Micro and Nano fraction collection
Collection of sample on two targets or MTP allows the simultaneous deposition of the sample on both MALDI plates and micro titer plates, especially when high flow rates are employed.
A second application of the collection of fractions in two distinct devices leads to the use of 2-dimensional Micro- or Nano-HPLC. In this case, commonly most of the sample from ion exchange separation (1st dimension) is saved in a micro titer plate and used for second orthogonal separation (e.g. reversed phase).
Only a small amount of the sample is spotted on a MALDI target for a preliminary investigation of the 1st dimension (Figure 4).
The collection of the eluate in drops or spots can be very often disadvantageous because of possible remixing of compounds separated nicely on the column, but collected in a single spot. In comparison to online HPLC-ESI/API-MS technique MALDI is an offline approach with a discontinuous interface between HPLC and MS.
In order to overcome this issue, SunChrom offers special developed targets for ABI and Bruker MALDI MS, where the sample needle remains on the target surface and moves continuously along the surface, depositing eluent mixed with matrix in meandering lines (Figure 5). An air blower dries these lines rapidly without remixing of compounds due to diffusion.
Figure 5: Continuous eluate deposition in meandering lines on special targets for ABI and Bruker MALDI mass spectrometer.
This target has a special surface without any coating to ensure the creation of a continuous line without interruption at any eluent composition from 100% water up to 100% acetonitrile.
If desired, more than one separation can be placed on a single target. After drying and inserting the target into the MALDI-MS, the laser beam of the mentioned ABI and Bruker MALDI can follow the lines in a continuous manner generating similar results to an online approach like HPLC-ESI-MS.