question about Ph Eur. relative retention time

[alemaggot]

Hi guys!

I have a question to you. I apply a pharmacopoea HPLC method. In monography of my interset compound is write that it retention time is about 13 min. But wha trepresent "about"? How can retention time vary from it? one minute? two minutes?
I can't found nothing about it in pharmacopea. Can you help me?

Another similar question is about impurity relative retention time. For example: in monogrhap there is write that imp. C must be eluite at 1.8 time from the sample peak. In my chromatogram I obtain 1.9. It's correct? What are limit for it?

Thank you very much!

Best regards

[tom jupille]

There is no universal specific answer, but common sense suggests that it depends on the complexity of the sample and the probability of mis-identifying a peak. Ideally, a validated method should specify system suitability conditions, including the allowed variation and allowed adjustment of conditions. Many compendial methods are old and inadequate in this regard.

[alemaggot]

Thank you Tom!

[Hollow]

maybe you'll find additional information (like example chromatogram and column type) on the knowledge base of EP
http://www.edqm.eu/site/Knowledge-Database-707.html

[JGK]

Hi guys!

I have a question to you. I apply a pharmacopoea HPLC method. In monography of my interset compound is write that it retention time is about 13 min. But wha trepresent "about"? How can retention time vary from it? one minute? two minutes?

Thank you very much!

Best regards

Since a value is quoted in minutes (with no decimal places) and assuming your HPLC system reports a retention time to 3 decmal places, "about 13 minutes" would cover the range 12.501 - 13.500 minutes.

[alemaggot]

Hi guys!

I have a question to you. I apply a pharmacopoea HPLC method. In monography of my interset compound is write that it retention time is about 13 min. But wha trepresent "about"? How can retention time vary from it? one minute? two minutes?

Thank you very much!

Best regards

Since a value is quoted in minutes (with no decimal places) and assuming your HPLC system reports a retention time to 3 decmal places, "about 13 minutes" would cover the range 12.501 - 13.500 minutes.

Mmm... If my retention time is about 16 minutes? It' a problem?

[tom jupille]

The EP has de facto default adjustment limits for things like flow rate and aqueous/organic ratio [European Pharmacopoeia 6.0 (2010) Section 2.2.4.6], which allow flow rate to be adjusted +/- 50% in order to meet system suuitability. If the retention time is of concern -- and if all the peaks of interest are shifted out by about the same percentage -- why not just increase the flow rate by about 20%?

[alemaggot]

I've made this adjustement. The flow rate decrease from 1.0 ml/min to 0.6 ml/min. Because I use a column with 4,6mm internal diameter instead a column with 6,0 mm column diameter.
Pharmacopoeia use a specific formula to adjust flow rate. You must apply it, and you must use value obtained from this calculation

Thanks

[tom jupille]

Okay, so how about tweaking the percent organic?

[alemaggot]

I don't change nothing in the mobile phase. So... Can I do it?
If I use the same column (I've read in Ph eur database), the same flow (after the adjustament), the same instrument parameter, why can't I repeat the Ph Eur retention time?

How can I justify other change?

[tom jupille]

There is such a thing as column-to-column variability. That's why they allow adjustment of conditions. So long as you stay within the adjustment limit and meet system suitability, you don't have to justify it.

[alemaggot]

The column that I must use is a polyvinil column. This column has bad column to column reproducibility, right? However system siutability is conform.
If I don't do other adjustment to arrange the retention time, is a problem for routinarie analysis?

[HPLCaddict]

Noone can say if that procedure works for routine analysis, even though it's an "holy" EP method. Cynical folks may say that using such a procedure is a sure way to produce problems in routine work:). If nobody here has hand-to-hand experience with that particular method you'll have to make your own experiences...
Apart from that, I don't see why you should not be allowed to tweak the flow-rate a bit further in order to be conform with the retention time. All you did now is to adjust it to the changed column diameter, this is not part of the tweaking options available to be conform with SST criteria.

[Hollow]

Cynical folks may say that using such a procedure is a sure way to produce problems in routine work:).

they're not cynical... just experienced

[jinzhaowang]

Cynical folks may say that using such a procedure is a sure way to produce problems in routine work:).

they're not cynical... just experienced

RRT makes no sence if u use a different C18 column. The best way for peak id is using impurity standard.