2.4. Quality assurance
Appropriate quality assurance procedures and precautions were taken to ensure
the reliability of the results. Samples were carefully handled to avoid contamination.
Glasswares were properly cleaned, and reagents were of analytical grades.
Deionized water was used throughout the study. Reagent blank determinations
were used to correct the instrument readings. For validation of the analytical procedure,
repeated analysis of the samples against internationally certified plant standard
reference material (SRM-1570) of National Institute of Standard and
Technology were used, and the results were found within ±2% of the certified
values.
2.5. Statistical analysis
The recorded data were subjected to two-way analysis of variance (ANOVA) to
assess the influence of different variables on the concentrations of heavy metals in
the vegetables tested. ANOVA for each vegetable was performed separately using
variables such as months and sites, as numbers of sites and month for each vegetable
tested varied. All the statistical analyses were computed with SPSS software version
12