Determination of chlorobenzenes in water samples based on fully automated microextraction by packed sorbent coupled with programmed temperature vaporization–gas chromatography–mass spectrometry

A fully automated method consisting of microextraction by packed sorbent (MEPS) coupled directly to programmed temperature vaporizer–gas chromatography–mass spectrometry (PTV–GC–MS) has been developed to determine the 12 chlorobenzene congeners (chlorobenzene; 1,2-, 1,3-, and 1,4-dichlorobenzene; 1,2,3-, 1,2,4-, and 1,3,5-trichlorobenzene; 1,2,3,4-, 1,2,3,5-, and 1,2,4,5-tetrachlorobenzene; pentachlorobenzene; and hexachlorobenzene) in water samples. The effects of the variables on MEPS extraction, using a C18 sorbent, and the instrumental PTV conditions were studied. The internal standard 1,4-dichlorobenzene d4 was used as a surrogate. The proposed method afforded good reproducibility, with relative standard deviations (RSD %) lower than 12 %. The limits of detection varied between 0.0003 μg L^?1 for 1,2,3,4-tetrachlorobenzene and 0.07 μg L^?1 for 1,3- and 1,4-dichlorobenzene, while those of quantification varied between 0.001 μg L^?1 and 0.2 μg L^?1 for the same compounds. Accuracy of the proposed method was confirmed by applying it to the determination of chlorobenzenes in different spiked water samples, including river, reservoir, and effluent wastewater.

A metal-organic framework sustained by a nanosized Ag12 cuboctahedral node for solid-phase extraction of ultra traces of lead(II) ions

We show that a metal-organic framework (MOF) sustained by a nanosized Ag12 cuboctahedral node can be applied to selectively extract traces of lead(II) ion from environmental water samples. The MOF was characterized by thermogravimetric and differential thermal analysis, scanning electron microscopy, FTIR, and X-ray diffraction. The effects of pH value, flow rates, of type, concentration and volume of the eluent, of break-through volume and potentially interfering ions on the separation and determination of lead were evaluated. Following desorption with EDTA, Pb(II) was quantified by FAAS. The use of the MOF results in excellent analytical figures of merit including an analytical range from 2 to 180 μg L^?1 of Pb(II) (R²?>?0.99); a limit of detection of 500 ng L^?1; an adsorption capacity of 120 mg g^?1; an extraction efficiency of >95 %, and a relative standard deviation of <4 % (for eight separate column experiments).

Highly sensitive SERS probe for mercury(II) using cyclodextrin-protected silver nanoparticles functionalized with methimazole

We have developed a surface-enhanced Raman scattering (SERS) probe for the determination of mercury(II) using methimazole-functionalized and cyclodextrin-coated silver nanoparticles (AgNPs). These AgNPs in pH 10 solution containing sodium chloride exhibit strong SERS at 502 cm^?1. Its intensity strongly decreases in the presence of Hg(II). This effect serves as the basis for a new method for the rapid, fast and selective determination of trace Hg(II). The analytical range is from 0.50 μg L^?1 to 150 μg L^?1, and the limit of detection is 0.10 μg L^?1. The influence of 11 metal ions commonly encountered in environmental water samples was found to be quite small. The method was applied to the determination of Hg(II) in spiked water samples and gave recoveries ranging from 98.5 to 105.2 % and with relative standard deviations of <3.5 % (n?=?5). The total analysis time is <10 min for a single sample.

Electrochemically controlled solid-phase micro-extraction of proline using a nanostructured film of polypyrrole, and its determination by ion mobility spectrometry

We report on a fast, simple and accurate method for the determination of proline in urine samples by employing a nanostructured film of conducting polypyrrole for electrochemically controlled solid-phase microextraction, and ion mobility spectrometry (IMS) for detection. This method has the advantages of simple sample preparation and a sensitivity of IMS to proline that is higher than that for other amino acids. The calibration curve is linear in the range of 0.5–60 μg L^?1 (4–521 nmol L^?1), and the detection limit is 0.2 μg L^?1. The electrochemical potentials for uptake and release were optimized. The method was successfully applied to the clean-up and quantitation of trace amounts of proline in urine samples.

