Single-walled carbon nanohorns immobilized on a microporous hollow polypropylene fiber as a sorbent for the extraction of volatile organic compounds from water samples

We have evaluated the behavior of single-walled carbon nanohorns as a sorbent for headspace and direct immersion (micro)solid phase extraction using volatile organic compounds (VOCs) as model analytes. The conical carbon nanohorns were first oxidized in order to increase their solubility in water and organic solvents. A microporous hollow polypropylene fiber served as a mechanical support that provides a high surface area for nanoparticle retention. The extraction unit was directly placed in the liquid sample or the headspace of an aqueous standard or a water sample to extract and preconcentrate the VOCs. The variables affecting extraction have been optimized. The VOCs were then identified and quantified by GC/MS. We conclude that direct immersion of the fiber is the most adequate method for the extraction of VOCs from both liquid samples and headspace. Detection limits range from 3.5 to 4.3 ng L^?1 (excepted for toluene with 25 ng L^?1), and the precision (expressed as relative standard deviation) is between 3.9 and 9.6 %. The method was applied to the determination of toluene, ethylbenzene, various xylene isomers and styrene in bottled, river and tap waters, and the respective average recoveries of spiked samples are 95.6, 98.2 and 86.0 %.

Magnetic nanoparticles modified with polydimethylsiloxane and multi-walled carbon nanotubes for solid-phase extraction of fluoroquinolones

We have surface-functionalized magnetic particles (MPs) with polydimethylsiloxane and multi-walled carbon nanotubes in a two-step reaction. The MPs were applied to solid-phase extraction of the fluoroquinolones ofloxacin, norfloxacin, ciprofloxacin, enrofloxacin prior to their determination by capillary liquid chromatography. The effects of sample pH, adsorption time, type of eluent, desorption time and desorption temperature were investigated. Under the optimum conditions, the extraction efficiencies are in the range from 81.5?% to 94.1?%, with relative standard deviations (RSDs) of <7.6?%. The detection limits vary from 0.24 to 0.48?ng?mL^?1. The method was applied to the analysis of spiked mineral water and honey. The recoveries for the fluoroquinolones in the real samples range from 84.0?% to 112?%, with RSDs ranging from 2.9?% to 7.8?%.

Microwave assisted headspace controlled-temperature single drop microextraction for liquid chromatographic determination of chlorophenols in aqueous samples

We report on an efficient one-step sample preconcentration technique by coupling microwave heating and cloud vapor zone (CVZ)-based headspace controlled-temperature single drop microextraction (HS-CT-SDME), and its application to headspace extraction of chlorophenols in aqueous solutions. Microwave irradiation is utilized to accelerate evaporation of analytes into the headspace sampling zone for the direct extraction of aqueous chlorophenols. A microdrop of extractant is suspended at the bottom of a bell-mouthed micropipette tip connected to a microsyringe needle. An external cooling system was adopted to control the formation of the CVZ around the SDME tip in the headspace sampling area. In the CVZ procedure, the warm headspace vapor is quickly cooled near the SDME tip, thus forming a dense cloud of analyte-water vapor; thereby enhancing the partition of the analytes into the SDME solvent. The chlorophenols are then determined by LC-UV detection. Under the optimized experimental conditions, the analytical signal is linearly related to the concentration of the chlorophenols range of 2.5–250?ng?mL^?1. The detection limits vary from 0.3 to 0.7?ng?mL^?1, and the precision (expressed as the relative standard deviation) from 3.7 to 13.3?%. The method was validated with real water samples, and the spiked recovery ranged between 92 and 103.1?% for river water, and between 85.1?% and 98.6?% for lake water. Compared to other methods, microwave assisted HS-CT-SDME is simple, rapid, sensitive, inexpensive and eco-friendly, and requires less sample and organic extractant.

