Bahruddin Saad

Solvent extraction of lanthanum(III) from acidic nitrate-acetato medium by Cyanex 272 in toluene

Abstract The extraction behavior of La(III) from acidic nitrate-acetato medium by bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272, H 2 A 2 ) in toluene either alone or in combination with trioctylphospine oxide (TOPO, B) has been investigated as a function of contact time, aqueous phase concentration of La 3+ , H + , NO 3 − and Ac − (acetate), Cyanex 272 and TOPO concentration in the organic phase and temperature. The distribution coefficient is found to decrease with increasing La 3+ concentration up to 7.34 mM La 3+ in the aqueous phase, after which it increases up to 9.79 mM La 3+ concentration and again decreases. The pH and log extractant concentration dependencies suggest that [La(Ac) 2 A·3HA] and [La(Ac)A 2 ·B] are extracted in the system without and with TOPO, respectively. The pH dependence of 1 indicates that one hydrogen ion is liberated in forming the complex for both the extraction system with TOPO and without TOPO. The distribution coefficient decreases with increasing acetate ion concentration at higher acetate ion concentrations with and without TOPO but is less dependent at low acetate concentrations. The synergistic effect of TOPO is found only at higher TOPO concentrations. These results suggest that the [La(Ac) 2 A·3HA] (o) and [La(Ac)A 2 ·B] (o) species are extracted in the system without and with TOPO, respectively. The temperature dependence data give the enthalpy of extraction, Δ H , of 60 kJ/mol. The equilibrium constant, K ex , is 10 −2.16 with a standard deviation of log K ex of 0.096 in the system without TOPO and 10 −2.58 with a standard deviation of log K ex of 0.21 for the extraction system with TOPO. The loading capacity of Cyanex 272 is found to be 15.97 g La(III)/100 g Cyanex 272. The phosphorus to lanthanum ratio of the solid complex obtained is 3.

Analysis of anions and cations in drinking water samples by Capillary Ion Analysis

Abstract The use of capillary ion electrophoresis (CIE, Waters’ tradename: Capillary Ion Analysis, CIA) for the analysis of four anions and four cations in drinking water samples available on the Malaysian market, such as natural mineral water, bottled drinking water and tap water, was investigated. In addition, zam-zam water (an underground water, much sought-after by Muslims and only available in Mekah, Saudi Arabia) was also analyzed. The anions analyzed were chloride, sulphate, nitrate and fluoride while the cations analyzed were potassium, calcium, sodium and magnesium. Results of this determination generally show a low content of anions and high content of calcium and magnesium in natural mineral water and non-detectable amounts of anions and cations in bottled drinking water. Out of the 15 mineral waters of different brands that were analyzed, four brands show anionic and cationic levels almost similar to that of tap water. With the exception of fluoride, an abnormally high level of both anions and cations were detected in all the zam-zam water samples analyzed, as compared to the other drinking waters.

Validated Stability Indicating Assay of Gemifloxacin and Lomefloxacin in Tablet Formulations by Capillary Electrophoresis

Abstract A capillary zone electrophoretic (CZE) method has been developed for the determination of gemifloxacin and lomefloxacin in pharmaceutical tablet formulations. The CZE separation was performed using a 75 µm×35 cm fused silica capillary under the following conditions: 25°C; applied voltage, 12 kV; 25 mM H3PO4‐NaOH running buffer (pH 8.5). The detection wavelength was 254 nm. Flumequine was used as internal standard. The method was suitably validated with respect to linearity, limit of detection and quantification, accuracy, precision, specificity, and robustness. The calibration was linear from 5 to 50 µg mL−1 for gemifloxacin and 10 to 60 µg mL−1 for lomefloxacin, and the limit of detection and quantification were 2.93, 4.91 µg mL−1, and 3.87, 8.93 for gemifloxacin and lomefloxacin, respectively. Recoveries ranging from 94.4–108.6% were obtained for both drugs. The method was successfully applied to the determination of gemifloxacin and lomefloxacin in pharmaceutical tablets. Excipients present in the tablets and degraded products from different stress conditions did not interfere in the assay.

