Water hardness monitoring via fluorescence

An automated method for monitoring and optionally controlling total hardness concentration in industrial water containing soluble calcium and soluble magnesium, the method comprising:

• combining an aliquot of water with (4) a magnesium-containing reagent whereby the soluble calcium within the aliquot of water is displaced by soluble magnesium, thereby creating a modified water sample having an increased soluble magnesium content;
• combining the modified water sample with a quantity of (1) a pH-buffered liquid and (2) a magnesium coordinating fluorescing reagent to produce a buffered water sample containing soluble magnesium;
• whereby the (2) magnesium coordinating fluorescing reagent coordinates with the soluble magnesium present in the buffered water sample to produce a coordinated magnesium compound;
• quantifying the increased soluble magnesium content in the buffered water sample via fluorescence measurement of the coordinated magnesium compound thereby determining the total hardness concentration of the water;
• wherein the (1) pH-buffered liquid comprises a water soluble, non-coordinating base capable of buffering the (1) pH-buffered liquid and the buffered water sample to a pH from 8 to 12;
• and wherein the (2) magnesium coordinating fluorescing reagent is selected from the group consisting of a water soluble, aromatic, ortho hydroxyl substituted azo dye;
• a water soluble, fused-ring heterocycle;
• and combinations thereof.

An automated method for monitoring and optionally controlling total hardness concentration of industrial water containing soluble calcium and soluble magnesium, the method comprising:

• A.
• combining a first aliquot of water and quantities of (1a) a first pH-buffered liquid, (2a) a first magnesium coordinating fluorescing reagent, and (3a) a first inert fluorescing agent to produce a buffered water sample;
• whereby the (2a) first magnesium coordinating fluorescing reagent coordinates with the soluble magnesium present in the first aliquot of water to create a coordinated magnesium compound within the buffered water sample;
• determining by light absorbance the concentration of any uncoordinated (2a) first magnesium coordinating fluorescing reagent in the buffered water sample;
• determining by fluorescence the concentration of the (3a) first inert fluorescing agent in the buffered water sample;
• determining the soluble magnesium concentration in the first aliquot of water via fluorescence measurement of the coordinated magnesium compound in the buffered water sample;
• optionally correcting the soluble magnesium concentration determined via fluorescence measurement of the coordinated magnesium compound to account for one or more of the following:
• variation in mixing ratio, variation in background effects, and variation in temperature, thereby allowing for the calculation of an adjusted soluble magnesium concentration in the water;
• and
• B.
• combining a second aliquot of water and quantities of (1b) a second pH-buffered liquid, (2b) a second magnesium coordinating fluorescing reagent, (3b) a second inert fluorescing agent, and (4b) a magnesium-containing reagent to create a modified water sample,
• whereby the (4b) magnesium-containing reagent reacts with soluble calcium in the second aliquot of water thereby displacing the soluble calcium with soluble magnesium and creating an increased soluble magnesium concentration in the modified water sample and the (2b) magnesium coordinating fluorescing reagent coordinates with the soluble magnesium present in the modified water sample creating a coordinated magnesium compound;
• measuring by light absorbance the concentration of uncoordinated (2b) magnesium coordinating fluorescing reagent in the modified water sample;
• measuring the fluorescence created by the (3b) inert fluorescing agent in the modified water sample in order to determine concentration of the inert fluorescing agent in the modified water sample;
• measuring the soluble magnesium concentration in the modified water sample via fluorescence measurement of the coordinated magnesium compound, the measurement of which corresponds to measuring the total hardness concentration in the second aliquot of water and the total hardness concentration in the water;
• optionally correcting the soluble magnesium concentration measured via fluorescence of the coordinated magnesium compound to account for one or more of the following:
• variation in mixing ratio, variation in background effects, and variation in temperature, thereby allowing for the calculation of an adjusted total hardness concentration in the water;
• and
• optionally subtracting the soluble magnesium concentration of the first aliquot of water from the total hardness concentration of the second aliquot of water to arrive at the soluble calcium concentration in the water;
• optionally taking action to control at least one process variable as a result of the measurements;
• and
• optionally repeating A and B;
• wherein the (1a) first and (1b) second pH buffered liquids are the same or different compositions having buffered pH from 8 to 12, the (2a) first and (2b) second magnesium coordinating fluorescing reagent are the same or different compositions, and the (3a) first and (3b) second inert fluorescing agent are the same or different compositions.