The contribution of cation exchange to solute retention for type-B alkylsilica columns (made from high-purity silica) has been examined in terms of the hydrophobic-subtraction (H-S) model of ...reversed-phase column selectivity. The relative importance of cation exchange in the separation of ionized bases by reversed-phase chromatography (RPC) varies with (a) column acidity (values of the column cation-exchange capacity
C), (b) mobile-phase pH and buffer concentration, and (c) the nature of the buffer cation. The effects of each of these separation variables on cation retention were examined. The contribution of cation exchange (and other ionic interactions) to solute retention is represented in the H-S model by properties of the solute (
κ′) and column (
C), respectively. Values of
κ′ for 87 solutes have been examined as a function of solute molecular structure, and values of
C for 167 type-B alkylsilica columns have been related to various column properties: ligand length (e.g., C
8 vs. C
18) and concentration (μmol/m
2), pore diameter (nm), and end-capping. These results contribute to a more detailed picture of the retention of cationic solutes in RPC as a function of separation conditions. While previous work suggests that the ionization of type-B alkylsilica columns is generally negligible with mobile-phase pH
<
7 (as a result of which cation exchange then becomes insignificant), the present study provides evidence for cation exchange (and presumably silanol ionization) at a pH as low as 3 for most columns.
Falls are a common cause of hospitalization, morbidity, and mortality among the elderly in the United States. Evidence-based imaging recommendations for evaluation of delayed intracranial hemorrhage ...(DICH) are not generally agreed upon. The purpose of this project was to evaluate the incidence of DICH detected by head computer tomography (CT) among an elderly population on pre-injury anticoagulant or antiplatelet (ACAP) therapy.
Data from a Level 1 Trauma Center trauma registry was used to assess the incidence of DICH in an elderly population of patients (≥65 years) who sustained a minor fall while on pre-injury ACAP medications. Counts and percentages are reported.
Data on 1076 elderly trauma patients were downloaded, of which 838 sustained a minor fall and 513 were found to be using a pre-injury ACAP medication. One patient (0.46%) with a DICH was identified out of 218 patients who received a routine repeat head CT. Aspirin and warfarin were the most common pre-injury ACAP medications and 19.27% (42/218) of patients were found to be using multiple ACAP medications.
Universal screening protocols promote immediate-term patient safety, but do so at a great expense with respect to health expenditures and increased radiation exposure. This analysis highlights the need for an effective risk assessment tool for DICH that would reduce the burden of unnecessary screenings while still identifying life-threatening intracranial hemorrhages in affected patients.
As reported previously, five solute-column interactions (hydrophobicity, steric resistance, hydrogen-bond acidity and basicity, ionic interaction) quantitatively describe column selectivity for 163 ...alkyl-silica, polar-group and cyano columns. In the present study, solute retention and column selectivity for 11 phenyl and 5 fluoro-substituted columns were compared with alkyl-silica columns of similar ligand length. It is concluded that two additional solute-column interactions may be significant in affecting retention and selectivity for the latter columns: (a) dispersion interactions of varying strength as a result of significant differences in bonded-phase polarizability or refractive index and (b) pi-pi interactions in the case of phenyl columns and aromatic solutes. These 16 phenyl and fluoro columns were also characterized in terms of hydrophobicity, steric resistance, hydrogen-bond acidity and basicity, and ionic interaction.
A total of 371 reversed-phase columns have now been characterized in terms of selectivity, based on five solute–column interactions (the hydrophobic-subtraction model). The present study illustrates ...the use of these data for interpreting peak-tailing and column stability. New insights are also provided concerning column selectivity as a function of ligand and silica type, and the selection of columns for orthogonal separations is re-examined. Some suggestions for the quality control of reversed-phase columns during manufacture are offered.
The PRAE Multidisciplinary Project Delorme, R.; Marchand, D.; Vallerand, C.
Nuclear physics news,
01/2019, Letnik:
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Journal Article
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The Platform for Research and Applications with Electrons (PRAE) facility
1
under construction in the Orsay campus of the Paris-Sud University is a multidisciplinary platform based on a ...high-performance new generation linear accelerator delivering a pulsed electron beam in the energy range 30-70 MeV, upgradable to 140 MeV. This project originates from the complementary expertise of several local scientific research communities involved in radiobiology, subatomic physics, instrumentation, and particle accelerator technologies to perform multidisciplinary studies of significant impact.
