Standard Potassium Ion Solution- Transfer 190.7 mg of Potassium chloride previously dried at 105ºC for 2 hours, to a 100-mL volumetric flask, dissolve in water, dilute with water to volume, and mix. Each mL contains 1.00 mg of potassium ion (K). 

Standard Sodium Ion Solution- Transfer 254.2 mg of sodium chloride, previously dried at 105ºC for 2 hours, to a 100-mL volumetrie flask, dissolve in water, dilute with water to volume, and mix. Each mL contains 1.00 mg of sodium ion (Na). 

Standard Preparation- Transfer a 50-mL aliquot of the Test Preparation to a 100-mL volumetric flask, add the volume(s) of Standard Ion Solution(s) specified in the individual monograph, dilute with water to volume, and mix. Quantitatively dilute aliquots of this solution with water as necessary to bring the concentration of the ion to be determined into the proper range for the flame photometer used. 

Test Preparation- Unless otherwise directed in the individual monograph, transfer 2.000 g of test specimen to a 100-mL volumetric flask, chill in an ice bath, add-5 mL of nitríc acid, swirl to dissolve and allow to warm to room temperature. Heat gently, if necessary, to obtain a clear or just slightly turbid mixture. Cool to room temperature, if necessary, dilute with water to volume and mix. Filter or centrifuge if necessary, to obtain a clear solution. 
Adjust the flame photometer to give a reading as near as possíble to 100 percent transmittance with the Standard Preparation at the wavelength setting giving maximum emission corresponding to the designated characteristic wavelength as shown in the accompanying table. Use an exit slit width corresponding as nearly as possible to the designated bandwidth. Record the transmittance reading, labeling it as S. Dilute aliquots of the Test Preparation with water as necessary to prepare a solution in which the concentration is similar to that in the Standard Preparation. Without changing any of the adjustments of the flame photometer, determine the emission of the solution as percent transmittance, and record the reading, labeling it as T. Readjust only the monochromator to the designated wavelength for background determination. Determine the emission of the solution at this wavelength  as percent transmittance, and record the reading, labeling it as B. 

The requirements of the test are met if the value of T minus B is less than  or equal to the value of S minus T.