The ability to identify and confirm a compound using mass spectrometry usually involves time consuming sample preparation and method development. The open-air ion source DART (Direct Analysis in Real Time) can ionize compounds in the gas, solid, or liquid phase without chromatography or sample preparation due to the interactions of helium metastable atoms with gas molecules commonly found in air. The coupling of the DART to a time-of-flight (TOF) mass spectrometer allows the rapid determination of an analyte's elemental composition based on accurate mass measurement and isotope peak intensities. Mass spectrometric fragmentation data can aid in the structural identification of an analyte as compounds produce characteristic fragment-ions based on their structure. The TOP's ability to produce fragmentation spectra was compared to the more traditional tandem mass spectral method (MS/MS) considering the TOF lacks the ability to select pre-cursor ions. The TOF produced in-source CAD (collisionally activated dissociation) spectra comparable to MS/MS spectra for three well known pharmaceuticals acetaminophen, phenylbutazone and clenbuterol. Further structural confirmation was explored through a determination of the number of active hydrogen atoms in an analyte molecule achieved by hydrogen/deuterium (H/D) exchange by treatment with deuterium oxide (D20) in the DART sample gap. Mass spectra acquired in the presence of D20 of analytes containing active hydrogen atoms associated with hydroxyl, amino and carboxylic acid groups showed that H/D exchange was predictable and reproducible. Using accurate mass measurement and isotope peak intensities, the elemental composition of an unknown captured on filter paper was identified as dipropylene glycol (DPG) analyzed directly from the surface of the filter paper. Data from in-source CAD and H/D exchange of both the unknown and authentic standards confirmed that the unknown was DPG. The cross-correlation of accurate mass measurement and isotope peak intensities, in-source CAD and HID exchange data provided an unambiguous identification of the contaminant melamine in dog food without the need for any sample preparation. Once analytes are identified and confirmed, quantitation of the analyte is desirable. The calibration curves here are constructed using the net extracted ion-current associated with the analyte relative to the internal standard. In cough syrup, a complicated matrix, the linearity, R2, is shown to be 0.992.

No description available.

No description available.

No description available.

An optimized method of extraction, an instrumental analysis method and data analysis was proposed for black writing inks based on direct infusion electrospray-mass spectrometry (ESI-MS). The sampling and analysis method is both minimally destructive and able to assess differences in inks from a reference collection of thirty ballpoint, gel, and rollerball inks. The methanol extracts of ink on paper samples were analyzed with three direct infusion (ESI-MS) methods. Each method varied scan voltage negative and positive, ESI fragmentor applied voltage (+120V, +0V, and -120V), and mobile phase additive. Direct infusion ESI-MS analysis, followed by pair-wise comparisons of the observed ion data in binary form allowed inks to be distinguished from each other. The photobleaching of the dye Basic Violet 3 (BV3) in ink-onpaper samples was examined to determine the use of degradation products as a marker of the age of the writing sample. The extent of photobleaching of BV3 was determined using several illumination sources. Pair-wise comparison of observed ion data was able to distinguish 29 of 30 ink samples using the combined three instrumental methods. Out of 435 pair-wise comparisons 429 pairs could be discriminated from each other using the combined three methods. This is a 98.6% discrimination with the combined analysis scheme

The design, synthesis and evaluation of chiral selectors that allow the determination of enantiomeric composition using electrospray ionization mass spectrometry are detailed herein. The enantiomers of the chiral selector were mass labeled at a distant site from the chiral recognition sites of the molecules. The mass-labeled enantiomers were mixed in a one-to-one ratio to form a quasi-racemate. Chiral recognition can be observed by comparing relative abundances of the pseudo-diastereomeric selector-analyte complexes in the mass spectrum. The observed sense of chiral recognition with mass spectrometry was consistent with that observed chromatographically using a corresponding chiral stationary phase in every case. The complex intensity fraction (CIF, intensity of one selector-analyte complex divided by the sum of the intensities for both selector-analyte complexes) is linear with the enantiomeric composition. The slope of this line is an indication of the extent of the enantioselectivity: the larger the slope, the more significant the enantioselectivity. In addition, this line can be used as a calibration curve for the quantitative determination of enantiomeric composition of the same analyte with unkown enantiomeric composition. Amide derivatives of DNB-amino acids were first used as pseudo-enantiomeric chiral selectors in the presence of added lithium chloride. The enantioselectivity values were smaller than those observed on chiral HPLC using the corresponding chiral stationary phase. The use of deprotonated DNB-amino acids as chiral selectors provides higher enantioselectivities, but with low ion abundances. Tertiary amine appended analogues of the chiral stationary phase DNB-Leucine were prepared. The amine was appended to provide a site for ready ionization (through protonation). The performance of chiral selectors of this type was compared to the original chiral selectors that lack this functional group. Chiral recognition was also observed in a reciprocal sense using proline-derived pseudo-enantiomeric chiral selectors and analytes similar to DNB-amino acid esters or amides. Optimization of the electrospray ionization conditions provided similar enantioselectivities to those from chiral HPLC. Libraries of tertiary amine appended derivatives of DNB-dipeptides, which were prepared through combinatorial peptide synthesis, were screened using electrospray ionization mass spectrometry. The use of electrospray ionization mass spectrometry as a discovery tool for new chiral selectors is discussed.

