How to create a custom norm

Besides the selected norms, the DHA Extension enables you to create your own norm that meets the conditions for analyzing the DHA data in your laboratory.

DHA Extension uses the DHA.csv file located in the COMMON subdirectory of the installation directory (for example, C:\CLARITY\ DataFiles\ Common\ DHA.csv). This file contains Compounds, Retention indexes, and other information required for DHA calculations. It also includes the RICustom column, which contains Retention indexes you will measure while developing your norm.

Follow as described below:

Step 1

Open the DHA.csv file in a spreadsheet application, for example MS Excel. The file uses a dot as the decimal separator. If your local settings of MS Excel or Windows use a comma as the decimal separator, this may corrupt the DHA.csv file when saving any changes. Before editing this file, change the local settings of your Windows to use a dot as the decimal separator.

Step 2

Measure the known n-Paraffins samples and create the DHA Calibration using the Custom norm. It is best to measure all the possible n-Paraffins to have an exact interpolation of the calculated Retention indexes. In order to create a full Calibration with all n-Paraffins, it is necessary to measure two standards (first for C1-C4 and then for C5-C15). As a minimum, you have to use C5-C11, however, extrapolations usually do not work.

Step 3

Open the measured chromatogram with the integrated C5-C15 n-Alkanes, and in the DHA Settings, select the Custom norm (edit DHA.csv) and click the Create DHA Calibration button. The displayed dialog automatically fills the n-Alkanes starting from C5. If you have measured the Retention times of C1-C4 n-Paraffins beforehand, fill them out manually based on the corresponding chromatogram.

Save the created DHA Calibration. Note that in this type of calibration, the option Retention Indexes use Log. Interpolation with Unretained Peak in the Calibration Options is automatically enabled. Now, you have prepared the initial DHA Calibration with n-Paraffins.

In the Calibration table, display the Reten. Index column. You can see that the calibration has automatically filled out the Retention indexes for the n-Paraffins.

Also, check the Reten. index column in the Chromatogram window - Result table,

Step 4

The next step is measuring the compounds and calculating the Retention indexes for your custom norm. You can now measure your data, including compounds for developing the Custom norm. The Retention indexes of the measured compounds are automatically calculated by Clarity based on the Retention indexes of n-Paraffins in the Calibration and Retention times in the Chromatogram. You have to obtain the Retention indexes of all compounds listed in the first column of the DHA.csv file and write them manually into the last RICustom column. This file will be used for generating the final DHA Calibration, which you will use for measuring the unknown data.

Step 5

Finally, you will create the DHA Calibration. Follow the detailed description in the chapter "How to measure DHA Data for the first time". The difference is in the DHA Settings, where you select the Custom norm and click the Create DHA Calibration button. The DHA Calibration will contain extrapolated Retention times calculated from the DHA Custom norm. Note that the dha.csv file is applied when opening the Clarity station. You need to restart Clarity for the modifications to take effect.