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.

---

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.

     

Anionization of volatile molecules on the surface of electrolytic solutions exposed to high electric fields

The anionization of molecules supplied from the gas phase onto a negatively charged [Cl]^? or [NO₃]^? ion donating surface has been investigated. The charged surface was prepared by exposing an aqueous solution of LiCl (or LiNO₃) and polyethylene oxide to a high external field as is done in negative ion field desorption mass spectrometry. The ionization of some monosaccharides and adenosine by [Cl]^? and [NO₃]^? attachment and of some acids by proton abstraction is reported.     

Gas-phase ion chemistry of Glu/Met systems.

A combined chemical ionisation and tandem mass spectrometry (MS/MS) approach has been used for investigation of the gas-phase ion chemistry of systems containing the amino acids Glu and Met, and the dipeptides gamma-Glu-Met and Met-Glu. The metastable fragmentation of the protonated dimer, (Glu)2H(+), reveals an intracluster reaction leading to the elimination of the Glu residue. The main features of the ion-molecule reactions observed in the systems containing Glu and Glu + Met can be described in terms of sequential adduct formation. The results obtained for the thermal dehydration of Glu were used to rationalise the formation of the proton-bound structures (Glu-H2O...H(+)...(Glu-H2O) and (Glu-H2O)3-H(+). The adduct ions, [(Glu-H2O) + H + Glu](+) and [(Glu-H2O) + H + Met](+), and further association products were also observed. The results lead to a reconsideration of the structural aspects proposed earlier for these species in the sense that they suggest that the systems correspond to a mixture of isomeric covalent and proton-bound structures. The thermal effects on the decomposition of the neutral (gamma-Glu-Met) and its protonated form, (gamma-Glu-Met)H(+), at m/z 279 were investigated, and dramatic changes in the MI spectra of the m/z 279 ion with temperature were found. A mechanistic explanation for the observed evolution of higher mass ion peaks in the mass spectra is developed.     

Qualitative estimation of the contents of seeping water and estimation of the flow velocity in clay barriers by impedance spectroscopy

In this work, the flow of different kinds of liquids (differences in polarity, aromaticity, molecular size) through a layer of Friedland clay and the interaction of these liquids with the clay particles are investigated by means of electrical impedance measurements. The instationary flow can be described by data obtained from complex impedance plots. The gradient of the ohmic part of the impedance gives information about the strength of the driving force and the speed of flow/diffusion of the liquid through the clay. Different kinds of liquids lead to completely different impedance spectra. From time-dependent impedance measurements on a layer of defined thickness, information can be gained about the contents of the liquid flowing or diffusing through the clay. The impedance spectroscopy could be a powerful method for the development of an in situ monitoring system in waste disposal sites having clay barriers. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

A host-guest optical sensor for aliphatic amines based on lipophilic cyclodextrin

A host-guest optical sensor for the determination of aliphatic amines as exemplified by octylamine is proposed. It is based on the reversible fluorescence enhancement of heptakis(2,6-di-O-isobutyl)-β-cyclodextrin(DOB-β-CD) hosting tetraphenylporphyrin (TPP) immobilized in poly(vinyl chloride) (PVC) membrane by aliphatic amine extracted from aqueous phase into membrane phase. The optimum membrane contained 1.15 wt % TPP, 6.15 wt % DOB-β-CD as sensing reagent and other membrane materials. The fluorescence enhancement of the membrane resulted from the formation of a stable three-component complex among DOB-β-CD, TPP, and aliphatic amines. With the optimum conditions described, the fluorescence response of the sensor to octylamine shows a good correlation with the theoretically derived equation in the range 1.0 × 10^–6 to 8.0 × 10^–4 mol/L. The response characteristics including reversibility, response time, reproducibility and lifetime and selectivity of this optical device are also discussed in detail. This sensor has also been applied for the determination of octylamine in water samples containing interferents with satisfactory recovery. Received: 21 November 1999 / Revised: 10 January 2000 / Accepted: 15 January 2000     

In-source decay of hyperbranched polyesteramides in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Hyperbranched polyesteramides (DA2), prepared from hexahydrophthalic anhydride (D) and diisopropanolamine (A) have been characterized, by use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), field desorption (FD)-MS, and electrospray ionization (ESI)-MS. MALDI of polyesteramides produces protonated molecules. The spectra show a complex chemical composition distribution and end-group distribution which are mainly composed of two series of homologous oligomers DnA(n)+1 - mH2O and DnA(n) - mH2O, where m = 1-2. Signals from protonated molecules DnAn+1 and DnAn are almost absent in the MALDI spectrum, whereas these ions are responsible for the base peak of DnA(n)+1 - mH2O and DnA(n) - mH2O (m = 1-2) clusters in the ESI spectrum. The absence of -OH end-groups signals in the MALDI spectrum is due to a metastable decay of protonated DnA(n)+1 and DnAn ions in the ion source of the MALDI mass spectrometer prior to ion extraction. In-source decay results in the formation of protonated lower DnA(n)+1 - mH2O and DnA(n) - mH2O oligomers and their corresponding neutrals, leading to wrong conclusions concerning the relative end-group distribution as a function of the degree of polymerization and the chemical composition.     

Site of protonation of benzonitrile hydrogen interchange in the protonated species

The site of protonation of gaseous benzonitrile in reactions with H ₃ ⁺ , CH₃OH ₂ ⁺ , and CH₃CNH⁺ as protonating agents has been examined by using tandem mass spectrometry in combination with deuterium and ¹³C labeling. Metastable and collision-induced dissociation studies of C₆X₅CNX⁺ (X = H or D) show that proton attachment occurs on the CN group. The metastably decomposing C₆X₅CNX⁺ leads only to C₆X₅ ⁺ + XCN. This reaction proceeds via a mechanism involving H⁺ (D⁺) transfer from the CN group to the phenyl ring in which H/D exchange occurs. The efficiency of the CN-to-ring H+ (DC ) transfer increases in the order para < meta < ortho position. Evidence for incomplete H/D atom randomization in C₆X₅CNX⁺ prior to XCN loss has been obtained. Both processes, CN-to-ring H/D exchange and H/D exchange at the phenyl ring, are affected by the internal energy of the C₆X₅CNX⁺ ions. The results have been interpreted in terms of the internal energy distribution of the ions fragmenting within the metastable time window. Collision-induced dissociation of C₆X₅CNX⁺ causes the energy-enriched ions to decompose by direct bond cleavage into C₆X ₅ ⁺ + XNC.     

The monitoring of water and water vapour diffusion into clay by impedance spectroscopy

The diffusion of water vapour into Bayard montmorillonite and the diffusion/flow of liquid water into Friedland clay were examined with impedance spectroscopy as a first step towards the development of an impedance based sensor system for the in situ monitoring of clay-based barriers for waste containment. By impedance measurements the diffusion of water vapour into clay and the leaching of liquid water through clay barriers can be monitored time-dependently and parameters can be derived from the data that can be used to predict the speed of diffusion/flow through the barrier. Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999.     

Inclusion of thiamine diphosphate and S-adenosylmethionine at their chemically active sites

[structure: see text] Molecular clips functionalized by phosphonate or phosphate groups bind thiamine diphosphate (TPP) and S-adenosylmethionine (SAM) with high affinity in water; both sulfur-based cofactors transfer organic groups to biomolecules. For TPP, various analytical tools point toward a simultaneous insertion of both heterocyclic rings into the electron-rich clip cavity. Similarly, SAM is also embedded with its sulfonium moiety inside the receptor cavity. This paves the way for enzyme models and direct interference with enzymatic processes.