Complete and simultaneous removal of ionic silver and silver nanoparticles by using an ionic liquid supported on a magnetic nanoparticle core.

The global pandemic situation due to COVID-19 has given rise to the massive use of disinfectant products, many of them based on silver atoms. After the use of these products, the silver passes into the aqueous effluents, becoming an emerging contaminant in waters. In this work, a novel procedure for the total and simultaneous removal of ionic and nanomeric silver in aqueous samples is introduced, employing magnetic nanoparticles wrapped with an ionic liquid (Fe3O4@IL) as a removal agent. Experimental variables such as pH, contact time, temperature, as well as pollutant and removal agent doses were studied to achieve the total elimination, exhibiting exceptional conditions for the removal of different concentrations of silvers species in water. The approach achieves 100% removal efficiency for the simultaneous removal of both silver species, goal not achieved previously. Also, 100% removal efficiency is reached for the both species separately, since ionic silver is adsorbed onto the Fe3O4, while nanomeric silver is extracted in the IL. Particularly, for concentrations within the range 50-200 µg L-1, total removal efficiency was reached for a wide range of temperatures and a pH range 7-9, achieved in just 15 min, for all cases. Additionally, the doses of Fe3O4@IL employed to remove all concentrations of silver were 13.7 mg. Characterization of Fe3O4@IL surfaces before and after the process was performed by means of Field Effect Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy. Fe3O4@IL was recycled by employing 100 µL of 1% HNO3 solution, allowing its use for 10 additional silver removal cycles without loss of efficiency. The study of adsorption kinetics and equilibrium isotherms reveal a Freundlich-type adsorption, which suggests affinity between sites in the complex surface of Fe3O4@IL, and Elovich kinetics, indicative of chemisorption onto a heterogeneous surface, while the temperature shows no effect on the results.

Liquid-phase microextraction with solidification of the organic floating drop for the preconcentration and determination of mercury traces by electrothermal atomic absorption spectrometry.

A procedure for the determination of traces of mercury by liquid-phase microextraction based on solidification of a floating organic droplet for separation and electrothermal atomic absorption spectrometry for final measurement has been developed. For this purpose, 50 microL of pre-heated (50 degrees C) undecanoic acid (UA), are added to 25 mL of aqueous sample solution at pH 5. The mixture, maintained at 50 degrees C, is stirred for 10 min using a high stirring rate in order to fragment the UA drop into droplets, thus favoring the extraction process. Next, the vial is immersed in an ice bath, which results in the solidification of the UA drop that is easily separated. Injection into the atomizer is carried out after gentle heating. The pyrolytic atomizers are coated with electrolytically reduced palladium that acts as an effective chemical modifier for more than 500 firings. Under the optimized conditions, the detection limit was 70 ng L(-1) mercury with an enrichment factor of 430. The relative standard deviation of the measurements was in the 2.1-3.5% range. Recovery studies applied to the determination of mercuric ions in bottled and tap water samples were in the 92-104% range.

Comparison of two derivatization-based methods for solid-phase microextraction-gas chromatography-mass spectrometric determination of bisphenol A, bisphenol S and biphenol migrated from food cans.

An environmentally friendly sample pretreatment system based on solid-phase microextraction (SPME) for the sensitive determination of bisphenol A (BPA), bisphenol S (BPS) and biphenol (BP) is described. Two derivatisation reactions to obtain volatile derivatives are compared. Derivatisation with acetic anhydride (AA) was performed in situ in a 5-mM Na(2)CO(3)/NaHCO(3) buffer solution and analytes were extracted by direct immersion (DI) using a PA fibre (85 microm) at 90 degrees C for 40 min with stirring at 1,500 rpm. For derivatisation with bis-(trimethylsilyl)trifluoroacetamide (BSTFA), the analytes were first extracted by DI using the PA fibre at 70 degrees C for 40 min with stirring at 500 rpm. The fibre was then removed, dried in a nitrogen stream for 2 min and introduced into the headspace of BSTFA at 50 degrees C for 30 s. After derivatisation, the analytes were desorbed in the injection port of the GC in the splitless mode at 280 degrees C for 4 min. The separation was carried out by coupling gas chromatography with mass spectrometry in the selected ion monitoring mode, GC-MS(SIM). The method allowed the determination of the migrating levels of bisphenols found in food cans, and it was validated for linearity, detection and quantitation limits, selectivity, accuracy and precision. Detection limits ranged from 3 to 16 pg mL(-1), depending on the compound, at a signal-to-noise ratio of 3. Recoveries obtained for spiked samples were satisfactory for all compounds. Levels of BPA were higher than those of BPS and the lowest contents were found for BP.

