Agilent has a first-generation forward-flush-flow (FFF) CFT flow-modulator and a recently introduced second-generation reverse-flush-flow (RFF) CFT flow modulator. The RFF flow modulator works better if your samples have high concentration analytes because it is less prone to breakthrough caused by sample overfilling the fixed volume of the sample loop embedded in the CFT device.
Besides the problem of direct connecting to mass spectrometry, flow modulation requires very careful optimization of column flows in both dimension, modulation period, and flush time (as part of modulation period), since all these factors are tightly coupled by the fixed volume of the sample loop. Once successfully optimized for a set of parameters, it will have to be re-optimized if anything in the system gets changed. So it is much less flexible than thermal modulation.
Thermal modulation can routinely get higher peak capacity than flow modulation does in the boiling point range similar to your samples. However, it was reported flow modulation does a better job for mcuh lighter compounds.
Most current thermal modulator requires consumption of cryogenic fluids, such as LN2 to trap down to C3 (propane). It could be logistically troublesome for some laboratories. Vendors like ZOEX and LECO can also provide their refrigerant model which traps down to C7, however.
You may also look into some new development, for example, at
www.jnxtec.com. This company has commercialized a solid-state, cryogen-free thermal modulator based on thermoelectric cooling (Peltier device).
In general, thermal modulator is more expensive than flow modulator, but the extra money is usually justifiable for the extra performance, flexibility, and ease of hyphenation to mass-spec.
Xiaosheng
