A pulsed ion deflection system for background reduction in 252Cf-plasma desorption mass spectrometry

Analytical chemists faced with complex problems such as food or drug analysis, chemical dump site analysis, or incorporation of xenobiotics and natural toxins into the food chain, require increasingly sophisticated analytical tools. Recent developments in mass spectrometry may be applied to some of these analytical problems. Negative chemical ionization mass spectrometry and to a lesser extent tandem mass spectrometry have passed the stage of expensive curiosities and are now vital screening tools. Negative chemical ionization is a powerful new method for the analysis of complex environmental samples for trace levels of both oxidizing and alkylating agents. Since these compounds comprise a large number of substances known to cause cancer or other environmental health problems, it seems likely that use of NCIMS will continue to grow. Tandem mass spectrometry has several advantages for the analysis of specific organic compounds in complex mixtures. Target compounds can be isolated and identified almost instantaneously at detection limits comparable and identified almost instantaneously at detection limits comparable to GC-MS with minimum sample preparation. A major deterrent to MS/MS is price ($400,000 or more). Also, the operator must know something about the sample and what to look for. Complete characterization of a sample by MS/MS is impractical. In the past, application of mass spectrometry to the determination of molecular weight and structure of polar (or thermally labile) compounds was severely limited. The limitations are due to inability to vaporize samples or to prevent thermal decomposition. The development of desorption chemical ionization, fast atom bombardment, secondary ionization mass spectrometry, and 252Cf plasma desorption mass spectrometry was in an attempt to rectify this situation. Each of the ionization techniques has advantages and limitations. With continued research into actual ionization/desorption process and continued instrumentation development (perhaps with a lower price tag), many of these techniques will become commonplace.

252Cf plasma desorption mass spectrometry in combination with protease treatment for localizing a non-linear zinc binding domain in human interleukin-3

Chromatographic characterization of HSV-1 gD 268–284 and IL-6 179–185 synthetic oligopeptides by reversed-phase high-performance liquid chromatography, automated Edman degradation and mass spectrometric analysis

A 252Cf plasma desorption mass spectrometer has been set up to analyse thin layers of non‐volatile organic samples. Molecular and fragment ions were produced and their mass was determined by a time‐of‐flight measurement. A novel interface combines a high‐performance liquid chromatograph with the 252Cf plasma desorption mass spectrometer in a twofold way: introducing the effluent continuously through a capillary inlet in the on‐line liquid chromatography mass spectrometry mode or transferring already prepared samples through a vacuum lock into the mass spectrometer in the off‐line liquid chromatography+mass spectrometry mode. The off‐line mode has been applied for the quantitative analysis of pharmaceuticals in blood using stable isotope labelled standards.

Chemischer InformationsdienstVolume 17, Issue 34 Physical Organic Chemistry ChemInform Abstract: The Use of a Stationary Cationic Surfactant as a Selective Matrix in 252Cf-Plasma Desorption Mass Spectrometry C. J. MCNEAL, C. J. MCNEALSearch for more papers by this authorR. D. MACFARLANE, R. D. MACFARLANESearch for more papers by this author C. J. MCNEAL, C. J. MCNEALSearch for more papers by this authorR. D. MACFARLANE, R. D. MACFARLANESearch for more papers by this author First published: August 26, 1986 https://doi.org/10.1002/chin.198634057Citations: 1AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume17, Issue34August 26, 1986 RelatedInformation

Comparative studies of natural and recombinant proteins by californium-252 plasma desorption and cesium ion liquid secondary ion mass spectrometry

The fragmentation of underivatized and peracetylated maltooligosaccharides, ranging in length from four to seven glucose residues, has been investigated by 252Cf plasma desorption mass spectrometry (PDMS). Investigations are made of the effects on the mass spectra of (1) peracetylation, (2) sample preparation by electrospray deposition onto metallic substrates versus adsorption onto nitrocellulose films, and (3) sodium addition to or elimination from the sample. Peracetylation enhances the mass spectrometric response of the oligosaccharides and also enables the efficient removal from the sample of water-soluble components such as sodium salts. A rapid and simple method has been developed for controlling the amount and type of fragmentation of peracetylated maltooligosaccharides. The method involves control of the amount of sodium in the sample introduced into the mass spectrometer. When a large molar excess of sodium is added to the sample, in the form of sodium chloride, the positive-ion mass spectrum is dominated by a peak corresponding to the sodium-cationized molecule. On the other hand, when the sample is completely depleted of sodium, the spectrum shows no quasimolecular ions [(M + Na)+ or (M + H)+] whatsoever and is instead totally dominated by fragment ion species. Thus, it proves feasible to alternate between a spectrum dominated by the (M + Na)+ ion peak and one dominated by fragment ions. This method has also been found to be useful in controlling the fragmentation of permethylated gangliosides.

