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Standard Interpretation

Standard: 2016
Section: V1M4, Section (f)


The 2016 TNI Standard states that for regression or average response/calibration factor calibrations, the minimum number of non-zero calibration standards shall be specified as in the table included.

According to the manufacturer, the acceptance criterion for pH, Conductivity, and Fluoride and Ammonia calibrations utilizing ISE electrodes is based on the slope of the instrument. As known from pH measurement and calibration, the slope is an indicator of ISE performance. For ISE curves, there is both a linear section and a non-linear section.

Therefore, my question is, for ISE calibrations such as Ammonia and Fluoride, and other meter based tests such as Conductivity and pH, is the minimum number of calibration standards listed in the TNI table applicable?

File Submitted with SIR: ISE Calibrations.pdf


Yes, they are applicable if the reference method describes a calibration procedure that includes average response/calibration factor or regression. Footnote b of V1M4 states, "Fewer calibration standards may be used only if equipment firmware or software cannot accommodate the specified number of standards. Documentation detailing that limitation shall be maintained by the laboratory."