LC/MS

Agilent 6470 Triple Quadrupole LC/MS system: Coming soon (ordered)!!!

 

It is difficult to identify unknown compound from the UV spectrum obtained using most common in HPLC ultra violet or photodiode array detectors (PDA). The only detector capable to provide qualitative (identification) information in HPLC is mass spectrometer.

Despite the power of GC/MS, only small percent of the 9 million registered compounds can be analyzed with the GC/MS. Similar to the GC/MS, LC/MS data provide information about the molecular weight, structure, identity and quantity of non-volatile, thermally labile, or charges compounds. Good examples are phenols, polymers, explosives, dyes, and biological compounds.

The figure 1 is a good illustration of the choice of the appropriate analytical technique for different classes of compounds.

 

                                                        Fig. 1

 

 

DEFINITIONS/ABBREVIATIONS

AP-spheric Pressure Electrospray Ionization:

  • Ions formed by solution chemistry
  • Good for thermal labile analytes
  • Good for polar analytes
  • Good for large molecules, such as proteins and peptides

APCI – Atmospheric Pressure Chemical Ionization:

  • Ions formed by gas phase chemistry
  • Good for volatile and/or thermally stable analytes
  • Good for non-polar analytes
  • Good for small molecules
  • Mechanism:

         Primary ion formation: H2O + e- ---->  H2O+. + 2e-
         Secondary ion formation: H2O+. + H2O ---->  H3O+ + OH.
         Positive analyte ion formation: H3O+.  + M (analyte) ---->  (M+H)+ (protonated) + H2O
         Negative analyte ion formation: OH. + M (analyte) ----->  (M-H)+ (deprotonated) + H2O