Measuring DHA data

Step 1

See the chapter "Specification" for an overview of specifications of the supported DHA norms. It is necessary to prepare your instrument and method according to the specifications of the particular norm to obtain valid results.

Step 2

In the System Configuration window (menu Clarity - Configuration…), open the Instrument Type Setting dialog via the button, and check the DHA option on Instrument 1.

For more details see also chapter Installation.

Step 3

After closing the System Configuration window, open Instrument 1. Now, create a new project: in the Login Dialog, select <New Project> in the Select Project drop-down list and click the OK button. In the Create Project or Save as... dialog, name your new project, and click OK.

Step 4

Now, you have to create a DHA Calibration according to the selected norm. DHA Calibration is a calibration that contains parameters required for the DHA calculations. Proceed as follows:

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 5

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 norm you intend to use 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 6

Now, you can prepare a method for measuring the unknown samples.

If you want to link the DHA Calibration to your measured chromatograms automatically, select the calibration file created in Step 5 using the Set… button in the Method Setup - Calculation window. Set other method parameters as necessary.

Step 7

Measure the unknown data using the Method created in the previous step and open the chromatograms.

In the Chromatogram window - DHA tab, you can find the DHA Results and DHA Group Results subtabs containing the desired results.