Hans-Rolf Schulten

Field desorption mass spectrometry of natural products—I: Steroid- and triterpene saponins

Field desorption mass spectra of underivatized oligoglycosides of spirostanol and its congeners and of hederagenin revealed the molecular weight and structural information. The basic predominance of the formation of stable ions of highly polar natural products (with 5–17 free OH functions) is clearly demonstrated. After the extraction and purification procedure from plant material the samples contained inorganic salts in concentrations between 0.01 and 0.1%. These salt impurities, mostly alkali halides, strongly promoted the attachment of alkali cations to the intact molecules and their fragments. The ions produced gave analytical information not only for the confirmation of the molecular weight but also for the identity of the aglycone and, to some extent, for the sequence of the sugars in the oligoglycosides. All spectra were recorded on photoplates at a resolution of better than 15000 and enabled the evaluation of the elemental composition of the ions generated. The drawbacks and merits of integrating ion recording using the photoplate for FD investigations of highly polar substances are discussed.

Coal tar analysis by mass spectrometry — a comparison of methods

Abstract The analyses of coal-derived hydropyrolysis tar fractions by a variety of mass spectrometric methods are compared, to identify common ground in the analytical results. Methods compared include high performance liquid chromatography interfaced with mass spectrometry (m.s.) by moving belts and a particle beam, low and high voltage solids injection probe to 350 °C, desorption chemical ionization (d.c.i.) using isobutane, field ionization (f.i.), field desorption (f.d.) and fast atom bombardment (f.a.b.). Aromatic and asphaltenic fractions of two hydropyrolysis tars are compared. The tars were produced at relatively low temperatures under gentle conditions. The results show that for the aromatics, the probe methods, solids injection, d.c.i. and f.i. all show similar masses and mass ranges for the aromatics ; differences reflect differences in sensitivity and conditions of ionization. F.d. involves ionization at a surface followed by desorption of the ion, and signals of different components are seen. For the asphaltenes, some components, mainly multi-hydroxyl derivatives of aromatics, are identified by probe methods (solids injection and f.i.m.s.) but f.d. again detects different material. F.a.b. produces evidence of the structure of the molecules detected — small aromatic and heterocyclic groups loosely linked together, rather than the very large, condensed aromatic structures expected of a high temperature coal tar. Further definition of the molecular structure of asphaltenes requires an improvement in separation techniques.

Field desorption mass spectrometry of natural products—II1: Physiologically active pennogenin—and hederagenin-glycosides

Abstract Field desorption mass spectra of underivatized saponios, naturel oligoglycosides of physiological activity, showed intense ions formed by attachment of alkali cations to the neutral molecule and to structurally highly significant subunits. This cationization was generated by small amounts of alkali salts which were present in samples after isolation from biological material. When the mass spectre were produced by laser-supported desorption and were recorded at high resolution on vapor-deposited AgBr plates unambiguous determination of the molecular weghts (in the mass range from 700 to 1400) was performed. Moreover, ions formed by direct bond cleavages in the oligosaccharide moiety of the natural saponins clearly gave information about the sequence of the sugar units in the molecule and their individual chemical structures. The formation of these fragments in FD-MS is discussed in relation to the well established mechanism of glycosidic bond cleavage by acidic solvolysis. In principle this comparison showed the usefulness of this approach for the interpretation of FD mass spectra of substances containing heteroatom linkages e.g., glycosides, esters, amides, imines, mercaptans, etc.

Pyrolysis-field desorption mass spectrometry of coal

Abstract Field desorption mass spectrometry of pyrolysis products of coal allows fast fingerprinting of organic and inorganic products. Two main groups of organic species are found: (1) from mass 200 to 800 represents a complex mixture of aliphatic, olefinic, aromatic and heterocyclic guest molecules which are volatilized from coal at low temperatures; (2) obtained at higher temperatures, from mass 800 to >3000 can be assigned to the host structure of the coal and gives a regular, highly reproducible, breakdown pattern. Selected, isolated macerals such as vitrinite, exinite and inertinite are clearly distinguishable by their characteristic peak sequence and intensity envelope in the high mass range. From this knowledge, an estimate of the maceral composition of the investigated bituminous coal is obtained. Using time-resolved pyrolysis consecutively with the generation of low- and high-mass pyrolysates, inorganic salts can be identified and multi-element analysis of metals achieved in the same sample. The time taken for a complete analysis is ≈30 min.

