How to create a custom norm

In addition to the available norms, the DHA Extension enables you to create your own set of custom parameters corresponding to the conditions of DHA data analysis in your laboratory.

DHA Extension uses the DHA.csv file located in the COMMON subdirectory of the installation folder (by default 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 need to measure while developing your custom norm.

Note that to prepare a custom norm, you first need to create an auxiliary calibration file, which will help you prepare the parameters for the custom norm. Once the necessary values are in the DHA.csv file, you can create a full calibration for the sample measurements. To achieve this, follow these steps:

Step 1

Open the DHA.csv file in a spreadsheet application, such as MS Excel.

Step 2

Measure the known n-paraffin samples. It is best to measure all the possible C1-C15 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 light hydrocarbons and then for C5-C15 hydrocarbons). As a minimum, you have to use C5-C11, however, extrapolations usually do not give precise results.

Step 3

If you measured the retention times of C1-C4 compounds, open this chromatogram and note down the four retention times.

Open the measured chromatogram with integrated C5-C15 n-alkanes. In the DHA Settingspane, fill out the Unretained Peak Time if known (usually the methane retention time). Select the Custom (edit DHA.csv) norm and click the Create DHA Calibration button. The displayed dialog automatically fills the retention times of n-alkanes from the standard, starting from C5. Fill out the retention times of C1-C4 n-alkanes manually, if measured beforehand (these values cannot be added later to the calibration, similarly to the Unretained Peak Time). Continue by clicking the Create button.

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.

Step 4

In the Calibration Summary Table, display the Reten. Index column. You can see that the retention indexes of C1-C15 n-paraffins are automatically filled.

Step 5

The next step is measuring the Retention Times of compounds listed in the first column of the DHA.csv file to obtain the necessary Retention Indexes for your custom norm. To link the prepared DHA Calibration to the measured chromatograms automatically, select the calibration file created in Step 3 using the Set… button in the Method Setup - Calculation window. Set other method parameters as necessary.

Step 6

Open the measured chromatogram(s). The Reten. Index column can be displayed in the Chromatogram window - Result Tablevia the Setup Columns dialog (accessible from the context menu). The Retention Indexes are automatically calculated by Clarity based on the Retention Indexes of the n-paraffins in the linked calibration and the measured Retention Times.

Once you have the Retention Indexes of the compounds in the DHA.csv file, enter them manually into the last RICustom column.

Step 7

Now, a complete DHA Calibration can be created and used for the sample data. You can follow the procedure in the chapter "Measuring DHA data", except for setting the Custom (edit DHA.csv)norm before clicking the Create DHA Calibration button. The resulting DHA Calibration will contain extrapolated Retention Times calculated based on the DHA Custom norm parameters. Note that the dha.csv file is applied when opening the Clarity station. You need to restart Clarity for the modifications to take effect.