Chromatography Forum

Hi, everyone!

I am trying to educate myself about modifiers used in mobile phases for LCMS and would like to know some good education resources.

I feel like I don't have a good grasp on the concept of modifiers and adducts, specifically when used for the LC mass spec interface. I am having trouble finding good resources on the internet and I am not sure if there are any helpful textbooks. I am sure there are but was wondering if anyone had specific recommendations.

Thank you!!

The web is really no place to learn LC-MS, which takes many years of hands-on experience just to learn the basics. However, for those who already have a good foundation in HPLC operation and use (which is what you want to start with when learning about how to use MS detectors), the web does provide many useful tables, short articles and "hints and tips" that can assist you.

If you have done any basic web searching (recommended), then here is one site which contains a great deal of 'free' authoritative information on HPLC, LC-MS, SFC.

"HPLC CHROMATOGRAPHY HINTS and TIPS FOR CHROMATOGRAPHERS [HPLC TRAINING ARTICLES]"; https://hplctips.blogspot.com

Here is a link to an article on LC-MS modifiers;
https://hplctips.blogspot.com/2014/06/p ... phase.html

Another on Adduct formation;
"Adduct formation in LC-MS Analysis (esp. ESI)". https://hplctips.blogspot.com/2011/12/a ... s-esp.html

Thank you very much for these! I have not seen this blog and it has already been very helpful.

Luckily, I am getting a lot of hands on experience at my job. Unfortunately, the previous person who was operating the LC-MS left before I got here so I am in charge of educating myself, hence the search for reliable and helpful sources of information.

The links posted are certainly somewhat useful, but I have a few objections:

- Modifiers: a lot are listed there, but usually you only need a few of these.

Starting points are:
formic acid (0.1%) for positive mode and
acetic acid (0.05%) for negative mode.
Despite what is written in the blog post, basic mobile phases are not the best choice for negative mode. Standard C18-columns won't tolerate pH>8, and acetic acid works better than e.g. carbonate in many cases.

If you want ammonium adducts or want to suppress sodium adducts, add to or replace acid with ammonium formate / acetate (5 mM).

With these four modifiers you can conduct >90% of your analyses.

In some cases it may be helpful to use ammonium fluoride as modifier, as it can strongly enhance response, especially in negative mode. Use very low concentrations (0.1 mM).

-Adducts:
you don't want sodium adducts if your doing MS/MS, since they usually give no useable fragmentation. You don't want sodium in your system at all, since you will be getting sodium adducts when you don't want them. Stay away from sodium.

In negative mode the most common species you get is [M-H]-, but there can be a lot of adducts also, like formate, acetate, chloride,...

A list of common adduct ions can be found in J. Am. Soc. Mass Spectrom., 10 (1999) 1174. https://www.sciencedirect.com/science/a ... 0599000902
(Open Access)

Look for applications on the websites of the instrument and column manufacturers, often they have good recommendations.

Thanks this was informative