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Test papers and strips are a great way to measure pH for those who need a fast and low cost option.
We've explored the key differences between these two types of tests below, and looked at what advantages each brings.
What is pH test paper?
Test papers are one continuous piece of paper which is soaked in indicator to show a particular pH change. These may be in booklets where you tear off one leaf, or in a long reel where you can tear off any length of paper you require.What are the advantages of pH paper over pH strips?
- Test with very small volumes - it is possible to place just one drop onto the paper and see the colour change, whereas with pH test strips you need to get sample on all of the pads. This makes pH paper the method of choice in some medical tests where the sample available is very small, such as with sweat, tears or some paediatric tests.
- Reach difficult samples - with a long reel you can tear off a long strip for reaching into the bottom of long test tubes or flasks.
- Simple, specific tests - generally very specific pH change tests are available as pH papers, for example Litmus paper has only one colour change - blue in alkaline conditions, red in acidic conditions. Phenolphthalein paper is similar, with a change from white to pink. This makes them simple and clear to work with when a fast estimate on pH is needed.
What are pH test strips?
Test strips, also known as indicator strips, have multiple pads mounted on a card or plastic backing strip. The overall colour change pattern seen across all of the pads gives the result.What are the advantages of pH strips over pH paper?
- Higher accuracy - generally pH strips are available with higher accuracy but covering a smaller range, for example only covering half of the pH scale but in small increments of 0.5 or even less.
- Clearer results, even in coloured solutions - as you can match up all of the pads colour changes you can make a better judgement of the colour change. This is especially useful when testing a coloured solution which could obscure some of the pads.
- Non-bleeding strips available - specialist strips which fix the dyes to stop any leaking out into the sample are available. This is great when you need to preserve the sample for other tests after the pH test.
- Key displayed on the strip - some strips have the colour key printed directly on each strip, this means that even if you separate them from the box (for example giving out to different people in a team or class) they can still interpret the result easily.