Magnetic titanium oxide nanoparticles for hemimicelle extraction and HPLC determination of organophosphorus pesticides in environmental water

We report on a method for the extraction of organophosphorus pesticides (OPPs) from water samples using mixed hemimicelles and magnetic titanium dioxide nanoparticles (Fe₃O₄@TiO₂) modified by cetyltrimethylammonium. Fe₃O₄@TiO₂ nanoparticles were synthesized by a hydrothermal process and then characterized by scanning electron microscopy and Fourier transform IR spectrometry. The effects of the quantity of surfactant, extraction time, desorption solvent, pH value, extraction volume and reuse of the sorbent were optimized with respect to the extraction of OPPs including chlorpyrifos, dimethoate, and trichlorfon. The extraction method was applied to analyze OPPs in environmental water using HPLC along with UV detection. The method has a wide linear range (100–15,000 ng L^?1), good linearity (r?>?0.999), and low detection limits (26–30 ng L^?1). The enrichment factor is ~1,000. The recoveries (at spiked levels of 100, 1,000 and 10,000 ng L^?1) are in the range of 88.5–96.7 %, and the relative standard deviations range from 2.4 % to 8.7 %.

Polythiophene-coated Fe3O4 nanoparticles as a selective adsorbent for magnetic solid-phase extraction of silver(I), gold(III), copper(II) and palladium(II)

We have developed a fast method for sensitive extraction and determination of the metal ions silver(I), gold(III), copper(II) and palladium(II). Fe₃O₄ magnetic nanoparticles were modified with polythiophene and used for extraction the metal ions without a chelating agent. Following extraction, the ions were determined by flow injection inductively coupled plasma optical emission spectrometry. The influence of sample pH, type and volume of eluent, amount of adsorbent, sample volume and time of adsorption and desorption were optimized. Under the optimum conditions, the calibration plots are linear in the 0.75 to 100 μg L^?1 concentration range (R²?>?0.998), limits of detection in the range from 0.2 to 2.0 μg L^?1, and enhancement factors in the range from 70 to 129. Precisions, expressed as relative standard deviations, are lower than 4.2 %. The applicability of the method was demonstrated by the successful analysis of tap water, mineral water, and river water.

Separation and preconcentration of trace quantities of copper ion using modified alumina nanoparticles, and its determination by flame atomic absorption spectrometry

We report on a sensitive, reliable and relatively fast method for separation, preconcentration and determination of trace quantities of copper(II) ion. It is making use of nanometer-sized γ-alumina nanoparticles modified with sodium dodecyl sulfate (SDS). The adsorptive potential was assessed via a Langmuir isotherm and the maximal sorption capacity was found to be 138 mg g^-1. The effects of pH values, amount of ligand, flow rate, type of eluting agent, volume of eluent, and the volume of sample were examined. The effects of interfering ions on the recovery of the analyte were also investigated. Copper ion was then determined by flame atomic absorption spectrometry. The relative standard deviation for five replicate determinations (at 50 μg L^?1 of copper) is 3.3%. The detection limit (at 3 s) is 2.5 μg L^?1. This method was validated with a certified reference material of oyster tissue (NIST SRM 1566b) and the results coincided well with the certified values. The procedure was successfully applied to the determination of Cu in water and food samples.

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.

Determination of formaldehyde based on the enhancement of the chemiluminescence produced by CdTe quantum dots and hydrogen peroxide

Water-soluble cadmium telluride quantum dots (CdTe QDs) capped with glutathione (GSH) display chemiluminescence (CL) emission on reaction with hydrogen peroxide (H₂O₂) in strongly alkaline medium. It is found that the CL is strongly enhanced on addition of formaldehyde in aqueous solution. A flow injection system was developed, and it is shown that there is good linearity between CL intensity and the concentration of formaldehyde in the 0.06–3.0 μg L^?1 range. The limit of detection is as low as 10 ng L^?1. The method was successfully applied to the determination of formaldehyde in indoor air after adsorption into an aqueous phase. The recoveries for the real samples range from 97 % to 102.5 %, and the relative standard deviation is <3.8 % for intra- and inter-assay precision.