A simple device for headspace sorptive extraction prior to gas chromatography-mass spectrometry analysis.

A device for headspace sorptive extraction (HSSE) combined with gas chromatography separation and mass spectrometry detection (GC-MS) is presented. The gadget is based on a simple magnetic disk that permits the stir bar to be placed at the top of the sample vial. The complete surface of the coated stir bar is exposed to the headspace atmosphere, and the movement of the bar caused by the magnetic stirrer in the liquid sample facilitates the sorption process. The final consequence is increased sensitivity and repeatability when compared with a glass-made comercial device for the same purpose. Successful determination of ten chlorobenzenes in waters testifies the good performance of the new device.

Head-space gas chromatography coupled to mass spectrometry for the assessment of the contamination of mayonnaise by yeasts.

Head-space (HS) gas chromatography (GC) coupled to mass spectrometry (MS) is proposed for the assessment of the contamination of mayonnaise as an alternative to plate counting, which is the technique commonly used for evaluating microbial contamination. More specifically, this method was applied in the detection of Candida metapsilosis and Zygosaccharomyces bailii, both of great importance in term of food spoilage since they are resistant to many of the common methods of food preservation. Different chemometric models were investigated using the data obtained by GC-MS (m/z profile, area of the chromatographic peaks and entire chromatographic profile), in order to obtain the highest classification success. The best results were obtained using the chromatographic profile (success rate of 92%). Contaminated samples could also be classified according to the concentration of yeast, obtaining a success rate of 87.5%. Finally, a chemometric model was constructed in an attempt to differentiate between strains.

Evaluation of solid-phase microextraction conditions for the determination of polycyclic aromatic hydrocarbons in aquatic species using gas chromatography.

This paper describes a headspace solid-phase microextraction (HS-SPME) procedure coupled to gas chromatography with mass spectrometric detection (GC-MS) for the determination of eight PAHs in aquatic species. The influence of various parameters on the PAH extraction efficiency was carefully examined. At 75 degrees C and for an extraction time of 60 min, a polydimethylsiloxane-divinylbenzene (PDMS/DVB) fiber coating was found to be most suitable. Under the optimized conditions, detection limits ranged from 8 to 450 pg g(-1), depending on the compound and the sample matrix. The repeatability varied between 7 and 15% (RSD). Accuracy was tested using the NIST SRM 1974b reference material. The method was successfully applied to different samples, and the studied PAHs were detected in several of the samples.

A headspace solid-phase microextraction procedure coupled with gas chromatography-mass spectrometry for the analysis of volatile polycyclic aromatic hydrocarbons in milk samples.

A sensitive and solvent-free method for the determination of ten polycyclic aromatic hydrocarbons, namely, naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo[a]anthracene and chrysene, with up to four aromatic rings, in milk samples using headspace solid-phase microextraction and gas chromatography-mass spectrometry detection has been developed. A polydimethylsiloxane-divinylbenzene fiber was chosen and used at 75 degrees C for 60 min. Detection limits ranging from 0.2 to 5 ng L(-1) were attained at a signal-to-noise ratio of 3, depending on the compound and the milk sample under analysis. The proposed method was applied to ten different milk samples and the presence of six of the analytes studied in a skimmed milk with vegetal fiber sample was confirmed. The reliability of the procedure was verified by analyzing two different certified reference materials and by recovery studies.

In situ ionic liquid dispersive liquid-liquid microextraction coupled to gas chromatography-mass spectrometry for the determination of organophosphorus pesticides.

Nine organophosphorus pesticides (OPPs) were determined in environmental waters from different origins using in situ ionic liquid dispersive liquid microextraction (IL-DLLME). This preconcentration technique was coupled to gas chromatography-mass spectrometry (GC-MS) using microvial insert thermal desorption, an approach that uses a thermal desorption injector as sample introduction system. The parameters affecting both the microextraction and sample injection steps were optimized. The proposed method showed good precision, with RSD values ranging from 4.1 to 9.7%, accuracy with recoveries in the 85-118% range, and sensitivity with DLs ranging from 5 to 16 ng L-1.

Glyoxal and methylglyoxal as urinary markers of diabetes. Determination using a dispersive liquid-liquid microextraction procedure combined with gas chromatography-mass spectrometry.

