Size fractionation of metals in wine using ultrafiltration

Ultrafiltration has been used to examine the size fractionation of lead, copper, iron, aluminium, calcium, potassium and sodium in white and red wines. Fractionation patterns demonstrated that the behaviour of lead is significantly diferent to the other metals considered. In red wine, there was a sudden decrease for lead between 100 000 and 30 000 nominal molecular weight cut off (NMWCO) and in white wine, a gradual decrease in the lead concentration was observed from 100 000 NMWCO. Iron was the only other metal which showed, for red wine, a size distribution pattern with a reduction in the iron concentration between 30 and 50% from 100 000 to 1000 NMWCO. Potential binding agents for lead and iron are discussed. The absence of any fractionation pattern for the other metals examined has been interpreted in terms of the metals existing as aquated cations (potassium and sodium), metal tartrate complexes (aluminium, copper and calcium) and either tartrate or phosphate for iron in white wine. The possibility of ultrafiltration disturbing kinetically facile processes, particularly for copper and calcium, is identified.