The Ambient Mass Spectrometry Imaging system can image sample surfaces under ambient native conditions, without sample preparation, and generate accurate localized mass spectra. This technology is ideal for studying the composition of non-homogeneous surfaces. It enables researchers to see where molecules of interest are located on almost any surface.
Successful applications range from the analysis of the distribution of pesticides on slices of fruits and vegetables, to the distribution analysis of finish materials on high-performance synthetic fibers or illegal drugs on hair. Ambient mass spectrometry imaging is a very new development and has already a wide range of application, especially in qualitative surface analysis.
The Synapt G2S mass spectrometer is equipped with a versatile ion source front, allowing to connect several ionization sources. The main feature is the Laser Ablation ElectroSpray Ionization (LAESI) source, equipped with a 2940 nm mid-infrared laser and an X-Y sample stage that can be thermostated from -10 to +60 °C. The LAESI technique provides m/z images by investigating a surface of several centimeters length and width, at a spot size of 200 micrometer; the size of tissues or cell clusters, and a little more than the size of single cells. The LAESI can be used for both small and large molecules of interest having medium to high polarity. In contrast, another ionization source equipped with an X-Y sample stage, named DART, ionizes a sample surface by directing a beam of excited helium gas onto the sample. Here small molecules having low to medium polarity can be imaged on surfaces centimeters long at a spot size of a few millimeters.
Biological tissues and aqueous samples are readily analyzed using a mid-infrared laser (2940 nm) in Laser Ablation Electrospray Ionization Mass Spectrometry (or LAESI-MS). The wavelength corresponds to the frequency of the O-H bond vibrations in water, therefore it results in the strong absorption of this wavelength by the water. Gas phase particles are created from the ablation of the sample due to this absorption of the mid–IR energy. These particles are subsequently ionized through interactions with an electrospray ionization (ESI) plume located above the sample at ambient pressure. The ions are sampled and analyzed by the mass spectrometer after interaction with the ESI plume.
Mass spectrometer: Waters Synapt G2-S HDMS 4k traveling wave ion mobility TOF
- Mass range: 20 – 40,000 Da
- Resolution: 40,000
- Mass accuracy: <2 mDa
- For imaging of surfaces: LAESI DP-1000 (Laser Ablation Electrospray Ionization) from Protea Biosciences
- smallest spatial resolution (pixel size of the image): 200 μm
- For objects: Direct Analysis in Real Time (DART) from IonSense
- smallest spatial resolution (pixel size of the image): 5 mm
- For UPLC: Electrospray ionization (ESI)
LAESI-MS supports a broad range of research in the fields of life sciences and material sciences, forensics, agriculture, food process monitoring, and many others.
Examples of successful applications of ambient imaging MS with LAESI
Spatial distribution profiling (2D and 3D imaging) of biomolecules in tissues or living cells is relevant in various research areas, such as:
- Plant sciences: plant metabolomics – by studying the composition of plant tissues such as leafs and stems.
- Food quality and safety: spatial distributions of pesticide residues and biotoxins on food surfaces.
- Microbiology: microbial chemical signaling studies of cell colonies on petri dishes.
- Material sciences: the analysis of finish layer distributions on synthetic high-performance fibers.
Examples of successful applications of ambient imaging MS with DART
- Forensics: retrospective timeline assessment of the intake of illegal drugs via imaging of hair.
- Material sciences: characterization of chip surfaces