Evaluating a Chromatogram

In first approximation the area of a chromatographic peak is proportional to its mass. Prerequisite for quantitative evaluation of peak masses is the knowledge of the proportional factor that joins area and mass of substance. This factor can be determined by calibration with a known amount of substance. A measurement containing peaks of known mass is termed reference measurement here and those peaks with a known mass are colored green in the display.

This means the determination of absolute masses in a chromatogram requires two measurements, the reference measurement with a known amount of substance and the main or test measurement containing an unknown amount of the same substance. It is mandatory, that these two measurements are conducted under the same conditions, the most important of which are: Split ratio, temperature program, gas type and pressure.

Way of proceeding:

· Open the main or test measurement by clicking the “Open measurement” button.

· Mark peak to be evaluated by double clicking the starting point and the end point of the peak. The area under the marked peak turns to blue.

· Click “Compare measurement” in the main menu. A second diagram shows up.

· Open the reference measurement by clicking the “Open reference” button. The reference chromatogram will appear in the upper diagram.

· Pan and zoom both measurements in order to have both the reference peak (green) and the test peak approximately one above the other.

· Click „Compare peak“, located on the left hand side of the peak table .

· Move the mouse cursor into the main measurement diagram. The shape of the cursor changes into a dotted line that runs through both diagrams. Position the line in order to have it run through both peaks and click left.

Comparing peaks

Now the mass and the peak factor are shown in the peak list. The calibrated peak turns green as its mass is known now. It makes sense to give this peak a name, so double click the corresponding name cell and enter the name. Don’t forget to save the changes!