The table above reflected deviations caused by errors in the experiment that can either be all or a combination of the following: loss of material by leaks and drips; imprecision in solution preparation, particularly in the standard solutions; presence of impeding ions and compounds with the absorbing species; polychromatic behaviour of light source of spectrophotometer that would lead to departures from Beer’s law; partial reduction of Fe
3+ with unfinished reaction of iron on 1,10-phenanthroline; faulty calibration of spectrophotometer