Methods development and application for triazine herbicides determination in fruits and vegetables: comparing the significance of solid phase extraction, QuEChERS extraction, and ultrasonic solvent extraction techniques.
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Date
2021
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Abstract
This work reports on a quick, easy, cheap, effective, rugged, and safe (QuEChERS), solid phase
extraction (SPE) and ultrasonic solvent extraction (USE), combined with liquid
chromatography-photodiode array detection (LC-PDA) method optimization for the analysis
of triazines pesticides. These LC-PDA analytical methods were optimized in terms of linearity
while SPE, USE, QuEChERS were optimized in terms of limits of detection (LOD), limit of
quantification (LOQ), percentage recoveries in order to improve their efficiency. The
optimized methods were then applied to fruits and vegetables from local markets to assess the
residues of the commonly used triazine pesicides (atrazine, simazine, propazine, ametrine,
terbuthylazine).
The results showed a good linearity with the R2 values above 0.99 for all the triazines analysed.
The LODs and LOQs ranged from 0.4 -1.4 μg/kg and 1.5 - 4.5 μg/kg for QuEChERS, 0.3 - 1.8
μg/kg and 1.4 - 4.9 μg/kg, for SPE. The recoveries ranged from 84 -102% for QuEChERS and
76 -119% for SPE, with relative standard deviation less than 20% for results of both methods.
These results showed that both QuEChERS and SPE proposed methods are sensitive indicating
that they can be effectively applied for the detection and monitoring of the selected triazines in
fruits and vegetables. The optimised QuEChERS and SPE methods were then applied to fruits
(apples, pears, bananas, avocado, and oranges) and vegetables (carrots, potatoes, tomatoes,
cucumber and spinach) to compare their applicability. The concentration of triazines were
detected in spinach (17 - 84 μg/kg), avocado (4 - 6 μg/kg), cucumber (10 - 14 μg/kg), tomato
(34 - 39 μg/kg), carrot (22 - 71 μg/kg), banana (19 – 38 μg/kg), orange (23 – 46 μg/kg), apple
(10 - 16 μg/kg) and pear (18-20 μg/kg). Simazine was detected in all fruits and vegetable
samples except in pear, while terbutylazine was not detected in all samples analysed. Propazine
and ametryn were only found in carrot while pear sample only had atrazine. The mean results
of both methods were not statistically different at 95% confidence level. QuEChERS can be
recommended for routine analysis of these triazines since it involves fewer extraction steps
compared to SPE and thus will require shorter analysis time.
The ultrasonic solvent extraction (USE) method was also optimized and applied with and
without solid-phase clean-up for analysis of triazines. The LOD and LOQ obtained ranged from
1.1-1.8 μg/kg and 3.4 - 5.2 μg/kg for USE with SPE clean-up and 0.6 - 1.0 μg/kg and 1.7 - 2.9
μg/kg for USE without SPE clean-up. The methods showed recoveries ranging from 75 - 81%
for USE with SPE clean-up, and 102 - 106% for USE without SPE clean-up with relative
standard deviation less than 15% for both methods. This implied that both methods are precise,
however, USE without SPE clean up showed to be more sensitive for the extraction of the
selected triazines pesticides in fruits and vegetables. The USE with and without SPE clean-up
methods was then applied to fruits (grapes, lemon, passionfruit and plum), and vegetables
(beetroot, bell pepper, cabbage and peas) samples. The concentration of triazines were detected
in beetroots (102 - 152 μg/kg), bell pepper (45 - 88 μg/kg), grape (14 - 22 μg/kg), lemon (3.2
-156 μg/kg), passionfruit (32 - 222 μg/kg), and peas (126 – 138 μg/kg) and plum (9 – 11 μg/kg).
Propazine was the most dominant triazine while terbuthylazine was not detected in all samples
analysed. Passionfruit was the most polluted while none of the analysed triazines was detected
in cabbage. All the triazines were quantified at levels below the maximum residue limits (MRL)
in all fruits and vegetables which reveals that they are not harmful to human health. This work
showed that proposed USE method can be considered an inexpensive, environmentally friendly
method that can be used for routine analysis and monitoring of the selected triazines. Moreover,
USE can be accurately applied without the additional SPE to assess the residual levels of
triazines in fruits and vegetables.
Description
Masters Degree. University of KwaZulu-Natal, Pietermaritzburg.