Page 29 - Volume 5, Issue 2, July 2012

© Benaki Phytopathological Institute
Bempelou et al. 58
Dithiocarbamate fungicides are pesti-
cides extensively used worldwide in agricul-
tural practice on a wide range of crops. Due
to their low acute toxicity combined with
strong action, low cost production and low
environmental persistence, the use of these
compounds is still increasing worldwide [16].
The determination of dithiocarbam-
ate (maneb, mancozeb, metiram, propineb,
thiram and ziram) residues is based on the
detection of their common degradation
product, which is carbon disulfide (CS 2).
Maximum residue limits (MRLs) set by Reg-
ulation 396/2005/EC are also referred to CS2,
with evident, however, the inability to dis-
tinguish the actual active compound (of di-
thiocarbamates) sprayed in the field.
The methods of analysis for the deter-
mination of dithiocarbamates are main-
ly based on the use of headspace gas chro-
matography (GC) [12], photospectrometric
techniques of absorption [14], GC with elec-
tron capture detector (ECD) or flame photo-
metric detector (FPD) [4] or mass spectrome-
try (MS) [1, 4, 7], while their determination as
parent compound has been reported by LC/
APCI/MS [3] and LC/ESI/MS [6]. The official
method of the European Community Refer-
ence Laboratory for single residue methods
is based on the determination of dithiocar-
bamates as CS 2 by GC/ECD [9].
Inorganic bromide (Br) atom [10097-32-2]
has atomic number 35, atomic mass 79.904,
and belongs to Group 17 (VIIA) of the Peri-
odic Table, the halogens. It is the degrada-
tion product of fumigants, mainly methyl
bromide, used for soil disinfection as well as
post-harvest treatment of plant products. It
can be absorbed by plants from treated soils
or it may be contained in fumigated prod-
ucts. Furthermore, the natural bromide con-
tent of most fresh plant materials is up to
5mg/kg [10]. Regarding that application of
methyl bromide is not further allowed in
agriculture, the determination of inorganic
bromide in plant products is imperative to
detect illegal uses.
Different analytical methods have been
published for the determination of the bro-
mide ion. They are based on x-ray fluores-
cence, spectroscopic [2], GC [14] and HPLC
techniques [14] with gas chromatography
being the most widely used. Recently, the
determination of inorganic bromide in plant
products was achieved by the use of GC/
ECD with the addition of internal standard
in the final extract [10].
In the present study our goal was to val-
idate two GC robust methods for the deter-
mination of dithiocarbamates and inorgan-
ic bromide in plant products with FPD with
sulphur filter and ECD detectors, respec-
tively, according to the requirements of the
SANCO Document 10684/2009.
Materials and methods
Chemicals and reagents
Analytical standard of thiram (99%) used
for the fortification experiments of the di-
thiocarbamates method was obtained from
Dr Ehrenstofer (Augsburg, Germany), a mix-
ture of 1-bromo-2-propanol and 2-bromo-
1-propanol analytical standard was used
for the identification of the bromide deriva-
tives and 3-bromo-1-propanol (99.5%) as in-
ternal standard were obtained from Chem-
Service (West Chester, UK). Carbon disulfide
(CS2) (density 1260mg/mL at 25οC) was pur-
chased by Merck, as well as potassium bro-
mide and were used as analytical standards.
Ethyl acetate, isooctane, ethanol and ace-
tone were of pesticide residues grade and
water of HPLC grade, all obtained from Lab
Scan (Dublin, Ireland).
Standard Solutions
Analytical standard stock solutions of thi-
ram and 3-bromo-1-propanol (internal stan-
dard) at 1000μg/L were made in acetone and
ethyl acetate and stored at -20oC. Stock solu-
tion of carbon disulfide at 1000μg/L in isooc-
tane was prepared anew every working day,
while the corresponding of potassium bro-
mide was prepared in water and stored at
8oC. Working standard solutions were pre-
pared in ethanol for thiram and in water for
bromide for the validation procedures. The
quantification of CS2 residues was based on