Letter: High-mass capabilities of positive-ion and negative-ion direct analysis in real time mass spectrometry

Portable Instrumentation for Ambient Ionization and Miniature Mass Spectrometers

We critically evaluate the current status of portable mass spectrometry (pMS), particularly where this aligns with ambient ionization. Assessing the field of pMS can be quite subjective, especially in relation to the portable aspects of design, deployment, and operation. In this review, we discuss what it means to be portable and introduce a set of criteria by which pMS and ambient ionization sources can be assessed. Moreover, we consider the recent literature in terms of the most popular and significant advances in portable instrumentation for ambient ionization and miniature mass spectrometers. Finally, emerging trends and exciting future prospects are discussed and some recommendations are offered.

Direct analysis in real-time tandem mass spectrometry method for the rapid screening of 11 new psychoactive substances in blood and urine

RATIONALE

With the continuous renewal of new psychoactive substances (NPS), the abuse of NPS has seriously harmed social security and public safety. The number of deaths from the abuse of NPS is increasing year by year. Therefore, there is an immediate need to develop an effective method for detecting NPS.

METHODS

Direct analysis in real-time tandem mass spectrometry (DART-MS/MS) was used to detect 11 NPS in blood and urine. The temperature of the ion source was optimized and set to 400°C. The mixture solvent of acetonitrile/methanol (4:1, v/v) was used as the precipitant. SKF-525 (2-(diethylamino)ethyl 2,2-diphenylpentanoate) was selected as the internal standard for quantification. After the pretreatment of the analytes in blood or urine, the supernatant was prepared for instrumental analysis.

RESULTS

The results indicated that the correlation coefficients (r2 ) of all analytes ranged from 0.99 to 1 in the linear range. The recoveries of 11 analytes at three spiked levels ranged between 83.4% and 110.4% in blood and between 81.7% and 108.5% in urine. The matrix effects of 11 analytes ranged between 79.5% and 109.5% in blood and between 85.0% and 109.4% in urine. The relative standard deviations of intra-day and inter-day precisions and repeatability were lower than 12.4%, 14.1%, and 14.3% in blood and lower than 11.4%, 13.9%, and 14.3% in urine, respectively.

CONCLUSION

The method established for the detection of 11 NPS could meet the needs for the rapid screening of NPS samples. The DART-MS/MS method has the advantages of being efficient, fast, and green. Therefore, it may become a promising technology for the detection of NPS in the future.

Negative-ion field desorption revitalized by using liquid injection field desorption/ionization-mass spectrometry on recent instrumentation

Field ionization (FI), field desorption (FD), and liquid injection field desorption/ionization (LIFDI) provide soft positive ionization of gaseous (FI) or condensed phase analytes (FD and LIFDI). In contrast to the well-established positive-ion mode, negative-ion FI or FD have remained rare exceptions. LIFDI provides sample deposition under inert conditions, i.e., the exclusion of atmospheric oxygen and water. Thus, negative-ion LIFDI could potentially be applied to highly sensitive anionic compounds like catalytically active transition metal complexes. This work explores the potential of negative-ion mode using modern mass spectrometers in combination with an LIFDI source and presents first results of the application of negative-ion LIFDI-MS. Experiments were performed on two orthogonal-acceleration time-of-flight (oaTOF) instruments, a JEOL AccuTOF GCx and a Waters Micromass Q-TOF Premier equipped with LIFDI sources from Linden CMS. The examples presented include four ionic liquids (ILs), i.e., N-butyl-3-methylpyridinium dicyanamide, 1-butyl-3-methylimidazolium tricyanomethide, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, and trihexyl(tetradecyl)phosphonium tris(pentafluoroethyl)trifluorophosphate), 3-(trifluoromethyl)-phenol, dichloromethane, iodine, polyethylene glycol diacid, perfluorononanoic acid, anionic surfactants, a tetraphosphazene silanol-silanolate, and two bis(catecholato)silanes. Volatile samples were delivered as vapors via the sample transfer capillary of the LIFDI probe or via a reservoir inlet. Condensed phase samples were applied to the emitter as dilute solutions via the sample transfer capillary. The compounds either yielded ions corresponding to their intact anions, A-, or the [M-H]- species formed upon deprotonation. This study describes the instrumental setups and the operational parameters for robust operation along with a discussion of the negative-ion LIFDI spectra of a variety of compounds.

Poly(2-vinylpyridine) as a reference compound for mass calibration in positive-ion matrix-assisted laser desorption/ionization-mass spectrometry on different instrumental platforms

Butyl-terminated poly(2-vinylpyridine) (P2VP), C₄H₉(C₇H₇N)_nH, is evaluated for use as an external and internal mass calibrant in positive-ion matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS). P2VP oligomers covering the m/z 450-4500 range are employed to calibrate a time-of-flight (TOF) mass spectrometer in linear and reflector mode, an ion mobility-quadrupole-time-of-flight (IM-Q-TOF) mass spectrometer, and a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. The proton affinity of P2VPs introduced by the numerous pyridyl groups leads to the almost exclusive formation of [M + H]⁺ ions with common acidic matrices like α-cyano-4-hydroxycinnamic acid (CHCA) and 2,5-dihydroxybenzoic acid (DHB) as well as with the non-acidic and aprotic matrices 1,8-dihydroxy-10H-anthracen-9-on (dithranol) and 2-[(2E)-3-(4-tert-butylphenyl)-2-methylprop-2-enylidene]malonitrile (DCTB). This prevalence of [M + H]⁺ ions evenly spaced at Δ(m/z) = 105.0578 renders butyl-terminated P2VP oligomers as convenient mass calibrants. The mass accuracies achieved across various m/z ranges with different mass analyzers and modes of operation are evaluated by using established standard compounds. Results as obtained by internal or external calibration are presented. Further, the compilation of mass reference lists tailored to suit the respective analyzer modes is discussed and those reference files are provided.

Saccharose cluster ions as mass calibrants in positive-ion direct analysis in real time-mass spectrometry

In positive-ion direct analysis in real time-mass spectrometry (DART-MS), mono-, di, and trisaccharides form [M+NH₄]⁺ ions. Some of them, in addition, yield abundant [M_n+NH₄]⁺ cluster ions (n = 1-6)), and thus, can serve for mass calibration. Saccharose, C₁₂H₂₂O₁₁, the most common sugar, also termed sucrose, is among the [M_n+NH₄]⁺ cluster ion forming species. Saccharose may therefore be employed as a cheap and ubiquitous mass calibration standard. The extent of saccharose cluster ion formation depends on the temperature of the DART gas, sample load, and instrumental parameters like trapping conditions of ions prior to mass analysis. This study identifies optimized experimental conditions and demonstrates the application of saccharose cluster ion-based mass calibration for accurate mass measurements in DART mode on a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer.