Rapid characterization of biomaterials by field ionization

The direct application of field ionization to complex biomaterials is described. Volatiles are characterized by gas chromatography mass spectrometry. Complex involatile materials are investigated by thermal degradation in high vacuum. The methodology and typical analytical features of pyrolysis of biopolymers and soft ionization of their pyrolysates in the high electric field are described. The combination of direct, in-source pyrolysis mass spectrometry and pyrolysis gas chromatography mass spectrometry is used in two steps. Firstly, for fast profiling of the complex materials and, secondly, for identification of significant products of the controlled thermal degradation process. In particular, temperature programmed/time-resolved pyrolysis field ionization mass spectrometry has been shown to be an efficient analytical tool as demonstrated for typical examples such as chitin, cellulose, hemicellulose, lignin, wood, peat and coal. Recent results on foodstuffs such as coffee, chocolate, tea and biscuits illustrate the potential of the combined methods for routine work.     

Curie-point pyrolysis field ionization mass spectrometry of carbohydrates: Part A: Methodology

Methodological aspects of Curie-point pyrolysis in combination with field ionization mass spectrometry for the characterization and identification of carbohydrates are reported. Some monomeric sugars and sugar derivatives have been investigated as a first step towards a basic understanding of the pyrolysis pathways of polysaccharides.Curie-point pyrolysis is performed inside the ion source of a double-focusing mass spectrometer close to the field ion emitter. The pyrolysis products are ionized in a high electric field and spectra of high mass resolution are recorded photographically. This procedure essentially avoids mass spectrometric fragmentation and yields almost exclusively molecular ions of the pyrolysates. The best experimental conditions for pyrolysis were determined by investigating the influences of pyrolysis temperature, temperature pulse length, exposure time and trace impurities on the pyrolysis products. At a temperature of 500°C and a pulse length of 4–6 s, the most significant pyrolysis fragments appear with high relative intensity. Although most of the pyrolysis products with higher volatility are pumped out of the ion source after an exposure time of 3 min, the more characteristic degradation products of lower volatility can still be registered after 10 min. The spectra of monosaccharides such as glucuronic acid, d-glucose and some of its methylated derivatives show significant differences which can be correlated structurally with the position of the substituent.     

Pyrolysis field ionization mass spectrometry of carbohydrates: Part b: Polysaccharides

The application of pyrolysis in combination with field ionization (FI) mass spectrometry for the characterization and identification of polysaccharides is reported. Polysaccharides such as xylan, agarose and alginic acid, which contain monomer subunits of different elemental composition, can be differentiated in a straightforward manner by the field ionization spectra of their Curie-point pyrolysates. Polysaccharides with hexosyl subunits, such as cellulose, galactan, laminaran and mannan, were pyrolysed by Curie-point pyrolysis and show photographically recorded FI spectra which differ in the relative heights of their pyrolysis peaks. Characteristic pyrolysis products are formed, which can be identified or assigned structures on the basis of accurate mass measurements, direct isotopic determination and by analogy with established chemical procedures and mechanisms.Oven pyrolysis of polysaccharides combined with electrical detection of the FI spectra at low mass resolution gives a higher sensitivity and better reproducibility for all peaks over the whole mass range. From sample amounts of about 40 μg, spectra are obtained by raising the oven temperature by 0.4°C/s. Utilizing repetitive magnetic scanning, registration and signal processing by the data system, the standard deviation of the peak heights for five repeated measurements is about 10%. Accumulation of about 30 spectra in a limited mass range on a multi-channel analyser gives results which vary by about 2–3% on average, despite a lower sample consumption (20–30 μg). Oven pyrolysis between 250 and 400°C yields significant differences in the spectra of differently linked mannans and allows an unequivocal differentiation of these isomers. Following FI, field desorption (FD) spectra were obtained from pyrolysis products condensed on the emitter surface by heating of the emitter wire between 10 and 30 mA. The cations of alkali metals, such as Na*, K* and Cs*, can be registered in this way. Most interesting is the detection of the molecular ions of monomer and oligomer subunits of the polysaccharides as complementary analytical information in the FD mode. Obviously, condensation of these neutral, thermal products on the emitter surface occurs without field ionization and desorption is initiated by supply of thermal energy to the adsorbed sample layer.     

Thermal degradation of spruce needles studied by time-resolved mass spectrometry and multivariate data analysis

In a study related to the impact of air pollution on forests, needles from a healthy and a severely damaged Norway spruce tree were analysed by temperature-programmed pyrolysis/field ionization (FI) mass spectrometry. Dried and pulverized spruce needles were heated at a rate of 0.6°C s^?1 to 450°C in the high vacuum of a FI ion source. Over 100 mass spectra were recorded electrically during each analysis. From each mass spectrum, average molecular weights of the pyrolysis products were calculated; their variation with pyrolysis temperature is discussed. The mass spectra in the range m/z 100–600 are used to calculate partial weight-loss curves. The FI mass spectra are evaluated by principal component analysis and factor rotation. The three-factor spectra based on loadings of the rotated principal components show typical FI signals which are produced during pyrolysis at low, medium and high temperatures. These signal patterns are interpreted as molecular ions of thermally stable, relatively volatile plant constituents and molecular ions of thermal degradation products derived from the thermolysis of carbohydrates, lignin and other biopolymers which occur in conifer needles. Medium- and high-temperature products of lignin can be distinguished. Principal component scores can be used to simulate the appearance of single FI signals, i.e., pyrolysis products. The evaluation of time-resolved pyrolysis and soft ionization mass spectrometric data from a single sample by principal component analysis and factor rotation appears to be suitable for characterization of the major chemical components and their thermal behaviour in complex biological samples.     

Using electrospray-assisted pyrolysis ionization/mass spectrometry for the rapid characterization of trace polar components in crude oil, amber, humic substances, and rubber samples

We describe the use of electrospray-assisted pyrolysis ionization/mass spectrometry (ESA-Py/MS) to selectively ionize trace polar compounds that coexist with large amounts of nonpolar hydrocarbons in crude oil, amber, humic substances, and rubber samples. Samples of different origins are distinguished rapidly by their positive ion ESA-Py mass spectra without prior separation or chemical pretreatment. During ESA-Py analysis, the samples in their solid or liquid states were pyrolyzed at 590, 630 or 940 degrees C using a commercial Curie-point pyrolysis probe. The gaseous pyrolysates were transferred into a glass reaction cell. The polar compounds (M) in the pyrolysates were then ionized by electrospray ionization (ESI), yielding protonated molecules (MH+). Although the major components of the pyrolysates are nonpolar hydrocarbons, their lack of functional groups that can receive a proton in the ESA-Py source results in no hydrocarbon ion signals being produced; thus, the positive ions detected in ESA-Py mass spectra all result from trace polar components in the pyrolysates.     

Investigations of model systems of the Maillard reaction: II. Pyrolysis—gas chromatography—mass spectrometry analysis of some non-volatile products of the reaction of d-glucose and 4-chloroaniline

Low molecular weight compounds resulting from the reaction of d-glucose with 4-chloroaniline were subjected to Curie-point pyrolysis, and the cleavage products were identified by gas chromatography—mass spectrometry. Based on their structures, some general features were detected which possibly are applicable to the structural analysis of higher molecular weight Maillard compounds of this type. It is shown in one example that pyrolysis and electron impact mass spectrometry obviously prefer similar fragmentation patterns. In addition to Curie-point pyrolysis, Pyrotest pyrolysis and dry distillation were also tested but yielded less reproducible results.     

