A microfluidic device for open loop stripping of volatile organic compounds

The detection of volatile organic compounds is of great importance for assessing the quality of water. In this contribution, we describe a miniaturized stripping device that allows fast online detection of organic solvents in water. The core component is a glass microfluidic chip that facilitates the creation of an annular-flowing stream of water and nitrogen gas. Volatile compounds are transferred efficiently from the water into the gas phase along the microfluidic pathway at room temperature within less than 5 s. Before exiting the microchip, the liquid phase is separated from the enriched gas phase by incorporating side capillaries through which the hydrophilic water phase is withdrawn. The gas phase is conveniently collected at the outlet reservoir by tubing. Finally, a semiconductor gas sensor analyzes the concentration of (volatile) organic compounds in the nitrogen gas. The operation and use of the stripping device is demonstrated for the organic solvents THF, 1-propanol, toluene, ethylbenzene, benzaldehyde, and methanol. The mobile, inexpensive, and continuously operating system with liquid flow rates in the low range of microliters per minute can be connected to other detectors or implemented in chemical production line for process control.

Aptamer-based label-free detection of PDGF using ruthenium(II) complex as luminescent probe

We report a simple, cost-effective, and label-free detection method, consisting of a platelet-derived growth factor (PDGF) binding aptamer and hydrophobic Ru(II) complex as a sensor system for PDGF. The binding of PDGF with the aptamer results in the weakening of the aptamer–Ru(II) complex, monitored by luminescence signal. A substantial enhancement in the luminescence intensity of Ru(II) complex is observed in the presence of aptamer due to the hydrophobic interaction. Upon addition of PDGF, the luminescence intensity is decreased, due to the stronger interaction between the aptamer and PDGF resulting in the displacement of Ru(II) complex to the aqueous solution. Our assay can detect a target specifically in a complex medium such as the mixture of proteins, at a concentration of 0.8 pM.

False Results Caused by Solvent Impurity in Tetrahydrofuran for MALDI TOF MS Analysis of Amines

Tetrahydrofuran (THF) is one of the most frequently used solvents in the MALDI TOF MS analysis of synthetic compounds. However, it should be used with caution because a trace amount of 4-hydroxybutanal (HBA) might be generated and accumulated in THF during storage. Since only a tiny amount of analytes is required in MALDI MS measurements, a trace amount of HBA might have a significant effect on the MS results. It was found that HBA will quickly react with primary and secondary amino compounds, leading to false results about the sample composition with an extra series of ions with additional mass of 70 Da in between. The formation of HBA can be inhibited by butylated hydroxytoluene (BHT) antioxidant. Therefore, when THF is required as the solvent for sample preparation, it is strongly recommended to use a BHT-stabilized one, at least for the analysis of compounds with amino groups.

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 %.

Detection of silver(I) ion based on mixed surfactant-adsorbed CdS quantum dots

Mixed cationic and anionic surfactants were adsorbed on cadmium sulfide quantum dots (CdS QDs) capped with mercaptoacetic acid. The CdS QDs can be extracted into acetonitrile with 98 % efficiency in a single step. Phase separation only occurs at a molar ratio of 1:1.5 between cationic and anionic surfactants. The surfactant-adsorbed QDs in acetonitrile solution display stronger and more stable photoluminescence than in water solution. The method was applied for determination of silver(I) ion based on its luminescence enhancement of the QDs. Under the optimum conditions, the relative fluorescence intensity is linearly proportional to the concentration of silver(I) ion in the range between 50 pmol L^?1and 4 μmol L^?1, with a 20 pmol L^?1 detection limit. The relative standard deviation was 1.93 % for 9 replicate measurements of a 0.2 μmol L^?1 solution of Ag(I).

Ultrasound-assisted emulsification–microextraction for the sensitive determination of ethyl carbamate in alcoholic beverages

A method based on ultrasound-assisted emulsification–microextraction (USAEME) was proposed in this contribution for the determination of ethyl carbamate (EC) in alcoholic beverages using gas chromatography coupled to triple quadrupole mass spectrometry. To achieve the determination of EC in alcoholic beverages, the influences on the extraction efficiency of type and volume of extraction solvent, temperature, ionic strength, alcohol content, and extraction time were studied, once the extraction solvent had been selected. The optimized conditions were 200.0 μL of chloroform at 30 °C during 5 min with 15 % (m/v) sodium chloride addition. The detection limit, relative standard deviations, linear range, and recoveries under the optimized conditions were 0.03 μg L^?1, 4.2–6.1 %, 0.1–50.0 μg L^?1, and 80.5–87.9 %, respectively. Moreover, the feasibility of the present method was also validated by real samples. To the best of our knowledge, this is the first time that USAEME has been applied to determine a strongly hydrophilic compound in alcoholic beverages.

