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The deviation from the classical elastic characteristics induced by the free surface energy can be considerable for nanostructures due to the high surface to volume ratio. Consequently, this type of size dependency should be accounted for in the mechanical behaviors of nanoscale structures. In the current investigation, the influence of free surface energy on the nonlinear primary resonance of silicon nanoshells under soft harmonic external excitation is studied. In order to obtain more accurate results, the interaction between the first, third, and fifth symmetric vibration modes with the main oscillation mode is taken into consideration. Through the implementation of the Gurtin-Murdoch theory of elasticity into the classical shell theory, a size-dependent shell model is developed incorporating the effect of surface free energy. With the aid of the variational approach, the governing differential equations of motion including both of the cubic and quadratic nonlinearities are derived. Thereafter, the multi-time-scale method is used to achieve an analytical solution for the nonlinear size-dependent problem. The frequency-response and amplitude-response of the soft harmonic excited nanoshells are presented corresponding to different values of shell thickness and surface elastic constants as well as various vibration mode interactions. It is depicted that through consideration of the interaction between the higher symmetric vibration modes and the main oscillation mode, the hardening response of nanoshell changes to the softening one. This pattern is observed corresponding to both of the positive and negative values of the surface elastic constants and the surface residual stress.

The development of rapid, inexpensive, and environmentally friendly sample-preparation techniques is a serious issue in chemical analysis. This explains the success of two new miniaturized liquid-phase microextraction techniques used as sample-preconcentration techniques for liquid chromatography – hollow fiber and single-drop liquid-phase microextraction. In hollow-fiber-based microextraction (HFME) a hollow fiber is filled with an organic solvent to establish and protect micro volumes of acceptor solution. This attractive, simple, low cost method, which is highly selective and enables substantial enrichment, has been compared with single-drop microextraction (SDME), using four aniline derivatives (3-chloroaniline, 3-bromoaniline, 2-nitroaniline, and 4-nitroaniline) as model compounds. The most important conditions and practical considerations for method optimization are discussed. The results showed that enrichment factors varied from 91.0 to 180.1 for SDME and from 106.43 to 286.33 for HFME. Extraction times were approximately equal. Stirring speeds selected for SDME and HFME were 800 and 900 rev min−1, respectively. Other quantitative data were almost identical.

The possibility of applying headspace microextraction into a single drop of solvent for the determination of methyl tert -butyl ether in aqueous solutions has been demonstrated. A drop of benzyl alcohol is used for extraction. The analyte is extracted by suspending a 1.8 μL extracting drop directly from the tip of a microsyringe fixed above an extraction vial with a septum such that the needle passes through the septum and the needle tip is positioned above the surface of the solution. After the extraction is finished, the drop is retracted back into the needle and injected directly into a GC column. Optimization of experimental variables (time, temperature, stirring rate and ionic strength of the solution) with respect to the extraction efficiency was investigated. The calibration range for methyl tert-butyl ether was 0.01–10 ppm and the detection limit 7 ppb. The relative standard deviation for 0.1 ppm methyl tert -butyl ether in water was 5.5%.

A simple liquid–liquid–liquid microextraction device of new design was used to pre-concentrate phenols from water samples before liquid chromatographic (LC) analysis. Extraction was induced by the pH difference inside and outside an organic phase located at the interface. The pH of the donor phase outside the organic phase was adjusted to 1 with HCl whereas the acceptor phase was a basic solution at pH 13. On stirring neutral phenols were extracted into the organic solvent then back-extracted into 1 μL of basic acceptor solution suspended from the tip of a micro syringe. The acceptor phase was then withdrawn into the micro syringe and injected directly into the LC. The technique uses a low-cost disposable extraction ‘device’ and is very convenient to operate. Up to 230-fold enrichment of analytes could be achieved. This procedure could also serve as a sample clean-up step because neutral and basic compounds were not extracted into the acceptor phase. The RSD (n = 5) was better than 6.2% and the linear calibration range was from 1 to 1000 µg–L−1 with r 2 ≥ 0.992.Optimization of experimental conditions (rate of stirring, ionic strength of the sample solution, concentration of reagents, time of extraction, and organic solvent volume) were also examined. The method was applied to the determination of phenols in tap and well waters.

We have prepared a new material for solid-phase microextraction (SPME) of volatile aromatic hydrocarbons by electropolymerization of pyrrole, carbon nanotubes, and titanium oxide on the surface of a stainless steel wire. This fiber-like wire was used for the headspace solid-phase microextraction of mixtures of benzene, toluene, ethylbenzene, and o-xylene (BTEX), followed by their quantitation by GC with FID detection. The fiber is easily prepared, robust, thermally stable, and has good extraction efficiency. Under optimal conditions, the detection limits (at an SNR of 3) are in the range from 0.01 to 0.04 ng mL −1 , and the limits of quantification (at an SNR of 10) are between 0.03 and 0.09 ng mL −1 . The relative standard deviations (RSDs) for one fiber (i. e. the repeatability; for n  = 5) range from 3.5 to 5.6 %, while the RSDs between fibers or from batch to batch (i.e. the reproducibility; for n  = 3) are in the range from 5.9 to 8.1 %. The method was successfully applied to (spiked) real water samples, the relative recovery percentages being between 93.7 and 106.2 %. Graphical abstract In the present work , polypyrrole-carbon nanotubes–titanium oxide composite coated onto 438 stainless steel wire have been successfully synthesized and were applied as adsorbent for the 439 headspace solid-phase microextraction of benzene, toluene, ethylbenzene, and o-xylene (BTEX).