The three-dimensional structure of humic substances and soil organic matter studied by computational analytical chemistry

A novel three-dimensional structural concept for humic substances and soil organic matter (SOM) is proposed which is based on previously published, comprehensive investigations combining geochemical, wetchemical, biochemical, spectroscopic, agricultural and ecological data with analytical pyrolysis. Direct, temperature-programmed pyrolysis in the ion-source of the mass spectrometer and soft ionization in very high electric fields (Py-FIMS) and Curie-point pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) were the main applied thermal methods. Emphasis is laid on molecular modelling and geometry optimization of complex, polydisperse structures of biomacromolecules using modern PC software (HyperChem^®). Trapping and binding of atrazine in an organo-mineral complex is introduced as a first example of simulation experiments for soil processes at atomic level (nanochemistry). Future applications of semi-empirical calculations and molecular dynamics in pyrolysis studies are outlined.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

Analytical pyrolysis of re-circulated leachates: Towards an improved municipal waste treatment

The harmless removal of municipal solid waste (MSW) requires the biodegradation of organic matter to decrease the risk of gaseous emissions and leaching of contaminants. We studied the re-circulation of leachates from an aerobic treated MSW in a lysimeter and compared these results with a similar laboratory study using small-scale reactors. The reduction of total organic C and biological and chemical oxygen demands provided clear evidence for the biodegradation of organic matter in MSW after 12 months of leachate re-circulation. Curie-point pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and pyrolysis-field ionization mass spectrometry (Py-FIMS) revealed that the biodegradation was more efficient in the large-scale lysimeter than in the laboratory reactors. Different from the laboratory experiments, carbohydrates and N-containing compounds were decomposed almost completely after 2 months. Furthermore, temperature-resolved Py-FIMS showed that leachate re-circulation led to a higher thermal stability of the residual, non-decomposed organic matter. In summary, the two analytical pyrolysis methods proved that the re-circulation of leachates through MSW promoted organic matter biodegradation and offers an improved aerobic waste treatment technology.     

Characterization of leukemic and normal white blood cells by Curie-point pyrolysis—mass spectrometry: I. Numerical evaluation of the results of a pilot study

A preliminary study was undertaken to determine the usefulness of Curie-point pyrolysis—mass spectrometry followed by computer analysis for character diseased white blood cells. White blood cells from normal, infected, polyeyrhemic and leukemic persons were pyrolyzed in front of the electron impact ion source of a quadrupole mass spectrometer on 510°C and 355°C Curie-point filaments. Visual inspection and computer assisted pattern analysis using the ARTHUR program revealed marked differences in the spectra among the different diagnostic categories. The 510°C pyrolysis—mass spectra from leukemic patients were found to have increased intensity at mass peaks related to RNA and DNA as well as decreased intensity at mass peaks related to choline containing phospholipids when compared to controls. The spectra from the polyeyrhemic patient and the two infected patients were found to have intermediate intensities for these two characteristic series. Pyrolysis at 355°C was found to enhance the differences seen in the 510°C pyrolysis spectra. Though the number of patients is too small to allow rigorous statistical analysis of the observed differences, numerical analysis of the spectra appears to hint at the possibility of using Curie-point pyrolysis—mass spectrometry as a diagnostic tool in discriminating different types of leukemias. An investigation with many more samples is needed to confirm these preliminary findings.     

Pyrolysis–gas chromatography mass spectrometry and field ionization mass spectrometry of polyquinones

Low- and high-molecular mass thermal decomposition products of five polyquinones with different linking aromatic structures have been analyzed by pyrolysis–gas chromatography and by direct (in-source) pyrolysis–field ionization mass spectrometry. The quantity of carboxyl groups present in the polymer is obtained by the amounts of carbon dioxide found by pyrolysis–gas chromatography. Assuming a radical thermal decomposition mechanism the distribution of ketoacidic and quinonoid segments along the macromolecular ladder could be estimated from the high-molecular mass products measured by pyrolysis–field ionization mass spectrometry. A random distribution of the two different segments was found for polyquinones with biphenylene and dibenzofuran subunits, while a structure built up of blocks of two or more identical segments was obtained for polyquinones with dibenzothiophene and diphenylmethane subunits. At the same time the anomalous structural moieties in the polyquinone ladders are also clarified with the help of the identification of the unexpected pyroysis products. Oxidated and bis-dibenzothiophene and bis-diphenylmethane subunits were found. The observed temperature dependence for the appearances of the thermal degradation products indicates that condensation and elimination reactions are taking place under the described pyrolysis conditions. Condensation in the ketoacidic segments forming new quinonoid segments proved to be important in the polymer which was a 100% poly(ketoacid), but negligible in the polyquinones containing ketoacidic segments up to 60%.     

