A.V. Karpov

Development of an Atmospheric Pressure Ion Mobility Spectrometer–Mass Spectrometer with an Orthogonal Acceleration Electrostatic Sector TOF Mass Analyzer

Recently developed ion mobility mass spectrometer is described. The instrument is based on a drift tube ion mobility spectrometer and an orthogonal acceleration electrostatic sector time-of-flight mass analyzer. Data collection is performed using a specially developed fast ADC-based recorder that allows real-time data integration in an interval between 3 and 100 s. Primary tests were done with positive ion electrospray. The tests have shown obtaining 100 ion mobility resolving power and 2000 mass resolving power. Obtained for 2,6-di-tert-butylpyridine in electrosprayed liquid samples during 100 s analysis and full IMS/MS data collection mode were 4 nM relative limits of detection and a 1 pg absolute limit of detection (S/N=3). Characteristic ion mobility/mass distributions were recorded for selected antibiotics, including amoxicillin, ampicillin, lomefloxacin, and ofloxacin. At studied conditions, lomefloxacin forms only a protonated molecule-producing reduced ion mobility peak at 1.082 cm(2)/(V s). Both amoxicillin and ampicillin produce [M + H](+), [M + CH3OH + H](+), and [M + CH3CN + H](+). Amoxicillin shows two peaks at 0.909 cm(2)/(V s) and 0.905 cm(2)/(V s). Ampicillin shows one peak at 0.945 cm(2)/(V s). Intensity of protonated methanol containing cluster for both ampicillin and amoxicillin has a clear tendency to rise with sample keeping time. Ofloxacin produces two peaks in the ion mobility distribution. A lower ion mobility peak at 1.051 cm(2)/(V s) is shown to be formed by [M + H](+) ions. A higher ion mobility peak appearing for samples kept more than 48 h is shown to be formed by both [M + H](+) ion and a component identified as the [M + 2H + M](+2) cluster. The cluster probably partly dissociates in the interface producing the [M + H](+) ion.

Analysis of new synthetic drugs by ion mobility time-of-flight mass spectrometry

Characteristic ion mobility mass spectrometry data, reduced mobility, and limits of detection (signal-to-noise ratio = 3) were determined for six synthetic drugs and cocaine by ion mobility time-of-flight mass spectrometry (IM-TOF-MS) with electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). The studied synthetic illicit drugs recently appeared on the recreational drug market as designer drugs and were methylone, 4-MEC (4′-methylethcathinone), 3,4-MDPV (3,4-methylenedioxypyrovalerone), JWH-210 [4-ethylnaphthalen-1-yl-(1-pentylindol-3-yl)methanone], JWH-250 [2-(2-methoxyphenyl)-1-(1-pentyl-1H-indol-3-yl)ethanone], and JWH-203 [1-pentyl-3-(2′-chlorophenylacetyl) indole]. Absolute reduced mobilities in nitrogen were 1.35, 1.28, 1.41, 1.30, 1.18, 0.98, 1.09, and 1.07 cm2 V−1 s−1, for methylone [M–H]+, methylone [M+H]+, 4-MEC [M–H]+, 4-MEC [M+H]+, 3,4-MDPV [M+H]+, JWH-210 [M+H]+, JWH-250 [M+H]+, and JWH-203 [M+H]+, respectively. Selected illicit drugs are easily identified by IM-TOF-MS during a 100 s analysis. Relative limits of detection ranged from 4 to 400 nM are demonstrated for these compounds. Such relative limits of detection correspond to 14 pg to 2 ng absolute limits of detection. Better detection limits are obtained in APCI mode for all the illicit drugs except cocaine. ESI mode was found to be preferable for the IM-TOF-MS detection of cocaine at trace levels. A single sample analysis is completed in an order of magnitude less time than that for conventional liquid chromatography/mass spectrometry approach. The application allows one to consider IM-TOF-MS as a good candidate for a method to determine quickly the recently surfaced designer drugs marketed on the internet as “bath salts,” “spice,” and “herbal blends”.

Letter: Compact analyzer for a laser time-of-flight mass spectrometer

Aspects of a new type of laser time-of-flight mass spectrometer are described in this letter. It is based on a wedge-shaped reflecting mirror and is used as an ion analyzer. The analyzer provides time focusing by both energy and divergence angle of ions. Time focusing of good quality is acquired in the energy range of ±20% of the average ion energy, which is, at least, two times wider than the energy range of the known ion optical systems for similar applications. The mass resolution of the analyzer is ∼600, while overall dimensions are very small (10 × 10 × 5 cm).

Letter: The formation of ion packages with ultrashort duration in laser ion source.

A new approach to the formation of ultrashort laser ion packages in the ion source of a time-of-flight (TOF) mass spectrometer for elemental analysis is described. This is achieved by installing a wedge-shaped reflector with special correcting plates. The reflector provides time and space focusing of the ion packages. Such time focusing allows the reduction of the ion package duration up to 1 ns. The proposed approach allows more than an order of magnitude increase in the resolution of the laser TOF mass spectrometer with an axially symmetric electrostatic analyzer to 10,000–13,000. In this Letter the theoretical calculations justifying the proposed method are presented.

A computer model of comprehensive modeling of the laser time-of-flight analyzer.

This article offers a new approach to computer modeling of time-of-flight analyzers of mass spectrometers. The main feature of the model is comprehensive tracking of the processes from the laser plasma generation until the final stage, on which the isotopic or elemental composition is determined for the analyzed solid sample. Apart from usual models based on SIMION-8 3D or similar software, this article proposes fundamentally new modeling stages. These stages are (1) generation and spread of laser plasma, (2) formation of the ion packages, (3) ion detection, and (4) formation and processing of the analytical signals. In order to provide consistent modeling of all the stages, special software units were developed. Program control of the analyzer ion optics (electrodes voltages) allows scan of mass spectra by ion energy. Additional complex of the programs provides simulation of mass spectra digitization, summation of digitized mass spectra for a wide range of variable parameters, and consideration of the discriminatory effects. According to the data, the software calculates ion-optical characteristics of the analyzer and the analytical parameters of measurement results.

Novel approach to constructing laser ionization elemental time-of-flight mass spectrometer:

The main advantages of laser sampling are associated with following features: sample preparations as well as consumables are not needed, low risk of sample contamination, good spatial resolution. In mass spectrometry, high laser irradiance can be used for both ablation and ionization processes. The method is especially profitable in time-of-flight mass spectrometry. A new principle of constructing laser ionization time-of-flight mass spectrometer based on wedge-shaped ion mirrors and the absence of electrostatic ion acceleration before mass analysis is discussed. Among advantages of the analyzer there are ability to provide temporal focusing of ions in a wide energy range (±20%), compactness of the analyzer, and minimization of the requirements for power supplies. The approach is expected to be profitable for standardless elemental analysis of solid samples, which should be possible at laser irradiation power density more than 3u2009×u2009109u2009W/cm2 that ensures complete ionization of all elements in a laser plasma. The analytical signal of each element is formed as the sum of the signals for all charge states and the energy scan of the mass spectra is provided.