Medium energy (100–300 keV) time-of-flight spectrometry for surface analysis uses the correlated detection of an energetic ion and the secondary electrons emitted as it passes through a carbon foil. When microchannel plates are employed in this detection scheme, a typical mean efficiency of detection of less than 30% is achieved. When instead a surface barrier detector is used to detect the ion, providing simultaneous acquisition of velocity and energy information, certain advantages are realized over the two microchannel plate configuration in the characterization of low level constituents of surfaces. Specifically, energy-discriminated gating of the start pulse was observed to nearly eliminate count rate dependent background in a time-of-flight spectrum. Further reduction in background was obtained by the selective elimination of forward recoil species or backscatters from the substrate. Replacement of the stop microchannel plate by a surface barrier detector has resulted in improved detection efficiency for He, as well as provided a means for further study of the processes which affect time-of-flight spectrometer response, including multiple scattering and secondary electron emission in the start foil. In this publication, we describe the application of this particle telescope to the backscattering analysis of gold on silicon and the forward scattering measurement of hydrogen in a self-supporting carbon film.

Small molecules as substrates for adsorption/desorption in 252Cf plasma desorption mass spectrometry

The grazing incidence surface-induced dissociation (GI-SID) of n-hexadecylpyridinium and verapamil ions generated by fission fragment desorption was studied. These molecules show the effect of enhanced surface-induced dissociation at grazing incidence as it was observed in former experiments with metal organic ions. A liquid film of perfluorinated polyether is used as collision surface. Small hydrocarbon fragment ions predominate in the GI-SID spectra. Pyridine ions appear as specific fragment ions in the GI-SID spectrum of n-hexadecylpyridinium. The GI-SID conversion efficiency varies in the range 40-70%. The experimental results are discussed within the scope of a quantum mechanical model which is based on the accumulation of internal molecular energy by resonant excitation of collective vibrational states and energy transfer to a trap bond due to dipole-dipole interactions. In this context the GI-SID spectra of n-hexadecylpyridinium and verapamil ions are compared with the fragmentation occurring in regular (252)Cf plasma desorption mass spectrometry.

Chicken intestinal calbindin-D28k is an intracellular protein which is believed to have a fundamental role in vitamin D-mediated transport of calcium. A mapping approach based on 252Cf plasma desorption mass spectrometry (PD mapping) was used to screen the DNA-deduced sequence of calbindin-D28k for sequence changes and post-translational modifications. In the PD mapping experiment, purified calbindin-D28k was cleaved with cyanogen bromide and the resulting peptides were subjected to PD mass spectrometric analysis either as a mixture or as high-performance liquid chromatography isolated fractions. The DNA-derived primary structure of calbindin-D28k was confirmed by rapid PD mass spectral identification of the CNBr peptide fragments, and the nature of the N-terminal blocking group was readily determined to be an acetyl group. The relatively non-destructive nature of the PD mass spectrometric analysis allowed the mapping of the N-terminal peptide through an additional in situ V8 protease enzymatic reaction.

N‐Acetylcysteine and nine N‐acetylcysteine conjugates of synthetic origin were characterized by positive‐ and negative‐ion plasma desorption mass Spectrometry. For sample preparation the electrospray technique and the nitrocellulose spin deposition technique were applied. The fragmentation of these compounds, which are best seen as S‐substituted desaminoglycylcysteine dipeptides, shows a similar behaviour to that of linear peptides. In the positive‐ion mass spectra intense protonated molecular ion peaks are observed. In addition, several sequence‐specific fragment ions (A+, B+, [Y + 2H]+, Z+), immonium ions (I+) and a diagnostic fragment ion for mercap‐turic acids (RM+) are detected. The negative‐ion mass spectra exhibit deprotonated molecular ions and in contrast only one fragment ion corresponding to side‐chain specific cleavage ([RXS]−) representing the xenobiotic moiety. In the case of a low alkali metal concentration on the target, cluster molecular ions of the [nM + H]+ or [nM ‐ H]− ion type (n = 1‐3) are observed. The analysis of an equimolar mixture of eight N‐acetylcysteine conjugates shows different quasi‐molecular ion yields for the positive‐ and negative‐ion spectra.

Bremsstrahlung photons measurement show elevated energy emission beyond critical energy in 28-GHz ECR and its nature is not revealed. Thus, the aim of this study is to unveil the nature of high end-point energies at the three measurement locations. Bremsstrahlung photons from a 28-GHz ECR ion source were measured at Busan center of Korean Basic Science Institute (KBSI). The gamma-ray detection system consists of three round type NaI(Tl) scintillation detectors placed 62 cm radially from the beam axis at the three measurement locations namely injection, centre and extraction sides of an ECR ion source, and a NaI(Tl) scintillation detector placed at the view port for monitoring photon intensity along the beam axis. Such design of the experiment was based on the inner structure of the ECR ion source and the shape of the ECR plasma. Also, bremsstrahlung photons were measured by exchanging the detector positions for studying systematic uncertainties. Monte Carlo simulation based on the Geant4 package was performed to take geometrical acceptance and the energydependent detection efficiency into account due to large non-uniformity in the material budget. True bremsstrahlung energy spectra from the 28-GHz ECR ion source were extracted using an inverse matrix unfolding method. The measured high end-point energies at the three measurement locations were 1.68 MeV, 1.72 MeV and 2.04 MeV for the injection, centre and extraction sides, respectively. The high end-point energy values of the measured bremsstrahlung photons beyond the theoretical energy value of 1.33 MeV were found to be correlated with the structure of the ECR ion source and the shape of the ECR plasma. Furthermore, the high end-point energy values resulting from the bremsstrahlung photons measurements in the 28-GHz ECR plasma are due to the higher number of unconfined electrons arriving at the chamber wall easily, and producing higher bremsstrahlung photons. The unconfined electrons are the results of imperfect magnetic confinement that cause electrons to escape from the plasma volume.

The Far Ultraviolet Spectroscopic Explorer (FUSE) satellite was launched into orbit on June 24, 1999. FUSE is designed to make high resolution ((lambda) /(Delta) (lambda) equals 20,000 - 25,000) observations of solar system, galactic, and extragalactic targets in the far ultraviolet wavelength region (905 - 1187 Angstrom). Its high effective area, low background and planned three year life allow observations of objects which have been too faint for previous high resolution instruments in this wavelength range. The FUSE instrument includes two large format microchannel plate detectors. Each detector system consists of two microchannel plate segments in a Z-stack configuration with double delay line anodes and associated electronics. High detector spatial resolution was required in order to obtain scientific data with high spectral resolving power, and low detector background was necessary in order to observe faint objects. We describe the performance of the FUSE detectors during their first year on orbit, including the mechanical and thermal stability, throughput, background, and flat field of the detector system. We will also discuss the regular single event upsets of the detector electronics, and the strategy adopted in order to minimize their impact on mission efficiency.

The time-of-flight mass spectrum of charged particles, which are created through two-step cw-laser photoionization of laser-cooled <sup>87</sup>Rb atoms in an ion-neutral hybrid trap, is quantitatively investigated to further facilitate the study of Rb<sup>+</sup>-Rb reactive collisions. A microchannel plate (MCP) is used to detect charged particles, and two spectral peaks corresponding to the <sup>87</sup>Rb<sup>+</sup> ions and the product <inline-formula><tex-math id="Z-20230423060254-1">\begin{document}$ \rm {}^{87}Rb_2^+ $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20222273_Z-20230423060254-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20222273_Z-20230423060254-1.png"/></alternatives></inline-formula> of the Rb<sup>+</sup>-Rb reaction were observed in the time-of-flight spectrum, respectively. The two peaks overlapped with each other and both showed an asymmetric profile. The information about the intensity, position, and half-width of the peak for a specific ion species was derived by fitting the time-of-flight spectrum with the probability density function of the Gumbel distribution. Then the relative ion intensity was converted into absolute ion number through the following steps. The rate equation of the total number of ions, which includes the number of atoms, the calibration factor of MCP, and the effective decay rate of ions in the ion trap, was established by modeling the photoionization of atoms. Combined with the absolute number of atoms measured by absorption imaging, the calibration factor in converting the ion intensity into the ion number was derived and the relative ion intensity was converted into the absolute number of ions. This provides a method of calibrating the MCP. The reliability of our calibration method was proved by the fact that the calibration factor in converting the intensity measured by MCP into particle number is independent of the duration of photoionization, the intensity and wavelength of the ionizing laser. Moreover, in order to explain the relationship between the peak width and temperature of the corresponding ion species, the time-of-flight spectra of the ions trapped in the ion trap were simulated by using COMSOL Multiphysics. The simulation results demonstrated that the large ion kinetic energy results in a narrow spectral peak. In sum, we quantitatively analyze and simulate the time-of-flight spectrum of the photoionization of cold atoms in the Rb<sup>+</sup>-Rb hybrid trap. The absolute number of ions is obtained by the intensity of the spectral peak, and the width of the spectral peak is related to the temperature of the ions. These results lay a foundation for the in-depth analysis of the ion-atom reaction collision and charged particle temperature relaxation in the photoionization of cold atoms, and thus further elucidating the subsequent collisional dynamics of ultracold plasmas.