Application of factor analysis for resolving thermogravimetric-mass spectrometric analysis spectra

Factor Analysis was used for extracting information out of the mixture mass spectra recorded in a thermogravimetric-mass spectrometric analysis. Principal component analysis (PCA) and a special diagram, the contour variance diagram (ContVarDia), were used for performing the factor analysis. The method was applied for studying the thermal decomposition of Kraton 1107 copolymer. Pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) was used for identification of the pyrolysis products of Kraton 1107. The application of factor analysis resulted in the determination of the main thermal decomposition steps and the prediction of the mass spectrum corresponding to each step. Those mass spectra were either pure spectra corresponding to main evolved gases or average spectra corresponding to multiple gases evolved in one decomposition step. The advantages and the limitations of the chemometric approach were discussed.     

Identification of amino acid thiohydantoin derivatives by chemical ionization mass spectrometry

The chemical ionization mass spectra of 16 amino acid thiohydantoins were examined using isobutane or ammonia as reagent gases. Except for a few cases, including some aromatic amino acids, the chemical ionization spectra were much simpler than the corresponding electron impact spectra. Therefore, the major component in the amino acid thiohydantoin mixture was easily detected by chemical ionization mass spectrometry. The combination of the chemical ionization method and thiohydantoin formation was applied successfully to the sequence analysis of model peptides.     

Extraction of information attributes from the mass spectrometric signals of air

The paper describes a new method of the extraction of information attributes from the processed signals, generalized spectral analysis in an adapted basis. Studies of the functional structure of mathematical foundations and an adaptable classification system of different signal types, including the quadrupole mass spectra of air, were carried out. Algorithms for the synthesis of basis functions adapted to orthogonal transforms of process signals were developed. The use of the method for analytical instrumentation was demonstrated by the processing of mass spectra recorded on a quadrupole mass spectrometer in the analysis of gases exhaled by humans.     

Quantification of several atmospheric gases from high resolution infrared solar spectra obtained at the south pole in 1980 and 1986

Simultaneous total column amounts of a number of minor and trace atmospheric gases above the South Pole in December 1980 and December 1986 have been deduced from analysis of high resolution solar absorption spectra recorded (by F. J. M. and F. H. M.) from Amundsen-Scott South Pole Station. These spectra also contain some limited information on the vertical profiles of the observed atmospheric gases.The data sets were recorded with a Bomem Michelson-type interferometer and analyzed with a spectral least-squares fitting procedure, utilizing the best available spectroscopic line parameters and absorption cross sections. Because the same instrument, line parameters, and analysis method have been used in analyzing the December 1980 and December 1986 data sets, the precision in comparing the column amounts from these two dates is rather high, about 10–20% for the stronger absorbing gases. For this reason, it has been possible to quantify or determine upper limits for differences between the December 1980 and December 1986 total column amounts, of a number of atmospheric gases including O₃, N₂O, HNO₃, CO₂, CH₄, and CF₂C_{1 2} (CFC 12). In addition, vertical column amounts for a number of atmospheric gases covered only in the December 1986 observations have been derived, including HC1, NO, NO₂, and C₂H₆. Some of these results will be discussed here. The HC1 measurements are especially interesting since the observed amounts are higher than expected from observations made at lower latitudes in the northern and southern hemispheres.     

Effects of heavy gases on the tandem mass spectra of peptide ions in the quadrupole ion trap

Heavy gases (xenon, argon, krypton, methane) have been used to improve the performance of the quadrupole ion trap when performing collision-induced dissociation on peptides. MS/MS spectra reveal that increased amounts of internal energy can be deposited into peptide ions and more structural information can be obtained. Specifically, the pulsed introduction of the heavy gases (as reported previously by Doroshenko, V. M.; Cotter, R. J.Anal. Chem. 1996, 68, 463) provides greater energy deposition without the deleterious effects that static pressures of heavy gas have on spectra. Internal energy deposition as indicated by a qualitative evaluation of MS/MS spectra shows pulsed introduction of heavy gases enables ions to obtain more internal energy than possible by using static pressures of the same heavy gases. A linear correlation is observed between the percentage of heavy gas added and the ratio of product ions used to reflect internal energy deposition. Results here also show that upon pulsed introduction of heavy gases, empirical optimization of a single frequency resonant excitation signal is no longer needed to obtain good MS/MS spectrometry efficiency. The presence of many low mass-to-charge ratio ions and the absence of side chain cleavages in the MS/MS spectra of peptides suggests that the propensity for consecutive fragmentations is increased with the pulsed introduction of heavy gases. In addition, by varying the delay time between introduction of the gas and application of the resonant excitation signal, the amount of fragmentation observed in MS/MS spectra can be changed.     

TG-DTA/FT-IR method for analyzing thermal decomposition mechanism of polyesters

An attempt to estimate the thermal decomposition mechanism of polymers using the simultaneous TG-DTA/FT-IR system was summarized. The library search of FT-IR spectra at various temperatures and of the subtraction spectrum obtained by subtracting the spectra at different temperatures were used to determine the types of evolved gases from poly(ethylene terephthalate) and poly(butylene terephthalate) at given stages of decomposition. The quantitative analysis of evolved gases was carried out using the specific gas profiles at the specific absorption band. The kinetic parameters were estimated from both TG and spectroscopic curves measured at various heating rates.     

