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 °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. Figure Headspace SPME sampling followed by GC–MS facilitates routine monitoring of PAHs in aquatic species     

Accurate quantification of freely dissolved organochlorine pesticides in water in the presence of dissolved organic matter using triolein-embedded cellulose acetate membrane

A novel method is described using triolein-embedded cellulose acetate membrane (TECAM) for accurate determination of the freely dissolved fraction of organochlorine pesticides (OCPs) in waters rich in dissolved organic matter (DOM). The performance of the method was tested with an air-bridge system for extracting OCPs from aqueous solutions with and without humic acid. In addition, the partition coefficients between humic acid and water (K _docs) for 20 OCPs were determined by TECAM with negligible depletion extraction. Results show that TECAM predominantly extracts the freely dissolved compounds and its extraction efficiency decreases significantly with an increase in concentration of humic acid in water. The proposed methodology is suitable for facile laboratory K _doc measurement for moderate to high hydrophobic compounds (log K _ow > 4). The linear relationship between log K _ow and log K _doc obtained in this study agrees well with the results reported earlier. The kinetic uptake rate constants (k _us) and TECAM–water partition coefficients (K _TECAMs) for the 20 OCPs were obtained using the controlled laboratory continuous-flow and static exposure system, respectively. These calibration parameters were used in the field experiment to estimate the freely dissolved concentrations of OCPs in the water of Taihu Lake in China. Our results show that TECAM can be used successfully to determine the freely dissolved OCPs in aquatic environments containing DOM, and the method is particularly suited for long-term water sampling. Figure Schematic diagram of water sampling with a triolein-embedded cellulose acetate membrane (TECAM)     

Determination of 43 polycyclic aromatic hydrocarbons in air particulate matter by use of direct elution and isotope dilution gas chromatography/mass spectrometry

We are reporting a method for measuring 43 polycyclic aromatic hydrocarbons (PAH) and their methylated derivatives (Me-PAHs) in air particulate matter (PM) samples using isotope dilution gas chromatography/high-resolution mass spectrometry (GC/HRMS). In this method, PM samples were spiked with internal standards, loaded into solid phase extraction cartridges, and eluted by dichloromethane. The extracts were concentrated, spiked with a recovery standard, and analyzed by GC/HRMS at 10,000 resolution. Sixteen ¹³C-labeled PAHs and two deuterated Me-PAHs were used as internal standards to account for instrument variability and losses during sample preparation. Recovery of labeled internal standards was in the range of 86–115%. The proposed method is less time-consuming than commonly used extraction methods, such as sonication and accelerated solvent extraction (ASE), and it eliminates the need for a filtration step required after the sonication extraction method. Limits of detection ranged from 41 to 332 pg/sample for the 43 analytes. This method was used to analyze reference materials from the National Institute of Standards and Technology. The results were consistent with those from ASE and sonication extraction, and these results were also in good agreement with the certified or reference concentrations. The proposed method was then used to measure PAHs on PM_2.5 samples collected at three sites (urban, suburban, and rural) in Atlanta, GA. The results showed distinct seasonal and spatial variation and were consistent with an earlier study measuring PM_2.5 samples using an ASE method, further demonstrating the compatibility of this method and the commonly used ASE method.      

Automated extraction of direct,reactive, and vat dyes from cellulosic fibers for forensic analysis by capillary electrophoresis

Systematic designed experiments were employed to find the optimum conditions for extraction of direct, reactive, and vat dyes from cotton fibers prior to forensic characterization. Automated microextractions were coupled with measurements of extraction efficiencies on a microplate reader UV–visible spectrophotometer to enable rapid screening of extraction efficiency as a function of solvent composition. Solvent extraction conditions were also developed to be compatible with subsequent forensic characterization of extracted dyes by capillary electrophoresis with UV–visible diode array detection. The capillary electrophoresis electrolyte successfully used in this work consists of 5 mM ammonium acetate in 40:60 acetonitrile–water at pH 9.3, with the addition of sodium dithionite reducing agent to facilitate analysis of vat dyes. The ultimate goal of these research efforts is enhanced discrimination of trace fiber evidence by analysis of extracted dyes. Figure Fitted absorbance response surface for extraction of a direct dye, C. I. yellow 58, using a ternary solvent system.     

