SCIENTIFIC PUZZLE

[pliva]

DEAR FRIENDS,
WE HAVE TUNED ISRADIPINE IN API3200 APPLIED BIOSYSTEM AND START WORKING. FOR SYSTEM SUITABILITY OUR SOP SAID TO INJECT 6 REPLICATE OF MQC BUT IT FAILS SOMETIMES. THEN MY BOSS TOLD US TO INJECT 8 REPLICATE AND TAKE THE LAST 6 TH INJECTION ONLY FOR SYSTEM SUITABILITY. NOW I DID IT BUT CANT NOT JUSTIFY SCIENTIFICALLY. I DID FINE TUNING ALSO BUT THE PROBLEM PERSIST. SO WHAT MIGHT BE THE REASON BEHIND. I AM BREAKING MY HEAD BUT CANT NOT FIND OUT THE ANSWER. LETS SEE WHO CAN SOLVE THIS PROBLEM.

WITH REGARD
PLIVA

[Keaka]

First off, typing in all caps is unncessary.

Secondly, the purpose of system suitability is to show that the entire system from the HPLC to MS is stable and suitable for the assay that you are doing. It is normal practice for many CRO's when operating and running analytical batches to run anywhere from 2-3 "System Conditioning" injections before proceeding with the six system suitability replicates. This is because the system may not be ready right off the bat due to various reasons (column not conditioned yet etc.).

[Nanuk]

I believe it's the typical practice to make replicate injections until you get five consecutive injections that meet CV's that you find acceptable, for example 5%, or perhaps 10% at the LLOQ. I have worked on compounds in the past that always required around 15 injections before the system settled into place. Some combinations of columns, mobile phases, drugs, equipment, etc require more injections to equilibrate than others. The number of injections you need to make shouldn't matter, unless it's very excessive or variable. That's the purpose of doing system suitability. Good luck.