There is a way to compare Hanna meters with household equipment, without using AA.
Use dilute hydrochloric acid as the titrate and EIS as the titrant. Add a sequence of known volumes of EIS (of unknown millimolarity) to a known volume of dilute HCl (of known millimolarity.) The titration can be done from inert plastic graduated cylinders into a beaker (costing a few bucks on eBay), though pipettes and burettes are more acccurate, precise and convenient. Take TDS readings with both Hanna meters at each step of the titration. Plot reciprocal volume of beaker contents versus TDS readings for each Hanna meter. This mode of data plot is more linearizing than raw data plots. Make a least-squares-fit (LSF) for each meter. The calculated slopes for each meter's LSF will give the relative calibration of the two meters. If this titration is repeated for a different dilution of HCl (but still of known millimolarity and volume, and using the same EIS titrants), then the then meter calibration can be calibrated in direct reference to the HCl standard. There is still a lot to be said for eyeballing it, though. Dripping EIS into dilute HCl, using an eyedropper, can give a qualitative (& even quantitative) sensory impression of the the Ag+ concentration in the EIS. Measuring millimolarity of HCl is much easier than total Ag concentration with AA. Matthew
