Active flow management in preparative chromatographic separations: a preliminary investigation into enhanced separation using a curtain flow inlet fitting and segmented flow outlet fitting

Active flow management in the form of curtain flow sample introduction and segmented outlet flow control has been shown to enable sample to elute through a chromatography column under the principles of the "infinite diameter column". Such an elution process avoids the detrimental effects of the heterogeneity of particle-packed chromatographic columns by injecting the sample directly into the radial core region of the column, thus avoiding wall effects. The process described herein illustrates how the principles of the infinite diameter column can be applied using conventional injection devices suitable for long-term analysis that requires robust protocols. Using this approach, sensitivity in separation was 2.5 times greater than conventional chromatography, yielding a product at twice the concentration. Benefits of curtain flow injection are thus relevant to both preparative-scale and analytical-scale separations.     

Vector properties of the O(1D2) fragment produced from the photolysis of ozone in the wavelength range of 298 to 320 nm

The speed averaged translational anisotropy and electronic angular momentum polarization of the O(1D2) atomic fragment formed from the photodissociation of ozone in the atmospherically important long wavelength region of the Hartley band (298 to 320 nm) have been measured using resonance enhanced multiphoton ionization time of flight mass spectrometry. The translational anisotropy parameter, beta, is found to decline from 1.1 for photolysis at 300 nm to a minimum value of 0 at 310 nm which is the threshold for production of O(1D2) in conjunction with the O2(a 1Deltag v = 0) molecular cofragment. For photolysis wavelengths greater than 310 nm, O(1D2) is formed from the dissociation of internally excited ozone molecules. The corresponding beta parameters are markedly lower than for atomic fragments produced with the same speed from the photolysis of ground state ozone molecules. This result is consistent with two different pathways contributing to the photolysis of internally excited ozone at the longest wavelengths studied corresponding to initial internal excitation either in the symmetric or asymmetric stretching vibration. In addition, the polarization of the atomic angular momentum has been determined with the incoherent polarization parameters a0(2)(||) and a0(2)(_|) increasing from values of -0.53 and -0.62 at 300 nm to -0.37 and -0.19 at 317 nm, consistent with the increasing contribution from the photolysis of internally excited ozone as the dissociation wavelength lengthens. Evaluation of these alignment parameters allows the populations of the magnetic substrates, mj, to be determined. For example, for a photolysis wavelength of 303 nm the populations of mj = 0, +/- 1, +/- 2 are in the ratio of 0.36: 0.56: 0.08 and this ratio is essentially independent of the photolysis wavelength. The coherent contribution to the atomic polarization is quantified by the Re{a1(2)(||, _|)} and Im{a1(1)(||, _|)} parameters and these are found to vary from -0.21 and 0.21 at 300 nm to -0.04 and 0.24 at 313 nm, respectively.     

The use of lead isotopic abundances in trace uranium samples for nuclear forensics analysis

Secondary ion mass spectrometry (SIMS), secondary electron microscopy (SEM) and X-ray analysis have been applied to the measurement of U-bearing particles with the intent of gleaning information concerning their history and/or origin. The lead isotopic abundances are definitive indicators that U-bearing particles have come from an ore-body, even if they have undergone chemical processing. SEM images and X-ray analysis can add further information to the study that may allude to the extent of chemical processing. The presence of “common” lead that does not exhibit a radiogenic signature is clear evidence of anthropogenic origin.     

Probing temperature-driven flow lines in a gated two-dimensional electron gas with tunable spin-splitting

We study the temperature flow of conductivities in a gated GaAs two-dimensional electron gas (2DEG) containing self-assembled InAs dots and compare the results with recent theoretical predictions. By changing the gate voltage, we are able to tune the 2DEG density and thus vary disorder and spin-splitting. Data for both the spin-resolved and spin-degenerate phase transitions are presented, the former collapsing to the latter with decreasing gate voltage and/or decreasing spin-splitting. The experimental results support a recent theory, based on modular symmetry, which predicts how the critical Hall conductivity varies with spin-splitting.     

Combining a DS-DBR laser with QPM-DFG for mid-infrared spectroscopy

Studies into the suitability of a novel, widely tunable telecom L-band (1563?C1613?nm) digital supermode distributed Bragg reflector (DS-DBR) laser for spectroscopy in the mid-IR are presented. Light from the DS-DBR laser was mixed with 1064?nm radiation in a periodically poled lithium niobate (PPLN) crystal to generate mid-IR light by quasi phase matching difference frequency generation (QPM-DFG). The resultant continuous wave radiation covered the range 3000?C3200?cm^?1 with powers of up to 2.6???W. The use of such laser light for spectroscopic applications was illustrated by performing absorption experiments on both narrow-band and broad-band absorbers, namely methane (CH₄) and methanethiol (CH₃SH). Wavelength modulation spectroscopy (WMS) on CH₄ demonstrated that the modulation characteristics of the DS-DBR laser observed in the near-IR were transposed to the mid-IR and yielded a sensitivity of 3.1×10^?6?cm^?1?Hz^?1/2 over a 47?cm path length. In the CH₃SH spectrum, the absorption feature at 3040?cm^?1 was identified as a potential useful region for monitoring this biomarker in exhaled breath at reduced pressures.