My team and I are new to HPLC/GC-MS quantification so we would appreciate some insight. Currently, we are trying to measure the concentration of organic acids within an organic solvent (tri-n-octylamine and oleyl alcohol (40% v/v)), aqueous solvent (water based microbial culture) and a pure substance (achieved through distillation). Will the reagents be different for each type of solvent? What solvents would be recommended for this procedure? Thanks.
Organic acids have ionization constants around 4.5; therefore you need to have them in deprotonated states for MS detection. Use volatile solvents that dissolve the acids and add volatile buffer that buffer above pH 4.5 like ammonium acetate.
A key Factor to consider in GCMS is the space of the liner, you need to select a solvent that for the given volume will vaporize but not expand too far and contaminate the exterior of the injector port and septa etc. The link below is a good calculator for deciding if your solvent/injection volume is a risk.
Guillaume is right that hexane is a good solvent but if you wish multiple injections then you will risk evaporation of the sample, iso-octane, nonane and dodecane are more stable but you need to be sure your compounds of interest will dissolve.
It depends on the pesticides you are analysing and also on the matrix from where the pesticides are being extracted. Ethyl acetate or acetonitrile are good solvents for this purpose. Generally modified QuEChERS methods prefer to use EA or ACN. These solvents can extract most of the pesticides present in a matrix, but still some matrices need different approaches. Selection of solvent depends on many factors like solubility, polarity; and as GCMS operates at high temperature, vapour generated from solvent after injecting sample plays important role. You can find good papers on this aspects.
It completely depends upon your sample and the pesticides you're looking for. As a general screening method QuEChERS is an outstanding method; we directly inject the acetonitrile without any major problems using large volume/low split ratio injections. Acetonitrile/QuEChERS is not good for some compounds. In those cases you're better off using a polar solvent with solvent exchange into MeCl2 or hexane.
As long as you're careful with your injection technique any solvent lighter than toluene will perform adequately.
For HPLC and GC MS you may use hydro-methanolic solvent for better results
- Badges
- Science topic
- Similar topics
- Chemistry, Organic
- Organic