Oxidative stresses from irritants such as hydrogen peroxide and ozone (O3) can cause dysfunction of the pulmonary surfactant (PS) layer in the human lung, resulting in chronic diseases of the respiratory tract. For identification of structural changes of pulmonary surfactant protein B due to the heterogeneous reaction with O3, field induced droplet ionization (FIDI) mass spectrometry is utilized. FIDI is a soft ionization method in which ions are extracted from the surface of microliter-volume droplets. We report the structurally specific oxidative changes of SP-B1-25 (a shortened version of human surfactant protein B) at the air-liquid interface. We also present studies of the interfacial oxidation of SP-B1-25 in a non-ionizable 1-palmitoyl-2-oleoyl-sn-glycerol (POG) surfactant layer as a model PS system, where the competitive oxidation of the two components is observed. Our results indicate that the heterogeneous reaction of SP-B1-25 at the interface is quite different from that in the solution phase. Compared to the nearly complete homogeneous oxidation of SP-B1-25, only a subset of the amino acids known to react with ozone is oxidized by direct ozonolysis in the hydrophobic interfacial environment, both with and without the lipid monolayer. Combining these experimental observations with the results of molecular dynamics simulations provides an improved understanding of the interfacial structure and chemistry of a model lung surfactant system when subject to oxidative stress.

We present the construction and implementation of a compact, low-power ambient pressure pyroelectric ionization source. The source comprises a z-cut lithium niobate or lithium tantalate crystal with an attached resistive heater mounted in front of the atmospheric pressure inlet of an ion trap mass spectrometer. Positive and negative ion formation alternately results from thermally cycling the crystal over a narrow temperature range. Ionization of 1,1,1,3,3,3-hexafluoro-2-propanol or benzoic acid results in the observation of the singly deprotonated species and their clusters in the negative ion mass spectrum. Ionization of triethylamine or triphenylamine with the source results in observation of the corresponding singly protonated species of each in the positive ion mass spectrum. Although processes in which ion formation occurs directly on the highly charged crystal surface may contribute to the observed signal, ion formation appears to result mainly from electrical discharges occurring on the surface of the crystal, from one z face to another. This dielectric breakdown originates from the high electric fields generated at the surface of pyroelectric crystals when they are thermally cycled by as little as 30 K from ambient temperature. Ion formation is largely unaffected by contamination of the crystal faces. This robust source might prove particularly useful in applications where unattended operation in harsh environments, long service lifetimes, and durability are desirable characteristics.

A laser ablation-miniature mass spectrometer (LA-MMS) for the chemical and isotopic measurement of rocks and minerals is described. In the LA-MMS method, neutral atoms ablated by a pulsed laser are led into an electron impact ionization source, where they are ionized by a 70 eV electron beam. This results in a secondary ion pulse typically 10-100 μs wide, compared to the original 5-10 ns laser pulse duration. Ions of different masses are then spatially dispersed along the focal plane of the magnetic sector of the miniature mass spectrometer (MMS) and measured in parallel by a modified CCD array detector capable of detecting ions directly. Compared to conventional scanning techniques, simultaneous measurement of the ion pulse along the focal plane effectively offers a 100% duty cycle over a wide mass range. LA-MMS offers a more quantitative assessment of elemental composition than techniques that detect ions directly generated by the ablation process because the latter can be strongly influenced by matrix effects that vary with the structure and geometry of the surface, the wavelength of the laser beam, and the not well characterized ionization efficiencies of the elements in the process. The above problems attendant to the direct ion analysis has been minimized in the LA-MMS by analyzing the ablated neutral species after their post-ionization by electron impaction. These neutral species are much more abundant than the directly ablated ions in the ablated vapor plume and are, therefore, expected to be characteristic of the chemical composition of the solid. Also, the electron impact ionization of elements is well studied and their ionization cross sections are known and easy to find in databases. Currently, the LA-MMS limit of detection is 0.4 wt.%. Here we describe LA-MMS elemental composition measurements of various minerals including microcline, lepidolite, anorthoclase, and USGS BCR-2G samples. The measurements of high precision isotopic ratios including (41)K/(39)K (0.077 ± 0.004) and (29)Si/(28)Si (0.052 ± 0.006) in these minerals by LA-MMS are also described. The LA-MMS has been developed as a prototype instrument system for space applications for geochemical and geochronological measurements on the surface of extraterrestrial bodies.