Ytterbium(III) is used as reagent for the determination of sulfite by measuring the formation of theYb(III)-sulfite complex through the variation of the light scattering intensity with time. The low solubilityof this complex causes an efficient dispersion of the radiation at 490 nm, which is measured at 980nm. Each kinetic datum is automatically obtained in only 0.5 s by stopped-flow mixing technique.The application of the initial rate method using a long emission wavelength minimizes the potentialinterference of fluorescent background signals from the sample matrix. The dynamic range of thecalibration graph is 1-250
g/mL,
and the calculated detection limit is 0.35
g/mL. The precision,expressed as relative st
andard deviation, is <6%. The method has been applied to the determinationof total sulfites in white wine samples, which requires only the sample dilution
and the use of twoaliquots to improve selectivity. However, the matrix effect found for red wines precludes the applicationof the method to the direct analysis of these samples. Analytical recoveries ranged from 96.0 to106.7%. The results obtained with the proposed method agreed with those provided by the
p-rosanilinemethod. Unlike this method, in which toxic reagents are required, the use of ytterbium(III) as analyticalreagent shows the advantage of its low acute toxic rating.Keywords: Ytterbium; long-wavelength measurements; total sulfite; white wine samples
