Determination of Sodium in Salt Substitute by Flame Emission Spectroscopy David E. Goodney Willamette University, Salem OR 97301 Flame Emission Spectroscopy (FES or Flame Photometry) is often the method of choice for the quantitative determination of Group 1A elements such as sodium or potassium. Specific procedures are available for the analysis of sodium or notassium in such materials as soil, water, cement, glass, serum, urine, and many other samples in which they are imoortant constituents ( 1 . 2 ) .The theury of FES is treated adkquately in standardqbantitative analysis ( 3 , 4 , 5 ) and instrumental analysis (6, 7,8)texts. Laboratory experiments for analysis of sodium or potassium hy FES are readily availahle (3,6,9,10); the samples analyzed may be artificial unknowns, cement, serum, or urine. The ubiquitous nature of sodium and potassium allows the sample chosen for a laboratory exercise to be a rather common material such as cement, urine, or, for this experiment, salt substitute. Salt substitute is a variable mixture of potassium chloride with substances such as fumaric acid, calcium hydrogen phosphate or potassium tartrate (depending on the brand) and is readily available in the local supermarket. Salt suhstitute is used as a replacement for table salt (NaCI) for those on a restricted sodium diet; and label claims usually state "less than 10 mg sodium per 100 g" of salt suhstitute. Thus, students can analyze a household product, get meaningful results by comparison with label claims, and appreciate the biochemical importance of sodium in the diet without having to supply blood or urine. Some interesting chemical problems arise because trace levels of sodium are determined in a sample solution with a high concentration of potassium salts. The relatively high ionic strength of the sample solution means that the so-called "matrix effect" cannot be ignored and samples cannot be compared directly with standard solutions containing only sodium a t low concentration. Moreover, adjusting the ionic streneth of standard solutions bv adding an appromiate .. . amount of potassium chloride does not solve the problem sinre even analvtical reagent chloride contains 411 to 30 - potassium . ppm (mgikg) sodium, compared to the approximately 100 oom in the salt suhstitute. Also, the potassium in the sample solution acts as an ionization supp