Determination of ppb-level phenol index using in-syringe dispersive liquid-liquid microextraction and liquid waveguide capillary cell spectrophotometry

We report on an in-syringe dispersive liquid-liquid microextraction (DLLME) technique and its application to the determination of the total phenol index in natural waters. Xylene was used as extraction solvent in combination with a mixture of acetonitrile and n-propanol as dispersion solvents. The analytical procedure consists of mixing the sample with buffer, reacting it with 4-aminoantipyrine and potassium hexacyanoferrate, DLLME, phase separation, and index quantification and was automated using the multisyringe flow injection analysis technique and takes 200?s only. DLLME was accomplished by aspiration of the mixture of extraction and dispersion solvents followed by the aqueous phases into the syringe at a high flow rate. Phase separation occurs due to aggregation of the floating extractant droplets (with their lower specific density) at the head of the syringe. The extractant containing the chromogenic reaction product is then pushed into an optical waveguide capillary cell and spectrophotometrically detected at 500?nm. Figures of merits include a low limit of detection (0.9?ppb), a preconcentration factor of 20, a linear dynamic range up to 140?ppb, and a general standard deviation of 3.1?%. The method enabled the concentration of phenols in well water samples to be determined with a mean recovery of 101?%.

Occupational exposure to complex mixtures of volatile organic compounds in ambient air: desorption from activated charcoal using accelerated solvent extraction can replace carbon disulfide?

A desorption study of 57 volatile organic compounds (VOCs) has been conducted by use of accelerated solvent extraction (ASE) and gas chromatography–mass spectrometry. Different solvents were tested to extract activated charcoal tubes with the objective of replacing carbon disulfide, used in official methods, because of its highly toxic health and environmental effects. Extraction conditions, for example temperature and number of cycles, were investigated and optimized. The definitive extraction procedure selected was use of acetone at 150 °C and two consecutive extraction cycles at a pressure of 1,500 psi. Considering a sample volume of 0.005 Nm³, corresponding to a sampling time of 8 h at a flow rate of 0.01 L?min^?1, the method was validated over the concentration range 65–26,300 μg?Nm^?3. The lowest limit of quantification was 6 μg?Nm^?3, and recovery for the 93 % of analytes ranged from 65 to 102 %. For most of the compounds, relative standard deviations were less than 15 % for inter and intra-day precision. Uncertainty of measurement was also determined: the relative expanded uncertainty was always below 29.6 %, except for dichlorodifluoromethane. This work shows that use of friendlier solvent, for example acetone, coupled with use of ASE, can replace use of CS₂ for chemical removal of VOCs from activated charcoal. ASE has several advantages over traditional solvent-extraction methods, including shorter extraction time, minimum sample manipulation, high reproducibility, and less extraction discrimination. No loss of sensitivity occurs and there is also a salutary effect on bench workers’ health and on the smell of laboratory air.

Ultrasound-assisted headspace ionic-liquid microextraction of polycyclic aromatic hydrocarbons at elevated temperatures

We have developed a method for ultrasound-assisted ionic-liquid (IL) microextraction at elevated temperatures. A sealed pipette tip was used to hold the IL. The polycyclic aromatic hydrocarbons naphthalene, acenaphthene and fluorene were headspace-extracted into a 30-μL volume of the IL at 60 °C. Cooling is not needed to control the temperature of the extraction solvent because it has almost zero vapor pressure. Following extraction, the analyte-loaded IL was submitted to HPLC with fluorescence detection. Under the optimal conditions, the limits of detection (at S/N?=?3) are 30, 30 and 10 ng L^?1 for naphthalene, acenaphthene and fluorene, respectively. Recoveries range from 86 to 110 %, and the extraction efficiency is better than previous methods by a factor of ~40. The technique was applied to the analysis of semivolatile pollutants (PAHs) in real aqueous samples.

Determination of methamphetamine, amphetamine and ecstasy by inside-needle adsorption trap based on molecularly imprinted polymer followed by GC-FID determination

We have developed a solvent-free and sensitive method for the identification and quantification of methamphetamine (MAMP), amphetamine (AMP) and ecstasy (MDMA) in human urine. It is based on the use of an inside-needle adsorption trap (INAT) and a molecularly imprinted polymer (MIP). The MAMP-MIP layer was coated on the internal surface of a hollow stainless steel needle, which was oxidized and silylated. It was used as the extraction needle. A model solution containing the drugs was slowly passed through the extraction needle. After adsorption of the analytes, the needle was directly transferred to the injector of a gas chromatograph, where the analytes were thermally desorbed, separated by GC, and detected with a flame ionization detector. The method does not require an extraction solvent, is fast and simple. The linear range of the calibration graphs are rather wide, and the limit of detection and the limit of quantification (LOQ) for MAMP are 12 and 40?ng?mL^?1, respectively. The relative standard deviations (RSD%) for six repeated experiments (at 500?ng?mL^?1 of MAMP) is 4.9?%. The relative recoveries obtained for MAMP in spiked human urine samples are in the range of 81–93?%.

