Jamal A. Sweileh

Critical evaluation and comparison of enrichment efficiency of multi-walled carbon nanotubes, C18 silica and activated carbon towards some pesticides from environmental waters

In this work, optimization of multi-residue solid phase extraction (SPE) procedures coupled with high-performance liquid chromatography for the determination of Propoxur, Atrazine and Methidathion from environmental waters is reported. Three different sorbents were used in this work: multi-walled carbon nanotubes (MWCNTs), C18 silica and activated carbon (AC). The three optimized SPE procedures were compared in terms of analytical performance, application to environmental waters, cartridge re-use, adsorption capacity and cost of adsorbent. Although the adsorption capacity of MWCNT was larger than AC and C18, however, the analytical performance of AC could be made close to the other sorbents by appropriate optimization of the SPE procedures. A sample of AC was then oxidized with various oxidizing agents to show that ACs of various surface properties has different enrichment efficiencies. Thus researchers are advised to try AC of various surface properties in SPE of pollutants prior to using expensive sorbents (such as MWCNT and C18 silica).

Applications of in situ detection with an auto-mated micro batch analyzer

Abstract A new batch-type microscale liquid-phase analyzer, called an automated micro batch analyzer (a.m.b.a.), is introduced. The reaction chamber, a 1500-μl capacity polypropylene microcentrifuge tube, is equipped with conductometric, potentiometric, fluorimetric and spectrophotometric sensors. The sample is loaded into a loop injector and blown into the reaction chamber by compressed gas. Various reagents are delivered to the chamber from pneumatically pressurized reservoirs equipped with inexpensive high-speed valves in the liquid-delivery lines. The valves are under microcomputer control and highly precise microliter aliquots can be delivered by controlling valve on-times. Examples illustrated include acid-base, precipitation and compleximetric titrations with the conductometric sensor; acid-base titrations with the potentiometric sensor; determination of hydrogen peroxide with the fluorimetric sensor; and acid-base titrations, studies of metal/ligand complexation, standrd addition, liquid-liquid extraction and distillation of volatile analytes with the spectrophotometric sensor.

Determination of cyanide and thiocyanate by a spectrophotometric flow-injection method

Abstract A rapid spectrophotometric flow-injection method is described for the determination of cyanide and thiocyanate. The method involves a two-step procedure in which the total concentration of both species is first determined (using sodium isonicotinate/sodium barbiturate reagents), after which the cyanide is complexed with nickel(II) and thiocyanate is quantified separately; the cyanide concentration is calculated by difference. Various parameters such as pH, temperature and nickel concentration were optimized. The method is applied to synthetic sample solutions and the results are compared with those obtained by the ASTM distillation method. The limits of detection for cyanide and thiocyanate are 0.05 and 0.08 μg ml−1, respectively, with a sample throughput rate of 10 h−1.

On-line flow injection solid sample introduction digestion and analysis : Spectrophotometric and atomic absorption determination of iron, copper and zinc in multi-vitamin tablets

Abstract An on-line flow injection system with solid sample introduction, digestion, treatment and analysis was proposed. The solid sample powder is inserted into a special chamber and carried by the digestion solution to a thermally heated PVC coil (1.4 mm i.d.). The analyte metal as the chloro-complex was retained on a coarse-particle (>0.5 mm) anion exchange resin mini column. The resin beads are held between two plastic screens which allow insoluble residue to pass through to waste. After a brief column wash, the analyte is eluted with diluted HNO3 and determined spectrophotometrically or by atomic absorption. The proposed novel configuration of the multi-channel pinch valve allows handling slurries without tube blockage or valve damage. The system performance was tested by the determination of Fe, Zn and Cu in multi-vitamin tablets. Fe was determined spectrophotometrically as the thiocyanate complex while Zn and Cu were determined by atomic absorption. Compared with conventional digestion and analysis procedures the flow system yields a reasonably accurate relative error (RE)

Preparation of an efficient sorbent by washing then pyrolysis of olive wood for simultaneous solid phase extraction of chloro-phenols and nitro-phenols from water

Simultaneous preconcentration of phenol, 2-chlorophenol, 3-chlorophenol, 4-chlorophenol, 2-nitrophenol, 4-nitrophenol, and 2,4-dinitrophenol was improved by using olive wood (OW) washed with ethanol then pyrolyzed at 200°C as preconcentrating sorbent. Various OW sorbents were prepared by either washing OW (with ethanol, ether, dichloromethane, tetrahydrofuran or n-hexane); or by pyrolysis (at 100, 150, 200, 250 or 300°C); or by combined pyrolysis/washing. The adsorbents were characterized by elemental analysis, total acidity/basicity, methylene blue relative surface area, point of zero charge, distribution coefficients of the phenols, and sample loading flow rate. It seems that washing and pyrolysis have removed compounds covering the OW pores, which improved the OW porosity and exposed more acidic groups on the OW surface. The pores and the surface acidic groups seem to play major role in phenols sorption. Ethanol-washed OW then pyrolyzed at 200°C gave the best preconcentration performance towards phenols (300 mg sorbent, 150 mL of the sample (pH 7), and elution with 3 mL of acetonitrile). The method was linear up to 100 μg L(-1); limit of quantification: 0.20-0.48 μg L(-1). The method could detect phenol and 2,4-dinitrophenol in industrial wastewater with spiked recovery range from 80.2% to 91.4% (± 1.1 to 5.5%RSD) for all the phenols.

