Carlos Alexandre Borges Garcia

A new amperometric biosensor for fructose using a carbon paste electrode modified with silica gel coated with Meldola's Blue and fructose 5-dehydrogenase

Abstract A carbon paste modified with silica gel coated with Meldolas Blue and fructose 5-dehydrogenase was used to construct a new biosensor for fructose. An efficient electron transfer mediation from the reduced enzyme to the carbon paste electrode was verified, at a low applied potential of 20mV vs. SCE, where interfering reactions are minimized. A linear response range for 0.1 to 0.8 mmoll −1 fructose was adjusted by the equation I = 0.0150( ± 0.006) + 0.618(± 0.011) [fructose], with a correlation coefficient of 0.999 and an rsd of 0.68% for n = 7. The biosensor was used to determine fructose in sweets and fruit jellies and the results present good recovery, higher than 96% in both cases. A stable response is observed over two months, when stored in a refrigerator, or for 300 measurements in continuous use.

Acetylsalicylic acid determination in pharmaceutical samples by FIA-potentiometry using a salicylate-sensitive tubular electrode with an ethylene-vinyl acetate membrane

Abstract The construction of a salicylate-sensitive tubular potentiometric electrode for flow injection analysis (FIA) is described, in which an ethylene-vinyl acetate (EVA) copolymeric membrane, 40% in vinyl acetate, is applied directly onto a conducting support consisting of a mixture of an epoxy resin and graphite. The tubular salicylate ion-selective electrode is based on tricaprylyl-trimethyl-ammonium (Aliquat™) salicylate as the ion-exchanger, supported on the polymeric matrix without plasticizer solvent. The tubular electrode showed a response of 58.3xa0mV per concentration decade within the 5.0×10−3–5.0×10−1xa0molxa0l−1 salicylate range in 0.1xa0molxa0l−1 Tris–HCl buffer (pH=7.5). Iodide is the main analytical interferent; the electrode response time was 5xa0s at 25°C. Determinations of acetylsalicylic acid in tablet samples by the proposed method exhibit relative errors lower than 2%, when compared with a spectrophotometric method. The useful lifetime of the tubular sensor is longer than 3 months.

New fructose biosensors utilizing a polypyrrole film and D-fructose 5-dehydrogenase immobilized by different processes

Abstract Two amperometric biosensors for fructose detection were developed by immobilizing d -fructose 5-dehydrogenase by two different immobilization processes. For the first biosensor, the occlusion enzymatic immobilization technique was employed, the enzyme being immobilized in a polypyrrole (PPY) film, over a platinum electrode containing sodium ferricyanide as mediator. With this sensor, about 100 analyses were performed over a period of 1 week with daily use. The second was constructed using the crosslinked covalent bond method, the enzyme being immobilized onto a PPY film doped with hexacyanoferrate supported on a platinum electrode surface. This biosensor was used for, approximately, 200 analyses in 2 weeks of continuous use. Analytical parameters, such as pH, ionic strength, interferences and response time of both sensors were also studied. The biosensors were utilized for fructose determinations in three different samples of dietetic products and presented a good correlation with the standard colorimetric method. A linear response range to both biosensors was 0.1–0.8xa0mmolxa0l −1 fructose with a r.s.d. of 0.68%.

USE OF METABOLISM TO EVALUATE THE SUBLETHAL TOXICITY OF MERCURY ON FARFANTEPANEUS BRASILIENSIS LARVAE (LATREILLE 1817, CRUSTACEAN)

Abstract Penaeid shrimp are important resources for worldwide fisheries and aquaculture. In Brazil, Farfantepenaeus brasiliensis, is an important commercially exploited species and an ideal animal for studying the impairment caused by the effects of heavy metals that are often detected in coastal areas. The main purpose of this study is to detect the acute toxicity of mercury to F. brasiliensis larvae, and to investigate its effects on oxygen consumption and ammonium excretion, which have not been carried out in this species before. We examined the acute toxicity Hg to F. brasiliensis larvae revealed at 24, 48, 72 and 96-h of exposure and the medium lethal concentration (LC50) values obtained were of 0.13 mg L−1; 0.054 mg L−1; 0.047 mg L−1 and 0.045 mg L−1, respectively. Furthermore, we also found that exposure of shrimp to Hg caused an inhibition in oxygen consumption of 53.42% lower than that of the control. However, after separate exposure to Hg, elevations in ammonium excretion were obtained, which were 217.64%, higher than the control.

Determination of potassium ions in pharmaceutical samples by FIA using a potentiometric electrode based on ionophore nonactin occluded in EVA membrane.

A simple and rapid method was developed for the K(+) ions determination employing a flow injection system using a flow-through electrode based on the naturally-occurring antibiotic ionophore nonactin occluded in a polymeric membrane. The nonactin ionophore was trapped in poly(ethylene-co-vinyl acetate) (EVA) matrix (40% w/w in vinyl acetate) and dispersed on the surface of a graphite-epoxy tubular electrode. The plasticizer-free all-solid-state potassium-selective electrode showed a linear response for K(+) concentrations between 5.0 x 10(-5) and 5.0x10(-2) M (r=0.9995) with a near-Nernstian slope of 51.5 mV per decade, when Tris-HCl buffer (pH 7.0;0,1 M) was employed as a carrier. The potentiometric-FIA system allows an analytical frequency of 120 samples per hour with a precision of 3.6%. The relative standard deviations (R.S.D.) for K(+) determination in pharmaceuticals samples, without any previous treatment, were lower than 4.0%, comparable to those obtained by flame photometry. Ammonium is the main analytical interference and the electrode response time was 5 s at 25 degrees C. The useful lifetime of the tubular sensor is longer than 3 months in continuous use.

Assessment of Trace Metal Levels in Catfish (Cathorops spixii) from Sal River Estuary, Aracaju, State of Sergipe, Northeastern Brazil

The concentrations of cadmium, copper, nickel, zinc, and lead were determined in the catfish (Cathorops spixii) from the Sal River estuary, Brazil, to evaluate the potential role of domestic and industrial effluents released without treatment on the quality of the estuarine environment with consequences to fish resources. Muscle, liver, and kidney samples were analyzed for trace metal composition by flame atomic absorption spectrophotometry. The mean concentration (microg/g wet weight) of trace metals in the tissues of C. spixii were as follows: cadmium = 1.65, 2.81, and 0.71 microg/g; copper = 29.07, 4.38, and 3.40 microg/g; zinc = 229, 312, and 15.57 microg/g; nickel = 1.22, 1.04, and 117 microg/g; and lead = 7.09, 10.77, and 11.18 microg/g. The results show that metal accumulation in organs indicates the difference between them. The results showed high concentrations of copper, zinc, nickel, lead, and cadmium in the Cathorops spixii compared with the maximum values registered from fish in studies reported in other coastal regions of Brazil.

Use of self-plasticizing EVA membrane for potentiometric anion detection.

In this work, five different types of membranes were developed responsible to anion-selective electrodes. The membranes were based on tri-caprylyl-trimethyl-ammonium chloride (Aliquat-336S) supported on poly(ethylene-co-vinyl-acetate) copolymer (EVA). The sensors were prepared by solubilizing the copolymer with the appropriate exchanger in chloroform, without using of any plasticizers. The ion-selective electrodes prepared using these membranes show the utility for anions determinations in the concentration range between 10(-5) and 10(-1) mol l(-1) in the steady-state. The membrane performance was also evaluated in FIA system using tubular electrode for salicylate and iodide. In FIA system, the electrode exhibited nernstian response for salicylate in the concentration range of 2.5x10(-3) and 1.0x10(-1), while for iodide from 5.0x10(-4) up to 1.0x10(-1) mol l(-1). The systems were employed for the salicylate and iodide determination in pharmaceutical samples obtaining a relative deviation of 1.6%, when compared to the reference method.

Determination of acetylsalicylic acid in tablets with salicylate ion selective electrode in a Batch Injection Analysis system

The feasibility of the use of a Batch Injection Analysis (BIA) system for potentiometric determination of acetylsalicylic acid in tablets, with a membrane ion selective electrode, was investigated. There is no significant difference between the results obtained by the proposed method and those obtained by the Standard British Pharmacopaeia method12 at the 95% confidence level. Values of 4% and 2.5% for R.S.D. were obtained by the application of the BIA-potentiometric method and for the injections respectively. About 90 determinations per hour can be performed with the proposed BIA potentiometric method.

Evaluation of the Chemical Composition of Dry Feeds for Dogs and Cats

Cat and dog feed production has increased worldwide, and much emphasis has been placed on the importance of determining the mineral composition of pet foods. In this work, the concentrations of Al, Ba, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Ni, P, Sr, V and Zn in dry feed for cats and dogs employing inductively coupled plasma-optical emission spectrometry (ICP OES) were determined and evaluated according to regulatory agencies. Forty-one dry feed samples (24 dog feed and 17 cat feed) were analyzed. The obtained concentrations ranged from 2.3 mg kg (Ba) to 2.8 g kg (Ca) in cat feeds, and from 3.8 mg kg (Cu) to 3.4 g kg (Ca) in dog feeds. The concentrations of P are in accordance with the Brazilian legislation, and Mn and Zn contents met the American legislation. The concentration values of Cu, K and Mg presented in some samples were below the limits established by American regulatory agency. Based on multivariate data analysis evaluated from flavors of the products and brands, it was concluded that the feed samples were uniform since there was no trend to group formation and classification according to their mineral composition, except one dog feed brand, which had a significant content of Al and Cu.