Ambient ionization mass spectrometry: A tutorial

Direct bioanalytical sample injection with 2D LC–MS

New analytical platforms have been developed in response to the need for attaining increased peak capacity for multicomponent complex analysis with higher sensitivity and characterization of the analytes, and high-throughput capabilities. This review outlines the fundamental principles of target and comprehensive 2D LC method development and encompasses applications of LC–LC and LC × LC coupled to MS in bioanalysis using a variety of online analytical procedures. It also provides a rationale for the usage of the most employed mass analyzers and ionization sources on these platforms.

Analysis of renal cell carcinoma as a first step for developing mass spectrometry-based diagnostics

Immediate diagnosis of human specimen is an essential prerequisites in medical routines. This study aimed to establish a novel cancer diagnostics system based on probe electrospray ionization-mass spectrometry (PESI-MS) combined with statistical data processing. PESI-MS uses a very fine acupuncture needle as a probe for sampling as well as for ionization. To demonstrate the applicability of PESI-MS for cancer diagnosis, we analyzed nine cases of clear cell renal cell carcinoma (ccRCC) by PESI-MS and processed the data by principal components analysis (PCA). Our system successfully delineated the differences in lipid composition between non-cancerous and cancerous regions. In this case, triacylglycerol (TAG) was reproducibly detected in the cancerous tissue of nine different individuals, the result being consistent with well-known profiles of ccRCC. Moreover, this system enabled us to detect the boundaries of cancerous regions based on the expression of TAG. These results strongly suggest that PESI-MS will be applicable to cancer diagnosis, especially when the number of data is augmented.

Recent advances in bioanalytical sample preparation for LC-MS analysis

Sample preparation has historically been, and continues to be, the most challenging part of the bioanalytical workflow. Several techniques have been developed over the years to deal with the problems of recovery and matrix effects in an effort to increase the reliability and robustness of the bioanalytical method. In recent years certain techniques have come into prominence and gained acceptance in routine sample preparation, and some have shown promise in their use in a discovery environment where speed is critical and method development time is often limited. The aim of this review is to examine several of these techniques and provide examples of their use from the literature, as well as comment on their utility in current workflows.

Building blocks for the development of an interface for high-throughput thin layer chromatography/ambient mass spectrometric analysis: a green methodology

Interfacing thin layer chromatography (TLC) with ambient mass spectrometry (AMS) has been an important area of analytical chemistry because of its capability to rapidly separate and characterize the chemical compounds. In this study, we have developed a high-throughput TLC-AMS system using building blocks to deal, deliver, and collect the TLC plate through an electrospray-assisted laser desorption ionization (ELDI) source. This is the first demonstration of the use of building blocks to construct and test the TLC-MS interfacing system. With the advantages of being readily available, cheap, reusable, and extremely easy to modify without consuming any material or reagent, the use of building blocks to develop the TLC-AMS interface is undoubtedly a green methodology. The TLC plate delivery system consists of a storage box, plate dealing component, conveyer, light sensor, and plate collecting box. During a TLC-AMS analysis, the TLC plate was sent to the conveyer from a stack of TLC plates placed in the storage box. As the TLC plate passed through the ELDI source, the chemical compounds separated on the plate would be desorbed by laser desorption and subsequently postionized by electrospray ionization. The samples, including a mixture of synthetic dyes and extracts of pharmaceutical drugs, were analyzed to demonstrate the capability of this TLC-ELDI/MS system for high-throughput analysis.

Improved spatial resolution in the imaging of biological tissue using desorption electrospray ionization

Desorption electrospray ionization imaging allows biomarker discovery and disease diagnosis through chemical characterization of biological samples in their native environment. Optimization of experimental parameters including emitter capillary size, solvent composition, solvent flow rate, mass spectrometry scan-rate and step-size is shown here to improve the resolution available in the study of biological tissue from 180 μm to about 35 μm using an unmodified commercial mass spectrometer. Mouse brain tissue was used to optimize and measure resolution based on known morphological features and their known relationships to major phospholipid components. Features of approximately 35 μm were resolved and correlations drawn between features in grey matter (principally PS (18:0/22:6), m/z 834) and in white matter (principally ST (24:1), m/z 888). The improved spatial resolution allowed characterization of the temporal changes in lipid profiles occurring within mouse ovaries during the ovulatory cycle. An increase in the production of phosphatidylinositol (PI 38:4) m/z 885 and associated fatty acids such as arachidonic acid (FA 20:4) m/z 303 and adrenic acid (FA 22:4) m/z 331was seen with the postovulatory formation of the corpus luteum.

Identification of isobaric amino-sulfonamides without prior separation

RATIONALE

Direct analysis mass spectrometry (DAMS) techniques offer increased speed of analysis without the need for sample preparation or prior separation. A feature of these techniques is that all ionisable species will typically be analysed at the same time which makes the ability to distinguish between isobaric compounds increasingly important.

METHODS

Investigations have been carried out to distinguish isomeric compounds by mass spectrometry only, without the use of any separation technique, in order to further understand the capabilities of DAMS techniques. The work focused on commercially available isomeric amino-sulfonamides, i.e. sulfalene, sulfameter, sulfamethoxypyridazine, sulfamonomethoxine, sulfadoxine, sulfadimethoxine, sulfisomidine, sulfamethazine, sulfamerazine, sulfaperine, sulfadiazine and sulfapyrazine.

RESULTS

All the isomeric compounds investigated could be distinguished from each other based on their tandem mass (MS/MS) spectrum or failing that, based on their MS(3) spectrum. Common fragmentation patterns/pathways were observed for groups of the sulfonamides and a rationale for the fragmentations observed is proposed. For the sulfonamides which contain a methoxy group on the pyrimidinyl, pyridazynil, or pyrazinyl ring, the fragmentation-directing feature is the positioning of the methoxy group in the ortho position of the ring with respect to the sulfonamide bond. The presence of an ortho substituent precludes the formation of the product ion resulting from the loss of aniline.

CONCLUSIONS

This work has demonstrated the usefulness of MS(n) fragmentation data in identifying and distinguishing isobaric structural isomers without the need for separation by high-performance liquid chromatography (HPLC), allowing the identification of compounds by DAMS techniques. This work has also highlighted patterns in the product ion data which has led to a postulation of how the protonation preference of a molecule can affect the product ions observed and how the presence of ortho substituents can affect this initial protonation preference.