Morphologically compatible mass spectrometric analysis of lipids in cytological specimens

Rapid Mass Spectrometric Calibration and Standard Addition Using Hydrophobic/Hydrophilic Patterned Surfaces and Discontinuous Dewetting

The rapid calibration chip (RCC) is a device that uses the fast and reproducible wetting behavior of hydrophilic/hydrophobic patterned surfaces to confine a series of differently sized droplets on a substrate to obtain a calibration curve. Multiple series of droplets can be formed within seconds by dipping an RCC into a calibration solution. No pipetting, sequential droplet deposition, or advanced equipment is required. The performance and reproducibility of RCCs were evaluated with an electrospray ionization triple-quadrupole mass spectrometer equipped with a liquid microjunction-surface sampling probe (LMJ-SSP) that allows for fast sampling of surfaces. Using circular hydrophilic areas with diameters ranging from 0.25 to 2.00 mm, liquid volumes of 4.6-70.6 nL could be deposited. Furthermore, the use of a second hydrophobic/hydrophilic patterned transfer chip can be used to add internal standard solutions to each calibration spot of the RCC, allowing to transfer a liquid volume of 22.5 nL.

The liquid micro junction-surface sampling probe (LMJ-SSP); a versatile ambient mass spectrometry interface

Ambient ionization methods have become important tools in mass spectrometry. The LMJ-SSP can significantly simplify/reduce lengthy sample preparation requirements associated with mass spectrometry analysis. Samples may be introduced through direct contact, insertion and droplet injection, enabling applications from drug discovery and surface analysis to tissue profiling and metabolic mapping. This review examines the underlying principles associated with the LMJ-SSP interface and highlights modifications of the original design that have extended its capability. We summarize different application areas that have exploited the method and describe potential future directions for the adaptable ambient ionization source.

In situ mass spectrometry analysis of intact proteins and protein complexes from biological substrates

Advances in sample preparation, ion sources and mass spectrometer technology have enabled the detection and characterisation of intact proteins. The challenges associated include an appropriately soft ionisation event, efficient transmission and detection of the often delicate macromolecules. Ambient ion sources, in particular, offer a wealth of strategies for analysis of proteins from solution environments, and directly from biological substrates. The last two decades have seen rapid development in this area. Innovations include liquid extraction surface analysis, desorption electrospray ionisation and nanospray desorption electrospray ionisation. Similarly, developments in native mass spectrometry allow protein-protein and protein-ligand complexes to be ionised and analysed. Identification and characterisation of these large ions involves a suite of hyphenated mass spectrometry techniques, often including the coupling of ion mobility spectrometry and fragmentation techniques. The latter include collision, electron and photon-induced methods, each with their own characteristics and benefits for intact protein identification. In this review, recent developments for in situ protein analysis are explored, with a focus on ion sources and tandem mass spectrometry techniques used for identification.

Rapid untargeted screening for drug residues in animal tissues with liquid microjunction surface sampling probe mass spectrometry

An untargeted screening method for the rapid identification of veterinary drug residues in incurred animal tissues using liquid microjunction surface sampling probe mass spectrometry (LMJSSP-MS) was developed. Current analytical methods for veterinary drug residue screening involve lengthy sample preparation, extraction, and instrumental analysis steps. This method identifies veterinary drug residues in several different incurred animal tissues more quickly than conventional analytical methods. This LMJSSP-MS method uses an ambient ionization technology called liquid microjunction surface sampling probe along with a data dependent scan function of a quadrupole orbitrap mass spectrometer. Collected product ion spectra are searched against the mzCloud™ online mass spectral database to identify veterinary drug residues found in incurred animal tissue samples. Examples of veterinary drugs identified with this method include flunixin, tilmicosin, pentobarbital, xylazine, and ketamine. Optimization of method parameters is described and discussed. The limit of identification (LOI) of this method is estimated to be approximately 1 μg g^-1 for xylazine and ketamine.