Quantitative field desorption mass spectrometry

Summary The first application of field desorption mass spectrometry (FD-MS) to the determination of the label content and the statistical isotopic distribution in radiolabelled substances is reported. The total amount of tritium in steroids such as [6,7-³H]estradiol and [2,4,6,7-³H]estradiol was estimated. Data are easily derived from the field desorption mass spectra which allow the calculation of the distribution of the radioisotope in the investigated biochemicals with an accuracy below 1%.The two main advantages of the technique reported here are the small sample consumption in the nanogram range (which is particularly important for radiolabelled chemicals of high specific activity) and the highmolecular ion abundance of polar substances (the thermal and mass spectrometric fragmentation is almost completely missing) which give optimal information about the isotopic composition of the intact molecule. In addition, the short analysis time by FD-MS of approximately 30 min for the complete isotopic determination and the good precision of a few tenths of a percent underline the utility of this new method for the assay of radioisotopes in compounds of biochemical, medical and environmental interest.For part XVIII see reference [1]     

Direct isotope determination of isotopically labelled lipids by field desorption mass spectrometry

Summary Lipids labelled with deuterium or carbon-14 have been investigated by field desorption mass spectrometry for determination of their degree of labelling. This application is demonstrated for free fatty acids, cholesterol, cholesteryl esters, triglycerides, and l--phosphatidylcholines. Comparison of the molecular ion groups of the non-labelled and of the labelled compounds enables a fast and reliable determination of the degree of labelling. For multiply labelled compounds the label distribution is also obtained from the molecular ion group. In addition, for cholesteryl esters and for phosphatidylcholines structurally significant fragment ions provide information about the position of the label. Several hundred nanograms of the compound are typically required for a single analysis with a relative standard error of 0.5–2 % in the value calculated for atom % hydrogen-2 or for the specific carbon-14 activity.

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Direkte Isotopenbestimmung von isotopenmarkierten Lipiden mit Hilfe der Felddesorptions-Massenspektrometrie

Zusammenfassung Der Markierungsgrad von isotopenmarkierten Lipiden, markiert mit Deuterium oder Kohlenstoff-14, wurde mit der Felddesorptions-Massenspektrometrie bestimmt. Diese Anwendung wird demonstriert für freie Fettsäuren, Cholesterin, Cholesterinester, Triglyceride und l--Phosphatidylcholine. Der Vergleich der Molekülionengruppen der unmarkierten Verbindungen mit denen der markierten Verbindungen gestattet eine schnelle und zuverlässige Bestimmung des Markierungsgrades als Atom% Deuterium oder als spezifische Radioaktivität und zeigt bei Mehrfachmarkierung zusätzlich die Verteilung der Markierung. Darüber hinaus geben struktursignifikante Fragmentionen bei Cholesterinestern und Phosphatidylcholinen Hinweise auf die Position der Markierung. Typischerweise werden einige hundert Nanogramm dieser Lipide für eine Analyse mit einer relativen Standardabweichung von 0,5–2% im errechneten Markierungsgrad benötigt.

     

On the determination of desorption temperatures in field desorption mass spectrometry

The field desorption temperatures of some compounds are determined by indirect heating of the emitters. The temperatures thus obtained are lower, compared with those determined by other authors. The reasons for this deviation are discussed.     

High resolution field desorption mass spectrometry

Summary The first complete mass spectra of unprotected dinucleotides e.g. TpT, GpU, ApC, and CpA are reported. In all cases these spectra make possible the determination of the molecular weight. In addition structural information about the building blocks of the dinucleotides can be obtained.

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Hochauflösungs-Felddesorptions-MassenspektrometrieIV. Dinucleotide

Zusammenfassung Die ersten vollständigen Massenspektren von underivatisierten Dinucleotiden wie TpT, GpU, ApC und CpA werden beschrieben. In allen Fällen ermöglicht die Felddesorptions-Massenspektrometrie die Bestimmung des Molekulargewichtes. Zusätzlich liefert die Methode wichtige Strukturinformation über die Bausteine der Dinucleotide.

