Patent ID: 8361804

Claim:
A method to determine the hardness of a wellbore fluid filtrate comprising the steps of: a) providing a sample of wellbore fluid filtrate; b) combining the sample of wellbore fluid filtrate with a buffer solution to produce a buffered sample, such that the pH of the buffered sample is greater than 7; c) combining a portion of an indicator precursor composition with the buffered sample to produce an analysis sample; and d) titrating the analysis sample with a standardized solution of EDTA to a colorimetric end point to determine the hardness of the wellbore fluid filtrate, wherein the indicator precursor composition comprises a colorimetric indicator and an inert filler comprising a salt of a weak acid and a strong base, and wherein the indicator precursor composition is a dry solid having a Hazardous Materials Identification System rating of 0-0-0-A.