We would like feedback on the possible effects of turning off the UV/VIS detector after analysis is complete, but before data has been calculated. If samples need to be re-injected, does turning the detector off & then back on affect the suitability of the system? Mobile phase flow rate is typically dropped to 0.1 mL/min after run is complete (during data analysis).

If you just turn the lamp off (not the entire detector), you should be OK. If you turn the detector completely off, on power up it usually runs an internal diagnostic check as well as calibration. It is the calibration that might through you off. I hope this helps and this is just my opinion.

Melissa

I think if the lamp is being turned off and then back on you should repeat your std curve, if this is a quantitative method? In our lab we would re-run system suit as well, technically you're starting a new assay since the flow has been changed.

If you frequently need to re-assay, maybe your test methodology and or process needs to be made more robust.

If the sample could be inspected by the FDA or EP you and it has to be re-injected you should pass the system suitability test even if nothing has changed !

This is part of an ongoing debate we are having at our company with regulated studies in a plant QC environment.

Generally when we perform a sys. suitability we demonstrate instrument precision, and acceptable tailing factor and resolution.

Questions for the group:
1. If the system is turned into some sort of idle mode (detector off and flow turned way down), are all of the system suitability tests again required or is demonstrating resolution and tailing factor on a sample/control good enough?
2. If a control is injected after coming out of idle mode and it produces reasonable results using the old calibration information, is it necessary to recalibrate?
3. When running multiple formulations, is it mandatory to demonstrate sys. suitability on each formula or just the one formulation with the tightest critical pairs?

Thanks

IMO, it all depends on how the method was validated. Was this type of situation (going to an idle mode, for example) mimicked during the validation? Then the validation data could be used to set criteria on a control run after the idle mode to determine if additional samples could be tested. Otherwise, you don't have any documentation to support turning the system up/on and then performing additional testing.

Why turn off your lamp at all? I've found that lamps that are frequently switched on and off don't last quite as long as those that are left in either state. If I have a situation in which the lamp will be used again within the next 12 hours or so, I simply leave it running and have found no ill effects from doing so. It might help remove a variable from your validation question.