Modeling and identification of electro-elastic nonlinearities in ultrasonic power transfer systems

Nonlinear Dynamics - We establish a nonlinear non-conservative mathematical framework for the acoustic-electro-elastic dynamics of the response of a piezoelectric disk to high-level acoustic...     

Glycine-based polymeric surfactants with varied polar head group: I. synthesis, characterization, and application in micellar electrokinetic chromatography

The monomers and polymers of four anionic amide type sodium undecenoxy carbonyl glycinate (SUCG) surfactants and four anionic carbamate type sodium undecenoyl glycinate (SUG) surfactants with 1-, 2-, 3-, and 4-glycine unit as head group were synthesized and characterized. The CMC and aggregation number (A) for all eight surfactants were determined using fluorescence spectroscopy. In addition, the CMC values of these surfactants were also projected by surface tension and CE. The CMC of the monomers decreases with increases in the size of glycine head groups and correlates well when the fluorescence method was compared to CE. The A number increases and partial specific volume (V) decreases with increase in size of the head group of both monomers and polymers. However, A and V are always lower for the polymers than the corresponding monomers. The electrophoretic and chromatographic parameters of micelle polymers of SUG and SUCG were also examined. The coefficient of EOF increases with the increase in size of the head group but the electrophoretic mobility decreases which results in a decrease in the elution range. The retention data suggest that the selectivity differences among the mono-, di-, and tripeptide derivatives of poly-SUCG surfactants are relatively higher compared to the derivatives of poly-SUG series.     

Preparation of ion-imprinted polyvinyl sulfonate-grafted silica particles for trace enrichment of Th(IV) prior to determination by inductively coupled plasma-mass spectrometry

Grafting from polymerisation technique has been used to prepare Th(IV) ion-imprinted polyvinyl sulfonate (IIPVS)-bonded silica particles. The graft polymerisation of vinyl sulfonate (VS) on the surface of silica particles was achieved in aqueous medium through thermal decomposition of surface-bound azo initiators (60°C) in the presence of thorium ion. The prepared material was characterised by Fourier transform infrared spectroscopy, differential scanning calorimetry and thermogravimetric analysis. The entrapped template ion was then removed using 2 M HCl. The experimental batch rebinding data were successfully described by the Langmuir–Freundlich model. The prepared material was then packed to a PTFE micro-column (20 mm × 3.0 mm, id) to evaluate its efficiency in column operations prior to determination by inductively coupled plasma-mass spectrometry (ICP-MS). The limit of detection of the method and breakthrough capacity of the column was evaluated as 0.074 µg L^?1 and 0.83 mg g^?1, respectively. The selectivity of the prepared polymer towards Th(IV) ion was investigated in the presence of some foreign competitor ions, including U(VI). Finally, the proposed method has been used to determine Th(IV) ion in real samples.     

Multivariate approach for the enantioselective analysis in micellar electrokinetic chromatography-mass spectrometry: I. Simultaneous optimization of binaphthyl derivatives in negative ion mode

A mixture of two molecular micelles polysodium N-undecenoxy carbonyl-l-leucinate, (poly-l-SUCL) and polysodium N-undecanoyl leucylvalinate, (poly-l-SULV) was utilized in micellar electrokinetic chromatography-electrospray ionization-mass spectrometry (MEKC-ESI-MS) to simultaneously separate and detect enantiomers of binaphthyl derivatives. Separation parameters such as background buffer composition, voltage, temperature, and nebulizer pressure were optimized using a multivariate central composite design (CCD). Baseline enantioseparation for both analytes was achieved. The CCD was also used in the optimization of sheath liquid and spray chamber parameters to achieve optimum ESI-MS response. The results demonstrate that CCD is a powerful tool for the optimization of MEKC-MS parameters and the response surface model analysis can provide in-depth statistical understandings of the significant factors required to achieve maximum enantioresolution and ESI-MS sensitivity.     

On-line metals preconcentration and simultaneous determination using cloud point extraction and inductively coupled plasma optical emission spectrometry in water samples

A new on-line cloud point extraction (CPE) system coupled to ICP-OES was designed for simultaneous extraction, preconcentration and determination of Cd²⁺, Co²⁺, Cr³⁺, Cu²⁺, Fe³⁺ and Mn²⁺ ions in water samples. This is based on the complexation of the metal ions with 1-(2-thenoyl)-3,3,3-trifluoraceton reagent (TTA) at pH 6.0 in the presence of non-ionic surfactant of Triton X-114. The micellar solution was heated above 60 °C and loaded through a column packed with cotton, which acts as a filter for retaining the analyte-entrapped surfactant-rich phase. Then the surfactant-rich phase was eluted using propanol:0.5 mol L⁻¹ nitric acid solution (75:25, v/v) at a flow rate of 3.0 mL min⁻¹ and directly introduced into the nebulizer of the ICP-OES. Several factors influencing the instrumental conditions and extraction were evaluated and optimized. Under the optimum conditions, the enhancement factors of the proposed method for target ions were between 42 and 97, the detection limits (DLs) were in the range of 0.1-2.2 μg L⁻¹. The relative standard deviations (R.S.D.s) at 100 μg L⁻¹ concentration levels of each ion were found to be less than 4.6%. Also, the calibration graphs were linear in the range of 0.5-100 μg L⁻¹ with the correlation coefficients within the range of 0.9948-0.9994.Finally, the developed method was successfully applied to the extraction and determination of the mentioned metal ions in the tap, well, sea and mineral water samples and satisfactory results were obtained.     

