Chromatography Forum

So, one thing I have learned the past year is that the calculations tied down in your company SOP are definitely not the same ones being used in other companies, and often people tell me they are downright wrong!

For instance, this is how my company calculates standard compliance which must pass the spec before either of the working standards can be used to quantify samples:

Typically prepare 2 working standards (A and B). To ensure compliance, the most common calculation is:

(Difference in weight adjusted areas/Mean of weight adjusted weights)*100
Spec is typically NMT 2.0% difference. If spec passes, then either A or B Standard can be used to quantify samples like assay, swabs, blends etc.

Do any users use this calculation? Its used all over our company!

I'm working at a CRO now and we use methods provided by customers for many things.

I am seeing lots of very similar calculations to check for standard consistency. I have not seen exactly what you are seeing, but the general format is to compare response ratios between 2 different standard preps. The general format is standard A weight/area * standard B area/weight where the result is 100+/- 1 or 2%.
Some methods also require response checks for the analytical standard throughout the run, comparing the area from each bracket against the initial 5 or 6 injections. This is generally of the form: (initial average - bracket average)/initial average NMT 1 or 2%.

Hi DR,

I have seen the general formula of Std Weight A/Area * Area/Std Weight B. I think the old weight adjusted areas hark back to old methods for assay and impurities we had back in the 80s or 90s and when our equipment migrated from HPLCs to UPLCs and UPLC-MS about 10 years ago, we just updated the methods but not the calculations. Its probably long overdue a change.