Keiji G. Asano

Coupling of an atmospheric-samling ion source with an ion-trap mass spectrometer☆

Abstract An atomospheric-sampling glow-discharge ionization source has been interfaced with an ion-trap mass spectrometer. Under optimum conditions, the efficiency of ion injection is 1–5%. Several factors have a significant effect on the ion injection efficiency, including the voltages on the three-element lens system situated between the ion-source exit and the ion-trap entrance end-cap, the pressure of the bath gas present in the ion-trap vacuum housing, the nature of the bath gas and the amplitude of the radiofrequency voltage applied to the ring electrode during ion injection. Collision-induced dissociation (and electron detachment from anions) is also observed for some ions on injection, depending on the conditions. The most important experimental variables in determining the extent to which dissociation (or electron detachment) occurs are the nature of the bath gas, the bath gas presure and the radiofrequency voltage applied to the ring electrode during injection. These effects are illustrated with data obtained for polyatomic anions injected from the golw-discharge ion source.

Electrochemical processes in a wire-in-a-capillary bulk-loaded, nano-electrospray emitter☆

Experiments are described that illustrate solvent oxidation, emitter electrode corrosion, and analyte oxidation in positive ion mode nano-electrospray mass spectrometry using a wire-in-a-capillary, bulk-loaded nano-electrospray emitter geometry. Time-lapsed color photography of pH and metal specific indicator solutions within operating nano-electrospray emitters, as well as temporal changes in the ions observed in the nano-electrospray mass spectra, are used to probe these reactions, judge their magnitude, and study the time dependent changes in solution composition and gas-phase ion signal brought about as a result of these electrochemical reactions. The significance of these observations for analytical applications of nano-electrospray mass spectrometry are discussed.

Chemical composition of fingerprints for gender determination.

This work investigates the chemical nature of fingerprints to ascertain whether differences in chemical composition or the existence of chemical markers can be used to determine personal traits, such as age, gender, and personal habits. This type of information could be useful for reducing the pool of potential suspects in criminal investigations when latent fingerprints are unsuitable for comparison by traditional methods. Fingertip residue that has been deposited onto a bead was extracted with a solvent such as chloroform. Samples were analyzed by gas chromatography/mass spectrometry (GC/MS). The chemical components identified include fatty acids, long chain fatty acid esters, cholesterol and squalene. The area ratios of ten selected components relative to squalene were calculated for a small preliminary experiment that showed a slight gender difference for three of these components. However, when the experiment was repeated with a larger, statistically designed experiment no significant differences between genders were detected for any of the component ratios. The multivariate Hotellings T2 test that tested all ten-component ratios simultaneously also showed no gender differences at the 5% significance level.

High explosives vapor detection by glow discharge ion trap mass spectrometry

The combination of atmospheric sampling glow discharge ionization with quadrupole ion trap mass spectrometry for the detection of traces of high explosives is described. Atmospheric sampling glow discharge provides a simple, rugged, and efficient means for anion formation while the quadrupole ion trap provides for efficient tandem mass spectrometry. Mass-selective ion accumulation and non-specific ion activation methods can be used to overcome deleterious effects arising from ion/ion interactions. Such interactions constitute the major potential technical barrier to the use of the ion trap for real-time monitoring of targeted compounds in uncontrolled and highly variable matrices. Tailored waveforms can be used to effect both mass-selective ion accumulation and ion activation. Concatenated tailored waveforms allow for both functions in a single experiment, thereby providing the capability for monitoring several targeted species simultaneously.

Laser desorption mass spectrometry and MS/MS with a three-dimensional quadrupole ion trap

Abstract An ion trap mass spectrometer (ITMS) has been modified to enable laser desorption mass spectrometry to be performed. The effects of the ion trap r.f. amplitude and helium bath gas pressure during desorption, along with the time delay between the laser pulse and the acquisition of the mass spectrum have been investigated. The ability to perform multiple stages of mass spectrometry (MS/MS) on laser-desorbed ions is also demonstrated.

Thermal dissociation in the quadrupole ion trap: ions derived from leucine enkephalin

Abstract Rates of dissociation of protonated leucine enkephalin and the b 4 + fragment ion derived from protonated leucine enkephalin have been measured as a function of helium bath gas temperature in a quadrupole ion trap. Dissociation rates were observed to be insensitive to the amplitude of the trapping voltage over the range of values studied. This observation, along with theoretical arguments based on predicted levels of “rf heating,” indicates that any internal excitation of the ions due to ion trap storage is minimal. The bath gas temperature can therefore be used to characterize the internal temperatures of the ions. This approximation is expected to be most valid for high mass ions and low mass bath gases, such as helium. Activation parameters were obtained from Arrhenius plots of the rate data, and master equation modeling of the activation, deactivation, and dissociation processes was performed to provide an indication as to how closely these ions approached high-pressure limit behavior. Protonated leucine enkephalin more closely approached the high-pressure limit than the b 4 + ion due to its larger size and the fact that the activation parameters were derived from somewhat lower dissociation rates. These studies suggest that the quadrupole ion trap operated in the presence of a light, heated bath gas can be used to obtain Arrhenius activation parameters from the dissociation kinetics of relatively high mass ions.

