Mg Of Multi-walled Carbon Nanotubes Research Articles

Determination of 35 prohibited pesticide residues in Saussurea costus by modified QuEChERS method based on multi-walled carbon nanotubes coupled with gas chromatography-tandem mass spectrometry

Saussurea costus, a perennial herb belonging to the Asteraceae family, is a vital ingredient in traditional Chinese medicine. Increased demands for the herb have led to its widespread cultivation in China, but the corresponding increase in pesticide use has raised concerns about pesticide residues. Such residues would affect the safety and global market potential of Saussurea costus. Thus, a simple method is crucial to detect pesticide residues. The QuEChERS technique, in combination with gas chromatography-tandem mass spectrometry (GC-MS/MS), is commonly used for residue detection. However, traditional adsorbents may be unable to purify complex herbal mixtures well, affecting accuracy and instrument performance. Choosing suitable purification materials for Saussurea costus samples with complex matrices is of significant importance. This study focused on the detection of 35 prohibited pesticides in Saussurea costus. A rapid detection method was established by combining the QuEChERS technique with GC-MS/MS and utilizing a combination of multiwalled carbon nanotubes (MWCNTs), octadecylsilane-bonded silica gel (C18), and anhydrous magnesium sulfate (MgSO4) as the purification adsorbent. The samples were extracted with acetonitrile, purified by an improved QuEChERS process, subjected to GC-MS/MS analysis in multiple reaction monitoring (MRM) mode, and quantified using the internal standard method. The purification effects of four materials (C18, MWCNTs, N-propyl ethylenediamine (PSA), and graphitized carbon black (GCB)) and their optimal dosages were investigated by considering the matrix characteristics of the samples. An orthogonal experimental design was employed to optimize the ratio of adsorbent combinations, and the optimal adsorbent combination was determined to be 450 mg of MgSO4, 400 mg of C18, and 50 mg of MWCNTs. Matrix effect (ME) evaluation of the S. costus matrix showed that 31 target compounds strongly exhibited matrix-enhancement effects. Thus, matrix-matched calibration was employed in this study. Methodological investigation revealed that the standard curves for the 35 pesticides exhibited good linearity, with correlation coefficients (r2) greater than 0.9970. The average recoveries at three spiked levels ranged from 69.6% to 126.9%, and the relative standard deviations (RSDs) for parallel groups were all less than 10%. The limits of detection (LODs) and quantification (LOQs) ranged from 0.2 to 5.4 μg/kg and from 0.6 to 18.1 μg/kg, respectively. The developed method was used to screen and detect 35 pesticide residues in 20 batches of S. costus samples, and the target compounds were detected in six batches. The proposed method is simple, sensitive, and accurate. Thus, it is suitable for the rapid screening and detection of the 35 pesticide residues in S. costus and provides technical support for the cultivation, production, and quality control of the herb.

Assessment of commercialized nylon membranes integrated with thin layer of MWCNTs for potential use in desalination process

In this work, multi-walled carbon nanotubes (MWCNTs) will be implemented as a coating material on commercial membranes (nylon) using Trix as a surfactant. Four masses of MWCNTs (5, 15, 30, and 60 mg) were used in the coating process. Many parameters were measured for both nylon and the four coated membranes. These parameters include their electrical properties, wettability, mechanical properties, surface and textural properties, permeability and rejection of salt. The findings indicated that Elongation within the range of 2.7–18%, tensile strength within the range of 2.5–3.4 MPa, and Young's moduli in the range of 63–154 MPa were found in the fabricated membranes arising from MWCNTs and surfactants dispersions. The performance of membrane rejection was examined using NaCl or MgSO4 single salts. The fabricated membrane containing 60 mg of MWCNTs, on the other hand, can reject electrolytes with a very low rejection ratio of less than 14% for NaCl and 10% for MgSO4. This made as ultrafiltration (UF) membranes, and therefore they can be used as pre-treatment membranes in desalination processes. Future study is required to improve the rejection of these coated membranes by adding more additives such as polymers or biopolymers.

