Ho Ming. Pang

Design of a pulsed valve for high‐pressure NH3 injection into supersonic beam/mass spectrometry

A novel design of a pulsed valve for high‐pressure injection of NH3 for supersonic jet expansions is presented. This valve can operate up to 200‐atm reservoir pressure at 180 °C with a pulse width down to 100 μs. This valve has been designed so that the solenoid core is not in contact with the carrier fluid so that it can be used with highly polar corrosive liquids or supercritical fluids. The ability to use supercritical NH3 as a means of injecting small thermally labile biological molecules into supersonic jet expansions for analysis by resonant two‐photon ionization in a time‐of‐flight mass spectrometer is demonstrated.

High-Pressure Fluid Injection in Supersonic Beam Mass Spectrometry With Resonant Two-Photon Ionization

Abstract A novel apparatus was designed for the introduction of supersonic jets of supercritical CO2, N2O and high-pressure hot liquids such as methanol and water. The key features of this experiment are a pulsed injection source, which was designed with efficient liquid nitrogen cryopumping to operate at pressures of up to 380 atm and nearly 200°C. The reduction in duty cycle provided by a pulsed source has allowed the use of a 200 μm orifice, which significantly increases the on-axis density in the jet compared to continuous expansions where a 10 μm orifice is customarily used. Resonant two-photon ionization is then used to softly ionize the molecules in the beam for mass analysis and detection in a time-of-flight mass spectrometer.

Supercritical fluid jet expansions of polar aromatic carboxylic acids using simple derivatization with detection by resonant two-photon ionization

Abstract In this work simple derivatization is used as a means of enhancing the solubility of polar aromatic carboxylic acids in supercritical CO 2 and N 2 O. The supercritical fluid is then expanded from 200 atm and 40°C through a pulsed injection orifice into vacuum as a supersonic jet for analysis by laser resonant two-photon ionization spectroscopy in a time-of-flight mass spectrometer. The use of derivatization reduces the polarity of these carboxylic acids and thus greatly enhances their solubility in these fluids. The result is that strong ionization signals from the jet are detected in the mass spectrometer at relatively low temperatures where these molecules, many of which are thermally labile, will not decompose. The laser ionization method allows soft ionization of these compounds where the molecular ion is generally the base peak and a characteristic fragment due to simple C α -C β cleavage is often observed. By monitoring the molecular ion as a function of wavelength a cold laser ionization spectrum with sharp spectral features can be obtained in these supersonic expansions from high pressure supercritical fluids thus demonstrating that optical selectivity is still retained even after derivatization.

Supercritical fluid injection of nonvolatiles with resonant two photon ionization detection in supersonic beam mass spectrometry

Supercritical fluids of N2O and CO2 are used to solubilize nonvolatile compounds for supersonic jet expansions. R2PI is then used to ionize these compounds in a time of flight mass spectrometer. By tuning the dye laser wavelength a cold wavelength ionization spectrum can be obtained that is characteristic of that species.

Improvements in sample introduction for mass spectrometry using pulsed high-pressure fluid injection with resonant two-photon ionization detection

Abstract Pulsed supercritical fluid and pulsed high-pressure liquid injection are used as means of introducing thermally labile biological species into a time-of-flight mass spectrometer (TOFMS) system. The analyte species are then ionized by resonant two-photon ionization, which can produce either soft ionization or extensive fragmentation on the basis of laser power and wavelength. Since the solvent is transparent to the laser radiation, hard ionization can be produced without physical separation of the analyte from the effluent jet expansion. In addition, the pulsed liquid injection method allows introduction of the sample from high-pressure fluids at relatively low temperatures without the extensive clustering that normally occurs in liquid expansions unless a much higher temperature is utilized. Using this method, we have been able to study the laser-induced ionization mass spectrometry of several classes of small polar biological molecules in a TOFMS.