The role of sulfur and sulfur isotope dilution analysis in quantitative protein analysis

The element sulfur is almost omnipresent in all natural proteomes and plays a key role in protein quantification. Incorporated in the amino acids cysteine and methionine, it has been served as target for many protein-labeling reactions in classic quantitative proteomic approaches based on electrospray or MALDI mass spectrometry. This critical review discusses the potential and limitations of sulfur isotope dilution analysis (IDA) by inductively coupled plasma—mass spectrometry (ICP-MS) for absolute protein quantification. The development of this approach was made possible due to the improved sensitivity and accuracy of sulfur isotope ratio measurement by ICP-MS in recent years. The unique feature of ICP-MS, compound-independent ionization, enables compound (species)-unspecific sulfur IDA. This has the main advantage that only one generic sulfur standard (i.e., one isotopically labeled sulfur spike) is required to quantify each peptide or protein in a sample provided that they are completely separated in chromatography or electrophoresis and that their identities are known. The principles of this approach are illustrated with selected examples from the literature. The discussion includes also related fields of P/S and metal/S ratio measurements for the determination of phosphorylation degrees of proteins and stoichiometries in metalloproteins, respectively. Emerging new areas and future trends such as protein derivatization with metal tags for improved sensitivity of protein detection in ICP-MS are discussed. Figure The key role of sulfur in protein quantification     

Advances in amino acid analysis

Amino acids are important targets for metabolic profiling. For decades, amino acid analysis has been accomplished by either cation-exchange or reversed-phase liquid chromatography coupled to UV absorbance or fluorescence detection of pre-column or post-column-derivatized amino acids. Recent years have seen great progress in the development of direct-infusion or hyphenated mass spectrometry in the analysis of free amino acids in physiological fluids, because mass spectrometry not only matches optical detection in sensitivity, but also offers superior selectivity. The advent of cryo-probes has also brought NMR spectroscopy within the detection limits required for the analysis of free amino acids. But there is still room for further improvement, including expansion of the analyte spectrum, reduction of sample preparation and analysis time, automation, and synthesis of affordable isotope standards. Figure Fully automated gas chromatography-mass spectrometry analysis of amino acids.     

SPME in environmental analysis

Recent advances in the use of solid-phase microextraction (SPME) in environmental analysis, including fiber coatings, derivatization techniques, and in-tube SPME, are reviewed in this article. Several calibration methods for SPME, including traditional calibration methods, the equilibrium extraction method, the exhaustive extraction method, and several diffusion-based calibration methods, are presented. Recent developed SPME devices for on-site sampling and several applications of SPME in environmental analysis are also introduced.      

Headspace sorptive extraction using silicone tubes for the determination of chlorobenzenes in water

A new approach for headspace sorptive extraction is presented and demonstrated for the determination of 12 chlorobenzenes in water samples. It consists of a silicone tube (15-mm length) arranged around a stainless steel rod. This device is fixed on a septum cap and exposed to the headspace of 50 mL of a salt-saturated water sample. After extraction (60-min optimized extraction time), thermodesorption is carried out by direct insertion of the silicone tube into the thermodesorption-gas chromatography-mass spectrometry system. Desorption of the analytes is performed at 250 °C for 5 min with a gas flow of 50 mL/min. Repeatability (relative standard deviation 5–10%), extraction yields (9–46%), enrichment factors (129–657), and detection limits (0.002–0.012 μg/L) were determined and four real water samples were analyzed with the headspace tube extraction. The results were verified by standard addition. A comparison of headspace tube extraction with other headspace enrichment techniques underlined the high extraction capacity of the proposed method. A big advantage of tube extraction is the low cost of the silicone material. The tubes can be discarded after single use, avoiding carryover problems and cross-contamination. Figure Scheme of the HS-tube extraction and thermodesorption system     

Determination of Etofenprox in environmental samples by HPLC after anionic surfactant micelle-mediated extraction (coacervation extraction)