Eleven cyanopropyl ("cyano") columns were characterized by means of a relationship developed originally for alkyl-silica columns. Compared to type-B alkyl-silica columns (i.e., made from pure ...silica), cyano columns are much less hydrophobic (smaller H), less sterically restricted (smaller S*), and have lower hydrogen-bond acidity (smaller A). Because sample retention is generally much weaker on cyano versus other columns (e.g., C8, C18), a change to a cyano column usually requires a significantly weaker mobile phase in order to maintain comparable values of k for both columns. For this reason, practical comparisons of selectivity between cyano and other columns (i.e., involving different mobile phases for each column) must take into account possible changes in separation due to the change in mobile phase, as well as change in the column.
Some alkylsilica columns carry a positive charge at low pH, as determined by anion-exchange with nitrate ion. In the present study, the relative positive charge for 14 alkylsilica columns was ...measured for a mobile-phase pH 3.0. All but 3 of these columns were found to carry a significant positive charge under these conditions. The relative positive charge on these columns was found to correlate approximately with two other column characteristics: relative cation-exchange behavior as measured by the hydrophobic-subtraction model (values of C-2.8), and slow equilibration of the column to changes in the mobile-phase—as evidenced by a slow change in the retention of anionic and cationic solutes with time. The origin of this positive charge may arise from the bonding process, with incorporation of some cationic entity into the stationary phase.
Posterior cortical atrophy (PCA) is a neurodegenerative disease affecting the posterior region of the brain. Little is known about both the impact of PCA on functioning and how to support patients on ...a daily basis. The purpose of this study was to describe the functional profile of DD, a woman diagnosed with PCA, as well as to explore a pilot cognitive rehabilitation program designed to optimize functioning in daily living. The ADL Profile was used to assess the daily tasks that DD chose to undertake. Four operations, i.e. formulate a goal, plan, carry out and verify goal attainment, were scored for each task. Difficulties were observed during the execution of all tasks, as she struggled to find items or showed unsafe behaviors. Impairments were also seen in formulating a goal and planning, especially for less routine tasks. DD identified two tasks to be addressed in rehabilitation: setting the table and dealing cards. Learning was optimized using errorless learning and compensatory aids when setting the table, while dealing cards received no intervention. Only setting the table improved significantly with time. Further studies should be conducted to portray a wider functional profile of people living with PCA and develop effective rehabilitation programs.
ABSTRACT
High‐resolution analysis (2277 samples) of magnetic susceptibility (MS) was performed on ∼700‐m‐thick Early–Middle Oxfordian marine marls of the Terres Noires Formation, SE France. MS ...variations within these sediments record sub‐Milankovitch to Milankovitch frequencies with long‐term eccentricity (405 kyr and ∼2 Myr) being the most prominent. The 405 kyr cycle was used as a high‐resolution geochronometer for astronomical calibration of this poorly constrained interval of Late Jurassic time. The estimated duration of this Early–Middle Oxfordian interval concurs with the current International Geologic Time Scale GTS2004 (∼4 Myr), but the estimated durations of the corresponding ammonite zones are notably different. The calibration improves the resolution and accuracy of the M‐sequence magnetic anomaly block model that was previously used to establish the Oxfordian time scale. Additionally, the 405 kyr cyclicity is linked to third‐order sea‐level depositional sequences observed for Early–Middle Oxfordian time. Strong ∼2 Myr cycles are consistent with long‐term eccentricity modulation predicted for the Late Jurassic. These cycles do not match second‐order sequences that have been documented for European basins; this raises questions about the definition and hierarchy of depositional sequences in the Mesozoic eustatic chart. Our results require substantial revisions to the chart, which is frequently used as a reference for the correlation of widely separated palaeogeographic domains. Finally, a long‐term trend in the MS data reflects a progressive carbonate enrichment of the marls expressing an Early Oxfordian global cooling followed gradually by a warming in the Middle Oxfordian. This trend also records a major transgressive interval likely peaking at the Transversarium ammonite zone of the Middle Oxfordian.
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