DETERMINATION OF CHROMIUM IN ENVIRONMENTAL-SAMPLES BY FLAME AAS WITH FLOW-INJECTION ONLINE COPRECIPITATION

A flow injection on-line coprecipitation flame atomic absorption spect rometric (FAAS) system for the determination of Cr was developed to im prove the sensitivity and selectivity of chromium determination in env ironmental samples, Cr(III) was preconcentrated and separated from pot ential interferents by on-line coprecipitation with Ianthanum hydroxid e. The precipitate was collected on the walls of a knotted reactor wit hout filtration, dissolved by 0.5 mol/L HCI at a flow rate of 6 mL/min and introduced into the nebulizer-burner system of the spectrometer. 1,10-phenanthroline and sulphosalicylic acid were added to the sample solution to eliminate interferences from Fe(II), Zn(II), and Al(III), Speciation of Cr(III) and Cr(VI) in water samples was achieved by redu cing Cr(VI) to Cr(III) for the determination of total Cr, and omitting the reduction for Cr(lll) determinations. A concentration efficiency of 22-fold per minute and a detection limit (3 sigma) of 0.8 mu g/L me re achieved for a 110-s loading time. The relative standard deviation (n=11) was 2.7% at the 50-mu g/L chromium level. The analytical result s obtained for human hair and water standard reference materials were in good agreement with the certified values.