Brian Goolsby

Identification of tetracycline antibiotics by electrospray ionization in a quadrupole ion trap

Tetracycline antibiotics, tetracycline, chlortetracycline, demeclocycline, doxycycline, minocycline, methacycline, oxytetracycline, and anhydrotetracycline, are examined by electrospray ionization in a quadrupole ion trap. Studies were undertaken to evaluate the use of metal complexation as an alternative to conventional proton attachment. A variety of metal cationization processes, including attachment of Na+, Mg2+, Ca2+, Co2+, Ni2+, and Cu2+ were probed. Infrared multiphoton photodissociation and collisionally activated dissociation (CAD) were compared for generation of diagnostic fragmentation patterns of protonated and metal cationized tetracyclines. The photodissociation spectra provide a more informative signature, including more low mass ions that are not observed upon CAD. The metal complexes dissociate by pathways that are similar to those observed for the protonated molecules.

Determination of alkali metal ion binding selectivities of calixarenes by matrix-assisted laser desorption ionization and electrospray ionization in a quadrupole ion trap

Abstract Matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) and electrospray ionization mass spectrometry (ESI-MS) are used to evaluate the alkali metal ion binding selectivities of a series of calixarenes. Each calixarene of interest is mixed with one or more alkali metal salts (1:100 ratio of calixarene to metal), either in the ESI solution or on the MALDI probe surface, and the relative binding selectivities are directly determined from the intensities of the calixarene/metal complexes in the mass spectra. For t -butylcalix[4]arene-tetraacetic acid tetraethyl ester (calixarene 1 ), complexation of Na + is favored over complexation of K + , in agreement with prior solution results obtained by conventional methods. For the three calixarenes that do not have t -butyl groups on the upper rims, the calixarenes preferentially bind K + over Na + , thus demonstrating that size selective complexation can be probed with both the ESI and MALDI methods. Collision-activated dissociation results indicate that the phenyl oxygens, but not necessarily the ethoxy ethyl oxygens of the lower rims, are the primary binding sites for the alkali metal ions.

Analysis of protonated and alkali metal cationized aminoglycoside antibiotics by collision-activated dissociation and infrared multi-photon dissociation in the quadrupole ion trap

Nine aminoglycoside antibiotics were analyzed in two quadrupole ion trap mass spectrometers using electrospray ionization. Structural information was obtained via collision-activated dissociation (CAD) and infrared multi-photon dissociation (IRMPD) of the protonated species. Several of the compounds, having multiple basic sites, preferred the doubly protonated form while some existed in the singly charged state or were distributed between single and doubly protonated species, allowing comparison of the fragmentation patterns of the two charge states. In general, IRMPD is as efficient as CAD, produces more low-mass fragment ions, and is more universally applied owing to its low dependence on trapping, pressure and tuning conditions. Alkali metal complexation using Li(+) and Na(+) was probed as a means of producing different fragmentation patterns, but in most cases the resulting fragmentation patterns were simplified versions of those obtained for the protonated analogs.

Characterization of β-lactams by photodissociation and collision-activated dissociation in a quadrupole ion trap

Electrospray ionization was used to introduce β-lactams, including cephalosporin and penicillin analogs, into a quadrupole ion trap for analysis by collision-activated dissociation (CAD) and infrared multiphoton dissociation (IRMPD). The two dissociation methods provided similar spectra; however, photodissociation requires substantially less tuning than is typically required to optimize CAD. Moreover, IRMPD was effective even at the elevated pressures introduced by the electrospray source. Both CAD and IRMPD promote cleavage across the β-lactam ring, resulting in highly diagnostic fragmentation patterns. Time-resolved and SWIFT methods were used to determine fragmentation genealogies of the ions created by IRMPD.

Solvent displacement in transition metal complexes

Abstract Ligand exchange reactions of transition metal ions solvated by two acetone or two acetonitrile molecules with multidentate polyethers or pyridyl ligands are undertaken in a quadrupole ion trap mass spectrometer. The ability of the polyether or pyridyl ligand to displace one or both solvent molecules is correlated with the number of binding atoms in the multidentate ligand, the flexibility of the ligand along with its ability to fully coordinate or encapsulate the metal ion, and the strength of the solvent/metal bonds. The smaller polyethers displace one solvent molecule, thus generating stable (M + + polyether + solvent) complexes. The larger polyethers rapidly displace both solvent molecules, leading to formation of stable (M + + polyether) complexes, because of the ability of the large polyethers to encapsulate or fully coordinate the metal ion. The pyridyl ligands tend to favor formation of (M + + pyridyl ligand + solvent) mixed-ligand complexes, regardless of the number of nitrogen atoms or flexibility of the pyridyl ligand. The pyridyl ligands are unable to fully encapsulate the metal ion, so one solvent molecule may remain bound to the metal ion.

