Simultaneous determination of furosemide and carbamazepine in biological matrices by solvent bar microextraction combined with high-performance liquid chromatography-diode array detector and central composite design.

A sensitive and simple sample pretreatment method based on a two-phase solvent bar microextraction (SBME) technique coupled with HPLC-diode array detector (DAD) was developed for simultaneous extraction and determination of trace amounts of furosemide and carbamazepine in human urine and plasma samples. The significance of operational factors on carbamazepine and furosemide extraction efficiency % (EE%) was screened using full factorial design (FFD) while central composite design (CCD) was used to model the entire process. A quadratic model was found convenient to correlate the extraction EE% of selected drugs with dominant experimental factors. A Pareto chart was also used to examine the importance of factors on drugs' EE%. The analytical performance of the method in urine and plasma samples demonstrated good linearity (R2 ˃ 0.992) with detection limits ranging from 4.2 to 10.9 µg L-1 , and extraction recovery over 89.45% for both drugs in urine and plasma samples. A comparison against published methods was also performed and the results revealed that the developed method exhibits a confident sensitivity, feasible operation, and simple analysis for both drugs. Finally, the practicability of the validated SBME-HPLC-DAD method was demonstrated by successfully applying it to the analysis of furosemide and carbamazepine in real patient urine samples.

Utilization of nanosize spent oil shale for water treatment: application of top-down nanonization technology for solid residues.

Since the dawn of nanoscience, producing nanomaterials in a simple, low-cost, and high-yield manner has been a major issue. For the commercial manufacturing of nanomaterials, various bottom-up and top-down methodologies have been established. High-energy dry ball milling is widely used for the production of diverse nanomaterials, nanograins, nanoalloys, and nanocomposites. Physical grinding of inorganic solid waste into nanosize (1-100 nm) has improved their industrial applications particularly as water adsorbent. Application of nanosize spent oil shale by top-down methodology as adsorbent for phenol is addressed in the current research. The collected spent oil shale (SiO2 and Al2O3 making 45% of the material) has microstructure with average particle size of 56.6 µm. The dry grinding was performed in a vibrating ball mill at various grinding time (5-150 min) while keeping the grinding parameters constant including number of balls, ball size, total mass, vibration frequency, and amplitude. Upon grinding, the mean particle diameter of the bulk material was reduced to 191.8 and 85.2 nm using 0.5 and 0.1 mm grinding balls, respectively. The effect of grinding time on particle size and surface area was investigated; both particle size and surface area were not affected after 60 min of grinding. Physical grinding by 0.1 mm balls has notably improved surface area and total pore volume by 52% and 62%, respectively. Although nanosize particles (85.2 nm) perform better than bulk material for phenol uptake, they underwent serious aggregation at pH > 2 and ionic strength > 1.0 mM. Hence, the 191.8-nm size is selected to assess the effect of mechanical grinding on adsorption rate and equilibrium capacity for phenol as a common pollutant. Upon nanonization, adsorption rate of phenol was highly increased from 0.39 to 4.43 mg g-1 min-1 as analyzed by pseudo-second-order model. Adsorption isotherms were adequately presented by Sips model (prediction error 5.4-7.2%) with a maximum phenol retention capacity of 39.29 mg/g after nanonization compared to 10.71 mg/g for the raw material. The performance of the nanosize spent oil shale for phenol retention was promising when compared with advanced adsorbents like multiwalled carbon nanotube.

Use of citric acid and garlic extract to inhibit Salmonella enterica and Listeria monocytogenes in hummus.