Immobilized L-ribose isomerase for the sustained synthesis of a rare sugar D-talose

• L-ribose isomerase (L-RI) immobilized on carbon nanomaterials. • L-RI enzyme loaded to the extent of 72–75% on CNMs. • The immobilized biocatalyst governed 12–14% bioconversion of D -tagatose to D -talose. • The immobilized L -RI can be efficiently recycled for 8–10 times. The biocatalytic enactment of immobilized enzyme mainly depends on the essential properties of the matrix and enzyme as well as on immobilization process and immobilization conditions. Carbon based nanomaterials (CNMs) such as graphene oxide (GOx) and multiwalled carbon nanotubes (MWCNT) preserve unique properties for enzyme immobilization via covalent conjugation and physical adsorption. L -ribose isomerase (L-RI) was immobilized on GOx and MWCNT through covalent linkage and surface adsorption. The hybrid composition of biocatalyst was characterized. Immobilization of L -RI (1 mg mL −1 ) on 0.05 mg GOx showed maximum relative activity with 70–75% loading of L -RI via the covalent (GOx@Co- L -RI) and adsorption (GOx@Ad- L -RI) method. On the other hand, 0.15 and 0.1 mg of MWCNT was found to be efficient for the immobilization of L -RI. Effect of different operational conditions like enzyme support ratio, immobilization time, and temperature was also investigated. Optimized conditions were used to study enzyme kinetics, reusability, biocatalytic conversion, metal ion effect, pH and temperature. Under optimized conditions, 72–75% of L -RI enzyme loading was achieved on CNMs via covalent conjugation and physical adsorption. Covalent linkage of L -RI with nanosupport (GOx and MWCNT) was observed to be the best for maximum relative activity. The catalytic efficiency (k cat ) of L -RI was increased by more than two-fold upon immobilization. The bioconversion of D -tagatose to D -talose by immobilized biocatalyst was 12–14%. The immobilized L -RI was found to be efficiently recycled for 8 times. After 8 cycles of reuse, activity recovery of L -RI immobilized on GOx and MWCNT was 55% and 41%, respectively.

First Investigations on the Removal of Tungsten Species from Water Using Multi-walled Carbon Nanotubes

A first study on the adsorptive removal of tungsten species from the aqueous phase by using the multi-walled carbon nanotubes (MWCNTs) is reported. The MWCNTs were employed for the uptake of tungsten species at pH 6 in batch experiments. It was observed that 100% of tungsten species were removed in 2 h, by employing 75 mg of MWCNTs from the aqueous solution containing 10 ppm of tungsten. Adsorption equilibrium data were fitted by the three isotherm models namely the Langmuir, Freundlich, and Sips isotherms and best described by a three-parameter Sips model. The maximum experimental adsorption capacity of MWCNTs for tungsten was 17.64 mg/g, while the adsorption capacity anticipated by the Langmuir and Sips isotherm models was 20.58 and 25.18 mg/g, respectively. The adsorption kinetic data was adequately fitted by a pseudo-second-order model. Our present findings ascertained that MWCNTs could be a potential adsorbent for the removal of tungsten species from the aqueous phase.

Genotoxicity evaluation of multiwalled carbon nanotubes: in vivo studies in mice

The toxicity of carbon nanoparticles in recent years has attracted much attention due to their active use in industry, medicine and agriculture, which brings not only obvious benefits, but also potential danger to the environment and human health. Getting into the natural environment, bioaccumulating and bioconcentrating in them, carbon nanotubes pose a real threat to mammals, since due to their high migration ability they can penetrate the food chain of animals and humans. Therefore, the aim of this study was to study the genotoxicity of carbon nanotubes in in vivo experiments on laboratory mice. For this, based on the method of single cell alkaline gel electrophoresis assay, studies were conducted to determine the effect of aqueous colloidal solutions of multiwalled carbon nanotubes on genotoxicity towards various tissues in laboratory mice. During these acute and subacute in vivo experiments we have established that orally introduced multiwalled carbon nanotubes colloids damage deoxyribonucleic acid in various organs. In particular, 0.5 mg of multiwalled carbon nanotubes administered daily for 21 days have a prominent genotoxic effect. Thus, the obtained results have illustrated that multiwalled carbon nanotubes can potentially affect the genetic material in mammals, orally administered nanotubes increase the rate of nuclear deoxyribonucleic acid destruction.

