What is the minimum number of concentrations needed to calibrate an instrument using a linear curve?

To calibrate an instrument using a linear curve, a minimum of three distinct concentrations is typically needed. This is because a single point would not provide information about the slope of the linear relationship, and two points could define a line but wouldn’t adequately ensure its reliability across the range of interest. By using three concentrations, one can not only establish a line but also assess the linearity of the response and identify any potential errors or deviations in the calibration, such as random noise or systematic bias. This allows for a more robust and reliable calibration, which is essential for accurate measurements in water quality analysis and other analytical fields.