Determination of Sodium and Potassium

Sodium and potassium are determined by flame photometry using a Model FP640, dual channel photometer, running LPG/compressed air.

  1. scale each of the Na and K channels to its midpoint using 5mM NaCl and 50uM KCl respectively
  2. measure the samples, noting the readings for both Na and K
  3. immediately following the measurement of the samples, measure a range of at least 6 standards for each of Na and K with the concentration range chosen to encompass the measurements obtained in 2 above
  4. construct a calibration curve for each of Na and K. Where the concentration range of the samples is large, construct two calibration curves as necessary.


  • the optical filters for each channel have bandwidths of <= 15nm and stray-light specifications of <= 0.5%, thus the instrument reading is relatively immune to interference from other elements and non-specific matrix effects.

Typical calibration Curves: