Separation and quantification of four isomers of indole-3-acetyl-myo-inositol in plant tissues using high-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry

Indole-3-acetyl-myo-inositol (IAInos) is one of the most important auxin conjugates for storage and transportation of auxin. The information of its composition, distribution, and metabolism is particularly desired for elucidating the related signal transduction pathways of the plant hormones. However, separation and quantification of the four individual IAInos isomers in plant tissues have not been reported so far. In this work, we first synthesized and isolated four IAInos isomers using semi-preparative high-performance liquid chromatography (HPLC). The IAInos isomer structures were characterized using liquid chromatography-electrospray ionization quadrupole time-of-flight tandem mass spectrometry (LC-QTOF/MS) and nuclear magnetic resonance spectroscopy (NMR). Using these pure compounds as internal or external standards, an efficient LC-MS method was developed for simultaneous detection of indole-3-acetic acid, methyl indole-3-acetic acid ester, and the four IAInos isomers in plant tissue samples. The linear working range and lower limit of detection for the four IAInos isomers are 10–2,000 ng mL^?1 and 5.0 ng mL^?1, respectively. The stabilities and interconversion pathways of IAInos isomers were studied using our synthetic isomers. It was found that two IAInos isomers existed in Zea mays kernels, while all of the four IAInos isomers were present in the roots of Arabidopsis thaliana. The content of IAInos in A. thaliana roots was much lower than in the Z. mays kernels. The methodology in this article provides useful techniques and methods for systematic study on the phytophysiology and phytochemistry of IAA conjugates and other related plant hormones.

Electrochemical synthesis of a novel platinum nanostructure on a glassy carbon electrode, and its application to the electrooxidation of methanol

We show that the addition of white dextrin during the electrochemical deposition of platinum nanostructures (nano-Pt) on a glassy carbon electrode (GCE) results in an electrochemically active surface that is much larger than that of platinum microparticles prepared by the same procedure but in the absence of dextrin. The nano-Pt deposits are characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy, and electrochemical methods. The SEM images reveal deposits composed of mainly nanoparticles and short nanorods. The GCE was applied as a novel and cost-effective catalyst for methanol oxidation. The use of nano-Pt improves the electrocatalytic activity and the stability of the electrodes.

Smart methanol sensor based on silver oxide-doped zinc oxide nanoparticles deposited on microchips

We have prepared calcined silver oxide-doped zinc oxide nanoparticles (NPs) by a hydrothermal method using reducing agents in alkaline medium. The doped NPs were characterized by UV/vis, FTIR, and X-ray photoelectron spectroscopy, and by X-ray powder diffraction and field-emission scanning electron microscopy. The NPs were deposited on microchips to result in a sensor that has a fast response to methanol in the liquid phase. Features include high sensitivity, low-sample volume, reliability, reproducibility, ease of integration, long-term stability, and enhanced electrochemical responses. The calibration plot is linear (r²?=?0.9981) over the 0.25 mmolL^?1 to 0.25 molL^?1 methanol concentration range. The sensitivity is ~7.917 μA cm^?2 mmolL^?2, and the detection limit is 71.0?±?0.5 μmolL^?1 at a signal-to-noise-ratio of 3.

Ultratrace determination of carbamate pesticides in water samples by temperature controlled ionic liquid dispersive liquid phase microextraction combined with high performance liquid phase chromatography

A simple and sensitive method was developed for the determination of three carbamate pesticides in water samples. It is based on temperature controlled ionic liquid dispersive liquid phase microextraction combined with high-performance liquid chromatography. The ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate was used as the extractant, and the factors affecting the extraction were investigated in detail. The detection limits obtained for isoprocarb, diethofencarb and fenothiocarb are 0.91, 0.45, and 1.40 μgL^-1, respectively, and the precisions are in the range between 1.0 and 1.8% (n?=?6). The method was validated with environmental water samples and the results indicate that it represents a viable alternative to existing methods.

Laser-Induced Hydrogen Radical Removal in UV MALDI-MS Allows for the Differentiation of Flavonoid Monoglycoside Isomers

Negative-ion matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectra and tandem mass spectra of flavonoid mono-O-glycosides showed the irregular signals that were 1 and/or 2 Da smaller than the parent deprotonated molecules ([M – H]^–) and the sugar-unit lost fragment ions ([M – Sugar – H]^–). The 1 and/or 2 Da mass shifts are generated with the removing of a neutral hydrogen radical (H*), and/or with the homolytic cleavage of the glycosidic bond, such as [M – H* – H]^–, [M – Sugar – H* – H]^–, and [M – Sugar – 2H* – H]^–. It was revealed that the hydrogen radical removes from the phenolic hydroxy groups on the flavonoids, not from the sugar moiety, because the flavonoid backbones themselves absorb the laser. The glycosyl positions depend on the extent of the hydrogen radical removals and that of the homolytic cleavage of the glycosidic bonds. Flavonoid mono-glycoside isomers were distinguished according to their TOF MS and tandem mass spectra.

