Synthesis of 2-Mercaptonicotinic Acid-Capped CdSe Quantum Dots and its Application to Spectrofluorometric Determination of Cr(VI) in Water Samples.

The CdSe quantum dots (QDs) capped with 2-mercaptonicotinic acid (H2MN) were prepared through a controllable process at 80 °C. The prepared QDs were characterized by XRD, TEM, IR, UV-Vis and fluorescence (FL) techniques. It was found that the QDs were nearly mono-disperse with the diameters in the range of 8-10 nm. These QDs are capable to exhibit strong FL even in concentrated acidic media. They exhibit an enhanced fluorescence in the presence of Cr(VI), which was used for the determination of Cr(VI) in water samples. The linear range was found to be 1 × 10(-7)-6.0 × 10(-6) M with the RSD and DL of 0.92 % and 5 × 10(-8) M, respectively. Except that Ca(2+) and Fe(3+) which can be eliminated through a simple precipitation process, the other co-existent ions present in natural water were not interfered. The recoveries obtained for the added amounts of Cr(VI) were in the range of 96.9-103.2 %, which denote on application of the method, satisfactorily.

A novel spectrofluorometric method for the determination of arsenic in human hair using Dy2O3-doped CeO2 nanoparticles.

This paper describes a simple and inexpensive method for the determination of arsenic in human hair samples based on spectrofluorometric detection. The applied Dy2O3-doped CeO2 (DDC) nanoparticles were synthesized using microwave-induced combustion technique and subjected to analytical samples containing As(V) species. At optimum conditions (pH 6, DDC concentration 3 mg L(-1) and excitation/emission wavelengths 250 nm/352 nm), the fluorescence emission of DDC nanoparticles was diminished by increasing the As(V) concentration present in the medium. The co-existent ions present in hair were not interfered. A method for the speciation of As(III) and As(V) is also described. The method was validated using a well-known separation/spectrofluorometric method. There was no significant difference at the 95% confidence level between the results of the two methods. The proposed method is characterized by a wide analytical concentration range (5.0 × 10(-8)-1.0 × 10(-5) M), a detection limit for As(V) of 1 × 10(-8) mol L(-1) and relative standard deviation of 1.4%. The recoveries for the spiked amounts of As(V) was found to be 93.3-104.0%.

Preconcentration determination of arsenic species by sorption of As(V) on Amberlite IRA-410 coupled with fluorescence quenching of L-cysteine capped CdS nanoparticles.

A simple and accurate method for arsenic speciation analysis in natural and drinking water samples is described in which preconcentration of arsenic as As(V) was coupled with spectrofluorometric determination. The extracted As(V) species with a column containing Amberlite IRA-410 were subjected to L-cysteine capped CdS quantum dots (QDs) and the fluorescence quenching of the QDs due to reduction of As(V) by L-cysteine was considered as a signal relevant to As(V) concentration. The As(III) species were also determined after oxidation of As(III) ions to As(V) with H2O2 and measurement of the total arsenic content. In treatment with 400 mL portions of water samples containing 30 µg L(-1) As(V), the relative standard deviation was 2.8%. The detection limit of arsenic was also found to be 0.75 µg L(-1) (1 × 10(-8) M). The reliability of proposed method was confirmed using certified reference materials. The trace amounts of arsenic species were then determined in different water samples, satisfactorily.

Rational design of heteropolyacid-based nanosorbent for hollow fiber solid phase microextraction of organophosphorus residues in hair samples.

A novel heteropolyacid-based supported ionic liquid (IL) mediated sol-gel hybrid organic-inorganic material is presented for effective use in hollow fiber solid phase microextraction (HF-SPME). We examined a Keggin-based IL that was evaluated in conjunction with sol-gel. This study shows that Keggin-based IL sol-gel generated porous morphology pro effective extraction media. The method was developed for the extraction of the organophosphorus pesticides (OPs); diazinon, fenitrothion and malathion from human hair samples. The OPs were subsequently analyzed with high performance liquid chromatography and photodiode array detection (HPLC-PDA). In the basic condition (pH 10-11), the gel growth process in the presence of IL was initiated. Afterward, this sol was injected into a polypropylene hollow fiber segment for in situ-gelation process. Parameters affecting the efficiency of HF-SPME were thoroughly investigated. Linearity was observed over a range of 0.02-50,000 µg/g and 0.0001-25,000 ng/mL with detection limits between 0.0074-1.3000 µg/g and 0.00034-0.84 ng/mL for the OPs in hair and aqueous matrices, respectively. The relative recoveries in the real samples, for OPs in the storekeeper hair ranged from 86 to 95.2%.

