Comparison of spectrophotometric and colorimetric methods
for the detection of methyl parathion pesticide residues extracted from
apples. Samples 1–4 represent apples sprayed with 0, 20, 60, and 100
μg mL−1 of methyl parathion, respectively. The light red region indicates
the app scanned as “+”, while the region in light blue indicates the app
scanned as “−”.