TM93-07 Problems with Laboratory pH analytical determinations

This tech memo addresses problems associated with the determination of regular pH (Lab Code 68) for low conductivity samples. Both long- and short-term problems exist with this analysis. District input is requested in order to help us best meet the needs of users of these data. Several problems have been noted by the National Water Quality Laborarory (NWQL) concerning pH values on low conductivity samples determined by the automated pH/conductance analytical line (Lab Code (LC) 68, WATSTORE code 403A). The long-term problem concerns samples submitted for regular pH which have conductivities less than 100 microsiemens per centimeter (μS/cm). The short-term problem concerned samples submitted for regular pH with conductivities less than 1200 μS/cm.