Electron capture negative ion and positive ion chemical ionization mass spectrometry of polychlorinated phenoxyanisoles

Several polychlorinated phenoxyphenols with three to nine chlorine atoms were examined as their methyl ethers by electron capture negative ion and positive ion chemical ionization and electron impact mass spectrometry. In chemical ionization studies methane, hydrogen, nitrogen, helium and argon were used as reagent gases. Selected compounds were also examined with deuteriomethane, ammonia and deuterioammonia as reagent gases. Utilization of chemical ionization spectra in conjuction with electron impact spectra provides substantial structural information about these compounds. Chemical ionization spectra provide information about chlorine atom substitution. The position of phenoxy substitution can be established from electron capture negative ion and positive ion spectra.     

Evolved Gas Analysis of Some Solid Fuels by TG-FTIR

FTIR spectrometry combined with TG provides information regarding mass changes in a sample and permits qualitative identification of the gases evolved during thermal degradation. Various fuels were studied: coal, peat, wood chips, bark, reed canary grass and municipal solid waste. The gases evolved in a TG analyser were transferred to the FTIR via a heated teflon line. The spectra and thermoanalytical curves indicated that the major gases evolved were carbon dioxide and water, while there were many minor gases, e.g. carbon monoxide, methane, ethane, methanol, ethanol, formic acid, acetic acid and formaldehyde. Separate evolved gas spectra also revealed the release of ammonia from biomasses and peat. Sulphur dioxide and nitric oxide were found in some cases. The evolution of the minor gases and water parallelled the first step in the TG curve. Solid fuels dried at 100°C mainly lost water and a little ammonia. This revised version was published online in August 2006 with corrections to the Cover Date.     

Analysis of a Complex Gaseous Mixture by TG-MS and TG-FTIR

The thermal decomposition of sodium ethyl xanthate (SEX) was used to compare the techniques of pyrolysis-gas chromatography-mass spectrometry (py-GC-MS), thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR), and TG-MS. In the py-GC-MS analysis, SEX was pyrolysed at 400°C in an inert atmosphere. Major gases evolved were carbon disulfide, diethyl sulfide, ethanol, and carbonyl sulfide. The TG of SEX exhibited a sharp mass loss at 201°C (42.3%) and a gradual mass loss at 217-325°C (20.8 %). The MS spectra of the evolved gases were complex due to overlapping of molecular, isotope, and fragment ion signals. Using the MS in selected ion monitoring mode, the major gases evolved were found to be carbon disulfide and carbonyl sulfide. The FTIR spectra of the evolved gases displayed vibrational frequencies due to alkanes, carbonyls, carbonyl sulfide, and carbon disulfide. From the analyses it was concluded that py-GC-MS provided unambiguous gas identification. Interpretation of the MS results was reliant on the py-GC-MS results, and the FTIR data was limited to identifying gases with very characteristic vibration frequencies. This revised version was published online in July 2006 with corrections to the Cover Date.     

On-line mass spectrometry in fermentation

The on-line application of mass spectrometry (m.s.) includes analysis of the fermentor gas phase by using a capillary inlet and analysis of the liquid phase by using membrane probes. Gas-phase measurements with a capillary inlet are fast and accurate for all gases of interest (O₂, N₂, CO₂, H₂, etc.). Liquid-phase measurements are done with steam-sterilizable membrane inlet probes, permitting direct analysis of dissolved gases and various volatiles. With these two inlets, automatic measurement of both the liquid and gas phases is possible when a microcomputer is used. This was applied to the batch fermentation of Bacillus subtilis. A further application of the membrane probe is evaluation of fermentation process state; this involves measuring the spectra of all detectable volatiles and correlating this information with the process state (e.g., product formation). Sufficient characteristic volatiles were found in various industrial fermentation samples. When mass spectra are treated by factor analysis, useful correlations are found with the product concentrations measured off-line. Calibration depending on the process conditions is necessary for this method, but it is widely applicable and allows automatic monitoring.     

Absorption spectra of lead, indium and barium atoms trapped in solid rare gas matrices

Vacuum ultraviolet absorption spectra of lead, indium and barium atoms trapped in solid rare gases are shown. These spectra were obtained photoelectrically and the matrix gases used were argon, krypton and xenon. The results are discussed in relation to previous work.     

