Browsing by Author "Ombaka, O."

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Characterization of clays from Tharaka-Nithi County in Kenya for industrial and agricultural applications
(2015) Njoka, E. N.; Ombaka, O.; Gichumbi, J. M.; Kibaara, D. I.; Nderi, O. M.
Clay samples from Tharaka-Nithi County in Kenya were characterized by hydrometer, X-ray fluorescence spectroscopy (XRF), atomic absorption spectroscopy (AAS), TGA, scanning electron microscopy (SEM) and powder diffraction (XRD) methods. The F-test and t-test were used to interpret the results. The major oxides present were Al2O3, SiO2 and the minor ones were CaO, TiO2, MnO, Fe2O3, K2O, MgO and Na2O. The values of SiO2 were greater than those of Al2O3, indicating that the samples were of clay minerals. The clay minerals with low cation exchange capacity (CEC) were present in the samples. The Atterberg limits showed that the inorganic clays of either low or intermediate plasticity having low contents of organic matter were present in the samples. The analysis further showed the availability of essential elements necessary for plant growth. The TGA analysis indicated that the decomposition of clay samples occurred in four steps. The scanning electron microscope photographs revealed that the samples contained a mixture of minerals of morphologies with crystallinity, high porosity and unstable under the electron beam. The major impurity in the clay is quartz, ranging from 22.6-31.9%. Albite is the most dominant component in the clay minerals contributing to 30.3 to 44.1%. The clay from the study area can be used as agro mineral additive to enhance soil fertility for crop production, a fluxing agent in ceramics and glass applications and also as functional fillers in the paint, plastic, rubber and adhesive industries after beneficiation.
Chemical And Mineralogical Analysis of Geophagic Materials Consumed By Pregnant Women In Eastern Nairobi And Nyanza Provinces In Kenya
(2011) Gichumbi, J.; Ombaka, O.
Geophagy is the purposeful or deliberate consumption of Earth and clay deposits by animals, including man. It is a special type of pica, which is defined as the craving and subsequent consumption of non-food substances. The geochemical and mineralogical composition of the geophagic materials consumed by pregnant women and sold in open air markets in Eastern, Nairobi and Nyanza provinces were studied. The mineralogical composition of selected soil samples was investigated using X-ray diffractometry (XRD).The XRD data showed that the soils in these areas consisted mainly quartz, and the clay mineral kaolinite. The preliminary elemental analysis was carried out using Energy dispersive x-ray fluorescence. The geophagic materials were subjected to standard digestion procedures and analyzed for Zn, Cu, Co, Pb and Cd by atomic absorption spectroscopy (AAS). Analysis results showed the geophagic materials contain elevated levels of Fe for a 2.5 g sample. The present study has shown that the geophagic materials from the three provinces open air markets consist mainly of silica and alumina. The levels of Pb exceeded the levels recommended by WHO/FAO limits of 0.01 ppm but the levels obtained for Cd in the samples from Nairobi exceed the WHO/FAO limits of 0.003 ppm
Geochemical and Mineralogical Characteristics of Geophagic Materials from Kiambu, Kenya
(2012) 22. Gichumbi, J.M.; Ombaka, O.; Gichuki, J.G.
Geophagia is the deliberate consumption of soil and clay. The practice of geophagia is due to reasons of culture, medicinal, religious and mineral deficiency. Geophagy is widespread among pregnant and breast feeding women in sub-Saharan Africa and this is evidenced by the sale of geophagic materials in markets across Africa. This study is aimed at studying the geochemistry and mineralogy of geophagic samples sold in Kiambu County, Kenya. The geophagic samples were analyzed by atomic absorption spectrometry, X-ray fluorescence spectrometry, X-ray diffractometry, Fourier transform infrared spectrometry. The results obtained showed that the materials consist mainly of silica (SiO2) and alumina (Al2O3). They also contain the elevated levels of iron oxides. The mineralogical analysis showed that quartz and kaolinite were the major phases. (2) (PDF) Geochemical and Mineralogical Characteristics of Geophagic Materials from Kiambu, Kenya. Available from: https://www.researchgate.net/publication/335635018_Geochemical_and_Mineralogical_Characteristics_of_Geophagic_Materials_from_Kiambu_Kenya [accessed Oct 29 2020].
