Spectrophotometric determination of phenylalanine in aqueous solutions with different acidity

A method for the determination of phenylalanine using spectrophotometric without preliminary correction solutions pH and use auxiliary chemical reagents has been developed. comparative analysis by varying acidity medium was carried out. The errors possibility their minimization were analyzed. It shown that analytical signal results amino acid in with different differ significantly due to presence various ionic forms vary magnitude molar absorption coefficient. found maximum value coefficient decreases series ε(Phe−)> ε(Phe+)> ε(Phe±) 20%. error determining concentration taking into account dependence optical density solution on strongly alkaline solutions. correlation dependences wavelength obtained experimentally. long-wavelength (bathochromic) shift band established upon transition from positive negative charge molecule increasing solution. Two ranges values have identified, which a change did not cause spectral changes. These regions where predominantly cationic Phe+ bipolar Phe± (pH < 8) region anionic Phe− > 10) form. regression equations allow choosing at any arbitrary presented. advantage developed approach is detection sensitivity ensuring less than 0.5% variation no more 0.3%. limit acid, calculated 3σ – test, (1.4 − 1.6) × 10-5 M. range determined contents (0.5 5.3) 10-3 efficiency proposed content sample "L-Phenylalanine" (Protein Company, Russia) drug standard addition shown. minimizing when applying technique control components process demineralization water-salt electrodialysis experimental membranes proven.