IC OQ - Troubleshooting Injector and Flow Rate Repeatability Test Failures

Issue

As part of an RPG based OQ for an IC system, the Injector or Flow Rate Repeatability test is failing %RSD.

Environment

• OQ
• ICS-6000
• ICS-5000
• Integrion
• Aquion
• AS-AP
• AS-DV
• Conductivity Detector (CD)

Resolution

Ensure the following:

1. Autosampler, Pump, and Detector have been properly PM'd (if not new), and the system is properly equilibrated. A few test injections should always be made after IQ/PM before testing commences.  Additionally for AS-AP:
   • Thorough flush of the sampler fluidics (20 syringe cycles, followed by washing fluidics for 5000 uL twice).
   • Transfer line calibration verified (perform the TLV calibration multiple times to confirm correctness).
   • Only vials listed in the AS-AP Operators manual (Reordering information section) should be used. 
   • Additionally:
     • Removing the vial septa helps improve Precision
     • Subtracting 2 ul from TLV helps ensure a bubble does get into the loop for full loop injections
     • Sonicating and degassing the syringe wash (5 minutes or so) can help lower RSD
2. Connect the Black PEEK, 20 ft 0.010 in. (0.25 mm) i.d. Tubing (052307) to the test loop.
   This will increase peak delay (RT closer to 20s) and reduce ripple / cell noise with CD.
3. Be sure the following Instrument Configuration & Method settings are present (as applicable):
   • Waste tubing from port 6 of the injection valve is drained into the sampler (AS-AP)
     
   • Injector Synchronization with Pump Stroke (Pump Link) = None
   • Pump Rear Seal Wash = Disabled
   • Puncture Offset = 3mm (AS-AP)
   • Drawspeed = 2 ul/s
   • Draw Delay = 4-8s
4. Verify that no liquid is pooling on the inject port (typically caused by an overtightened fitting in the connection of the transfer line to the injection port).
5. When processing, ensure you are not integrating the early solvent peak and that you are grabbing the Nitrate peak. You may need to adjust the Integration RT window, or inhibit integration for the first few seconds. Tailing sensitivity factor (Cobra) can also be adjusted for the back end of the peak, but make sure the integration is not excluding any of the main peak area.
    

Analysis

This is test to similar to the Factory Injector Precision test. However, RT is not being analyzed for pump flow rate precision (it is tested gravimetrically). Nitrate peaks integrate at ~.1mins (6s), leaving you with a really small RT value. Thus, the recommended test loop is too short for the RPG testing. 

All other troubleshooting applies to Factory Precision and RPG Repeatability testing.

NOTE: See article, AS-AP Poor RSD or Inconsistent Peak Areas for an additional resource that could be helpful. 

Cause

The cause can be due to multiple factors:

• System not properly PM'd or equilibrated
• System configuration / setup issues
• Instrument method settings
• Processing method settings