Adapt the sensitivity value

Decreasing the sensitivity means that the default calculated threshold in the similarity curve is lowered by this percentage. The full range for sensitivity is from 0 % to 100 %, where the default calculated threshold is at 50 % of the full available range (in the middle). You can use 50 % of the range for increasing and 50 % for decreasing the threshold.

By changing the sensitivity value you influence the threshold value:

• A sensitivity value lower than 50 % (default setting) will cause the threshold value to decrease. Thus a lower match factor will be sufficient to classify a spectrum as pure. 0 % means that a spectrum is considered pure even if there is no similarity at all.

• A sensitivity valued higher than 50 % will cause the threshold value to increase, thus a higher match factor will be required to classify a spectrum to be pure. 100 % means that the spectrum must be absolutely identical to the apex spectrum. Due to noise this is almost impossible.

 

Similarity curve

Because the similarity curve is displayed in a nonlinear way (logarithm), this will not map to the match factors in a one to one relation. If you decrease/increase the sensitivity, for example, by 20 % (threshold is moved by 20 %), this may appear bigger or smaller on the display, depending on where the actual threshold boundary is currently placed.

The sensitivity value does not influence the similarity values themselves. It only changes the threshold value and thus the criteria for a green or red coloring of the similarity curve and of the resulting UV Purity value. For more details on the calculation, see UV impurity check .

For example, the following figures show the same peak with different sensitivity settings:

Low sensitivity - this peak is considered pure

Default sensitivity - this peak is considered impure

High sensitivity - this peak is considered impure

The processing method allows you to set the sensitivity individually for each identified compound (Compounds > Spectra > Compound Table tab), and generally for non-identified peaks (Compounds > Spectra > UV Impurity Check tab).

To find the correct sensitivity value to get a passed result, the bisection method can be used. For example:

1. Start with sensitivity value of 50 - purity fails.

2. Try sensitivity value of 25 - passes, therefore increase to get a fail.

3. Try sensitivity value of 38 - passes, therefore increase to get a fail.

4. Try sensitivity value of 44 - passes, therefore increase to get a fail.

5. Try sensitivity value of 47 - fails, therefore decrease to get a passed.

6. Try sensitivity value of 45 - fails, therefore decrease to get a passed.

7. Try sensitivity value of 44 - passes.

The minimal sensitivity value to get passed is now 44.

For more robustness you can use the value 43 as sensitivity value.