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     

Determination of acetone in seawater using derivatization solid-phase microextraction

Acetone plays an important role in the chemistry of both the atmosphere and the ocean, due to its potential effect on the tropospheric HO_x (= HO + HO₂) budget, as well as its environmental and health effects. We discuss the development of a mobile, sensitive, selective, economical and facile method for the determination of acetone in seawater. The method consists of derivatizing acetone to its pentafluorobenzyl oxime using 1,2,3,4,5-pentafluorobenzylhydroxylamine (PFBHA), followed by solid-phase microextraction (SPME) and analysis by gas chromatography/mass spectrometry (GC/MS). A detection limit of 3.0 nM was achieved. The buffering capacity of seawater imposes challenges in using the method’s optimum pH (3.7) on seawater samples, requiring calibration standards to be made in buffered salt water and the acidification of seawater samples and standards prior to extraction. We employed the technique for analysis of selected surface seawater samples taken on the Nordic seas during the ARK-XX/1 cruise (R.V. Polarstern). An upper limit of 5.5–9.6 nM was observed for acetone in these waters, the first acetone measurements reported for far North Atlantic and Arctic waters. Simplified schematic of transformations of organic compounds at the atmosphere–ocean interface     

Nuclear magnetic resonance of mass-limited samples using small RF coils

Figure Schematic diagram of a typical arrangement used for hyphenating chemical microseparations (e.g. capillary HPLC, CE, or CEC) with microcoil NMR detection     

Novel gel-based rapid test for non-instrumental detection of ochratoxin A in beer

A rapid easy-to-use immunoassay was optimised for the non-instrumental detection of ochratoxin A (OTA) in beer. The analytical method involves preconcentration on the immunoaffinity layer inside a column followed by direct competitive ELISA detection in the same layer. The visual cut-off value, i.e. the lowest OTA concentration resulting in no colour development, was 0.2 μg L^-1. Assay validation was performed using samples spiked with OTA. Thirty-seven naturally contaminated samples were screened with the gel-based method developed and no false-negative results were obtained. The method described offers a simple, rapid and cost-effective screening tool, thus contributing to better health protection of consumers. Figure Gel-based immunoassay of spiked beer samples.     

Determination of trapidil in human serum and urine by derivative UV spectrophotometry after selective solid-phase extraction

A novel analytical technique able to determine the anti-ischemic drug trapidil in human serum and urine is proposed. In order to achieve satisfactory sensitivity and selectivity, an extraction procedure was required to isolate the drug from complex matrixes such as serum and urine. A solid-phase extraction procedure was investigated to both increase the analyte concentration and eliminate the interfering molecules present in large amounts in both matrixes. Optimization of the extraction step was realized by selecting a new polymeric sorbent based on a surface-modified styrene–divinylbenzene polymer which provided fast and efficient drug extraction. Drug quantification was performed by using the third-order derivative spectra of the SPE eluates. Absorbance specific signals at ³D_335,316 and ³D₃₁₆ nm for urine and serum, respectively, were demonstrated to be directly proportional to drug concentration and barely affected by residual matrix interferences. Under the optimized experimental conditions the calibration plots were linear over the concentration range 0.2–50 μg mL⁻¹. The method was validated by analysis of a series of spiked samples. Accuracy (recovery of 95 and 94% for serum and urine, respectively) and precision (RSD below 4%) were good. Figure Assay of Trapidil in biological fluids by SPE and derivative spectrophotometry     

Rapid response behavior,at room temperature,of a nanofiber-structured TiO<Subscript>2</Subscript> sensor to selected simulant chemical-warfare agents

A chemical prototype sensor was constructed based on nanofiber-structured TiO₂ and highly sensitive quartz resonators. The gas-sensing behavior of this new sensor to selected simulant warfare agents was investigated at room temperature. Results showed rapid response and good reversibility of this sensor when used with high-purity nitrogen. This provides a simple approach to preparation of materials needed as chemical sensors for selected organic volatiles or warfare agents. Figure Sensing behavior of TiO₂ nanofiber sensor to chemical vapors     

Headspace mass spectrometry methodology: application to oil spill identification in soils

In the present work we report the results obtained with a methodology based on direct coupling of a headspace generator to a mass spectrometer for the identification of different types of petroleum crudes in polluted soils. With no prior treatment, the samples are subjected to the headspace generation process and the volatiles generated are introduced directly into the mass spectrometer, thereby obtaining a fingerprint of volatiles in the sample analysed. The mass spectrum corresponding to the mass/charge ratios (m/z) contains the information related to the composition of the headspace and is used as the analytical signal for the characterization of the samples. The signals obtained for the different samples were treated by chemometric techniques to obtain the desired information. The main advantage of the proposed methodology is that no prior chromatographic separation and no sample manipulation are required. The method is rapid, simple and, in view of the results, highly promising for the implementation of a new approach for oil spill identification in soils. Figure PCA score plots illustrate clear discrimination of types of crude oil in polluted soil samples (e.g. results are shown for vertisol)     

