Ultramicro- and Micro-Determination of Chloride by Argentimetric Titration with the Indicator Dichiorofluorescein

A reliable ultramicro modification of the Franco and Klein (1) determination for chloride, using 20 pi. of plasma, is described. A second procedure, requiring 0.2 ml. of plasma and substituting a titrating syringe for a buret, is suggested as a fast and adequate substitute in the absence of either extensive laboratory facilities or trained personnel. Data on reproducibility and recovery, and a comparison with another chloride procedure are presented. The limitations of the procedures are discussed. THE SIMPLICITY AND RELIABILITY of the method of Franco and Klein (1) for determining chloride in serum recommend it for adaptation to the micro and ultramicro scale. Titration with silver nitrate using dichlorofluorescein dye as an indicator for determining the chloride in biologic fluids, was first suggested by Saifer and Kornblum (2). Franco and Klein (1) introduced preliminary precipitation of the protein with the Somogyi barium hydroxide-zinc sulphate procedure (3). The principle of this argentimetric-adsorption indicator titra-tion has been well described by Klein (4). The ultramicro modification to be described here is a precise and accurate procedure using 20 J. of plasma. It is reasonably fast, re-quiring about 1 hour for the analysis of 12 samples in duplicate. The syringe titrating technic of Scribner (5) has been employed i