Yahya R. Tahboub

Anodic destruction of 4-chlorophenol solution

The electrochemical oxidation of 4-chlorophenol solutions was studied using a dimensional stable anode (DSA), made of pure titanium sheet mesh coated with Ti/TiO(2) and RuO(2) film. An electrochemical cell with one working electrode and two counter-electrodes was designed. A gas collecting system to collect the electrolysis gaseous products was also designed. The influence of current density (6.51-21.58 mA/cm(2)), pH (2.0-12.6) and initial 4-chlorophenol concentration (25-100 mg/l) on the destruction was investigated. Complete elimination was successfully achieved within 2 h for most investigated conditions. Highest rates of elimination were achieved at a pH of 12.6.A new approach to calculate the current efficiency (CE) of the cell was proposed. The volumes of the gases produced at the anode and at the cathode were the basis for the new CE calculations. It was observed that the worst CE was approximately 20% and the best CE was approximately 89%. The most efficient pH was at 12.6 and the most efficient current density was at 11.39 mA/cm(2).

Pyrrolizidine alkaloids from Echium glomeratum (Boraginaceae).

The methanolic extract of the whole plant of Echium glomeratum Poir. (Boraginaceae) has afforded five pyrrolizidine alkaloids, three that were (7S, 8R)-petranine (1), (7S, 8S)-petranine (2), and (7R, 8R)-petranine (3a) or (7R, 8S)-petranine (3b), comprising a tricyclic pyrrolizidine alkaloids subclass; and two that were known but to the species: 7-angeloylretronecine (4) and 9-angeloylretronecine (5). All compounds were tested against a human tumor panel for cytotoxicity; no activity was observed (EC50 values>20microg/ml).

Monitoring of Polychlorinated Biphenyls in Surface Water Using Liquid Extraction, GC/MS, and GC/ECD

Abstract A rapid and reliable analytical method, at trace level concentration was developed and validated for monitoring polychlorinated biphenyls (PCBs) in Jordanian surface water. The method combines the advantage of liquid extraction together with gas chromatography‐mass spectrometry (GC/MS) and gas chromatography‐electron capture detector (GC/ECD). The performance of the method was evaluated by analyzing certified reference material (CRM) of the analytes and applied on real water samples collected from different sites in Jordan. A mixture of 60∶40 dichloromethan‐petroleum ether was chosen as a convenient binary solvent for liquid–liquid extraction. The GC conditions for GC/MS were optimized using He as a carrier gas, temperature programming, and chlorpropham as an internal standard (IS). The conditions for GC/ECD were performed using N2 gas and a temperature program from 160 to 280°C with different increasing rates. The method of GC/MS in the selective ion mode (SIM) gave linear relationships for all PCBs tested between 0.60–6.0 µg/l with R 2=0.9934 (n=7×18). Recoveries from spiked water samples ranged between 87.6 and 91.4%. The mean accuracy and precision obtained were 4.9% and 2.16%, respectively. The mean of detection limit was 0.14±0.04 µg/l. In GC/ECD, linear relationships for all PCBs examined over the range of 0.3–2.4 µg/l was verified as characterized by a linear regression equation and correlation coefficient, R 2=0.9915 (n=12). The average precision and accuracy were 4.86% and 5.21%, respectively. Analyses results clarified that none of the examined Jordanian water samples contained any of the searched for PCBs within the detection limit achieved.

Effect of Counter Electrode Material on the Anodic destruction of 4-Cl Phenol Solution

The electrochemical oxidation of solutions of 4-Cl -phenol was studied using a dimensional stable anode (DSA). An electrochemical cell with one working electrode and two counter electrodes was used. Four counter electrodes—lead, zinc, brass and copper—were tested under different pH values—namely, 2.3, 7.0 and 12.6. Complete elimination was successfully achieved. The experimental results show a considerable influence of the counter electrode material on the rate of destruction. In addition, the pH affects the destruction rate versus the counter electrode material. At a pH of 12.6, the rate of destruction using copper was higher than when using lead, while at a pH of 2.3, this behaviour was reversed. Furthermore, at a pH of 7.0, all the tested counter electrode materials had almost the same performance.

Phase-resolved fluoroimmunoassay of human serum albumin

Abstract In the homogeneous immunoassay of human serum albumin described, a difference in fluorescence lifetime is used along with a small difference in fluorescence intensity to discriminate between the free and the antibody-bound labelled antigen. The immunoassay is based on the use of phase-resolved fluorescence measurements, in which sinusoidally-modulated excitation is combined with phase-sensitive detection to generate time-dependent signals which are integrated over a pi-interval to produce phase-resolved intensities. Texas Red was used as the fluorescent label. Negligible matrix effects were observed from serum, and a comparison of values determined by using the phase-resolved fluoroimmunoassay with values provided by the hospital from which the samples were obtained yielded a correlation coefficient of 0.996.

