In the present study, a novel and eco-friendly sequential injection analysis (SIA) system
with spectrophotometric detection was developed for determination of Cd(II) in vegetable
samples. The method is based on the reaction of 8-hydroxyquinoline with Cd(II) as a
less-toxic complexing agent in H2SO4 solution, resulting in a light yellow colored complex
monitored at 360 nm. The SIA parameters were optimized to obtain the best sensitivity
and minimum reagent consumption. Under the optimum conditions, linear calibration graphs
over the ranges of 0.04-1.0 mg L-1 and 1.5-5.0 mg L-1 were established. Due to the limitation
of Beer’s law, the maximal absorption of the complex was observed at Cd(II) concentration
of 1.0 mg L-1. Above which the absorbance decreased with curvature and started to be linear
with low slope. The useful calibration graph for Cd(II) in vegetable sample was the first one.
The limit of detection was 0.01 mg L-1, with the intra-day and inter-day precisions were less
than 1.5%. The proposed method was successfully applied to the determination of Cd(II) in
different vegetable samples (chinese kale, false pakchoi, cabbage, lettuce, cucumbers, coriander,
water convolvulus, yard long bean, tomatoes, and potatoes) after appropriate sample
pretreatment. The obtained results were in good agreement with those obtained by the
ICP-MS standard method, verified by the student t-test at the 95% confidence level.