Two-dimensional capillary gas chromatography without intermediate trapping. Electron capture detector quantitation of an amino alcohol (KABI 2128) in serum after trifluoroacetylation

A two- dimensional gas chromatograph based on the Deans switching principle is described. The unit comprises two separate ovens, each containing a fused silica capillary column. The columns are joined in a specially designed manifold permitting heart cuts to be performed without significant decrease in efficiency. The switching speed and the retention time stability of the system made it possible to perform heart cuts of only a few seconds' duration. The system has been used under isothermal conditions for the determination of an amino alcohol (KABI 2128) in the low ng/ml range after trifluoroacetylation and with electron capture detection. A much shorter clean-up procedure could be used in combination with the two-dimensional gas chromatograph as compared to a method using a single glass capillary column.     

Amidinoethylation—a new reaction—IV : The amidinoethylation of alcohols: a facile synthesis of 3-alkoxy-N,N'-substituted-propanamidines

The amidinoethylation of alcohols takes place by the addition of sodium alkoxides 2 (R¹ = Me, Et) to the CC double bond of a variety of N,N'-substituted-propenamidines 1 (Method A). This illustrates the activation of the CC double bond by the conjugated amidine function and provides a new class of Michael acceptors for alcohols. However, this activation is poorer than with other nucleophiles or Michael acceptors. The amidinoethylation makes available 3-alkoxy-N,N'-substituted-amidines not easily accessible by other classical methods. However, it is demonstrated that the general N,N'-substituted-amidine synthesis via the nitrilium salts can also apply to nitrile compounds having an alkoxygroup present on the molecule (method B). Since the cyanoethylation of alcohols (4) is a very fast and facile reaction the method B is the preferred strategy for the synthesis of 3-alkoxy-N,N'-substituted-propanamidines 3.     

Dispersion phenomena in reactors for flow analysis

Both coiled open tubular reactors and packed-bed reactors can be used in flow analysis. Band broadening and pressure drop in these reactors are discussed. Theoretical analysis shows that packed-bed reactors are to be preferred. It is shown that for a given residence time and equal band-broadening values the pressure drop over a packed-bed reactor is lower than over a coiled open tubular reactor. Rules for optimal design are given for coiled tubular reactors and packed-bed reactors. The application of both reactors is shown for the spectrophotometric determination of phosphate with a vanadomolybdate reagent yielding a yellow colour.     

On [Na(POCl3)4]+ Complex Ion Formation: Conductivity,Raman, and NMR studies in the system phosphoryl chloride–sodium tetrachloro aluminate and related compounds

The system POCl₃–NaAlCl₄ was investigated by measuring the conductivity and the Raman and NMR spectra (²⁷Al, ²³Na and ³¹P) as a function of the mol fraction x of NaAlCl₄ in POCl₃. Additionally, Raman spectra of POCl₃ solutions of NaFeCl₄, LiAlCl₄, LiFeCl₄, and KAlCl₄ were recorded. In solutions containing Li⁺ or Na⁺ ions a liquid to solid (or jelly) phase transition was observed under certain conditions, dependent on salt concentration and temperature. Observed changes in the Raman spectra of the electrolyte solutions in comparison to the pure solvent POCl₃ demonstrate the existence of interactions. Clearly, the POCl₃ eigenfrequencies and hence the molecules are pertubed. The formation of [M(POCl₃)₄]⁺ complexes (M = Li, Na) can be deduced from the Raman measurements. NMR investigations support this conclusion. For assigning of Raman spectra, (Li⁺, K⁺) cation and ([FeCl₄]^?, [SbCl₆]^?) anion substitutions were employed.     

BRCA1 mutation screening using restriction endonuclease fingerprinting-single-strand conformation polymorphism in an automated capillary electrophoresis system

Efficient mutation scanning techniques are needed for the rapid detection of novel disease-associated mutations and rare-sequence variants of putative importance. The large size of the breast cancer 1 gene (BRCA1) and the many mutations found throughout its entire coding sequence make screening for mutations in this gene particularly challenging. We have developed a method for screening exon 11 of the BRCA1 gene based on restriction enzyme digestion of fluorescence-labeled polymerase chain reaction (PCR) products followed by single-strand conformation polymorphism (SSCP) using an automated capillary electrophoresis system, denoted capillary restriction endonuclease fingerprinting (REF)-SSCP electrophoresis. Using this strategy on a control set of samples, we were able to detect 17 of 18 known sequence alterations. The method was then applied to screen 73 Norwegian females with family histories of breast and/or ovarian cancer. A total of 172 sequence alterations were detected, including substitutions, insertions, and deletions. One novel substitution of unknown function was identified. Sequencing of all samples negative in the capillary REF-SSCP system gave no additional mutations confirming the high sensitivity of the described methodology. Capillary REF-SSCP electrophoresis appeared as a technically convenient technique, requiring amplification of fewer PCR fragments than traditional SSCP. The novel strategy allows high-throughput mutation scanning without radioactive labeling and polyacrylamide gel electrophoresis (PAGE).     

