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    STUDIA CHEMIA - Ediţia nr.1-2 din 2001  
         
  Articol:   PHOTOMETRIC DETERMINATION OF BIURET IN MELTED UREA USING FLOW INJECTION ANALYSIS.

Autori:  FRENŢIU TIBERIU, MICHAELA PONTA, EUGEN DARVASI, LADISLAU KÉKEDY-NAGY, IOAN MĂRGINEAN, EMIL A. CORDOŞ. 		 
       
         
  Rezumat:  A sensitive, rapid and automatable flow injection fotocolorimetric analysis is described for the determination of biuret in melted urea as blue-violet [CuBt(OH)2]2- complex in strongly basic medium (pH13). The automatic system consists of a refractometer and a double beam automated photometer equipped with a green filter (530-570 nm). The sample and reagents (CuSO4 5H2O 15 g l-1 and an alkaline solution of tartrate 50 g l-1 in NaOH 40 g l-1) are mixed in a 4:1:1 volumetric ratio. The kinetic study and the absorption spectra have shown the development of [CuBt(OH)2]2- complex in the system urea-biuret-Cu-tartrate as a result of the decomposition of tartric complex according to a 1:1 stoechiometry. The experimental conditions were optimised at 555 nm where the best limit of detection, calibration and analytical sensitivities are obtained. For a detection limit of 0.05 % biuret in urea (m/m), the method allows the quantitation of biuret in the range 0.25-2.5% with an RSD lower than 10%. This approach offers significant advantages in terms of speed (5 samples/hour), automation and precision compared with existing manual procedures.  
         
     
         
         
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