John C. Helmer

Evaluation of fundamental properties of a silica capillary used for capillary electrophoresis

Abstract A model was developed that accounts for the decrease in the electroosmotic flow in a capillary electrophoresis system when the buffer concentration is increased. Important parameters are: the initial charge per unit area at the silica capillary wall, Qo; a compact layer of molecules of constant thickness do that exists between the capillary wall and the buffer; and the equilibrium constant, Kwall, between the cations in the buffer and adsorption sites on the silica capillary. An excellent fit of an equation derived from the model to experimental results was obtained. Values for the above parameters were determined in a number of different buffers and the effect of pH, buffer composition and column coatings on these parameters was evaluated.

Separation of seven tricyclic antidepressants using capillary electrophoresis

Abstract Seven tricyclic antidepressants, protriptyline, desipramine, nortriptyline, nordoxepin, imipramine, amitriptyline and doxepin, were separated using capillary electrophoresis. Because the tricyclic antidepressants were similar in structure and mass, careful manipulation of the electroosmotic flow and the electrophoretic mobilities was required for an optimal separation. In the systematic approach we have developed, the differential electrophoretic mobilities were first maximized by adjusting pH. Next, increasing the buffer concentration improved the separation at the expense of migration times by reducing the electroosmotic flow. Full resolution was achieved by the addition of methanol to the buffer which decreased both the electroosmotic flow and the electrophoretic mobilities of the samples.

Structure relations in the x-ray photoelectron spectra of three chromium compounds

Abstract The chemical shift in electron binding energy, magnetic splitting of electron shells, and structures in the valence band are examined for chromium in the 3 + and 6 + oxidation states. The splitting of the Cr 3 s energy level is associated with the appearance of a sharp Cr 3 d line in the valence band. The relative chemical shift in the Cr 2 p 3 2 line between Cr 2 O 3 and K 2 Cr 2 O 7 is verified in the mixed compound KCr 3 O 8 which contains both types of Cr ions, and the structure of this compound is verified by the X-ray photoelectron spectra. The spin-orbit intensity ratio of the 2 p doublet of Cr 6+ is 3, instead of the theoretical value of 2, and the spin-orbit splitting is less than for Cr 3+ . In the 3 p level of Cr the relative chemical shift is 3.5 eV whereas for the 2 p 3 2 level the shift is only 2.4 eV. The differences in chemical shift and intensity ratio can not be explained.

New method for the determination of impurity levels with respect to the bands of the host crystal(ZnS:Mn)

Abstract The relative location of electronic levels of some deep luminescence centers, e.g. transition metal or rare earth centers, with respect to the host lattice has been accessible to experimental investigations in the past only in those cases where charge transfer could be observed. One of the systems where this was not the case is ZnS:Mn. We now measured the kinetic energy distribution of electrons emitted from samples due to X-ray (AlK a ) excitation. Thus we determined the energy location of a number of atomic levels of Zn, S and Mn in samples of ZnS, MnS and ZnS:Mn (3%). The results consistently indicate that the Mn 3d state lies about 3 eV below the top of the ZnS valence band. The method employed may be useful for the investigation of similar crystal-impurity systems.

Transition gas flow in drag pumps and capillary leaks

Modern turbomolecular pumps include a drag stage in the exhaust, operating roughly in the pressure range of 10 mTorr–10 Torr. Flow conditions range from molecular flow at the drag inlet, to viscous flow at the outlet, known as ‘‘transition’’ flow. In general, models of transition flow in drag pumps have not been developed. Moreover, the model of a Gaede pump given in journals and textbooks up to the present, gives values of compression ratio that are orders of magnitude too high. In 1913, Gaede proposed a differential equation for transition flow in a drag pump. He did not solve the general equation, and the model was incomplete. We have developed a new model that takes transition flow in a differential element and integrates it over the length of the pump. This model is modified by a ‘‘pumping leak’’ expression for the gas stripper, which separates the inlet from the outlet. The result is compared with experimental measurements, and good agreement is obtained over the entire pressure range from molecular...

Induced electron emission spectroscopy of reduced lead silicate glass (X-ray photoemission)

Abstract A measurement of the induced electron emission spectrum (IEE) of lead in reduced lead silicate glass indicates that the lead in this system exists in three different charge states Pb 0 , Pb 1+ , and Pb 2+ . An electronic hopping conduction mechanism employing these three states is proposed.