Desenvolvimento de métodos analíticos para a determinação multielementar em amostras de cervejas.

Abstract

Beer is an attractive alcoholic beverage because it is light, refreshing and has peculiar sensory characteristics. In the present work, analytical strategies were developed for the determination of inorganic species in beer samples. In the first step, an analytical method was developed for the determination of Cl, Fe and Si in beer samples using the strategies of sequential and simultaneous determination by high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS) in combination with high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS GF MAS). First, Cl was determined using 600 °C and 1700 °C as the pyrolysis and vaporization temperatures, respectively, using In as a forming agent of the InCl molecule. Then, Si and Fe were simultaneously determined from the same sample aliquot using 2600 °C as the atomization temperature. A solution of Pd/Mg was used as a chemical modifier. The matrix effect was evaluated, and the results indicated that external calibration was possible using aqueous standard solutions. The limit of detection and quantification were, respectively, 0.05 and 0.17 mg L-1 for Cl, 0.08 and 0.26 mg L-1 for Si, and 2.0 and 6.7 μg L-1 for Fe. Recovery tests presented interval between 85 and 120% for the three analytes. The concentration range found in the samples varied between 106 - 277 mg L-1 for Cl, 15 - 37 mg L-1 for Si, and < 20–73 μg L-1 for Fe. In the second step, an evaluation of different elements (Be, Ga, In, Sc and Y) was performed as candidates for internal standards (IS) for the determination of Al, Ba, Co, Cr, Cu, Fe, Mn, Ni, Sr, Zn, Ca, Mg, Na, K in beer samples using microwave-induced plasma optical emission spectrometry (MIP OES). The analytical performance for each potential IS was established based on the limit of detection, limit of quantification, addition and recovery tests and accuracy obtained in the determination of each analyte. In the presence of the recommended IS, the limit of detection varied, in mg L-1, from 0.23 to 4.6 for microelements and between 10 and 620 for the macroelements. The limit of quantification, in mg L-1, was between 0.78 and 15.4 and between 30 and 970 for the microelements and macroelements, respectively. The precision values of the measurements were less than 1.0% for all analytes. The methods developed in this work can be considered easy to apply, generating the minimum amount of residues and presented adequate analytical characteristics, such as: precision, accuracy and sensitivity for the determination of inorganic species in beers using different analytical techniques.