Hanna Instruments HI 84442 - Manual (Page 7)

7
PRINCIPLE OF OPERATION
Water alkalinity determination is performed by titration with acid reagent to pH end point.
Alkalinity is expressed as:
• Total alkalinity determination by titration at 4.5 pH (following the reactions):
If sample ph > 8.3 pH, then:
2HO
¯
+ H
2
SO
4
→ 2H
2
O + SO
4
2¯
2CO
3
2¯ + H
2
SO
4
→ 2HCO
3
+ SO
4
2¯
Otherwise:
2HCO
3
¯
+ H
2
SO
4
→ 2H
2
CO
3
+ SO
4
2¯
It is important that the samples are protected against atmospheric factors (store them in sealed
bottles that are completely filled) and avoid vigorous shaking, mixing and long exposure to air.
The HI 84442 minititrator is designed to determine the potentiometric titration in a very low range
(mg/mL as CaCO
3
).
HI 84442-55 is used for pump calibration.
Titratable Alkalinity in waters, as performed on the HI 84442 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 calibration involves the analysis of a known volume of a known solution
(standard provided) and compensate for changes in pump dosing that may occur due to many factors
including tube stretching or aging. This procedure should be performed regularly.
REQUIRED REAGENTS
Code
Description Quantity/Test
HI 84442 - 50 Titrant 1 mL
HI 84442 - 55 Pump Calibration Solution 1 mL
Note: To ensure the titrant concentration stability, the HI 84442-50 titrant stock solution is 10
times more concentrated than used during titrations. Pay attention to dilute titrant in
1:10 ratio (v/v) before use.