46The study presents the assessment of uncertainty calculation generated, within the analysis of selected 23 organophosphrus pesticides residues of bottle guard. The samples were prepared by using a modified quick, easy, cheap, effective, rugged and safe (QuEChERS) analytical protocol. Multiresidue method used for analysis of samples consisted of (i) acetonitrile extraction, (ii) PSA/C18 clean-up and (iii) identification/quantification of residues by GC utilizing either (nitrogen–phosphorus) or mass-selective detectors (quadrupole analyzer) were evaluated. Major sources like weighing of standard, purity of certified reference material, precision study i.e repeatability and standard solution preparation for calculation of uncertainty of method, was considered. Identification of uncertainty sources, quantification of uncertainty sources and calculation of combined uncertainty are steps for calculation of uncertainty. All the individual uncertainty calculated are combined, later converted to expanded uncertainty.