Analysis of trace amounts of chlorobenzenes in water samples: An approach towards the automation of dynamic hollow fiber liquid-phase microextraction

We have combined dynamic hollow fiber liquid-phase microextraction with GC and electron capture detection for the quantitative determination of five chlorobenzenes in water samples. Extraction is based on an automated dynamic extraction device called TT-tube extractor which consists of a polypropylene hollow fiber mounted inside a stainless steel tube. Toluene is used as the extraction solvent that fills the lumen and pores of the hydrophobic fiber and flows through the lumen of the fiber using a programmable syringe pump. The type of organic solvent, ionic strength, diameter of the TT-tube, sample volume, and the times for extraction and dwelling were optimized. Under optimum conditions, the method gives limits of detection as low as 10–100?ng?L^?1, a linear dynamic range of 0.05–100?μg?L^?1, and relative standard deviations of <7% (n?=?6). The preconcentration factor can be as large as 562–973. In an example for a practical application, the chlorobenzenes were successfully determined in environmental aqueous samples. The hollow fiber membrane can be used at least 20 times without any carry-over or loss in extraction efficiency. The system is inexpensive and convenient, and requires minimal manual handling.

Using electrospray laser desorption ionization mass spectrometry to rapidly examine the integrity of proteins stored in various solutions

Electrospray laser desorption ionization mass spectrometry (ELDI/MS) allows the rapid desorption and ionization of proteins from solutions under ambient conditions. In this study, we have demonstrated the use of ELDI/MS to efficiently examine the integrity of the proteins stored in various solutions before they were further used for other biochemical tests. The protein standards were prepared in the solutions containing buffers, organic salts, inorganic salts, strong acid, strong base, and organic solvents, respectively, to simulate those collected from solvent extraction, filtration, dialysis, or chromatographic separation. Other than the deposit of a drop of the sample solution on the metallic sample plate in an ELDI source, no additional sample pretreatment is needed. The sample drop was then irradiated with a pulsed laser; this led to desorption of the analyte molecules, which subsequently entered the ESI plume to undergo post-ionization. Because adjustment of the composition of the sample solution is unnecessary, this technique appears to be useful for rapidly evaluating the integrity of proteins after storage or prior to further biochemical treatment. In addition, when using acid-free and low-organic-solvent ESI solutions for ELDI/MS analysis, the native conformations of the proteins in solution could be detected.

Preconcentration of erbium(III) ions from environmental samples using activated carbon modified with benzoyl hydrazine

A method was established for the preconcentration of trace concentrations of Er(III) ion using activated carbon modified with benzoyl hydrazine. Parameters affecting solid-phase extraction such as pH value, shaking time, flow rate, sample volume were systematically studied. At a pH of 3.0, the maximum static adsorption capacity of the sorbent is 59.8?mg?g^?1 for Er(III), and the time for quantitative adsorption (>95%) is as short as 2?min. The adsorbed Er(III) was quantitatively eluted with 2?mL of 1.0?M hydrochloric acid and then determined by inductively coupled plasma optical emission spectrometry. The limit of detection (3??) is 73?ng?g^?1, and the relative standard deviation is <2.0% (n?=?8). The method was validated by analyzing certified reference materials and successfully applied to the determination of trace Er(III) in environmental samples.

Comparison of the performance of pyridine-functionalized nanoporous silica particles for the extraction of gold(III) from natural samples

We have developed a technique for the solid-phase extraction of gold using various kinds of pyridine-functionalized nanoporous silica prior to its determination in various samples using FAAS. The effects of solution pH, sample and eluent flow rate, sample volume and of potentially interfering ions are compared. The limits of detections vary from 28 to 53?pg?mL^?1. The accuracy and precision are between 99.8% and 98.3?% and 0.7 to 1.6?% (RSD), respectively. The method was successfully applied to several standard reference materials.

