Integrated microwave digestion and hydride generation in a head space system with selenium hydride preconcentration on carbon nanotubes for wine pomace analysis

LOPEZ, AYELEN; PABLO H. PACHECO; VÁZQUEZ, SANDRA; LARA, RODOLFO; MARATTA, ARIEL

Vitória, Espírito Santo, Brazil

Simposio; 14th RIO SYMPOSIUM ON ATOMIC SPECTROMETRY; 2017

Selenium (Se) is an essential trace element for animals and humans. Selenium integrates glutation peroxidase, an enzyme with antioxidant activity, related to cancer prevention. In the environment, Se is present in both soil and water, and can be mobilized through the roots of plants or aquatic organisms thus entering the food chain. Then fertilizing plants with selenium is nutritional relevant.1, 2 Grapes (Vitis vinifera) offers different processed products like wines, and by-products called pomace that include grape skins and seeds. Different elements usually precipitate during the fermentation stage in the elaboration of wine, forming part of the by-product.3 Some research indicates that appropriate use of agro-industrial waste, such as grape pomace, could have an impact on agricultural productivity and soil fertility through composting.4 Therefore, assess the environmental impact of this practice is necessary, especially in essential elements like selenium.This research describes a method to analyze selenium in pomace samples in an integrated microwave assisted digestion-head space vial. Selenium hydrides were preconcetrated on oxidized carbon nanotubes (CNTs) in an FI system with Electrothermal Atomic Absorption Spectrometry (ETAAS) for determination. A multivariate statistical optimization was performed to establish optimal working conditions. Sample quantity, nitric acid volume, hydrogen peroxide concentration and eluent volume were most influencing factors. A high extraction efficiency (94%) was achieved, with a preconcentration factor of 80 when 200 mg of sample were placed in the headspace vials. In a first step 4 mL of 0.5 M HNO3 and 3 mL of 30 % H2O2 (v v-1) were added to the sample in the HS vial and exposed to microwave radiation. A second step involved addition of 2 mL of 2% NaBH4 (m v-1) for hydride generation and preconcentration on oxidized carbon nanotubes (CNTs). Then, it was eluted with 20 uL of 5% HNO3 (v v-1). The detection limit was 3.0 ng L-1. Precision (%RSD) corresponds to 5.3% (n = 10). The main advantages of the proposed methodology are integrated digestion and hydrides generation, minimal sample consumption, reduction of reagents volume and concentration; and reduction of time of analysis.