Is it possible to interpret Quantab Chloride test strip results that exceed the Quantab Unit on the bottle label?
Interpreting over range Quantab Chloride test strip results
The relationship between the quantab unit (QU) and parts per million concentration (ppm) is both lot specific and non-linear. Because of this there is no way to determine the what ppm concentration is of any QU that is not on the label, only it's relative result to values that are on the label.
For example using the below label; the numbers on that label are likely different from the label on a bottle that was recently ordered and received. That is because the example is a from a different lot. If a QU result of 7.1 is obtained using the example lot, it's not possible to determine the specific ppm result, only that it is between 542 ppm and 583 ppm.
The listed range for the example which is Chloride QuanTab® Test Strips (Product # 2744940) is 30-600 ppm , the lowest number on the bottle is 1 QU=31 ppm and the highest number in this case 7.4 QU=628 ppm which are both ~30 and ~600 ppm. So for any result over 7.4 QU (whether it be 8 QU or 8.5 QU), report the result as > 628 ppm and over the range of the test strip.
The reason that the numbers on the strip go up to near 10 is because the QU that is approximately equal to 600 ppm will vary between test strip lots. On some strips ~600 ppm as low as 7.5 QU like the example, for others it could be as high as 9.0 QU.
If a QU result is above the highest QU on the label, the options are:
- Accept that the ppm concentration is over range and an exact concentration cannot be reported
- If using low range test strips, redo the test with higher range test strips.
- If using high range test strips, the sample can be diluted and the result multiplied by the dilution factor.