by
XL » Sun Apr 22, 2007 10:11 pm
To Jason, is it possible that on the RP column you were using, lactic acid peak was too close to the void and interfered with other non-retentive impurities? If it is the case, a column different retention mechanism (selectivity) needs to be tried.
To SIELC_Tech, since it seems to me that you had some "wonderings" about Acclaim Mixed-Mode WAX-1, the followings are my opionins on this subject:
1. Acclaim Mixed-Mode WAX-1 column has an hydrophobic alkyl chain with an anion-exchange functionality at the top. Thus it is an RP modified anion-exchange stationary phase. By comaprison, Primesep columns have ion-exchange groups at the bottom of alkyl chains, thus they are ion-exchange modified RP columns. Therefore, it is at least inaccurate to call them "analogs".
2. Like you don't use non-endcapped C18 to separate basic molecules at mid-pH due to the secondary interaction of un-reacted silanol groups, you don't want to use an anion-exchange embedded RP column, like Primesep B, to analyze acidic compounds without manipulating the mobile phase. The remedy is, as shown in most of your applications, to suppress the ionization of the acidic analytes by using lower pH. This way, the selectivity control by ionic strength is not fully utilized. And Primesep B and B2 columns don't provide useful selectivity for separating important hydrophilic organic acids, including quinic, glycolic, lactic, acetic, formic, ascorbic, etc (this statement is based on my first-hand experience. Please correct me if I am wrong by showing an example).
For acidic molecule contianing separations, Acclaim Mixed-Mode WAX-1 is a better choice complementary to RP columns since it takes full advantage of selectivity control of ionic strength, pH, organic content.
3. The Acclaim Mixed-Mode WAX-1 column is compatible with MS friendly buffers such as ammonium acetate or formate, TFA. However, compared to phosphate buffer, all this mobile phases have high UV backgrounds, and don't fully utilize ionic strength to control selectivity. Therefore, phosphate-based applications was the initial focus. We will share the applications based on MS-friendly mobile phase that can't be tackled by a RP column and are of great interest at a proper time.
4. To a broader sense, chromatographers are seeking the most straighforward and easiest solutions for the analytical challenges. From that standingpoint, RP chromatography is always preferred, and that is why the ODS column has always been the workhorse. Unfortunately (or fortunately), RP columns (C18, C8, polar-embedded, etc) often fall short when encountering highly hydrophilic compounds, which is when Mixed-Mode columns (AX for acidics, CX for basics) and HILIC columns (for neutrals, and sometimes for acidics and/or basices, too) come into play. I don't think that Mixed-Mode columns are universal columns good for everything because it is rather inconvenient if not difficult to use compared to a RP column. However, in many applications they do provide superior solutions to the RP counterparts. Therefore, I view mixed-mode columns as specialty columns with broad applications.
Finally, every products has certain strengths and weaknesses. I feel it is more constructive to focus on helping people to solve problems by sharing technical insights and recommending proper products (produced either by your companies or by others). Don't you think?
Regtards,