Multi-Walled Carbon Nanotubes as Efficient Sorbent for the Solid Bar Microextraction of non-Steroidal Anti-Inflammatory Drugs from Human Urine Samples

Background: The determination of NSAIDs (ketoprofen, diclofenac, and ibuprofen) in urine samples provides useful information for assessing their safety, therapeutic effect, and their mechanism of action. Urine samples are characterized by their complexity and low concentration of the target analytes, which make their direct analysis difficult. In this work, the potential of multi-walled carbon nanotubes (MWCNTs) as Solid Bar Microextraction (SBME) adsorbents for extraction and preconcentration of selected drugs from urine samples have been investigated. Methods: Five SBME devices (contains 10 mg of MWCNTs) were placed in 30 mL of adjusted pH 2 water samples and stirred for 40 minutes. After finishing the extraction, the devices were ultrasonicated in 250 µL of methanol for 5 min to desorb the selected drugs and analyzed using HPLC-DAD. Results: The analytical performance of the whole method was evaluated in water samples. Limits of detection and quantitation were in the ranges of (0.36- 0.52) and (1.2- 1.7) µg L-1, respectively, and the Relative Standard Deviation (RSD) < 5.7% over a concentration range of 5-100 µg L-1. Application: The proposed method was successfully applied to the analysis of selected drugs in spiked human urine samples. The absolute recovery obtained by spiking the urine samples at three concentration levels: 5, 50 and 100 µg L-1 of selected NSAIDs were from 48.8% to 53.5%. Conclusion: The proposed SBME using MWCNT as a sorbent material can be a useful alternative sample preparation technique for the routine determination of NSAIDs in urine samples at therapeutic levels with very simple sample pretreatment. Furthermore, the application of the developed SBME method might be extended to study the determination of selected non-steroidal anti-inflammatory drugs in veterinary urine samples. Keywords: Multi-walled carbon nanotubes, solid bar microextraction, non-steroidal anti-inflammatory drugs, urine, liquid chromatography, ketoprofen.

Development of Small Pressure Sensing Unit using Nano-Materials

Precise measurement of low and high pressures for various types of applications has always been a challenge. Various types of nano-materials exhibit the property of change in electrical resistance upon the application of pressure. In this paper, we develop a handy pressure sensing unit for measuring minor changes in pressures by measuring changes in electrical resistance of the compressed nano-materials. The unit consists of a cylindrical arrangement upon which load is applied. This cylinder is connected with a Data Acquisition System (DAQ) to obtain the variations in voltage. We used multi walled carbon nanotubes (MWCNTs) as the transducer. Considering that the inner structure of these nanotubes is hollow, the vacant spaces allow larger flow of current through them. The experiment has been conducted using a small setup in which nearly 5 mg of MWCNTs were used and static pressure was varied from 150 gm to 5.13 kg in steps. The experiment was conducted for both loading and unloading cycles. It has been observed that when the external pressure increased from 0 to 1.2MPa, the electrical resistance fell by nearly 65% from 5.434 Ohm to 1.889 Ohm. The results obtained during present study are very useful in estimating the unknown external static loads by calibrating them with change in electrical resistance or voltage drop across the setup.

Application of multiwalled carbon nanotubes for the preconcentration and determination of organochlorine pesticides in water samples by gas chromatography with mass spectrometry.

A fast, sensitive, and convenient technique consisting of a miniaturized solid-phase extraction method named microextraction in packed syringe coupled with gas chromatography and mass spectrometry was developed for the preconcentration and determination of some pesticides, including hexachlorobenzene, heptachlor, alachlor, aldrine, and metolachlore, in natural water samples. Carboxyl-purified multiwalled carbon nanotubes were used as a sorbent in microextraction in packed syringe. Based on this technique, 6.0 mg of multiwalled carbon nanotubes was inserted in the syringe between two polypropylene frits. The analytes would be adsorbed on the solid phase, and would subsequently be eluted using organic solvents. The influence of some important parameters involved including the solution pH, type, and volume of the organic desorption solvent, and amount of the multiwalled carbon nanotubes sorbent on the extraction efficiency of the selected pesticides were investigated. The proposed method showed a good linearity in the range of 0.1-25.0 ng/mL and low limits of detection in the range of 0.02-0.19 ng/mL using the selected ion-monitoring mode. Reproducibility of the method was in the range of 3.3-8.5% for the studied pesticides. Also to evaluate the matrix effect, the developed method was applied to the preconcentration and determination of the selected pesticides in different water samples.