The combination of liquid phase microextraction (LPME) based on a single drop and gas chromatography flame ionization detector (GC-FID) was used for separation and determination of amitriptyline and nortriptyline in human plasma and urine samples. The sample solution was kept alkaline (pH 12), then a microdrop of organic solvent (isooctane) was suspended in the donor solution; after extraction, the organic microdrop was injected into the GC-FID. Experimental LPME conditions were optimized. Finally, the enrichment factors (89.5–139.0), the relative standard deviation (RSD%, n = 5) 1.1–8.5, linearity ranges (0.05–20 μg mL−1), and the limits of detections (0.01, 0.02 μg mL−1) for selected drugs were evaluated.

A novel microextraction method termed ionic liquid-based submerged single drop microextraction combining liquid chromatography (LC) was developed for the determination of aromatic amines in environmental water samples. This method is simple and rapid for the determination of three aromatic amines (2-nitroaniline, 3-chloroaniline and 4-bromoaniline) which were selected as model compounds for validation of this new mode of microextraction. This technique combines extraction and preconcentration of the analytes in one step before determination by LC-UV, and the ionic liquid was used instead of the organic solvent as extractant. Several important parameters influencing the extraction efficiency such as the volume of the aqueous sample solution (donor phase), extraction time, pH of the donor phase and salt effect were investigated. Under the optimized conditions, acceptable enrichment factors (132–186) and relative recoveries (82–98%) were obtained for the extraction of the target analytes in real water samples. The calibration curves were linear with correlation coefficients ranging from 0.9983 to 0.9989 and RSDs (n = 5) of 4.9–6.8%. The LODs for the three aromatic amines were 1–2.5 μg L−1 at a signal-to-noise ratio (S/N) of 3.

The purpose of the present work is to develop a simple, rapid, sensitive and accurate method for the derivatization and subsequently preconcentration of Hg(II) and the determination of its derivative, diphenylmercury, in natural water samples using gas chromatography-flame ionization detection. The method is based on the diphenylation using phenyl boronic acid, subsequent extraction of phenylmercury into a single drop of an organic solvent (toluene), followed by gas chromatography-flame ionization detection GC-FID analysis of the extract. The pH of the feed solution was kept in pH 5 with acetate buffer solution. Thus, the optimized conditions are: organic solvent, toluene; derivatization time, 10 min; extraction time, 15 min; microdrop volume, 1.6 μL; stirring rate, 600 rpm; sample volume, 5 mL. The limit of detection (LOD), calculated on the basis of five replicates was 0.02 μg mL−1. The relative standard deviation of the method (RSD%, n = 5) was 3.0. Linear range was between 0.05 and 5 μg mL−1 and preconcentration factor obtained for phenyl-mercury was 105.

Directly Suspended Droplet Microextraction (DSDME) was used for the determination of two tricyclic antidepressant drugs (TCAs), amitriptyline and nortriptyline. In this technique, an aqueous sample is agitated with a stirring bar, creating a mild vortex at the center of the vial. A droplet of an immiscible organic solvent is placed at the bottom of the vortex. After 20 min a portion of the organic droplet is withdrawn with a syringe and injected into the GC. Experimental conditions, such as the extraction solvent, extraction time, solvent volume, stirring rate, pH and salt addition were optimized. In order to evaluate the practical application of the method, relative standard deviations, linearity range and limits of detection were calculated. Typical enrichment factors were 167 and 179 for amitriptyline and nortriptyline, respectively. The method was applied to the determination of these drugs in urine samples.

Metal chelated of five tetradentate β-ketoamine Schiff bases derived from dl-stilbenediamine and meso-stibenediamines were examined for the separation of coper (II), nickel (II), palladium (II) and oxovanadium (IV) by capillary column gas chromatography, with flame ionization (FID) or microwave induced plasma atomic emission (MIP-AED) detection. Complete separation between copper (II), nickel (II), palladium (II) and oxovanadium (IV) chelates was obtained for each chelate system examined. Linear response for the metal chelates of bis (acetylpivalylmethane) dl-stilbenediimine was from 0.86–8.6 ng of complex, corresponding to ca. 6–23 pg of metal. The reagent bis (acetylacetone) dl-stilbenediimime was evaluated for the determination of copper and nickel using precolumn derivatization, followed by extraction into dichloromethane and detection using MIP-AED.