Determination of Ni (II) in beverages without any sample pretreatment by adsorptive stripping chronopotentiometry (AdSCP)

The purpose of this paper was to use adsorptive stripping chronopotentiometry for the determination
of Ni (II) in worldwide consumed beverages without any sample pretreatment, using dimethilglyoxime
(DMG) as complexing agent and a glassy carbon mercury film electrode as the working electrode. Ni
(DMG)2 complex is adsorbed onto the mercury film at an electrolysis potential of -500 mV for 60 s
and then reduced by a -5 íA constant cathodic current. The sensitivity of the method was studied
for certified reference water and black tea in the pH range 6.5-11. At pH 9.5 in ammonia buffer, a
detection limit of 0.2 íg L-1 was achieved; the instrumental precision (expressed as rsd %) was
1.5%, and the accuracy, expressed as obtained recoveries both from certified and not certified
matrixes, ranged from 93.0 to 95.5 %. The chronopotentiometric analysis executed on commercial
beverages provided evidence that black tea samples were the richest source of Ni (II) (1500-3700
íg L-1), followed by coffee (100.0-300.5 íg L-1); bottled mineral water showed a Ni (II) concentration
lower than 4.6 íg L-1. Among alcoholic beverages, red wines presented the highest content of Ni (II)
(55.5-105.0 íg L-1). Significant differences were noticed between Ni (II) levels of fermented and
distillated alcoholic beverages; moreover, canned cola and beer did not show higher Ni (II) levels
with respect to the glass-bottled products.