Calibration Examples
Using Different ISTD Amounts (Variable ISTD)

Due to the method itself or the properties of the internal standard substance, i.e., the Internal Standard, it is sometimes impossible to add exactly the same amount of ISTD. To solve this problem, Chromeleon provides the Use sample amount as reference (Variable Internal Standard) option. Use this option to define the ISTD as variable internal standard substance. (The option is accessible via the F8 box of the Standard column in the peak table.)

In this case, you do not need to enter the amount of the internal standard substance in the Amount column of the peak table (this is not possible), but in the ISTD Amount column of the sample list. It is not important whether Internal/External or Internal is selected as calibration method. In this way, it is possible to enter the amount of an internal standard substance separately for each sample. The following entries are required:

Sample List

Enter the amount of the internal standard substance directly in the ISTD Amount column of the sample list:

QNT Method/Peak Table Tab

Apart from the substance serving as internal standard, enter all amount values as before. Then, select the internal standard substance as follows:

If all three samples contain two relevant substances only as in the example, make the following entries in the Standard column, using the F8 input box.

• For substance 1, select Use this peak as Internal Standard and thus define this substance as the internal standard.

• In addition, enable the Use sample amount as reference (Variable Internal Standard) option to define the ISTD as variable internal standard substance.

The yellow coloring of the line and the ISTD: Var. Internal or ISTD: Var. Int/Ext entry indicate that the assignment is correct. The corresponding Amount column cells are automatically set to 1.

Make all other QNT File entries as before. The peak table appears as follows:

QNT Method/Amount Table Tab

Enter the amount values for the unknown substances contained in the standard sample in the Amount column of the Amount table of the QNT Editor:

Evaluation

Evaluation is similar to the corresponding evaluation with a constant amount of the internal standard substance. However, slightly different calibration and evaluation formulas are used.

For a detailed description of the differences between standard methods, refer to Calibration  Evaluation with Various Standard Methods.

For an overview of the different calibration possibilities with internal standard substances provided by Chromeleon, refer to Calibrating  Calibrating with an Internal Standard Substance.