Measurement uncertainty of spectrophotometric determination of hexavalent chromium in water

Hexavalent chromium, +6 oxidation state of chromium, is known to be human carcinogen besides damaging respiratory system, kidney, liver, skin and eyes and it can be discharged to surface waters through industrial processes such as welding on stainless steel, painting and electroplating. For the determination of this carcinogen hexavalent chromium in water, one of the most common analytical methods is the colorimetric diphenylcarbazide method. But, in order to report an analysis accurately, the measurement uncertainty of the parameter must be accompanied to the result of the analysis. The aim of this study is to present the measurement uncertainty of hexavalent chromium in water that is determined by the colorimetric method. The sources of uncertainty are specified by a cause-effect diagram and enlarged by using the calculations, thus giving the budget of uncertainty. At the end of the calculations, it was found that the measurement uncertainty was dominantly affected by the calibration curve whereas the precision had no significant effect on the measurement uncertainty. The expanded relative uncertainty was determined as ±0.05 with 95% confidence level.