Ionic liquid mediated sol-gel sorbents for hollow fiber solid-phase microextraction of pesticide residues in water and hair samples.

An ionic liquid mediated sol-gel sorbents for hollow fiber solid-phase microextraction (HF-SPME) was developed for extraction of the pesticides: diazinon, fenitrothion, malathion, fenvalerate, phosalone and tridemorph from human hair and water samples. The analytes were subsequently analyzed with high performance liquid chromatography and diode array detection (HPLC-DAD). Preliminary experiments were carried out in order to study experimental conditions for pesticides' extraction from spiked hair and water samples with HF-SPME using hollow fiber-supported ionic liquid mediated sol-gel sorbent. The sol-gel nanocomposites were reinforced with nanoparticles such as carboxylic functionalized multi-walled carbon nanotubes (COOH-MWCNTs), amino functionalized multi-walled carbon nanotubes (NH(2)-MWCNTs), nano SiO(2), nano TiO(2) and nano MgO comparatively to promote extraction efficiency. In this device, the innovative solid sorbents were developed by the sol-gel method via the reaction of tetraethylorthosilicate (TEOS) with 2-amino-2-hydroxymethyl-propane-1,3-diol (TRIS). In the basic condition (pH 10-11), the gel growth process in the presence of ionic liquid and nanoparticles was initiated. Then, the sol was injected into a polypropylene hollow fiber segment for in situ gelation process. Parameters affecting the efficiency of HF-SPME were thoroughly investigated. Linearity was observed over a range of 0.01-25,000 ng/mL with detection limits between 0.004 and 0.095 ng/mL for the pesticides in the aqueous matrices and 0.003-0.080 ng/mL in the hair matrices. The relative recoveries in the real samples ranged from 82.0% to 94.0% for the pesticides store seller's hair and the work researchers' hair. Results are showing the great possibilities of HF-SPME-HPLC-PDA for analysis of pesticides in biological and environmental samples.

Comparison of sorption behavior of Th(IV) and U(VI) on modified impregnated resin containing quinizarin with that conventional prepared impregnated resin.

This paper reports the results obtained by studying the ion-exchange properties of a new solvent impregnated resin (SIR), which was prepared by impregnation of quinizarin (1,4-dihydroxyanthraquinone, QNZ) on Amberlite XAD-16 after nitration of the benzene rings present in its structure. The sorption behavior of Th(IV) and U(VI) on/in the modified SIR was compared with that of the SIR prepared via the conventional method. It was observed that sorption capacity and sorption rate of the modified SIR are significantly greater than the conventional one. The modified SIR was then applied to the extraction of Th(IV) and U(VI) ions at the presence of many co-existence metal ions. The results obtained denote on successful application of this new SIR to analysis of natural water samples spiked to Th(IV) and U(VI) ions.

Optimization of a novel method for determination of benzene, toluene, ethylbenzene, and xylenes in hair and waste water samples by carbon nanotubes reinforced sol-gel based hollow fiber solid phase microextraction and gas chromatography using factorial experimental design.

A novel design of solid phase microextraction fiber containing carbon nanotube reinforced sol-gel which was protected by polypropylene hollow fiber (HF-SPME) was developed for pre-concentration and determination of BTEX in environmental waste water and human hair samples. The method validation was included and satisfying results with high pre-concentration factors were obtained. In the present study orthogonal array experimental design (OAD) procedure with OA(16) (4(4)) matrix was applied to study the effect of four factors influencing the HF-SPME method efficiency: stirring speed, volume of adsorption organic solvent, extraction and desorption time of the sample solution, by which the effect of each factor was estimated using individual contributions as response functions in the screening process. Analysis of variance (ANOVA) was employed for estimating the main significant factors and their percentage contributions in extraction. Calibration curves were plotted using ten spiking levels of BTEX in the concentration ranges of 0.02-30,000ng/mL with correlation coefficients (r) 0.989-0.9991 for analytes. Under the optimized extraction conditions, the method showed good linearity (0.3-20,000ng/L), repeatability, low limits of detections (0.49-0.7ng/L) and excellent pre-concentration factors (185-1872). The best conditions which were estimated then applied for the analysis of BTEX compounds in the real samples.

