Fluorescent moiety tagged polymers for use in monitoring cleanliness of mold surfaces

A method of controlling the concentration of a corrosion inhibitor in closed loop cooling water, comprising:

• (a) introducing into the cooling water a corrosion inhibiting composition comprising at least one copper corrosion inhibiting compound and at least one tagged polymer comprising a polymer including a fluorescent moiety in the backbone of the polymer chain, the tagged polymer included in the composition in an amount of from about 0.01% to about 50% by weight of the composition, so as to form a cooling water mixture having an initial concentration of the composition,
• (b) feeding the cooling water mixture through a circulating loop that circulates the cooling water past a copper surface,
• (c) on a sample of the cooling water mixture downstream from the copper surface in the circulating loop, measuring a fluorescence signal of the sample to determine a circulating concentration of the composition in the cooling water mixture, and
• (d) if the circulating concentration is determined to be less than the initial concentration, introducing a fresh amount of the composition into the cooling water mixture downstream from the extracting of the sample and upstream from the copper surface in the circulating loop.