Investigation Of Physicochemical and Bacteriological Characteristics Of Water Samples From Irigu River Meru South, Kenya
(2012-11) Ombaka, O.; Gichumbi, J. M.
Physicochemical and bacteriological parameter levels of river Irigu were investigated during wet and dry season in order to assess the degree of pollution .The results obtained were compared with WHO standards for drinking water. The physicochemical parameters analyzed were in compliance with the WHO standards except pH, turbidity, phosphorous, iron, manganese, Pb and Al. The values of MPN of coliform organisms /100 ml and E.Coli/100 ml were above the recommended values by WHO. The water from Irigu is not safe for domestic use and requires purification. There is need for awareness programs to educate local villagers to safeguard the river.
Rapid,Economical and selective Compexometric Determination of Iron (III) in its synthetic alloys using 3 hydroxy-3 phynyl-1-(2,4,6-tribromophynyl)
(2019-09) Ombaka, O.; Musundi, S. W.; Gitonga, L. K.; Kibara, D.; Olivia, A. N.
The present study describes a simple, selective, rapid and economical method for the determination of iron (III) in its synthetic alloys using 3-hydroxy -3- phenyl-1- (2,4,6- tribromophenyl) triazene as metallochromic indicator in the 𝑃𝐻 and temperature range of 2.5-3.0 and 20 − 600𝑐 respectively. The colour and shape of the synthesized indicator was light yellow shinning needles having melting point of 590𝑐. It was crystallized from ethanol. The results of elemental study showed that, the values of C, H, N obtained experimentally agrees very well with those obtained theoretically. The colour at the end point changes from violet to light yellow using EDTA as a titrant. There is no interference in either determination from common metal and anion ions other than Pb(II), Cr(II), Mo(VI), Mn(II), U(vI), Cu(II), Cd(II), 𝐹−, 𝑃𝑂4 3−, 𝐶2𝑂4 2−, 𝐻𝑃𝑂4 2−. Reproducible and accurate results are obtained for 5.59 -1.12mg of Iron with relative error less than ±1.79% and standard deviation not more than 0.10%. The results of the test method and reference method (Atomic absorption spectrophotometric) showed that, there is no statistical difference in the results by the two methods.
Screening of Plant Extracts Possessing Methylenedioxyphenyl (MDP) Group as Potential Synergists in Insecticide Formulations using the Maize Weevil, Sitophilus Zea-mais (Motsch.)
(Merit Research Journals, 2020) Michura, A.J.G; Magana, A.; Ombaka, O.; Gachoka, K.
Synergists are compounds that are either negligibly toxic or non-toxic to insects when applied on their own, but enhance the efficacy of an insecticide. Many insects are able to detoxify insecticide molecules and survive their application. Early studies found that most methylene-dioxyphenyl (MDP) agents themselves possess relatively low intrinsic toxicity, but strongly influence the actions of other xenobiotic in mammals and insects. The current commercial synergist, Piperonyl butoxide (PBO), though effective as a synergist, is not classified as an organic product in many countries. With the current focus on decreasing environmental contamination and increasing demand for organic products, a natural compound for use as a synergist would be ideal. Searches for effective synergists have not yet yielded many compounds that have the viability equivalent to that of PBO. This paper screened plant extracts possessing MDP rings as potential synergists in insecticides formulations using the maize weevil, Sitophilus zea-mais. Dose-mortality experiments were carried out on S. zea-mais at four concentrations of synergists. Topical application of synergist on S. zea-mais was done in triplicate in a CRD. Experiments were conducted under controlled laboratory conditions of 27 ± 2OC and 60 ± 5%RH with normal daylight hours. Analysis of Variance (ANOVA) was used to obtain the mean mortality differences of S. zea-mais at P ≤ 0.05 while Duncan’s Multiple Range Test (DMRT) was used to rank significant concentration means within a synergist. Black pepper seed hexane extract (BPSHE) and PBO after 48 h exposure were statistically significant (P ≤ 0.05) with the average percentage mortalities of 10% and 20% at 10,000 ppm and 20,000 ppm respectively, while PBO and Coriander leaves hexane extract (CLHE) were significant P ≤ 0.05 after 72 h. PBO was the most toxic synergist (36.67 ± 3.33%) followed by CLHE (26.67 ± 3.43%) at 20,000 ppm. It can be concluded that the plant extracts tested and statistically significant at a particular exposure time can be used to replace the standard PBO in insecticide formulations since their inherent toxicity is low. At a higher concentration (20,000 ppm) PBO was the most toxic synergist which could be contributing to the toxicity of insecticide when used in formulations.