Determination of microcystin-LR with a glassy carbon impedimetric immunoelectrode modified with an ionic liquid and multiwalled carbon nanotubes

We report on a sensitive, simple, label-free impedance-based immunoelectrode for the determination of microcystin-LR (MCLR). The surface of the electrode was modified with a composite made from multiwalled carbon nanotubes and an ionic liquid, and with immobilized polyclonal antibody against MCLR. Cyclic voltammetry and impedance spectroscopy were applied to characterize the modified electrode. It is found that the multi-walled carbon nanotubes act as excellent mediators for the electron transfer between the electrode and dissolved hexacyanoferrate redox pair, while the ionic liquid renders it biocompatible. The method exhibits a wide linear range (0.005 μg?L-1 to 1.0 μg?L-1), a low detection limit (1.7 ng?L-1) and a long-term stability of around 60 days. The ionic liquid 1-amyl-2,3-dimethylimidazolium hexafluorophosphate gave the best impedimetric response. The new immunoelectrode is sensitive, stable, and easily prepared. It has been successfully applied to the determination of MCLR in water samples.

FAAS slurry analysis of lead and copper ions preconcentrated on titanium dioxide nanoparticles coated with a silver shell and modified with cysteamine

We report on the separation and preconcentration of lead(II) and copper(II) ions using silver-coated titanium dioxide nanoparticles modified with cysteamine, and their determination by slurry analysis via flame atomic absorption spectrometry. The ions were adsorbed via a conventional batch technique, and the ion-loaded slurry was separated and directly introduced into the spectrometer, thereby eliminating a number of drawbacks. The effects of pH, amount of sorbent, slurry volume, sample volume and other ions on the recovery were investigated. Under optimized experimental conditions, copper and lead can be recovered within the 95% confidence level in certificated waste water, but also in spiked sea water samples. The technique is fast, simple, and leads to complete elution. The limit of detection (3δ, at n?=?10) was 0.37 μg L^?1 for Cu(II), and 0.38 μg L^?1 for Pb(II).

Determination of Pt and Pd in particles emitted from automobile exhaust catalysts using ion-exchange matrix separation and voltammetric detection

We report on the ion-exchange separation of Pt and Pd from the main elements emitted from catalysts of gasoline-fueled cars by exploiting the selective chelating ion exchanger Lewatit MonoPlus TP-214. Pt and Pd were then eluted with a recovery of 92% and 96%, respectively, using an acidified solution of thiourea, and the eluent was analyzed by sequential voltammetry. The detection limits are 0.04 μg L^?1 and 1 μg L^?1 for Pt and Pd, respectively, and the relative standard deviation is about 4.0% (for n?=?10). The procedure was successfully applied to particles emitted from automobile exhaust catalysts of four capacity engine vehicles. Graphite furnace atomic absorption spectrometry was also employed for reasons of comparison. Emission by four vehicles with 1400, 2600, 3200, and 4800 cc engines, respectively, ranged from 19 to 28 ng km^?1 for Pt, and from 102 to 150 ng km^?1 for Pd.

Sensitive detection of trace hemoglobin using fluorescence method based on functionalized quantum dots

The fluorescence quenching of quantum dots by hemoglobin has been demonstrated to depend on surface functionalization, and this property has been utilized to construct a novel fluorescent method for rapid, sensitive, and selective detection of trace hemoglobin in urine at microgram level. This method shows low interference and high selectivity for hemoglobin with a limit of detection of 4.3 μg L^?1 in water and 66.1 μg L^?1 in urine, which are lower than those of currently used methods in labs and clinics. Spike and recovery tests in raw, acidified, and alkalized urine samples exhibit good recovery rates for the spiked concentrations close to the limit of detection.