Improved MALDI-TOF Microbial Mass Spectrometry Imaging by Application of a Dispersed Solid Matrix

The key step in high quality microbial matrix-assisted laser desorption/ionization mass spectrometry imaging (microbial MALDI MSI) is the fabrication of a homogeneous matrix coating showing a fine-grained morphology. This application note addresses a novel method to apply solid MALDI matrices onto microbial cultures grown on thin agar media. A suspension of a mixture of 2,5-DHB and α-CHCA is sprayed onto the agar sample surface to form highly homogeneous matrix coatings. As a result, the signal intensities of metabolites secreted by the fungus Aspergillus fumigatus were found to be clearly enhanced.

Ionic liquid magnetic bar microextraction and HPLC determination of carbamate pesticides in real water samples

We have developed a simple method for the microextraction of the carbamate pesticides carbofuran, pirimicarb, and carbaryl. It is termed ionic liquid magnetic bar microextraction (ILMB-ME) and based on an ionic liquid deposited on a magnetic stirrer bar placed in a sealed short PCR tube into which microholes where pinned. When placed in a vial containing the aqueous sample solution, the ILMB tumbles freely in the aqueous solution and the carbamates are extracted into the ionic liquid phase which then was determined by HPLC. The enrichment factors for carbofuran, pirimicarb, and carbaryl are 107, 94, 95, respectively. The limits of detection, calculated as three times the signal-to-noise ratio (S/N), are 1.4?μg?L^?1 for carbofuran, 3.4?μg?L^?1 for pirimicarb, and 1.7?μg?L^?1 for carbaryl. The repeatability, carried out by extracting water samples spiked with carbamate levels of 200?μg?L^?1, yielded relative standard deviations between 2.9 and 6.0?%, (for n?=?5). The recoveries of all the three fungicides from tap, lake and rain water samples at spiking levels of 5 and 50?μg?L^?1 are in the range from 86 to 98?%, and from 80 to 96?%, respectively. We conclude that this is a simple, practical and efficient method for the determination of fungicide residues in real water samples.

Differential pulse anodic stripping voltammetric determination of Cd and Pb at a bismuth glassy carbon electrode modified with Nafion, poly(2,5-dimercapto-1,3,4-thiadiazole) and multiwalled carbon nanotubes

A simple, cheap, and nonpolluting method was developed for the cloud point extraction of gold (Au) and palladium (Pd). It is based on the complexation reaction of Au and Pd with 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP) and micelle mediated extraction of the complex using the non-ionic surfactant poly(ethylene glycol) mono-p-nonylphenyl ether (PONPE 7.5). Under the optimized experimental conditions, the enrichment factors are 16 and 17 for Au and Pd, respectively, for 15?mL of preconcentrated solution. The limits of detection are 3.8???g?L^?1 and 1.8???g?L^?1 for Au and Pd, respectively. The relative standard deviations are 1.4% for Au and 0.6% for Pd (n?=?11). The method was successfully applied to the determination of Au and Pd in certified reference materials and mine samples.

Highly sensitive carbon paste electrode with silver-filled carbon nanotubes as a sensing element for determination of free cyanide ion in aqueous solutions

We report on newly synthesized Ag(I)-filled multiwall carbon nanotubes as a potential sensing element in ion-selective carbon paste electrodes for the determination of free cyanide in aqueous solution. The electrode was obtained by entrapping the silver-filled nanotubes into a carbon paste and displays a Nernstian response with a slope of 59.8?±?0.3?mV decade^?1, a very wide linear range (from 21.0?nM to 0.1?M of cyanide), a lower detection limit of 13.0?nM, and a response time of <2?min. The operational lifetime is up to 3?months without significant deviation in normal function.

