fumonisin

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huiqi
huiqi's picture
fumonisin

Hey guys, i'm currently analysing fumonisins using LC/MS. I observed that when I dissolve the standard of fumonisins in 50:50 ACN:H2O, I am able to get a peak but however, when I dissolve it in pure ACN, the peak disappeared.

Any idea what caused it?

Dr. Analytical
Dr. Analytical's picture
Please provide some

Please provide some additional details on your system:
column, mobile phase, and any other sample preparation steps that you are using.

However, this sounds like a solubility problem. While these are large molecules, they do contain polar functional groups such as carboxylic acids, alcohols, amines, etc. These all enhance water solubility. So, when you switched from acn:water to acn, you reduced the polarity of the dissolving solvent, so perhaps the compounds never dissolved. Or maybe they dissolved and then precipitated on the walls of the flask or container. Also, if you are filtering your solutions (always a good idea for LC!), you may lose some material on the filter.

And the pH of the water can have a significant impact on solubility. If the water pH is > 6, the carboxylic acis are ionized, and the molecules have a negative charge. This makes them more water soluble, and less acn-soluble. At a lower pH, the opposite is true. So, you could try dissolving in acn that contains a little formic acid, for example.

Since you had a peak in the first experiment, let's assume that your LC-MS system is working properly.

Hope this helps. Write back with more information or results.

huiqi
huiqi's picture
hi dr analytical,

hi dr analytical,

your explanation really gave me a better view of the possibilities. the mobile phase that i'm using is 5mM ammonium acetate in water and 0.1% formic acid in ACN. it start with 5% H2O for 8 mins and switch to 50% ACN.

i didn't filter the standard this time round as it's pure standard hence i usually skip the filtering step for standards. and yeah, my lcms is working well as there's peaks for all the other mycotoxins.

it's really interesting to isolate the cause of it. perhaps i will try out to see if its the pH or the solubility that's causing the observation.

thanks a lot! :)

Dr. Analytical
Dr. Analytical's picture
Perhaps you had a typo in

Perhaps you had a typo in your explanation - do you really have ammonium acetate in A and formic acid in B? If so, I would simplify the system so it is either all acetate or all formate. It may not relate to your current problem. but solving problems will be easier.

And did you mean that you start with 5% water or 5% acetonitrile?

For any LC system that uses a gradient, your most important solubility issue is getting the analytes into solution so that they can get to the column for separation. So, dissolve your samples in your "starting" mobile phase, or something similar.

huiqi
huiqi's picture
hi dr analytical,

hi dr analytical,

eh, i did have a typo error, it starts with 5% ACN.

however, the additives are what i've typed which is 5mM ammonium acetate in water and 0.1% formic acid in ACN. yeah, i agree that two different types of additives might complex the adduct ions formed but we tried out and compared, the adduct ions formed are almost the same when we use just formic acid in water and ACN. that's why we went ahead to use two different additives.