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.

Luminescent Ru(bpy)3 2+-doped silica nanoparticles for imaging of intracellular temperature

Silica nanoparticles doped with the luminescent temperature probe Ru(bpy)₃ ²⁺ were prepared by a modified Stöber method and are shown to enable optical sensing of intracellular temperatures. Based on the regrowth of silica nanoseeds, the ruthenium probe was easily incorporated and then covered with a shell of pure silica. The resulting nanothermometers were immune to the quenching by oxygen owing to the outer silica layer. The nanoparticles were further coated with poly-L-lysine in order to reduce cytotoxicity and to warrant cellular uptake. The luminescence of these nanosensors is rather sensitive to temperature in the physiological range (25–45 °C), with a decrease of ?1.26 % in intensity per °C increase in temperature. The nanosensors were internalized into living cells of a hepatocellular carcinoma cell line along with gold nanorods. These display longitudinal surface plasmon resonance absorption at ~808 nm that causes a local rise in temperature. The microscopically captured luminescence intensity of the nanosensors after 808 nm irradiation of the gold nanorods decayed with increasing temperature, thereby indicating successful imaging of temperature.

Miniaturised enzymatic conductometric biosensor with Nafion membrane for the direct determination of formaldehyde in water samples

A new conductometric enzyme-based biosensor was developed for the determination of formaldehyde (FA) in aqueous solutions. The biosensor was prepared by cross-linking formaldehyde dehydrogenase from Pseudomonas putida with bovine serum albumin in saturated glutaraldehyde vapours (GA) at the surface of interdigitated gold microelectrodes. Nicotinamide adenine dinucleotide cofactor (NAD⁺) was added in solution at each measurement to maintain enzyme activity. Addition of a Nafion layer over the enzyme modified electrode resulted in a significant increase of biosensor signal due to enhanced accumulation of protons generated by enzymatic reaction at the electrode surface. Different parameters affecting enzyme activity or playing a role in ionic transfer through the Nafion membrane were optimised. In optimal conditions (0.045 mg enzyme, 30 min exposure to GA, 0.3 μL of a 1 % (v/v) Nafion solution deposit, measurement in 5 mM phosphate buffer pH 7 containing 20 μM NAD⁺), the biosensor signal was linear up to 10 mM FA, and the detection limit was 18 μM. Relative standard deviations calculated from five consecutive replicates of FA solutions were lower than 5 % in the 1–10 mM range. The biosensor was successfully applied to the determination of FA in spiked water samples (tap water and Rhone river water), with recoveries in the 95–110 % range.

A highly selective fluorescent probe for the detection of palladium(II) ion in cells and aqueous media

We report on a fluorescent probe for the optical (and even bare eye) detection of palladium(II) ion which causes the probe to undergo a strong increase in absorbance and fluorescence. The probe is easily synthesized from rhodamine B hydrazide and 9-anthraldehyde and displays high selectivity over other metal ions. Fluorescence intensity and absorbance are linearly proportional to the concentration of Pd(II) in the 0–7 μM and 0–1 μM concentration range, respectively, with detection limits of 0.21 μM and 0.03 μM. The probe can detect Pd(II) with virtually no interferences by other metal ions and anions. It was applied to intracellular imaging of Pd(II) in living cells and to its determination in a palladium-containing catalyst and in spiked water samples.

Ultrasound-assisted emulsification microextraction of organolead and organomanganese compounds from seawater, and their determination by GC-MS

We describe a simple method for the simultaneous determination of organolead and organomanganese compounds in seawater samples. It is based on ultrasound-assisted emulsification microextraction. Trimethyllead, triethyllead, tetraethyllead, cyclopentadienylmanganese tricarbonyl and its methyl derivative were separated and determined using gas chromatography and mass spectrometry. Trimethyllead and triethyllead were derivatized with sodium tetraphenylborate before being submitted to the preconcentration step. Detection limits ranged from 7.0 to 41 ng L^?1 depending on the compound. Recoveries ranged from 84 to 118 %, depending on the compound and the sample analyzed. Seawater samples were collected at different sites of the Cartagena Bay and none of the target analytes were found at levels above the corresponding detection limits.