Recently, the consumption of hummus has become popular in the United States, European countries, and Canada, and unfortunately, several foodborne outbreaks and recalls have been reported due to its contamination with Listeria monocytogenes and Salmonella enterica. The current study aimed to investigate the inhibitory activity of 0.5, 1.0, and 1.5% citric acid (CA) and 1.0, 2.0 and 3.0% garlic extract (GE) toward S. enterica and L. monocytogenes in hummus stored at 4, 10 and 24 °C. L. monocytogenes grew well in untreated (control) hummus samples at all tested temperatures, whereas S. enterica grew only at 10 and 24 °C. CA at 0.5 to 1.5% reduced L. monocytogenes numbers by 3.0-3.3 log CFU/g at 4 °C, 1.7-3.9 log CFU/g at 10 °C, and 0.9-1.4 log CFU/g at 24 °C. Numbers of S. enterica were reduced by 0.6-1.7, 4.1-4.9 and <1.5 log CFU/g, at 4, 10 and 24 °C, respectively, compared to the control during 10 d storage. GE at 1.0-3.0% also reduced numbers of L. monocytogenes at 10 d by 0.7-3.0, and 1.3-3.6 log CFU/g at 4 and 10 °C, respectively, and numbers of S. enterica by 0.7-1.2, 1.8-2.6 and 0.5-1.6 log CFU/g, at 4, 10 and 24 °C, respectively, compared to the control. Chromatographic analysis of GE revealed the presence of four organosulfur compounds including diallyl disulfide, diallyl trisulfide, 2-vinyl-(4H)-1,3-dithiin and 3-vinyl-(4H)-1,2-dithiin where the latter was the predominant compound with a level of 22.9 mg/g which significantly contributed to the inhibitory effect of GE. CA and GE are adequate natural antimicrobials in hummus to reduce L. monocytogenes and S. enterica numbers and enhance product safety.

Factorial Investigation of Cobalt Retention by Ti and Fe Oxides-Modified Carbon Nanotubes: Multivariate Against Univariate Analysis.

Fe/Ti-oxides-modified-carbon nanotubes CNTs nanocomposites were prepared and tested toward Co removal from solution under different operational conditions. The final performance of the nanocomposites for Co was highly dependent on the type and loaded amount of the oxides. The nanocomposites were characterized by standard methods and the results evidenced that the presence of CNTs hampers the growth of Fe3O4 and TiO2 particles and forming smaller nano-particles leading to better Co removal from solution. Analysis of isotherms at different temperatures indicated that Co retention was two-fold increased upon adding Ti-oxides up to 90.2%. All isotherms were fairly presented using Langmuir-Freundlich isotherm and most surfaces have high heterogeneity particularly after deposition of oxides. The combined influence of the factors was investigated by running a multivariate analysis. An empirical equation was generated by principal component analysis (PCA) for predicting Co retention assuming different relationships and the binary-interaction behavior between factors was the most dominant: Co retention (mg/g) = 5.12 + 1.25Conc + 1.47Temp - 1.38CNT% - 6.03Ti% - 5.03Fe% - 0.01Conc2 + 0.12Temp2 - 0.55CNT%2 - 1.53Ti%2 - 3.44Fe%2 + 0.17Conc × Temp + 0.07Conc × CNT% + 0.07Conc × Ti% + 0.10Conc × Fe% + 0.21Temp × CNT% + 0.10Temp × Ti% + 0.17Temp × Fe% - 1.67CNT% × Ti% - 1.45CNT% × Fe% - 4.11Ti% × Fe%. The most dominant factors on Co retention were temperature and concentration (positive linear correlation) and the positive interaction between temperature/concentration and temperature/CNTs mass. PCA indicated that the coefficient Temp × CNTs (+0.21) was higher than Temp × Ti% (+0.10). The negative coefficients of Ti/Fe with CNTs (1.45-4.11) indicated better Co retention at higher Ti/Fe loads and lower mass of CNTs. The results support that fact that incorporation of CNTs with Ti/Fe oxides may have a positive synergic impact on Co retention.

Comparison of the sorption capacity of basic, acid, direct and reactive dyes by compost in batch conditions.

