RESUMO

Common snook (Centropomus undecimalis) is one of the most important marine species under commercial exploitation in the Gulf of Mexico; for this reason, interest in developing its culture is a priority. However, larviculture remains as the main bottleneck for massive production. In this sense, our objective was to determine the changes of digestive enzymes activities using biochemical and electrophoretic techniques during 36 days of Common snook larviculture fed with live preys (microalgae, rotifers, and Artemia). During larviculture, all digestive enzymatic activities were detected with low values since yolk absorption, 2 days after hatching (dah) onwards. However, the maximum values for alkaline protease (6,500 U mg protein(-1)), trypsin (0.053 mU × 10(-3) mg protein(-1)), and Leucine aminopeptidase (1.4 × 10(-3) mU mg protein(-1)) were detected at 12 dah; for chymotrypsin at 25 dah (3.8 × 10(-3) mU mg protein(-1)), for carboxypeptidase A (280 mU mg protein(-1)) and lipase at 36 dah (480 U mg protein(-1)), for α-amylase at 7 dah (1.5 U mg protein(-1)), for acid phosphatases at 34 dah (5.5 U mg protein(-1)), and finally for alkaline phosphatase at 25 dah (70 U mg protein(-1)). The alkaline protease zymogram showed two active bands, the first (26.3 kDa) at 25 dah onwards, and the second (51.6 kDa) at 36 dah. The acid protease zymogram showed two bands (RF = 0.32 and 0.51, respectively) at 34 dah. The digestive enzymatic ontogeny of C. undecimalis is very similar to other strictly marine carnivorous fish, and we suggest that weaning process should be started at 34 dah.

Assuntos

RESUMO

The apparent electrophoretic mobilities of indomethacin in beta-cyclodextrin at a range of concentrations were measured directly by capillary electrophoresis. Three different linear plots and a non linear plot are proposed for the apparent binding constant calculations, based on the fact that the molar ratio of the inclusion complex was 1:1. K values obtained at 298 K were 421 M(-1) (double reciprocal fit), 488 M(-1) (x-reciprocal fit), 428 M(-1) (y-reciprocal fit) and 490 M(-1) (non linear fit). The corresponding K values at 313 K were 380 M(-1) (double reciprocal fit), 355 M(-1) (x-reciprocal fit), 366 M(-1) (y-reciprocal fit) and 339 M(-1) (non linear fit). Using the proposed methods, the binding constant of the indomethacin-beta-cyclodextrin inclusion complex can be obtained easily. The methods have been applied to obtain the values of the constant K under different experimental conditions. Under optimized conditions the K constant is temperature dependent and non-arrhenian behaviour was observed.

Assuntos

RESUMO

A high-performance capillary electrophoretic (CE) method has been developed for obtaining electropherograms of various extracts and the commercial formulation (fingerprints) of Hedera helix L used in Argentina as a cough's treatment. Also, a capillary zone electrophoresis (CZE) method was developed for the search, identification and determination of some possible adulterants. These likely adulterants are common synthetic drugs used in respiratory diseases (antitussive, decongestant and bronchodilator agents). Under optimum conditions, the analytes (ephedrine, codeine, diphenhydramine and constituents of H. helix formulations) were separated within less than 10 min in 20 mM sodium tetraborate buffer (pH 9.0). The present procedure was validated with respect to selectivity, linearity range, limits of detection (LOD) and quantification (LOQ), precision (repeatability and intermediate precision), solution stability and accuracy; the results obtained were satisfactory. Good linearity was obtained over two orders of magnitude and detection limits (S/N = 3) were better than 1.2 microg ml(-1) for all analytes. The CE methodology was successfully applied to the search and subsequent determination of ephedrine, codeine and diphenhydramine in H. helix extracts and its phytopharmaceutical products.

Assuntos

RESUMO

An alternative and new system for on-line preconcentration of arsenic by sorption on a mini-column associated to hydride generation--inductively coupled plasma--optical emission spectrometry determination was studied. It is based on the sorption of arsenic on a column packed with ethyl vinyl acetate (EVA) turnings and the use of La(III) as co-precipitant reagent. This polymeric material was employed here for the first time as filling material for column preconcentration. It could work both as adsorbent and as sieve material. Sample and co-precipitant agent (lanthanum nitrate) were off-line mixed and merged with ammonium buffer solution (pH 10.0), which promoted precipitation and quantitative collection on the small EVA turnings. The arsenic preconcentrated by co-precipitation with lanthanum hydroxide precipitate was subsequently eluted with hydrochloric acid, which was the medium used for hydride generation. Considering a flow rate of 5 ml/min, three enrichment factors were obtained, 28-, 38- and 45-fold at three different sampling times, 60, 120 and 180s; respectively. The detection limits (3s) obtained for each case were 0.013, 0.009 and 0.007 microg/l. Additionally, the calculated precisions expressed as relatively standard deviation (R.S.D.) were 0.9, 1.3 and 1.1%. Satisfactory results were obtained for the determination of arsenic in standard reference material NIST 1643e Trace Elements in Water and drinking water samples.

Assuntos

RESUMO

An on-line procedure for the determination of traces of total mercury in environmental and biological samples is described. The present methodology combines cold vapor generation associated to atomic absorption spectrometry (CV-AAS) with preconcentration of the analyte on a minicolumn packed with activated carbon. The retained analyte was quantitatively eluted from the minicolumn with nitric acid. After that, volatile specie of mercury was generated by merging the acidified sample and sodium tetrahydroborate(III) in a continuous flow system. The gaseous analyte was subsequently introduced via a stream of Ar carrier into the atomizer device. Optimizations of both, preconcentration and mercury volatile specie generation variables were carried out using two level full factorial design (2(3)) with 3 replicates of the central point. Considering a sample consumption of 25mL, an enrichment factor of 13-fold was obtained. The detection limit (3sigma) was 10ngL(-1) and the precision (relative standard deviation) was 3.1% (n=10) at the 5microgL(-1) level. The calibration curve using the preconcentration system for mercury was linear with a correlation coefficient of 0.9995 at levels near the detection limit up to at least 1000microgL(-1). Satisfactory results were obtained for the analysis of mercury in tap water and hair samples.

