Conway method

A further disadvantage of the Conway method is that the volume of solution in the center well is critical and must be pipetted with volumetric precision as well as dispatch. The Conway dishes must be prepared considerably in advance of their use, for the danger of contamination becomes excessive if they are prepared at the bedside. The Seligson technique requires no quantitative measurements except for the volume of the unknown specimen, since the ammonia diffused is concentrated in a very small volume, all of which is transferred by dipping it into the colorimeter tube. The volume of acid which coats the diffusion rod is... 

A recent study of the Conway method applied to whole blood (R2) stresses the importance of the ammonia derived from the breakdown of blood constituents in the highly alkaline diffusion medium and recommends a correction for this. It is suggested that two diffusions be performed, one for 40 and one for 80 minutes. The difference between the two values would represent the actual preformed ammonia of the blood. This problem has been discussed by others (B6, S3), as well as by Conway (C5). The requirement for a 40-minute diffusion in order to obtain a complete yield of ammonia from the sample is a major handicap of the Conway apparatus. The Seligson method requires only 10 to 20 minutes, resulting in much less time for artifact. The use of the titration of basic (R2) leads to the inclusion of much volatile base which is not ammonia, and much of the apparent formation of ammonia during diffusion is probably volatile amines, for it is not seen so constantly using Nesslerization methods. 

Tashiro s Indicator. The stock solution is made by mixing 200 ml. of 1 per cent, alcoholic methyl red with 50 ml. of 0-1 per cent, alcoholic methylene blue. Both dyes must be dissolved in pure alcohol. For use, 1 part of stock solution is mixed with 1 part of alcohol and 2 parts of distilled water. This is an example of a screened indicator, or one in which the colour change is made more distinct by addition of a second pigment (methylene blue) to cut out part of the spectrum. The indicator is used in the Conway methods for the micro-analysis of ammonia and urea. 

Conway, B. E. Electroanalytical Methods for Determination of AI2O3 In Molten Cryolite 26... 

Haas-Laursen, D. E., Hartley, D. E. and Conway, T. J. (1997). Consistent sampling methods for comparing models to CO2 flask data, /. Geophys. Res. 102, 19059-19071. 

Molecular diffusion ( ) has been used in various ways in micro analysis. In Figure 27, is seen the Conway diffusion dish, in which the substance to be tested is placed on the outside, and the reagent is placed in the central cup. The cup is covered, and after a time, the substance being analyzed diffuses into the central cup where it produces an effect which can then be interpreted in various ways. In the Figure, carbon monoxide is being determined. This same method is very useful for alcohol determination, where dichromate oxidizes the alcohol after it diffuses into the dichromate from the blood. 

Conway, E. J. and O Malley, E. Microdiffusion methods. Ammonia and urea using buffered absorbance (revised methods for ranges greater than 10 mu/g N). Biochem. 

The introduction of the Game of Life, developed by John Conway, ignited a burst of interest in CA models in the 1970s. At that stage, they were regarded mainly as a curiosity and few researchers anticipated that there would be much direct application for them in the physical and life sciences. Steven Wolfram s work in the 1980s on the use of CA in physics3 established the method as one with potential in many scientific problems and since then numerous scientific applications have appeared. 

Leverentz, B., Conway, W.S., Alavidze, Z., Janisiewicz, W.J., Fuchs, Y., Camp, M.J., Chighladze, E. and Sulakvelidze, A. (2001) Examination of bacteriophage as a biocontrol method for Salmonella on fresh-cut fruit a model study . Journal of Food Protection, 64, 1116-1121. 

To summarise, AC methods have proved most successful where the system is straightforward and can be modelled analytically. By measurement over a wide range of frequencies the constants for the reaction steps constituting the model can be established and, particularly if adsorbed species are involved, AC methods have proved very powerful indeed, with a major area of application being in the study of metal passivation, as discussed in detail elsewhere in the book. An example of this behaviour in practice is provided by the work of Conway s and Hillman s groups on chlorine evolution at platinum. Several mechanisms for this reaction have been proposed, including both Volmer and Heyrovsky types ... 

Before considering different theoretical approaches to determining the free energies and other thermodynamic properties of ionic solvation, it is important to be aware of a problem on the experimental level. There are several methods available for obtaining these quantities for electrolyte solutions, both aqueous and nonaqueous some of these have been described by Conway and Bockris162 and by Padova.163 For example, enthalpies of solvation can be found via thermodynamic cycles, free energies from solubilities or galvanic cell potentials. However the results... 

