9
Pr
INCIPLE
OF
O
PE
rA
TION
4. PRINCIPLE OF OPERATION
Water alkalinity determinations are based on the neutralization of all basic species contained in the
sample by titration with an acid:
OH¯ + H
+
H
2
O
In an ideal solution, the endpoint of an alkalinity titration corresponds stoichimetrically to the
complete neutralization of all the bases present. Due to the complex sample matrix, titrations are
typically performed to a fixed pH endpoint. Two types of alkalinity can be determined based on
the selected endpoint Total Alkalinity (pH 4.5) or Strong Alkalinity (pH 8.3). The endpoint can be
determined visually using a color indicator (i.e. phenolphthalein or bromocresol green), however
this endpoint can be become objective depending on the analysts. The
HI84531
removes this issue
by titrating to a fixed pH endpoint (4.5 or 8.3) determined by the user. The concentration can vary
significantly with the selected pH endpoint. For precise analysis the sample size, volume of titrant
added and titrant concentration must be known.
The
HI84531
Total Alkalinity Mini Titrator utilizes a simple sample preparation, a high quality dosing
pump for titrant additions, potentiometric endpoint determination and instantaneous computations.
To maintain the high accuracy of the mini titrator a simple pump calibration is required. The pump
calibration uses a known quantity of a known solution to compensate for changes in the dosing
system, this procedure should be performed regularly.