Hanna Instruments HI 84432 - Manual (Page 7)

7
PRINCIPLE OF OPERATION
Fruit juice acidity is determined by neutralization of 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.
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/100 mL) of the predominant acid (citric,
malic or tartaric acid).
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.
For precise results the sample and titrant volume and the titrant concentration must be known.
It is important to titrate fresh samples of the fruit juice. For increased measurement precision keep
the fruit juices in capped 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
instantaneous 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 a minimum of
daily.
REQUIRED REAGENTS
Code
Description Quantity/Test
HI 84432 - 50 Titrant 1 mL
HI 84432 - 55 Pump Calibration Solution 2 mL