Academic literature on the topic 'Pneumatically assisted desorption/ionization'

La spettrometria di massa è una delle tecniche più rilevanti in tossicologia clinica e forense. Il suo sviluppo e il miglioramento si basano sull'invenzione e l'uso di nuove sorgenti di ioni, nuovi metodi di ionizzazione, nuovi analizzatori di massa e nuove tecniche di pre-trattamento dei campioni. Una recente innovazione è la capacità di registrare spettri di massa su campioni reali direttamente nel loro ambiente nativo, senza preparazione del campione o pre-separazione. In questo ambito è stato descritto un nuovo metodo di ionizzazione/desorbimento chiamato DESI (desorbimento Electrospray ionizzazione), in seguito è stato sviluppato un metodo chiamato Dessì (Desorbimento Sonic Spray ionizzazione), a prima vista simile a DESI, ma in fondo sostanzialmente diverso. Questa tesi consiste nello sviluppo di una nuova interfaccia di desorbimento / ionizzazione per indagare il vero meccanismo coinvolto nella formazione di ioni, perché abbiamo ritenuto questo passaggio propedeutico per garantire il successivo uso del metodo in campo tossicologico analitico. Abbiamo verificato che il contributo pneumatico è preponderante per ottenere risultati. Quindi, la nostra nuova interfaccia di desorbimento/ionizzazione utilizza solo uno spray di solvente puro, senza alcuna tensione elettrica applicata allo sprayer. Un aspetto fondamentale di questo progetto, applicato a diverse matrici complesse, è il numero di parametri di funzionamento controllabili che possono essere studiati e ottimizzati per ottenere un'efficace analisi di superficie. Le variabili più importanti prese in considerazione sono state la geometria della sorgente (l'angolo di spray e l'angolo di diffusione di ioni, come pure le varie distanze nell'allineamento dello spray, del campione e dello spettrometro di massa) e la caratteristica dello spray (il contenuto del solvente ed il gas di portata). Tutte le misurazioni sono state eseguite in condizioni di ionizzazione positiva e negativa, variando tensione del capillare, pressione del gas di nebulizzazione, il flusso di gas al capillare e la temperatura del capillare. L'acquisizione è stata prodotta in modalità multiple mass spectra (MSn). Abbiamo applicato questa nuova soluzione tecnica per l'identificazione di composti tal quali, di principi attivi in campioni di farmaci mediante analisi diretta di compresse, principi attivi contenuti in specie vegetali. Gli sviluppi futuri saranno connessi ad applicare l’analisi diretta di analiti presenti sulle superfici originali di interesse nel settore tossicologico per il campionamento in vivo su superfici di tessuti, per individuare l’esposizione a farmaci e xenobiotici, oltre alla possibilità di costruire un’immagine chimica della distribuzione spaziale di analiti sulle superfici dei campioni.<br>Mass spectrometry is one of the most relevant techniques in clinical and forensic toxicology. Its development and improvement are based on the invention and utilization of new ion sources, new ionization methods, new mass analyzers and new sample pre-treatment techniques. A recent innovation is the ability to record mass spectra on ordinary samples in their native environment, without sample preparation or pre-separation. In this field, a new desorption ionization method called DESI (Desorption Electrospray Ionization) has been described; subsequently, method called DeSSI (Desorption Sonic Spray Ionization), at first sight similar to DESI, but in deep substantially different, has been developed. This thesis consist in developing a new desorption/ionization interface to investigate the real mechanism involved in ions formation because we considered that propaedeutic for the extensive use of the method in the toxicological analytical field. We verified that the pneumatic contribution is preponderant to the obtained results. Hence, our new desorption/ionization interface uses only a spray of pure solvent with no high voltage on needle. A key aspect of this project, applied to several complex matrix, is the number of controllable operating parameters that can be investigated and optimized to obtain an efficient surface analysis. The most important variables are taken in consideration were the source geometry (the spray angle and the ion uptake angle, as well as the various distances in aligning the spray, sample and mass spectrometer) and the characteristic of sprayer (contents of the solvent spray and gas flow rate). All measurements have been performed in positive and negative ionization conditions, varying capillary voltage, nebulizing gas pressure, drying gas flow and end plate temperature. Acquisition was in multiple mass spectrometry mode (MSn). 2 We have applied this new technical solution to compound identification, active principles and drugs identification in direct tablet analysis, active principles and drugs identification in vegetable species. Future developments will be related to apply the direct analysis of analytes present on the original surfaces of interest in the toxicological field for in vivo sampling of living tissue surfaces, to identify drug and xenobiotic exposure, besides the chemical imaging of spatial distribution of analytes onto sample surfaces.

Thesis (Ph. D.)--Southern Illinois University Carbondale, 2008.<br>"Department of Chemistry." Keywords: Enhanced MALDI, MALDI-MS, On-probe separation, Protein-surface interactions, Sublayers, Surface binding capacity. Includes bibliographical references (p. 130-148). Also available online.

Proteomics is an increasingly important area of biological research and has gathered much attention over recent years. Major challenges that make a proteomic analysis difficult are sample complexity, diversity and dynamic range. Progress in the area of proteomics relies heavily on new analytical tools for the sensitive, selective, and high-throughput studies of target analytes. It is estimated that there are several hundred thousand proteins in a human cell. In order to be able to analyze such a complex sample, an analytical method must be capable of separating and detecting many different sample peaks. The complexity of such samples indicates that a single separation method will not be able to provide the needed resolution. If two methods that are orthogonal are combined, then the peak capacity of the combined system is the product of the two individual peak capacities. Development of such systems would cater to the current demands of proteomics studies. Matrix assisted laser desorption/ionization (MALDI) mass spectrometry has evolved into a primary analytical tool for proteomics research. MALDI is fast and efficient and has a high tolerance to non-volatile buffers and impurities. The samples for MALDI are typically applied to solid supports after having been subjected to off-line liquid or gel separations. Several methods have been reported involving various chromatographic or electrophoretic separation methods. However, the current methods often require highly sophisticated sample handling systems, which are often expensive and in need of skilled human resources. The current demands of proteomic analyses require fast, efficient and inexpensive methods for separation to fully harness the capability of MALDI mass spectrometry. In this work a microfluidic device has been designed to perform dynamic isoelectric focusing (DIEF) based protein separation with digital sample deposition directly on a MALDI target for offline analysis. DIEF is related to capillary isoelectric focusing which and can facilitate the interface without the loss of the separation resolution. Compared to traditional capillary isoelectric focusing (cIEF) DIEF uses additional high-voltage power supplies to control the pH gradient by manipulating the electric field. The proteins can be focused at a desired sampling position according to their isoelectric point, to be collected for further analysis by MALDI mass spectrometry. DIEF has a peak capacity of over a thousand and offers an ease of interfacing to other techniques making it a preferred separation method for the interface with mass spectrometric techniques such as MALDI. The design of the microfluidic device is based on a digital droplet fractionation. Multiple fractions of the sample solution from DIEF are generated to retain the resolution and to act as an additional separation mode. The microfluidic device is controlled by actuating pneumatic valves built into the device. The DIEF operational parameters were optimized according to the surface functionality and the design of the microfluidic device. A suitable MALDI sample preparation method was found by studying different existing methods. The methods were studied using test proteins prepared in solutions having the additives used in the experiment. A simple mixture of three proteins was used to demonstrate the application of the developed method. The separation between the proteins insulin, hemoglobin and the myoglobin was demonstrated by varying the separation resolution in three experiments.