Protonation-Induced Chirality Drives Separation by Differential Ion Mobility Spectrometry.

Upon development of a workflow to analyze (±)-Verapamil and its metabolites using differential mobility spectrometry (DMS), we noticed that the ionogram of protonated Verapamil consisted of two peaks. This was inconsistent with its metabolites, as each exhibited only a single peak in the respective ionograms. The unique behaviour of Verapamil was attributed to protonation at its tertiary amino moiety, which generated a stereogenic quaternary amine. The introduction of additional chirality upon N-protonation of Verapamil renders four possible stereochemical configurations for the protonated ion: (R,R), (S,S), (R,S), or (S,R). The (R,R)/(S,S) and (R,S)/(S,R) enantiomeric pairs are diastereomeric and thus exhibit unique conformations that are resolvable by linear and differential ion mobility techniques. Protonation-induced chirality appears to be a general phenomenon, as N-protonation of 12 additional chiral amines generated diastereomers that were readily resolved by DMS.

Open Port Interface for Coupling Capillary Electrophoresis and Mass Spectrometry: Performance Evaluation for Capillary Isoelectric Focusing.

Capillary electrophoresis (CE) combined with mass spectrometry (MS) is a powerful analytical technique that utilizes the resolving power of CE and the mass-detection capabilities of MS. In many cases, CE is coupled to MS via a sheath-flow interface (SFI). This interface has a simple design and can be easily constructed; however, it often suffers from issues such as MS signal suppression, interference of MS and CE electrical circuits, and the inability to set an optical point of detection close to the capillary end due to the specific design of the coupling union. In this paper, we describe a novel coupling of CE and MS based upon the open port interface (OPI). The OPI differs from classical sheath flow interfaces by operating at flow rates at least 1 order of magnitude higher. In addition to the flow rate difference, the OPI provides more efficient mixing of the capillary eluates with the transport fluid and thus minimizes MS signal suppression. In this work, we compared the performance of OPI and SFI in a series of capillary isoelectric focusing (cIEF) experiments with 5 pI markers, carbonic anhydrase II and NIST antibody. The evaluation criteria for the comparison of the OPI and SFI were analytical sensitivity, reproducibility, and pI marker linearity. Given the extent of sample dilution in the OPI, we also compared the peak resolution determined using an upstream UV detector to those determined by the downstream mass spectrometer. The results suggested that the OPI configuration reduced signal suppression, with no adverse effect on peak resolution. In addition, the OPI provided better decoupling of the CE and MS potentials as well as reduced signal dependence upon the sheath liquid composition. While these results are preliminary, they suggest that the OPI is a viable approach for CE-MS coupling.

Product ion scanning using a Q-q-Q linear ion trap (Q TRAP) mass spectrometer.

The use of a Q-q-Q(linear ion trap) instrument to obtain product ion spectra is described. The instrument is based on the ion path of a triple quadrupole mass spectrometer with Q3 operable as either a conventional RF/DC quadrupole mass filter or a linear ion trap mass spectrometer with axial ion ejection. This unique ion optical arrangement allows de-coupling of precursor ion isolation and fragmentation from the ion trap itself. The result is a high sensitivity tandem mass spectrometer with triple quadrupole fragmentation patterns and no inherent low mass cut-off. The use of the entrance RF-only section of the instrument as accumulation ion trap while the linear ion trap mass spectrometer is scanning enhances duty cycles and results in increased sensitivities by as much as a factor of 20. The instrument is also capable of all of the triple quadrupole scans including multiple-reaction monitoring (MRM) as well as precursor and constant neutral loss scanning. The high product ion scanning sensitivity allows the recording of useful product ion spectra near the MRM limit of quantitation.

Metabolite profiling study of propranolol in rat using LC/MS/MS analysis.

Metabolite profiling is one of the most challenging fields in applied mass spectrometry. Mass spectrometry was used to characterize the metabolites of propranolol, a beta-adrenergic receptor antagonist containing numerous oxidation sites. Propranolol is extensively metabolized, with most metabolites appearing in urine. Urine samples were collected from young adult male Sprague-Dawley rats. Structural identification of various metabolites was performed by LC/MS/MS, using a PE SCIEX triple quadrupole instrument (PE SCIEX API 3000). Metabolites were itemized using several LC/MS/MS techniques, including Q3 full scan and precursor and constant neutral loss experiments. A looped experiment technique revealed the presence of mono- and di-hydroxylated metabolites as well as regio isomers of hydroxy- and dihydroxy-propranolol glucuronides and propranolol glucuronic acid. Propranolol glucuronide was not observed, while the presence of dealkylated metabolites was suggested but not confirmed.