A straightforward means of coupling preparative high‐performance liquid chromatography and mass spectrometry

Abstract

Flow splitting to a mass spectrometer is a common way of coupling a highly specific detector to preparative or semi-preparative high-performance liquid chromatography (HPLC) purification of combinatorial libraries, drug metabolites, and characterizable impurities. The sensitive mass spectrometer consumes only a small fraction of the analyte while providing online structure-specific detection, and its output can thus be used to trigger collection of the desired fraction. Coupling mass spectrometry to preparative HPLC is difficult due to the susceptibility of the detector to fouling under conditions of high analyte concentration or solute amount, or to changes in solvent composition. We report here on a device, the mass rate attenuator (MRA), which automatically produces split ratios over a range of 100:1 to 100 000:1 under programmable user control. The MRA is a flow-control device that periodically gates a small aliquot from one liquid stream into another. The design allows the user to set the frequency of the gating without interruption of the HPLC flow stream. The MRA also allows control of the volume of the aliquot that is transferred between the flow streams. This additional control, compared to passive splitting devices, facilitates optimization of the tubing connecting the separation, detection and collection events. We demonstrate that such optimization can reduce the volume of the collected fraction without compromising recovery, thus reducing the time spent in evaporating solvents to reclaim purified products.

Hydrogen‐Bond‐Mediated Asymmetric Cascade Reaction of Stable Sulfur Ylides with Nitroolefins: Scope, Application and Mechanism

“…The total recovery percentage of effluent ( TR ) collected from CPC and which was not used for the MS analysis, as well as the percentage of effluent lost from the MS detection ( EL ), can be calculated from Eqn. (1):24 …”

“…A simple approach to solve this problem and generate smooth peak profiles consisted in increasing the scan time from 0.2 to 0.8 s, as indicated in Fig. 2 24…”

“…To our knowledge, the benefit of an active flow‐splitter has not been explored for the coupling of CCC to MS, although this kind of splitter has largely proved its advantages in preparative LC/MS 24. Indeed, an active flow‐splitter device such as the variable flow‐splitter (VFS) enables successive and discontinuous transfers of small aliquots of effluent from a primary LC separation stream to an independent secondary auxiliary stream directed to the mass spectrometer, regardless of pressure differences.…”

Automated semipreparative purification with mass spectrometric fraction collection trigger: Modeling and experimental evaluation of a setup employing passive splitting

“…Both active and passive splitting devices have been successfully incorporated into instrumental setups for mass-triggered fractionation [3,12,15,16]. A comparison of active and passive splitters for preparative HPLC has shown that active splitting devices (also called mass rate attenuators) offer minimal peak broadening and easy adaptation to a broad range of flow rates, split ratios, and make-up flows [17]. Nevertheless, due to abrasion of the rapidly moving parts, rotor seals have to be exchanged on a regular basis.…”

“…Besides the maintenance aspect, the employment of active splitters adds additional acoustic noise exposure to working environments. Moreover, peak profiles need to be smoothed by suitable averaging because of the discontinuous transfer of liquid between the donor and acceptor stream [17]. Passive splitters, on the other hand, are more difficult to optimize but hold the advantage of null maintenance and noise level, and continuous transfer of liquid from one effluent stream to the other.…”