Characterization of a hybrid ion trap

A new ion trap is constructed of a cylindrical ring electrode and hyperbolic end caps. The premise is to determine the effect ring electrode geometry has on the operation of the ion trap. A model for the potential and electric field within the trap is developed. The model is used to show how adjusting the geometric parameters of the cell could be used to reduce the presence of higher order fields or optimize other desired properties. The stability diagram is mapped experimentally and using the standard definition forqz, the qeject was determined to be 0.76. A proposed modification for the definition ofqz, which adjusts for the shape of the cylindrical ring electrode, results in a qeject of 0.93. The trap is shown to have a linear scanning relationship, resolved isolation and unit mass resolution. (Int J Mass Spectrom 190/191 (1999) 47‐57)

The Evaluation of Hexafluorobenzene as an Environmentally Benign Dielectric Etch Chemistry

Hexafluorobenzene was evaluated as an alternative chemistry for dielectric etch applications in a high density plasma etch chamber with reduced global warming emissions. Processes based on hexafluorobenzene exhibited global warming emissions reductions as high as 97% compared to a C 3 F 8 -based process, which is the greatest reductions level of any alternative chemistry examined to date on this tool. Using hexafluorobenzene, it is possible to operate in a regime of high etch rate and high polymerization. There are several issues, however, that need to be addressed if this chemistry is to be used for high performance dielectric etching. This material is a liquid at room temperature, which makes it difficult to deliver process gas to the chamber. In addition, this chemistry is highly polymerizing, resulting in excess polymer deposition on chamber walls leading to significant process variability for standard chamber clean times Significantly longer chamber clean times were required between each etch to remove the excess polymer.

Solid-Phase Extraction in Conjunction with Matrix-Assisted Laser Desorption Ionization/Quadrupole Ion Trap Mass Spectrometry for the Determination of Benzoylecgonine in Urine

A matrix-assisted laser desorption ionization/quadrupole ion trap/mass spectrometer (MALDI-QIT-MS) system is evaluated for the rapid analysis of benzoylecgonine, a cocaine metabolite, from human urine after solid-phase extraction (SPE). Collisionally activated dissociation (CAD) is utilized to provide unambiguous confirmation of benzyolecgonine. In addition, MALDI-QIT-MS is shown to be a viable, rapid quantitative method of analysis for benzoylecgonine with the inclusion of a deuterated benzoylecgonine internal standard. Linearity was established from 1 to 10 μg/mL of benzoylecgonine in urine. A clinical urine sample known positive for benzoylecgonine was analyzed by MALDI-QIT-MS. The results indicate a mean concentration of 6.2 μg/mL [7.4% relative standard deviation (RSD), n = 3] of benzoylecgonine by the MALDI method, which is in good agreement with the result of 7.1 μg/mL (7.0% RSD, n = 3) obtained by a standard gas chromatography (GC)-MS procedure. Therefore, the MALDI method is demonstrated to be a rapid method for the quantitation of benzoylecgonine without post-SPE derivatization and chromatographic separation. Finally, the MALDI method is briefly extended to another class of analyte, methadone, and [(±)-2-ethyl-1,5-dimethyl-3,3-diphenyl-pyrrolinium] (EDDP), a methadone metabolite, to demonstrate that the technique holds potential for a wide range of analytes.

Reduction of semiconductor process emissions by reactive gas optimization

Tailoring the chemical environment in plasmas by addition of reactive gases to affect byproduct formation has been demonstrated to reduce perfluorocompound (PFC) emissions. Perfluorocompound emissions from dielectric etch processes are reduced by oxygen addition, which reduces polymerization and increases etch rates, primarily by affecting the fluorine or carbon in the plasma, and secondarily, by affecting resist erosion. Oxygen or water vapor introduced upstream of plasma abatement devices reduces PFC reformation by preferentially combining with carbon and fluorine-containing radicals to form thermodynamically favorable byproducts that are non- or low-global warming. Introducing oxygen to low-k chemical vapor deposition (CVD) chamber clean processes also reduces PFC emissions, primarily by reducing CF/sub 4/ by forming thermodynamically stable CO and CO/sub 2/. Analogously, adjusting the fuel or the oxidizer flow in fuel-fired abatement devices provides a higher flame temperature where thermal cracking of higher molecular weight low-k CVD organosilicon precursors can more readily occur, allowing the carbon-rich precursors to more completely oxidize.