Analysis by LC-DAD-MS

 

In addition to a regular HPLC with diode-array detector, EnzyScreen has available a (brandnew, december 2004) LC-DAD-MS, from Agilent Technologies. The MS is a quadrupole MS of the type 1100 SL, which has a detection limit (for the reference compound reserpine) below 1 pg for both electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI).

 

Main applications LC-DAD-MS:

 

1) Highly sensitive, high-throughput analysis for known substances in complex matrices in SIM-mode.

 

For these applications, the MS is set to detect only these masses corresponding to (fragments of) the known substances in which one is interested (so called Selective-Ion-Mode or SIM-mode). Since the MS 'focusses'  to detect the selected masses only, the sensitivity is extremely high, and is often in the low pg range or lower. An additional advantage of operating the MS in the 'SIM mode', is that baseline separation of components is not required. As a consequence, short colums, and steep gradients can be used, resulting in short run times and a high-throughput. Main application areas include i) analysis for certain (desired) metabolites in our custom screenings, and ii) residue analysis for (undesired) antibiotics, pesiticides, etc. in e.g. food products.

 

2) Full Analysis and fingerprinting of complex mixtures of natural compounds

 

In these cases, the MS is set to detect all masses in a certain range (scan mode). All components of the mixtures are then detected by the MS-detector. The combination of UV-spectral data (generated by the diode-array detector) and MS-data are generally sufficient to get a good indication of the chemical structures. Further information on the chemical structure can be obtained by running samples at a higher 'Fragmentor Voltage" resulting in stronger fragmentation of the parent ions/molecules.

 

 

Contract-analysis projects:

 

Enzyscreen performs contract-analysis, especially in the field of residue analysis (see above). Purified samples (protein and fats removed) can be supplied in 384-well or 96-well microtiter plates, as well as in regular HPLC-vials. Also, unpurified samples can be handled; EnzyScreen generally uses solid-phase extractions (also in microtiter plates) or solvent extractions for the work-up of complex matrices such as food products.

Wouter Duetz has a long-standing experience with the development of high-throughput LC-MS applications during his previous position as a lecturer and group leader at the Institute of Biotechnology at the ETH Zurich.