How is alkalinity measured

The alkalinity of a sample is determined by titration using a standard acid (either 0.02N sulphuric or hydrochloric acid) and is expressed as equivalent milligrams CaC03 per litre. The results for alkalinity can be reported in two different units, depending on the end-point selected for the titration. p-alkalinity (phenolphthalein alkalinity) is the term commonly used for the quantity measured by titration to pH 8.3 and total alkalinity or m-alkalinity (methyl orange alkalinity) are terms commonly used for the quantity measured by titration to pH 4.5.