Determination of trace total inorganic arsenic by hydride generation atomic fluorescence spectrometry after solid phase extraction-preconcentration on aluminium hydroxide gel

We describe a simple, effective, inexpensive and rapid method for the determination of trace amounts of total inorganic arsenic in water samples by means of a modified solid phase preconcentration procedure using an aluminium hydroxide gel sorbent and hydride generation atomic fluorescence spectrometry (HGAFS). This method avoids the traditional extraction procedures that are time- and solvent-consuming. The effects of quantity of adsorbent, solution pH, adsorption time and potentially interfering ions were studied. Under the optimal conditions, the detection limit is 3 ng?L^?1, and the enrichment factor is 167. The calibration plot is linear in the range from 0.05 to 10 μg?L^?1, with a correlation coefficient of 0.9992. The relative standard deviation (RSD) was less than 6.1 % (n?=?5) and recoveries in spiked environmental water were >100 %. The method was successfully applied to the determination of total inorganic arsenic in natural water samples.

A molecularly imprinted polymer for solid phase extraction of allantoin

We describe a molecularly imprinted polymer (MIP) for the solid-phase extraction of the skin protectant allantoin. The MIP was deposited on the surface of monodisperse silica microspheres possessing acroyl groups on the surface (MH-SiO₂). The resulting MIP microspheres (MH-SiO₂@MIP) showed a 3.4-fold higher adsorption capacity and a 1.9-fold better selectivity for allantoin than the respective non-imprinted polymer (MH-SiO₂@NIP). The monolayer adsorption capacities of the MH-SiO₂@MIP and the MH-SiO₂@NIP were calculated with the help of the Langmuir model and found to be 6.8 and 1.9 mg?g^?1, respectively. Adsorption kinetics fit a pseudo-second order rate mechanism, with an initial adsorption rate of 1.44 for the MH-SiO₂@MIP, and of 0.07 mg?g^?1?min^?1 for the MH-SiO₂@NIP. The material can be regenerated, and its adsorption capacity for allantoin remains stable for at least five regeneration cycles. It was successfully used as a sorbent for the selective solid-phase extraction of allantoin from Rhizoma dioscoreae.

Quinolinium ionic liquid-modified silica as a novel stationary phase for high-performance liquid chromatography

A novel stationary phase based on quinolinium ionic liquid-modified silica was prepared and evaluated for high-performance liquid chromatography. The stationary phase was investigated via normal-phase (NP), reversed-phase (RP), and anion-exchange (AE) chromatographic modes, respectively. Polycyclic aromatic hydrocarbons, phthalates, parabens, phenols, anilines, and inorganic anions were used as model analytes in chromatographic separation. Using the newly established column, organic compounds were separated successfully by both NP and RP modes, and inorganic anions were also separated completely by AE mode. The obtained results indicated that the stationary phase could be applied in different chromatographic modes, with multiple-interaction mechanism including van der Waals forces (dipole–dipole, dipole–induced dipole interactions), hydrophobic, π–π stacking, electrostatic forces, hydrogen bonding, anion-exchange interactions, and so on. The column packed with the stationary phase was applied to analyze phthalates and parabens in hexane extracts of plastics. Tap water and bottled water were also analyzed by the column, and nitrate was detected as 20.1 and 13.8 mg L^?1, respectively. The results illustrated that the stationary phase was potential in practical applications.

Speciation of inorganic arsenic in environmental waters using magnetic solid phase extraction and preconcentration followed by ICP-MS

A new method was developed for the speciation of inorganic arsenic in environmental water by using selective magnetic solid-phase extraction followed by inductively coupled plasma mass spectrometry. It is found that As(V) selectively adsorbed on amino-modified silica-coated magnetic nanoparticles (MNPs) in the pH range from 3 to 8, while As(III) is not be retained. The As(V)-loaded MNPs can be separated easily from the aqueous sample solution by simply applying an external magnetic field. The adsorbed As(V) was quantitatively recovered from the MNPs using using 1 M nitric acid. Total inorganic As was extracted after the permanganate oxidation of As(III) to As(V). Parameters affecting the separation were investigated systematically, and the optimal separation conditions were established. Under the optimal conditions, the limit of detection is 0.21 ng L^?1, and the precision is 6.8% (at 10 ng L^?1, for n?=?7). The method was applied to the speciation of inorganic arsenic in environmental water of tobacco growing area.