A method is described for determination of residues of the insecticide Etofenprox in environmental samples. Anionic surfactant micelle-mediated extraction (coacervation extraction) was evaluated for isolation of Etofenprox before HPLC. The optimum conditions used for extraction included: 0.09 g sodium dodecanesulfonate (SDoS), 3.1 mL (3.3, for concentrations below 0.04 mg L⁻¹) 12 mol L⁻¹ HCl, 5 min vortex stirring, 5 min centrifugation at 4000 rpm, 2 h equilibration time. The limits of quantification (LOQ) and detection (LOD) were 0.01 and 0.004 mg L⁻¹, respectively, and recoveries obtained from five real samples ranged from 94.33±2.48 to 100.13±2.71%. The precision of the method was good; relative standard deviations (RSD) were less than 7%.      

Selective solid-phase extraction of bisphenol A using molecularly imprinted polymers and its application to biological and environmental samples

Molecularly imprinted polymers (MIPs) were prepared using bisphenol A (BPA) as a template by precipitation polymerization. The polymer that had the highest binding selectivity and ability was used as solid-phase extraction (SPE) sorbents for direct extraction of BPA from different biological and environmental samples (human serum, pig urine, tap water and shrimp). The extraction protocol was optimized and the optimum conditions were as follows: conditioning with 5 mL methanol–acetic acid (3:1), 5 mL methanol, 5 mL acetonitrile and 5 mL water, respectively, loading with 5 mL aqueous samples, washing with 1 mL acetonitrile, and eluting with 3 mL methanol. MIPs can selectively recognize, effectively trap and preconcentrate BPA over a concentration range of 2–20 μM. Recoveries ranged from 94.03 to 105.3 %, with a relative standard deviation lower than 7.9 %. Under the optimal condition, molecularly imprinted SPE recoveries of spiked human serum, pig urine, tap water and shrimp were 65.80, 82.32, 76.00 and 75.97 %, respectively, when aqueous samples were applied directly. Compared with C18 SPE, a better baseline, better high-performance liquid chromatography separation efficiency and higher recoveries were achieved after molecularly imprinted SPE.      

Capillary electrophoretic separation of humic substances using hydroxyethyl cellulose as a buffer additive and its application to characterization of humic substances in a river water sample

We have developed a concise tool for the investigation of the transition of humic substances in environmental water. The separation of water-soluble humic substances was achieved rapidly and effectively by capillary electrophoresis using a polyacrylamide-coated capillary and a phosphate electrophoretic buffer solution (pH 7.0) containing hydroxyethyl cellulose. The separation mechanism was assessed using the ultrafiltration technique. The effect of the complexation of humic substances with metal ions was studied by using the proposed method. When Fe(III) ions or EDTA was added to the sample solution of fulvic acid, a distinct change in the electropherogram pattern based on the conformational change of fulvic acid was observed. The successful application of the proposed method to the characterization of humic substances in a river water sample was also demonstrated. Figure Addition of Fe(III) ions or EDTA to a solution containing fulvic acid (FA) results in a distinct change in the electropherogram pattern, which reflects the conformational change of FA: this forms the basis for the characterization of humic substances in river water samples     

Optimization of a sensitive method for the determination of nitro musk fragrances in waters by solid-phase microextraction and gas chromatography with micro electron capture detection using factorial experimental design

A solid-phase microextraction method (SPME) followed by gas chromatography with micro electron capture detection for determining trace levels of nitro musk fragrances in residual waters was optimized. Four nitro musks, musk xylene, musk moskene, musk tibetene and musk ketone, were selected for the optimization of the method. Factors affecting the extraction process were studied using a multivariate approach. Two extraction modes (direct SPME and headspace SPME) were tried at different extraction temperatures using two fiber coatings [Carboxen–polydimethylsiloxane (CAR/PDMS) and polydimethylsiloxane–divinylbenzene (PDMS/DVB)] selected among five commercial tested fibers. Sample agitation and the salting-out effect were also factors studied. The main effects and interactions between the factors were studied for all the target compounds. An extraction temperature of 100 °C and sampling the headspace over the sample, using either CAR/PDMS or PDMS/DVB as fiber coatings, were found to be the experimental conditions that led to a more effective extraction. High sensitivity, with detection limits in the low nanogram per liter range, and good linearity and repeatability were achieved for all nitro musks. Since the method proposed performed well for real samples, it was applied to different water samples, including wastewater and sewage, in which some of the target compounds (musk xylene and musk ketone) were detected and quantified. Figure Stardardized Pareto charts for the main effects and interactions     

