7
PRINCIPLE OF OPERATION
Fruit juice acidity is determined by neutralization of the all available hydrogen ions present in the
sample, with a strong base solution:
H
+
+HO
-
H
2
O
In an ideal solution, the end point of an acid titration corresponds stoichiometrically to the complete
neutralization of the acids present.
Using a pH electrode allows an end point at 8.2 pH to be automatically detected. End point
detection by potentiometric method is more objective than the end point detection using the
indicators.
The
HI 84432
minititrator is designed to determine the acidity of fruit juices by potentiometric
titration. The result of the titration are displayed in % (g/100mL) of the predominant acid (citric,
malic or tartaric acid).
For precise results is important to know the sample volume and the titrant volume and concentration.
It is important to titrate fresh samples of the fruit juice. For increased measurement precision keep
the fruit juices in caped vessels (avoid prolonged exposure to air). Also avoid refrigerating the juice
as significant portion of the tartaric acid (ex. grapes juice) will precipitate out and the results
obtained will be lower then expected results.
Titratable Acidity in fruit juices, as performed on the
HI 84432
minititrator, utilizes a simple sample
preparation, a high quality peristaltic dosing pump for titrant, potentiometric endpoint detector and
instantaneaous computations. To maintain the high precision of the titrator, a simple pump calibration
procedure is required. The pump calibration involves the analysis of a known volume of a known
solution (standard provided) and compensates for changes in pump dosing that may occur due to
many factors including tube stretching or aging. This procedure should be performed regularly.
