Procedures for the enhancement of selectivity in liquid phase chemiluminescence detection

An overview of liquid phase chemiluminescence (CL) processes is presented and the potential for CL detection in liquid chromatography (LC) is discussed, with particular reference to the luminol and peroxyoxalate reactions. Post column ion displacement from a solid phase reagent [a cation exchange resin in the copper(II) form] followed by catalysis of the luminol reaction is used for the quantification of mixtures of weak acids after separation by ion-exclusion chromatography. Polyaromatic hydrocarbons (PAHs) released during the combustion of biomass fuels are separated by reversed-phase chromatography and quantified by their sensitizing effect on the peroxyoxalate reaction. This procedure is also used for the determination of carboxylic acids in non-aqueous media after selective pre-column derivatization with a fluorescent label (9-anthracenemethanol).     

13C NMR coupling constants in delocalized organo-alkali metal compounds. Models of polymerization systems

2,5-Diphenyl-2,5-dipotassiohexane, 2-lithio-4,4-dimethyl-2-phenylpentane, and 1-lithio-2,5,5-trimethylhexene-2 have been prepared, all labelled with¹³C in the position adjacent to the alkali metal atom. The¹³C NMR spectra of these compounds have been measured and the¹³CC coupling constants found for the charged atom. The first two compounds have coupling constants consistent with an sp² hybridized C_α, with relatively little effect of the charge on the coupling constant. The third compound, when dissolved in either THF or benzene, gave much smaller coupling constants, which are more difficult to interpret.     

Ferromagnetic spin alignment in head-to-tail coupled oligo(1, 4-phenyleneethynylene)s and Oligo(1,4-phenylenevinylene)s bearing pendant p-phenylenediamine radical cations

The intramolecular and long-range ferromagnetic coupling between p-phenylenediamine radical cations in head-to-tail coupled oligo(1, 4-phenyleneethynylene)s and oligo(1,4-phenylenvinylene)s between neighbors and next-nearest neighbors is described. UV/vis/near-IR experiments show that the radical cations are localized in the pendant p-phenylenediamine units of the conjugated oligomers. The ESR spectra of these oligo(1,4-phenyleneethynylene) and oligo(1, 4-phenylenvinylene) di(radical cation)s are consistent with those of a triplet state. A linear behavior is observed for the doubly integrated ESR intensity of the DeltaM(s) = +/-1 and DeltaM(s) = +/-2 signals with the inverse temperature (I approximately 1/T), consistent with Curie's law. This behavior indicates a triplet ground-state diradical with a large triplet-singlet energy gap or possibly a degeneracy of singlet and triplet states.     

The use of microemulsions in flow injection analysis: Spectrofluorimetric determination of primary amines

The use of microemulsion in flow-injection systems is considered, with particular reference to the determination of C₆C₁₀ primary amines by derivatization with o-phthal-aldehyde and 2-mercaptoethanol. Microemulsions provide an ideal interface for reactions between a water-soluble reagent and a non-aqueous sample. The effect of reaction conditions (R value, droplet concentration, pH and flow rate) on the fluorescence signal is discussed and calibration data for three primary alkylamines are given.     

Electrochemical biosensors in the assay of antibiotics

Certain antibiotics such as amphotericin B and nystatin are known to interact selectively with cholesterol in bilayer lipid membranes, resulting in changes in the transmembrane electrical properties. The possibilities for use of this effect in selective trace organic analysis are demonstrated by experiments performed with a simple electrical circuit incorporating a conventional research pH meter. Transmembrane resistance-based responses correlate with aqueous antibiotic concentration and are rapid and reversible. The limit of detection of the technique is approximately 10^-9 M of stimulant.     

A study of coated-wire potassium-valinomycin and sodium-monensin ion-sensing systems by use of a conventional field-effect transistor

Polymer films containing a sodium or potassium ion-selective exchanger were coated onto platinum wire and incorporated into a potentiometric arrangement. Comparative results obtained by utilizing different measuring devices, one a conventional pH-meter and the other a field-effect transistor (FET) in series with an electrometer, are discussed. The linear range of either system is comparable with that of other electrochemical techniques. Possible applications of such a device are described.