Determination of ortho-phenylphenol, diphenyl and diphenylamine in apples and oranges using HPLC with fluorescence detection

Abstract A reversed-phase high performance liquid chromatographic (RP-HPLC) method for the determination of the fungicides ortho-phenylphenol (OPP), diphenyl (DP) and diphenylamine (DPA) is developed. A mobile phase consisting of methanol:water (70:30) and fluorescence detection ( E x and E m set at 285 and 340 nm, respectively) was used. The fungicide residues were extracted with ethyl acetate, and concentrated prior to the HPLC analysis. The proposed HPLC method was clearly superior as compared to an earlier report that was based on a mobile phase of acetonitrile:methanol:water (47:13:40 v/v) for the determination of DP, OPP and thiabendazole, especially with respect to lower detection limits and faster analysis times. Limits of detection were 0.005, 0.100 and 0.02 ppm for OPP, DP and DPA, respectively. Recovery studies that were done by fortifying apples and oranges at 0.25 and 0.50 ppm levels respectively, were satisfactory (average percent recoveries of 108.8 and 84.0%, respectively for apples and oranges). Results on the determination of these fungicides in several apple and orange samples will also be discussed.

Kinetics of lanthanum(III) extraction from nitrate-acetato medium by Cyanex 272 in toluene using the single drop technique

Abstract The rate of forward extraction of La(III) from nitrate-acetato medium by bis-(2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272, H2A2) dissolved in toluene has been measured by the single drop technique. The rate of mass transfer per unit area is found to be proportional to [La(III)], [H2A2](o) and [H+]−1 at the interface. The forward extraction rate constant, kF, has been measured to be 10−7.0 m/s. From the temperature dependence of rate measurement, the values of Ea, ΔS±, ΔH± and ΔG300± are calculated to be 71 kJ/mol, −155 J/mol K, 69 kJ/mol and 115 kJ/mol, respectively. The rate expression can be written as; F La =10 −7.0 [ La 3+ ][ H 2 A 2 ] ( o ) [ H + ] ( i ) −1 kmol / m 2 s Analysis of the rate expression suggests that the formation of [La(HA2)]2+at interface from La3+and HA2− is the rate-determining step for the forward extraction of La(III). Negative entropy of activation suggests that the above rate-determining step occurs via the SN2 mechanism.

Determination of Ofloxacin Enantiomers in Pharmaceutical Formulations by Capillary Electrophoresis

Abstract A capillary electrophoretic method for the separation of the enantiomers of ofloxacin using carboxymethyl‐β‐cyclodextrin (CM‐β‐CD) as chiral selector is described. The effect of the type of cyclodextrin and its concentration, buffer concentration, and its pH, as well as instrumental parameters, such as applied voltage and temperature were systematically studied. The highest resolution of ofloxacin enantiomers obtained was around 2.8. This was achieved using Tris‐citrate buffer (pH 4.5) that contained 3 mg mL−1 CM‐β‐CD and using UV detection (254 nm), applied voltage (12 kV), and capillary temperature of 25°C. Acceptable validation criteria for selectivity, precision, linearity, limit of detection, and quantitation were also included. Recoveries between 98.3–103.4% were obtained when the method was used to determine the enantiomers of ofloxacin that were spiked to placebos. The proposed method is fast, sensitive, inexpensive, and its usefulness was demonstrated for the analysis of five pharmaceutical preparations, two of which just contained the S‐ofloxacin while the other three contained both isomers as racemic mixtures.

Determination of oxolinic acid in feeds and cultured fish using capillary electrophoresis

Abstract A capillary electrophoretic method was developed for the determination of the antibiotic oxolinic acid. The electrolyte composed of a buffer solution (10 mM phosphate, pH 9.00) and methanol (9:1) was found to be the most suitable for this separation. The effect of type of buffer, its pH and concentration as well as injection times and applied voltage on the migration of oxolinic acid was also studied. Key analytical characteristics of the method are as follows: detection limit (signal-to-noise ratio 3), 0.08 μg ml −1 ; linear range, 0.5–40 μg ml −1 ; migration time, 5.3 min; relative standard deviation for within-day and day-to-day variation of 1.67 and 2.24%, respectively. The method, in conjunction with a solid phase extraction procedure, was successfully applied for the analysis of spiked oxolinic acid in fish feeds and fish muscles. The recoveries of oxolinic acid from spiked feeds and muscle tissues were 81.15 and 84.80%, respectively.