Glyoxal (GO) and methylglyoxal (MGO) are α-oxoaldehydes that can be used as urinary diabetes markers. In this study, their levels were measured using a sample preparation procedure based on salting-out assisted liquid-liquid extraction (SALLE) and dispersive liquid-liquid microextraction (DLLME) combined with gas chromatography-mass spectrometry (GC-MS). The effect of the derivatization reaction with 2,3-diaminonaphthalene, the addition of acetonitrile and sodium chloride to urine, and the DLLME step using the acetonitrile extract as dispersant solvent and carbon tetrachloride as extractant solvent were carefully optimized. Quantification was performed by the internal standard method, using 5-bromo-2-chloroanisole. The intraday and interday precisions were lower than 6%. Limits of detection were 0.12 and 0.06ngmL-1, and enrichment factors 140 and 130 for GO and MGO, respectively. The concentrations of these α-oxoaldehydes in urine were between 0.9 and 35.8ngg-1 levels (creatinine adjusted). A statistical comparison of the analyte contents of urine samples from non-diabetic and diabetic patients pointed to significant differences (P=0.046, 24 subjects investigated), particularly regarding MGO, which was higher in diabetic patients. The novelty of this study compared with previous procedures lies in the treatment of the urine sample by SALLE based on the addition of acetonitrile and sodium chloride to the urine. The DLLME procedure is performed with a sedimented drop of the extractant solvent, without a surfactant reagent, and using acetonitrile as dispersant solvent. Separation of the analytes was performed using GC-MS detection, being the analytes unequivocal identified. The proposed procedure is the first microextraction method applied to the analysis of urine samples from diabetic and non-diabetic patients that allows a clear differentiation between both groups using a simple analysis.

Cloud point extraction and gas chromatography with direct microvial insert thermal desorption for the determination of haloanisoles in alcoholic beverages.

A sensitive analytical procedure for the determination of four haloanisoles (2,4,6 trichloroanisole, 2,4,6-tribromoanisole, 2,3,4,6-tetrachloroanisole and pentachloroanisole) related with cork taint defects in wines, in different types of alcoholic beverages has been developed. The analytes were extracted from the matrix samples by cloud point extraction (CPE) using Triton X-114 heated to 75°C, and the surfactant rich phase was separated by centrifugation. By means of direct microvial insert thermal desorption, 20µL of the CPE obtained extract was submitted to gas chromatography-mass spectrometry (GC-MS) analysis. The parameters affecting the CPE and microvial insert thermal desorption were optimized. Quantification was carried by matrix-matched calibration using an internal standard. Detection limits ranged between 12.9 and 20.8ngL(-1), depending on the compound, for beer and wine samples, whereas for whiskies values in the 46.3-48ngL(-1) range were obtained, since these samples were diluted for analysis. Recoveries for alcoholic beverages were in the 89-111% range, depending on the analyte and the sample.

Direct sample introduction-gas chromatography-mass spectrometry for the determination of haloanisole compounds in cork stoppers.

A solventless analytical method is proposed for analyzing the compounds responsible for cork taint in cork stoppers. Direct sample introduction (DSI) is evaluated as a sample introduction system for the gas chromatography-mass spectrometry (GC-MS) determination of four haloanisoles (HAs) in cork samples. Several parameters affecting the DSI step, including desorption temperature and time, gas flow rate and other focusing parameters, were optimized using univariate and multivariate approaches. The proposed method shows high sensitivity and minimises sample handling, with detection limits of 1.6-2.6ngg-1, depending on the compound. The suitability of the optimized procedure as a screening method was evaluated by obtaining decision limits (CCα) and detection capabilities (CCß) for each analyte, which were found to be in 6.9-11.8 and 8.7-14.8ngg-1, respectively, depending on the compound. Twenty-four cork samples were analysed, and 2,4,6-trichloroanisole was found in four of them at levels between 12.6 and 53ngg-1.

Dispersive liquid-liquid microextraction for the determination of nitrophenols in soils by microvial insert large volume injection-gas chromatography-mass spectrometry.

A rapid and sensitive procedure for the determination of six NPs in soils by gas chromatography and mass spectrometry (GC-MS) is proposed. Ultrasound assisted extraction (UAE) is used for NP extraction from soil matrices to an organic solvent, while the environmentally friendly technique dispersive liquid-liquid microextraction (DLLME) is used for the preconcentration of the resulting UAE extracts. NPs were derivatized by applying an "in-situ" acetylation procedure, before being injected into the GC-MS system using microvial insert large volume injection (LVI). Several parameters affecting UAE, DLLME, derivatization and injection steps were investigated. The optimized procedure provided recoveries of 86-111% from spiked samples. Precision values of the procedure (expressed as relative standard deviation, RSD) lower than 12%, and limits of quantification ranging from 1.3 to 2.6ngg(-1), depending on the compound, were obtained. Twenty soil samples, obtained from military, industrial and agricultural areas, were analyzed by the proposed method. Two of the analytes were quantified in two of the samples obtained from industrial areas, at concentrations in the 4.8-9.6ngg(-1) range.