Review: derivatization in mass spectrometry--5. Specific derivatization of monofunctional compounds

The present paper is complementary to the foregoing reviews and describes some additional methods of the derivatization of particular functional groups mainly to enhance the structural information content of electron ionization and chemical ionization mass spectra. Derivatization approaches for the modification of unsaturated compounds, alcoholic, carboxylic, carbonyl, amine and other functional groups, are discussed. Derivatization for separation and quantitative determination of chiral enantiomeric compounds is also considered. Preliminary chemical and physicalchemical degradation for structure elucidation of high molecular weight compounds (biopolymers, synthetic polymers) is mentioned. Chemical aspects of derivatizations and characteristic mass spectral features of derivatives are described briefly. Some particular applications of chemical modification, in conjunction with mass spectral measurements for the analysis of various important bioorganic compounds and compounds in biological fluids, air, environmental etc., are considered.     

Mass spectrometric and factor discriminant analysis of complex organic matter from the bacterial culture environment of Bacteroides gingivalis

Curie point evaporation and pyrolysis mass spectrometry were applied to the analysis of samples from cultures of Bacteroides gingivalis, an anaerobic microorganism isolated from the dental sulcus of human patients. Gaseous metabolites were sampled on ferromagnetic wires with an absorbent coating of activated carbon. Smears of bacteria and media after growth were analysed on normal ferromagnetic wires. The mass spectra from analyses at the Curie-point temperatures of 358°C and 510°C were examined with a specially adapted factor discriminant analysis program based on ARTHUR. The bacteria were characterized mainly by their volatile fractious. Mass spectra of the media after growth reflected physiological differences between the strains. The absorbent wire technique proved useful for evaluation of gaseous metabolites. Curie-point evaporation and pyrolysis mass spectrometry was found to be especially useful for preliminary screening of samples of organic matter from the various compartments of the bacterial environment.     

Identification of some polymeric materials by low-temperature pyrolysis mass spectrometry

The application of low-temperature pyrolysis mass spectrometry to the identification of some commercial and synthetic polymers using a direct insertion probe and electron ionization has been studied. The polymers were analyzed directly in the solid probe of a mass spectrometer within the ion source at 70 eV electron impact. The quadrupole mass spectrometer, equipped with a gas chromatogram software and library of low molecular weight compounds, was used to characterize the polymers by measuring the chemical structure of the repeat units and the end groups, and to examine the thermal degradation pathways. The polymers investigated show different degradation pathways. Investigation of sequences and determination of composition of copolymers were studied. Total ion pyrogram and spectrum subtractions were used to separate and measure spectra of pyrolysis steps at distinctly different temperatures.     

A comparison of various pyrolysis experiments for the analysis of reference humic substances

The interpretation of the results of pyrolysis studies of humic substances is fraught with difficulties if only a single analytical technique is employed for substructure analyses. In this paper we have carried out investigations into humic substances utilising the additional information from the combination of gas chromatography/infrared spectroscopy and gas chromatography/mass spectrometry detection following Curie-point pyrolysis at five different temperatures. The results were compared to those obtained from conventional flash pyrolysis. The aim was to ensure the validation of the results of the compounds identified by at least one other spectroscopic technique. Some 30 substances have been positively identified by infrared spectroscopy, although their appearance is dependent on pyrolysis method and temperature. Most assignments were validated by mass spectrometry or the substance class confirmed.     

Derivatization of synthetic polymers in mass spectrometric studies

The review describes various derivatization approaches employed for the investigation of synthetic polymers by mild ionization mass spectrometry (fast atom and ion bombardment, matrix-assisted laser desorption/ionization, electrospray/ionization). The potentials of chemical methods for modification of end- and side-chain functional groups without the decomposition of molecules are demonstrated. Methods of the preliminary chemical degradation of polymer molecules for the investigation of their microstructure are considered. The possibilities of the chemical modification of polymer surfaces for the identification and quantitative determination of functionalized fragments are shown.     

