Directory: 04 Poor Sensitivity
File name: 02_sample_not_collected

Note: There was no problems with mobile phase or needle wash or any method changes.

Symptom #

This is the marijuana metabolite at the lower limit of quantitation (the LLOQ) calibrator. Normally, the quantifier peak is about between 2000 - 3000 counts per second for the peak area. And in the problem chromatogram it's only 330.

Investigation, Troubleshooting Tool and Root Cause #

Investigation and Tools used:

1. Q: Check the system suitability tests results.
   A: We had not done a system suitability test for THC on that day, but we did do a system suitability test for vitamin D and that passed. The result for vitamin D can’t prove the LCMS performance is good for THC, because the vitamin D is positive mode, and the THC is a negative mode. We can’t rule out the LC-MS/MS yet.
2. Q: Run a THC LLOQ calibrator from the previous batch.
   A: The peak area looks normal. We can rule out autosampler, LC and MS.
3. Q: Check the pressure trace.
   A: Normal. We can rule out leak concern.
4. Q: We are suspicious sample preparation.
   A: We use solid phase extraction. The technician forgot to take the waste bin away before they add the eluting solvent.

Root Cause: Sample was lost at the last step in the extraction using solid phase extraction.

Reference: MSACL. The Basics of LC-MSMS Troubleshooting: Tools, Strategy, Cases

Go to “POOR SENSITIVITY”