| Abstract | U ovom radu optimizirana je i vrednovana nova metoda određivanja N-acetil-L-cisteina analizom slijednim injektiranjem uz spektrofotometrijski detektor. Metoda se temelji na redoks-reakciji, u kojoj tiolna skupina N-acetil-L-cisteina reducira bis(batokuproindisulfonato)kuprat(II) kompleks. Pri tome nastaje vrlo stabilan kompleks narančaste boje, bis(batokuproindisulfonato)kuprat(I) kompleks. Nastali kompleks postiže apsorpcijski maksimum pri λ = 483 nm. Optimizacijom su obuhvaćeni kemijski parametri (pH-vrijednost i molarni omjer BCS i Cu2+), kao i parametri SIA sustava (redoslijed injektiranja, volumni protok osnovne otopine, volumen injektiranja reagensa, volumen injektiranja analita, volumen petlje zadržavanja i duljina reakcijske uzvojnice). Za optimiziranu metodu određeno je linearno dinamičko područje u rasponu od 4,0 × 10–7 mol L–1 do 4,0 × 10–5 mol L–1, uz pripadajuću jednadžbu pravca: y = 7134 x + 0,0043 i koeficijent linearne regresije, R2 = 0,9996. Određene su granica dokazivanja (LOD = 1,3 × 10–7 mol L–1) i granica određivanja (LOQ = 4,0 × 10–7 mol L–1). U određivanju analita, ne interferiraju tvari koje se uobičajeno nalaze u sastavu farmaceutskih pripravaka. Vrednovanje metode uključivalo je ispitivanje točnosti (iskoristivosti), prenošenja signala te dosega (potpunosti reakcije). Mjerenjem niza od 15 uzastopnih injektiranja standardne otopine analita, utvrđena je ponovljivost metode uz relativno standardno odstupanje, RSD = 2,62 %, dok je učestalost mjerenja 20 uzoraka na sat. Uspoređeni su rezultati razvijene metode određivanja N-acetil-L-cisteina sa standardnom metodom koju propisuje Farmakopeja. |
| Abstract (english) | In this study, a new method for the determination of N-acetyl-L-cysteine using sequential injection analysis with spectrophotometric detector had been optimized and validated. The method is based on a redox reaction in which the thiol group of N-acetyl-L-cysteine reduces the bis(bathocuproinedisulfonate)cuprate(II) complex. This produces a very stable orange complex, the bis(bathocuproinedisulfonate)cuprate(I) complex. The resulting complex reaches an absorption maximum at λ = 483 nm. The optimization included chemical parameters (pH value and molar ratio of BCS and Cu2+), as well as parameters of the SIA system (sequence of injection of sample and reagent, volume flow of carrier solution, injection volume of the reagent, injection volume of analyte, volume of holding coil and reaction coil length). The method found to be linear over the range from 4.0 × 10–7 mol L–1 to 4.0 × 10–5 mol L–1, the following equation had been determined: y = 7134 x + 0.0043 and the correlation coefficient, R2 = 0.9996. Limit of detection (LOD = 1.3 × 10–7 mol L–1) and the limit of quantification (LOQ = 4.0 × 10–7 mol L–1) were determined. No interferences were observed from the excipients that are commonly present in the pharmaceutical formulations. Validation of the method included evaluating accuracy, carry over and extent of reaction. Repeatability was confirmed based on results of 15 sequential injections of standard analyte solution with relative standard deviation, RSD = 2.62%, at a sampling rate of 20 analysis per hour. Results of the developed method for the determination of N-acetyl-L-cysteine were compared with results of the standard Pharmacopoeial method. |
