Analysis of partially resolved liquid chromatographic peaks using dynamic modeling with the kalman filter

Establishing a calibration model is an important part of any mathematical method for multi-component determination. Use of a calibration model based on single spectra is subject to error, because the model spectrum chosen may not be representative of the response over the full range of the calibration. Alternative calibration models require more time to establish calibration, an these may not be convenient for real-time determinations. A novel calibration method is reported for use with Kalman filters. The method, dynamic modeling, is based on the use of libraries of calibration spectra. The set of used to describe the model at any time is based on component concentrations, estimated for the multi-component mixture, as determined from the Kalman filter, so that several spectra can be used to best describe a varying response. Through application of the dynamic modelingt to simulated and real chromatograms, it is demonstrated that use of the method decreases estimation errors cause by model data mismatches, and that full benefit can be obtained from relatively small libraries.     

Reaction of γ-picoline N-oxide with ketenimines in the presence of organic acids: Preparation of α-acyloxyamides

A synthesis of a-acyloxyamides is described which utilizes the reaction of 7-picoline N-oxide and various organic acids with diphenylketene N-p-tolylimine.     

Determination of pentachlorophenol by negative ion chemical ionization with membrane introduction mass spectrometry

Pentachlorophenol (PCP) was used as a model compound to explore the potential of desorption chemical ionization (DCI) in the determination of polychlorinated pesticides using membrane introduction mass spectrometry (MIMS). A direct insertion membrane probe was modified so that a chemical ionization plasma could be established at the membrane surface. Using selected ion monitoring (SIM) in a tandem triple quadrupole mass spectrometer with isobutane chemical ionization (CI), the PCP detection limit under positive chemical ionization is 20 ppb whereas negative CI gives detection limits in the low ppb range. This performance is achieved without any pre-treatment or derivatization of the sample. Negative ion CI gives a signal that is linear over a concentration range of 2-1000 ppb. Comparison of data obtained with low ppb samples of 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol and pentachlorophenol suggests that the sensitivity of this analytical procedure increases with increase in the number of electronegative substituents in the molecule.     

Investigation of the asymmetric ionic Diels-Alder reaction for the synthesis of cis-decalins

The ionic Diels-Alder reaction, whereby an alpha,beta-unsaturated acetal in combination with a Lewis or Bronsted acid forms an equilibrium concentration of an activated dienophile, has been developed to provide an enantioselective synthesis of cis-decalins. Cyclohex-2-enone type chiral acetals of (2R,3R)-butane-2,3-diol have been screened against Lewis and Br?nsted acids with a variety of dienes and are efficient for the synthesis of a limited subset of cis-decalin structures. Diastereoselectivities of 73% and 82% have been found for the asymmetric ionic Diels-Alder reaction between the chiral acetal derivatives of cyclohex-2-enone (6) and 2-methylcyclohex-2-enone (18) with 2,3-dimethyl-1,3-butadiene (7). Terminal substituents on the diene partner in general render the system unreactive. However a synthetically useful cis-decalin 31, derived from the reaction of 2-methylcyclohex-2-enone and Z-3-t-butyldimethyl-silyloxypenta-1,3-diene has been prepared in enantiomerically pure form in 74% isolated yield using this asymmetric ionic Diels-Alder protocol.     

Aggregate, Polymer and Cluster Formation from Metal-Imino Carboxylate Complexes

Reaction of tris-(2-aminoethyl)amine (tren) andthe sodium salt of an -ketocarboxylic acid, typically sodium pyruvate, affordsin the presence of a lanthanide ion aseries of complexes and aggregates includingmononuclear, cyclic tetranuclear and polymerspecies of [L¹]^3- ([L¹]^3-=N[CH₂CH₂N=C(CH₃)COO^-]³).The aggregation of these and related d-block elementcomplexes with Na⁺ ions leadsto the formation of polymeric materials, and thefactors influencing the formation and controlof these various aggregation states are discussed.Metal cations also template the aggregationof the fragment [Ni(L²)] ([L²]^2- =CH₂[CH₂N = C(CH₃)COO^-]₂)to give, in high yield, the polynuclearaggregates {[Ni(L²)]₆M}^x+(M = Nd, Pr, Ce, La, x = 3; M = Sr, Ba, x = 2). The structures of{[Ni(L²)]₆M}^x+ show aninterstitial twelve co-ordinate, icosahedralcation M^x+ encapsulated by six [Ni(L²)]fragments. In the presence ofNa⁺, aggregation of [Ni(L²)] fragments affords {[Ni(L²)]₉Na₄(H₂O)(MeOH)(ClO₄)}³⁺ thestructure of whichshows four Na⁺ ions templating the formation ofa distorted tricapped trigonal prismatic[Ni(L²)]₉ cage. Thus, control overconstruction of various polynuclear cages viaself-assembly at octahedral junctions can beachieved using main group, transition metaland lanthanide ion templates.     

Chlorine nitrate photolysis by a new technique: very low pressure photolysis

Very low pressure photolysis (VLPØ) of chlorine nitrate was performed in a quartz Knudsen cell. The light source was a 2500 W high-pressure xenon lamp, and a modulated molecular-beam mass spectrometer was used to monitor the concentration of ClONO₂ and photolysis products. Because of the low pressures used (? 10^?3 torr) and the short residence time in the cell (≈1 s), secondary reactions were unimportant and the primary products could be directly identified. The primary photolysis products (λ ≈ 2700 Å) are atomic chlorine and NO₃ free radical. Chlorine atoms were identified both by the appearance of Cl₂ (wall recombination product; the walls were not poisoned) and by HCl produced when C₂H₆ was added to the cell. Nitrate free radical was directly identified as a mass peak at m/e = 62, as well as by chemical titration with nitric oxide: NO₃ + NO → 2NO₂. It was verified by direct tests that the peak at m/e = 62 did not arise from possible HNO₃ contamination or from N₂O₅, a possible secondary product. This titration reaction was used to measure quantitatively a lower limit to the primary quantum yield, φ ? 0.5 ± 0.3. This represents a lower limit because of the unknown extent of the secondary photolysis of NO₃ under our conditions. We believe this to be the first observation using mass spectrometry of the NO₃ free radical. The quantum yield for atomic chlorine is φ = 1.0 ± 0.2. N₂O was used to test for O(¹D) according to the reaction, O(¹D) + N₂O → products; none was observed. Triplet oxygen, O(³P) was observed to the extent of ≈ 10% by the reaction O(³P) + NO₂ → NO + O₂, but this yield can also be due to the photolysis of NO₃ free radical produced in the primary step. We conclude that the predominant reaction pathway is

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