Chromatography Forum

Hi,

We have a new LC method and have been asked to run bracket check standards every 20 samples.

We make our calibration standards from a high purity reference material. My idea was to run one of these calibration samples (near the mid-point) every 20 samples to determine if the result is within a certain %tolerance of the same initial calibration value.

Another analyst says we can’t use the same calibration sample vial and should instead prepare a completely separate standard (from the same reference material as the calibration samples are made from) at the same concentration as my proposed sample above and run than as the check standard. Basically the same sample as above but made independent and not used for the calibration curve.

I can’t really see why we’d use method 2, so I’m hoping to get some input from the experts here.

Appreciate any guidance!

The purpose of using a bracketing standard injected after the samples is to check the system stability, not to check your weighing and diluting skills. So, you don't have to use a separately prepared solution for this purpose.

Another analyst says we can’t use the same calibration sample vial and should instead prepare a completely separate standard (from the same reference material as the calibration samples are made from) at the same concentration as my proposed sample above and run than as the check standard. Basically the same sample as above but made independent and not used for the calibration curve.

Appreciate any guidance!

THAT analyst is incorrect. So in "today's world" is most likely to get promoted !!!!

Another analyst says we can’t use the same calibration sample vial and should instead prepare a completely separate standard (from the same reference material as the calibration samples are made from) at the same concentration as my proposed sample above and run than as the check standard. Basically the same sample as above but made independent and not used for the calibration curve.

Appreciate any guidance!

THAT analyst is incorrect. So in "today's world" is most likely to get promoted !!!!

You get promoted to your level of incompetence. It happened at my lab. Not fun to deal with. Make sure you document document document!

You get promoted to your level of incompetence. It happened at my lab. Not fun to deal with. Make sure you document document document!

The good ol' Peter Principle !!! Happened way too many times to count.

Worst for me was when a woman from a sensory department was put in charge of our department, lasted two miserable years. The day this re-organization was announced, she actually stated to me "I don't know a thing about analytical chemistry" while tilting her head from side to side, and I had to restrain myself from replying "No Sh*t, Sherlock !!!"

Another analyst says we can’t use the same calibration sample vial and should instead prepare a completely separate standard (from the same reference material as the calibration samples are made from) at the same concentration as my proposed sample above and run than as the check standard. Basically the same sample as above but made independent and not used for the calibration curve.

I think your colleague is confusing a 'bracketing standard' with a 'check standard'. For quantitative analyses, it is often good practice to prepare a second standard solution to verify the concentration of your calibration solution, but this is a completely different system suitability check than a bracketing standard. Bracketing is almost always performed using the same solution used for calibration (generally using a single point, if you're running a multi-point calibration).