Aliquots of 1450 of ultraspure water,for aqueous calibration, or 950 , when preparing a standard addition graph,were directly piptteed into a quartz cell, followed by addition of 250, of solution containing 0.35M of sulfuric asid and 0.065M of hydrochloric, 250 of a 0.06M As(III) solution and 250 of a0.005M Ce(IV) solution.