RESUMO
The ion-molecule reactions of ions from acetone, dimethyl ether, 2-methoxyethanol, and vinyl methyl ether with vincamine were investigated. Reactions with dimethyl ether result in [M+13](+) and [M+45](+) products, reactions with 2-methoxyethanol produce [M+13](+) and [M+89](+) ions, and reactions with acetone or vinyl methyl ether ions generate predominantly [M+43](+) ions. Collision-activated dissociation and deuterium labeling experiments allowed speculation about the product structures and mechanisms of dissociation. The methylene substitution process was shown to occur at the hydroxyl oxygen and the phenyl ring of vincamine for dimethyl ether reactions, but the methylene substitution process was not favored at the hydroxyl oxygen for the 2-methoxyethanol reactions, instead favored at the 12 phenyl position. The reaction site is likely different for the 2-methoxyethanol ion due to its capability for secondary hydrogen-bonding interactions. For the [M+45](+) and [M+89](+) ions, evidence suggests that charge-remote fragmentation processes occur from these products. In general, the use of dimethyl ether ions or 2-methoxyethanol ions for ionmolecule reactions prove highly diagnostic for the characterization of vincamine; both molecular weight and structural information are obtained. Limits of detection for vincamine with dimethyl ether chemical ionization via this technique on a benchtop ion trap gas chromatography-tandem mass spectrometer are in the upper parts per trillion range.
RESUMO
Competitive reactions of dimethyl ether ions are used to probe the steric and substituent effects of substituted phenols and anisoles in a quadrupole ion trap. The relative percentages of protonation and methylene substitution from the reactions of dimethyl ether ions show a correlation with size, location, and number of subsrituents on the aromatic ring. Although gas-phase basicity measurements of the phenols show no discernible correlation with the percentages of competitive reactions, semiempirical calculations show a good correlation between the trend in heats of formation and the trend in methylene substitution percentage. Reactions with deuterated compounds show that the methylene substitution reaction occurs on the ring.
RESUMO
BACKGROUND: The efficiency and reproducibility of patch tests remain controversial. OBJECTIVE: Our purpose was to determine the efficiency and reproducibility of patch tests and to identify factors influencing these features. METHODS: We double-tested 1285 patients concomitantly with 10 standard allergens by manually filled test chambers. Additional information was obtained from all patients with a standardized protocol. RESULTS: Patch test efficiency was good (> or = 0.94) with all 10 allergens. In contrast, nonreproducibility of patch tests was strongly allergen dependent, ranging from 0.2 for nickel sulfate to 0.6 for formaldehyde. The likelihood of nonreproducible allergic reactions increased when more than four positive reactions were seen at the same time, and with another positive reaction located in close proximity to an allergic reaction. Sex and age of patients, atopy, dermatitis at distant sites, sleeping habits, and the time of allergen exposure (24 or 48 hours) did not affect the rate of nonreproducible results. CONCLUSION: To increase patch test reproducibility, specific preparations of patch test allergens need to be improved. Furthermore, amplification effects by synchronous neighboring positive reactions should be excluded.
