Chromatography Forum

Hi,
I am using 5 conditioning QCs (pooled sample) at the start of the run for my untargeted metabolomics run order. when you change to negative ion mode, is there a need to run the 5 conditioning QCs again or one QC should be enough. Positive and negative mode are done on the same day.

Secondly when you inject QCs at different points in the run order, do you inject from a single vial or prepare different QCs such as QC1, QC2 etc...

Thanks,

Regards,
Harsha

I presume by QC your meaning 'quality checks'. From my point of view this is a reference standard and you are performing 'system suitability' as required by USP section <621> and demonstrating that your chromatographic system is suitable for the analysis.

Based on this thought switching modes is the equivalent of switching detectors and YES you must perform a minimum of 5 QC checks.

In method development and validation they should have demonstrated whether 1 or more vials are suitable. However, organics are known to be volatile and evaporate leaving the reference standard more concentrated. Thus, I recommend several unique vials.

Hello

Based on this thought switching modes is the equivalent of switching detectors and YES you must perform a minimum of 5 QC checks.

I agree with HPLC chemist although I would say that switching modes between pos/neg is equivalent to e.g. changing wavelength in UV detector, not switching detectors

Regards

Tomasz Kubowicz

Hi,
Thanks for the reply. When i mean QC it is a pooled urine sample. I am also running one std test mix. I am following the run order according to (Want et al., 2010. Global metabolic profiling procedures for urineusing UPLC–MS. Nature protocols)

I shall include 5 QCs as suggested in the negative ion mode. Thanks.

Just a question, Are these conditioning QCs required to be run everyday of the run?. Thanks

Regards,
Harsha