I think Inertsil is just a brand name. Having said that, not all C18 columns are the same. You can get changes in peak shape, elution order and selectivity depending on the extent of end-capping, polymeric vs. monomeric C18, polar-embedded vs. straight C18 etc.

Inertsil is just a brand name (GL Sciences).

While some "C18" columns are similar, most are not. C18 column types vary as many physical and chemical processes describe each column. Even columns with similar physical parameters do not always provide results which are comparable. *Now, there are some important exceptions to this. For example some of the popular HPLC supports actually have just one manufacturer. The manufacturer then sells the support to a wide range of companies (distributors and re-sellers) who pack the same material into their own columns using their own "labels" and brand names. The re-sellers do not want you to know which material it really is as they could lose their competitiveness (just buy it from someone else for less). The packing material in this case is identical and any differences between them are due to the actual packing process (**Packing columns which result in reproducible separations is actually very difficult to do well. Some companies do a better job than others). IOW: Even columns packed with identical supports may not yield identical results!

There are hundreds of different C18 columns on the market. They are classified into groups by the USP using 'L' #'s to help you compare them. You can find dozens of tables on the web that will show you the physical differences in the core supports used (C18 is just the coating). In most cases, this popular phase is functionalized onto DIFFERENT silica supports. What are the differences? Well, for silica supports their are different pore sizes (large pores for large molecules, small pores for small molecules), different shapes (spherical, irregular), particle size, purity levels (Type A, B...) and so on... Then there are all of the differences in functionalized chemistry on the supports to make them C4, C8 or C18 columns (lots of differences there such as carbon load, cross-linking...).

So yes, there are very important differences between "C18" columns which can result in you developing a method that works well on one column brand and type and not at all on another.

http://www.usp.org/usp-nf/new-chromatographic-columns-online-database

A very thorough answer. Thanks Bill!

Yup.... Inertsil is Just a brand for Columns of LC as well as GC like other brands / column manufacturers (Waters, Agilent, Phenomenex, Shiseido, Thermo etc).

Mr. Bill already explained lot about columns chemistries and applications !!!

Dear Fuad Al-Rimawi 

As above mentioned, Inertsil is just a brand name (GL Sciences) for C18 RP-column.

As various different form of C18 column are available based on chemical derivetization. Sepration, resolusion, and retention time very column to column and also depend on nature of molecule to be purify. Not all types of RP- column are suitable for all type of compounds. 

Bill,

When I was still in the lab, Inertsil did not seem to be re-sold to "own-label" suppliers.

It's one of a number of supports that sometimes shows non-linear adsorption isotherms for remarkably low sample loadings (of the order of 1 µg on a standard 4.6mm id column). Peaks tend to be triangular, as in preparative chromatography, but that is not necessarily a fault. This has been discussed in the literature; there must exist saturable minority sites, but I didn't find a convincing explanation.

The columns are popular in pharmaceutical QC (assay and impurities) perhaps (speculation on my part) because the non-linearity might be associated with displacement effects whereby an impurity is in effect ejected from the overlapping main peak. Conversely, and here is a warning... a minor peak can be "tagged along" by a major overlapping peak, and consequently not detected (see Figure 4 in our 2002 article).

The USP's "L" listings don't provide any information at that level.

We discussed the subject in a couple of publications:

Chromatographic instrumentation and techniques for the quality control of pharmaceutical products.   C.R. Lee, J.P. Porziemsky, M. Gaspar and A.M. Krstulovic   LC-GC Int. 9, 414-427 (1996).

Applications of LC-MS methodology in the development of pharmaceuticals.     Krstulovic, Ante M.; Lee, Christopher R.; Firmin, Sandra; Jacquet, Geraldine; Nguyen Van Dau, Celine; Tessier, Dominique.    LC-GC Europe  (2002),  15(1),  31-32, 34-38, 40-41. 

Chris: I made no statement that Inertsil was ever re-sold as an OEM product ???

Fuad asked a very general question. The USP table is a good starting place to help him and others understand the many documented physical differences in popular C18 columns. There are many other types of tables, some with more detail available too for those with specific concerns or interests.

Bill,

I just thought it useful to know that Inertsil one of those supports that are relatively less likely to have an equivalent from another manufacturer, so in the event that you have to apply an existing method that specifies it you may (or hopefully may not) have little choice. We used Inertsil a lot, largely on grounds of reliability and long-term reproducibility.

I agree that tables giving details of commercial supports are a huge impovement over the situation not so long ago (in Europe at least) where monographs gave only very general information like "octadecylsilyl". If I were developing a new method today I would certainly start with one of the "L"-type lists you find in the catalogues.

A point to be emphasised is that there are a number of proprietary supports that may look "generic" from their description but have very useful unique distinguishing features.  By the same token, a method may become "locked"  to  a column that has no second source. This can sometimes be of concern to a regulatory authority: LC columns can never be totally specified by their published description, and this is the straight answer to Fuad's question.

I know it's ancient history, but this explains why 3 decades or so ago the pharmacopeias appeared slow and ponderous about allowing LC methods in official monographs. I still recall a rather angry conference discussion in about 1983. Whatever the field (and not just analysis), composite materials have always been a challenge when validating mission-critical equipment and applications.