Calibration Examples
Correcting Sample Preparation Errors (Internal/External Calibration)

It is possible to eliminate errors occurring during sample preparation by calibrating using the internal/external method. If you use the internal/external method, an internal standard substance, i.e., the Internal Standard (= ISTD), is used to adapt the external calibration to the corresponding sample. Exactly that amount of the internal standard substance is added to each standard sample and each unknown sample that makes sure that the concentration is identical in all sample vials. The following entries are required:

Sample List

In the simplest case, only one standard sample is available. In this case, the sample list looks, for example, as follows:

QNT Method/Amount Table Tab

Enter the amounts of the single substances contained in the standard sample in the Amount column of the Amount table of the QNT Editor:

QNT Method/Peak Table Tab

The internal standard substance is defined in the peak table. 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 substance. (The light yellow background of the line and the ISTD: Internal entry indicate that the assignment is correct.)

• In the F8 input box of substance 2, select Internal/External. In the Associated ISTD Peak field, select the standard substance serving as internal/external standard (here: Subst. 1).

• If necessary, repeat this operation for every additional substance that should be calibrated based on the internal/external method.

After completing the input, the substance 2 is labeled Int/Ext Subst. 1 in the Standard column. In addition, substance 1 is labeled as the internal standard for internal/external calibration. The description ISTD: Internal is changed to ISTD: Int/Ext and the yellow coloring of the Subst. 1 line is intensified:

Amount Calculation

Chromeleon automatically calculates the amount values for the substance 2. The calculation is performed according to the formula for amount calculation (for more information, refer to Formula for Amount Calculation in the Glossary section). In case of internal/external calibration, the ISTD factor is used to correct the external calibration, using the ISTD amount determined for the respective sample.

The ISTD factor considers the ratio of the (nominal) amount entered in the peak table to the amount that was determined for the respective sample due to the peak area:

Using this formula, Chromeleon calculates the amount for substance 2 that has been adapted by the deviation of substance 1.

For detailed information about how to calculate the amount of unknown substances using internal/external calibration, refer to  Internal/External Calibration: Calculation.

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