Screening for drugs in serum by electrospray ionization/collision-induced dissociation and library searching

Abstract

Factors influencing in-source collision-induced dissociation (ESI/CID) of organic molecules in a Perkin-Elmer/SCIEX ionspray source have been investigated. Breakdown curves of four drugs and organic compounds were acquired by monitoring the intensities of MH+ and specific fragment ions while ramping the orifice voltage. Haloperidol, diazepam, 1,4-acetamido-acetoxybenzene and diacetamido-1,2-benzene were found to be substances with characteristic breakdown curves, with maximums and points of intersection at orifice voltages between 20 and 70 V. The breakdown curves of haloperidol were used for comparison of ESI/CID with ionspray and turboionspray sources on three PE/SCIEX-API instruments. Using standardized source parameters and mass resolution, very similar fragmentation graphs were obtained for haloperidol with all instruments. Infusion of varying concentrations of haloperidol (0.1 to 10 micrograms/mL with ionspray, and 0.01 to 1 microgram/mL with turboionspray) yielded comparable breakdown curves. With turboionspray, a preconcentration of the aerosol occurred, yielding higher ion abundances. Solvent pH and the ratio of aqueous ammonium formate/acetonitrile had minor effects on the degree of fragmentation of haloperidol in a wide range. With these preconditions, a currently expanding mass spectral library of 400 drugs was set up by liquid chromatography/mass spectrometry with alternating orifice voltages (20, 50, and 80 V, respectively) in a looped experiment. An example of drug identification in a patient's serum with library search is shown.

In-source CID mass spectral libraries for the “general unknown” screening of drugs and toxicants

“…Similar or close fragmentation conditions were reported by other teams [8][9][10], except that all of them used three different fragmentation voltages in the positive-ion mode and none in the negative-ion mode. Moreover, as no final spectra were reconstructed by addition of the different spectra generated for a given compound, different libraries corresponding to the different fragmentation conditions had to be built and searched, sometimes leading to confusing results.…”

“…It can be easily used, with or without chromatographic separation, to confirm the identity of suspected compounds as long as fragmentation energy is standardised (in terms of nature and pressure of collision gas, and ion kinetic energy) and a library of mass spectra of compounds of interest is built [3,4]. As an alternative we [5] and others [6] have suggested using in-source CID. The fragments produced by in-source CID, generally used as confirmation ions for quantitative methods using single-quadrupole instruments, are most generally the same as those produced by conventional CID in the collision cell of a MS/MS instrument.…”

Improvement in LC–MS calibration by addition of fragment signals

“…In practice, when the ionisation energies are the same, LC-MS mass spectra are laboratory and instrument specific [4]. For this reason, the spectrum libraries have not yet been satisfactorily established and different approaches have been proposed [5,6].…”

A method for monitoring and controlling reproducibility of intensity data in complex electrospray mass spectra: A thermometer ion-based strategy

“…During this process, analyte molecules undergo collisional energy transfers that may result in fragmentation (i.e., in-source collision-induced dissociation; CID). Many factors can influence this process [28], including the position of the secondary sampling orifice relative to the supersonic plume [28], temperature effects [31][32][33][34], the pressure and nature of the gas with which the analyte ions collide [24,34], the nature of the solvent from which the ions are desorbed [8,24], and the time scale between the activation of the ions in the source and their ultimate analysis [28]. Moreover, changes related to changes in local pressure and spray droplet evaporation, which affect ion temperatures, along with the distance between the sprayer tip and the sampling orifice have also been implicated [29,35].…”

“…By using benzylpyridinium ions with different substitutions, the energy of fragmentation can be customized to the instrument or parameter being assessed. Studies that attempted to probe energy deposition effects and reproducibility have been done with other classes of molecules, including drugs, peptides, and carbohydrates [8,9,36,37]. However, none of these molecules have the specific combination of properties, described above, that make the benzylpyridinium-based thermometer ion species particularly useful as probes of MS performance.…”