Research on biosorption of organic dyes is an important subject for the development of clean technologies for the treatment of textile wastewater. In this work, the process of sorption of four textile dyes of different natures, namely Basic Violet 10 (BV10), Acid Red 27 (AR27), Direct Blue 151 (DB151) and Reactive Violet 4 (RV4) onto two composts, pine bark compost and municipal solid waste compost, has been studied. For this, sorption kinetics and equilibrium sorption at different solution pH values (3.0-7.0) and salinity (0-1.0 M KCl) conditions have been assessed in batch experiments. Sorption rates were relatively slow for BV10, reaching equilibrium only after 24 h, and faster for the rest: around 5-6 h for RV4 and AR27 and 2 h for DB151. Kinetics of dye sorption followed a pseudo-first order model, except that of DB151, which was better described by a pseudo-second order model. The sequence of adsorption capacity for both composts was as follows: BV10 > DB151 > RV4 > AR27. In general, dye sorption at the equilibrium was adequately described by the Langmuir model, what allows to estimate maximum retention capacities for each dye by the composts. At the best removal conditions, pine bark compost presented maximum sorption capacities of 204 mg g-1 for BV10, 54 mg g-1 for DB151, 23 mg g-1 for RV4, and 4.1 mg g-1 for AR27, whereas municipal solid waste compost showed maximum sorption of 74 mg g-1 for DB151, 38 mg g-1 for RV4, 36 mg g-1 for BV10, and 1.6 mg g-1 for AR27. Sorption increased at acid pH in all cases, likely because of modification of charges of the dyes and higher electrostatic attraction, whereas increasing salinity also had a positive effect on sorption, attributed to a solute-aggregation mechanism in solution. In conclusion, organic waste-derived products, like composts, can be applied in the removal of colorants from wastewater, although they would be more effective for the removal of basic cationic dyes than other types, due to electrostatic interaction with mostly negatively-charged composts.

Competitive extraction of Li, Na, K, Mg and Ca ions from acidified aqueous solutions into chloroform layer containing diluted alkyl phosphates.

Alkyl phosphates were extensively used in liquid-liquid extraction of lanthanides and actinides, but to a lesser extent for alkali and alkaline earth metals. The high amount of alkyl phosphate, which is usually used in the organic layer (>40 wt%), is not favoured due to its corrosive effect and toxicity. In the present work, diluted chloroform solutions (20.0 mM) of tri-n-butyl phosphate (TBP), tris(2-ethylhexyl) phosphates (TRIS) and bis(2-ethylhexyl) phosphate (BIS) were investigated for their extraction of Li, Na, K, Mg and Ca ions. The extraction experiments were conducted on 7.0 M HNO3 aqueous solutions containing 60.0 mM of metal ions in binary (Li+ and Mg2+), ternary (Li+, Na+ and K+) and quinary (Li+, Na+, K+, Mg2+ and Ca2+) mixtures. The Li+ selectivity over Mg2+ was very high in the binary system. Remarkably, increasing HNO3 concentration in the aqueous layer had opposing effect on the extraction of Li+ (positive) and Mg2+ (negative). However, the selectivity for Li+ became less dramatic in the case of ternary and quinary system, though the selectivity varied with initial metal concentrations. The amounts of water and NO3- transferred into the organic layer demonstrated their synergistic effect on extracting metal ions. In the ternary and quinary systems, the total concentrations of metal ions in the organic layer (ranged from 49 to 85 mM) were higher than the concentration of ligand in the organic layer (20.0 mM), suggesting that metal ions may be extracted into water/ligand/NO3- aggregates in the organic layer. TBP, TRIS and BIS do not have significant difference in their extraction behaviour. The FTIR results indicated formation of P+-O-M+/M2+ in the solid TBP/metal complex.

Advanced spectrophotometric chemometric methods for resolving the binary mixture of doxylamine succinate and pyridoxine hydrochloride.

The prediction power of partial least squares (PLS) and multivariate curve resolution-alternating least squares (MCR-ALS) methods have been studied for simultaneous quantitative analysis of the binary drug combination - doxylamine succinate and pyridoxine hydrochloride. Analysis of first-order UV overlapped spectra was performed using different PLS models - classical PLS1 and PLS2 as well as partial robust M-regression (PRM). These linear models were compared to MCR-ALS with equality and correlation constraints (MCR-ALS-CC). All techniques operated within the full spectral region and extracted maximum information for the drugs analysed. The developed chemometric methods were validated on external sample sets and were applied to the analyses of pharmaceutical formulations. The obtained statistical parameters were satisfactory for calibration and validation sets. All developed methods can be successfully applied for simultaneous spectrophotometric determination of doxylamine and pyridoxine both in laboratory-prepared mixtures and commercial dosage forms.