Solid-phase extraction of lead(II) ions using multiwalled carbon nanotubes grafted with tris(2-aminoethyl)amine

Multiwalled carbon nanotubes were grafted with tris(2-aminoethyl)amine (MWCNTs-TAA) and employed for solid phase extraction and preconcentration of trace lead ions prior to its determination by inductively coupled plasma optical emission spectrometry. The material was characterized by FT-IR and Raman spectroscopy, thermosgravimetric and elemental analysis. The effects of pH value, shaking time, sample volume, elution conditions and potentially interfering ions were investigated. Under the optimum conditions, the maximum adsorption capacity is 38?mg?g^?1 of Pb(II), the detection limit is 0.32?ng?mL^?1, the enrichment factor is 60, and the relative standard deviation is 3.5% (n?=?6). The method has been applied to the preconcentration of trace amounts of Pb(II) in environmental water samples with satisfactory results.

Multiwalled carbon nanotubes modified with 2-aminobenzothiazole modified for uniquely selective solid-phase extraction and determination of Pb(II) ion in water samples

A solid phase extraction method is presented for the selective preconcentration and/or separation of trace Pb(II) on multiwalled carbon nanotubes modified with 2-aminobenzothiazole. Inductively coupled plasma optical emission spectrometry was used for detection. The effects of pH, shaking time, sample flow rate and volume, elution condition and interfering ions were examined using batch and column procedures. An enrichment factor of 100 was accomplished. Common other ions do not interfere in both the separation and determination. The maximum adsorption capacity of the sorbent at optimum conditions is 60.3?mg?g^?1 of Pb(II), the detection limit (3??) is 0.27?ng?mL^?1, and the relative standard deviation is 1.6% (n?=?8). The method was validated using a certified reference material, and has been applied to the determination of trace Pb(II) in water samples with satisfactory results.

Voltammetric determination of bisphenol A in food package by a glassy carbon electrode modified with carboxylated multi-walled carbon nanotubes

A highly sensitive and mercury-free method for determination of bisphenol A (BPA) was established using a glassy carbon electrode that was modified with carboxylated multi-walled carbon nanotubes. A sensitive oxidation peak is found at 550?mV in linear sweep voltammograms at pH?7. Based on this finding, trace levels of bisphenol A can be determined over a concentration range that is linear from 10?nM to 10⁴?nM, the correlation coefficient being 0.9983, and the detection limit (S/N?=?3) being 5.0?nM. The method was successfully applied to the determination of BPA in food package.

Extraction of neurotransmitters from rat brain using graphene as a solid-phase sorbent, and their fluorescent detection by HPLC

A simple, cost-effective and efficient method was developed for the determination of glycine, gamma-aminobutyrate and taurine in rat brain using graphene as a sorbent for solid-phase extraction. The analytes were eluted from a graphene-packed solid-phase extraction cartridge with methanol, derivatized at their amino groups with the fluorescent label 4-carboxy-2,6-dimethylquinoline N-hydroxysuccinimide ester, and then separated and fluorescently detected by HPLC. The type and volume of eluent, sample pH, extraction time and sample volume were optimized with respect to sensitivity and precision. Under optimal conditions, linear response is obtained in the concentration range from 0.1 to 50?μg?g?1, with correlation coefficients of >0.990. The limits of detection are 23.4?ng?g^?1 (gamma-aminobutyrate), 45.3?ng?g^?1 (glycine) and 67.5?ng?g^?1 (taurine) (S/N?=?3). The results reveal the potential of graphene as a sorbent in the analysis of biological samples.

Molecularly imprinted dispersive solid-phase microextraction for determination of sulfamethazine by capillary electrophoresis

We have developed a rapid, selective and efficient method for dispersive solid-phase microextraction (DSPME) using microbeads of a molecularly imprinted polymer (MIP). It enables the pre-concentration of sulfamethazine and sample clean-up prior to capillary electrophoresis with UV detection. The microbeads were synthesized via precipitation polymerization using sulfamethazine, methacrylic acid and ethylene glycol dimethacrylate (EGDMA) as the template molecule, the functional monomer and the cross-linking monomer, respectively. Characterization by SEM displayed the high uniformity and dispersibility of the MIP microbeads. The adsorption and desorption of sulfamethazine and the parameters for CE were optimized to result in a limit of detection of 1.1?μg?L^?1, which is 373-fold lower than that of direct CE detection. The equilibration time of extraction was reduced to 5?min, and the selectivity of the microbeads was significantly improved compared to the non-imprinted polymer. The method was successfully applied to the determination of trace sulfamethazine in several milk samples, with recoveries in the range of 89?% to 110?%.