Versatile IEEE-488 data acquisition and control routines for a diode array spectrophotometer

The UV-visible diode array spectrophotometer is a work-horse instrument for many laboratories. This article provides simple data acquisition and control routines in Microsoft QuickBasic for a HP-8452A diode array spectrophotometer interfaced to an IBM PC/XT/AT, or compatible, microcomputer. These allow capture of full spectra and measure absorbance at one or several wavelengths at preset time intervals. The variance in absorbance at each wavelength is available as an option

Computer-controlled apparatus for automated development of continuous flow methods

An automated apparatus to assist in the development of analytical continuous flow methods is described. The system is capable of controlling and monitoring a variety of pumps, valves, and detectors through an IBM PC-AT compatible computer. System components consist of two types of peristaltic pumps (including a multiple pump unit), syringe pumps, electrically and pneumatically actuated valves, and an assortment of spectrophotometric and electrochemical detectors. Details of the interface circuitry are given where appropriate. To demonstrate the utility of the system, an automatically generated response surface is presented for the flow injection determination of iron(II) by its reaction with 1,10-phenanthroline

<b>Factors affecting particle retention in thermal field-flow fractionation</b>

In this paper, we report a range of factors which affect the retention of colloidal particles in thermal field-flow fractionation (ThFFF). These results are observed among different sizes of polystyrene (PS) latex particles suspended in both aqueous and nonaqueous liquid carriers and very low density lipoproteins in a phosphate buffer. These factors include particle size and chemical composition, field strength, cold-wall temperature of the channel and the nature of the suspension medium. These results show that ThFFF can be used to fractionate colloidal particles according to size and that for an unknown colloidal sample material, a calibration curve must be obtained using particles of similar composition. This is necessary because the degree of retention of the colloidal material is dependent on chemical composition of sample material as evidenced by the chemical composition study. The potential of using ThFFF for physico-chemical characterization of colloidal material is illustrated through the evaluation of thermal diffusion coefficient of PS particles as a function of size, cold-wall temperature, and carrier solution composition. The tunabiliy of the extent of retention of the colloidal particles in a ThFFF channel is illustrated by results of the influence of field strength on retention

Removal of Cu(II) from Aqueous Solution Using a Micaceous Mineral of Kenyan Origin

A micaceous mineral (MicaM) available locally in Kenya was utilized as an inexpensive and effective adsorbent for the removal of Cu 2+ ions from aqueous solution. The effects of contact time, pH, temperature, adsorbate and adsorbent concentrations, and the concentration of electrolyte on the removal of Cu 2+ ions were studied. Maximum removal of Cu 2+ ions occurred over the pH range 4.0–7.0. The adsorption of Cu 2+ ions increased with an increase in the dose ratio of mineral to Cu 2+ ion concentration and decreased with adsorbent particle size. Isotherm analysis of the adsorption data obtained at 25°C showed that the adsorption of Cu 2+ ions on MicaM followed both the Langmuir and Freundlich isotherms. The uptake of Cu 2+ ions increased on increasing the pH of the solution from 1.5 to 7.0 as well as on increasing the temperature from 25°C to 60°C. An adsorption capacity of 0.850 g/g was achieved for MicaM towards the Cu 2+ ion. This study has demonstrated that locally abundant micaceous mineral can be used as an effective adsorbent for the treatment of waters containing Cu 2+ ions without any prior chemical pretreatment

Thermal stability of Vernonia galamensis seed oil

. The physicochemical changes of refined vernonia oil?RVO (which naturally contains epoxidized triglycerides) upon heating was evaluated and is reported in this manuscript. A boiling point range of 183 &#176;C to 190 &#176;C (at 760 mm Hg) for the vernonia oil was obtained using the Siwolobboff's method. The oil changed its physical appearance and consistency in the course of the heating. A homogenous free?flowing beige?sand shade refined vernonia oil at room temperature (25 &#176;C) was transformed irreversibly to an intense?brown shade, becoming increasingly more viscous with increase in temperature, and ceasing to flow momentarily at 188 &#176;C. On cooling to room temperature, the oil solidified into a brown rubber?like elastic material. The oil also exhibited a reduction in its oxirane content from 1.39&#177;0.004 equivalent HBr kg?l at 25 &#176;C to 0.542&#177;0.002 equivalent HBr kg?l at 70 &#176;C. This signifies a 61% drop in oxirane content for the 45 &#176;C temperature rise. These findings point towards a thermally driven polymerization and/or decomposition of the refined vernonia oil (RVO). (Received May 20, 2000, revised December 13, 2000) Bull. Chem. Soc. Ethiop. 2000, 14(2), 161-16

Thermal stability of <i>Vernonia galamensis</i> seed oil

The physicochemical changes of refined vernonia oil-RVO (which naturally contains epoxidized triglycerides) upon heating was evaluated and is reported in this manuscript. A boiling point range of 183 °C to 190 °C (at 760 mm Hg) for the vernonia oil was obtained using the Siwolobboff's method. The oil changed its physical appearance and consistency in the course of the heating. A homogenous free-flowing beige-sand shade refined vernonia oil at room temperature (25 °C) was transformed irreversibly to an intense-brown shade, becoming increasingly more viscous with increase in temperature, and ceasing to flow momentarily at 188 °C. On cooling to room temperature, the oil solidified into a brown rubber-like elastic material. The oil also exhibited a reduction in its oxirane content from 1.39 plus or minus 0.004 equivalent HBr kg-l at 25 °C to 0.542 plus or minus 0.002 equivalent HBr kg-l at 70 °C. This signifies a 61% drop in oxirane content for the 45 °C temperature rise. These findings point towards a thermally driven polymerization and/or decomposition of the refined vernonia oil (RVO)

<b>Kinetics and thermodynamics of aqueous Cu(II) adsorption on heat regenerated spent bleaching earth</b>

This study investigated the kinetics and thermodynamics of copper(II) removal from aqueous solutions using spent bleaching earth (SBE). The spent bleaching earth, a waste material from edible oil processing industries, was reactivated by heat treatment at 370 ^oC after residual oil extraction in excess methyl-ethyl ketone. Copper adsorption tests were carried out at room temperature (22±3 ^oC) using 5.4 x 10^-3C M metal concentrations. More than 70% metal removal was recorded in the first four hours although adsorption continued to rise to within 90% at 42 hours. The pH, adsorbent dosage and initial concentrations were master variables affecting RSBE adsorption of Cu(II) ions. The adsorption equilibrium was adequately described by the Dubinin-Radushkevich (D-R) and the Temkin isotherms and the maximum sorption capacity derived from the D-R isotherm was compared with those of some other low cost adsorbents. The adsorption process was found to follow Lagergren Pseudo-second order kinetics complimented by intra-particle diffusion kinetics at prolonged periods of equilibration. Based on the D-R isotherm adsorption energy and the thermodynamic adsorption free energy ∆G, it was suggested that the process is spontaneous and based on electrostatic interactions between the metal ions and exposed active sites in the adsorbent surface