Chromatography Forum

hello everyone,
I want to ask a question, how to understand the "eqivalent" in the following sentence: the liquid chromatograph is equipped with a 4.6 mm i.d.*15cm, column that contains 3 um packing L7(or equivalent), can I replace the column with 4.6 mm i.d.*25cm, column that contains 5 um packing L7. if the retention time, resolution etc. system suitability between the two kinds column is same, can I say the two columns is "eqivalent"?
thanks for your any response.

zhengmin.

I would say yes, becuase you've documented that you meet the requirements using the 5u column. Remember, even "official" test procedures don't investigate every possibility, they just report what they used and what worked. They probably just used 3u and never tried 5u from same supplier, likely due to time, manpower, etc. In our lab we get something to work, then revise only if there are issues, opportunities for cost savings or increased efficiencies, etc.

In the old times, the USP did no permit any changes in the column dimensions. Nowadays, they have become more flexible. The current guidelines (at least from about half a year ago), are as follows:

The length can be changed from -50% to + 100%, the column diameter +/- 25%, the particle size - 50%, the flow rate +/- 50% and the temperature by +/- 10 degrees C.

The way you want to go, i.e. to a larger particle, is not allowed.

Thanks of all.
Now I use the 0.5% TFA, it is very acid(USP method), I used the WATERS and SUPLECO column. the Performance of the column is worsened sharply. but I can not buy the column which can used in acid. how can i do ?
Dear Uwe neue, can you tell me how can i get the current guidelines? thank you very much.

sincerely
zhengmin.

I got them from the Pharmacopeial Forum, which we have in our library. In this publication, they put the changes in their procedures up for discussion before they establish them officially. The same material was presented at the USP conference last fall.

thank you very much. I will find out it.

Uwe, don't you mean that the USP accepts those changes you detailed as "tweaks" which don't require studies? If the chromatographer shows he meets resolution, system suitability, why wouldn't the 5u particle be allowed, if he dodcuments the data is equivalent? System suitability means showing that the system is capable of providing the required measurement, doesn't it?

Sorry about the typing error with "because" in my previous post (I can spell a lot better than I can type).

System suitability is a test against established parameters of an analysis. These parameters are determined outside a system suitability test. Thus the fact that system suitability can be established with a column that does not fulfill the requirements of the analysis is irrelevant.

The dilemma is actually much deeper, and the USP's approach to the problem is to give the user some flexibility. In my opinion, if a method has been established on a particular column brand, one can not arbitrarily change the column brand to hope to get the same results. (Of course, this is also a function of the complexity of the analysis.) The USP has the problem that they are not able to specify the column, since this could be construed as support for a commercial enterprise, i.e. the column manufacturer. Thus they give the user some flexibility in the choice of the column dimensions etc., as outlined above.

I was under the impression, that the "tweaks" must take place before validation. Wouldn't the results be invalid if a different column type was used than during method validation?

USP has proposed that "tweaks" within reasonable ranges be allowed as necessary to meet system suitability. These would occur when the method is being run (i.e., after being run). The risk, of course, is that of poorly defined system suitability criteria.