splitting peak

[Gali]

We have a problem with the peak of a spike matrix. It was eluting as an unique peak in both the standard solution and the spike sample. Now the peak in the spike splites. Standard and sample solutions are in methanol: H2O (50:50).

Matrix : scallop tissue
Standard: domoic acid
Mobile phase: PO4H3 (pH 2.5):Acetonitrile
Column : C18

Thank you for your help

Gali

[Consumer Products Guy]

What happens if you acidify the sample with H3PO4 then inject?

[chromatographer1]

Secondary amine with three carboxylic acid groups in a 'neutral' pH solvent being injected into an acidic mobile phase on a reversed phase LC column.
A pH adjustment of the sample prior to injection or spiking would most likely correct the peak splitting problem. Splitting could be caused by too large an organic component in the sample solution. It is possible that the appropriate sample solvent requires a smaller organic percentage or a larger polar solvent percentage and that the sample matrix has changed and has affected that ratio.

CPGuy has a good plan to fix the either problem of a slightly more basic sample matrix than was faced before or a sample solvent that is too strong for reversed phase LC.

Let us know when it works.

best wishes,

Rod