Taylor (1952), 43 (Equation for die temp of expln) 59, Table 14 (Approximate relations of temps of expln to heats of expln) 33) F.S. Harris Jr, The Measurement of Temperature in Explosives , Univ of Utah Tech Mem (Aug 31, 1953) (A literature survey giving a summary of methods of measuring temps developed on deton of expls) 34) J.H. Hett J.B. Gilstein, A Study of Techniques for the Measurement of Detonation Spectra and Temperatures , ResDiv of NYUniv, Final Rept May 14, 1953. Contract DA-30-069-ORD-945 35) J.B. Conway et al, JACS 77, 2026-27 (1955) (The production of a flame temp of 5000°K) 36) F.C. Gibson C.M. Mason,... 

RT/aF. One would expect such a result if the double layer is behaving as an ideally polarizable double layer ( Section 6.4.3) and there is, e.g., no adsorbed intermediate to slow down the decay. Figure 8.8 shows this case. When there is an adsorbed intermediate radical of significant concentration, the decay method can be used to determine the potential dependence of the fraction of the surface covered by the radical (Conway and Tilak, 1982). 

For reviews, see Schafer Top. Curr. Chem. 1990, 152. 91-151, Angew. Chem. Int. Ed. Engl. 1981, 20, 911-934 [Angew. Chem. 93,978-1000) Fry Synthetic Organic Electrochemistry, 2nd ed. Wiley New York. 1989, pp. 238-253 Eberson Utley, in Baizer Lund Organic Electrochemistry Marcel Dekker New York, 1983, pp. 435-462 Gilde Methods Free-Radical Chem. 1972, 3, 1-82 Eberson, in Patai The Chemistry of Carboxylic Acids and Esters, Wiley New York, 1969, pp. 53-101 Vijh Conway Chem. Rev. 1967, 67, 623-664. 

Trifluoroacetic acid [76-86-7] M 114.0, f.p.-15.5°, b 72.4 , d 1.494, n 1.2850. The purification of trifluoroacetic acid, reported in earlier editions of this work, by refluxing over KMnOa for 24h and slowly distilling has resulted in very SERIOUS EXPLOSIONS on various occasions, but not always. This apparently depends on the source and/or age of the acid. The method is NOT RECOMMENDED. Water can be removed by making 0.05% in trifluroacetic anhydride (to diminish water content) and distd. [Conway and Novak JPC 81 1459 1977]. It can be refluxed and distd from P2O5. It is further purified by fractional crystn by partial freezing and again distd. 

Cheek, D. B. Estimation of the Bromide Space with a Modification of Conway s Method. J. Appl. Physiol. 5, 639 (1953). 

Hoffman, H., Stuehr, J., and Yeager, E. (1966). Studies of relaxation effects in electrolytic solutions with the pressure-step methods. In Chemical Physics of Ionic Solutions (B, E. Conway and R. G. Barradas, eds.), pp. 255-227. Wiley, New York. 

Determination.—Analytical methods for determination of D-glucuronic acid have been discussed recently by Artz and Osman.6 Decarboxylation is the most accurate method, and is generally used for determination of D-glucuronic acid from plant sources. Some modifications have been introduced recently for small quantities.26 Other methods, such as reduction, measurement of optical rotation, and an array of color tests,27 are of limited value. Levvy28 has applied a cerimetric method using a Conway burette. 

It should be emphasized that none of the methods in categories (ii) and (iii) that have been used to obtain the absolute enthalpies of hydration of ions is theoretically rigorous. For example, Conway and Salomon (54) have made a detailed critique of the Halliwell—Nyburg type of treatment. If the water dipole orientation is not exactly opposite at cations and anions, as seems to be indicated by various previous calculations (55, 56), then the assumption that the difference between heats of hydration of cations and anions of the same radius originates from the ion-quadrupole interaction could be inaccurate. However, the results given in Table 7 are probably reliable to within a few kcal mole-1, despite the fact that it is impossible to assess their accuracy specifically. They indicate that an anion has a more negative absolute heat of hydration than a cation of the same crystal radius. 

The column and planar configurations just discussed are the most common modes of LC but not the only ones. At least four different methods have been proposed for performing LC without a solid support, and two have survived as viable methods. The term countercurrent chromatography is applied to these techniques, and a review of their development has been written by Ito and Conway.6 Countercurrent chromatography will not be discussed further here, but it should be noted that it has one main advantage it is free from undesirable adsorption and catalytic effects that sometimes result from the use of solid supports. 

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