裂解色谱法甲基化试剂碱性对多不饱和脂肪酸降解和异构化的影响

采用最佳比例裂解甲基化试剂,消除了强碱性甲基化试剂对油脂中多不饱和脂肪酸降解和异构化作用的影响。考察了不同比例甲基化试剂的碱性对多不饱和脂肪酸降解和异构化的程度。     

Pyrolysis/chemical ionization mass spectrometry of polymers

Pyrolysis/mass spectrometric studies have been made on polystyrene, poly(vinyl chloride), and poly(methyl methacrylate) with electron ionization (EI) and chemical ionization (CI) mass spectrometry and a variable temperature probe for direct insertion into the source of the mass spectrometer. Similar results obtained with EI and CI mass spectrometry are in agreement with previous experiments. Advantages of the simplification of spectra in the CI made, as well as the advantages of using both techniques for identification of pyrolysis products, are discussed.     

Comparison of EI and metastable atom bombardment ionization for the identification of polyurethane thermal degradation products

Polyurethanes are widely used in the manufacture of commercial products such as foams and paints. During combustion, these polymers can generate isocyanates, which induce adverse health effects. Polymer pyrolysis (Py) hyphenated with mass spectrometry (MS) allows the investigation of polymer thermal degradation over time/temperature. A diphenylmethanediisocyanate (MDI) polyurethane foam was analyzed with electron ionization (EI) and metastable atom bombardment (MAB) ionization at a pyrolysis temperature of 400 °C. The recently introduced MAB ionization source uses discrete energy stored in metastable atoms of gases to ionize the analytes. This characteristic allows modulation of the ionization energy by simply changing the ionization gas. The extensive fragmentation of molecular ions observed using EI 70 eV is not totally eliminated with EI 10 eV. However, only molecular ions are observed with MAB using N₂ as the ionization gas. Temperature gradients were used to separate the products generated during the thermal degradation of a 1,6-hexamethylenediisocyanate (HDI) polyurethane paint. The analysis of mass spectra was facilitated owing to a selective desorption of pyrolysis products. Furthermore, changing the MAB ionization gas allows elucidation of the structure of the pyrolysis products by controlling the extent of their fragmentation. During these experiments, isocyanic acid, methyleneisocyanate, ethyleneisocyanate, propylisocyanate and butylisocyanate were detected.     

Mass spectrometric behavior of levoglucosan under different ionization conditions and implications for studies of cellulose pyrolysis

Pyrolysis-mass spectrometric studies of cellulose indicate low abundances of levoglucosan in the product spectrum compared to the yield values determined in more conventional types of pyrolysis studies. To examine the reason for these conflicting observation, levoglucosan was examined under different ion source conditions and ionization modes to ascertain the relative contributions of thermal degradation and ionization fragmention to the low abundances of the levoglucosan molecular ion. Low-energy electron ionization using conventional sample volatilization and molecular-beam sampling is compared to chemical ionization using methane, isobutane, and ammonia as reagent gases, and to field ionization and desorption. The mass spectrometric fragmentation patterns under the various systems indicate that studies of cellulose pyrolysis underestimate the amount of levoglucosan formed due to ionization fragmentation and thermal rearrangement reactions in the ion source. Several peaks, including m/z 126 and 144, are dominated by the contribution from the fragmentation of levoglucosan.     

Pyrolysis mass spectrometry of terephthalate polyesters using negative ionization

The usual method of studying thermal degradation mechanisms of polymers in vacuo is to use electron ionization pyrolysis mass spectrometry. This can lead to mass spectral fragmentation from the 70 eV electrons used. Low energy electrons (10–15 eV) produce a low abundance of positive ions. However, if a molecule is prone to capture a thermal energy electron, then negative ions are produced in high abundance. This report describes the negative ion pyrolysis mass spectrometry of polyethylene terephthalate and polybutylene terephthalate.