Quantitative Felddesorptions-Massenspektrometrie VI

SummaryThe combination of a mass spectrometer with a time averaging computer is utilized for quantitative recording of field desorption ion currents. It is demonstrated that the relative intensities of [M]+, [M + H]+ and [M + Na]+ ion groups can be determined with an average error of 0.4% by intergrating electric recording of a large number of cyclic scans. Applications of this direct isotope analysis to the identification of compounds as well as to the determination of the label content of stable isotope labelled substances are introduced and discussed.ZusammenfassungDie Kombination Massenspektrometer-Vielkanalanalysator wird zur quantitativen Aufnahme von Felddesorptions-Ionenströmen benutzt. Es wird gezeigt, daß die relativen Intensitäten von [M]+, [M + H]+ und [M + Na]+-Ionengruppen mit integrierender elektrischer Registrierung über eine Vielzahl von cyclischen Scans mit einem mittleren Fehler von 0,4% gemessen werden können. Anwendungen dieser direkten Isotopenanalyse zur Identifizierung von Verbindungen sowie zur Bestimmung des Markierungsgrades von stabilisotopen-markierten Substanzen werden vorgestellt und diskutiert.

Time- and temperature-resolved field ionization mass spectrometry of coals and their extracts

Abstract Field ionization mass spectra of three coals (85, 78 and 72 wt% C, daf) and their pyridine extracts were obtained between 50 and 500 °C using the direct introduction system with a linear heating rate of 1.0 °Cs −1 . Scan numbers and temperatures were plotted versus the total ion current (thermograms) and selected ion intensities (profiles). All spectra of coals and extracts showed that the volatile material gives almost exclusively molecular ions with f.i.m.s. and mainly comprises substances in the range 200 to 800 daltons. The spectra of a coal and its respective extract show striking similarity. The yields of volatiles from the coals ranged from 11 to 30 wt%, daf. The thermograms of extracts were clearly shifted towards lower temperatures compared with those of the coals. The profiles of selected ions show at low and high mass resolution that the same substance may be volatilized over the whole heating range from 50 to 500 °C, indicating that the volatilized material had been clathrated in the coals and that thermally induced diffusion preceded its evaporation. The diffusion of molecules occluded in the pore structure or chemical species generated by thermal fragmentation is assumed to occur at the initial step of all technical processes such as liquefaction, carbonization, combustion and gasification. In general, the behaviour of a coal is expected to depend strongly upon the amount of material capable of diffusion, which is characteristic for the processes of coal utilization at a given heating rate. Time-/temperature-resolved field ionization mass spectrometry of coal offers a unique means of fast and reliable monitoring of such characteristics.

Field ionization mass spectrometry of organic compounds

Abstract A review is given on field ionization mass spectrometry of organic compounds. Four different subjects are treated and illustrated by means of significant examples: Experimental techniques, surface reactions induced by high electric fields, the kinetics of fast unimolecular decompositions of ions, and qualitative and quantitative analyses of organic compounds by field desorption methods.

Qualitative and quantitative trace-metal analysis in physiological fluids of multiple sclerosis patients by field desorption mass spectrometry

Abstract Trace metals such as aluminium, barium, cesium, chromium, cobalt, copper, and rubidium have been identified in microlitre samples of urine, serum, and cerebrospinal fluid of patients suffering from multiple selerosis. Quantitative determinations of rubidium in the urine of seven patients were performed and gave an average concentration of 1.20 ± 0.02 mg I−1 (14.0 μmol I−1). As a control, the rubidium levels in the urine of twelve healthy volunteers were determined, averaged and found to be approximately twice as high, namely 2.52 ± 0.07 mg I−1 (29.5 μmol I−1). The time-dependence for the excretion of rubidium in the urine from one patient was established for a period of 24 h and correlated with the renal function. Further, initial values for the concentration of Rb+ ions in serum (2.2 μmol I−1) and cerebrospinal fluid (0.15 μmol I−1) could be established. The novel method for trace analysis of metals in microlitre samples of human material using stable-isotope dilution and field desorption mass spectrometry allows direct, fast and reliable estimation of nanogram to picogram amounts of metals. The typical analysis time is 15–20 min and the precision and accuracy obtained within a few tenths of a percent. The sensitivity of the technique for rubidium is extraordinarily high, between 1.1 and 9 × 10−7 C μg−1. The detection limit for Rb+ ions lies below 10−15 g. A newly developed technique using electrolytical deposition of trace metals such as chromium, manganese, iron, nickel, copper, gallium, silver, gold, thallium and uranium on the emitter surface from a complex, biological matrix showed improvements in sensitivity by a factor of approximately 20.

Basic steroid saponins from aerial parts of Fritillaria Thunbergii

Abstract From the aerial parts of Fritillaria thunbergii, three glycosidal Solanum alkaloids (basic steroid saponins) were isolated together with minor

An eight-ring phlorotannin from the brown alga Himanthalia elongata

Abstract From an acetylated fraction of Himanthalia elongata extract, an eight-ring phenolacetate was isolated and its structure elucidated with the aid of field desorption mass spectrometry and other spectroscopic methods.