Evaluation of three headspace sorptive extraction coatings for the determination of volatile terpenes in honey using gas chromatography-mass spectrometry.

Headspace sorptive extraction (HSSE) was used to preconcentrate seven monoterpenes (eucalyptol, linalool, menthol, geraniol, carvacrol, thymol and eugenol) for separation by gas chromatography and mass spectrometry (GC-MS). Three commercially available coatings for the stir bars, namely Polydimethylsiloxane (PDMS), polyacrilate (PA) and Ethylene glycol-silicone (EG-Silicone), were tested, and the influential parameters both in the adsorption and the thermal desorption steps were optimized. PDMS provided the best sensitivity for linalool, geraniol, menthol and eucalyptol, whereas EG-Silicone was best for extracting the phenolic monoterpenes studied. Considering the average obtained slopes from all compounds, PDMS pointed as the best option, and the analytical characteristics for the HSSE-TD-GC-MS method using this coating were obtained. Quantification of the samples was carried out by matrix-matched calibration using a synthetic honey. Detection limits ranged between 0.007 and 0.032 ng g(-1), depending on the compound. Twelve honey samples of different floral origins were analyzed using the HSSE-GC-MS method, the analytes being detected at concentrations up to 64 ng g(-1).

Direct sample introduction gas chromatography and mass spectrometry for the determination of phthalate esters in cleaning products.

A method using direct sample introduction (DSI) coupled to gas chromatography-mass spectrometry (GC-MS) is developed for the determination of six phthalate esters (dimethyl, diethyl, dibutyl, butylbenzyl, diethylhexyl and dioctyl phthalate) in cleaning products. The different variables involved in the DSI step, including venting time and temperature, vaporisation time and temperature, injector heating temperature and gas flow rate and pressure, were evaluated and optimised using Taguchi orthogonal arrays. The proposed method, using calibration against methanolic standards, showed good linearity in the 0.05-15 µg g(-1) range and good repeatability, with RSD values ranging from 3.5% to 5.7%. Quantification limits between 0.010 and 0.041 µg g(-1), depending on the compound, were attained, while recovery assays provided values from 83% to 115%. Twenty-seven cleaning products were analysed using the DSI-GC-MS method, being four phthalates (dimethyl, diethyl, dibutyl and diethylhexyl phthalate) found in fourteen of them at concentration levels in the 0.1-21 µg g(-1) range. Compared with the most common GC injection technique, which uses the split/splitless injector, the proposed DSI procedure provided larger peak areas and lower detection limits, as result of the greater injected volume and reduction in noise.

Determination of pesticides in waters by capillary gas chromatography with atomic emission detection.

Capillary gas chromatography with atomic emission detection (GC-AED) was successfully used to separate and quantify 14 pesticides (organochlorines, organophosphorus compounds and pyrethrins) in water samples after liquid-liquid extraction with ethyl acetate. Monitoring the emission lines for elements such as chlorine, bromine and sulfur ensures nearly specific chromatograms for these elements, and markedly increases selectivity. Calibration curves were obtained by plotting peak area versus concentration and the correlation coefficients relating to linearity were at least 0.999. Each chromatographic separation takes 21 min and, since two injections are necessary, it requires approximately 1 h to analyze one sample. The method shows a precision of 4.3-8.2% (RSD), depending on the compound. The application of liquid-liquid extraction with ethyl acetate led to recoveries from spiked samples ranging from 76 to 113%. The sensitivity and linearity for the elements chlorine, sulfur, nitrogen and phosphorus were checked under the optimized conditions at their customary emission wavelength. The sensitivity and linearity for these compounds decreased in the order (atom and emission wavelength) Cl (479 nm)>S (181 nm)>P (178 nm)>N (174 nm). A study of the GC-AED system's response to chlorine concentration in eight pesticide molecules was performed and a linear relationship was found with a correlation coefficient of 0.987.

Purge-and-trap capillary gas chromatography with atomic emission detection for volatile halogenated organic compounds determination in waters and beverages.

