What is the cause of poor reproducibility for liquid-loaded standards?

There are a number of reasons that can give rise to poor reproducibility with your thermal desorption analysis (generally defined as RSD being >10%). Common problems are:

• Loading too much solvent: We recommend a maximum injection volume of 1 µL, to avoid loss of the lighter compounds and poor reproducibility. Where possible, try to chose a solvent that is not retained by your sorbents, and more volatile than your compounds of interest.

• Sub-ambient trapping temperature:>A ‘cold trap low temperature’ of 20–25°C is recommended for most tube-based applications to prevent retention of large volumes of solvent or water.

• Mismatched flows with MFCs:If your TD instrument is fitted with a mass flow controller (MFC) on the split, it is important to ensure that the split flow during the pre-trap-fire purge and trap desorption stages are the same, to avoid a change in split ratio at the moment of injection, and consequent poor reproducibility.

To help you identify the cause of poor reproducibility in your case, please contact support@markes.com with the following details:

• Instrument serial number.

• TD method (screenshots are best).

• The loading method for your standard.

We recommend using our Calibration Solution Loading Rig (CSLR), which has been designed specifically for loading liquid standards onto thermal desorption tubes. For more information on calibration and standards, please refer to Application Note 007.