油气化探样品芳烃分析中干扰因素的识别

通过对全国各大油田典型油气的分析,提出各种油气的三维荧光光谱和固定波长同步荧光光谱特征峰和共性峰。利用三维荧光光谱可以判断油气的属性,油气性质的精细分析尚要依靠同步荧光光谱。钻井过程常常加入磺化沥青或原油,三维荧光光谱可以进行很好的干扰识别;钻遇煤层或含煤层段,根据煤的三维荧光等值线图加以判断。人类活动、化石燃料的不完全燃烧均能造成芳烃的污染,在取样和处理分析数据时应该进行校正。湖相和海相沉积物含有丰富的多环芳烃,采用固定能量同步荧光光谱分析效果更佳。     

Pulsed discharge emission detector — Application to analytical spectroscopy of permanent gases

Summary This publication contains our initial development of a pulsed discharge emission detector (PDED) (patent pending). It uses a pulsed high voltage discharge in helium, which provides a stable source for atomic and polyatomic emission spectroscopy. We have evaluated this detector for both quantitative and qualitative analysis of a range of chemical compounds. Emission spectra observed from the pulsed high voltage discharge are valuable for spectral analysis. The results obtained for selected permanent gases in the ultraviolet, visible and infrared regions of the optical spectrum indicate that these spectra can be used for compound identification after a chromatographic separation. The data are unique in our opinion and serve as a basis for the future development and investigation of the analytical significance of this detection method.Dedicated to Professor Leslie S. Ettre on the occasion of his 70th birthday.     

Rapid analysis of coke oven gas by capillary gas chromatography

A porous layer open tubular (PLOT) column has been used for monitoring the light hydrocarbons and permanent gases produced in coking plants. The method, which offers a simple alternative to traditional multi column techniques, entails a single injection on to a Carboplot 007 capillary column and simultaneous thermal conductivity and flame ionization detection. The simplified approach proposed is restricted to coke oven gas analysis: application to other gas mixtures has not been considered. The reliability of this procedure compares favorably with that of traditional methods; the technique is also much less time-consuming: seven individual gases can be determined on-line every fifteen minutes. Primary and secondary gas standards were used to determine response curves for the gases. The method also facilitates reliable calculation of heat values associated with the burning of the fuel gas mixtures.     

Analyse des composes fluores corrosifs par chromatographie gazeuse : Controle du fluor libre

A purely chromatographie and sufficiently general method is described for the analysis of molecular fluorine in permanent inert gases or in other corrosive fluorine compounds (UF₆, HF). The method is also applied to the analysis of permanent inert gases (even in trace quantities) in the same fluorine compounds. In this method, one or several chemical “precolumns” are placed in series with a gas-liquid chromatography column. The “precolumn” system retains or destroys the corrosive compounds (UF₆, HF, F₂) and the chromatography column separates the components formed.     

Fluorine-induced chemiluminescence detection of biologically methylated tellurium,selenium, and sulfur compounds

Summary The sensitive detection of volatile, methylated selenium and tellurium compounds based on capillary gas chromatography coupled to fluorine-induced chemiluminescence detection is described. The method requires no sample derivatization, and the detection limits for selenides and tellurides (low pg range) are the lowest reported to date. This technique can resolve and speciate complex mixtures of methylated tellurium, selenium, and sulfur gases and is useful for analysis of selenium and tellurium gases in environmental samples that also contain usually interfering reduced sulfur gases. Applications of the technique for analysis of bacterial and fungal headspace samples are presented.     

Selective two-quantum laser excitation of molecules with overlapping absorption lines

A method of two-quantum excitation of molecules at Doppler-broadened transitions in a standing-wave radiation field is considered. It is shown that it is possible to increase the excitation selectivity of molecules with overlapping absorption lines when using spectra of two-photon absorption. Estimations of two-quantum transition probabilities for molecular gases are given.     

Charge inversion and neutralization–reionization mass spectra of some alkoxide ions

The charge inversion mass spectra of C₁ to C₃ alkoxide ions have been obtained using He, N₂ and O₂ as collision gases. The three collision gases show similar efficiencies for collisional charge inversion and produce similar mass spectra, although fewer high-energy oxenium ions are formed when O₂ and N₂ are used as collision gases. Using two collision cells and an intermediate deflector electrode the alkoxide ions have been neutralized in the first collision cell and the fast neutrals ionized in the second cell. The neutralization–reionization mass spectra obtained are similar to the direct charge-inversion mass spectra indicating that mainly alkoxyl radicals are produced, although, depending on the neutralization collision gas and the alkoxide ion studied, other neutrals are formed in small yields. Deuterium isotopic labelling has been used to show that the main fragmentation reactions of the unstable oxenium ions formed involve 1,1-elimination of H₂ or an alkane.     

The chemical ionization mass spectrometry of RDX

The fragmentation pathways of RDX in chemical ionization mass spectrometry have been rationalized, using data from different reagent gases, including CD₄ and iso-C₄D₁₀. The dependence of spectra taken with different gases on the acid strength of the reactant ions in the gases is accounted for.     

Free radicals in irradiated unstabilized polypropylene, as seen by diffuse reflection absorption-spectrophotometry

The introduction of UV-Vis absorption spectrophotometry to the study of radiation chemistry of polymers has opened the possibility to investigate even very opaque samples. The virgin powder polypropylene, as obtained from the industrial production line, shows after irradiation unstable products of radiolysis. Until now they were investigated mainly by EPR method. Optical absorption spectra (by diffuse reflection spectrophotometry) contribute to better identification and study of changes in time, temperature and diffusion of reactive gases. Studying the formation of stable compounds, which do not produce EPR signal, we are able to examine these species on the basis of their electronic spectra. The most important results concern the peroxides in irradiated polypropylene.