A rapid and simple microwave-assisted digestion procedure for spectrophotometric determination of titanium dioxide photocatalyst on activated carbon

Deposition of titanium dioxide (TiO(2)) on activated carbon (AC) surface has been widely utilized for the production of TiO(2)/AC photocatalyst, which can be used in photo-degradation of pollutants. In this work, a fast and simple digestion procedure has been developed for the spectrophotometric quantitative analysis of TiO(2) in TiO(2)/AC photocatalyst. Microwave-assisted digestion was used in the procedure. The microwave-digestion procedure was optimized using the single-variable method. Variables optimized included time of ashing, effective digestion time, volume and concentration of sulfuric acid, effect of adding a digestion catalyst, effect of sample pulverizing and on-off time cycle of the microwave. The analysis was completed spectrophotometrically after addition of hydrogen peroxide to the digested solution. Procedure precision and accuracy was tested by application to photocatalyst samples containing known amounts of TiO(2), and compared with previously published spectrophotometric procedures. The proposed microwave procedure was capable of recovering 98.4-101.1% of TiO(2) in the catalyst in less than 10min, without the need for sample ashing. Analytical precision is 1.42-2.39% relative standard deviation (R.S.D.). In terms of accuracy and precision, the proposed microwave procedure was comparable with other procedures, but the proposed microwave procedure was superior in terms of shorter procedure duration.

Bio-separation, speciation and determination of chromium in water using partially pyrolyzed olive pomace sorbent.

Speciation of Cr(III)/Cr(VI) from water using olive pomace (OP) was improved by partial pyrolysis of OP. The sorbents were characterized by physicochemical techniques. Sorption of Cr(III) on raw and partially pyrolyzed OP sorbents followed Freundlich isotherm and second-order rate kinetics. OP pyrolyzed at 150°C (sorbent OP-150) exhibited maximum sorption capacity, favorability and the lowest sorption energy. Sorption was exothermic and spontaneous for the raw-OP and OP pyrolyzed at 100 or 150°C; but endothermic and non-spontaneous for OP pyrolyzed at 200, 250, 300 or 400°C. A speciation method of chromium was proposed, in which Cr(III) was selectively retained at pH 3 on sorbent OP-150; while total Cr was determined after reduction of Cr(VI). The method was selective with a detection limit for Cr(III) of 1.58 μg L(-1). The method was applied on natural and industrial waters (recoveries >97.7%, RSDs <9%) and on tobacco leaves certified reference material (INCT-PVTL-6).

Phosphate rock treatment with citric acid for the rapid potentiometric determination of fluoride with ion-selective electrode.

A fast method for sample treatment of phosphate rock has been developed for the purpose of quantitative leaching (98-100%) of fluoride but less of the interfering cations such as iron and aluminum. Citric acid (0.5 M) was used to extract fluoride in 15-45 min. Leaching of iron and aluminum is minimal, and these ions are complexed with citric acid. The leaching method was optimized with respect to sample size, citric acid concentration, leaching time and temperature. The analysis was completed by the rapid determination of fluoride with ion-selective electrode. The proposed treatment method was applied to phosphate rock samples from Jordan and Morocco and yielded accurate results as compared to the standard steam distillation from strong acid solution followed by thorium nitrate titration.

Novel automated micro batch analyzer

An automated micro batch analyzer (AMBA) system is described. The sample is introduced into an air‐tight reaction chamber (a polypropylene microcentrifuge tube) by a loop injector made from two three‐way valves by flowing gas. Reagents/diluents are introduced into the chamber from pneumatically pressurized reservoirs provided with on‐off valves. A microprocessor‐controlled timer controls valve status and thus provides control of delivered volumes. Gas bubbles are introduced through the bottom of the chamber to perform mixing; the mixed liquid is then discharged into an optical detector via a bubble gate by superincumbent pressure. The bubble gate allows the data‐acquisition system to collect data only when liquid is actually in the detection cell. For simple fast reactions, throughput rates of 210 samples/h could be obtained.

Separation and flame atomic absorption spectrometric determination of total chromium and chromium (III) in phosphate rock used for production of fertilizer

Due to the commercial value of phosphate rock (PR) as a fertilizer precursor, it is necessary to investigate its heavy metals content. Chromium (Cr) may present as Cr(III) or Cr(VI) in PR; but quantitative differentiation between them is not an easy task. This is due to possible interconversion of Cr species during the digestion/leaching process. In this work, ultrasound digestion (USD) of PR was optimized (300 mg PR, 4.0 mL of 4.0 mol L(-1) nitric acid, 15 min sonication) for the sake of leaching Cr species prior to their determination by flame atomic absorption spectroscopy. Using multi-walled carbon nanotube (MWCNT) as adsorbent, solid phase extraction (SPE) was used to separate Cr(III) from the digestate at pH 9, while total Cr was estimated after reducing Cr(VI) into Cr(III). The optimum USD/SPE method gave LOQ and LOD of Cr(III) of 0.96 mg kg(-1) and 0.288 mg kg(-1), respectively. The method sensitivity was 1.44×10(-3) AU kg mg(-1) within the studied Cr concentration range (5-400 mg kg(-1)). The USD/SPE method was validated by analyzing lake sediments LKSD-4 certified reference material, and by comparison with classical digestion method (CD). Application of USD/SPE on Jordanian PR samples gave total Cr rang 29.1-122.0 mg kg(-1) (±1.4-6.3), while Cr(III) ranged between 23.8 and 101.7 mg kg(-1) (±1.3-5.5). AFPC Rock Check Program samples gave total Cr range 238.9-394.7 mg kg(-1) (±11.5-24.1), while Cr(III) ranged between 202.4 and 335.8 mg kg(-1) (±11.4-18.3). These results were very close to the results obtained by the CD method.