We get requests from time to time from customers wanting a Yes/No response at a specific pH. To our knowledge, this is not readily done using our papers or strips.

All of our pH test strips use pH indicator dyes that go through some color transition through some pH range. The range can be small or large, but it almost always covers at least a few pH units. In practice, what happens is that as the pH goes through the range, the color goes through a series of color changes, for example, blue to green to yellow, then to red. We are able to utilize this to create color blocks at various pH values and have the strips geared towards semi-quantitative applications.

We suspect the customers asking for a Yes/No response are thinking that the trigger is at a specific pH because some literature only states one pH point for the color change. For example, pH X – above this it is blue, below this it is red. In reality, this is not what usually happens.

Litmus paper is an interesting example. It is slightly different. For example, blue litmus transitions from blue to red in the neutral region, and the stronger the acid, the more immediate and intense the development of the red color. It doesn’t go through any other color changes, probably because litmus has many dyes present and they tend to meld together into a more uniform color. The reverse is also true of red litmus paper. Because these transitions are single color and occur over several pH units, these papers are best used for qualitative applications.

We are also sometimes asked to develop a strip with pH colors defined in very narrow pH units, for example, in 0.1 increments. While any number can be printed, in reality, this gives the false impression of accuracy. In practice, most strips and papers are no better than about 0.4-0.5 pH increments. The three pad test strips try to provide better accuracy by utilizing several test pads together.

Otherwise, the best we can do is help you find a pH test strip that has a fairly clear transition in the area you are looking to target.