Supercritical Fluid Chromatography of Drugs: Parallel Factor Analysis for Column Testing in a Wide Range of Operational Conditions.

Retention mechanisms involved in supercritical fluid chromatography (SFC) are influenced by interdependent parameters (temperature, pressure, chemistry of the mobile phase, and nature of the stationary phase), a complexity which makes the selection of a proper stationary phase for a given separation a challenging step. For the first time in SFC studies, Parallel Factor Analysis (PARAFAC) was employed to evaluate the chromatographic behavior of eight different stationary phases in a wide range of chromatographic conditions (temperature, pressure, and gradient elution composition). Design of Experiment was used to optimize experiments involving 14 pharmaceutical compounds present in biological and/or environmental samples and with dissimilar physicochemical properties. The results showed the superiority of PARAFAC for the analysis of the three-way (column × drug × condition) data array over unfolding the multiway array to matrices and performing several classical principal component analyses. Thanks to the PARAFAC components, similarity in columns' function, chromatographic trend of drugs, and correlation between separation conditions could be simply depicted: columns were grouped according to their H-bonding forces, while gradient composition was dominating for condition classification. Also, the number of drugs could be efficiently reduced for columns classification as some of them exhibited a similar behavior, as shown by hierarchical clustering based on PARAFAC components.

Selective removal of dibenzothiophene from commercial diesel using manganese dioxide-modified activated carbon: a kinetic study.

With a total concentration of 7055 mgS/kgfuel, the content of organosulphur compounds (OSCs) in local diesel is 20 times higher than the regulated value. Analysis revealed that 30% of OSC is originated from dibenzothiophene (DBT). It is known that DBT is a hardly removable compound and selective adsorbents are often needed for its removal with low affinity for other diesel components. In this work, a selective adsorbent based on surface modification of activated carbon (AC) by MnO2 is prepared for DBT removal from diesel. The porous nature of AC enabled carrying large amounts of MnO2 particles to end up with a selective adsorber for DBT. The best performance was observed at a surface loading of 26.8% of Mn and DBT is favourably removed over mono- and diaromatics hydrocarbons in diesel. Adsorption kinetics of DBT is studied under a high initial concentration of 835-11,890 mg/kg and at a ratio of 11 cm3/g (diesel:carbon). The results indicated a fast removal process after surface modification where 96% of the surface is occupied within 30 min of interaction. Kinetic data were best presented by reaction-based models with low prediction error sum of squares values 0.5-47.0, while, diffusion-based models showed limited application for modelling DBT adsorption. Accordingly, adsorption process is controlled by surface reactions and pore diffusion has a minor role in the overall process. The modified adsorbent is satisfactorily regenerated using n-hexane at 65°C.

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.

A simple and accurate analytical method for determination of three commercial dyes in different water systems using partial least squares regression.

A simple analytical procedure is proposed for simultaneous determination of three common dyes (Basic Blue 9, Brilliant Blue E-4BA, and Reactive Blue 2) in natural waters without prior separation of the solutes. A popular chemometric method, partial least squares regression PLS-1, was effectively applied for spectral resolution of a highly overlapping system. At the best modeling conditions, mean recoveries and relative standard deviations (RSD) for dyes quantification by PLS-1 were found to be 102.1 (4.4), 95.7 (8.4), and 98.9 (6.2) for Basic Blue, Brilliant Blue, and Reactive Blue, respectively. The estimated limits of detection (LOD) were estimated using net-analyte signal concept and were 0.11, 0.52, 0.49 mg L(-1) for Basic Blue, Brilliant Blue, and Reactive Blue, respectively. The quantitative determination of dyes spiked in real water samples was carried out successfully by PLS-1 with satisfactory recoveries for dyes (90-106%).

