Residue Testing With pH Strips
Q. Can I use pH paper to confirm cleaning and rinsing of labware to comply with lab accreditation requirements?
A. If you are going to use pH strips to comply with lab accreditation requirements, you need to verify that your detergents are not interfering with the strips and papers. Detergents and surface active agents can interfere with some pH paper by causing a decrease of several pH units in reading. Please test any pH paper you intend to use with these detergents to determine if there is any interference before adapting this procedure for use with pH paper.
If deionized water is used as the sample water, a slight amount (10-20 mg/L) of reagent grade, non-buffering salt (NaCl, CaCl2) should be added to the sample water to allow pH meter to function properly. If you want to avoid contaminating clean glassware, dump the glassware testing solution into a triple rinsed beaker and then add the non-buffering salt prior to measuring the pH with a meter.
For more information, please read our article, Detergent Residue Testing Using a pH Meter, pH indicator, or Test Kit.