No abstract

The dynamics of the expanding material plume after irradiation of a matrix sample with two different infrared (IR) lasers, an Er:YAG laser of ca. 100 ns and an optical parametric oscillator (OPO) laser system of 6 ns pulse duration, were investigated by imaging the plumes with nanosecond time resolution. Both lasers emitted at an identical wavelength of 2.94 microm. Laser exposure parameters were typical for infrared matrix-assisted laser desorption/ionization mass spectrometry (IR-MALDI-MS); glycerol was employed as a liquid matrix to provide a homogeneous sample and reproducible plume formation. A Nd:YAG laser (532 nm; 8 ns) was used as the illumination source and a CMOS camera with a ten-bit dynamic range served for recording of the images. Dark-field as well as scattered light illumination was employed to preferentially image the gaseous and particulate components of the plume, respectively. During the initial phase of its expansion (ca. 1 micros) the plume appears to consist of a continuous cloud of material of varying density. At later times after exposure, individual particles of several micrometers in size dominate the images. For both laser pulse durations material ejection was observed for times as long as 100 micros postexposure. Subtle but distinct differences in the plume dynamics are observed for the two different pulse durations. They are related to a transition between the regimes below and above acoustic confinement. The experimental findings are compared to results obtained in two previous studies by photoacoustic analysis of the desorption process and IR-laser postionization of the plume.

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) is a rapidly growing method in many elds of the life sciences. For many analyte classes, however, its sensitivity is limited due to poor ionization e ciencies. To mitigate this problem, we here introduce a novel and cost-effective postionization scheme at high repetition rates based on the interplay of single-photon photoionization and subsequent charge transfer reactions. Importantly, the ne vacuum conditions of a dual ion-funnel ion source effectively thermalize the evolving MALDI plume and enable ample gas-phase reactions as well as the addition of chemical dopants that crucially support chemical ionization. Supported by acetone dopant, [M + H] + /[M-H] − signals of numerous glycerophospho-, sphingo-, and further lipids, registered from mammal brain and kidney sections, were boosted by up to three orders of magnitude, similar to results obtained with laser-based postionization (MALDI-2). Experiments utilizing deuterated matrix and dopant, however, indicate complex ionization pathways different from MALDI2.

No abstract

Low‐pressure photoionization (LPPI) is a versatile tool for the mass spectrometric detection of (semi‐)volatile organic compounds, (s)VOC. Here, a dual‐ion funnel MALDI/ESI ion injector was equipped with a direct‐inlet LPPI module. A radio‐frequency (RF) drive enabled the implementation of three Kr discharge lamps in a novel design optimized for efficient photoionization and undisturbed ion trajectories. Supported by expansion and collisional cooling and, optionally, dopant vapor, primarily intact radical ions and protonated molecules were generated. Molecular identification was supported by the high‐resolving power of an Orbitrap mass analyzer. In our proof‐of‐concept study, exhaled human breath and head‐space sampled coffee grounds were characterized with this high‐throughput technique. From breath, a few hundred and for the coffee roasts more than thousand distinct (s)VOC features were recorded. Principal component analysis enabled the differentiation of coffee grounds by origin and roasting protocol.