Assuntos

RESUMO

An on-line flow injection (FI) preconcentration-electrothermal atomic absorption spectrometry (ETAAS) method is developed for trace determination of chromium in drinking water samples by sorption on a conical minicolumn packed with activated carbon (AC) at pH 5.0. The chromium was removed from the minicolumn with 1.0% (v/v) nitric acid. An enrichment factor (EF) of 35-fold for a sample volume of 10ml was obtained. The detection limit (DL) value for the preconcentration method proposed was 3.0ngl(-1). The precision for 10 replicate determinations at the 0.5mugl(-1) Cr level was 4.0% relative standard deviation (R.S.D.), calculate with the peak heights obtained. The calibration graph using the preconcentration system for chromium was linear with a correlation coefficient of 0.9992 at levels near the detection limits up to at least 50mugl(-1). The method was successfully applied to the determination of Cr(III) and Cr(VI) in drinking water samples.

RESUMO

The present paper proposes an on-line preconcentration procedure for lead determination in Ilex paraguariensis (St. Hilaire) samples by ultrasonic nebulization associated to inductively coupled plasma optical emission spectrometry (USN-ICP-OES). It is based on the precipitation of lead(II) ion on a minicolumn packed with polyurethane foam using 2-(5-bromo-2-pyridilazo)-5-diethylaminophenol (5-Br-PADAP) as precipitating reagent. The collected analyte precipitate was quantitatively eluted from the minicolumn with 20% (v/v) nitric acid. An enhancement factor of 225-fold was obtained (15 for USN and 15 for preconcentration). The detection limit (DL) value for the preconcentration of 10.0 ml of sample was 40.0 ng/l. The relative standard deviation (R.S.D.) was 3.0% for a Pb concentration of 1 microg/l, calculated from the peak heights obtained. The calibration graph using the preconcentration system for lead was linear with a correlation coefficient of 0.9997, at levels near the detection limits up to at least 100 microg/l. The preconcentration procedure was successfully applied to the determination of lead in mate tea samples.

Assuntos

RESUMO

A method for the on-line preconcentration of copper using a minicolumn packed with activated carbon and its subsequent determination by inductively coupled plasma optical emission spectrometry (ICP-OES) coupled with flow injection (FI) was studied. In order to determinate the copper concentration present in parenteral solutions; it was retained on activated carbon (AC) at pH 9.5. A sensitivity enrichment factor of 30-fold was obtained with respect to the copper determination by ICP-OES without preconcentration. The detection limit for the preconcentration of 25 ml of sample was 0.1 microgl(-1). The precision for the ten replicate determinations at the 2.5 microgl(-1) Cu level was 3.0% relative standard deviation (R.S.D.), calculated with the peak heights. The calibration graph using the preconcentration method for cooper species was linear with a correlation coefficient of 0.9996 at levels near the detection limits up to at least 200 microgl(-1). The method was successfully applied to the determination of copper in parenteral solutions.

Assuntos

RESUMO

The objective of this work was to develop a method to determine the metal content in wine samples from the province of Mendoza in Argentina. Ten samples of white wine and 10 samples of red wine available in the supermarket were analyzed for the metals aluminium, cadmium, calcium, chromium, copper, iron, nickel, lead and zinc by electrothermal atomic spectrometry (ETAAS) and ultrasonic nebulization was coupled to inductively coupled plasma optical emission spectrometry (USN-ICP-OES). The aluminium, cadmium, calcium, copper, iron, lead, zinc, chromium concentrations were between 17.0-18.0 microg l(-1), 1.0-4.7microg l(-1), 10.0-15.0 mg l(-1), 23.0-28.0 microg l(-1), 480-790 microg l(-1), 50-90 microg l(-1), 24-130 microg l(-1), and <0.2-6.25 microg l(-1), respectively. The levels compare well with those reported for similar wines from some other parts of the world. A significant aspect in this paper is the samples mineralization step, which allowed the direct determination of the metals. Concerning to the Cd determination, a refluxing digestion system was used for the pretreatment of the samples.

Assuntos

RESUMO

The present paper proposes an on-line preconcentration procedure for cadmium determination in drinking water samples. It is based on the precipitation of cadmium(II) ions on a knotted reactor (KR) using 1(2-thiazolylazo)-p-cresol (TAC) as complexing reagent. The optimization step was performed using a full factorial design involving the variables: pH, eluent concentration (nitric acid) and TAC concentration. The results of this experiment demonstrated that these variables at chosen levels are not statistically significant. Under optimized experimental established conditions, analytical parameters for the preconcentration method were: a detection limit of 40.0 ng/l, precision as relative standard deviation (RSD) of 1.2 and 1.0%, for cadmium concentration of 2.5 and 20.0 microg/l, respectively. The preconcentration factor considering the slopes of the analytical curves with and without preconcentration is 23 for a sample volume of 10 ml. This system shows a sampling frequency of 25 h(-1). In order to check the accuracy, the standard reference material, NIST SRM 1643d trace elements in water was analyzed. A comparison, using t-test demonstrates that there is not significant difference among the achieved results with proposed method and the certified values. The addition/recovery experiments in the samples analyzed demonstrated the accuracy and applicability of the system developed for cadmium determination in water samples.

Assuntos