HPLC-ICP-MS and HPLC-ES-MS/MS characterization of synthetic seleno-arsenic compounds

Various toxicological and metabolic interactions have been reported to exist between arsenic and selenium. In the present study, synthetic seleno-arsenic compounds, potentially suitable for probing metabolic interactions between these two elements, were prepared and tentatively characterized by using high-performance liquid chromatography (HPLC)–electrospray tandem mass spectrometry and HPLC–inductively coupled plasma mass spectrometry. In analogy to the recently identified thio-arsenic species, which can be prepared from their corresponding oxo-arsenic species via reaction with H₂S, the seleno-arsenic compounds were also derived from oxo-arsenic compounds via reaction with H₂Se. Figure H₂Se bubbled into solutions containing oxo‐arsenosugars converts them into their seleno‐arsenosugar analogues.     

Evaluation of two methods for the extraction of antioxidants from medicinal plants

The efficiencies of two traditional extraction methods used in Chinese medicine (the decoction method and the maceration method) were evaluated for the extraction of antioxidants from medicinal plants. A group of medicinal plants possessing nutritious and tonic functions were chosen as model plants. A commonly used extraction method was used as a reference method. The antioxidant capacities and total phenolic contents of the extracts were measured by ferric-reducing antioxidant power and Trolox equivalent antioxidant capacity assays as well as the Folin–Ciocalteu method, respectively. The results obtained indicated that the two traditional extraction methods could effectively extract antioxidants from medicinal plants. These extraction methods can be applied to the analysis and purification of antioxidants in plants, respectively. At home, people can use these methods to extract antioxidants from plants for consumption. In the food industry, these methods could be utilized to prepare crude extracts from plants containing antioxidants for use as food additives. Figure Relation and comparison of extraction efficiencies of two traditional extraction methods with the reference method Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

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%.      

Cross validation of multiple methods for measuring pyrethroid and pyrethrum insecticide metabolites in human urine

The objective of our study was to compare three vastly different analytical methods for measuring urinary metabolites of pyrethroid and pyrethrum insecticides to determine whether they could produce comparable data and to determine if similar analytical characteristics of the methods could be obtained by a secondary laboratory. This study was conducted as a part of a series of validation studies undertaken by the German Research Foundation’s Committee on the Standardization of Analytical Methods for Occupational and Environmental Medicine. We compared methods using different sample preparation methods (liquid–liquid extraction and solid-phase extraction with and without chemical derivatization) and different analytical detection methods (gas chromatography–mass spectrometry (single quadrupole), gas chromatography–high resolution mass spectrometry (magnetic sector) in both electron impact ionization and negative chemical ionization modes, and high-performance liquid chromatography–tandem mass spectrometry (triple quadrupole) with electrospray ionization). Our cross validation proved that similar analytical characteristics could be obtained with any combination of sample preparation/analytical detection method and that all methods produced comparable analytical results on unknown urine samples. Cross-method comparison using unknown urine samples revealed reasonably good agreement for any combination of the methods tested     

Determination of cadmium in grains by isotope dilution ICP–MS and coprecipitation using sample constituents as carrier precipitants

A coprecipitation method using sample constituents as carrier precipitants was developed that can remove molybdenum, which interferes with the determination of cadmium in grain samples via isotope dilution inductively coupled plasma mass spectrometry (ID-ICPMS). Samples were digested with HNO₃, HF, and HClO₄, and then purified 6 M sodium hydroxide solution was added to generate colloidal hydrolysis compounds, mainly magnesium hydroxide. Cadmium can be effectively separated from molybdenum because the cadmium forms hydroxides and adsorbs onto and/or is occluded in the colloid, while the molybdenum does not form hydroxides or adsorb onto the hydrolysis colloid. The colloid was separated by centrifugation and then dissolved with 0.2 M HNO₃ solution to recover the cadmium. The recovery of Cd achieved using the coprecipitation was >97%, and the removal efficiency of Mo was approximately 99.9%. An extremely low procedural blank (below the detection limit of ICPMS) was achieved by purifying the 6 M sodium hydroxide solution via Mg coprecipitation using Mg(NO₃)₂ solution. The proposed method was applied to two certified reference materials (NIST SRM 1567a wheat flour and SRM 1568a rice flour) and CCQM-P64 soybean powder. Good analytical results with small uncertainties were obtained for all samples. This method is simple and reliable for the determination of Cd in grain samples by ID-ICPMS. Figure Overview of a coprecipitation method using sample constituents     

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.      

Electrokinetic sample extraction and enrichment: a new method for the isolation of analytes from sludge-type matrices

Electrokinetic sample extraction and enrichment is introduced as a newly developed concept for the analysis of substances in sludge-type or paste-like matrices. It is based on electrokinetic transport phenomena as electromigration and electroosmosis occurring when an electrical field is applied to the fresh, wet samples. Problems usually associated to sample drying can be avoided, e.g., losses of volatile analytes or contamination. We have designed and built a suitable apparatus for electrokinetic sample extraction and enrichment. Appropriate operating conditions (field strength, buffer composition, concentration, and volume) were identified in experiments with an artificial sludge model and real-world lake sediments. A proof of principle of the method was provided by the electromigrative extraction and online enrichment on a solid-phase sorbent disk of an azo dye from a diatomaceous earth slurry. Electroosmotic extraction and enrichment of a cyanobacterial hepatotoxin at trace levels was finally investigated as an application example using lake sediments. Rather clean extracts were obtained even with high organic content sediment samples, as shown by high-performance liquid chromatography with diode array detection.      

