Analysis of formaldehyde in tobacco smoke by high performance liquid chromatography

Formaldehyde in tobacco smoke is allowed to react with 2,4-dinitrophenylhydrazine to form the dinitrophenylhydrazone. This derivative is extracted with chloroform and concentrated. The residue in methylene chloride is separated and analyzed by high performance liquid chromatography. A column packed with 10-micron silica is used for separation. The internal standard is triphenylene. This method can also be used for the analysis of other carbonyl compounds in tobacco smoke that react to form hydrazone derivatives.     

A Structural and Theoretical Study of the Thiophosphinite and Dithiophosphinate Anions

Two novel lithium compounds containing either the phosphorus-chalcogenide anions [Ph ₂ PS]^? or [Cy ₂ PS ₂ ]^? were isolated as decomposition products in the attempted formation of phospha(V)guanidinate anions. Lithium diphenylthiophosphinite was structurally characterized as the dimeric TMEDA adduct [Li(Ph ₂ PS)(TMEDA)] ₂ (1), in which a rare example of the κ ¹ -S bonding mode was observed for the anion. The dicyclohexyldithiophosphinate anion was incorporated into an aggregated structure with molecular formula [Li ₅ (Cy ₂ PS ₂ ) ₄ (OH)] ₂ (2). DFT calculations were performed on the isolated [R ₂ PS]^? and [R ₂ PS ₂ ]^? anions (R = Ph, Cy), indicating delocalization of electron density into the P-S bonds for each model, in agreement with bond-lengths taken from crystallographic data.     

Statistical sampling of carbon nanotube populations by thermogravimetric analysis

Carbon nanotubes are one of the most promising nanomaterials available with applications in electronics devices, sensing, batteries, composites and medicine. Strict control of the carbon nanotube chemistry and properties is necessary as the applications proceed into more specialized areas. Thermogravimetric analysis (TGA) is one analytical method currently utilized for the characterization of carbon nanotubes. Though TGA can provide quantitative measurements of the composition of a sample, many researchers do not ensure the variance of the sample is properly captured. This research demonstrates for four single-wall carbon nanotube (SWCNT) samples how to statistically evaluate the material with TGA to ensure that the variance within the material is represented. SEM results are used to help reach conclusions about purity of the material by providing a visual means for inspection. This data is used to select the SWCNT material with the lowest variability and highest quality, as evaluated by composition and reproducibility.     

Subjective ratings of whole-body vibration for single- and multi-axis motion

Real-world whole-body vibration exposures comprise motion in fore-aft, lateral, and vertical directions simultaneously. There can also be components of roll, pitch, and yaw. If evaluating vibration with respect to human response, most investigators will use methods defined in ISO 2631-1. This uses frequency weightings that were originally derived from laboratory studies of the subjective responses to vibration in one direction at a time. This paper describes experiments that were carried out using a 6 degree-of-freedom vibration simulator to validate the applicability of ISO 2631-1 in multi-axis environments. Fifteen subjects were exposed to 87 stimuli comprising single-axis, dual-axis, and tri-axial random vibration, to which they were required to produce subjective ratings. It is shown that in this study the root-sum-of-squares method of summation of subjective ratings in individual axes was an adequate technique for prediction of subjective rating of multi-axis vibration. Better agreement between objective and subjective measures of vibration was obtained for unweighted vibration than for frequency weighted signals. The best agreement for this study was achieved when axis multiplying factors were set at 2.2 and 2.4 for x- and y-axis vibration, respectively. Different values could be appropriate for other postures, seats, and vibration conditions and should be determined in future studies.     

Practical considerations for preparing polymerized phospholipid bilayer capillary coatings for protein separations

Phosphorylcholine (PC) based phospholipid bilayers have proven useful as capillary coating materials due to their inherent resistance to non-specific protein adsorption. The primary limitation of this important class of capillary coatings remains the limited long-term chemical and physical stability of the coatings. Recently, a method for increasing phospholipid coating stability in fused silica capillaries via utilization of polymerized, synthetic phospholipids was reported. Here, we expand upon these studies by investigating polymerized lipid bilayer capillary coatings with respect to separation performance including run-to-run, day-to-day and column-to-column reproducibility and long-term stability. In addition, the effects of pH and capillary inner diameter on polymerized phospholipid coated capillaries were investigated to identify optimized coating conditions. The coatings are stabilized for protein separations across a wide range of pH values (4.0–9.3), a unique property for capillary coating materials. Additionally, smaller inner diameter capillaries (≤50 μm) were found to yield marked enhancements in coating stability and reproducibility compared to wider bore capillaries, demonstrating the importance of capillary size for separations employing polymerized phospholipid coatings.     

On the use of the rotation minimizing frame for variational systems with Euclidean symmetry

We study variational systems for space curves, for which the Lagrangian or action principle has a Euclidean symmetry, using the Rotation Minimizing frame, also known as the Normal, Parallel, or Bishop frame. Such systems have previously been studied using the Frenet–Serret frame. However, the Rotation Minimizing frame has many advantages, and can be used to study a wider class of examples. We achieve our results by extending the powerful symbolic invariant calculus for Lie group–based moving frames, to the Rotation Minimizing frame case. To date, the invariant calculus has been developed for frames defined by algebraic equations. By contrast, the Rotation Minimizing frame is defined by a differential equation. In this paper, we derive the recurrence formulae for the symbolic invariant differentiation of the symbolic invariants. We then derive the syzygy operator needed to obtain Noether's conservation laws as well as the Euler–Lagrange equations directly in terms of the invariants, for variational problems with a Euclidean symmetry. We show how to use the six Noether laws to ease the integration problem for the minimizing curve, once the Euler–Lagrange equations have been solved for the generating differential invariants. Our applications include variational problems used in the study of strands of proteins, nucleid acids, and polymers.     

Comparison of the apparent masses and cross-axis apparent masses of seated humans exposed to single- and dual-axis whole-body vibration

Humans are exposed to whole-body vibration in many types of environment. In almost all cases, the vibration to which the human is exposed comprises multi-axis vibration, such that vibration occurs in all directions simultaneously. Despite the complex nature of vibration to which humans are exposed in the workplace, almost all laboratory studies investigating the biomechanical response of the person have been completed using single-axis simulators. This paper presents a study whereby 15 male subjects were exposed to single-axis whole-body vibration in the x-, y- and z-directions and dual-axis vibration in the xy-, xz-, and yz-directions using a 6 degree-of-freedom vibration simulator. All vibration magnitudes were 0.4 ms⁻² rms in each axis. Acceleration and force was measured in the x-, y-, and z-direction during all trials. Subjects sat in two postures (‘back-on’ and ‘back-off’) on a flat rigid seat. Apparent masses measured using single-axis and dual-axis vibration stimuli showed comparable results; similarly, cross-axis apparent masses (i.e. the ratio of the force in one direction to the acceleration in another direction) were almost identical for the single- and dual-axis vibration stimuli. All results were in agreement with data previously published using single-axis vibration. In most cases, the peaks in the apparent mass and the cross-axis apparent mass occurred at a slightly lower frequency for the dual-axis vibration than for the single-axis vibration. It is hypothesised that this change is due to a nonlinear effect, analogous to that which occurs with increasing vibration magnitude for single-axis vibration.     

Synthesis and chemistry of the ionophore antibiotic tetronasin

Studies towards the synthesis and biosynthesis of tetronasin, an acyltetronic acid ionophore are described, together with an account of some novel methodology which is more widely applicable for the synthesis of other acyltetronic acids.