674
F.D. Madureira et al.
Table 3. Continued. 0.01 mg kg 1 0.05 mg kg 1 0.075 mg kg 1 0.1 mg kg 1 0.125 mg kg 1
Pesticide Omethoate Oxamyl Penconazol Pendimethalin Permethrin cis trans Phenthoate Phorate Phosalone Phosmet Picolinafen Pirimicarb Pirimiphos-ethyl Prochloraz Profenofos Propiconazole Propoxur Pyraclostrobin Pyrazophos Pyridaben Pyridate Pyrimethanil Spiroxamine Tebuconazole Tebufenozide Thiabendazole Thiacloprid Thiamethoxam Triasulfuron Triazophos Trichlorfon Trifloxystrobin
Linear calibration range (mg kg 1) 0.0075 0.0075 0.0075 0.0075 0.02 0.0075 0.02 0.0075 0.0075 0.0075 0.0075 0.0075 0.0075 0.0075 0.0075 0.02 0.0075 0.0075 0.0075 0.0075 0.0075 0.0075 0.0075 0.0075 0.0075 0.0075 0.0075 0.0075 0.0075 0.02 0.0075
– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –
0.10 0.10 0.10 0.10 0.125 0.10 0.125 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.125 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.125 0.10
Rec. (%)
RSD (%)
Rec. (%)
RSD (%)
Rec. (%)
RSD (%)
83 89 92 87 – 89 – 90 86 90 94 85 84 90 92 – 85 87 88 85 85 90 88 87 81 88 91 95 87 – 90
10 10 14 11 – 15 – 13 15 11 8 9 17 9 11 – 11 13 9 7 18 6 8 13 12 12 13 17 9 – 10
86 93 88 88 85 91 93 92 92 91 93 91 93 90 92 95 90 87 89 87 93 93 91 83 92 96 93 96 92 95 93
12 9 10 8 9 10 17 9 9 8 9 8 12 8 10 8 9 11 9 8 16 7 10 10 14 10 15 14 9 10 9
89 95 89 89 88 90 91 94 90 93 92 90 87 90 91 93 90 88 89 89 92 93 94 94 95 95 99 95 88 93 92
11 11 8 7 9 5 12 11 10 7 11 6 9 7 9 10 9 11 8 8 13 6 8 10 14 13 15 14 8 10 9
Rec. RSD (%) (%) 89 93 93 90 88 93 96 94 88 93 94 91 94 91 93 94 91 86 91 87 93 94 94 94 97 92 95 94 91 94 93
12 11 10 7 9 10 15 9 10 10 9 7 8 9 9 9 9 12 7 7 13 6 9 10 13 13 15 13 7 12 8
Rec. (%) – – – – 92 – 91 – – – – – – – – 95 – – – – – – – – – – – – – 92 –
RSD LOD LOQ (%) (mg kg 1) (mg kg 1) – – – – 9 – 14 – – – – – – – – 11 – – – – – – – – – – – – – 9 –
0.002 0.003 0.002 0.003 0.007 0.002 0.01 0.002 0.001 0.002 0.002 0.002 0.003 0.003 0.002 0.006 0.002 0.003 0.002 0.002 0.006 0.001 0.002 0.002 0.002 0.002 0.005 0.003 0.002 0.01 0.003
0.01 0.01 0.01 0.01 0.05 0.01 0.05 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.05 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.05 0.01
Note: n.q., not quantified.
approaches, as described in Eurachem Guide (Eurachem 2000). The weighing of samples, the measurements of volume of the extraction solvent added to the sample, the calibration curve and intralaboratory reproducibility were the principal uncertainty sources associated with the method. It was noted that the uncertainty relating to measurement of volume and weighing of the samples were negligible in comparison with the other uncertainty sources. Since the calibration curve comprises the uncertainty of various steps, such as weighing of standards, extraction procedure, instrumental analysis and statistical treatment of data, the main contribution to method uncertainty arises from construction of the calibration curves for most of the validated pesticides. The percentage expanded uncertainty (U%) for each pesticide, was determined at every spiking level for which repeatability and reproducibility studies were carried out, is showed in Table 4. For the compounds that presented calibration curve between 0.0075 and
0.10 mg kg 1, the uncertainty was calculated at levels of 0.01, 0.05, 0.075 and 0.10 mg kg 1. For the analytes whose calibration curves were set from 0.02 to 0.125 mg kg 1, the uncertainty was assessed at spiking levels of 0.05, 0.075, 0.10 and 0.125 mg kg 1. As can be seen from Table 4, the expanded uncertainty is typically less than 35% and, thus, agrees with Sanco requirements which establishes a default expanded uncertainty value of 50%. However, for some of the pesticides studied, there are uncertainty values at 50%, which can be considered high. For such pesticides, a greater dispersion in analytical results was observed from validation assays, leading to calibration curves in which the prediction limits cover a broader range of instrumental responses and, therefore, a higher variability. The compounds that present smaller uncertainty values generated instrumental response with a lower variability and, thus, calibration curves with prediction limits covering a narrower range. Figure 4 depicts calibration curves for the two