Environment

• Thermo Scientific Dionex AS-AP Autosampler

Resolution

Note: The exact sample path depends on the configured injection mode and optional hardware. The AS-AP can use different push, pull, full-loop, partial-loop, sequential, simultaneous, concentrator, and optional-valve configurations. Confirm the actual configuration before applying a repair recommendation.

The AS-AP contains a syringe and syringe valve that control movement of wash liquid, sample, and waste through the autosampler. Standard fluidic components include the wash liquid line, syringe valve, syringe, buffer line, sampling needle, syringe waste line, wash port, waste port, injection port, and sample-transfer line as applicable to configuration.

• Stop the sequence and identify when the leak occurs.

  Determine whether liquid appears during:

  • Syringe priming
  • Needle/fluidics washing
  • Sample aspiration or dispensing
  • Injection
  • Valve switching
  • Idle operation

  Do not replace components until the operation that produces the leak has been identified.

• Clean and dry the accessible fluidic area.

  Remove accumulated liquid so the first new wet location can be identified.

  Inspect the syringe, syringe valve, valve tubing connections, wash line, buffer line, syringe waste line, wash port, injection port, transfer tubing, optional valves, and drip area.

• Run a syringe prime and observe the syringe circuit.

  Watch the following locations while the syringe primes:

  • Syringe barrel
  • Syringe plunger/seal area
  • Syringe-to-valve connection
  • Wash-reservoir line connection
  • Buffer-line connection
  • Syringe waste-line connection
  • Syringe valve body

  If the syringe barrel is cracked or the syringe itself leaks, replace the syringe.

  If liquid appears specifically where the syringe attaches to the syringe valve, inspect the syringe-valve gasket before replacing the valve.

  If a tubing connection at the syringe valve leaks, inspect and correctly tighten or replace the affected fitting or tubing.

  The AS-AP documentation identifies leaking syringes, syringe-valve connections, fittings, and liquid lines as individual leak sources. Man-IC-AS-AP-Ops-July2025-DOC06… 065437_AS-AP_Service Manual_Rev…

• If the syringe circuit remains dry, run a manual wash cycle.

  Observe:

  • Wash reservoir line
  • Syringe valve
  • Buffer line
  • Needle
  • Wash port
  • Waste path

  If the leak occurs only during wash operation, concentrate troubleshooting on the wash-liquid supply, tubing/fittings, wash port, and waste/drain path rather than the injection system.

• Inspect the injection port during a controlled injection.

  Watch the needle as it enters the injection port.

  If liquid collects on top of or around the injection port, inspect:

  • Needle alignment
  • Needle insertion depth
  • Needle condition
  • Injection-port connection
  • Sample-transfer line
  • Air in the transfer path

  Thermo Fisher identifies incorrect needle depth or alignment as possible causes of leakage at the injection port. The AS-AP troubleshooting documentation also identifies air in the sample-transfer line as a condition that can allow fluid movement to continue after syringe motion stops. Man-IC-AS-AP-Ops-July2025-DOC06…

• Inspect sample-transfer tubing and fittings.

  Trace the sample path from the injection port toward the injection valve or other configured valve.

  Look for:

  • Cracked tubing
  • Loose connections
  • Damaged ferrules
  • Damaged fitting bolts
  • Tubing pulled partially out of a fitting
  • Leakage at a valve connection

  Replace damaged liquid lines or fitting components rather than repeatedly overtightening a leaking connection.

• If an optional high-pressure valve is installed, determine whether the leak is external or internal to the valve.

  If liquid appears at a tubing connection, inspect the fitting and tubing.

  If liquid appears from behind the valve stator rather than at an external fitting, the valve rotor/stator sealing surfaces may require service or rebuilding.

  The AS-AP troubleshooting documentation lists leaking high-pressure valves separately from leaking fittings and broken liquid lines. 065437_AS-AP_Service Manual_Rev…

• Check the waste and drain system.

  Confirm that drain and waste lines are:

  • Connected
  • Unrestricted
  • Not kinked
  • Routed downward appropriately
  • Not submerged in waste in a way that prevents proper drainage

  A drainage problem can cause normal wash or overflow liquid to accumulate inside or beneath the autosampler and appear to be an active fluidic leak.

• Use the first-wet-location rule.

  Do not diagnose the leak based only on where liquid eventually collects.

  Identify the first location that becomes wet during the operation that produces the leak.

  Use the following interpretation:

  Observation	Most likely area to investigate
  Syringe barrel or plunger becomes wet	Syringe
  Syringe-to-valve junction becomes wet	Syringe-valve gasket or connection
  Syringe-valve tubing fitting becomes wet	Fitting or tubing
  Leak occurs only during wash	Wash line, buffer path, wash port, waste path
  Liquid appears on top of injection port	Needle alignment/depth, needle condition, injection-port interface
  Liquid continues briefly after syringe stops	Air or residual fluid movement in transfer path
  Transfer tubing becomes wet	Tubing or fitting damage
  Liquid appears behind optional valve stator	High-pressure valve sealing components
  Liquid collects only in bottom of sampler	Trace upstream source and verify drainage

• Correct only the identified fault and retest.

  After the repair:

  • Prime the syringe.
  • Run a manual wash.
  • Perform controlled injections.
  • Verify no new liquid appears.
  • Confirm normal sample delivery and injection repeatability.

  If the repair affected sample introduction, verify performance under the customer's original injection method rather than only under the simplified leak test.

Analysis