Quantification of atrazine and its metabolites in urine by on-line solid-phase extraction–high-performance liquid chromatography–tandem mass spectrometry

We have developed a method using on-line solid-phase extraction–high-performance liquid chromatography–tandem mass spectrometry (SPE-HPLC-MS/MS) and isotope dilution quantification to measure atrazine and seven atrazine metabolites in urine. The metabolites measured were hydroxyatrazine, diaminochloroatrazine, desisopropylatrazine, desethylatrazine, desethylatrazine mercapturate, atrazine mercaturate and atrazine itself. Our method has good precision (relative standard deviations ranging from 4 to 20% at 5, 10 and 50 ng/mL), extraction efficiencies of 67 to 102% at 5 and 25 ng/mL, relative recoveries of 87 to 112% at 5, 25, 50 and 100 ng/mL limits of detection (LOD) ranging from 0.03 to 2.80 ng/mL. The linear range of our method spans from the analyte LOD to 100 ng/mL (40 ng/mL for atrazine and atrazine mercapturate) with R ² values of greater than 0.999 and errors about the slope of less than 3%. Our method is rapid, cost-effective and suitable for large-scale sample analyses and is easily adaptable to other biological matrices. More importantly, this method will allow us to better assess human exposure to atrazine-related chemicals. Figure A schematic representation showing the elution of the analytes from the solid-phase extraction cartridge onto the analytical column for chromatographic separation prior to MS/MS analysis     

Element fingerprinting of marine organisms by dynamic reaction cell inductively coupled plasma mass spectrometry

A method for the determination of sixteen elements (Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Se, Sn, V, Zn) in seafood by dynamic reaction cell inductively coupled plasma mass spectrometry (ICP–DRC–MS) is presented. A preliminary study of polyatomic interferences was carried out in relation to the chemical composition of marine organisms belonging to different taxa. Acid effects and other matrix effects in marine organisms submitted to closed-vessel microwave digestion were investigated as well. Ammonia was the reactive gas used in the DRC to remove polyatomic ions interfering with ²⁷Al, ⁵²Cr, ⁵⁶Fe and ⁵¹V. Optimal conditions for the simultaneous determination of analytes were identified in order to develop a fast multielement method. A suite of real samples (mussels and various fish species) were used during method development along with three certified reference materials: BCR CRM 278R (mussel tissue), BCR CRM 422 (cod muscle) and DORM-2 (dogfish muscle). The proposed analytical approach can be used in conjunction with suitable chemometric procedures to address quality and safety issues in aquaculture and fisheries. As an example, a case study is described in which mussels from three farming sites in the Venice Lagoon were distinguished by multivariate analysis of element fingerprints.      

Dispersive liquid–liquid microextraction using an in situ metathesis reaction to form an ionic liquid extraction phase for the preconcentration of aromatic compounds from water

A novel microextraction method is introduced based on dispersive liquid–liquid microextraction (DLLME) in which an in situ metathesis reaction forms a water-immiscible ionic liquid (IL) that preconcentrates aromatic compounds from water followed by separation using high-performance liquid chromatography. The simultaneous extraction and metathesis reaction forming the IL-based extraction phase greatly decreases the extraction time as well as provides higher enrichment factors compared to traditional IL DLLME and direct immersion single-drop microextraction methods. The effects of various experimental parameters including type of extraction solvent, extraction and centrifugation times, volume of the sample solution, extraction IL and exchanging reagent, and addition of organic solvent and salt were investigated and optimized for the extraction of 13 aromatic compounds. The limits of detection for seven polycyclic aromatic hydrocarbons varied from 0.02 to 0.3 μg L⁻¹. The method reproducibility produced relative standard deviation values ranging from 3.7% to 6.9%. Four real water samples including tap water, well water, creek water, and river water were analyzed and yielded recoveries ranging from 84% to 115%.      

