Process mass spectroscopy

The principal techniques for determining the microstmcture of phenoHc resins include mass spectroscopy, proton, and C-nmr spectroscopy, as well as gc, Ic, and gpc. The softening and curing processes of phenoHc resins are effectively studied by using thermal and mechanical techniques, such as tga, dsc, and dynamic mechanical analysis (dma). Infrared (ir) and electron spectroscopy are also employed. 

Mass Spectrometer. The mass spectrometer is the principal analytical tool of direct process control for the estimation of tritium. Gas samples are taken from several process points and analy2ed rapidly and continually to ensure proper operation of the system. Mass spectrometry is particularly useful in the detection of diatomic hydrogen species such as HD, HT, and DT. Mass spectrometric detection of helium-3 formed by radioactive decay of tritium is still another way to detect low levels of tritium (65). Accelerator mass spectroscopy (ams) has also been used for the detection of tritium and carbon-14 at extremely low levels. The principal appHcation of ams as of this writing has been in archeology and the geosciences, but this technique is expected to faciUtate the use of tritium in biomedical research, various clinical appHcations, and in environmental investigations (66). 

Historically, measurements have classified ambient hydrocarbons in two classes methane (CH4) and all other nonmethane volatile organic compounds (NMVOCs). Analyzing hydrocarbons in the atmosphere involves a three-step process collection, separation, and quantification. Collection involves obtaining an aliquot of air, e.g., with an evacuated canister. The principal separation process is gas chromatography (GC), and the principal quantification technique is wdth a calibrated flame ionization detector (FID). Mass spectroscopy (MS) is used along with GC to identify individual hydrocarbon compounds. 

The main experimental techniques used to study the failure processes at the scale of a chain have involved the use of deuterated polymers, particularly copolymers, at the interface and the measurement of the amounts of the deuterated copolymers at each of the fracture surfaces. The presence and quantity of the deuterated copolymer has typically been measured using forward recoil ion scattering (FRES) or secondary ion mass spectroscopy (SIMS). The technique was originally used in a study of the effects of placing polystyrene-polymethyl methacrylate (PS-PMMA) block copolymers of total molecular weight of 200,000 Da at an interface between polyphenylene ether (PPE or PPO) and PMMA copolymers [1]. The PS block is miscible in the PPE. The use of copolymers where just the PS block was deuterated and copolymers where just the PMMA block was deuterated showed that, when the interface was fractured, the copolymer molecules all broke close to their junction points The basic idea of this technique is shown in Fig, I. 

X-ray scattering studies at a renewed pc-Ag/electrolyte interface366,823 provide evidence for assuming that fast relaxation and diffu-sional processes are probable at a renewed Sn + Pb alloy surface. Investigations by secondary-ion mass spectroscopy (SIMS) of the Pb concentration profile in a thin Sn + Pb alloy surface layer show that the concentration penetration depth in the solid phase is on the order of 0.2 pm, which leads to an estimate of a surface diffusion coefficient for Pb atoms in the Sn + Pb alloy surface layer on the order of 10"13 to lCT12 cm2 s i 820 ( p,emicai analysis by electron spectroscopy for chemical analysis (ESCA) and Auger ofjust-renewed Sn + Pb alloy surfaces in a vacuum confirms that enrichment with Pb of the surface layer is probable.810... 

The conversion of 70 to the final PPV 60 is then carried out thermally at relatively low processing temperatures (about 100-150 °C) with elimination of (unstable) alkylsulfinic acid. TGA-mass spectroscopy, FT-IR, UV/Vis and CP/MAS NMR spectroscopy are all consistent with quantitative elimination and formation of PPV 60. 

Perhaps the most revolutionary development has been the application of on-line mass spectroscopic detection for compositional analysis. Polymer composition can be inferred from column retention time or from viscometric and other indirect detection methods, but mass spectroscopy has reduced much of the ambiguity associated with that process. Quantitation of end groups and of co-polymer composition can now be accomplished directly through mass spectroscopy. Mass spectroscopy is particularly well suited as an on-line GPC technique, since common GPC solvents interfere with other on-line detectors, including UV-VIS absorbance, nuclear magnetic resonance and infrared spectroscopic detectors. By contrast, common GPC solvents are readily adaptable to mass spectroscopic interfaces. No detection technique offers a combination of universality of analyte detection, specificity of information, and ease of use comparable to that of mass spectroscopy. 