Development of liquid phase microextraction method based on solidification of floated organic drop for extraction and preconcentration of organochlorine pesticides in water samples

A simple and efficient liquid-phase microextraction (LPME) in conjunction with gas chromatography-electron capture detector (GC-ECD) has been developed for extraction and determination of 11 organochlorine pesticides (OCPs) from water samples. In this technique a microdrop of 1-dodecanol containing pentachloronitrobenzene (internal standard) is delivered to the surface of an aqueous sample while being agitated by a stirring bar in the bulk of solution. Following completion of extraction, the sample vial was cooled by putting it into an ice bath for 5 min. Finally 2 μL of the drop was injected into the GC for analysis. Factors relevant to the extraction efficiency were studied and optimized. Under the optimized extraction conditions (extraction solvent: 1-dodecanol; extraction temperature: 65 °C; sodium chloride concentration: 0.25 M; microdrop and sample volumes: 8 μL and 20 mL respectively; the stirring rate: 750 rpm and the extraction time: 30 min), figures of merit of the proposed method were evaluated. The detection limits of the method were in the range of 7-19 ng L⁻¹ and the RSD% for analysis of 2 μg L⁻¹ of OCPs was below 7.2% (n = 5). A good linearity (r² ≥ 0.993) and a relatively broad dynamic linear range (25-2000 ng L⁻¹) were obtained. After 30 min of extraction, preconcentration factors were in the range of 708-1337 for different organochlorine pesticides and the relative errors ranged from −10.1 to 10.9%. Finally the proposed method was successfully utilized for preconcentration and determination of OCPs in different real samples.     

Synthesis, spectroscopic and thermal studies of transition metal complexes derived from benzil and diethylenetriamine

A macrocyclic ligand, bdta (where bdta=3,6,9,12,15,18-hexaaza-1,2,10,11-tetraphenyl-2,9,11,18-tetraenecyclododecane) has been prepared by cyclocondensation of benzil with diethylenetriamine which efficiently encapsulates transition as well as pseudo-transition metal ions leading to the formation of M(bdta)Cl2 type complexes [where M=Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II)]. The analytical, spectroscopic and magnetic moment data suggests an octahedral geometry for all the complexes. EPR spectra of Mn(II) and Cu(II) show considerable exchange interaction in the complex. They are non-conducting in DMSO. The TGA profile of the ligand and its complexes are identical and consists of two discreet stages. The voltammogram of Cu-complex exhibits a quasi-reversible one-electron transfer wave for Cu(II)/Cu(I) couple.     

Polymeric alkenoxy amino acid surfactants: III. Chiral separations of binaphthyl derivatives

Micellar electrokinetic chromatography (MEKC) was investigated for the enantiomeric separations of three binaphthyl derivatives ((+/-)-1,1'-bi-(2-naphthol) (BOH), (+/-)-1,1'-binaphthyl-2,2'-diyl hydrogenphosphate (BNP), and (+/-)-1,1'-binaphthyl-2,2'-diamine (BNA)) using two recently synthesized chiral polymeric surfactants (polysodium N-undecenoxy carbonyl-L-leucinate (poly-L-SUCL) and polysodium N-undecenoxy carbonyl-L-isoleucinate (poly-L-SUCIL)) in our laboratory. Enantiomeric separation (resolution and selectivity) of the binaphthyl derivatives was influenced by polymerization concentration of the monomeric surfactant, pH, type and concentration of the background electrolyte (BGE) as well as concentration of the polymeric surfactant. Two BGEs (dibasic phosphate and Tris-borate) were compared for this study. The use of dibasic phosphate as BGE in poly-L-SUCL provides baseline resolution of (+/-) BOH and (+/-) BNP, however, no resolution and selectivity at all was observed for (+/-) BNA. A similar approach was adopted with Tris-borate-poly-L-SUCL system at fixed pH 10.1, which resulted in baseline resolution of all three binaphthyl derivatives. Although R(s) of binaphthyl derivatives was always higher and electroosmotic flow (EOF) was always lower using Tris-borate than with dibasic phosphate, the selectivity values for the two buffer systems did not differ significantly. In addition, it was found that poly-L-SUCL provided better enantiomeric resolution and selectivity for (+/-) BOH and (+/-) BNA, while poly-L-SUCIL provided enhanced enantiomeric resolution but similar enantioselectivity for (+/-) BNP. This indicates that the depth of analyte penetration into the palisade layer and the micellar core are responsible for chiral recognition of hydrophobic analyte (e.g., (+/-) BOH, and (+/-) BNA) whereas for moderately hydrophobic analyte (e.g., (+/-) BNP) interaction with the polar head group seems to dictate chiral recognition. Simultaneous enantioresolution of all three binaphthyl derivatives was possible in a single electrophoretic run using either poly-L-SUCL or poly-L-SUCIL. Further comparison of the two polymeric surfactants showed that poly-L-SUCL provided slightly longer analysis time than poly-L-SUCIL but the use of the former polymeric surfactant should be preferred due to its ability to provide complete baseline resolution and higher selectivity of all the three atropisomers with a wider chiral window.     

Utility of ionic liquids in analytical separations

Ionic liquids (ILs), as separation media, have made significant contributions in the past decades in advancing research in gas chromatography (GC), liquid chromatography (LC), and capillary electrophoresis (CE). This review, covering reports published from the mid 1980s to early 2007, shows how ILs have been used so far in separation science, originally primarily as GC stationary phases and later as mobile phase additives (both millimolar and major percent levels) for LC and CE. Representative GC and LC chromatograms as well as CE electropherograms are shown. In addition, the very recent findings on the development of ionic liquids with surfactant properties and its applications for chiral and achiral analysis are discussed.