Evaluating the utility of ion mobility separation in combination with high-pressure liquid chromatography/mass spectrometry to facilitate detection of trace impurities in formulated drug products

Many formulated products contain complex polymeric excipients such as polyethylene glycols (PEGs). Such excipients can be readily ionized by electrospray and may be present at very high concentrations, thus making it very difficult to identify trace level impurities such as degradants in samples, even if hyphenated techniques such as liquid chromatography/mass spectrometry (LC/MS) are used. Ion mobility (IM) spectrometry is a very rapid gas-phase separation technique and offers additional separation capability within the LC timeframe. This work investigates the use of an IM separator in combination with high-pressure liquid chromatography (HPLC) and MS, to improve the separation of drug-related materials from excipients, thus aiding the identification of trace-level impurities in an anti-HIV medication, Combivir.     

Implicit time‒accurate solutions on unstructured dynamic grids

In this paper an unstructured multigrid algorithm is used as an iterative solution procedure for the discrete equations arising from an implicit time discretization of the unsteady Euler equations on tetrahedral grids. To calculate unsteady flows due to oscillating boundaries, a novel grid movement algorithm is introduced in which an elliptic equation with a non‒linear diffusion coefficient is used to define the displacement of interior grid nodes. This allows large grid displacements to be calculated in a single step. The multigrid technique uses an edge‒collapsing algorithm to generate a sequence of grids, and a pseudo‒time‒stepping smoother. On the coarser grids, no grid motion is used. Instead, surface normals are rotated consistently and transfer/interpolation weights are based on the time‒averaged grid co‒ordinates. A 2D NACA0012 test case is used to validate the programme. 3D results are presented for the M6 wing and a full aircraft configuration. © 1997 John Wiley & Sons, Ltd.     

New measurement of exotic decay of 225Ac by 14C emission

The branching ratio of ²²⁵Ac decay by emission of ¹⁴C was remeasured under improved experimental conditions by using a radioactive source produced at the ISOLDE mass-separator at CERN and a nuclear track detector technique. The result, B = λ_14C/λ_α = (4.5±1.4)10^-12, is consistent with the anomalously high value obtained in the 1993 experiment, thus confirming the importance of nuclear-structure effects in this exotic decay. Received: 20 July 2001 / Accepted: 28 November 2001     

The importance of peri-interactions in determining the half-chair conformation of the dihydropyran ring in 2-benzopyrans. Stereochemical consequences

peri-Interactions are important in determining both the conformation of the dihydropyran ring of 2-benzopyrans as well as the stereochemistry of its substituents.     

Suzuki route to regioregular polyalkylthiophenes using Ir-catalysed borylation to make the monomer, and Pd complexes of bulky phosphanes as coupling catalysts for polymerisation

We have applied palladium complexes of bulky, electron-rich phosphane ligands as catalysts for the Suzuki synthesis of highly head-to-tail regioregular polyalkylthiophenes from 2-(5-bromo-4-n-alkyl-thiophen-2-yl)-4,4,5,5-tetramethyl-[1,3,2]dioxaborolane. The monomer can be prepared in high yield by Ir-catalysed borylation of 2-bromo-3-hexylthiophene, without the need for organolithium reagents or strong bases.     

Tailoring the microwave permittivity and permeability of composite materials

The microwave permittivity (ɛ_r) and permeability (μ_r) of composite materials are tailored by adding various loading agents to a host plastic and are subsequently modeled using the Maxwell Garnett theory and second order polynomials. With the addition of manganese zinc ferrite, strontium ferrite, nickel zinc ferrite, barium tetratitanate and graphite powders, materials with values of ɛ′, e″, μ′, μ″ as high as 22, 5, 2.5 and 1.7 have been obtained. Permittivity and permeability data are calculated at 2.0245 GHz from reflection and transmission measurements performed in a 7 mm coaxial test line. The Maxwell Garnett (MG) theory successfully models ɛ_r if the filling factor is less than 0.30 and ratio |ɛ₁| (host)/ |ɛ₂| (powder) is greater than 0.04. As this ratio decreases, the MG theory is shown to be independent of ɛ₂ and second order polynomials are used to effectively model the dielectric constant. Polynomials are also used for the ferrite composites because it was determined that the MG theory was unable to model μ_r. This deficiency is attributed to the difference of domain structures that exist in powdered and sintered ferrites.     

Adjoint and defect error bounding and correction for functional estimates

We present two error estimation approaches for bounding or correcting the error in functional estimates such as lift or drag. Adjoint methods quantify the error in a particular output functional that results from residual errors in approximating the solution to the partial differential equation. Defect methods can be used to bound or reduce the error in the entire solution, with corresponding improvements to functional estimates. Both approaches rely on smooth solution reconstructions and may be used separately or in combination to obtain highly accurate solutions with asymptotically sharp error bounds. The adjoint theory is presented for both smooth and shocked problems; numerical experiments confirm fourth-order error estimates for a pressure integral of shocked quasi-1D Euler flow. By employing defect and adjoint methods together and accounting for errors in approximating the geometry, it is possible to obtain functional estimates that exceed the order of accuracy of the discretization process and the reconstruction approach. Superconvergent drag estimates are obtained for subsonic Euler flow over a lifting airfoil.     

Biochemical data-processing with microcomputers : Part 3. On-line data acquisition from a continuous flow analyzer

A program, written in BASIC, is described which allows data acquisition from a continuous flow analyzer. The program was developed for a readily available microcomputer, but should be easily modified for use on similar machines. Once the peak height has been measured, the concentration of the analyte is calculated by reference to a previously defined calibration. The program is designed to handle data from more than one channel, although there is a practical limit of 3–4 simultaneously active channels. The results of the separate assays are collated and printed as a group for each specimen, even when the analytical methods require different times for completion.