Characteristics of organosulphur compounds adsorption onto Jordanian zeolitic tuff from diesel fuel.

The removal of organosulphur compounds (ORS) from diesel fuel is an important aspect of Jordanian's effort to reduce air pollution. Currently, the total sulphur content in Jordanian diesel fuel is 12,000 ppmw (1.2%, wt/wt), but Jordanian government has recently introduced new restrictions that will reduce this level gradually to internationally acceptable levels. The zeolitic tuff (ZT), from Tlul Al-Shahba region, was characterised using various analytical techniques. It was found that the Freundlich model fitted the adsorption isotherms more accurately than the Langmuir model; indicating that the ZT had a heterogeneous surface. The Langmuir adsorption capacity values for the three particle size ranges (100-200), (300-400), and (500-600) microm were 7.15, 6.32, and 5.52 mg/g and the column capacities were 4.45, 2.57, and 1.92 mg/g, respectively. The spent ZT was regenerated by washing with n-heptane with an efficiency of 81.5%. Two adsorption mechanisms were investigated. One is that the interaction of thiophene with the Brønsted site of the ZT through S atoms; the other is via C-S bond cleavage in thiophene-derived carbocations to form unsaturated fragments on the Brønsted acid sites.

Application of chemometrics and FTIR for determination of viscosity index and base number of motor oils.

The viscosity index (VI) and the base number (BN) of motor oils are the most important parameters to be measured in order to assess their performance and service time. Both parameters were simply obtained for virgin and recycled motor oil samples using multivariate calibration based on the FTIR data. Analysis showed that the PLS-1 has outperformed CLS and PCR for the oil parameters prediction. Five and four PLS-1 latent variables were found optimum to obtained the VI and the BN from the FTIR data; respectively. With high accuracy (99-102%) and precision (3-11%), the BN could be determined over the range 4.57-16.45mgKOHg(-1) and the VI over the range 96-153. The outputs of the PLS-1 were found comparable to those obtained by the expensive and time-consuming ASTM methods. This developed method is highly recommended for quick monitoring of the motor oil quality parameters.

Simultaneous determination of pesticides at trace levels in water using multiwalled carbon nanotubes as solid-phase extractant and multivariate calibration.

The application of solid-phase extraction with multivariate calibration for simultaneous determination of three toxic pesticides in tap and reservoir waters was presented. The proposed analytical method was used for the determination of atrazine, methidathion, and propoxur in complex water samples without the need for chromatographic separation. Among the applied multivariate calibration methods, partial least squares (PLS-1) method was found the most effective for pesticides quantification. Multiwalled carbon nanotubes (MWCNTs) adsorbent showed a perfect extraction/preconcentration of pesticides present at trace levels. The experimental factors that affect pesticides extraction by MWCNTs adsorbent such as sample volume, eluent volume, solution pH, and extraction flow rate were studied and optimized. The figures of merit of the proposed method were: limits of detection 3, 2, and 3 microg l(-1) and linear ranges 5-30, 3-60, and 5-40 microg l(-1) for atrazine, methidathion, and propoxur, respectively. A good precision was reported for the method, R.S.D. values were always less than 5.0%. Satisfactory results were reported for simultaneous determination of trace levels of pesticides in complex matrices. In tap water, the percent recoveries for pesticides were extended from 95 to 104% and R.S.D. from 1 to 3%, while lower recoveries were observed in reservoir water: 84-93% (R.S.D.: 1-3). Although the pesticides can be accurately quantified by SPE and liquid chromatography, SPE-PLS-1 method was found simpler and operated at lower running costs.

Preparation of highly selective solid-phase extractants for Cibacron reactive dyes using molecularly imprinted polymers.