Ionic liquid-assisted multiwalled carbon nanotube-dispersive micro-solid phase extraction for sensitive determination of inorganic As species in garlic samples by electrothermal atomic absorption spectrometry

A highly sensitive dispersive micro-solid phase extraction (D-μ-SPE) method combining an ionic liquid (IL) and multi-walled carbon nanotubes (MWCNTs) for inorganic As species (As(III) and As(V)) species separation and determination in garlic samples by electrothermal atomic absorption spectrometry (ETAAS) was developed. Trihexyl(tetradecil)phosphonium chloride IL was used to form an ion pair with the arsenomolybdate complex obtained by reaction of As(V) with molybdate ion. Afterwards, 1.0mg of MWCNTs was dispersed for As(V) extraction and the supernatant was separated by centrifugation. MWCNTs were re-dispersed with tetradecyltrimethylammonium bromide surfactant and ultrasound followed by direct injection into the graphite furnace of ETAAS for As determination. Pyrolysis and atomization conditions were carefully studied for complete decomposition of MWCNTs and IL matrices. Under optimum conditions, an extraction efficiency of 100% and a preconcentration factor of 70 were obtained with 5mL of garlic extract. The detection limit was 7.1ngL−1 and the relative standard deviations (RSDs) for six replicate measurements at 5μgL−1 of As were 5.4% and 4.8% for As(III) and As(V), respectively. The proposed D-μ-SPE method allowed the efficient separation and determination of inorganic As species in a complex matrix such as garlic extract.

Determination of eight pesticides of varying polarity in surface waters using solid phase extraction with multiwalled carbon nanotubes and liquid chromatography-linear ion trap mass spectrometry

We describe a MWCNT-based method for the solid-phase extraction of eight pesticides from environmental water samples. The analytes are extracted from 100 mL samples at pH 5.0 (containing 5 mmol L−1 of KCl) by passing the solution through a column filled with 20 mg of multiwalled carbon nanotubes. Following elution, the pesticides were determined by LC and electrospray ionization hybrid quadrupole linear ion trap MS. Two selected reaction monitoring transitions were monitored per compound, the most intense one being used for quantification and the second one for confirmation. In addition, an information-dependent acquisition experiment was performed for unequivocal confirmation of positive findings. Matrix effect was not found in real waters and therefore the quantitation was carried out with calibration graphs built with solvent based standards. Except for cymoxanil, the detection and quantitation limits in surface waters are in the range from 0.3 to 9.5 ng L−1 and 1.6 to 45.2 ng L−1, respectively. Recoveries from spiked ultrapure water are ~100 %, except for the most polar pesticides methomyl and cymoxanil. The same behavior is found for real water samples (except for phosalone). The relative standard deviation is <10 % in all cases.

카본나노튜브에 흡착된 휴믹산의 탈착에 관한 연구

Concerns have been raised over the impact of nano materials on soil and groundwater environment with the increasing attention to the potential applications of carbon nano materials in various fields. Particularly, carbon nano materials introduced into water environment readily make complexes with humic acid (HA) due to their hydrophobic nature, so there have been increasing numbers of studies on the interaction between HA and carbon nano materials. In this study, we investigated the solubility of HA and multiwalled carbon nanotubes (MWCNT) in three different surfactant solutions of sodium dodecyl sulfate (SDS), Brij 30 and Triton X-100, and evaluated whether the HA can be effectively desorbed from the surface of MWCNT by surfactant. The objective of this study was to determine the optimal adsorption condition for HA to MWCNT. Futhermore, sodium dodecyl sulfate (SDS), Brij 30, Triton X-100 were used to elucidate the effect of desorption and separation on adsorbed HA on MWCNT. As a result, HA solution with 12.7 mg of total organic carbon (TOC) and 5 mg of MWCNT showed the highest adsorption capacity at pH 3 reacted for 72 hrs. Weight solubilizing ratio (WSR) of surfactants on HA and MWCNT was calculated. HA had approximately 2 times lower adsorption capacity for the applied three surfactants compared to those of MWCNT, implying that the desorption of HA may occur from the HA/ MWCNT complex. According to the results of adsorption isotherm and weight solubilizing ratio (WSR), the most effective surfactants was the SDS 1% soluiton, showing 53.63% desorption of HA at pH 3.