This analytical methodology deduces the four photooxidative processes. The data on the total CO2 evolved from the samples were measured by gas chromatography and the isotopic C02 ( 6C02 and 4°C02) data by GC/mass spectroscopy. The rate constants of the two major photooxidative degradation processes at 25°C were deduced from h 18o2 per -(C H NO)- (i.e., to produce C02 product, t = 42 hr) at 196°C and the other from 02 per -(C H NO)- (i.e., to 2produce C02 product, t = 8 min) at 196°C. The rate constants of the former process was estimated as 1.10 x 10- 1 mole sec-- - and the latter as 1.03 x lO-- - 1 mole-- - sec-- -. The activation energies of these two processes were deduced as 10.8 kcal/mole for the former and 15.7 kcal/mole for the latter. 

The industrial application of Plasma Induced Chemical Vapour Deposition (PICVD) of amorphous and microcrystalline silicon films has led to extensive studies of gas phase and surface processes connected with the deposition process. We are investigating the time response of the concentration of species involved in the deposition process, namely SiH4, Si2H6, and H2 by relaxation mass spectroscopy and SiH2 by laser induced fluorescence. 

A range of tetradentate Schiff-base ligands have also been employed to prepare discrete aluminum alkoxides. The most widely studied system is the unsubstituted parent system (256), which initiates the controlled ROP of rac-LA at 70 °C in toluene. The polymerization displays certain features characteristic of a living process (e.g., narrow Mw/M ), but is only well behaved to approximately 60-70% conversion thereafter transesterification causes the polydispersity to broaden.788 MALDI-TOF mass spectroscopy has been used to show that even at low conversions the polymer chains contain both even and odd numbers of lactic acid repeat units, implying that transesterification occurs in parallel with polymerization in this system.789... 

Figure 5.3. TDS of solution-processed a-Si films. Three samples were prepared by the thermal decomposition of polysilane under the following conditions sample a, 300 °C for 10 min sample b, 300 °C for 120 min and sample c, 540 °C for 120 min. Desorbed gases from the samples were analyzed using mass spectroscopy while the samples were heated in a vacuum. [Reproduced with permission from Ref. 10. Copyright 2006 Nature Publishing Group.]...

The second family of secreted proteins that is covalently lipidated is the family of Wnt proteins. They are also involved in numerous processes like proliferation of stem cells, specification of the neural crest, and the expanding of specific cell types. The correct regulation of this pathway is important for animal development. Willert and coworkers were the first to isolate an active Wnt molecule. Mass spectroscopy studies carried out with the isolated protein revealed that cysteine 93 is palmitoylated. Mutating this amino acid to alanine led to almost complete loss of the signaling activity. Later in 2006, a second lipidation was found on a serine in Wnt3a. " In this case, the hydroxyl side chain is acylated with palmitoleic acid. This unsaturated fatty acid seems to be crucial for the progression of the protein through the secretory pathway. The attachment of two different lipid chains may therefore serve different functions. ... 

Similar studies were carried out with benzoic acid on porous palladium electrodes [150]. The objective of this work was to investigate the adsorption processes and the reactivity of benzoic acid on different noble metals, in order to compare these results with those obtained for related aromatic compounds. On-line mass spectroscopy analysis of volatile products revealed that the adsorption of benzoic acid is irreversible at platinum while it is mainly reversible on palladium. Accordingly, different catalytic activity of platinum and palladium was found in the electrooxidation. 

Other electrochemical processes of organic compounds on Pb electrodes or electrodes with UPD Pb have been studied - formaldehyde [323], oxalic acid [386], trichloro- and trifluoroethane [387], 1-phenylethylamine [388], 3-hydroxychi-nuclidine [388], dichlorodifluoromethane [389], polychlorobenzenes [390], 1-propa-nol [391], pyrrole polymerization [392], and inorganic compounds - phosphine [388] and sulfate(IV) ions [393]. Simultaneous catalytic or inhibiting influence of organic solvents - acetonitrile, dimethyl-sulfoxide, and Pb + presence on electrooxidation of small organic molecules on Pt electrodes has been studied using on-line mass spectroscopy [394],... 

A very common and useful approach to studying the plasma polymerization process is the careful characterization of the polymer films produced. A specific property of the films is then measured as a function of one or more of the plasma parameters and mechanistic explanations are then derived from such a study. Some of the properties of plasma-polymerized thin films which have been measured include electrical conductivity, tunneling phenomena and photoconductivity, capacitance, optical constants, structure (IR absorption and ESCA), surface tension, free radical density (ESR), surface topography and reverse osmosis characteristics. So far relatively few of these measurements were made with the objective of determining mechanisms of plasma polymerization. The motivation in most instances was a specific application of the thin films. Considerable emphasis on correlations between mass spectroscopy in polymerizing plasmas and ESCA on polymer films with plasma polymerization mechanisms will be given later in this chapter based on recent work done in this laboratory. 

---