Abstract

The suitability of spectrophotometric methods using cuvette tests (CT) for determination of ammonia (NH₄⁺-N), nitrates (NO₃^--N), total phosphates (РО₄^3--Р) and chemical oxygen demand (COD) in real wastewater were evaluated by comparison with corresponding Bulgarian national standard methods (BS). The CT methods are based on measuring of ready-to-use cuvettes (bar-coded reagent vials) inwavelength range of 340 to 900 nm. Nine wastewater samples from the  inlet of the wastewater treatment plant of Sofia city were collected in the period of three months and the above mentioned quality indicators were measured in parallel both with CT and BS methods. Mean values of ten replicate determinations for each of the samples were compared statistically using Dixon’s t-test and linear regression model. Excellent linear correlation (R² > 0.99) was found. As another mean of comparison, all the methods (CT and BS) for the determination of all the  quality indicators were validated and uncertainties were estimated. Based on this, all data were compared and proved statistically equivalent.

Key words: Method comparison, method validation, uncertainty estimation, cuvette tests, linear regression, spectrophotometer, wastewater.