Determination of fluoroquinolones in bovine milk samples using a pipette-tip SPE step based on multiwalled carbon nanotubes prior to CE separation

A simple CE-UV method was developed for the simultaneous determination of ciprofloxacin, norfloxacin, and ofloxacin in milk samples. The optimum separation was obtained using a 20 mM ammonium dihydrogenphosphate solution with 2 mM cetyltrimethylammonium bromide at pH 3.0 as the BGE. Satisfactory resolution for structurally very similar analytes, like norfloxacin and ciprofloxacin, was achieved without including any organic solvent. Milk samples were prepared using a simple/extraction procedure based on acidic protein precipitation followed by an SPE step using only 5 mg of multiwalled carbon nanotubes as the sorbent material. The LODs for the three compounds were between 7.5 and 11.6 μg/L and the RSDs for the peak areas were between 2.6 and 4.9%. The complete method was applied to spiked real milk samples with satisfactory recoveries for all analytes (84-106%).

Incorporation of Multiwalled Carbon Nanotubes into Electrospun Softwood Kraft Lignin-Based Fibers

Intrinsic properties such as mechanical and electrical conductive properties make carbon nanotubes an ideal nanofiller for reinforcement of polymer materials. In this study, multi-walled carbon nanotubes (MWNTs) were suspended in various fractionated softwood kraft lignin (SKL) concentrations and electrospun into fibers. Solutions prepared from F1–3SKL suspensions contained aggregated MWNTs, which led to spraying and droplet accumulation during fiber formation. By contrast, MWNT suspensions prepared with F4SKL were well dispersed and readily electrospun into fibers. Increasing the F4SKL concentration in the MWNTs’ suspension resulted in better electrospinnability. Adding 10 mg of F4SKL enabled as much as 18.6 mg of MWNTs (or 6 wt% based on fiber weight) to be dispersed and electrospun into fibers. The resulting MWNT-reinforced SKL fibers were then thermostabilized and carbonized and the resulting carbon fibers characterized. Unfortunately, the mechanical properties of the fibers did not improve with incorporation of MWNTs. However, the electrical conductivity increased from 2.3 to 3.0 S/cm when incorporating 6 wt% MWNTs into the fibers.

Simultaneous determination of six resorcylic acid lactones in feed using liquid chromatography–tandem mass spectrometry and multi-walled carbon nanotubes as a dispersive solid phase extraction sorbent

A simple and cost-effective pre-treatment procedure was developed for six resorcylic acid lactones (RALs) in feed using dispersive solid phase extraction (dSPE) with multi-walled carbon nanotubes (MWCNTs). The sample was analysed after purification by ultra-high performance liquid chromatography–negative electrospray ionisation tandem mass spectrometry (UHPLC–ESI-MS/MS). After extraction with acetonitrile/water (80:20, v/v) and dilution with water, a dSPE procedure was carried out with MWCNTs. The pH value of the extract, the extraction time for MWCNTs, the type and amount of MWCNTs and the type of eluent were optimised to increase the sample throughput and the sensitivity. The samples were quantified using the internal standard zearalenone-D6. The absolute recoveries of the target compounds from feed samples were most efficient when using 100mg of MWCNTs with an outer diameter of less than 8nm and a length of 10–30μm, and ethyl acetate was shown to be the most suitable solvent for desorbing the target compounds from the MWCNTs. The mean recoveries from fortified swine mixed feed samples ranged from 95.3% to 107.2% and had relative standard deviations lower than 10%; the limits of detection and quantification for RALs were in the ranges of 0.20–0.29μg/kg and 0.54–0.78μg/kg, respectively.

