Folin’s Test: ESTIMATION OF TITRABLE ACIDITY

Titrable acidity of urine is expressed as the amount ofalkali required to titrate or neutralize the acid present in the urine. The_titrable acidity, in the normal urine, is mainly due to the presence of acid phosphate ions (H2P04 ) and to a small extent due to organic acids (Urates, oxalates and citrates).

Folin’s Method:

PRINCIPLE:

The urine is titrated with standard NaOH solution. Phenolphthalein is used as an indicator. Potassium oxalate is added to precipitate the calcium present in the urine, because on neutralization calcium phosphate precipitates are formed Which interfere with the end point.

REAGENTS:

0.1N NaOH,
Potassium Oxalate Crystals,
1% Phenolphthalein.

PROCEDURE:

To 25ml urine in a 100ml Erlenmeyer flask add 5 gm Potassium oxalate crystals and 1-2 drops of 1% phenolphthalein.
Mix thoroughly by Vigorous shaking for 1-2 minutes.
Titrate the contents of the flask with 0.1N NaOH tilled in the burette, until a faint pink colour persists. Note the burette reading and calculate the titrable acidity.

CALCULATIONS:

Average volume of Urine = l500ml/day Volume of urine used = 25ml
Volume of 0. IN NaOH used = ‘a’ml
1ml urine will require = ‘ a ’ X 0.1N NaOH/25ml
1500ml urine will require = ‘a’ ×1500/25
= ‘A’ ml of 0.1NaOH

Therefore, Titrable Acidity of Urine = ‘A’ ml

NORMAL RANGE:

Titrable Acidity of Urine = 200-500ml/day

Interpretations:

T itrable acidity of urine depends almost entirely upon the diet of the individual. It is low on vegetable diet and becomes high on a diet rich in proteins, meat, milk, cheese, rice, whole-Wheat products, plums and other acid forming foods. It also increases during fasting due to increased fat metabolism going on in the body. Samples of urine collected shortly after a meal may be alkaline due to the prevailing “Alkaline Tide.

In acidosis, the acidity of the urine increases. Bacterial decomposition of urea, a constituent of the urine, occurring within the urinary tract will increase the amount of ammonia thus resulting in a decrease in the acidity of urine. The same happens if urine is left in contact with the air.