Solid-phase preconcentration of cadmium(II) using amino-functionalized magnetic-core silica-shell nanoparticles, and its determination by hydride generation atomic fluorescence spectrometry

We report on the synthesis and evaluation of aminated-CoFe₂O₄/SiO₂ nanoparticles that can serve as a selective solid-phase sorbent for the extraction of cadmium ion. The nanoparticles consist of a magnetic CoFe₂O₄ core and an amino-modified silica shell. They can efficiently extract cadmium(II) ion and then can be isolated from the sample solution due to the magnetic nature of the core. The effects of the experimental conditions on the extraction process were optimized. Cadmium was then quantified by hydride generation atomic fluorescence spectrometry. The resulting calibration curve is linear in the concentration range of 0.01–10 μg?L^?1, the instrumental detection limits (3σ) is 3.15 ng?L^?1 and the relative standard deviation is 4.9 % at the 1.0 μg?L^?1 level (for n?=?11). The enrichment factor is 50 (for 50 mL samples), and the adsorbent can be used for at least 45 cycles of preconcentration and elution. The method was applied to the determination of cadmium in environmental water samples, and successfully validated by analyzing two certified reference materials.

Ultra-sensitive spectrophotometric determination of nickel after complexation and membrane filtration

We report on a simple, sensitive and selective method for the spectrophotometric determination of Ni²⁺ in water samples. The analyte ions were collected on a membrane filter in the form of their red complex with 1-(2-pyridylazo)-2-naphthol (PAN), and the absorption spectra of the colored membrane filters were acquired. Effects of pH value, sample volume, and amount of PAN were examined in order to optimize sensitivity. The interference by common other ions was eliminated using appropriate masking agents. The absorbance is linearly related to the concentration of Ni²⁺ in the ranges from 0.3 to 1.5 μg L^?1, and from 2 to 10 μg L^?1, respectively, the correlation coefficients (R²) being 0.9871 and 0.9954. Under the optimal conditions, the detection limit is 0.1 μg L^?1. The recoveries in case of spiked samples are between 95.0% and 101.5%, and the relative standard deviations range from 2.8% to 4.1%.

Screen-printed electrode-based electrochemical detector coupled with in-situ ionic-liquid-assisted dispersive liquid–liquid microextraction for determination of 2,4,6-trinitrotoluene

A novel method is reported, whereby screen-printed electrodes (SPELs) are combined with dispersive liquid–liquid microextraction. In-situ ionic liquid (IL) formation was used as an extractant phase in the microextraction technique and proved to be a simple, fast and inexpensive analytical method. This approach uses miniaturized systems both in sample preparation and in the detection stage, helping to develop environmentally friendly analytical methods and portable devices to enable rapid and onsite measurement. The microextraction method is based on a simple metathesis reaction, in which a water-immiscible IL (1-hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, [Hmim][NTf₂]) is formed from a water-miscible IL (1-hexyl-3-methylimidazolium chloride, [Hmim][Cl]) and an ion-exchange reagent (lithium bis[(trifluoromethyl)sulfonyl]imide, LiNTf₂) in sample solutions. The explosive 2,4,6-trinitrotoluene (TNT) was used as a model analyte to develop the method. The electrochemical behavior of TNT in [Hmim][NTf₂] has been studied in SPELs. The extraction method was first optimized by use of a two-step multivariate optimization strategy, using Plackett–Burman and central composite designs. The method was then evaluated under optimum conditions and a good level of linearity was obtained, with a correlation coefficient of 0.9990. Limits of detection and quantification were 7 μg L^?1 and 9 μg L^?1, respectively. The repeatability of the proposed method was evaluated at two different spiking levels (20 and 50 μg L^?1), and coefficients of variation of 7 % and 5 % (n?=?5) were obtained. Tap water and industrial wastewater were selected as real-world water samples to assess the applicability of the method.

Preconcentration and determination of lead(II) by microextraction based on suspended cadion covered zirconia nanoparticles in a surfactant media

We have developed a method for the microextraction of lead(II) ion. It is based on the use of suspended zirconia nanoparticles modified with the reagent cadion. Pb(II) ions in the sample are adsorbed onto the modified zirconia nanoparticles suspended in the solution of a non-ionic surfactant. After cloud formation and phase separation by sedimentation, the surfactant rich phase was acidified and diluted to 100 μL with 3.0 mol L^?1 nitric acid and ultrasonicated for a few seconds to desorb the analyte from the sorbent. The mixture was centrifuged and 10 μL of the supernatant liquid phase along with 10 μL of the Pd/Mg modifier were submitted to the electrothermal atomic absorption spectrometer. The parameters affecting the extraction efficiency were optimized by the univariable method. Under the optimized conditions, a sample volume of 40 mL resulted in an enhancement factor of 384 and a detection limit (defined as 3S_b/m) of 2.2 ng L^?1. The method was successfully applied to the determination of Pb(II) in water, tea and rice samples. Accuracy was determined by the recovery experiments and the analysis of two certified reference materials.