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Abbreviations MS mass spectrometry, mass spectrum - TMS trimethylsilyl - FD field desorption - M molecular ion - HR high resolution - e.h.c. emitter heating current - BAT best anode temperature Part III: Schulten, H.-R., Kümmler, D.: Sulphonic acids and sulphonates. Z. Anal. Chem.278, 13 (1976).     

Laser assisted field desorption mass spectrometry

The method of indirectly heating the emitter wire with a laser is introduced into field desorption mass spectrometry. Use of this method results in improved sensitivity, more reliable high resolution performance, and extension of field desorption mass spectrometry to the area of high temperature chemistry.     

Accelerated reactions in field desorption mass spectrometry

Field desorption mass spectrometry under ambient conditions is used to study solution‐phase organic reactions in micro‐volumes. Reagent solution is transferred onto the microdendrites of the field emitter, and reaction products are examined online by mass spectrometry. Three reactions, hydrazone formation by phenyl hydrazine and indoline‐2,3‐dione, the Katritzky reaction between a pyrylium salt and anisidine, and the Hantzsch synthesis of 1,4‐dihydropyridine, were investigated, and reaction acceleration was observed to different extents. The increase in rate relative to the corresponding bulk reactions is attributed to solvent evaporation (simple concentration effect) and to the increase of surface‐to‐volume ratio (enhanced interfacial reactions). A distinguishing feature of this method of reaction acceleration, relative to that based on nano electrospray ionization, is the observation of radical cations and the formation of radical cation products. The study also breaks new ground in using field emitters at atmospheric pressure.     

On field desorption mass spectrometry of salts

The types of ion occurring in the field desorption mass spectra of inorganic and organic salts are discussed. In contrast to general experience with field desorption mass spectrometry molecular ions are either absent or of low intensity. The energetically and kindetically favoured process of cluster formation, however, generates ions from which the molecular structure can be easily derved. Some specific aspects for the analyses of salts by field desrption mass spectrometry are outlined.     

High resolution field desorption mass spectrometry III

Summary For the examples shown in this study in all cases FD-MS allowed the determination of the molecular weight and the elemental composition. Some of the characteristic features of sulphonic acids and sulphonates in field desorption are described. The method is obviously very well suited for the analysis of non-volatile technical products (e.g. dyestuffs, detergents, drugs). Information about the molecular weight, the structure, organic and inorganic by-products and impurities is obtained and thus the applicability of FD-MS to the analysis of actual analytical problems is clearly demonstrated.

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Hochauflösungs-Felddesorptions-MassenspektrometrieIII. Sulfonsäuren und Sulfonate

Zusammenfassung Für die untersuchten Verbindungen ergab FD-MS in allen Fällen das Molekulargewicht und die Bruttoformel. Einige der charakteristischen Merkmale von Sulfonsäuren und Sulfonaten bei der Felddesorption werden beschrieben. Die Methode ist für die Analyse nichtflüchtiger, technischer Produkte (z. B. Farbstoffe, Detergentien, Pharmazeutica) sehr gut geeignet. Sie liefert Informationen über das Molekulargewicht, die Struktur, organische und anorganische Nebenprodukte und Verunreinigungen.

Part II.: Schulten, H.-R., Games, D. E.: Glycosides. Biomed. Mass Spectrom. 1, 120 (1974).     

Matrix effects in negative-ion field desorption mass spectrometry

The negative ion mode of field desorption mass spectrometry is matrix dependent. The matrix is used to facilitate the desolvation of ions at field strengths below the onset of field induced electron detachment. The role of the matrix in the desolvation mechanism for negative ions is briefly described and the main properties of a matrix solution, such as viscosity, solubility for complex salts and acids, and adhesion to the emitter surface, on the ion formation are discussed. The application of matrix mixtures with strong adhesion to the emitter surface even at elevated temperatures and high field strengths are considered to be important for the further improvement of this ionization method.     

Analysis of carotenoids by field desorption mass spectrometry

The mass spectra of a variety of authentic carotenoids covering a range of structural types have been studied using the field desorption technique. All the compounds examined show the molecular ion as the base peak, even where this ion is of very low intensity in the electron-impact spectra. Little fragmentation is observed, but thermal decomposition can be induced in certain cases by using higher emitter currents. Application to a simple mixture of authentic compounds and a more complex mixture of sedimentary origin shows the potential of the method in the rapid qualitative screening of carotenoids in crude extracts.     

