The determination of chloride in body fluids by direct titration

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Abstract
To estimate the chloride content of body fluids, with the exception of blood and urine, the following technique is proposed. Add 1 ml. of milk, cerebrospinal fluid or gastric juice to 10-15 ml. of water. Then add 5 ml. of an acetate buffer solution (pH 5). By using this buffer solution the combination of Ag with protein is reduced to a minimum, and an accurate estimation is obtained in fluids containing up to 3% of protein. Titrate with AgNO3, using dichlorofluoresceine, and arranging the whole bulk to have a concentration of 0.1 mg.% of the dye. In urine the urea prevents the adsorption of dichlorofluoresceine, but a mixture of dichlorofluoresceine (0.1 mg.%) and eosin (0.2 mg.%) works satisfactorily if the pigments are first removed with charcoal. With blood it is necessary to remove the protein before titrating, using the following technique:[long dash]To 1 ml. of serum or plasma add 9 ml. of buffer solution (pH 4.6-4.7). Heat for 2 min. in a boiling water bath and, after cooling and filtering, adjust the pH of an aliquot of the filtrate to 5.0 with more of the buffer solution. For whole blood the buffer used is between 5.25 and 5.5, and the adjustment to pH 5 made with acetic acid. 10 mg. of salt are added and the fluid titrated, using dichlorofluoresceine. The amount of salt added is subtracted from the result. It was found necessary to add the extra salt to avoid complications when the urea content was higher than the chloride content.

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