Multi-walled carbon nanotubes–dispersive solid-phase extraction combined with liquid chromatography–tandem mass spectrometry for the analysis of 18 sulfonamides in pork

A simple and cost-effective pre-treatment procedure was developed for 18 sulfonamides in pork using dispersive solid phase extraction (dSPE) with multi-walled carbon nanotubes (MWCNTs). The sample was analysed after purification by ultra high-performance liquid chromatography-positive electrospray ionisation tandem mass spectrometry (UHPLC-ESI-MS/MS). After extraction with phosphate buffer (pH 6.0), a dSPE procedure was conducted with MWCNTs. The pH value of the extract, extraction time with MWCNTs, type and amount of MWCNTs and type of eluent were optimised to increase the sample throughput and sensitivity. The samples were quantified using sulfamethazine-(13)C6 as an internal standard. The recoveries of the target compounds from the pork samples were most efficient when 150mg of MWCNTs with an outer diameter of less than 8nm and a length of 0.5-2μm was used. A mixture of acetonitrile/50mM ammonium acetate (95:5, v/v) was shown to be the most suitable solvent for desorbing the compounds from the MWCNTs. The proposed method was validated according to the European Commission Decision 2002/657/EC, which determines linearity, specificity, decision limit (CCα), detection capability (CCβ), recovery, precision and stability.

Multi-walled carbon nanotube modified carbon paste electrode as a sensor for the amperometric detection of l-tryptophan in biological samples

An electrochemical sensor for the amperometric determination of l-tryptophan (Trp) was fabricated by modifying the carbon paste electrode (CPE) with multi-walled carbon nanotubes (MWCNTs) using drop cast method. 4.0μL of the dispersion containing 2.0mg of MWCNTs in 1.0mL of ethanol was drop cast onto the electrode surface and dried in hot air oven to form a stable layer of MWCNTs. The electro-catalytic activity of the modified electrode towards the oxidation of Trp was thoroughly investigated. The modification with MWCNTs has greatly improved the current sensitivity of CPE for the oxidation of Trp. A very minimal amount of the modifier was required to achieve such a high sensitivity. The field emission scanning electron microscopy (FESEM) images revealed a uniform coverage of the surface of CPE by MWCNTs. Nyquist plots revealed the least charge transfer resistance for the modified electrode. The analytical performance of the modified electrode was examined using amperometry under hydro-dynamic conditions. The two linear dynamic ranges observed for Trp were 0.6–9.0μM and 10.0–100.0μM. The amperometric determination of Trp did not suffer any interference from other biomolecules. The detection limit of Trp at modified electrode was (3.30±0.37)×10−8M (S/N=3). The analytical applications of the modified electrode were demonstrated by estimating Trp in the spiked milk and biological fluid such as blood serum. The modified electrode showed good reproducibility, long-term stability and anti-fouling effects.

Dispersive Micro Solid-Phase Extraction Using Multiwalled Carbon Nanotubes for Simultaneous Determination of Trace Metal Ions by Energy-Dispersive X-ray Fluorescence Spectrometry

A methodology based on dispersive micro solid-phase extraction (DMSPE) using multiwalled carbon nanotubes (MWCNTs) as solid sorbent prior to measurement with energy-dispersive X-ray fluorescence (EDXRF) spectrometry is proposed. The procedure consists of chelating of nickel, cobalt, copper, and lead ions with ammonium pyrrolidinedithiocarbamate (APDC) and posterior adsorption of metal chelates on MWCNTs (1 mg) dispersed in the aqueous samples (100 mL). DMSPE promotes immediate interaction between the metal chelates and MWCNTs and shortens time of sample preparation in comparison with classical solid-phase extraction. After microextraction process, MWCNTs are collected onto filter and directly measured by EDXRF. With this technique, the direct quantification of metal species held in solid materials is possible and, therefore, the elution step can be avoided. The effects of various experimental parameters such as pH of the solution, amounts of MWCNTs and APDC, sample volume, and time of stirring were investigated. With the best analytical conditions (1 mg of MWCNTs, 2 mg of APDC, 100 mL sample volume, pH = 7, and 5 min time of stirring), Co(II), Ni(II), Cu(II), and Pb(II) can be simultaneously determined with very good recoveries (101%, 98%, 96%, 99%, respectively) and detection limits (0.43, 0.11, 0.46, 0.15 ng mL(-1), respectively). The method was applied in determination of trace metal ions in tap water and wastewater samples.

