Mark Allen Dearth

Reaction of benzotriazole ultraviolet light absorbers with free radicals

Abstract The photolysis of benzotriazole ultraviolet light absorber additives (Bz-UVAs) in acrylic/melamine clearcoats suggests that Bz-UVAs are destroyed by clearcoat-driven photooxidation chemistry. Tinuvin 900 is converted to parent benzotriazole and phenol ring oxidation products. Bz-UVAs are not destroyed by photolysis in acrylic/melamine clearcoats in the absence of oxygen. Solution photolysis experiments reveal that Bz-UVAs are not attacked by free radicals generated by thermal decomposition of azoisobutyronitrile (AIBN) or cumene hydroperoxide (CHP) in ethanol or cyclohexane. Bz-UVAs are also not attacked by free radicals generated by photolytic decompostion of AIBN or CHP in cyclohexane. Bz-UVAs, however, are destroyed when AIBN or CHP are photolytically decomposed in ethanol. Photolysis without oxygen leads to Bz-UVA phenol ring solvent and initiator adducts. Photolysis with oxygen leads to cleavage to form free benzotriazole and to destruction of the phenol ring. It is suggested that an excited state of the non-planar Bz-UVA form may be susceptible to free radical attack. Detailed liquid chromatography tandem mass spectrometry (LC/MS/MS) product analysis results are reported in a companion paper.

The LC/MS/MS characterization of photolysis products of benzotriazole-based ultraviolet absorbers

The photodegradation of Tinuvins P, 328, and 900 (Ciba-Geigy) under mild conditions was confirmed by conducting photolysis in methanol, ethanol, and acetonitrile solvents with azo(bis)isobutyronitrile (AIBN, a radical source) or cumene hydroperoxide. Benzotriazole was the major photolytic product observed. In addition to cleavage products, adducts of the parent UV absorber (UVA) were also observed. The identities of various photoproducts were determined by HPLC with UV diode array detection and by combined HPLC and tandem mass spectrometry (MS/MS). Among the photoproducts identified by MS/MS were benzotriazole, phenolic fragments, and solvent-UVA adducts. The photoproducts identified provide evidence that photochemical degradation is initiated by chemical attack on the phenol ring, which can result in cleavage of the benzotriazole functionality, displacement addition of radicals to the phenolic ring, loss of alkyl ligands from the phenolic ring, and loss of unsaturation in the phenolic ring. The predominance of mass spectral evidence did not support a reaction pathway involving the phenyl hydroxyl group.

Nitric oxide-assisted atmospheric pressure corona discharge ionization for the analysis of automobile hydrocarbon emission species

Nitric oxide reagent gas has been found to improve the sensitivity and robustness of the atmospheric pressure corona discharge ionization (APCDI) process. Sensitivity has been increased by a factor of 20–100, depending on the compound, over APCDI without nitric oxide. The robustness (defined as the sensitivity to matrix interferences) of APCDI in the presence of water has been improved by a factor of 3 over normal APCDI. These improvements are due in part to a modification of the commercial inlet system and ionization chamber that allows the chamber and sample gases to be heated to 100 and 350°C, respectively. Nitric oxide was chosen as the reagent gas because of the variety and selectivity of its interaction with hydrocarbons with differing functional groups. Product ions of nitric oxide ionization and their subsequent tandem mass spectra are presented and discussed for selected alkanes; alkenes, alkylbenzenes, alcohols; aldehydes, and an ether. A tandem mass spectrometry (unique parent ion-daughter ion transition) method was developed to quantify compounds of specific interest in vehicle emissions. The absolute sensitivity for these compounds, under ideal conditions, was determined and ranges from 0.006 ppb for xylene (most sensitive) to 80 ppb for C8 (or larger) normal alkanes. Routine sensitivity for real-world samples was in the single parts per billion range for aromatic and olefinic species. Potential applications include the real-time, on-line monitoring of selected hydrocarbons in automobile exhaust.

Atmospheric chemistry of CFC replacement compounds : synthesis of bis(trifluoromethyl) trioxide and anomalies in its mass spectral analysis

Abstract The photolysis of CF 3 H/F 2 /O 2 mixtures is shown to be a rapid and simple method for the production of pure samples of CF 3 O 3 CF 3 . Complications associated with the mass spectrometric analysis of CF 3 O 3 CF 3 are highlighted.