Browsing by Author "Shiundu, P.M"

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    Automated exploration and exploitation of flow-injection response surfaces
    (Elsevier, 1990) Wadell, A.P; Shiundu, P.M; Wentze, P.D
    Three-dimensional plots of instrumental responses vs. chemical concentrations or flow parameters have been 1 obtained in an automated manner on a computer-controlled flow-injection methods development system. Consideration of several alternative responses for flow-injection systems is shown to help characterize a chemistry more thoroughly and reveal the best experimental conditions. One may see the effects of individual experimental variables (reagent concentrations, pH, flow-rates, etc.), the interactions of these variables, instrumental factors and limitations of the surface exploration procedure employed. Chemical systems studied were the photometric determination of phosphate, palladium(II), iron(II) and persulfate. The propriety of automated response surface mapping is demonstrated and the efficacies of simplex and grid search approaches to response surface exploration are contrasted. Responses obtained include absorbance at peak maximum, relative standard deviation of maximum absorbance, time from injection to peak maximum and wavelength of maximum absorbance. Higher dimensional response surface representations of peak shape and absorbance spectra are also presented. The results show that the response chosen governs the general shape of the surface and the height at any point. This approach to automated characterization of chemical reactions in flow analysis is critically assessed
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    Effect of heavy metal pollution on microalgae richness and diversity in Lake Victoria
    (2009) Mwita, CJ; Nguu, EK; Wasonga, CO; Shiundu, P.M
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    On farm green manure trials: 1997–1998.
    (1998) Kirungu, B. A. M; Kamwana, S; Shiundu, P.M; Kasiti, J
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    Release kinetics of a synthetic tsetse allomone derived from waterbuck odour from a tygon silicon dispenser under laboratory and semi field conditions.
    (2009) Shem, P. M; Shiundu, P.M; Gikonyo, N K; Ali, A.H; Saini, R.K
    The tsetse allomone consisted of pentanoic, hexanoic and heptanoic acids, guaiacol, geranylacetone, 2-undecanone and -octalactone. These compounds were dispensed singly or as a blend from dispensers with 6.028 cm2 diffusion area under laboratory conditions in a two-choice wind tunnel in which the wind speed was maintained constant at 20 cm/sec and the room temperature and relative humidity kept at 24±1°C and 65±5%, respectively. The loss in mass of individual compounds was assessed gravimetrically. Zero-, first- and second-order rate models were tested to determine the release kinetics of the individual compounds and the blend. Comparison of the models using correlation index (R2) indicated that the release of individual compounds followed first-order kinetics while release of the blend followed zero-order kinetics. In the semi field trials, the individual compounds dispensed singly followed first-order release kinetics while their blends followed zero-order release kinetics. It was however, interesting to note that the release kinetics of the individual components of the blend followed zero-order kinetics under semi-field conditions in contrast with the behavior exhibited by the individual components dispensed singly. The compounds placed in dispensers exposed to direct sunlight exhibited higher rate constants than those in the dispensers placed under shade. The rate of release was found to be slightly higher during the first 24 hours and then became steady, obeying Fick's law of diffusion. The release rates were observed to depend on the surface area of the tygon tubing and generally increased with temperature. Rate constants established under laboratory conditions were slightly lower than those obtained under semi field conditions. The results indicate that temperature could be the major environmental determinant of release rates with other variables like relative humidity having little or no effect. However, the magnitude of the effect of temperature on the release rates was not easily demonstrated with the field data. It is thus evident that the release of the compounds was not a simple function of temperature; with the release rates at higher temperatures being lower than would be expected. The zero-order rate equation best described the release of the blend, which was found to be diffusion-controlled. Up to 10,876,155 more results found for "???"
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