Spectrophotometric Determination of Iron (III) by New Analytical Reagents Derived from Coupling Arylhydroxylamine and Aryldiazonium salt
(2012) Ombaka, O.; Gichumbi, J. M.
A highly sensitive and selective spectrophotometric method is developed for the determination of iron(III) in aqueous solution withhydroxytriazenes. In this work, the effect of pH variation, the composition of the complex of Fe3+ to hydroxytriazenes, precision, Sandell'ssensitivity and interference studies were investigated. This investigation was done under the optimum reaction conditions and otherimportant analytical parameters. Hydroxytriazenes reacts with the Fe3+ and forms coloured complexes. The Fe(III) complex is detected atλmax = 410 nm and pH range 3-4 for reagent no(i), 530 nm and 4-5 for reagent no (ii), 410 nm and 4.5 -5.5 for reagent (iii), 396 nm and 3.5-5.0 for reagent (iv), 467 nm and 2.5-3.5 for reagent no.(vi). Beer-Lambert's law is obeyed in the concentration range (1.0-5.0) × 10-5M,(1.5-9.0) × 10-5 M, (0.5-4.0) × 10-5 M, (0.3-1.8) × 10-5 M, (0.6-3.6) × 10-5 M, (2-12) × 10-5 M for nos. (i), (ii), (iii), (iv), (v), (vi)respectively. The molar ratio of Fe(III) to the hydroxytriazenes was found as 1:3. The limiting concentration for interference for 35diverse ions are reported. The standard deviation ranges between 0.019 to 0.088. The Sandell's sensitivity in ng/cm3 ranges between2.5.579 to 4.189. Reagent nos. (iii), (iv), (v), which were very sensitive were used to determine the level of iron in veg etable samples fromBaharini, Nakuru To wn and the results obtained were compared with those of atomic absorption spectrophotometer.
Synthesis and insecticidal activities of some selected hydroxytriazenes. Journal of Environmental Chemistry and Ecotoxicology
(2011-10) Ombaka, O.; Gichumbi, J. M.
Eight hydroxytriazenes were synthesized and then subjected to spot tests. The composition of these hydroxytriazenes was analyzed using elemental analysis and their physical characteristics like melting point, crystal shape and colour were studied into details. The synthesized compounds were screened for their insecticidal activities against one day old male Drosophila melanogaster Meig (vinegar flies or fruit flies). Out of all the eight compounds screened, 3-hydroxy-3-m-tolyl-1-m-nitrophenyltriazene, 3- hydroxy-3-m-tolyl-1-p-methoxyphenyltriazene, 3-hydroxy-3-n-propyl-1-o-chlorophenyltriazene were the most active having LC50 values of 2.898, 3.898 and 1.812 ppm respectively. The least active compound is 3-hydroxy-3-m-tolyl-1-phenyltriazene having the value of 16.850 ppm. Heptachlor, a commercial product, had LC50 value of 1.570 ppm.