The solvent venting injection technique in capillary supercritical fluid chromatography

A solvent venting technique for injection of volumes up to 1 μl on 50 μm i.d. SFC columns has been compared to direct injection methods. The peak broadening and peak splitting observed with direct injection have been examined and found to be related to the starting pressure, the column temperature, and the sample solvent, in addition to the sample volume. The solvent venting technique removed peak splitting and improved the column efficiency. With a proper selection of experimental conditions, the sample recovery was 100%. The major part of the solvent was eluted in 15–20 s. Several applications have been demonstrated.     

A gas electron diffraction and ab initio quantum-mechanical investigation into the molecular structure of tricyclo-(3.1.002,4)-hexane

The structure of tricyclo-(3.1.00^2,4)exane has been determined by gas phase electron diffraction. The molecule has an inversion centre. The mean carbon—carbon bond length, averaged over both three- and four-membered rings is 1.508 A. A model with equal C-C bond lengths fits to the measured diffraction intensities. The four-membered ring is planar with valency angles of 90°, while the carbon atoms of the three-membered rings form isosceles triangles. Ab initio quantum mechanical calculations at the STO-3G level support this geometry. The valency angle CCC (between three- and four-membered rings) for the equilateral four-membered ring model has been found experimentally to be 109.9°. The average C-H bond distance (1.080 Å) is small as a result of increased s-character in these bonds in agreement with reported INDO—LMO calculations.     

Multimonomer partitioning in latex systems with moderately water-soluble monomers

Simple equations describing monomer partitioning in latices during intervals 2 and 3 in emulsion polymerization with any number of low to moderately water soluble monomers were derived from the extended Morton equation by making various assumptions. It appears that it is mainly the combinatorial entropy of mixing that governs the partitioning behavior, and that other contributions to the free energy of the monomers in the polymer particles are marginal. Experimental results with styrene, methyl methacrylate, and methyl acrylate confirm the validity of the assumptions. In interval 3 of emulsion polymerization the sum of all contributions to the free energy of the monomers in the particles other than the combinatorial entropy of mixing can be taken as a constant that is dependent only on the monomer composition in the particles and independent of the degree of swelling of the particles. The only parameters one needs to know to calculate the monomer concentrations in all phases with help of the derived equations, are the saturation concentrations of each monomer in the polymer particles, and the saturation concentrations of each monomer in the aqueous phase. © 1994 John Wiley & Sons, Inc.     

Reversed phase and normal phase liquid chromatography on poly(1-vinyl-2-pyrrolidone) or poly(1-vinylimidazole) bonded silica using γ-methacryloxypropyltrimethoxysilane as coupling agent. Stationary phases 23

Summary A method for preparing selective phases for reversed phase and normal phase liquid chromatography is described. Two different polymeric modified silica gel phases were prepared by simultaneously bonding with -methacryloxypropyltrimethoxysilane as coupling agent. Modification of these polymer phases was achieved by treatment with poly(1-vinyl-2-pyrrolidone) or poly(1-vinylimidazole). By eluting a number of standard mixtures containing polyaromatics and haloaromatics, the selectivity of each phase was evaluated. In reversed phase mode, the partition of sample components between mobile phase and stationary phase was found to be similar for polymer phases and -methacryloxypropylsilyl phase. In normal phase mode, only the poly(1-vinyl-2-pyrrolidone) phase or the poly(1-vinylimidazole) phase could interact electronically with aromatic nuclei.Part 22: see [1]     

Anomalous vibrational relaxation of a hot S*1 state of 3,4-benzpyrene in 2-methylpentane

Two anomalous emission bands in the fluorescence spectrum of 3,4-benzpyrene, dissolved in 2-methylpentane, have been studied as a function of temperature. These emissions originate from the second excited singlet state S₂, and from a vibrationally excited S₁ (S^*₁) respectively. From the temperature dependence of the relative yield and the decay time of the S^*₁ emission it can be concluded that the vibrational relaxation of this state is hampered. The rate constant for this relaxation process is smaller that 4 > 62;x 10⁷ sec^?1.