Analysis for Potassium, Sodium, Chloride, and Water in a 2-4 Sample of Extracellular Fluid' IKTRODI-CTION This paper dexribes a syst,em of analysis for mexburing I<, Ka, ('1, and wat#er in a 2-~1 sample of mammalian c.stracellular fluid. The m&hods were developed in the course of a study (2) of t#he fluid formed by the choroid plexus of the cat,.
Various micro methods for determining thcsc sc?vernl clcc%rolytes singly are already available. Micro (:I :LIMI~SW. lwing bot.h wlorimet~ric and electrometric techniques, have been described; C clnd, when wrrkd out with microvolumetric glassware, some of these are c*np:tble of measuring amount,s of Cl as low as 4 X 10PIO mole (5) or r:~wl 3 X IO-l2 mole (6). Solomon and Caton (7) have descrihcd a micro flame photometer capable of determining Nn and I< at levels similar t80 those reported here. Keynes and Ilewis (4) have measured comparahlr amounts of Na by wt,i-at8ion analysis; but this t euhnique has been less wcwssful for t,he measurement of I<! partic&rly in t,hc presence of appreciable amounts of Yil.
The methods described in t,his paprr (~1 be cwricd out. \-ith conventional glassware, a sbandard spectrophotometer, and a flame phot,ometel adapted to micro levels. The individual analysts are coordinated to permit, thr measurement of the t,hree major &,racellulnr clectrolyt,es and water on a Angle specimen. We believe this ,syst,em provides a useful combinaGon of ease and accuracy of performance with Fmallness of specimen size.