Analysis of pesticides residues in environmental water samples using multiwalled carbon nanotubes dispersive solid‐phase extraction

In this manuscript, a dispersive SPE method based on the use of multiwalled carbon nanotubes has been developed for the determination of 15 organophosphorus pesticides residues including some of their metabolites (disulfoton sulfoxide, ethoprophos, cadusafos, dimethoate, terbufos, disulfoton, chlorpyrifos-methyl, malaoxon, fenitrothion, pirimiphos-methyl, malathion, chlorpyrifos, terbufos sulfone, disulfoton sulfone, and fensulfothion) from real environmental waters (run-off, mineral and tap water) by GC with nitrogen phosphorus detection. Factors that affect the enrichment efficiency such as sample volume, multiwalled carbon nanotubes amount, and volume of eluent were studied. The optimized method was validated in terms of matrix-matched calibration, recovery, precision, and accuracy for the three analyzed samples. In this last case, the developed Student's t test demonstrated that there were no significant differences between real and spiked concentrations. Optimum dispersive SPE conditions (extraction of 200 mL of water, pH 6.0, with 130 mg of multiwalled carbon nanotubes, elution with 25 mL of dichloromethane for run-off and tap water and 30 mL for mineral water) allowed the quantitative extraction of analytes at levels lower than the maximum residues limits legislated by the European Union, with LODs between 1.16 and 93.6 ng/L. Absolute recovery values achieved were in the range of 67-107% (RSD values <10.1%).

Dynamic Impact Absorption Behaviour of Glass Coated with Carbon Nanotubes

Boro-silicate glass samples were coated with chemically treated multi-walled carbon nanotubes (MWCNTs) to study the resistance offered by the coatings under the high strain rate impact. Impact testing of these glass samples was performed on Split Hopkinson Pressure Bar (SHPB), where strain rates were varied from 500/s to 3300/s. However, the comparisons were limited to samples subjected to a strain rate of 2300/s to 3000/s so that the effect of only variable deposits of coatings on the stress-strain behavior of glass can be studied. Variable deposits (0.1 mg to 0.8 mg) of MWCNTs were coated uniformly on glass samples having a disc shape with a fixed surface area (79 mm2) to observe the effect of the coating on the impact absorption capacity of glass. It was observed that the small thickness of about 25 μm formed due to the fact that 0.2 mg of MWCNTs deposit spread over the surface increased the impact absorption capacity of the glass pieces by nearly 70%. However, beyond this amount when the deposit was increased to 0.4 mg, the coating thickness got doubled to nearly 49 μm and this led to a fall in absorption capacity which remained static till 0.8 mg deposit. However, even this decrease in capacity was able to absorb 30% more impact than offered by pure glass sample.

Ultrasound-assisted solid-phase extraction using multiwalled carbon nanotubes for determination of cadmium by flame atomic absorption spectrometry

Ultrasound-assisted solid-phase extraction (SPE) with multiwalled carbon nanotubes (MWCNTs) as a solid sorbent and 1-(2-pyridylazo)-2-naphthol (PAN) as a chelating agent was developed for the determination of trace and ultratrace amounts of Cd(II) ions in aqueous samples. The solution containing Cd(II) complexed with PAN was passed through the syringe filter with a PVDF membrane loaded with 25 mg of MWCNTs. The elution process was performed with 2.0 mL of 2.0 mol L−1 HNO3 with assistance of sonication. In order to obtain the high recovery of the Cd(II) ions, the proposed procedure was optimized for various analytical parameters such as pH, amounts of PAN, sample volume, and elution conditions such as volume and concentration of eluent and influence of sonication and temperature. The investigation shows that sonication considerably improves the recovery, whereas temperature does not influence the elution process. Under optimized conditions Cd(II) ions can be determined with very good recovery (99 ± 3%), precision (RSD = 3.2%) and detection limit (0.3 ng mL−1) for an enrichment factor of 50. The effect of common coexisting ions was also investigated. Cd(II) can be determined in the presence of heavy metal ions and alkali metals. The proposed ultrasound-assisted SPE was applied for the determination of Cd(II) in water samples and biological samples (Lobster Hepatopancreas).