31P NMR study on the autophosphorylation of insulin receptors in the plasma membrane

A nonradioactive ³¹P nuclear magnetic resonance (NMR) spectroscopy protocol has been developed and used to investigate in vitro autophosphorylation of insulin receptors. Optimum experimental conditions have been explored, and the effects of Mn²⁺ and phosphocreatine (PCr) on the determination of the phosphorylation reaction have been assayed. The method was used to monitor the time courses of the phosphorylation reaction in solution. The results from this NMR study were in agreement with observations of insulin receptor phosphorylation made by using Western blotting.      

Determination of trace platinum by supramolecular catalytic kinetic spectrofluorimetry of β–cyclodextrin–platinum–KBrO3–salicylaldehyde furfuralhydrazone

A supramolecular catalytic kinetic spectrofluorimetric method was developed for the determination of platinum(IV) and the possible mechanism of catalytic reaction was discussed. The method was based on the fluorescence-enhancing reaction of salicylaldehyde furfuralhydrazone (SAFH) with potassium bromate, which was catalysed by platinum(IV) in a water–ethanol medium. β–Cyclodextrin (β-CD) obviously sensitized the determination at pH 5.20 and 25°C. Under optimum conditions, the β-CD–platinum–KBrO₃–SAFH supramolecular kinetic catalytic reaction system had excitation and emission maxima at 372 and 461 nm, respectively. The linear range of this method was 0.60–180 ng ml⁻¹ with a relative standard deviation of 1.2%, and the detection limit was 0.18 ng ml⁻¹. Investigation of the mechanism and the effects of interferences is presented. The proposed method was applied successfully to determine trace platinum(IV) in the chemotherapeutic drug cisplatin and serum from patients with satisfactory results.      

Certification of methylmercury in cod fish tissue certified reference material by species-specific isotope dilution mass spectrometric analysis

A new cod fish tissue certified reference material, NMIJ CRM 7402-a, for methylmercury analysis was certified by the National Metrological Institute of Japan in the National Institute of Advanced Industrial Science and Technology (NMIJ/AIST). Cod fish was collected from the sea close to Japan. The cod muscle was powdered by freeze-pulverization and was placed into 600 glass bottles (10 g each), which were sterilized with γ-ray irradiation. The certification was carried out using species-specific isotope dilution gas chromatography inductively coupled plasma mass spectrometry (SSID–GC–ICPMS), where ²⁰²Hg-enriched methylmercury (MeHg) was used as the spike compound. In order to avoid any possible analytical biases caused by nonquantitative extraction, degradation and/or formation of MeHg in sample preparations, two different extraction methods (KOH/methanol and HCl/methanol extractions) were performed, and one of these extraction methods utilized two different derivatization methods (ethylation and phenylation). A double ID method was adopted to minimize the uncertainty arising from the analyses. In order to ensure not only the reliability of the analytical results but also traceability to SI units, the standard solution of MeHg used for the reverse-ID was prepared from high-purity MeHg chloride and was carefully assayed as follows: the total mercury was determined by ID–ICPMS following aqua regia digestion, and the ratio of Hg as MeHg to the total Hg content was estimated by GC–ICPMS. The certified value given for MeHg is 0.58 ± 0.02 mg kg⁻¹ as Hg. Figure NMIJ CRM 7402-a: cod fish tissue for MeHg analysis     

Stripping analysis of heavy metals in tap water using the bismuth film electrode

A commercially available screen-printed carbon electrode coated with an ex situ deposited bismuth film (BiSPCE) has been applied to the determination of Pb(II) and Zn(II) ions in tap water (Barcelona water distribution network) by means of stripping voltammetry (SV) and stripping chronopotentiometry (SCP). A good reproducibility of the measurements and a satisfactory agreement between SV and SCP data were observed for both heavy metal ions. Although, in principle, the procedure could be also suited to the determination of Cd(II), this species was not detected. The results were also consistent with the routine ICP-OES measurements of the water distribution company, thus confirming the potential usefulness of such BiSPCE disposable devices for the analysis of heavy metals in natural waters.