Determination of selenium in nuts by cathodic stripping potentiometry (CSP)

The aim of this work was to determine the selenium content in nut samples by cathodic stripping potentiometry. Dry-powdered nuts were digested by HNO3 and dissolved with concentrated hydrochloric acid. To avoid the interference of natural oxygen, the potentiometric determination of selenium was carried out in an electrolyte solution consisting of 2 M CaC2 and 4 M HCl. The analysis was executed applying an electrolysis potential of -150 mV for 60 s and a constant current of -30 μA. Under these conditions, detection limits lower than 1.0 ng-1 were obtained for selenium analysis in nuts. The relative standard deviation of these measurements (expressed as rsd %) ranged from 0.44 to 0.88% while recoveries ranged from 90.2 to 95.3%. The results obtained with the proposed method were compared with those obtained via hydride vapor generation atomic absorption spectroscopy, a common method for determining selenium. The results of the two methods agreed within 5% for almond, hazelnut, and pistachio samples. The mean concentrations of selenium determined in Sicilian samples of almond, hazelnut, and pistachio were 531 ± 1, 865 ± 1, and 893 ± 4 μg/kg, respectively.