Paul M. Shiundu

Adsorption and detection of some phenolic compounds by rice husk ash of Kenyan origin

Rice husk ash (RHA) obtained from a rice mill in Kenya has been used as an inexpensive and effective adsorbent (and reagent) for the removal (and detection) of some phenolic compounds in water. The abundantly available rice mill waste was used in dual laboratory-scale batch experiments to evaluate its potential in: (i) the removal of phenol, 1,3-dihydroxybenzene (resorcinol) and 2-chlorophenol from water; and (ii) the detection of 1,2-dihydroxybenzene (pyrocatechol) and 1,2,3-trihydroxybenzene (pyrogallol) present in an aqueous medium. The studies were conducted using synthetic water with different initial concentrations of the phenolic compounds. The effects of different operating conditions (such as contact time, concentration of the phenolic compounds, adsorbent quantity, temperature, and pH) were assessed by evaluating the phenolic compound removal efficiency as well as the extent of their color formation reactions (where applicable). RHA exhibits reasonable adsorption capacity for the phenolic compounds and follows both Langmuir and Freundlich isotherm models. Adsorption capacities of 1.53 x 10(-4), 8.07 x 10(-5), and 1.63 x 10(-6) mol g(-1) were determined for phenol, resorcinol and 2-chlorophenol, respectively. Nearly 100% adsorption of the phenolic compounds was possible and this depended on the weight of RHA employed. For the detection experiments, pyrocatechol and pyrogallol present in water formed coloured complexes with RHA, with the rate of colour formation increasing with temperature, weight of RHA, concentration of the phenolic compounds and sonication. This study has proven that RHA is a useful agricultural waste product for the removal and detection of some phenolic compounds.

Influence of bulk and surface composition on the retention of colloidal particles in thermal field-flow fractionation

Abstract In this paper we report a wide range of cases in which the retention of colloidal particles in thermal field-flow fractionation (FFF) shows a strong dependence on the chemical composition of the particles or of the particle surfaces. These results are observed among similar particles (such as different latexes) or between dissimilar particles (including latexes as well as inorganic and metallic colloids). These compositional effects are observed for particles suspended in both aqueous and nonaqueous carrier liquids. The dependence of retention on composition is complementary to its dependence on particle size, which has been amply demonstrated in previous studies. The compositional effect is attributed to the dependence of the thermal diffusion coefficient on compositional factors. A number of cases are presented here where compositional effects are significant. Examples include the baseline resolution of 0.30-μm silica particles and 0.300-μm polystyrene (PS) particles and a large difference in retention times between 0.232-μm PS and 0.229-μm polymethylmethacrylate (PMMA) latexes in aqueous suspensions. Also, metallic particles (e.g., palladium) were less retained than silica particles, with latex particles most retained. The resolution of equal-size particles in the nonaqueous carrier liquid acetonitrile is also demonstrated. Surface compositional effects have also been found in this study. These effects suggest the possibility of colloidal surface analysis by thermal FFF. The potential for performing both bulk and surface compositional analysis of particles by thermal FFF makes this FFF technique complementary to both sedimentation FFF and flow FFF techniques for the analysis of complex particulate materials.

Size and compositional studies of core-shell latexes using flow and thermal field-flow fractionation

Two field-flow fractionation (FFF) techniques, flow FFF and thermal FFF, have been used as complementary techniques in a study of core-shell latex particles. Different types of physicochemical information about the particles can be obtained since the fields used in the two techniques interact with different particle properties. The hydrodynamic diameters (and diameter distributions) of the latex particles were measured as a function of pH using flow FFF. Retention in thermal FFF was found to depend on shell composition. These FFF techniques, used together, are shown to be capable of characterizing both the physical size and shell composition of this important class of particles.

Retention behavior of metal particle dispersions in aqueous and nonaqueous carriers in thermal field-flow fractionation

Until quite recently, theories on thermophoresis of particles predicted very low thermophoretic velocities of metal particles in liquids. This prediction was based on the understanding that the very high thermal conductivities of metals relative to most liquid media resulted in quite low temperature gradients across the metal particle thereby leading to low net force on the particle. In this paper, we report the retention behavior of submicrometer size metal particles of silver (Ag), gold (Au), palladium (Pd) and platinum (Pt) suspended in both aqueous and organic (specifically, acetonitrile and tetrahydrofuran) carrier liquids in thermal field-flow fractionation (ThFFF). The dependence of the metal particle retention on various factors such as particle composition, amount of added electrolyte, carrier liquid composition, field strength, channel thickness, and carrier flow-rate is evaluated and discussed. A comparison in particle retention behavior among equal-sized metal, latex and silica particles is also provided.

High-Level Heterologous Expression of Bacillus halodurans Putative Xylanase Xyn11A (BH0899) in Kluyveromyces lactis

The putative xyn11A structural gene (BH0899) encoding a family-11 xylanase from alkaliphilic Bacillus halodurans strain C-125 was heterologously expressed in the yeast Kluyveromyces lactis CBS 1065 and secreted to a level of 156 μg/ml under selective culture conditions in shake flasks. The Xyn11A production level in shake flask cultures of K. lactis CBS 1065 was higher than that reported for other xylanase genes placed under the control of the regulated LAC4 promoter on a plasmid containing an entire sequence of pKD1 from Kluyveromyces drosophilarium. Recombinant Xyn11A was highly active over pH range from 3 to 10, with maximal activity around pH 7. The enzyme showed a specific activity of 628 U/mg-protein on birchwood xylan as substrate, but no cellulase or β-xylosidase activity.