Speciation determination of chromium using 1,4-diaminoanthraquinone with spectrophotometric and spectrofluorometric methods.

A highly sensitive and selective method has been proposed for speciation determination of trace amounts of Cr(III) and Cr(VI) in water samples using 1,4-diaminoanthraquinone (1,4-DAAQ). The method is based on mixing an organic phase containing 1,4-DAAQ with an acidic solution (pH 1) of Cr(VI), which is accomplished with absorbance decreasing or luminescence quenching of the organic phase due to a partial oxidation of the 1,4-DAAQ content. After oxidation of Cr(III) to Cr(VI) and determining the total chromium content, Cr(III) content is obtained by subtracting. All of the variables were studied in order to optimize the reaction conditions. No considerable interference was observed due to the presence of coexisting anions and cations. The calibration graphs were linear in the range 3.0 x 10(-7)-3.0 x 10(-6) and 1.0 x 10(-7)-4.0 x 10(-6) M with detection limits of 3.5 x 10(-8) and 2.1 x 10(-9) M for absorptiometry and fluorometry, respectively. Validation of the measurements was confirmed using standard reference materials and a certificated method.

Sorption of Cr(VI) by Amberlite XAD-7 resin impregnated with brilliant green and its determination by quercetin as a selective spectrophotometric reagent.

A new chelating polymeric sorbent as an extractant-impregnated resin (EIR) has been developed using brilliant green (BG) and Amberlite XAD-7 resin. The BG-impregnated resin showed superior binding affinity for Cr(VI) in the presence of many co-existing ions and no considerable interference was observed. The influence of various physicochemical parameters on the recovery of Cr(VI) were optimized by both static and dynamic methods. The Langmuir adsorption isotherm gave a satisfactory fit of the equilibrium data. The kinetic studies performed for Cr(VI) sorption revealed that <45 min was sufficient for reaching equilibrium metal ion sorption. A preconcentration factor of 100 was found for the column-mode extraction. The spectrophotometric determination of eluted Cr(VI) was carried out using quercetin as a selective reagent. The calibration graphs were linear in the range 5.0 x 10(-8) to 4.0 x 10(-7)M with a detection limit of 8 x 10(-9)M. The proposed method has been successfully employed for the analysis of natural water. The recoveries for the Cr(VI) amounts spiked to the samples were >93%, which confirmed accuracy of the measurements.

Cr(III)/Cr(VI) speciation determination of chromium in water samples by luminescence quenching of quercetin.

A highly sensitive and selective method has been proposed for direct speciation determination of trace amounts of chromium in water samples using quercetin. The method is based on mixing 5 mL of diluted quercetin solution dissolved in n-amyl alcohol with 5 mL of acidic solution (pH 1) of Cr(VI), which is accomplished with luminescence quenching of the organic phase due to partially oxidation of quercetin content. Cr(VI) is determined by measuring the diminished content of quercetin with spectrofluorometric method (lambda(ex)=276 nm, lambda(em)=331 nm). After oxidation of the Cr(III) content to Cr(VI) and determination of the total chromium as Cr(VI), the Cr(III) is obtained by subtracting. All the variables were studied in order to optimize the reaction conditions. No considerable interference was observed due to the presence of co-existing anions and cations. The calibration graphs were linear in the range 1.0 x 10(-7) to 2.0 x 10(-6)M with the detection limits of 9.1 x 10(-9)M. The R.S.D. obtained for 1.0 x 10(-6)M of Cr(VI) was 1.7% (n=7). Validation of the measurements was confirmed using standard reference materials. The method was applied to determine the chromium species in natural water samples. The recoveries obtained for the spiked amount of chromium species were >98%, which denote on satisfactorily application of the method.

Separation and preconcentration of Ag(I) in aqueous samples by flotation as an ion-associate using iodide and ferroin followed the determination by flame atomic absorption spectrometry.

A simple method for separation/preconcentration and determination of Ag(I) in aqueous samples is described. The method is based on formation of an ion-associate between Ag(I)-iodide complex and ferroin, which can be floated at the interface of the aqueous/n-heptane phases. The flotation process was carried out using 500-ml aliquot of the aqueous solution and the floated layer was dissolved in 5 ml of 1 M HNO3 containing methanol (50% v/v) as the solvent. The Ag(I) content was then determined by flame atomic absorption spectrometry (FAAS). The method so could be considered as an enrichment process, was achieved to a quantitative feature, when the pH of the solution was adjusted to 4 and the concentrations of iodide and ferroin were about 3.2 x 10(-4) M and 6.25 x 10(-5) M, respectively. The LOD and RSD (n = 7) were obtained 1.0 x 10(-8) M and 2.4%, respectively. It was found that a large number of cations and anions even at high considerably foreign ion/Ag(I) ratios were not interfered. The method was applied satisfactorily to recovery of Ag(I) from different aqueous samples.