Disposable E-Tongue for the Assessment of Water Quality in Fish Tanks

A disposable screen-printed e-tongue based on sensor array and pattern recognition that is suitable for the assessment of water quality in fish tanks is described. The characteristics of sensors fabricated using two kinds of sensing materials, namely (i) lipids (referred to as Type 1), and (ii) alternative electroactive materials comprising liquid ion-exchangers and macrocyclic compounds (Type 2) were evaluated for their performance stability, sensitivity and reproducibility. The Type 2 e-tongue was found to have better sensing performance in terms of sensitivity and reproducibility and was thus used for application studies. By using a pattern recognition tool i.e. principal component analysis (PCA), the e-tongue was able to discriminate the changes in the water quality in tilapia and catfish tanks monitored over eight days. E-tongues coupled with partial least squares (PLS) was used for the quantitative analysis of nitrate and ammonium ions in catfish tank water and good agreement were found with the ion-chromatography method (relative error, ±1.04- 4.10 %).

Paraquat sensors containing membrane components of high lipophilicities

Abstract In the first part of this paper, the development of high-performance paraquat selective potentiometric sensors based on octamethylcyclotetrasiloxane is described. In the fabrication of these sensors, the use of highly lipophilic PVC-based membrane components, namely, plasticizer and anionic sites, is emphasized. The electrochemical characteristics of such sensors were evaluated and compared with earlier paraquat ion-selective electrodes (ISEs) that were based on the same sensing compound but with nitrophenyl octyl ether (NPOE) as plasticizing solvent and also based on dibenzo-30-crown-10. The use of bis(1-butylpentyl)decane-1,1-diyldiglutarate (BBDG) and tetra- n -undecyl 3,3′,4,4′-benzophenone tetracarboxilate (TBT) as plasticizer in conjunction with either sodium tetrakis[3,5-bis(trifluoromethyl)phenyllborate (NTB) or potassium tetrakis(4-chlorophenyl) borate (KTPB) as membrane additives all yielded functional paraquat selective chemical sensors of Nernstian slopes. Although the selectivity profile of these electrodes were slightly inferior as compared to a similar membrane system that uses NPOE as a plasticizer but was better than the earlier reported paraquat ISEs based on dibenzo-30-crown-10. A distinct advantage of the paraquat sensors described here was their resistance to fouling by surfactants as compared to earlier sensors that used NPOE as a plasticizer. The second part of this paper deals with the usage of the promising membrane systems described above when applied on the surface of platinum wire and subsequently used as a flow-through potentiometric detector. A brief description of the flow-through detector design and optimization of the flow-injection analysis (FIA) set-up were also presented. Analysis of 0.01–0.l mM paraquat dichloride in backgrounds of well, river and lake waters when performed in the FIA mode gave excellent recoveries. A throughput of 85 samples h −1 can be achieved with this system.

Development and Validation of a Capillary Zone Electrophoresis Method for the Determination of Ofloxacin in Tablets

Abstract A capillary zone electrophoresis (CZE) method has been developed for the determination of the antibiotic ofloxacin in tablets. The CZE separation was performed using 75 µm × 35 cm fused silica capillary under the following conditions: 25°C; applied voltage, 12 kV; 25 mM H3PO4-NaOH running buffer (pH 8.5). The detection wavelength was 254 nm. Flumequine was used as internal standard. The method was suitably validated with respect to linearity, limit of detection and quantification, accuracy, precision, specificity, and robustness. The calibration was linear from 5 to 50 µg mL−1 and the limit of detection and quantification were 1.24 and 4.01 µg mL−1, respectively. Recoveries ranging from 99.71–102.4% were obtained in the determination of ofloxacin that were spiked to placebos. Excipients in the commercial tablets and degraded products from different stress conditions did not interfere in the assay. The method was successfully applied to the determination of ofloxacin in pharmaceutical tablets.