Air and Blood Lead Levels in Lead Acid Battery Recycling and Manufacturing Plants in Kenya

The concentration of airborne and blood lead (Pb) was assessed in a Pb acid battery recycling plant and in a Pb acid battery manufacturing plant in Kenya. In the recycling plant, full-shift area samples taken across 5 days in several production sections showed a mean value ± standard deviation (SD) of 427 ± 124 μg/m3, while area samples in the office area had a mean ± SD of 59.2 ± 22.7 μg/m3. In the battery manufacturing plant, full-shift area samples taken across 5 days in several production areas showed a mean value ± SD of 349 ± 107 μg/m3, while area samples in the office area had a mean ± SD of 55.2 ± 33.2 μg/m3. All these mean values exceed the U.S. Occupational Safety and Health Administrations permissible exposure limit of 50 μg/m3 as an 8-hr time-weighted average. In the battery recycling plant, production workers had a mean blood Pb level ± SD of 62.2 ± 12.7 μg/dL, and office workers had a mean blood Pb level ± SD of 43.4 ± 6.6 μg/dL. In the battery manufacturing plant, production workers had a mean blood Pb level ± SD of 59.5 ± 10.1 μg/dL, and office workers had a mean blood Pb level ± SD of 41.6 ± 7.4 μg/dL. All the measured blood Pb levels exceeded 30 μg/dL, which is the maximum blood Pb level recommended by the ACGIH®. Observations made in these facilities revealed numerous sources of Pb exposure due to inadequacies in engineering controls, work practices, respirator use, and personal hygiene.

Isolation and characterization of polymeric and particulate components of acrylonitrile–butadiene–styrene (ABS) plastics by thermal field‐flow fractionation

Thermal field-flow fractionation (ThFFF) is shown here to be capable of isolating the polymeric and rubber particulate components of acrylonitrile–butadiene–styrene (ABS) plastic in a simple analytical procedure. To facilitate the separation, the ionic strength of the two carrier liquids used here (THF and DMF) was brought up to 0.10 mM to increase the retention of the rubber particles. At a field strength (temperature drop) δT of 50 K, the two components were well separated, although the polymer component was not completely resolved from the void peak due to its low molecular weight. To facilitate a more rapid separation of the components, both field programming and high flow-rate conditions were examined in some detail. Both the particle-size distribution (PSD) of the rubber particles and the molecular weight distribution (MWD) of the polymer components were obtained using ThFFF. Measured MWD and PSD agreed favorably with PSD determined by dynamic light scattering and MWD obtained by size-exclusion chromatography.

Automated exploration and exploitation of flow-injection response surfaces

Abstract 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.

Practical implications of ionic strength effects on particle retention in thermal field-flow fractionation

Modification of ionic strength of an aqueous or non-aqueous carrier solution can have profound effects on the particle retention behavior in thermal field-flow fractionation (ThFFF). These effects can be considered as either advantageous or not depending on the performance criteria under consideration. Aside from the general increase in retention time of particulate material (latexes and silica particles), our experiments indicate improvement in resolution with increases in electrolyte concentration. Absence of an electrolyte in the carrier solution causes deviations from the theoretically expected linear behavior between the retention parameter lambda (a measure of the extent of interaction between the applied field and the particle) and the reciprocal temperature drop across the channel walls. A negative interaction parameter delta(w), of about -0.170 was determined for 0.105- and 0.220-microm polystyrene (PS) latex particles suspended in either a 0.25 or a 1.0 mM TBAP-containing acetonitrile carrier and for 0.220 microm PS in 0.50 and 1.0 mM NaCl-containing aqueous medium. This work also demonstrates that optimum electrolyte concentrations can be chosen to achieve reasonable experimental run-times, good resolution separations, and shifts in the steric inversion points at lower field strengths, and that too high electrolyte concentrations can have deleterious effects such as band broadening and sample loss through adsorption to the channel accumulation surface. The advantages of using ionic strength rather than field strength to effect desired changes are lowered power consumption and possible application of ThFFF to high temperature-labile samples.

Spectrophotometric Method for Determination of Sulfide with Iron(III) and Nitrilotriacetic Acid by Flow Injection

A manual colorimetric method for determination of sulfide has been adapted to flow injection, systematically optimized, and more fully characterized. Its intended application is for measurement of sodium sulfide reagent strength in pulp process streams, and sulfide contamination in effluent from Kraft pulp mills. In the flow-injection method developed, a sample solution containing sulfide is reacted with a mixture of iron(III) and nitrilotriacetic acid under ammoniacal conditions. The absorbance of the intensely-colored green product of this reaction is measured at 636 nm. Excess sulfite is present as a color stabilizer. A linear dynamic range of 20-100 ppm sulfide is readily achieved; the relative standard deviation is less than 1.2% (n = 10) throughout this range, and 0.37% (n = 10) midrange at 60 ppm. The usable dynamic range is 8-250 ppm sulfide. Long-term stability of the method is ensured by periodically performing an automatic cleaning cycle using a hydrochloric acid wash solution. This prevents tube discoloration and removes any precipitates which are formed under strongly alkaline conditions. The sample throuhput rate is at least 30/hr, given alternate acid wash cycles.