Alkalinity, Total

Test Method Technical Information


Tests For: Total alkalinity in natural and treated waters
Test Range: 0–500 mg/L CaCO3
Reagent Chemistry Used: Bromocresol Green
Basis of Test Method: Standard Method 2320-B, ISO15923-2:2017
Method Detection Limit*: 9.1 mg/L
Limit of Quantification**: 18.5 mg/L

*The Method Detection Limit (MDL) is defined as the minimum measured concentration of a substance that can be reported with 99% confidence to be different from the method blank results.
**The Limit of Quantification (LOQ) is the smallest quantity that can be detected with reasonable certainty for a given analytical procedure.

Testing for Alkalinity

Natural and treated waters may contain a variety of dissolved alkaline substances such as carbonates, bicarbonates, hydroxides and, to a lesser extent, borates, phosphates and silicates. In water at neutral pH the alkalinity derives mainly from the presence of bicarbonates.
Total alkalinity is an important test in determining the aggressiveness or scale forming tendency of the water. If the total alkalinity is low the water may be aggressive and cause corrosion to pipe work and structures; if the total alkalinity is high the water may more readily promote scale formation. Alkalinity control is therefore an important part of many water treatment programmes.

The Palintest Alkaphot test uses a colorimetric method and covers the total alkalinity range 0 – 500 mg/l CaCO3. The test is particularly suitable for checking natural and drinking waters, swimming pool water, boiler water, etc.

Reagent Chemistry

The Palintest Alkaphot test is based on a unique colorimetric method and uses a single tablet reagent. The test is simply carried out by adding a tablet to a sample of the water. Under the conditions of the test, a distinctive range of colours from yellow, through green, to blue is produced over the alkalinity range 0 – 500 mg/l CaCO3. The colour produced in the test is indicative of the alkalinity of the water and is measured using a Palintest Photometer.

Best Practice Advice for Testing

  • Ensure the tablet is totally dissolved with no remaining particles for accurate results
  • Carefully stir to ensure no reagent particles are stuck to side of test tube or crush rod

Acid Demand

Alkalinity is defined as the capacity of water to neutralise acid and is expressed as an equivalent concentration of calcium carbonate. Acid demand, also called acid capacity, is the amount of acid needed to reduce the pH level of a sample. For all intents and purposes, this is effectively the same thing, but acid demand is expressed as an amount of acid.

Acid demand is most commonly used in swimming pool water management. Like alkalinity, acid demand can be determined by the titration of an acid into a water sample until a specific pH indicator changes colour. In some cases, the commercially available treatment product (containing an acid such as citric, muriatic or hydrochloric) is used as the titrant. The result can then be extrapolated to give a volume of the treatment product required for the entire pool.

Palintest’s acid demand test provides a way to determine acid demand by giving the result of a total alkalinity tablet test in units of mmol/L. This will be how many moles of acid are required to treat each litre of water in the pool. By cross referencing this with the concentration of acid in the treatment product being used and the volume of the pool, the amount of the treatment product needed can be calculated.

Please note: The above is an explanation of the rationale behind this test. Always follow all instructions exactly as they are given on any treatment product being used.

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”).