Citric Acid Determination by Dual Wavelength Spectrophotometry

In this study, a dual wavelength spectrophotometric method was presented on the basis of Cu²⁺‐NH₃ complex decomposition by the citrate ion and the formation of Cu²⁺‐citrate complex. Sum of the absorbance decreasing at 600 nm (λ_max for Cu²⁺‐NH₃ complex) and the absorbance increasing at 750 nm (λ_max for Cu²⁺‐citrate complex) was used in quantification. This method is very selective, fast and inexpensive but relatively less sensitive. The calibration curve is linear in the range of 0.4–8 mmol/L with a detection limit of 0.13 mmol/L. The relative standard deviation (RSD%) for the six repeated determinations (2 mmol/L) is 1.75%. Interference studies of more than twenty common compounds, which are present in the studied samples, were carried out. Only oxalic and ascorbic acids are serious interferes and which interferences were eliminated by simple procedures. Finally, the proposed method was successfully applied in the determination of citric acid content in ORS powder and some fruit juices.