FLOW-INJECTION SPECTROPHOTOMETRIC DETERMINATION OF BORON IN CERAMIC MATERIALS

A flow injection spectrophotometric method for the determination of bo ron in ceramic materials is described. The method is based on spectrop hotometric measurement of the decrease in the pH produced by the react ion between boric acid and mannitol in the presence of an acid-base in dicator. A bichannel FI (flow injection) manifold in which the sample solutions were injected into deionized water (at pH 5.4) and the strea m was later merged with the reagent stream (a mannitol solution contai ning 1 x 10(-4) mol l(-1) bromocresol green at pH 5.4), was used. Tran sient signals were monitored at 616 nm. A theoretical model which desc ribes the dependence between the absorbance values and boric acid conc entration is presented. The model predicts a non linear dependence bet ween the absorbance or increment in absorbance and the boric acid conc entration. In contrast, the model predicts a linear dependence between the inverse of the absorbance values and the boric acid concentration . The calibration graphs (1/A vs mu g ml(-1) B2O3) were linear over th e range 1-30 mu g ml(-1) of B2O3. The relative standard deviations wer e 0.7 and 0.4% for 4 and 8 mu g ml(-1) of B2O3, respectively. The limi t of detection was 0.02 mu g ml(-1) of B2O3 (3 sigma criterium). The m ethod was used to determine boron in nine ceramic materials with very different nominal boron compositions. The results were compared with t hose obtained using a potentiometric titration method as reference met hod. No significant differences (at 95% probability level) were found between the proposed and reference methods. The method is rapid, relia ble, precise and free of interferences. (C) 1998 Elsevier Science B.V.