Alkalinity M and P

(Alkaphot M/P)

Test Method Technical Information


Tests For: Alkalinity M and P in boiler water and other industrial waters
Test Range: 0–500 mg/L CaCO3
Reagent Chemistry Used: DPD

Test Reagent Chemistry Used Method Detection Limit (mg/L)* Limit of Quantification (mg/L)**
Alkalinity M Methyl Orange 1.21 3.86
Alkalinity P Phenolphthalein 14 44

Testing for Alkalinity M/P

The Alkalinity of water is caused by the presence of alkaline substances such as hydroxides, carbonates, bicarbonates and, to a lesser extent, silicates and phosphates. Quantitatively alkalinity is the capacity of the water to react with acid to a specified pH end point. The value obtained will depend on the pH indicator used. Two measures of alkalinity are conventionally applied – Alkaphot M (Alkalinity to methyl orange) and Alkaphot P (Alkalinity to phenolphthalein).

Alkalinity is an important test parameter in a number of industrial water uses, notably in boiler water treatment. Boilers and steam raising plant are normally operated under conditions of high alkalinity in order to minimise corrosion and the monitoring of alkalinity is an important control test.

The Palintest Alkaphot M and Alkaphot P tests provide a simple means of checking Alkalinity M and Alkalinity P levels over the range 0–500 mg/L CaCO3. The tests are particularly suited to boiler and industrial waters. The alkalinities specifically due to carbonates, bicarbonates and hydroxides can be calculated from the various data obtained

Reagent Chemistry

The Palintest Alkaphot M and Alkaphot P tests are both based on unique colorimetric methods. These methods offer considerable advantages over the titrimetric methods traditionally used for measuring these parameters.
The tests are each based on the use of a single tablet reagent containing a precisely standardised amount of acid combined with a colour indicator. The tests are simply carried out by adding the appropriate tablet to a sample of the water under test. Over the alkalinity range of each test a distinctive series of colours is produced – from yellow through green to blue in the case of the Alkaphot M test and from colourless to purple in the case of the Alkaphot P test. The colour produced in each of the tests is indicative of the alkalinity and is measured using a Palintest Photometer.

EPA, Definition and Procedure for the Determination of the Method Detection Limit, Revision 2, Dec 2016.
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the “Gold Book”).