How can air spikes be removed from a Lachat Flow Injection Analysis system?

Document ID

Document ID TE7988

Version

Version 5.0

Status

Status Published

Published Date

Published Date 05/21/2019
Question
How can air spikes be removed from a Lachat Flow Injection Analysis system?
Summary
Air spike removal from a Lachat Flow Injection Analysis (FIA) system
Answer
Air spikes generally appear as tall narrow spikes which may occur on peaks and/or the baseline between peaks. Generally the air spike itself does not contribute much area but can affect proper integration of the peaks. Large spikes or multiple spikes might add significant area to a blank or low concentration. For these reasons, air spikes should be minimized.
  • If air spikes occur only on peaks, the air is likely being injected along with the sample.
    • Verify the valve timing. Time to valve can be determined by running dye as a sample. See the article titled, How is valve timing optimized on the Lachat QC8500 FIA?
    • If valve timing is set correctly and the problem is not resolved, it may indicate the air is coming in at the valve. Verify the fittings on the valve and consider trying a different injection valve.
  • If air spikes seem to be random and occur on the baseline in between peaks, the air is not being injected with the sample, This can be a concern with reagent off gassing or with air entering into the system.
    • Consider degassing reagents. See the article titled, Do Lachat reagents have to be degassed with Helium?
    • Check the flow cell connections and remove the flow cell from the detector to look for signs of leaking. Make sure the writing on the flow cell faces down. Also verify that the flow from the manifold goes into the bottom connector of the flow cell and that the waste line goes to the top connection. If the flow cell is not oriented or connected properly air may accumulate in the flow cell. See the article titled, Are there any tips for getting rid of bubbles in my Lachat FIA flow cell?
    • A bad connection or bad piece of tubing could be a point of entry for air. If you can see air visible on the manifold you can trace where it starts and focus on something prior to this point. Occasionally, issues occur when using steel pin connectors with smaller sized duraprene/santoprene pump tubes. Try placing a plastic nipple between transmission tubing and duraprene/santoprene pump tubes. Check the flow cell connections and remove flow cell from the detector to look for signs of leaking.
    • Also if the manifold calls for a back pressure loop, make sure this is installed correctly. See the article titled, What is the purpose of a back pressure loop added after the flow cell in some Lachat methods?

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