We have developed a centrifugal analyzer with both fluorescence/light-scatter and conventional absorbance optics. The instrument is used in this investigation to study the formation of antigen-antibody complexes by light scattering and turbidimetric measurements, and to develop assays for human immunoglobulins G, A, and M. Concentrations are calculated from a nonlinear least-squares fit of calibrators, and antigen excess is automatically detected from kinetic curve characteristics. Precisions and patients’ results are presented, and assay sensitivity and reliability in the detection of antigen excess are compared. We also investigated the effects of centrifugal force on complex formation. Both nephelometry and turbidimetry can be very satisfactorily adapted to centrifugal analyzers. We present a model to describe the observed differences between the light-scatter and the turbidity data.
A differentially pumped double-focusing mass spectrometer was suitably modified for the study of metastable ions and collision-induced metastables. At high resolution the same instrument easily resolved protonated and deuterated ions of the same nominal mass. Accordingly, metastable ions and isotope effects in the mass spectra of CH4, CH3D, CH2D2, and CD4 were reinvestigated with this instrument in order to resolve certain ambiguities in previous studies. All four protonated molecular ions exhibited hydrogen-loss metastables, while CD4+ exhibited a corresponding unimolecular elimination of a deuterium atom. In addition to these true metastables, essentially every conceivable collision-induced metastable decay process was also observed. The observed relative intensities and isotope effects in the normal spectra are rationalized with general statistical arguments and with more complete calculations using the quasiequilibrium theory of mass spectra. The behavior of the rates at threshold and their effect on methane metastable intensities are also discussed.
An improved statistical theory of mass spectra is here applied to the fragmentation of five alkanes: n-hexane, 2-methylpentane, 3-methylpentane, n-heptane, and n-octane. The calculated breakdown curves are compared with the experimental curves obtained from photoionization studies by Steiner, Geise, and Inghram. The major fragmentations, the metastable ions, and the "missing metastable" ions are computed for gas temperatures of 0° and 300 0 K. The improved quasiequilibrium theory yields satisfactory breakdown curves for the above molecules using physically reasonable activated complexes and activation energies, and without requiring introduction of artificial parameters such as an "effective number of oscillators." t Now at Dow Chemical Corp., Midland, Mich. EI, activation energy in electron volts; F+, fragment ion; re, reaction coordinate; r, rotation of the product;AC, assumed activated-complex configuration; t, translation of the product; rf, ring formation; pdf, partial double-bond formation; se, steric effect.
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