Acetone sensor based on solvothermally prepared ZnO doped with Co3O4 nanorods

This paper describes a reliable and sensitive method for sensing dissolved acetone using doped nanomaterials. Large-scale synthesis of ZnO nanorods (NRs) doped with Co₃O₄ was accomplished by a solvothermal method at low temperature. The doped NRs were characterized in terms of their morphological, structural, and optical properties by using field-emission scanning electron microscopy coupled with energy-dispersive system, UV-Vis., Fourier transform IR, X-ray diffraction, and Xray photoelectron spectroscopy. The calcinated (at 400 °C) doped NRs are shown to be an attractive semiconductor nanomaterial for detecting acetone in aqueous solution using silver electrodes. The sensor exhibits excellent sensitivity, stability and reproducibility. The calibration plot is linear over a large concentration range (66.8 μM to 0.133 mM), displays high sensitivity (~3.58 μA cm^?2 mM^?1) and a low detection limit (~14.7?±?0.2 μM; at SNR of 3).

Selective microextraction of carbaryl and naproxen using organic–inorganic monolithic columns containing a double molecular imprint

We report on an organic–inorganic hybrid material that was double imprinted with the insecticide carbaryl and the anti-inflammatory drug naproxen by a single-step method and that can serve for selective microextraction of the two analytes. The materials, in the form of monolithic columns, were characterized by scanning electron microscopy and Fourier transform IR spectra. A simple, rapid and sensitive method was then developed for the simultaneous determination of carbaryl and naproxen in lettuce and river water using these columns for microextraction, HPLC for separation, and a diode array for UV detection. The limits of detection (at S/N?=?3) and quantification (at S/N?=?10) are in the ranges of 2.5 – 8.8 μg kg^?1 and 2.3 – 8.0 μg L^?1 for lettuce and Yangtze River water, respectively. The recoveries of this method range from 93.0 to 108 % (in case of analyzing lettuce and river water), and relative standard deviations are <8.9 %.

A three phase dispersive liquid-liquid microextraction technique for the extraction of antibiotics in milk

We have developed a 3-phase method for dispersive liquid-liquid microextraction of ß-lactam antibiotics in milk. Chloroform and acetonitrile serve as the solvents for extraction and disperssion, respectively, where Aliquat 336 is the carrier. An experimental design based on Plackett-Burman and Central composite designs were applied for the screening and optimization of significant parameters in the extraction method. The experimental conditions for extraction were optimized, and the subsequent HPLC assay gave relative standard deviations and detection limits in the range of 4.3–8.5 % and 50–500 μg L^-1, respectively. Preconcentration factors are in the range of 80–125.

An inorganic–organic hybrid material based on ZnO nanoparticles anchored to a composite made from polythiophene and hexagonally ordered silica for use in solid-phase fiber microextraction of PAHs

We report on an inorganic–organic hybrid nanocomposite that represents a novel kind of fiber coating for solid-phase microextraction (SPME) of polycyclic aromatic hydrocarbons (PAHs). The material is composed of ZnO nanoparticles, polythiophene and hexagonally ordered silica, and displays good extraction capability due to its nanostructure. The nanocomposite was synthesized by an in-situ polymerization technique, and the ZnO nanoparticles were anchored to the pores in the walls. The ZnO/polythiophene/hexagonally ordered silica (ZnO/PT/SBA-15) nanocomposite was then deposited on a stainless steel wire to obtain the fiber for SPME of PAHs. Optimum conditions include an extraction temperature of 85 °C (for 30 min only), a desorption temperature of 260 °C (for 2 min), and a salt concentration (NaCl) of 20 % (w/v). The detection limits are between 8.2 and 20 pg mL^?1, and the linear responses extend from 0.1 to 10 ng mL^?1. The repeatability for one fiber (for n?=?5), expressed as relative standard deviation, is between 4.3 and 9.1 %. The method offers the advantage of being simple to use, rapid, and low-cost (in terms of equipment). The thermal stability of the fiber and high relative recovery (compared to conventional methods) represent additional attractive features.

Advantages of Monodisperse and Chemically Robust “SpheriCal” Polyester Dendrimers as a “Universal” MS Calibrant

The utilization of dendrimer calibrants as an alternative to peptides and proteins for high mass calibration is explored. These synthetic macromolecules exhibited a number of attractive advantages, including exceptional shelf-lives, broad compatibility with a wide range of matrices and solvents, and evenly spaced calibration masses across the mass range examined, 700–30,000 u. The exceptional purity of these dendrimers and the technical simplicity of this calibration platform validate their broad relevance for high molecular weight mass spectrometry.

