The ability of electrospray ionization mass spectrometry (ESI MS) to analyze heavy aromatic petroleum fractions using silver nitrate as a reagent compound to form characteristic adduct ions has been examined. The complexation of aromatic compounds containing long alkyl substituents with the silver ion leads to the formation of abundant adduct ions such as [M + Ag]+ and [2M + Ag]+. The concentration of the [2M + Ag]+ ions can be reduced by increasing the sampling cone voltage. Molecular ions and other adduct ions may also be formed depending on the structure of the aromatic molecule. Results obtained from the analysis of representative heavy petroleum fractions and vacuum residues by the Ag+ ESI MS method and conventional ionization methods were in good agreement. The current method extends the applicability of electrospray ionization to the analysis of neutral hydrocarbons in heavy aromatic petroleum fractions. It is simple and compatible with widely available LC/MS instrumentation. The extreme complexity of the Ag

A method has been developed for the reduction of the chemical formulas of compounds in complex mixtures from the isotopic peak distributions of high-resolution mass spectra. The method is based on the principle that the observed isotopic peak distribution of a mixture of compounds is a linear combination of the isotopic peak distributions of the individual compounds in the mixture. All possible chemical formulas that meet specific criteria (e.g., type and number of atoms in structure, limits of unsaturation, etc.) are enumerated, and theoretical isotopic peak distributions are generated for each formula. The relative amount of each formula is obtained from the accurately measured isotopic peak distribution and the calculated isotopic peak distributions of all candidate formulas. The formulas of compounds in simple spectra, where peak components are fully resolved, are rapidly determined by direct comparison of the calculated and experimental isotopic peak distributions. The singular value decomposition linear algebra method is used to determine the contributions of compounds in complex spectra containing unresolved peak components. The principles of the approach and typical application examples are presented. The method is most useful for the characterization of complex spectra containing partially resolved peaks and structures with multiisotopic elements.

Ensembles of sulfur capped, cadmium sulfide nanocrystals (CdS/S NCs) which exhibit photoluminescence (PL) emission line widths of 15−35 meV at 20 K have been obtained. These CdS/S NCs were synthesized using a new variant of the electrochemical/chemical (E/C) method:  Cadmium (Cdo) NCs were first electrodeposited from an aqueous Cd2+ plating solution using a train of 8−10 ms plating pulses separated by ≈1.0 s “mixing” segments at the open circuit potential. These Cdo nanoparticles were then oxidized to Cd(OH)2, and CdS/S NCs were obtained by exposure of Cd(OH)2 nanoparticles to H2S at 300 °C. Ensembles of 200 000−400 000 CdS/S NCs prepared using this “multipulse” technique exhibited PL emission lines narrower than 35 meV. CdS/S NCs were also synthesized using the same E/C method except that a single Cdo plating pulse was employed, and these CdS/S NCs exhibited PL emission line widths of 125−180 meV. TEM analysis of Cd(OH)2 precursor particles confirms that the narrower lines obtained using multipulse Cdo electrodeposition result from improved size monodispersity of the CdS core, which is attributed to the diffusional decoupling of Cdo nanoparticles during growth.

The coupling of gas chromatographic simulated distillation with mass spectrometry for the determination of the distillation profiles of crude oils is reported. The method provides the boiling point distributions of both weight and volume percent amounts. The weight percent distribution is obtained from the measured total ion current signal. The total ion current signal is converted to weight percent amount by calibration with a reference crude oil of a known distillation profile. Knowledge of the chemical composition of the crude oil across the boiling range permits the determination of the volume percent distribution. The long-term repeatability is equivalent to or better than the short-term repeatability of the currently available American Society for Testing and Materials (ASTM) gas chromatographic method for simulated distillation. Results obtained by the mass spectrometric method are in very good agreement with results obtained by conventional methods of physical distillation. The compositional information supplied by the method can be used to extensively characterize crude oils.