Chemistry Reference
In-Depth Information
3.4. Quantitative determinations
All samples were quantified using the method of external standards. The linear
concentration range was derived from the calibration graphs. Seven-point calibration curves
for each compound were found to be linear ranging from 0.05 to 2.0 µg/ml, with 1/x
weighting and with correlation coefficients (r
2
) of >0.995. SIM traces were integrated for
quantitation purposes. The limit of detection (LOD) and limit of quantification (LOQ) were
estimated from the computer-generated software using a signal-to noise ratio (S/N)
program. The LOD and LOQ were determined based on a signal to noise ratio of 3 and the
limit of quantification (LOQ) was based on a signal to noise ratio of 10.
The internal standard was evaluated qualitatively only to confirm the injection of the sample
extract. Normalization against the internal standard was not considered feasible because of
unpredictable and varying matrix effects for several of the matrices studied in this work. A
matrix-matched standard was also prepared by spiking the final extract; a fortification
standard was added to the blank sample that had been extracted using the same procedure.
3.5. Pesticide recoveries
Recovery of pesticides from the fortified samples was calculated relative to that from a
solvent standard and a matrix-matched standard. The acceptable percentage ranges for
recovery (accuracy) and CV (precision) was based on CODEX criterion for method
validation.
Recoveries and coefficients of variation of triazoles from fortified orange samples are shown
in Table 2 and Fig. 6. Samples were spiked at 0.05mg/kg, 0.5mg/kg and 1mg/kg. The
recoveries for these triazoles were from 60% to 145% with CV of 2.3 to 13.1% Most of the
compound recoveries give more than 70% and fufills the codex acceptable recovery range.
The recovery for Cyproconazole, tebuconazole and propiconazole at 1.0 mg/kg and
myclobutanil at 0.05 mg/kg falls outside the acceptable range but the CV is within the
acceptable range. Overall average recovery was 95% at all 3 fortification levels and all
compounds met the CODEX CV acceptable range.
Orange
0.5 mg kg
-1
1.0 mg kg
1
0.05 mg kg
-1
Triadimenol
9.3 (2.3)
59.6 (7)
89.1 (11.4)
88.9 (4.7)
Cyproconazole
128.8 (4.9)
75.2 (4.9)
Myclobutanil
83.9 (5.5)
103.0 (3.9)
144.9 (4.8)
Triadimefon
89.7 (2.7)
65.7 (7.1)
85.9 (3.1)
Tebuconazole
98.5 (4.0)
142.4 (5.5)
100.9 (5.3)
Fenbuconazole
73.1 (5.9)
111.4 (3.9)
91.84 (13.1)
Hexaconazole
117.0 (7)
87.0 (5.4)
74.8 (6.4)
Propiconazole
75.0 (4.7)
121.5 (3.2)
69.4 (9.8)
Difenoconazole
118.7 (4.3)
86.2 (5.9)
87.7 (9)
Table 2.
Recovery of Triazoles in orange (n=5)
