments. The cathodically pretreated BDD electrode ensured a better-defined anodic peak and higher current intensity. Thus, by applying the cathodically pretreated BDD electrode and square-wave voltammetry (SWV), the analytical curve was linear from 0.01 to 0.25 µmol L−1 (correlation coefficient of 0.994), with sensitivity and limit of detection of 12.2 µA L µmol−1 and 2.0 nmol−1, respectively. This nanomolar limit of detection is the lowest recorded so far with modified and unmodified electrodes.

A simple and fast method to detect freebase cocaine in artificial saliva by square wave voltammetry (SWV) using carbon paste electrode

The consequences of consuming and commercializing illicit drugs including cocaine, con­stitute a serious problem for authorities and the whole society. Cocaine is usually identified in the laboratory conditions by chromatographic or spectroscopic methods. Electro­che­mical techniques have also gained prominence because they are fast and easy to use, have many applications, and provide reproducible and reliable results. Therefore, in the present study, a voltammetric method was developed to detect freebase cocaine using carbon paste electrode and methanol as the main cocaine solvent. The developed method was applied to detect cocaine in the artificial saliva by the square wave voltammetry (SWV). The current values increased linearly with the concentration of cocaine, which afforded construction of the analytical curve. The limit of detection (LoD) and the limit of quantify­cation (LoQ) were determined as 0.90 µg/mL and 2.41 µg/mL, respectively. For compa­rison purposes, HPLC-DAD chromatographic method was also applied to detect cocaine. The corresponding analytical curve gave LoD = 0.043 µg/mL and LoQ = 0.130 µg/mL. Although showing better analytical results, HPLC-DAD method could not detect cocaine in saliva samples without previous treatment, what makes the electrochemical method much more attractive for this type of detection.

Efficient electrochemical detection of geosmin in environmental waters

A new electrochemical sensor based on molecular imprinting technology was developed, for rapid and sensitive detection of the odorous substance geosmin (GSM) in water. In this method, the molecularly imprinted membrane was successfully modified on the surface of the glassy carbon electrode (GCE) using the electrochemical deposition method. In the presence of the target analyte (geosmin), the target analyte occupies the detection site and the detection signal will attenuate. As the concentration of the target analyte increases, the attenuation of the electrical signal becomes more pronounced. This sensor can quantitatively detect geosmin at concentrations as low as 5 ng/L, which is currently the lowest limit of detection (LOD) for GSM detection by an electrochemical sensor in reported studies. The modified GCE provided an analytical curve for GSM detection in the range of 5–200 ng/L.

USO DE UM SCANNER DE MESA E ESPUMA DE POLIURETANO PARA QUANTIFICAÇÃO DE FERRO TOTAL EM CÁPSULAS DE SUPLEMENTOS ALIMENTARES

In this work, an alternative and low-cost technique for the extraction and quantification of Fe (total) from food supplements by digital image analysis is shown. The method is based on the complexation of Fe ions in solution with the 8-hydroxyquinoline ligand, forming a colored complex that is extractable from aqueous solution to polyurethane foam, coloring this one, which was initially white, to brown. After the acquisition and treatment of the digital image generated by the foam, the quantification of Fe is performed. Interference and recovery tests show that the method is not affected by concomitants in the sample. The method was applied to 3 different types of dietary supplements, and these results were compared to those obtained by FAAS, showing statistical equivalence. The limits of quantification obtained in this work was 1.78 μmol L-1, the limit of detection was 0.53 μmol L-1, the accuracy was 97.5 + 4.8% and the precision was 8.45%. The analytical curve was linear from 2.0 to 10.0 μmol L-1, with a r2 of 0.9975.

NEW VOLTAMMETRIC METHOD FOR DETERMINATION OF PHENANTHRENE IN GROUNDWATER

This work proposes a new method for the determination of phenanthrene (FEN) in aqueous medium with a cobalt phthalocyanine modified glassy carbon electrode (ECV / CoPc), using Differential Pulse Voltammetry (VPD), whose oxidation of FEN occurs between 1,3 and 1,4 V. The electrode was modified with a 1x10-3 mol∙L-1 CoPc methanolic solution containing 10% Nafion. For voltammetric measurements in Differential Pulse mode, an amplitude of 0.7V and a scan rate of 0.04V s-1 were used. Experimental parameters were optimized for the purpose of determination of FEN in groundwater collected in a water well of a São Luis-MA fuel station. Under these optimized conditions, an analytical curve was obtained in the 0.49 to 2,4 μM concentration range, with a detection limit of 1,2 x 10-10 mol∙L-1. The method was applied to a real groundwater sample from a water well located at a fuel station, and an average concentration of 0.037 μM FEN was found (n = 5), presenting a variation coefficient of 0.88, indicating good precision. Accuracy was assessed by the recovery test, whose average value was 99.9%. These results indicate that the proposed procedure is a good alternative for the analysis of FEN in natural water.

Analysis of sulfamethoxazole by square wave voltammetry using new carbon paste electrode

In this work a new model of carbon paste electrode was employed to determine sulfamethoxazole (SMX), an antibiotic used to treat infections in human and veterinary medicine, by the square wave voltammetric modality (SWV). More specifically, the elec­trochemical behavior of SMX was investigated by cyclic voltammetry (CV), and the quantitative analysis of SMX was provided by SWV. The analytical curve was obtained with a linear correlation coefficient (r) of 0.985 and standard deviation (SD) of 0.005 μA. Limits of detection and quantification were found as 2.3×10-6 and 7.7×10-6 mol L-1, respectively. According to the obtained results, the new carbon paste prototype electrode can successfully be employed in this kind of electroanalytical applications.

Sulfamethoxazole sorption in eutrophic Regolithic Neosol

ABSTRACT This study aimed to evaluate sulfamethoxazole sorption kinetics and isotherms using batch method. The experiment was carried out in typic eutrophic Regolithic Neosol (0-20 and 20-60 cm layers) located in the private reserve of the Riacho do Papagaio farm, in São João, PE, Brazil. The tests were carried out under laboratory conditions at 24 ºC and sulfamethoxazole concentration was determined by high-performance liquid chromatography. The sorption experiment through the batch method used sulfamethoxazole solutions with concentrations of 10-3, 5.10-4, 10-4, 5.10-5, 10-5 and 5.10-6 mol L-1 to obtain the analytical curve. For this soil, sulfamethoxazole sorption kinetics was best described by a second-order model and the sorption isotherms were linear. Sulfamethoxazole predominantly interacts with organic matter in this type of soil. The results obtained in this study show that the antibiotic sulfamethoxazole exhibits low adsorption, posing a higher risk of contamination to the groundwaters in this region at pH ≈ 7.