Ion internal temperature and ion trap collisional activation: protonated leucine enkephalin

Abstract Protonated leucine enkephalin has been used as a prototypical high-mass ion to yield a quantitative estimate of the relationship between the amplitude of the resonance excitation voltage used in an ion trap collisional activation experiment, and the internal temperature to which an ion can be elevated over the bath gas temperature. The approach involves the measurement of the ion dissociation rate as a function of resonance excitation voltage, and the correlation of dissociation rate with ion internal temperature. The relatively high ion trap dissociation rates observed under typical resonance excitation conditions preclude the direct application of the Arrhenius equation to derive internal temperatures. An empirical determination of the relationship between ion internal temperature and dissociation rate over the rate range of interest here was made via the systematic variation of bath gas temperature. The data suggest a very nearly linear relationship between ion internal temperature and resonance excitation voltage, at least under conditions in which ion ejection is minimal. It is shown that protonated leucine enkephalin ions can be elevated by about 357 K over the bath gas temperature using a monopolar resonance excitation voltage of 540 mV p − p(qz = 0.163) without significant ion ejection. It is also demonstrated that ion internal temperature can be readily increased by increasing the bath gas temperature, by accelerating the ions in the presence of a room temperature bath gas (i.e. conventional ion trap collisional activation), or by a combination of the two approaches.

Bath gas temperature and the appearance of ion trap tandem mass spectra of high-mass ions

Abstract Bath gas temperature effects upon the appearance of ion trap tandem mass spectra of protonated leucine enkephalin have been studied under a variety of ion activation conditions and over a bath gas temperature range of 298–486 K. Bath gas temperature was found to have two possible effects upon the identities and abundances of product ions observed in tandem mass spectra. At high parent ion dissociation rates (>10 s−1) and short activation times ( 10 s−1), relatively long ion activation times (

Protonated water and protonated methanol cluster decompositions in a quadrupole ion trap

Abstract Electrospray mass spectra of water and methanol have been studied with a quadrupole ion trap operated with background gas pressures of 2 × 10 −5 −2 × 10 −3 Torr. In each case, the most abundant ions observed consist of protonated clusters of varying size, e.g. (H 2 O) n H + in which n ranges up into the twenties. For clusters of n > 6 or so, rapid desolvation is observed. For intermediate values of n , the desolvation rate constants can be readily measured in the typical time frame of a quadrupole ion trap experiment. The internal temperature of the cluster ions can be estimated from the known thermochemical parameters and the measured decomposition rate constants. In all cases, the temperature exceeds that of the bath gas but is significantly less than 1000 K. It is also noted that the ion temperature is inversely proportional to the logarithm of the bath gas pressure.

Effective ion internal temperatures achieved via boundary activation in the quadrupole ion trap: protonated leucine enkephalin

The dissociation rate of protonated leucine enkephalin in a quadrupole ion trap was measured as a function of the proximity to which the ions are brought to a stability boundary. A bath gas temperature of 480 K was used so that a dissociation rate could be readily measured even when the parent ions were remote from a stability boundary. Changes in the dissociation rate as a function of d.c. potential applied to the ring electrode of the ion trap, used to bring ions close to a stability boundary, could then be attributed to the ‘boundary activation’ process. A relationship between dissociation rate and parent ion effective internal temperature, derived from a study involving conventional ion trap resonance excitation, was used to estimate effective ion internal temperatures achieved under the boundary activation conditions used here. Effective ion internal temperatures 170 K above the bath gas temperature could readily be achieved using boundary activation. However, the efficiency of the overall boundary activation experiment was compromised by an initial rapid parent ion loss that occurred upon application of the d.c. potential. After correction for this initial ion loss, dissociation rates and relatively low ion ejection rates could be measured. Effective ion internal temperatures achieved with boundary activation are similar to those observed previously using conventional resonance excitation. However, the generally poorer efficiencies associated with boundary activation that are observed with resonance excitation at high dissociation rates suggests that higher ion internal temperatures can be achieved with conventional resonance excitation. Copyright