Negative ion field desorption mass spectrometry of anionic surfactants

Summary Negative ion field desorption mass spectrometry has been applied to detergents containing anionic surfactants. The mass spectra demonstrate a high selectivity for the detection of the sulphonates (concentration limit 10^–5 mol/l). The spectra do not contain fragment ions nor ionization products from non-ionic components of the mixture.

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Felddesorptions-Massenspektrometrie negativer Ionen zur Analyse von anionischen Tensiden

Zusammenfassung Die Felddesorptions-Massenspektrometrie negativer Ionen wurde zur direkten Mischungsanalyse von Detergentien, die anionaktive Tenside enthalten, angewendet. Die Massenspektren zeigen eine hohe Selektivität der Methode für den Nachweis der Sulfonate (Konzentrationsgrenze 10^–5 mol/l). Die Spektren enthalten weder Fragmentionen noch Ionisierungsprodukte nichtionischer Komponenten der Mischung.

     

Evaluation of field desorption mass spectrometry for the analysis of polyethylene

Field desorption mass spectrometry (FD-MS) has been evaluated for the analysis of low molecular weight polyethylene by using samples in the molecular weight range 600–2000 u as determined by gel permeation chromatography. The repeat units and end groups were characterized by FD-MS, but it was demonstrated that accurate molecular weight distribution data cannot be obtained for polyethylene by FD-MS because there is mass discrimination against the higher molecular weight polymers.     

Matrix-assisted laser desorption ionization mass spectrometry for identification of shrimp

Matrix-assisted laser desorption ionization (MALDI) time of flight mass spectrometry was used to identify shrimp at the species level using commercial mass spectral fingerprint matching software (Bruker Biotyper). In the first step, a mass spectrum reference database was constructed from the analysis of six commercially important shrimp species: Litopenaeus setiferus, Farfantepenaeus aztecus, Sicyonia brevirostris, Pleoticus robustus, Pandalopsis dispar and Pandalus platyceros. This step required a desalting procedure for optimum performance. In the second step, the reference database was tested using 74 unknown shrimp samples from these six species. Correct identification was achieved for 72 of 74 samples (97%): 72 samples were identified at the species level and 2 samples were identified at the genus level using the manufacturer's log score specifications. The MALDI fingerprinting method for the identification of shrimp species was found to be reproducible and accurate with rapid analysis.     

The identification of chlorophenoxyphenols in soil and water samples by solvent extraction and field desorption mass spectrometry

The identification of microgram amounts of chlorophenoxyphenols is shown to be possible by solvent extraction and subsequent field desorption mass spectrometry (f.d.m.s.). Although the extraction step is performed under acidic conditions, the presence of humic and fulvic materials did not interfere in the interpretation of the f.d.m.s. spectra of soil and water samples contaminated with chlorophenoxyphenols. The pattern of oligomeric series and chlorine isotope clusters characteristic of the chlorophenoxyphenols as well as the soft-ionization properties (minimal fragmentation) of f.d.m.s. make this procedure well-suited for use in the rapid screening of liquid samples for the chlorophenoxyphenols.     

Methyl transfer in field desorption mass spectrometry of ammonioalkanecarboxylate hydrochloride salts

Intramolecular methyl transfer has been observed previously in pyrolysis electron impact mass spectra of complex ammonioalkanecarboxylates. We present here field desorption mass spectra results of more simple N,N,N-trimethylammoniocarboxylate hydrochloride salts and their N,N,N-perdeuterotrimethylammonium analogs in which we observe methyl transfer. We demonstrate that mechanisms for this and other fragmentation and rearrangement processes are dependent on anode heating current. Addition of the protonating agent p-toluenesulfonic acid suppresses most ions except the protonated molecular ion.     

Detection of C-nitroso dimer formation by field desorption mass spectrometry

Field desorption mass spectrometry is shown to be a useful technique for observing dimer formation in C-nitroso compounds. Mixed dimer formation (RN₂O₂R′) is shown to be readily observed by field desorption mass spectrometry.