Flotation separation and electrothermal atomic absorption spectrometric determination of thallium in wastewater samples.

The proposed method is a simple process for the determination of trace amount of thallium(I) in the environmental wastewater samples by electrothermal atomic absorption spectrometry. The wastewater samples were obtained from the environment of a cement plant and subjected to a simple treatment, such as adjusting pH and masking the interfering ions, to prepare for the flotation process in which the thallium(I) content was floated as an ion-association complex using iodide and Rhodamine B at the interface of aqueous/cyclohexane layers. The floated layer was then separated and dissolved in 2 ml of a solution, which was 1% to H2SO4 and 50% to methanol, respectively. Aliquots of 10-microl of this solution were subjected to the graphite furnace to determine the thallium(I) content. The flotation process can be carried in a weak acidic medium in which the interfering effects owing to certain metal ions were eliminated by masking them as neutral citrate chelates. The dynamic range for the determination was found to be 1.0 x 10(-8) - 1.0 x 10(-7) mol l(-1). The RSD was 3.2% and the DL was 2.5 x 10(-9) mol l(-1) (calculated as 3SD of the blank). The reliability of the method is demonstrated by the analysis of a synthetic wastewater in which the recovery was found to be 94%.

Sensitized extraction spectrophotometric determination of Hg(II) with dithizone after its flotation as ion-associate using iodide and ferroin.

This paper describes a simple and highly selective method for the separation, preconcentration and spectrophotometric determination of extremely low concentration of mercury. The method is based on the flotation of an ion-associate of HgI(4)(2-) and ferroin between aqueous and n-heptane interface at pH 5. The ion-associate was then separated and treated with ammonia and dithizone solutions to extract only the mercury chelate with CH(2)Cl(2). The measurement is feasible when the volume of the water sample containing Hg(II) was varied over 50-800ml. Beer's law was obeyed over the concentration range of 8x10(-9) to 1.6x10(-7)moll(-1) with an apparent molar absorptivity of 6.53x10(6)lmol(-1)cm(-1) for a 500ml aliquot of the water sample. The detection limit (n=7) was 5.0x10(-10)moll(-1) and the R.S.D. (n=5) for 8.0x10(-7)moll(-1) of Hg(II) was 3.7%. A notable advantage of the method is that the determination of Hg(II) is free from the interference of almost all cations and anions found in the environmental and waste water samples. The determination of Hg(II) in tap, synthetic sea water and human hair samples was carried out by the present method and cold vapor atomic absorption spectrometry (CV-AAS). The results were satisfactorily comparable so that the applicability of the proposed method was confirmed to the real samples.

Flotation-spectrophotometric determination of mercury in water samples using iodide and ferroin.

This paper describes a simple and highly selective method for separation, preconcentration and spectrophotometric determination of trace amounts of mercury. The method is based on the flotation of an ion-associate of HgI4(2-) and ferroin between aqueous and n-heptane interface at pH 5. The ion-associate was then separated and dissolved in acetonitrile to measure its absorbance. Quantitative flotation of the ion-associate was achieved when the volume of the water sample containing Hg(II) was varied over 50 - 800 ml. Beer's law was obeyed over the concentration range of 3.2 x 10(-8) - 9.5 x 10(-7) mol l(-1) with an apparent molar absorptivity of 1 x 10(6) l mol(-1) cm(-1) for a 500 ml aliquot of the water sample. The detection limit (n = 25) was 6.2 x 10(-9) mol l(-1), and the RSD (n = 5) for 3.19 x 10(-7) mol l(-1) of Hg(II) was 1.9%. A notable advantage of the method is that the determination of Hg(II) is free from the interference of the almost all cations and anions found in the environmental and waste water samples. The determination of Hg(II) in tap, synthetic waste, and seawater samples was carried out by the present method and a well-established method of extraction with dithizone. The results were satisfactorily comparable so that the applicability of the proposed method was confirmed in encountering with real samples.