VOLUME 30, NO5, OCT 2008
123
 
Electrochemical and Computational Interpretations of Hydrogen-bonding of Naphthoquinones with Methanol

ABDUR RAHMAN ,RUMANA QURESHI ,SAFEER AHMED ,

Cyclic Voltammetry technique was used to study the hydrogen bonding of MeOH with electroreduced naphthoquinones. The positive shift in both reduction waves of the compounds was investigated with the continuous increase in MeOH concentration. From the observed shifts, equilibrium constants and number of MeOH molecules bonded to anion and dianion of the naphthoquinone were calculated. The ‘quinone-MeOH’ interactions were resolved as hydrogen bonding. Following the calculations substituent and solvent effects were addressed. To support experimental results computational studies were also carried out. The theoretical results obtained from CNDO/CI method rationalized and logically explained the observed positive shift in the peaks. Three types of computations were made (i) Theoretical U.V spectral studies for the neutral, anion, dianion and their hydrogen bonded complexes. (ii) Geometries of neutral, anion, dianion and the corresponding hydrogen bonded complexes with MeOH. (iii) Charge transfer study so as to know about the transfer of charges during the formation of these complexes. 
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Adsorption of Aqueous Solutions of Carboxylic Acids on Montmorillonite, Silicalite, H-ZSM-5 and their Na+- and Li+- Exchanged Forms

MEGAN PUKALA ,SHER AKBAR ,SUDEEP PUNNATHANAM ,

The adsorption of binary carboxylic acid-water solutions on montmorillonite clay, silicalite, H-ZSM-5 zeolites and Li-exchanged montmorillonite, Na- and Li-exchanged ZSM-5 has been studied. The purity, morphology and textural properties were characterized by XRD and SEM techniques. Liquid phase adsorption experiments were carried out at room temperature in screwed cap septum 14 mL round bottom vials. The mole fractions before and after adsorption were determined refractometrically. Montmorillonite clays swelled to jell-form in aqueous carboxylic acid solutions indicating no significant separation selectivity for water or carboxylic acid. The zeolites showed hydrophobicity in the order: silicalite > H-ZSM-5 > Na- ZSM-5 > Li- ZSM-5. The uptake of carboxylic acid was found in the order: C2H5COOH > CH3COOH > HCOOH. At higher concentration the adsorption of carboxylic acids decreased.
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Trace Elements Detection in Urine by Atomic Absorption Spectroscopy

SHERAZ SHAFIQ ,S.ARIF KAZMI ,KHAULA SHIRIN ,

A technique has been developed to minimize matrix effects in urine for the estimation of trace elements by atomic absorption spectrophotometer using Flame or electro thermal atomization. The matrix and pH effects are known to change the absorption. This study may be useful for the determination of trace elements in the absence of standard/certified reference materials of urine. Our interest was the determination of trace elements in urine. For this purpose a standard urine solution was made up for the estimation of elements. At least 3-5 standard calibration curves were taken for each element. Percentage recoveries were also determined and found satisfactory. The following percentage recoveries for different elements were found; Ca (101.5 %), Mg (102.9 %), Fe (101.6 %), Zn (102.8 %), Cu (99.05 %), Cr (100.6 %) and for Ni (105.3 %).The same elements in aqueous standards were also determined against the above calibration curves to see if they could be used instead of the stock standards. The observed concentration of aqueous standards was found to be different from actual values except copper, e.g. 4.0 µg/ ml Ca was found to be 4.67, 0.30 µg/ ml Mg was 0.32, 0.40 µg/ ml Fe was 0.47, 0.50 µg/ ml Zn was 0.52, 40 ng/ mg Cr was 39.15 and 80 ng/ ml Ni was found 98.76.  No difference between the actual and observed values of copper was found. Values of observed aqueous standards may be taken as standard concentration against which respective elements can be estimated.
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Cation Exchange Behaviour of NiO

SYED TASLEEM ,MUHAMMAD SAFDAR ,MUHAMMAD TAHIR SIDDIQUE ,HAMIDULLAH MARWAT ,ABDUL NAEEM ,SYED M USTAFA ,

The surface characterization of nickel oxide was performed using various physicochemical methods. Batch adsorption technique was used to measure the adsorption of calcium onto NiO. The adsorption experiments of Ca by NiO were conducted at different temperatures and concentrations of the metal ion. The effect of pH on Ca removal from aqueous solution was also studied to observe the sorption behavior of NiO at different pH values. Langmuir model was used to interpret the cation exchange sorption of Ca onto NiO. The proton stoichiometry was derived from Kurbatov-type plot. The isosteric heat of adsorption (DH) revealed that adsorption process was endothermic.
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NOx Emissions from Light Weight Vehicles

TAHIRA SHAFIQ ,TAYYABA AFTAB ,MUHAMMAD TARIQ ,NAZ IMTIAZ ,

The objective of this presentation is to evaluate quality of air in terms of emissions of nitrogen oxide released from two stroke and four stroke operating vehicles selected from various industries and to compare the efficiency of engines and fuels (CNG, Petrol and Diesel). It was observed that in 43 samples tested for NOx emissions by - non dispersive infra-red technology (NDIR),  the switching of fuel from gasoline and diesel to compressed natural gas and two strokes to four stroke engines reduce the air emission burden. The concentration of NOx varies in the range from 0.0 to 20.5% for four-stork and 9.4-45.4% in two stroke engines while the reduction in concentration was 0.1 to 0.15 with the use of CNG.
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Thermal Degradation of 7, 8-Dimethyl-10-Formylmethylisoalloxazine in Acid Solution: A Kinetic Study

