Analytical filter papers are generally made of fibrous cellulose which has the potential to adsorb metal ions. In this study, blue band ashless filter paper was used to demonstrate one of the sources of error in the determination of the concentration of Fe2+, Co2+, Mn2+, Cd2+, Cu2+, Pb2+ and Zn2+ ions. For this purpose, the metal ion content of standard solutions in the 1-100 mg/l concentration range was analysed via FAAS before and after the filtration process. The corresponding results and the calculated percentage errors due to adsorption are presented. The effect of pH on the adsorption process was also investigated. Activated carbon and soil samples were spiked with each metal ion and the solid phases from the resulting solutions were separated by both filter paper methods and centrifugation. In the statistical estimation of the results, the paired t-test was applied for non-filtered and filtered solutions in the concentration range 1-100 mg/l using the data analysis tools available in MS Excel (R). The use of filter paper caused systematic errors, particularly at lower metal concentrations, and hence centrifugation or a filtering process using techniques other than filter paper is favoured as a better approach towards estimating the concentration of heavy metal ions from aqueous solution.