Selective polymeric extractants were prepared for preconcentration of Cibacron reactive red dye, a dye that is often applied with Cibacron reactive blue and Cibacron reactive yellow for dyeing of fabrics. The best extractant was fabricated (in chloroform) using methacrylic acid (as monomer), ethylene glycol dimethacrylate (as crosslinker), AIBN (as initiator for polymerization), and red dye as template molecule, with a molar stoichiometric ratio of 8.0:40.0:2.5:0.63, respectively. The structure of the molecularly imprinted polymer (MIP) was robust, and resisted dissolution up to 260 degrees C. Compared with the un-imprinted polymer, the imprinted product has a large specific surface area which improved its adsorption capacity. The effect of imprinting was obvious from the adsorption capacity measured at pH 4 for red dye (the imprinted molecule), which was increased from 24.0 to 79.3 mg g(-1) after imprinting. Equilibrium adsorption studies revealed that the dye-imprinted-polymer enables efficient extraction of red dye even in the presence of blue and yellow dyes which have similar chemical natures to the red dye. The selectivity coefficients S (red dye/dye), were 13.9 and 17.1 relative to the yellow and blue dyes, respectively. The MIP was found to be effective for red dye preconcentration, with a preconcentration factor of 100, from tap water and treated textile wastewater. The factors affecting extraction of red dye by the MIP were studied and optimized. Under the optimized extraction conditions, red dye was selectively quantified in the presence of other competing dyes at a concentration of 20 microg L(-1) from different water systems with satisfactory recoveries (91-95%) and RSD values (approximately 5.0%).

Determination of motor gasoline adulteration using FTIR spectroscopy and multivariate calibration.

In this paper, an attempt has been made to develop a feasible procedure for the prediction of quality parameters of motor gasoline and to discriminate between the different adulterated motor gasoline samples using density values, distillation temperatures and Fourier transform infrared (FTIR) analyses along with multivariate calibrations without the need for using chromatographic separation or other expensive instruments such as an octane number analyser. Ten blend mixtures of regular and super motor gasoline were prepared in order to study density, distillation temperatures and FTIR spectra characteristics for each blend. Distillation temperatures for the pure and blend mixtures of regular and super motor gasoline at initial boiling point (IBP) to final boling point (FBP) at 5%Vol. interval were obtained. Accurate and complete distillation data on the uncontaminated fuel would be essential for comparison. Thirteen peaks of the absorbance at the wavenumbers: 434, 461, 484, 673, 694, 1030, 1086, 1217, 1231, 1460, 1497, 1606 and 3028 cm(-1) were chosen to perform the multivariate calibration. The results obtained were expected to be useful in determination and differentiation purposes, providing information on whether the density values, distillation temperatures and FTIR analyses along with multivariate method could be an appropriate feature for differentiating a particular pure motor gasoline sample from the others. The observed differences in the specific spectral bands are investigated and discussed. They have proven to be an effective combination in the pursuit of management's differentiation goals.

Solid-phase extraction and simultaneous determination of trace amounts of sulphonated and azo sulphonated dyes using microemulsion-modified-zeolite and multivariate calibration.

A simple and rapid analytical method for the determination of trace levels of five sulphonated and azo sulphonated reactive dyes: Cibacron Reactive Blue 2 (C-Blue, trisulphonated dye), Cibacron Reactive Red 4 (C-Red, tetrasulphonated azo dye), Cibacron Reactive Yellow 2 (C-Yellow, trisulphonated azo dye), Levafix Brilliant Red E-4BA (L-Red, trisulphonated dye), and Levafix Brilliant Blue E-4BA (L-Blue, disulphonated dye) in water is presented. Initially, the dyes were preconcentrated from 250 ml of water samples with solid-phase extraction using natural zeolite sample previously modified with a microemulsion. The modified zeolite exhibited an excellent extraction for the dyes from solution. The parameters that influence quantitative recovery of reactive dyes like amount of extractant, volume of dye solution, pH, ionic strength, and extraction-elution flow rate were varied and optimized. After elution of the adsorbed dyes, the concentration of dyes was determined spectrophotometrically with the aid of principle component regression (PCR) method without separation of dyes. The results obtained from PCR method were comparable to those obtained from HPLC method confirming the effectiveness of the proposed method. With the aid of SPE by M-zeolite, the concentration of dyes could be reproducibly detected over the range 25-200 ppb for C-Yellow and L-Blue and from 50 to 250 ppb for C-Blue, C-Red, and L-Red. The multivariate detection limits of dyes were found to be 15 ppb for C-Yellow and L-Blue and 25 ppb for C-Blue, C-Red, and L-Red dyes. The proposed chemometric method gave recoveries from 85.4 to 115.3% and R.S.D. from 1.0 to 14.5% for determination of the five dyes without any prior separation for solutes.