Preconcentration of mercury(II) using a thiol-functionalized metal-organic framework nanocomposite as a sorbent

A novel type of porous metal-organic framework (MOF) was obtained from thiol-modified silica nanoparticles and the copper(II) complex of trimesic acid. It is shown that this nanocomposite is well suitable for the preconcentration of Hg(II) ions. The nanocomposite was characterized by Fourier transfer infrared spectroscopy, X-ray powder diffraction, energy-dispersive X-ray diffraction and scanning electron microscopy. The effects of pH value, sorption time, elution time, the volume and concentration of eluent were investigated. Equilibrium isotherms were studied, and four models were applied to analyze the equilibrium adsorption data. The results revealed that the adsorption process obeyed the Langmuir model. The maximum monolayer capacity and the Langmuir constant are 210 mg g^?1 and 0.273 L mg^?1, respectively. The new MOF-based nanocomposite is shown to be an efficient and selective sorbent for Hg(II). Under the optimal conditions, the limit of detection is 20 pg mL^?1 of Hg(II), and the relative standard deviation is <7.2 % (for n?=?3). The sorbent was successfully applied to the rapid extraction of Hg(II) ions from fish, sediment, and water samples.

An automated headspace solid-phase microextraction followed by gas chromatography–mass spectrometry method to determine macrocyclic musk fragrances in wastewater samples

A fully automated method has been developed for determining eight macrocyclic musk fragrances in wastewater samples. The method is based on headspace solid-phase microextraction (HS-SPME) followed by gas chromatography–mass spectrometry (GC-MS). Five different fibres (PDMS 7 μm, PDMS 30 μm, PDMS 100 μm, PDMS/DVB 65 μm and PA 85 μm) were tested. The best conditions were achieved when a PDMS/DVB 65 μm fibre was exposed for 45 min in the headspace of 10 mL water samples at 100 °C. Method detection limits were found in the low ng L^?1 range between 0.75 and 5 ng L^?1 depending on the target analytes. Moreover, under optimized conditions, the method gave good levels of intra-day and inter-day repeatabilities in wastewater samples with relative standard deviations (n?=?5, 1,000 ng L^?1) less than 9 and 14 %, respectively. The applicability of the method was tested with influent and effluent urban wastewater samples from different wastewater treatment plants (WWTPs). The analysis of influent urban wastewater revealed the presence of most of the target macrocyclic musks with, most notably, the maximum concentration of ambrettolide being obtained in WWTP A (4.36 μg L^?1) and WWTP B (12.29 μg L^?1), respectively. The analysis of effluent urban wastewater showed a decrease in target analyte concentrations, with exaltone and ambrettolide being the most abundant compounds with concentrations varying between below method quantification limit (<MQL) and 2.46 μg L^?1.

A nanosized cadmium(II)-imprinted polymer for use in selective trace determination of cadmium in complex matrices

We describe a nanosized Cd(II)-imprinted polymer that was prepared from 4-vinyl pyridine (the functional monomer), ethyleneglycol dimethacrylate (the cross-linker), 2,2′-azobisisobutyronitrile (the radical initiator), neocuproine (the ligand), and Cd(II) (the template ion) by precipitation polymerization in acetonitrile as the solvent. The imprinted polymer was characterized by X-ray diffraction, thermogravimetric analysis, differential thermal analysis, and scanning electron microscopy. The maximum adsorption capacity of the nanosized sorbent was calculated to be 64 mg g^?1. Cadmium(II) was then quantified by FAAS. The relative standard deviation and limit of detection are 4.2 % and 0.2 μg L^?1, respectively. The imprinted polymer displays improve selectivity for Cd(II) ions over a range of competing metal ions with the same charge and similar ionic radius. This nanosized sorbent is an efficient solid phase for selective extraction and preconcentration of Cd(II) in complex matrices. The method was successfully applied to the trace determination of Cd(II) in food and water samples.