Charge detection mass spectrometry has been used to detennine the mass of double-stranded, circular DNA and single-stranded, circular DNA in the range of 2500 to 8000 base pairs (1.5-5.0 MDa). Simultaneous measurement of the charge and velocity of an electrostatically accelerated ion allows a mass detennination of the ion. Positive ion mass spectra of electrosprayed commercial DNA samples supplied in Tris-EDTA buffer, diluted in 50 vol. % acetonitrile, were obtained without cleanup of the sample.

No abstract

The first photoelectron bands of 1-propyl, 1-butyl, isobutyl, neopentyl, and 2-butyl radicals have been obtained. Adiabatic and vertical ionization potentials, respectively, are 8.15 ± 0.02 and 8.43 ± 0.02 eV for 1-propyl radical, 8.02 (+0.04 -0.1) and 8.50 ± 0.04 eV for 1-butyl radical, 7.93 (+0.03 -0.1) and 8.31 ± 0.03 eV for isobutyl radical, 7.88 ± 0.05 and 8.25 ± 0.03 eV for neopentyl radical, and 7.25 ± 0.02 and 7.59 ± 0.03 eV for 2-butyl radical. From recently determined or estimated heats of formation of the radicals, heats of formation of the corresponding carbonium ions are calculated to be 210.5 ± 1.1 kcal/mol for 1-propyl cation, 201.9 ± 3 kcal/mol for 1-butyl cation, 197.9 ± 3 kcal/mol for isobutyl cation, 188.8 ± 2.3 kcal/mol for neopentyl cation, and 181.0 ± 1.1 kcal/mol for 2-butyl cation. The energetics of ion solvation processes are assessed from a comparison of the gas-phase results to solution data where these ions are generated as nascent products of ionization processes or are proposed as reaction intermediates in isomerization reactions. With the exception of the 1-propyl radical spectrum, the spectra exhibit no resolved vibrational structure. The possible origins of a weakly resolved 540 ± 160 cm"1 vibrational progression observed on the 1-propyl radical band are discussed. An analysis of these spectra, along with those of ethyl and 2-propyl radicals, reveals treads in ionization potentials that may be interpreted in terms of inductive and hyperconjugative effects of methyl substituents ß to primary or secondary cation centers.

No abstract

Charge detection mass spectrometry (CDMS) has been used to rapidly analyze polymerase chain reaction (PCR) products with a minimum of sample cleanup after the PCR reaction. PCR products of 1525 base pairs (bp), 1982 bp and 2677 bp were detected by CDMS, where simultaneous measurement of the charge and velocity of an electrostatically accelerated ion allows a mass determination of the ion. We extended the investigation to a longer doublestranded, linear DNA sample by also analyzing linearized pBR322 (4361 bp). Positive ion mass spectra and ion charge-state distributions were obtained for these electrosprayed DNA samples. Instrumental conditions were studied using a commercially available, linearized pUC18 sample (2682 bp).