The rotational (TR) and vibrational (Tv) temperatures of N2 molecules were measured in a high-pressure cylindrical dielectric barrier discharge (C-DBD) source in Ne with trace amounts (0.02 %) of N2 and dry air excited by radio-frequency (rf) power. Both TR and Tv of the N2 molecules in the C 3 Πu state were determined from an emission spectroscopic analysis the 2 nd positive system (C 3 Πu −→ B 3 Πg). Gas temperatures were inferred from the measured rotational temperatures. As a function of pressure, the rotational temperature is essentially constant at about 360 K in the range from 200 Torr to 600 Torr (at 30 W rf power) and increases slightly with increasing rf power at constant pressure. As one would expect, vibrational temperature measurements revealed significantly higher temperatures. The vibrational temperature decreases with pressure from 3030 K at 200 Torr to 2270 K at 600 Torr (at 30 W rf power). As a function of rf power, the vibrational temperature increases from 2520 K at 20 W to 2940 K at 60 W (at 400 Torr). Both TR and Tv also show a dependence on the excitation frequency at the two frequencies that we studied, 400 kHz and 13.56 MHz. Adding trace amounts of air instead of N2 to the Ne in the discharge resulted in higher TR and Tv values and in a different pressure dependence of the rotational and vibrational temperatures.

No abstract

Electron ionization (EI) mass spectra are not very helpful for characterizing ortho, meta, and para isomers of underivatized haloanilines since their spectra are virtually identical. In contrast, when the amino group of chloro-, bromo-, or iodoanilines is transformed to an N-formyl, N-acetyl, or N-benzoyl derivative, the spectra of the derivatives reveal a highly dramatic loss of a halogen radical, instead of an HX elimination usually expected from an "ortho effect." For example, the spectra of N-formyl, N-acetyl, and N-benzoyl derivatives of ortho isomers of chloro-, bromo-, and iodoanilines show a very prominent peak at m/z 120, 134, and 196, respectively, for the loss of the corresponding halogen atom.

No abstract

Recent developments in the fields of organic synthesis, process research, and biopharmaceuticals are leading to increasingly complex mixtures of closely related species that often prove challenging for analysis, separation, and characterization. Herein, computer-assisted modeling using LC Simulator (ACD/Labs) software is introduced as an initial analytical framework to isolation and purification workflows, enabling the rapid increase of scale-up productivity (kkD: kilograms of purified analyte per kilogram of stationary phase per day) of target pharmaceuticals in multicomponent mixtures. This approach allows us to achieve dramatic increases of kkD while minimizing solvent consumption and hazardous waste by accomplishing three main goals: (1) selectively improving the resolution of only target analytes for the maximum loading while also reducing the cycle time, (2) changing the elution order of the target peaks to prevent coelution caused by undesirable tailing components while increasing sample loading, and (3) enabling the generation of three-dimensional (3D) resolution maps that serve as a database to reduce preparative optimization when similar reaction mixtures are encountered, as typically occurs in the development and manufacturing of new drug substances. Chromatographic simulations served to generate 3D resolution maps with robust separation conditions that matched the outcome of subsequent experimental data (overall relative standard deviation (RSD) of retention times <3% between simulated and experimental conditions). The optimal separation procedures generated through this strategy were successfully applied to the preparative isolation and purification of multicomponent mixtures of closely related species using readily available reversed-phase liquid chromatography (RPLC) and ion-exchange chromatography (IEC) instrumentation, resulting in a substantial increase of purification workflow efficiency in all cases. This computer-assisted modeling approach enables more efficient, cost-effective, and greener preparative chromatography workflows.