Pilar Bermejo Barrera

Determination of As, Cd, Pb and Se in DORM-1 dogfish muscle reference material using alkaline solubilization and electrothermal atomic absorption spectrometry with Ir+Rh as permanent modifiers or Pd+Mg in solution

Abstract In this work, tetramethylammonium hydroxide (TMAH) was used to solubilize the DORM-1 dogfish muscle certified reference material as a model substance for the determination of As, Cd, Pb and Se by electrothermal atomic absorption spectrometry (ET AAS). The sample was mixed with a small amount of TMAH and heated to 60 °C for 10 min in a water bath. After dissolution, As and Se were determined using palladium and magnesium nitrates as a chemical modifier added in solution. For Cd and Pb, best results were obtained with a mixture of 250 μg of each of iridium and rhodium as permanent modifiers. In both cases, the calibration was performed with aqueous solutions in 0.2% v/v HNO 3 . The temperature program for each analyte was optimized using pyrolysis and atomization curves established with the fish reference material. The detection limits in dry samples and the characteristic mass values were: Cd 0.005 μg g −1 and 0.9 pg; Pb 0.04 μg g −1 and 7.6 pg; As 0.4 μg g −1 and 13 pg and Se 0.6 μg g −1 and 20 pg, respectively. Results from the determination of these elements in the DORM-1 certified fish reference material were within the 95% confidence interval of the certified values.

Especiação de cobre e chumbo em sedimento do Rio Tubarão (SC) pelo método Tessier

The sequential extraction procedure proposed by Tessier and total digestion were applied for the analysis of sediment samples from Tubarao River. The recoveries were between 93.5 and 102.5% for Cu and 99.2 and 111% for Pb. The precision was tipically better than 6% for Cu and 3% for Pb. Comparison of the values obtained for the total digest with the sum of the extracted fractions showed that there were no significant losses in the extraction steps so that the method can be used for the monitoring availability and mobility of these analytes. According to ten points of sampling, was possible to determined the average of labiles phases (fractions 1 and 4) for Pb and Cu: 33.70% and 18.18%, respectively; and the inert phases (fraction 5- residual): 66.30% for Pb and 81.82% for Cu.

Spectrophotometric determination of molybdenum with thiocyanate and pyrogallol

Abstract A new extraction-spectrophotometric method for Mo determination with thiocyanate and pyrogallol in MIBK is reported. The mixed ligand complex obeys Beers law between 0.04 and 1 μg of Mo/ml and molar absorptivity is 100,000 liters · mol −1 · cm −1 . The absortion spectra and the effects of acidity, amount of reagents, time, and temperature are also studied, together with the stoichiometry of the complex, the reproducibility and precision of the method, and the susceptibility to interference of the common ions.

Development and application of molecularly imprinted polymer – Mn-doped ZnS quantum dot fluorescent optosensing for cocaine screening in oral fluid and serum

A molecularly imprinted polymer - Mn-doped ZnS quantum dot-based fluorescence probe for cocaine abuse screening has been prepared and applied to complex samples such as serum and oral fluid. The fluorescent sensing material was prepared by anchoring a selective MIP for COC on the surface of polyethylene glycol (PEG) modified Mn-doped ZnS quantum dots (QDs). Simple and low cost methods have thus been optimized for assessing cocaine abuse in serum and oral fluid by monitoring fluorescence quenching when cocaine (COC) is present (optimized operating conditions with 1.5mL of 200mgL-1 MIP-coated QDs solution, pH 5.5, and 15min before fluorescence scanning). The matrix effect was found to be important when analyzing oral fluid and serum, and several strategies based on centrifugation for oral fluid and solid phase extraction (SPE) for serum were explored. Two analytical methods were developed for oral fluid. The first one (direct method) requires a centrifugation step (6°C, 4000rpm, 20min) to avoid the matrix effect, and allows for cocaine determination by using an aqueous calibration (1:20 dilution). The second method was developed for oral fluid sampled by Salivette devices, and also requires a further centrifugation (6°C, 4000rpm, 20min) of the recovered oral fluid. This method, however, requires the standard addition technique (1:20 dilution) because of the existence of the matrix effect. Regarding serum samples, a direct method (serum dilution) was not possible, and an SPE procedure was needed to avoid the matrix effect (use of aqueous calibration). The limits of detection and quantification when using the Salivette method were 0.035mgL-1and 0.117mgL-1, respectively; whereas, 0.015mgL-1 (LOD) and 0.050mgL-1 (LOQ) were obtained for serum.