Troubleshooting Tecan Liquid Handling: Solving the "Mystery Drip"

[Quick Answer]

Is your Tecan system dripping? Follow these four priority steps:

• Clear Air Bubbles: Run a Flush command (15mL Waste / 20mL Cleaner) via Direct Commands to eliminate bubbles from the liquid system.
• Check Hardware: If droplets occur after flushing, or are seen before power-on/during stand-by, check for air accumulation in the Source tank, FAWA pump, 3-way valve fittings, and syringes. Check the tightness of all fittings on the 3-way valves and syringes.
• Check for Clogs: If a water drop stays on the tip specifically after flushing, inspect for a clogged probe or clogged fixed tip.
• Adjust Software: If droplets only occur after dispensing (at the plate or waste), lower the Z-dispense height or adjust Liquid Class airgaps.

Why is my deck wet?

In a high-throughput lab, precision and accuracy are the pillars of data integrity. A stray droplet is more than a mess—it’s a volumetric error and a contamination risk.

If you notice droplets on your fixed tips or DiTi cones during stand-by mode—or even before switching the instrument on—your liquid system is likely leaking. Once a run begins, this issue often manifests as a droplet dripping onto the worktable during waste container dispensing. If this occurs during every script run, the system requires troubleshooting to ensure volumetric accuracy and prevent sample contamination.

Phase 1: Eliminating Air Bubbles (The Flush Command)

Air is the most common culprit for dripping because it is compressible. Unlike liquid, which is rigid in a closed system, trapped air acts like a spring. When the syringe pump stops, the compressed air expands, forcing a "weeping" droplet out of the tip.

The Resolution: Before running your script, use the “Flush” command under the “Direct” command section to eliminate bubbles:

• Set Volume in Waste to 15 mL.
• Set Volume in Cleaner to 20 mL.
  

Ensure a sufficient amount of water is flushed through the channel to eliminate all bubbles from the liquid system before re-running the script. This step alone often resolves the dripping issue.

Phase 2: Identifying the "Where" and "When"

If the dripping persists after a flush, you must isolate the source of the droplet. Observe if the droplet is accumulating on the DiTi Tip or Fixed Tip after the instrument is initialized. Ask these three diagnostic questions:

Q1: Does the droplet occur after the flushing water command?

If Yes: You must check for air accumulation or clogs.

• For Air: You need to check where the leakage (accumulating air bubbles) occurs within the liquid system. Inspect the Source tank, FAWA Pump, tubing fitting inlets and outlets from the 3-way valves on the diluter, and the syringes. Additionally, check the tightness of all fittings on the 3-way valve and the syringe to ensure an airtight seal.
• For Clogs: If a water drop remains on the tip immediately after flushing, it may be caused by a clogged probe or clogged fixed tip.

Q2: Was the droplet carried over from the microplate after dispensing?

Q3: Does the droplet occur after dispensing everything into the waste container?

If Yes to Q2 or Q3: You may need to lower the Z-dispense position or make adjustments regarding the Liquid Class (e.g., trailing air gap, leading air gap, or relevant dispensing actions).

Phase 3: Applying Adjustments

If Phase 2 isolated the issue to the dispensing (Q2 or Q3), follow these steps to adjust your software parameters in EVOware:

1. Access the Editor: Double-click the Aspirate/Dispense command. Select "Editor..." under the liquid class section.
   
   
   
2. Identify Category: Choose the volume category matching your volume (e.g., Standard <15.01-500.01uL>).
   
   
   
3. Adjust Airgap: Within the editor window, you can adjust the airgap volume within Aspirate, or check the box for "Trailing Airgap after each Dispense" under the Dispense tab.
   
   
   
   
   
4. Save: Press OK to save the settings.

Crucial Note on Liquid Classes

The "Water Free Dispense" is the default liquid class; you will not be able to change these default classes. To make adjustments, you must either:

• Duplicate the liquid class you are using (save it as a different name).
• Use existing Custom classes (for example: LC_Aspirate 1,LC _Aspirate 2, and LC_Dispense 1).

Please try duplicating these classes and then make the necessary changes to the new ones without modifying the originals. Important: Make sure to select the desired liquid class within all aspirate and dispense commands under the liquid class sections.

Phase 4: Resolution for Clogged Tips/Probes

If your diagnosis points to a blockage (Q1), follow this hierarchy of cleaning to restore "patency" (an unobstructed path) for the liquid. follow this decontamination and rinsing protocol to clear the fluid path:

1. Chemical Soak
   • Flush the system thoroughly using a Liquinox solution.
   • Retain the solution within the tubing and the probe.
   • Allow the system to soak for exactly one hour to ensure proper decontamination.
2. DITI Water Rinse
   • Flush the system with DI water from the source tank.
   • Continue rinsing until all air bubbles have been completely removed from the tubing system.
     
   • Verify that the fluid path is clear and bubble-free before proceeding to the next operation
3. Clearing: If the orifice remains blocked, use the cleaning needle (found in your Tecan Accessory Box) to gently clear the path.
4. Flush: Immediately after using the needle, run a System Flush (15mL/20mL) to ensure any dislodged particles are washed out of the probe and into the waste.
   

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