A method for the simultaneous determination of 10 volatile halogenated organic compounds (VHOCs), including four trihalomethanes (THMs), in waters and beverages was developed. The analytes were stripped from the aqueous sample by a flow of helium, preconcentrated in a capillary trap and thermally desorbed using a purge-and-trap (PT) system. This was followed by capillary gas chromatography with microwave-induced plasma atomic emission spectrometry (GC-AED). For element-specific detection, three wavelengths were monitored, corresponding to chlorine (479 nm), bromine (478 nm) and iodine (193 nm). Each chromatographic run took 21 min, including the purge time. After careful choice of the experimental conditions, the performance of the system was evaluated. Calibration curves were obtained by plotting peak area versus concentration and the correlation coefficients for linear calibration were at least 0.9987. Detection limits, calculated for 5 ml sample volume, ranged from 0.05 microg l(-1) for chloroform to 0.5 microg l(-1) for tetrachloromethane. The method was successfully applied to the quantitative analysis of water samples of different origin and also of several beer and juice samples. The tap water samples analyzed contain variable concentrations of the four trihalomethanes, ranging from 1.0 to 66.5 microg l(-1), depending of the compound. Whereas chloroform, bromodichloromethane and bromoform were found in some of the juice samples, only chloroform was detected in the beer samples. The method is reliable and can be used for routine monitoring in water and beverages.

Determination of phenols in wines by liquid chromatography with photodiode array and fluorescence detection.

A reversed-phase LC method, optimised for the separation of trans- and cis-resveratrol, catechin, epicatechin, quercetin and rutin, is reported. Analyses were performed on a reversed-phase column by gradient elution. Detection was carried out by photodiode array, although the use of a fluorimetric detector considerably lowered the detection limits for catechin, epicatechin and both resveratrol isomers. Identification by the two different detection systems was based on retention characteristics, UV spectra and peak purity index were compared with commercial standards. The procedures were applied to the determination of the phenolic compounds in different types of wines and musts.

Determination of copper, cobalt, nickel, and manganese in baby food slurries using electrothermal atomic absorption spectrometry.

The analytical conditions for the electrothermal atomic absorption spectrometric determination of copper, manganese, nickel, and cobalt in different types of baby foods using slurried samples are presented. Suspensions were prepared in a medium containing 0.1% w/v Triton X-100, 30% v/v concentrated hydrogen peroxide, 1% v/v concentrated nitric acid, 1% w/v ammonium dihydrogenphosphate (only for copper atomization), and one drop of silicon antifoam. The slurries were homogenized by using a potter and were introduced directly into the furnace. The amount of analyte extracted to the liquid phase was investigated. The graphite furnace conditions were optimized for each element. No matrix effect was observed, and calibration could be carried out using aqueous standard solutions. The detection limits were 3.4, 2.1, 5.4, and 3.7 pg for copper, manganese, nickel, and cobalt, respectively. The reliability of the procedures was checked by statistically comparing the results obtained with those found by using a previous microwave-oven mineralization stage and by analyzing several certified reference materials.

Direct determination of copper and zinc in cow milk, human milk and infant formula samples using electrothermal atomization atomic absorption spectrometry.

Infant formula and powdered milk samples were suspended in a medium containing 20% ethanol, 0.65% nitric acid, 6% hydrogen peroxide and 0.1% ammonium dihydrogenphosphate and directly introduced in the electrothermal atomizer. Liquid milk samples were diluted with this suspension solution. The build-up of carbonaceous residues inside the atomizer was avoided by using a combination of hydrogen peroxide and nitric acid. Fast programs were used to simplify the heating cycles. Calibration was carried out using aqueous standards and the detection limits for copper and zinc were found to be 70 and 15 pg, respectively. The metal contents of several milk samples obtained by direct introduction of the samples agree with those obtained by means of a conventional procedure based on the total dissolution of the samples. The reliability of the methods was also confirmed by analyzing three certified reference materials. The free and protein binding fractions were measured by ultrafiltration membrane permeability of the milk samples.

Determination of phenylpropanolamine and methoxamine using flow-injection with fluorimetric detection.

A new flow-injection procedure for the determination of phenylpropanolamine and methoxamine is proposed. The method is based on the derivatization reaction of the primary amine group with o-phthalaldehyde in the presence of 2-mercaptoethanol using fluorimetric detection. The calibration graphs based on peak areas were linear in the ranges 5-200 ng ml(-1) for phenylpropanolamine and 0.2-6 ng ml(-1) for methoxamine. The detection limits were 3.8 and 0.13 ng ml(-1), respectively. The methods were applied to the determination of the drugs in commercial pharmaceutical preparations.