DETERMINATION OF NITRATE IN CARBON-BLACK BY FLOW-INJECTION ANALYSIS (FIA) WITH POTENTIOMETRIC DETECTION

This paper reports the potentiometric detection of nitrate in carbon b lack samples by flow injection analysis (FIA). The detection system us ed consisted of a nitrate sensitive tubular electrode without inner re ference solution, incorporating a PVC membrane with an ionic sensor ba sed on tris(4,7-diphenyl-1,10-phenantroline) nickel(II) dissolved in 2 -nitrophenyloctyl ether as the solvent mediator. According to the work ing characteristics of the tubular electrodes, a double channel flow i njection system was constructed and optimised for direct sample analys is in a reduced time-frame. A solution of Pb(CH3COO)(2), PbO, CH3COOK and NH2SO3H was used as ionic strength and pH adjuster for both sample s and standards. The tubular electrodes showed a linear response for a concentration of at least 5 10(-5) mol.L-1 with a slope of 58.3 +/- 0 .9 mV/decade and a reproducibility of +/- 0.1 mV within two successive calibrations. Analysis of 10 different samples from several factories showed satisfactory results with average recoveries of about 100.5% /- 1.5% and a variation coefficient of 1.5%. With the proposed system, a sampling rate of 120 samples/h was obtained.