Influence of secondary preparative parameters and aging effects on PLGA particle size distribution: a sedimentation field flow fractionation investigation

Poly(lactic-co-glycolic acid) particles in the 200–400-nm size range were formulated through nanoprecipitation and solvent evaporation methods. Different concentrations of the polymer and stabilizer (Pluronic® F 68) were tested in order to identify the best conditions for making poly(lactic-co-glycolic acid) particles of suitable size, stable in time, and to be used as carriers for brain-targeting drugs. The particles with the best characteristics for delivery system design were those formulated by nanoprecipitation with an organic/water phase ratio of 2:30, a polymer concentration of 25 mg/mL, and a surfactant concentration of 0.83 mg/mL; their surface charge was reasonably negative (approximately -27 mV) and the average size of the almost monodisperse population was roughly 250 nm. Particle characterization was obtained through ζ-potential measurements, scanning electron microscope observations, and particle size distribution determinations; the latter achieved by both photon-correlation spectroscopy and sedimentation field flow fractionation. Sedimentation field flow fractionation, which is considered more reliable than photon-correlation spectroscopy in describing the possible particle size distribution modifications, was used to investigate the effects of 3 months of storage at 4 °C had on the lyophilized particles.

A highly sensitive caffeine immunoassay based on a monoclonal antibody

A new immunoassay has been developed based on a commercially available anti-caffeine monoclonal antibody and a de novo synthesized tracer, using horseradish peroxidase and UV–visible detection. Caffeine, which is frequently found in surface waters, can be quantified with a relative error lower than 20% for concentrations above 0.025 μg L^?1 (limit of quantitation, direct analysis). The limit of detection is 0.001 μg L^?1 and can be reduced by solid-phase extraction (SPE). Moreover, with minor adaptations, the assay can be used to quantify caffeine in several beverages, shampoo, and caffeine tablets. The results obtained by ELISA correlate well with those from liquid chromatography–tandem mass spectrometry (LC–MS–MS) for the tested matrices. Several surface waters from Berlin were analysed and all tested positive for caffeine, with concentrations higher than 0.030 μg L^?1. In one run 66 samples can be analysed within 2 h.

Quinolinium ionic liquid-modified silica as a novel stationary phase for high-performance liquid chromatography

A novel stationary phase based on quinolinium ionic liquid-modified silica was prepared and evaluated for high-performance liquid chromatography. The stationary phase was investigated via normal-phase (NP), reversed-phase (RP), and anion-exchange (AE) chromatographic modes, respectively. Polycyclic aromatic hydrocarbons, phthalates, parabens, phenols, anilines, and inorganic anions were used as model analytes in chromatographic separation. Using the newly established column, organic compounds were separated successfully by both NP and RP modes, and inorganic anions were also separated completely by AE mode. The obtained results indicated that the stationary phase could be applied in different chromatographic modes, with multiple-interaction mechanism including van der Waals forces (dipole–dipole, dipole–induced dipole interactions), hydrophobic, π–π stacking, electrostatic forces, hydrogen bonding, anion-exchange interactions, and so on. The column packed with the stationary phase was applied to analyze phthalates and parabens in hexane extracts of plastics. Tap water and bottled water were also analyzed by the column, and nitrate was detected as 20.1 and 13.8 mg L^?1, respectively. The results illustrated that the stationary phase was potential in practical applications.

Dispersive liquid-liquid microextraction of phenolic compounds using solidified floating organic droplets, and their determination by HPLC

We have developed a simple and efficient method for dispersive liquid-liquid microextraction of 4-nitrophenol, 2-naphthol and bisphenol A in real water samples. It is making use of solidified floating organic droplets of 1-dodecanol which has low density and a proper melting point. The type and volume of extraction solvent and dispersive solvent, the effect of salts, pH value and extraction time were optimized and resulted in enrichment factors of 84 for 4-nitrophenol, 123 for 2-naphthol, and 97 for bisphenol A. The limits of detection by HPLC are 1.50, 0.10 and 1.02 ng · mL^?1, respectively. Excellent linearity is observed in the concentration range from 10 to 800 ng · mL^?1, with coefficients of correlation ranging from 0.9988 to 0.9999. The relative standard deviations (for n?=?5) are from 3.2 to 5.3 %, and relative recoveries for the three phenols in tap, river and spring water range from 85.0 to 105.0 %, 98.3 to 110.0 %, and 98.6 to 109.0 %, respectively.