Total Hardness by Photometric Titration
Method Abstract #129
Scope and Application
This method determines the total hardness of a water sample using a colorimetric titration. Conforms to EPA Methods 130.1, ASTM 1126 and Standard Methods 2340 C. Calcium specific hardness can also be completed by the colorimetric method by adding the appropriate hardware. By adding calcium hardness, total, calcium and magnesium can be analyzed.
The total hardness is determined by the colour change in an EDTA titration at pH 10. The sample is mixed with a pH 10 buffer solution, and indicator solution and an initial reading is taken. The sample is then titrated with EDTA until the colour change endpoint is reached. The hardness is calculated using the endpoint.
Sample Titration Curve
*Data for this measuring range was obtained using laboratory prepared standards formulated from calcium carbonate. The measuring range may be increased by using larger capacity analysis vessels and/or auto-dilution.
**The Method Detection Limit (MDL) calculation procedure was obtained from US EPA 40 CFR Appendix B to Part 136 – Definition and Procedure for the Determination of the Method Detection Limit. Results may differ depending on laboratory practices and sample matrix.