IQBAL AHMAD ,FAIYAZ HUSSAINMADANI VAID ,

The thermal degradation of 7, 8-dimethyl-10-formylmethylisoalloxazine (FMF) in acid solution under anaerobic conditions has been studied. A specific spectrophotometric method has been used to determine FMF in the presence of degradation products. FMF has been found to undergo second-order reaction in the dark to form lumichrome and side chain products. The second-order rate constants for the reactions at 40-60 oC are in the range of 1.05 – 4.40 L mole-1 min-1. The activation energy and the frequency factor for the reaction have been calculated as 15.0 kcal/mole (62.8 kJ/mole) and 2.43 x 1010 L mole-1 min-1, respectively. A reaction scheme for the bimolecular degradation of FMF has been suggested.
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Capillary-Gas Chromatographic Determination of Phenylpropanolamine Using Acetylacetone as Derivatizing Reagent in Pharmaceutical Preparations

KULSOOM ABBASI ,MUHAMMAD YAR KHUHAWAR ,MUHAMMAD IQBAL BANGER ,

An analytical procedure has been developed for the gas chromatographic determination of phenylpropanolamine hydrochloride (PPA. HCl) using acetylacetone (AA) as derivatizing reagent. Elution is carried out from the column HP-5 (30m X 0.32 mm i.d) with film thickness 0.25 µm at initial column temperature 70°C for 5 min, followed by heating rate 10°C/ min up to 120°C with total run time 20 min. Injection port and detector temperatures were maintained at 270°C and 300°C. Nitrogen flow rate was 2ml/ min and detection was by FID.  The split ratio was 10:1. The linear calibration was obtained with 50 to 750 µg/ ml PPA with detection limit of 15 µg/ ml. Under the condition ephedrine did not form, the derivatives with AA but separated from PPA derivatives. The linear calibration curve for ephedrine was obtained with 225-903 µg/ ml with detection limit of 103 µg/ ml.The method was used for the determination of PPA from Sinutab and Tavegyl -D tablets, and ephedrine from Ephedrine tablets.  The coefficient of variation for the analysis of pharmaceutical preparation was obtained within 0.78 % to 0.89 %.
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Evaluation of Macro and Micro Elements in Lawsonia inermis (Mehndi)

JAVED IQBAL ,AMEERA JAVED ,G H SHAIKH ,F A KHAN ,HANNA AHMED ,

Thirty-five samples of different varieties of Henna (Mehndi) were analyzed for the detection of macro and micro elements and protein contents to assess their effect on hair. The concentration of micro elements, i.e., Zn, Mn, Cu, Co and Fe was found to be in the range of 0.002 to 0.033, 0.002 to 0.132, 0.001 to 0.01, 0.00012 – 0.0074 and 0.005 to 5.200 mg/g, respectively, whereas chromium was not detected in none of the samples analyzed. The concentration of the four macro elements studied, i.e., Ca, Mg, Na and K was found to be in the range of 0.219 – 39.273, 0.018 – 9.433, 0.40 – 10.0 and 0.095 – 17.0 mg/g respectively. Percentage of protein in branded and unbranded samples was found to be in the range of 9.824 - 13.024%, and in black Henna 25.989 to 27.114 %, which are comparatively higher then other samples.
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Flow Injection Determination of Antibacterial Drug Trimethoprim in Pharmaceutical Preparations with Tris(2,2′-Bipyridyl)Ruthenium(III) Chemiluminescence

AMIR WASEEM ,ABDUL NABI ,MOHAMMAD YAQOOB ,

In the present study, a simple and sensitive chemiluminescence method using tris(2,2′-bipyridyl)ruthenium(III) with flow injection detection is reported for the analysis of trimethoprim in pharmaceutical preparations. The calibration graph was linear over the concentration range of 0.05- 5.0 µg mL-1 with relative standard deviations (n = 4) in the range 1.0 – 2.5%. The limit of detection (3s blank) was 0.008 µg mL-1 with a sample throughput of 100 h-1. The effect of some organic compounds, common excipients used in pharmaceutical preparations, cations & anions were studied for trimethoprim determination. Ru(bipy)32+  was chemically oxidized to Ru(bipy)33+ online using lead dioxide mini column.
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The ESR Method to Detect the Irradiated Fish and Beef Bones

SHAHEEN ATTA ,SAEED A NAGRA ,TAUFIQ AHMED ,AURANG ZEB ,

Electron spin resonance (ESR) spectroscopy was employed for identification and quantification of the more stable free radicals generated by irradiation in bones of fish and beef. The samples were irradiated 1-5 kGy with gamma rays using Co-60 source. ESR spectroscopy was employed to detect irradiation in samples of fish and beef bones.  The results revealed that the irradiated samples showed strong asymmetric signals with g1 2.002 ± 0.001 and g2 1.998 ± 0.001 respectively, which was a clear indication of irradiation. The control samples were not irradiated and showed typical low intensity symmetric signals at g-value of 2.005 ± 0.001 revealing the absence of radiation treatment. It was also observed that intensities of signals due to hydroxyapatite radicals for 5 kGy were normally higher than 1 kGy radiation dose, showing the dose dependency.
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