International Congress BIOLOGICAL PRODUCTS - Gruppo di ...

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DETERMINATION OF Cd (II), Cu (II), Pb (II), AND Zn (II) IN BIOLOGICAL AND NOT BIOLOGICAL
CITRUS ESSENTIAL OILS BY DERIVATIVE POTENTIOMETRIC STRIPPING ANALYSIS (dPSA)
Dugo Giacomo, Giuffrida Daniele, Drogo Alessandra, La Pera Lara
Dipartimento di Chmica Organica e Biologica Università di Messina Salita Sperone, 31, 90166 S. Agata -Messina
Citrus essential oils are complex mixtures of many classes of volatile (85-98%) and not volatile (15-2%)
compounds (1); they are used in food and cosmetic farm as aromatizer and in pharmaceutical industry as additives of
some drugs (2). Their wide use implies a strict control of the presence of organic and inorganic contaminants as heavy
metals. There is a lack of available data regarding to the presence of heavy metals: some reports concerning to the
micro-elements composition of citrus peel extracts were found (3,4). Metals levels in citrus essential oils mostly
depend on the type of soil, agrochemical treatments, but also on extraction procedures as scraping or pressing, since
the fruits inevitably come in contact with metallic surfaces (5). In this work potentiometric stripping analysis is used to
determine the content of Cd (II), Cu (II), Pb (II) and Zn (II) in lemon, mandarin, orange and bergamot non biological
essential oils produced in Sicily and Calabria in the crop year 1999 (6). Moreover 13 samples of bergamot biological
essential oils and 13 samples of non-biological essential oils produced in Calabria in the crop year 2000, were studied.
MATERIALS AND METHODS
Reagents
All oils are sampled in dark glassy bottles, with blind nipples, and stored at 4°C until the analyses. Ultra pure
hydrochloric acid (34-37%), Hg (II) (1000 µgmL -1 , 1M in hydrochloric acid) and Cd (II), Cu (II), Pd (II), Pb (II), Zn (II)
(1000 µgmL -1 , 0.5 N in HNO3) standard solutions were purchased by Panreac (Barcelona, Spain); Ga (NO3)3⋅3H2O (5 g,
99.9%) was purchased by Aldrich Chem. Co. (Milwakee, WI, USA). The extracts were filtrated on a carbon column
Supelclean ENVI-Carb SPE (0.5 g, 6 mL), purchased by Supelco (Bellefonte, PA, USA).
Apparatus
Metals analysis are carried out by a PSA ION 3 potentiometric stripping analyzer (Steroglass, S. Martino in Campo,
Perugia, Italy), connected to an IBM-compatible personal computer. The analyzer operates under the control of the
NEOTES 2.0.1 software package (Steroglass). The determination is carried out in a conventional three-electrode cell.
The working electrode was a glassy carbon one coated with a thin mercury film; reference electrode was an Ag/AgCl
electrode (KCl 3M), and a platinum wire auxiliary electrode was used.
Procedures
Hydrochloric acid extraction
A 8.60 g (10.00 mL) sample aliquot and a 10 mL volume of 36% ultrapure-hydrochloric acid (Panreac, Barcellona), are
introduced in a teflon beaker. The extraction was carried out for about 30 min under magnetic stirring at the temperature
of 90 °C. The acid sample, was transferred in a separating funnel and let to cool for about 5 minutes. In order to favour
the separation of the two phases, the mixture is spiked with 1.0 mL ultrapure methanol, then the acid layer was collected
in a 20.00 mL flask. The organic layer is extracted again with 4.50 mL of concentrated hydrochloric acid for 5 min,
under the same conditions described, and then washed with 4.50 mL of boiling water; washings were added to the acid
extracts and made up to the mark with water. The obtained solution was passed through a carbon column. The filtered
solution was used for the simultaneous determination of Cd (II), Cu (II), Pb (II), and Zn (II).
Potentiometric determination
All analysis were executed in a conventional three electrodes cell; working electrode was a glassy carbon electrode
coated with a Hg film, the reference one was an Ag/AgCl electrode, the counter was a Pt electrode. The concentrations
of Cd (II), Cu (II), Pb (II), and Zn (II) were simultaneously determined. 1.00 mL of acid extract, 17.50 mL of ultrapure
water, 1.00 mL of 1000 µg mL -1 Hg (II) as oxidant agent and 0.50 mL of 10 µg mL -1 Ga (III) - in order to prevent
Cu-Zn complexes formation on the mercury film (6)- were put into the electrochemical cell. The quantitative analysis
was executed by the multiple points standard additions method. The potentiometric parameters are reported on table 1.
Method performances
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