Which method is colorimetric for potassium measurement?

• A. Ion selective electrode (ISE)
• B. Flame photometry
• C. Lockhead and Purcell (colorimetric)
• D. Atomic absorption spectrometry

Answer: (C)

Potassium can be measured colorimetrically when a chemical reaction with a chromogenic reagent produces a colored product, and the color intensity is read with a spectrophotometer to quantify concentration. This approach relies on a color change that correlates with how much potassium is present, typically using a calibration curve to convert absorbance to an actual concentration. The Lockhart and Purcell method is an example of this type, where the potassium-dependent color change is the signal being measured.

In contrast, other methods are not colorimetric: ion-selective electrodes measure the electrical potential related to potassium activity across a selective membrane; flame photometry detects the light emitted by excited potassium atoms in a flame; atomic absorption spectrometry measures the reduction in light intensity as potassium atoms in the sample absorb light at a specific wavelength. The colorimetric method stands out because it translates chemical color change directly into a quantitative readout.