HPLC solution stability

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This is my first post here, so hello to all.

I'm wondering if anyone could shed some light on the titled subject.

Ill dive straight in.

Talking about pharma HPLC validation. In the company i work for we perform solution stability studies on the solutions for analysis.

In the validation protocol we state that a solution is stable for a defined length of time (for example 72 hours).

Once validated, methods are written stating "samples/ std solution zstable for 72 hour"

Personally i interpret this as all solutions must be prepared and injected with in this window. By doing this the accuracy and integrity of data is maintained.

It would not be ideal, for example, to make up solutions then inject them on the 71st hour.

A point to a paper or good reference would be appreciated also. Cheers
I can't point you to a specific paper, but I can make some general comments:
- If you are going to claim 72 hour stability, it would be good to have at least one data point longer than that (always interpolate, never extrapolate).
- Along the same lines, look at the time-series of your results. If the response is dropping off sufficiently steeply that you would fail at 73 hours, that represents a serious robustness problem that should probably be addressed.
- in any case, once you inject, the sample is no longer in the original solution; it's in the mobile phase. You could inject at 71:59 and still be within the letter of the spec.
-- Tom Jupille
LC Resources / Separation Science Associates
tjupille@lcresources.com
+ 1 (925) 297-5374
Thanks for your reply.

Interpolate - that pretty much sums up my thinking.

Regarding injecting at 71 hours. In this regard the sequence would start on the 71st hour, however, in the case of a large related substance sequences may not finish until the 95 hour (24 hours later).

I've heard the argument that if the sequence is set off before 71st hour, that the SST injections (throughout) RSD% is a indication that solution stability is being maintained (assuming that stds are made at the same time as samples). However, i'd make the argument that samples have a different matrix components and therefore not directly comparable.
Regarding injecting at 71 hours. In this regard the sequence would start on the 71st hour, however, in the case of a large related substance sequences may not finish until the 95 hour (24 hours later).


To evaluate the sample stability you cannot specify a time limit for when you start the sequence, the sample stability should be related to the injection time of the actual sample. At least that's how I tend to interpret it.
I completely agree with you that SST alone cannot be used for this as the sample matrix may impact stability. Also, the SST may not even be the same substance as the sample all the times which makes such an argument invalid.
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