Chemistry Reference
In-Depth Information
2.2. Chemicals and reagents
The fungicides: cyproconazole, difenoconazole, fenbuconazole, hexaconazole, myclobutanil,
propiconazole, tebuconazole, triadimefon and triadimenol were purchased from Pestanal,
Riedel-de Haen (Seelze, Germany) with purity ranging from 95-100%. Acetonitrile,
methanol, ethyl acetate of HPLC grade and residue analysis grade were obtained from
Labscan and Merck (Darmstadt, Germany). Formic acid which was added to the mobile-
phase acetonitrile was purchased from Fluka.
Salts used for the dispersive clean-up were anhydrous magnesium sulfate and sodium
acetate which were obtained from Merck and Mallinckrodt. The SPE sorbent used was
Bondesil PSA, 40µm from Varian. Deionized water (<8cm MΏ resistivity) was obtained
from the Milli-Q Advantage A10 Pure Water System (Millipore, Bedford, MA, USA). All
solvents were filtered using a 0.45µm nylon membrane filter from Whatman (Maidstone,
England).
2.2.1.
Stock and working solutions
Stock solutions of 1000 µg/ml were prepared in methanol by dissolving approximately
0.020g of the individual standards in 20mL of methanol and stored at 4
o
C in a reagent bottle.
Intermediate standard solution mixtures of 50 and 10 µg/ml were prepared in methanol and
standard working solutions at various concentrations were prepared daily by appropriate
dilution of the stock solution or the intermediate standard solution in methanol.
2.3. Methods
2.3.1. Extraction and clean-up
The extraction method used was based on QuEChERS method [6] and modified by Aysal et
al., 2007 [7]. The samples were chopped into smaller pieces and homogenised using a food
processor. 30g of the homogenised sample was placed in a 250ml borosilicate bottle and
extracted with 60ml of ethyl acetate, 30g of anhydrous sodium sulfate and 5g of sodium
hydrogen carbonate. 10 ml of the extract was centrifuged at 2500 rpm for 2 min followed by
clean-up with PSA sorbent and anhydrous magnesium sulfate. After clean-up, 5 mL of the
extract was reduced to almost dryness under a stream of nitrogen and was redissolved in
methanol.
2.3.2. Recovery studies
Four types of fruits and vegetables namely carrot, cabbage, tomato and orange were used
for the recovery studies which represent root and tuber vegetables, brassica leafy vegetables,
fruiting vegetables and citrus fruits according to the CODEX classification of commodities.
The samples for recovery determination were prepared by spiking with the standard
solution. Each sample was fortified with nine triazole standards at 0.05, 0.5 and 1.0 µg/ml
and five replicates at these fortification levels for each matrix. The fortified samples were