A predictive-kinetic method for the quantitation of amino acids with ninhydrin

Abstract The development and evaluation of a predictive-kinetic method for quantifying amino acids based on reactions with ninhydrin are described. Conditions are developed for which reactions are pseudo-first-order in the amino acid. Absorbance vs. time data from the kinetic region of the reaction (1–3 half-lives) are fitted to a first-order model to predict the total absorbance change that would occur if the reaction were monitored to completion. Computed absorbance changes vary linearly with amino acid concentration between 1 × 10 −5 and 5 × 10 −5 mol l −1 . Results are virtually independent of changes in temperature (± 1° C) and ninhydrin concentration (± 3 × 10 −3 mol l −1 ).

Kinetic spectrophotometric method for the simultaneous quantitation of amino acids in two- and three-component mixtures

Abstract The development and evaluation of a kinetic method for the simultaneous quantitation of two- and three-component mixtures of amino acids are described. The method is based on reaction with ninhydrin. Multipoint kinetic data collected during one or more half-lives of the slower-reacting component are processed with a nonlinear regression program to resolve the data into the concentrations of the individual components in the mixture. Results demonstrate good linearity between prepared and calculated concentrations of each component and total amino acid in the mixture (10–50 μM). Slopes of least-squares fits of calculated vs. prepared concentrations vary from 0.98 to 1.13 and intercepts vary from −0.1 to 2.9 μM with standard errors of the estimate ( S yx ) between 0.67 and 1.7 μM.

Determination of Phthalates in Jordanian Bottled Water using GC–MS and HPLC–UV: Environmental Study

A simple, accurate and reliable method was presented and validated for the simultaneous monitoring of six phthalates at trace level concentrations in seven different brands of commercial bottled mineral water from Jordan. Liquid-liquid extraction with a mixture of methylene chloride-petroleum ether (20:80, v/v) was used for isolation and enrichment of the phthalates and sample cleanup. This was followed by gas chromatography-mass spectrometry (GC-MS) for identification and high-performance liquid chromatography (HPLC) with ultraviolet detection for quantification. The linear range of the GC-MS calibration curve was 0.3-1.2 µg/L with a mean correlation coefficient (R(2)) of 0.9920 ± 0.0063, the detection limit was < 0.1 µg/L and the percentage recovery was >90%. For HPLC, the linear range was 0.5-10 mg/L with R(2) = 0.9985 ± 0.0012 and an average detection limit of 0.20 ± 0.15 µg/L. The results indicated that the Jordanian bottled water was contaminated with dibutyl-, di-2-ethylhexyl- and di-n-octyl-phthalate, with total phthalate concentrations between 8.1 and 19.8 µg/L. Increasing the storage temperature of the bottled water increased the content of leached phthalates in the water (total concentration of 23-29.2 µg/L).

Chromatographic behavior of co-eluted plasma compounds and effect on screening of drugs by APCI-LC–MS(/MS): Applications to selected cardiovascular drugs

Chromatographic behavior of co-eluted compounds from un-extracted drug-free plasma samples was studied by LC–MS and LC–MS/MS with positive APCI. Under soft gradient, total ion chromatogram (TIC) consisted of two major peaks separated by a constant lower intensity region. Early peak (0.15–0.4 min) belongs to polar plasma compounds and consisted of smaller mass ions (m/z<250); late peak (3.6–4.6 min) belongs to thermally unstable phospholipids and consisted of fragments with m/z<300. Late peak is more sensitive to variations in chromatographic and MS parameters. Screening of most targeted cardiovascular drugs at levels lower than 50 ng/mL has been possible by LC–MS for drugs with retention factors larger than three. Matrix effects and recovery, at 20 and 200 ng/mL, were evaluated for spiked plasma samples with 15 cardiovascular drugs, by MRM–LC–MS/MS. Average recoveries were above 90% and matrix effects expressed as percent matrix factor (% MF) were above 100%, indicating enhancement character for APCI. Large uncertainties were significant for drugs with smaller masses (m/z<250) and retention factors lower than two.

Determination of Major and Minor Elements in Granite by Inductively Coupled Plasma and X-ray Fluorescence Spectrometry

Abstract The development and evaluation of an analytical method for the determination of major and minor elements in granite by ICP-AES and XRF are described. The method applies a standard addition method to generate calibration standards for XRF measurements by ICP-AES from samples to be analyzed. Reliable results were obtained by using simple versions of ICP and XRF, and combined with the pressed-powder pellets for sample preparation. Least squares data for parameters measured by this method vs. reported value for a granite standard reference material gave a slope of 1.002 ± 0.005 and an intercept of -0.029 ± 0.07. The coefficients of variation vary between 0.53% for the largest oxide and 8.3% for the lowest oxide.