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).

Effect of dimensions of multi-walled carbon nanotubes on its enrichment efficiency of metal ions from environmental waters.

The effect of dimensions (length and external diameter) of multi-walled carbon nanotubes (MWCNTs) on its preconcentration efficiency towards some metal ions (Pb2+, Cd2+, Cu2+, Zn2+ and MnO4(-)) from environmental waters prior to their analysis by flame atomic absorption spectroscopy (FAAS) was investigated. MWCNTs (as-received from the manufacturer) of various external diameters and lengths were involved. Other variables optimized included effects of pH of water sample, composition and volume of eluent, mass of the MWCNTs, breakthrough volume and coexisting ions. Maximum recovery of metal ions was obtained at pH 9 where it was thought that precipitation of metals as their hydroxides played the major factor in metals uptake by MWCNT. It was suggested that the use of appropriate dimensions of MWCNTs may support the trapping process of the precipitated metal hydroxides by MWCNTs. It was found that long MWCNT of length 5-15 microm and external diameter 10-30 nm gave the highest enrichment efficiency towards almost all the targeted metal ions. It could be used for preconcentration of MnO4(-), Cu2+, Zn2+ and Pb2+ with almost full recovery; but not for Cd2+ due to its low recovery. The optimized solid phase extraction (SPE) procedure was capable of determining metal ions in the linear range 20-100 ng mL(-1) (except for Zn2+ from 20 to 150 ng mL(-1)). Detection limits were 0.709 ng mL(-1) for MnO4(-), 0.278 ng mL(-1) for Pb2+, 0.465 ng mL(-1) for Cu2+, 0.867 ng mL(-1) for Zn2+. Application of the optimized SPE procedure to environmental waters (tap water, reservoir water and stream water) gave spike recoveries of the metals in the range of 81-100%.

Sorption of Zn(II), Pb(II), and Co(II) using natural sorbents: equilibrium and kinetic studies.

Natural Jordanian sorbent (consisting of primary minerals, i.e., quartz and aluminosilicates and secondary minerals, i.e., calcite and dolomite) was shown to be effective for removing Zn(II), Pb(II) and Co(II) from aqueous solution. The major mineral constitutions of the sorbent are calcite and quartz. Dolomite was present as minor mineral and palygorskite was present as trace mineral. The sorbent has microporous structure with a modest surface area of 14.4 m(2)g(-1). pH(zpc) (pH of zero point charge) of the sorbent was estimated by alkaline-titration methods and a value of 9.5 was obtained. The sorption capacities of the metals were: 2.860, 0.320, 0.076 mmol cation g(-1) for Zn(II), Pb(II) and Co(II) at pH 6.5, 4.5 and 7.0, respectively. The shape of the experimental isotherm of Zn(II) was of a "L2" type, while that of Pb(II) and Co(II) was of a "L1" type according to Giles classification for isotherms. Sorption data of metals were described by Langmuir and Freundlich models over the entire concentration range. It was found that the mechanism of metal sorption was mainly due to precipitation of metal carbonate complexes. The overall sorption capacity decreased after acid treatment, as this decreased the extent of precipitation on calcite and dolomite. The effect of Zn(II) ions concentration on sorption kinetics was investigated. Kinetic data were accurately fitted to pseudo-first order and external diffusion models which indicated that sorption of Zn(II) occurred on the exterior surface of the sorbent and the contribution of internal diffusion mechanism was insignificant. Furthermore, the sorption rate of Zn(II) was found to be slow, where only 10-20% of the maximum capacity was utilized in the first 30 min of interaction.