No description available.

No description available.

This dissertation elucidates a greater understanding of the vaporization and electrospray post-ionization mechanisms when using femtosecond laser pulses for desorption of surface molecules and electrospray ionization for capture and mass analysis of the gas phase ions. The internal energy deposition from nonresonant vaporization with femtosecond laser pulses was measured using dried and liquid samples of p-substituted benzylpyridinium ions and peptides. In the comparison of the experiments of using 800 nm and 1042 nm laser pulses, it was found that there are different vaporization mechanisms for dried and liquid samples. It was established that LEMS is a "soft" mass analysis technique as it resulted in comparable internal energy distributions to ESI-MS with one caveat; multiphoton excitation of dried samples results in extensive fragmentation at higher pulse energies. The quantitative aspects of the laser electrospray mass spectrometry (LEMS) technique were established using various multicomponent mixtures of small biomolecules. Experiments with LEMS resulted in similar quantitative characteristics to ESI-MS except that ESI-MS demonstrated a greater degree of ion suppression when using higher concentrations, particularly in the four-component mixture. The lack of ion suppression in the LEMS measurements was due to the ~1% neutral capture efficiency and most likely not a result of nonequilibrium partitioning. This was supported by the excess charge limit not being surpassed in the LEMS experiments and the quantitative analysis requiring the use of response factors. This dissertation also expanded upon the use of multivariate analysis for the classification of samples that were directly mass analyzed without any sample preparation using LEMS. A novel electrospray complexation mixture using cationic pairing agents, a lipid, and sodium acetate enabled the simultaneous detection of positive, neutral and negative charged features of inorganic-based explosive residues in a single experiment. This complexation mixture also enabled the detection of new features from an RDX-based propellant mixture. Principal component analysis (PCA) proved reliable for accurate classifications of the explosive mixtures. PCA was also used for accurate classification of eight phenotypes of Impatiens plant flower petals after mass analysis with LEMS. The PCA loading values were used to identify the key biomarkers in the classification. These important mass spectral features were identified as the biologically-relevant anthocyanins, which are phytochemicals that are responsible for the color of the flower petals. / Chemistry

<p dir="ltr">While electrospray ionization facilitates the mass determination of smaller analytes, ESI of macromolecular native protein complexes is complicated by narrow charge state distributions and overlapping charge states, hindering mass analysis. This problem is further exacerbated with heterogeneous protein mixtures that yield ions of similar <i>m/z</i> values. Charge-reduction of a selected precursor population via ion/ion reaction provides further <i>m/z</i> separation and utilizes an extended mass range, allowing for mass determination. All experiments were performed on a TripleTOF 5600 quadrupole TOF mass spectrometer (SCIEX), modified for ion/ion reactions. Alternatively pulsed nano-electrospray ionization allowed for sequential injection of reagent and analyte ions. Selected cations were reacted with different anions, and charge-reduced product ions were mass analyzed on a TOF with modifications and tuning for an extended <i>m/z</i> range of 200,000+. Charge reduction via proton transfer reaction (PTR) involves a perfluorinated anion reacting with a multiply charged cation and results in the loss of one proton removal at a time. Through multiple iterations of PTR, the overlapping charge states of protein ions (from an unstained protein standard mixture consisting of 12 recombinant proteins of masses10kDa-200kDa) within the <i>m/z</i> 6500-8500 and <i>m/z</i> 4000-5000 ranges, generated under native conditions by ESI, transforms to a product spectrum with single-digit charge states, thereby deconvoluting the precursor “blob”.</p>