The separation of synthetic mixtures of glucose and fructose and also inverted sucrose feedstocks using countercurrent chromatographic techniques

Summary A pilot scale semi-continuous countercurrent chromatographic Refiner (SCCR4) unit packed with a Zerolit 225 resin in the Ca²⁺ form has been used to separate synthetic mixtures of glucose and fructose and also inverted sucrose feedstocks into glucose-rich and fructose-rich products.For the same process conditions less pure fructose-rich products were found when using inverted sucrose feedstocks than with synthetic mixtures of glucose and fructose. However, anion-exchange resins Duolite A113 in the (HSO ₃ ^– ) form did not produce any variation in product purities with change of feed source.     

The hearing aid feedback path: mathematical simulations and experimental verification

Acoustic feedback in hearing aids has received little attention in the literature. Feedback occurs when stability conditions of the open-loop transfer function of an in situ hearing aid are violated. Solving the feedback problem will first require knowledge of the open-loop transfer function. Included in the open-loop transfer function is the acoustical path by which sound emanating from the earmold vent returns to the microphone (i.e., the feedback path). Reported herein are two different mathematical procedures for simulating transfer functions of the feedback path of an eyeglass-type hearing aid. In one procedure the vent exit was modeled as a point source of sound located on a flat plane, while it was treated as a point source on a sphere in the other. Results of laboratory experiments indicate that the mathematical models accurately predict those acoustic phenomena for which they were intended: point sources on plane and spherical baffles. Results of manikin experiments showed both models to be less accurate for simulating the feedback path around the human head. The maximum difference between experiment and theory was 6 dB at one frequency. Surprisingly, the flat-baffle model produced better agreement with experimental results than did the sphere model.     

Three-dimensional speckle interferometric investigation of the stress-intensity factor along a crack front

The variation in Mode I stress-intensity factor throughout the thickness of an ASTM standard compact tension specimen was determined using scattered-light speckle interferometry. Two very thin sheets of coincident coherent light traveling in opposite directions were passed through a Plexiglas specimen normal to the crack faces. A double-exposed photograph of the scattered-light speckle pattern was taken while the specimen was subjected to a small load increment. From this double-exposed photograph, the change in the crack-opening displacement could be determined. From the information about the crack-opening displacement in the region of the crack tip, the stress-intensity factor was calculated for various interior planes and on the surface of the specimen. For the compact tension specimen tested, the stress-intensity factor did not vary throughout the specimen's thickness. The method of scattered-light speckle interferometry proved to be very powerful in solving this complex three-dimensional problem.     

Temperature profiles in a controlled-stress parallel plate rheometer

Actual melt temperatures are rarely measured directly when conducting rheological characterisations of materials in non-ambient conditions despite the potentially large influence temperature may have on the rheological data. For rheometers that use only a temperature-regulated lower plate, it is likely that the set point and true melt temperatures differ, an effect that becomes significant when characterising melts or suspensions close to phase-change events like crystallisation. This work investigates the magnitude of these effects for a controlled-stress rheometer featuring a temperature-controlled lower plate. The lower plate was fitted with a serrated cover disc that was found to exacerbate temperature deviations from the desired set point. Steady-state radial and vertical temperature profiles within the sample were measured and compared with the predictions of a finite element analysis model. The deviations between set point and measured temperatures were successfully predicted by the simulation for two typical gap heights for a thermoplastic, ceramic paste. The non-ideal heat transfer characteristics were also investigated numerically for a representative polymer system that demonstrated the increased deviations from ideal values for lower thermal conductivity materials.

Incubation in cyclohexene decomposition at high temperatures

A detailed master equation simulation has been carried out for the thermal unimolecular decomposition of C₆H₁₀ in a shock tube. At the highest temperatures studied experimentally [J. H. Kiefer and J. N. Shah, J. Phys. Chem., 91, 3024 (1987)], the average thermal vibrational energy is greater than the reaction threshold and therefore 〈ΔE〉 (up and down steps) is positive for molecules at that energy, rather than negative; the converse is true at lower temperatures. The calculated incubation time, in which the decomposition rate constant rises to 1/e of its steady state value, is found to be only weakly dependent on temperature (at constant pressure) between 1500 K and 2000 K and to depend almost exclusively on 〈ΔE〉_d (down steps, only), and not on collision probability model. Simulations of the experimental data show the magnitude of 〈ΔE〉_d depends weakly on assumed collision probability model, but is nearly independent of temperature. The second moment 〈ΔE〉^½ is found to be independent of both temperature and transition probability model. The experimental data are not very sensitive to the possible energy-dependence of 〈ΔE〉_d for a wide range of assumptions. It is concluded that the observed experimental “delay times” probably can be identified with the incubation time; further experiments are desirable to test this possibility and obtain more direct measures of the incubation time.     

Additive-free clicking for polymer functionalization and coupling by tetrazine-norbornene chemistry

Herein we report the use of a tetrazine-norbornene inverse electron demand Diels-Alder conjugation applied to polymer end-functionalization and polymer-polymer coupling. The reaction was found to be applicable to polymer-polymer coupling, as judged by SEC, DOSY NMR, and LCxSEC analyses, giving diblock copolymers by merely mixing the constituent homopolymers together under ambient conditions, using no catalyst, additive, or external stimulus.     

Desorption electrospray ionisation mass spectrometry reveals in situ modification of a hindered amine light stabiliser resulting from direct N-OR bond cleavage

Detection and characterisation of structural modifications of a hindered amine light stabiliser (HALS) directly from a polyester-based coil coating have been achieved by desorption electrospray ionisation mass spectrometry (DESI-MS) for the first time. In situ detection is made possible by exposing the coating to an acetone vapour atmosphere prior to analysis. This is a gentle and non-destructive treatment that allows diffusion of analyte to the surface without promoting lateral migration. Using this approach a major structural modification of the HALS TINUVIN?123 (bis(1-octyloxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate) was discovered where one N-ether piperidine moiety (N-OC(8)H(17)) is converted to a secondary piperidine (N-H). With the use of 2-dimensional DESI-MS imaging the modification was observed to arise during high curing temperatures (ca. 260 °C) and under simulated physiological conditions (80 °C, full solar spectrum). It is proposed that the secondary piperidine derivative is a result of a highly reactive aminyl radical intermediate produced by N-O homolytic bond cleavage. The nature of the bond cleavage is also suggested by ESR spin-trapping experiments employing α-phenyl-N-tert-butyl nitrone (PBN) in toluene at 80 °C. The presence of a secondary piperidine derivative in situ and the implication of N-OR competing with NO-R bond cleavage suggest an alternative pathway for generation of the nitroxyl radical-an essential requirement in anti-oxidant activity that has not previously been described for the N-ether sub-class of HALS.     

Use of a Single Capillary Electrophoresis Method as a Routine Identity Test for Batch Release of a Range of Pharmaceutical Products

Two independent and orthogonal analytical methods are required when performing identity testing of pharmaceutical products during routine release testing. A microemulsion electrokinetic chromatography method has been developed and validated for routine use as an identity test to release various pharmaceutical products including tablets, capsules and creams. Implementation of the method involved optimisation of parameters to achieve reliable routine operation. Rinsing procedures, in particular, were found to be essential to obtain consistent profiles and migration times. The method has replaced, and offers the potential to replace, a number of methods including HPLC and IR due to the considerable cost and time savings obtained through its use. This method has been successfully approved by the US FDA as a part of 2 New Drug Applications, is registered in Japan, and is in routine QA use within a factory environment.