Newbie Needs Help Understanding Chromatogram Data

Basic questions from students; resources for projects and reports.

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Hello - Let me begin by stating that I am not a chromatographer. I am actually a Sales Person for a company that manufactures chromatography consumables. I have been slowly trying to increase by knowledge base about chromatography but as a manufacturer we do not get very much exposure to laboratories. If my question sounds stupid just keep in mind that I am not technical but I am trying to learn as much as possible.

I received the following feedback from one of my customers and they noted the following differences between two consumables. They analyzed the same sample but used two different consumables.

Sample analyzed: Zoledronic Acid

Area with Product A: 7917066.98
Area with Product B: 7177961.61

% RSD with Product A: 1.53
% RSD with Product B: 0.6

The customer flagged this as "different." I am trying to get information from them about why this difference is something worth noting. In the meantime, could somebody help me to understand what this means for a chromatographer? I have my own interpretation of this but I have no idea if it's realistic. If all else was equal would one of these products be considered better than the other? If so, why? I removed the names from both because I welcome honest feedback. Again, please keep in mind I know very little about chromatography but I am willing to learn.

Thank you in advance for your advice and insight.
In addition to myriad unidentified potential variables, whether the differences are "real" or not depends on the type of consumable that was changed. It also depends on the number of runs going into the areas and RSDs reported, the quality of installation/use of the consumable as well as the number of consumable items being compared.
Thanks,
DR
Image
Thanks for the quick reply, I appreciate it! I should have been more specific about the consumables, sorry. The consumables are the septa, caps and vials. Product A contained one set of caps, septa, and vials as a kit and Product B contained a different type of caps, septa, and vials as another kit.
To expand a bit on DR's post, there is still not enough information.

If all the tests were done:
- on the same day
- on the same instrument
- by the same analyst
- with the samples "randomized" (i.e., the different sets of consumables intermingled)
- with sufficient replicates to get meaningful statistics (very roughly speaking, 5 or more injections of each sample and 5 or more sets of each consumable).

Then yes, it looks like there *is* a statistically significant difference between the two sets.

If any of those conditions were *not* met, then you really can't tell anything (coincidence is not causality!).
-- Tom Jupille
LC Resources / Separation Science Associates
tjupille@lcresources.com
+ 1 (925) 297-5374
Tom and DR,

Thanks for your insight. I am looking into your points above. That makes a lot of sense.

Assuming that the customer comes back and says that they performed at least 5 tests of each and the rest of your criteria was met what would you infer about the difference between the consumables?

If all of your criteria is met would it be fair to suggest that:
a - The lower %RSD shows that Product B is more consistent for analysis than Product A?
b - The higher area is a result of higher levels of solvent evaporation with Product A?
c - If no solvent is used in this analysis (which would surprise me) that Product B has higher levels of evaporation or the glass vial is adsorbing the acid because it registered a lower surface area under the chromatogram.

I am hoping to understand if my inference is even relevant to the application based on my limited understanding of problems I have seen with differing types of quality of septa and vials. Or if I am totally off base with this.

Thanks again for your insight. Giving me some things to consider about the test protocol itself was very helpful!

Adam
Again, without access to the actual data, it's little better than guesswork.

You would have to run an F-test on the data. An Excel spreadsheet can calculate the F value for you (it's a built-in function), and you can evaluate the probability that the variances differ from this on-line calculator:
http://www.danielsoper.com/statcalc3/calc.aspx?id=7
-- Tom Jupille
LC Resources / Separation Science Associates
tjupille@lcresources.com
+ 1 (925) 297-5374
Another thing that I didn't see mentioned (and if someone has, my apologies) is that if there were any trends noted during the runs. For instance in the set with the greater %RSD, did it trend from lower area counts to higher area counts over the course of the run? This could show possible loss of solvent. Conversely, if the area counts decreased over the course of the run it could potentially be degradation whether through interaction with the vial, or the septa or greater exposure to light etc etc.

I do echo the thoughts that without seeing the raw data as well as the conditions, there is really no way to interpret just a %RSD and area count.
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