RESUMO
The development of a new method to determine the presence of the organoarsenic additives p-arsanilic acid (ASA), roxarsone (ROX) and nitarsone (NIT) in livestock feeds by high performance liquid chromatography coupled to ultraviolet oxidation hydride generation atomic fluorescence spectrometry (HPLC-UV/HG-AFS) after microwave assisted extraction (MAE) was proposed. Chromatographic separation was achieved on a C18 column with 2% acetic acid/methanol (96:4, v/v) as the mobile phase. The limits of detection (LODs) were 0.13, 0.09 and 0.08mgL-1, and the limits of quantification (LOQs) were 0.44, 0.30 and 0.28mgL-1. The relative standard deviations (RSDs) for ASA, ROX and NIT determined from five measurements of the mixed calibration standard were 3.3, 5.3, and 5.4%, respectively. MAE extraction of phenylated arsenic compounds using 1.5M H3PO4 at 120°C for 45min allowed for maximum recoveries (%) of total arsenic (As) and organoarsenic species, with no degradation of these compounds. The extraction of total As was approximately 97%, and the As species recoveries were between 95.2 and 97.0%. The results of the analysis were validated using mass balance by comparing the sum of extracted As with the total concentration of As in the corresponding samples. The method was successfully applied to determine the presence of these compounds in feed samples. ASA was the only As species detected in chicken feed samples, with a concentration between 0.72 and 12.91mgkg-1.
Assuntos
Ração Animal , Gado , Animais , Arsênio , Cromatografia Líquida de Alta Pressão , Análise de Alimentos , Micro-Ondas , Espectrometria de FluorescênciaRESUMO
In this study, a multisyringe chromatography system (MSC) using a C18 monolithic column was proposed for the on-line monitoring of the photocatalytic degradation of isoniazid (INH, 10 mg L(-1)) and pyrazinamide (PYRA, 5mgL(-1)) mixtures in aqueous solution using a small sample volume (200 µL) with an on-line filtration device in a fully automated approach. During the photocatalytic oxidation using TiO2 or ZnO semiconductor materials, total organic carbon (TOC) and the formed intermediates were analyzed off-line using ion chromatography, ion exclusion HPLC, and ESI-MS/MS. The results showed that TiO2 exhibits a better photocatalytic activity than ZnO under UV irradiation (365 nm) for the degradation of INH and PYRA mixtures, generating 97% and 92% degradation, respectively. The optimal oxidation conditions were identified as pH 7 and 1.0 g L(-1) of TiO2 as catalyst. The mineralization of the initial organic compounds was confirmed by the regular decrease in TOC, which indicated 63% mineralization, and the quantitative release of nitrate and nitrite ions, which represent 33% of the nitrogen in these compounds. The major intermediates of INH degradation included isonicotinamide, isonicotinic acid, and pyridine, while the ESI-MS/MS analysis of PYRA aqueous solution after photocatalytic treatment showed the formation of pyrazin-2-ylmethanol, pyrazin-2-ol, and pyrazine. Three low-molecular weight compounds, acetamide, acetic acid and formic acid, were detected during INH and PYRA decomposition. PYRA was more resistant to photocatalytic degradation due to the presence of the pyrazine ring, which provides greater stability against OH attack.
Assuntos
Antituberculosos/isolamento & purificação , Monitoramento Ambiental/métodos , Isoniazida/isolamento & purificação , Pirazinamida/isolamento & purificação , Poluentes Químicos da Água/isolamento & purificação , Purificação da Água/métodos , Antituberculosos/análise , Antituberculosos/efeitos da radiação , Catálise , Cromatografia Líquida de Alta Pressão , Monitoramento Ambiental/instrumentação , Desenho de Equipamento , Isoniazida/análise , Isoniazida/efeitos da radiação , Oxirredução , Processos Fotoquímicos , Pirazinamida/análise , Pirazinamida/efeitos da radiação , Espectrometria de Massas por Ionização por Electrospray , Espectrometria de Massas em Tandem , Titânio/química , Raios Ultravioleta , Poluentes Químicos da Água/análise , Poluentes Químicos da Água/efeitos da radiação , Purificação da Água/instrumentação , Óxido de Zinco/químicaRESUMO
In this work, nitrogen-doped ZnO material was synthesized by the sol-gel method using zinc acetate as the precursor and urea as the nitrogen source (15, 20, 25 and 30% wt.). For comparative purposes, bare ZnO was also prepared. The influence of N doping on structural, morphological, optical and photocatalytic properties was investigated. The synthesized catalysts were characterized by XRD, SEM-EDS, diffuse reflectance UV-Vis spectroscopy, BET and XPS analysis. The photocatalytic activity of N-doped ZnO catalysts was evaluated during the degradation of a mixture of herbicides (2,4-D and picloram) under visible radiation ≥400 nm. The photo-absorption wavelength range of the N-doped ZnO samples was shifted to longer wavelength compared to those of the unmodified ZnO. Among different amounts of dopant agent, the 30% N-doped ZnO material showed higher visible-light activity compared with pure ZnO. Several degradation by-products were identified by using HPLC and ESI-MS/MS. The enhancement of visible photocatalytic activity of the N-doped ZnO semiconductor could be mainly due to their capability in reducing the electron-hole pair recombination.
Assuntos
Ácido 2,4-Diclorofenoxiacético/química , Herbicidas/química , Nitrogênio/química , Processos Fotoquímicos , Picloram/química , Óxido de Zinco/química , Óxido de Zinco/síntese química , Catálise , Técnicas de Química SintéticaRESUMO
The presence of arsenic (As) in agricultural food products is a matter of concern because it can cause adverse health effects at low concentrations. Agricultural-product intake constitutes a principal source for As exposure in humans. In this study, the contribution of the chemical-soil parameters in As accumulation and translocation in the maize crop from a mining area of San Luis Potosi was evaluated. The total arsenic concentration and arsenic speciation were determined by HG-AFS and IC-HG-AFS, respectively. The data analysis was conducted by cluster analysis (CA) and principal component analysis (PCA). The soil pH presented a negative correlation with the accumulated As in each maize plant part, and parameters such as iron (Fe) and manganese (Mn) presented a higher correlation with the As translocation in maize. Thus, the metabolic stress in maize may induce organic acid exudation leading a higher As bioavailability. A high As inorganic/organic ratio in edible maize plant tissues suggests a substantial risk of poisoning by this metalloid. Careful attention to the chemical changes in the rhizosphere of the agricultural zones that can affect As transfer through the food chain could reduce the As-intoxication risk of maize consumers.
Assuntos
Arsênio/análise , Monitoramento Ambiental , Poluentes do Solo/análise , Zea mays/química , Agricultura , México , Mineração , Solo/químicaRESUMO
Peroxisomicine A1 (PA1) is a dimeric hydroxyanthracenone isolated from fruits of plants belonging to the genus Karwinskia. Showing selective toxicity between malignant and benign cell lines, it is currently under screening as an antineoplastic agent. Very little is known about its mechanism of action. In the present work the extent of binding of this substance with Bovine Serum Albumin (BSA) and Human Serum Albumin (HSA) at pH 7.2 and 7.4 has been evaluated using the spectrophotometric method. Absorbance of PA1 was altered by the presence of albumin and this property was used to generate binding isotherms. The investigation was carried out at four different temperatures. The data were analyzed by assuming two types of binding sites. Results indicated that PA1 binds to both albumins at physiological pH, which is reflected by the affinity constants of the order of 10(5). There are two types of binding sites in the albumin for PA1; with the electrostatic forces being discarded, the hydrophobic and hydrogen bond are more probable. Binding with HSA is stronger than with BSA.