The accuracy of QAC tests strips does not depend on the pH value of solutions to be tested in the range of 1.86 – 9.2 pH, but rather it depends on buffering capacity. When the pH of a solution to be tested is a result of acidic or alkaline compounds without buffering capacity, then the accuracy of the test is not influenced. In the case that the pH of a solution to be tested is a result of a buffer, then the measure of influence depends on the buffering capacity of the solution.
Test:
Sets of control solutions with QAC concentrations 0 – 50 – 100 – 200 – 400 ppm were prepared in following solutions:
- Hydrochloric acid /0.1 M/, pH 1.1
- Tartaric acid /0.1M/ , pH 1.86
- McIlvaine buffers (0.1M citric acid, 0.2 M disodium hydrogen phosphate), pH 2.2 – 3.0 – 4.0 – 5.0 – 6.0 – 7.0 – 8.0 – 9.0
- Sodium tetraborate /0.01M/ , 9.20
The table below contains readings according to the regular color chart:
pH buffer /b/ | 0 ppm QAC | 50 ppm QAC | 100 ppm QAC | 200 ppm QAC | 400ppm QAC |
1.1 | 0 | 0 | 0 | ≤50 | 50 |
1.86 | 0 | 50 | 100 | 200 | 400 |
2.2 /b/ | 0 | 0-50 | 50 | 100 | 200 |
3.0 /b/ | 0 | 50 | 100 | 200 | 400 |
4.0 /b/ | 0 | 50 | 100 | 200 | 400 |
5.0 /b/ | ≤ 50 | 100 | 200 | 400 | ≥400 |
6.0 /b/ | 50 | 200 | 400 | higher | higher |
7.0 /b/ | 100 | 400 | ≥400 | higher | higher |
8.0 /b/ | 200 | 400 | higher | higher | higher |
9.0 /b/ | 400 | higher | higher | higher | higher |
9.2 | 0 | 50 | 100 | 200 | 400 |