Forensic analysis of anthraquinone,azo, and metal complex acid dyes from nylon fibers by micro-extraction and capillary electrophoresis

The extraction and separation of dyes present on textile fibers offers the possibility of enhanced discrimination between forensic trace fiber evidence. An automated liquid sample handling workstation was programmed to deliver varying solvent combinations to acid-dyed nylon samples, and the resulting extracts were analyzed by an ultraviolet/visible microplate reader to evaluate extraction efficiencies at different experimental conditions. Combinatorial experiments using three-component mixture designs varied three solvents (water, pyridine, and aqueous ammonia) and were employed at different extraction temperatures for various extraction durations. The extraction efficiency as a function of the three solvents (pyridine/ammonia/water) was modeled and used to define optimum conditions for the extraction of three subclasses of acid dyes (anthraquinone, azo, and metal complex) from nylon fibers. The capillary electrophoresis analysis of acid dye extracts is demonstrated using an electrolyte solution of 15 mM ammonium acetate in acetonitrile/water (40:60, v/v) at pH 9.3. Excellent separations and discriminating diode array spectra are obtained even for dyes of similar color. Figure Capillary electropherogram of three acid dyes extracted from nylon 6,6 thread     

Investigation of sample-purification procedures for MALDI-based proteomic studies

Purification methods for proteomics samples are of crucial concern for improving the quality of the sample delivered to the mass spectrometer. They constitute the link between the mass spectrometer and protein processing and peptide isolation steps that usually require solvents, buffers, or detergents completely incompatible with MS-analysis conditions. This work describes three new clean-up procedures using synthetic membranes and polymer media and compares them with standard procedures. The efficiency of each of the purification procedures was studied via application to four standards and two membrane proteins. This work highlights the importance of versatility in sample preparation, especially for MS-based proteomic investigations. Figure PMF spectra obtained after MALDI-TOF measurements of bovine mitochondrial complex III (A) and complex IV (B) in-solution digests, with and without purification     

A novel headspace solid-phase microextraction method for the exact determination of organochlorine pesticides in environmental soil samples

A novel method of determining organochlorine pesticides (OCPs) is described. It is based on solid-phase microextraction (SPME) and gas chromatography–electron capture detection. During the development of the method, soil samples were prepared, spiked with standard solution, and then aged for some time. Extraction conditions such as the extraction time, the NaCl content, the volume of water, the extraction temperature and the desorption time were investigated and optimized. The limits of detection obtained using the method ranged from 0.10 to 0.51 ng g⁻¹, and relative standard deviations were lower than 10% for most organochlorine pesticides. Real soil samples were successfully analyzed using the proposed method. The results from the method developed here were in good agreement with those obtained using ultrasonic extraction. The result demonstrates that aging soils spiked with standard solution is an important method development step, because the soil samples obtained using this approach are more like real soils than those obtained when aging is not used.      

Application of high-resolution EFTEM SI in an AEM

In this work we show how energy-filtered imaging can be used to obtain spectrum images of electron energy-loss spectrometric data. Focus is placed on improved energy resolution within these data sets. Using two multilayer samples (GaN/AlN and InP/InAs), we demonstrate the advantages of spectrum-imaging and its extended mapping capabilities. Plasmon-ratio maps are used to quickly create high-contrast material maps with high signal-to-noise ratio, ratio-contrast plots are used to gain optimum settings for the ratio maps, and plasmon-position maps are used to map small shifts of the energy position of bulk plasmon peaks. Figure Scheme of EELS SI and derived plasman-position map     

Critical evaluation of sample pretreatment techniques

Sample preparation before chromatographic separation is the most time-consuming and error-prone part of the analytical procedure. Therefore, selecting and optimizing an appropriate sample preparation scheme is a key factor in the final success of the analysis, and the judicious choice of an appropriate procedure greatly influences the reliability and accuracy of a given analysis. The main objective of this review is to critically evaluate the applicability, disadvantages, and advantages of various sample preparation techniques. Particular emphasis is placed on extraction techniques suitable for both liquid and solid samples. Figure Miniaturised extraction techniques allow sensitive analysis of also small sample volumes.     

Determination of the titanium content of human transferrin by inductively-coupled plasma-atomic-emission spectroscopy

We report a simple method that combines dialysis, as a purification method, with the multielement capability of ICP to determine the titanium-to-transferrin mole ratio at physiological pH, under buffer conditions. The method, by means of which titanium and transferrin are determined simultaneously, enabled us to assess the binding capacities of different titanocene complexes. Figure Titanocene dichloride