RESUMO
We report a microfluidic electrochemical immunosensor for Xanthomonas arboricola (XA) determination, based on the covalently immobilization of monoclonal anti-XA antibody (anti-XA) on a previously amino functionalized SBA-15 in situ synthesized in the central channel of a glass-poly(dimethylsiloxane) microfluidic immunosensor. The synthetized amino-SBA-15 was characterized by N2 adsorption-desorption isotherm, scanning electron microscopy and infrared spectroscopy. XA was detected by a direct sandwich immunoassay through an alkaline phosphatase (AP) enzyme-labeled anti-XA conjugate. Later, the substrate p-aminophenyl phosphate was converted to p-aminophenol by AP. The enzymatic product was detected at +100mV on a sputtered gold electrode. The measured current was directly proportional to the level of XA in walnut trees samples. The linear range was from 5 × 102 to 1 × 104CFUmL-1. The detection limit was 1.5 × 102CFUmL-1, and the within- and between-assay coefficients of variation were below 5%. Microfluidic immunosensor is a very promising tool for the early and in situ diagnosis of XA in walnuts avoiding serious economic losses.
Assuntos
Anticorpos Imobilizados/química , Análise de Alimentos/instrumentação , Imunoensaio/instrumentação , Juglans/microbiologia , Dispositivos Lab-On-A-Chip , Nanoestruturas/química , Xanthomonas/isolamento & purificação , Aminação , Desenho de Equipamento , Microbiologia de Alimentos , Limite de Detecção , Nanoestruturas/ultraestrutura , Dióxido de Silício/químicaRESUMO
A new, simple, and selective method for preconcentration and determination of Cr(VI) in aqueous samples. After adsorption in "batch mode" on Aliquat 336-AC, determinations were made directly on the solid by X-ray fluorescence spectrometry, which had the advantage of not requiring the step of elution of the chromium retained. The enrichment factor was calculated considering that the tablets obtained from 10 mL solution of Cr(VI) (1000 µg L(-1)) had a final thickness of 0.64 mm and a diameter of 16.7 mm; the volume deposited on the pellet was 0.14 cm(3). The preconcentration factor obtained was 71-fold, which was highly satisfactory for chromium trace analysis by XRF. Finally, the method was successfully applied to the determination of Cr(VI) in drinking water samples.
Assuntos
Cromo/isolamento & purificação , Extração em Fase Sólida/métodos , Espectrometria por Raios X/métodos , Abastecimento de Água/análise , Água/análise , Adsorção , Carvão Vegetal/química , Sensibilidade e Especificidade , Extração em Fase Sólida/economia , Espectrometria por Raios X/economiaRESUMO
The heavy metal mercury (Hg) is a neurotoxin known to have a serious health impact even at relatively low concentrations. A slurry method was developed for the sensitive and precise determination of mercury in human serum blood samples by cold vapor generation coupled to atomic fluorescence spectrometry (CV-AFS). All variables related to the slurry formation were studied. The optimal hydrochloric concentration and tin(II) chloride concentration for CV generation were evaluated. Calibration within the range 0.1-10 microg L(-1) Hg was performed with the standard addition method, and compared with an external calibration. Additionally, the reliability of the results obtained was evaluated by analyzing mercury in the same samples, but submitted to microwave-assisted digestion method. The limit of detection was calculated as 25 ng L(-1) and the relative standard deviation was 3.9% at levels around of 0.4 microg L(-1)Hg.
Assuntos
Técnicas de Química Analítica/métodos , Mercúrio/sangue , Calibragem , Desenho de Equipamento , Análise de Injeção de Fluxo/métodos , Ácido Clorídrico/química , Mercúrio/análise , Micro-Ondas , Reprodutibilidade dos Testes , Espectrometria de Fluorescência/métodos , Temperatura , Compostos de Estanho/químicaRESUMO
Cloud point extraction (CPE) has been used for the pre-concentration of mercury, after the formation of a complex with 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (5-Br-PADAP), and later analysis by electrothermal atomic absorption spectrometry (ETAAS) using polyethyleneglycolmono-p-nonyphenylether (PONPE 7.5) as surfactant. The chemical variables affecting the separation step were optimized. Under the optimum conditions, i.e, pH 8.5, cloud point temperature 80 degrees C, 5-Br-PADAP=4x10(-5) mol L(-1), PONPE 7.5=0.2%, sample volume=1.0 mL, an enhancement factor of 22-fold was reached. The lower limit of detection (LOD) obtained under the optimal conditions was 0.01 microg L(-1). The precision for 10 replicate determinations at 2.0 microg L(-1) Hg was 4.0% relative standard deviation (R.S.D.). The calibration graph using the pre-concentration system for mercury was linear with a correlation coefficient of 0.9994 at levels near the detection limits up to at least 16 microg L(-1). The method was successfully applied to the determination of mercury in biological samples and in certified reference material (QC METAL LL3).