Preparative reproducibility

The logk obtained by MEKC, MEEKC and LEKC were also compared with membrane permeability reference data by Ornskov et al. [92]. An improved correlation was obtained in the order MEKC>MEEKC>LEKC. Thus, LEKC appears to provide experimental conditions that mimic more closely physiological membranes [93], However, liposomes and vesicles remain unstable and difficult to prepare reproducibly. Their use is then devoted to some parhcular applicahons. 

Preparation of the acetylenic dichloride by conversion of the diol in pyridine with neat thionyl chloride is difficult to control, and hazardous on a large scale. Use of dichloromethane as diluent and operation at —30°C renders the preparation reproducible and safer [1], During distillation at up to 110°C/7-8 mbar, slight overheating of the residue to 120°C caused explosive decomposition [2], Sensitive to detonator, sometimes to mechanical shock [3],... 

The main advantage of this polymerization is that it can be carried out at room temperature without an energy input. PACA nanoparticles have been prepared reproducibly at a semi-industrial level and can be made aseptically [57]. 

Figure 14. Apparatus to allow ion beams to be used in surface preparation. Reproduced with permission from Ref. 83. Copyright 1983, Elsevier Science Publishers B.V.

If Form I could no longer be prepared reproducibly, then Abbott needed to be able to develop a viable formulation of Form II. Both plans were fully executed. After considerable work, the process group discovered a number of contributing factors to the appearance of Form II. Ultimately, the solution to the problem was a simple one batches of ritonavir were seeded with Form I crystals to encourage precipitation of the desired polymorph. 

Figure 5.9 IR spectroscopic images of phase separation of PBD—DAP blends (50 wt.% DAP) taken immediately after sample preparation. Reproduced from figure 2 of Ref. 27, with permission.

Vinyl esters of trialkylacetic acid copolymerize randomly with vinyl acetate. Paint latices with a very low residual monomer content, based on vinyl acetate-W 911 copolymers, can be prepared reproducibly via a variant of the monomer emulsion addition technique, when a relatively large part of the anionic emulsifier is present in the initial reactor charge. 

BSA was effective for the derivatization of purine and pyrimidine bases [456] and nucleosides [457]. Bases were silylated by heating at 150°C with BSA—acetonitrile (1 3) for 45 min. It was stated that under these conditions the TMS derivative of guanine can be prepared reproducibly, but both cytosine and 5-methylcytosine provided two peaks. Silylation of nucleosides, including pseudouridine, was carried out by heating at 120°C with a 100-fold excess of BSA for 2 h. With the use of OV-17 as the stationary phase, this procedure was adopted for the determination of the composition of ribonucleic acids. 

Fischer, D. J., Simulation of Flood for Preparing Reproducible Water-... 

Simulation of the Flood for Preparing Reproducible Water-Damaged Books... 

Figure 12.2. MWNTs dispersions at 0.01 wt% in various solvents one week after their preparation. [Reproduced by permission of Kautschuk Gummi Kunststoffe from L. Bokobza and M. Rahmani "Carbon nanotubes Exceptional reinforcing fillers for silicone rubbers", KGK, 62,112,2009].

Electrode-Preparation and Aging. Electrode preparation procedures are given by Keston (14) and by Ives and Janz (II). Electrodes were prepared from a paste containing 90% silver oxide and 10% silver bromate placed on a platinum spiral and heated in a furnace for 7 min at 650°C. Janz and Taniguchi (12) have reviewed the preparation, reproducibility, and stability of this electrode. Taylor and Smith (13) found the equilibrium potential to be stable within 0.02 mV. Electrodes... 

THE RECOVERY DATA OF VERAPAMIL FROM COMMERCIAL PREPARATIONS. REPRODUCED WITH PERMISSION FROM (I33 ... 

Because of the difficulty in preparing reproducibly active duplicate samples of catalyst, it has been suggested that to have a uniform catalyst for a series of reactions it is best to prepare a larger amount of the Raney nickel and to use portions of it for the various individual reactions. This, however, is not as straightforward as it might seem. The more active catalysts, W3-W7, lose their... 

Once samples have been prepared consistently, it is possible to prepare reproducible assay data. If an assay is reproducible, analysis of a reaction aliquot will give identical results when two portions of this aliquot are sampled and assayed. The true value of a rugged IPC assay is demonstrated when a skilled coworker can readily reproduce the assay. Tips for generating reproducible assay data are shown in Table 7.3. 

Figure 1. Relative integrator response (arbitrary units) for several methods of sample preparation. (Reproduced from Ref, 12. Copyright 1977, American Chemical Society).

Figure 4.1 Solvent preparation. Reproduced by permission of Hewlett-Packard.

Using these techniques, it was possible to prepare reproducible samples suitable for testing, albeit with considerable difficulty in the case of solid epoxies. 

In practice, separation of enantiomers by the use of chiral stationary phases is not free from problems. Chiral stationary phases are difficult to prepare reproducibly, are sometimes of lower chromatographic efficiency than expected, and optimization of separation conditions is restricted by the fixed nature of the chiral centres. Chiral mobile phases are free from many of these problems, optimization of the separation is more convenient, and conventional reversed-phase columns may be used. Thus N-(2, 4-dinitrophenyl)-L-alanine-n-dodecyl ester has been used as a non-ionic chiral mobile phase additive for the resolution of 1-azahexahelicenes by reversed-phase chromatography. The resolution obtained was found to be a function of the mobile phase polarity and the concentration of chiral additive used. 

Figure 31. An Arrhenius plot for the discoloration of a liquid multisulfa preparation (Reproduced from Ref. 301 with permission of the American Pharmaceutical Association.)...

Metal organo- and hydro-sols can be obtained with exceptionally high metal concentrations (surfactant-stabilized metal alloy nanoparticles are easily accessible via the co-reduction of different metal salts. As shown in Fig. 2.1, even the inner structure of the colloidal alloy particles can be tailored by adjusting the reduction conditions and/or preparative pathways to prepare homogeneous [8, 36, 37], gradient [38-40] or egg-sheU type [41] nano-alloys. Reductive stabiHzation ... 

Figure 6-10. Representative spray pyrolysis system used for particle preparation. (Reproduced with permission from ref 82. Copyright 2003 Elsevier LTD.)...

Figure 8. Effect of tryptophan modification by NBB (2-hydroxy-5-nitrobenzylbromide) on anticomplementary activity of rabbit IgG and its Fc fragment. IgG was first modified and then heat-aggregated. Modified Fc was tested as such. Results refer to 100 /i,g of each preparation. Reproduced with permission from Allan and Isliker (1974a) copyright 1974, Peigamon Press, Ltd.

The presence of defects in a given surface structure may also play an important role in the electrocatalytic process. Normally, long-range ordered domains are separated from each other by step or kink sites. The substrate atoms that belong to kink or step sites have special adsorption properties since they have a lower coordination number, that is, they have a lower number of nearest neighbor substrate atoms than the surface atoms in a well-ordered domain. These properties may result in an increased catalytic activity. In order to model the real surfaces, stepped and kinked surfaces are used since they have a well-defined distribution of these sites and they can be prepared reproducibly. 

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