Analysis of native and APTS-labeled N-glycans by capillary electrophoresis/time-of-flight mass spectrometry

The glycosylation of proteins is of particular interest in biopharmaceutical applications. The detailed characterization of glycosylation based on the released carbohydrates is mandatory since the protein stability, folding, and efficacy are strongly dependent on the structural diversity inherent in the glycan moieties of a glycoprotein. For glycan pattern analysis, capillary electrophoresis with laser-induced fluorescence using 8-aminopyrene-1,3,6-trisulfonic acid (APTS)-labeled glycans is used frequently. In this paper, a robust capillary electrophoresis–mass spectroscopy method both for the analysis of APTS-labeled glycans and unlabeled charged glycans is presented. The background electrolyte consists of 0.7 M ammonia and 0.1 M ε-aminocaproic acid in water/methanol 30:70 (v/v). High separation efficiency including separation of structural isomers was obtained. The method was validated in terms of reproducibility and linearity. Submicromolar sensitivity is achieved with linearity up to 24 μM. The ability to analyze APTS-labeled, as well as unlabeled, charged glycans enables the determination of labeling and ionization efficiency: APTS-labeled glycans show a factor of three better ionization efficiency compared to non-labeled native glycans. The presented method is applied to the analysis of pharmaceutical products. Furthermore, the system can be applied to the analysis of 2-ANSA-labeled glycans, though separation efficiency is limited.

Visual detection and microplate assay for Staphylococcus aureus based on aptamer recognition coupled to tyramine signal amplification

We have developed a specific method for the visual detection of Staphylococcus aureus based on aptamer recognition coupled to tyramine signal amplification technology. A biotinylated aptamer specific for S. aureus was immobilized on the surface of the wells of a microplate via biotin-avidin binding. Then, the target bacteria (S. aureus), the biotinylated-aptamer-streptavidin-HRP conjugates, biotinylated tyramine, hydrogen peroxide and streptavidin-HRP were successively placed in the wells of the microplate. After adding TMB reagent and stop solution, the intensity of the yellow reaction product can be visually inspected or measured with a plate reader. Under optimized conditions, there is a linear relationship between absorbance at 450 nm and the concentration of S. aureus in the 10 to 10⁷ cfu mL^?1 concentration range (with an R² of 0.9976). The limit of detection is 8 cfu mL^?1.

Micro-solid phase extraction of ochratoxin A, and its determination in urine using capillary electrophoresis

We describe a simple, environmentally friendly and selective technique for the determination of ochratoxin A (OTA) in urine. It involves (a) the use of a molecularly imprinted polymer as a sorbent in micro-solid-phase extraction in which the sorbent is contained in a propylene membrane envelope, and (b) separation and detection by capillary electrophoresis (CE). Under optimized conditions, response is linear in the range between 50 and 300 ng mL^?1 (with a correlation coefficient of 0.9989), relative standard deviations range from 4 to 8 %, the detection limit for OTA in urine is 11.2 ng mL^?1 (with a quantification limits of 32.5 ng mL^?1) which is lower than those of previously reported methods for solid-phase extraction combined with CE. The recoveries of OTA from urine spiked at levels of 50, 150 and 300 ng mL^?1 ranged from 93 to 97 %.

Carbon-based magnetic nanocomposites in solid phase dispersion for the preconcentration some of lanthanides, followed by their quantitation via ICP-OES

We report on a method for the extraction of the lanthanide ions La(III), Sm(III), Nd(III) and Pr(III) using a carbon-ferrite magnetic nanocomposite as a new adsorbent, and their determination via flow injection ICP-OES. The lanthanide ions were converted into their complexes with 4-(2-pyridylazo)resorcinol, and these were adsorbed onto the nanocomposite. Fractional factorial design and central composite design were applied to optimize the extraction efficiencies to result in preconcentration factors in the range of 141–246. Linear calibration plots were obtained, the limits of detection (at S/N?=?3) are between 0.5 and 10 μg?L^?1, and the intra-day precisions (n?=?3) range from 3.1 to 12.8 %. The method was successfully applied to a certified reference material.

A sensitive immunosorbent bio-barcode assay based on real-time immuno-PCR for detecting 3,4,3',4'-tetrachlorobiphenyl

A functionalized gold-nanoparticle bio-barcode assay, based on real-time immuno-PCR (IPCR), was designed for the determination of 3,4,3',4'-tetrachlorobiphenyl (PCB77). 15 nm gold nanoparticles were synthesized, and modified with thiol-capped DNA and goat anti-rabbit IgG. The nanoparticle probes were used to replace antibody–DNA conjugate in the IPCR, and were fixed on the PCR tube wall via the immune reaction. Real-time PCR was performed to quantify the DNA signal directly. Under optimized conditions, the new method was used to detect PCB77 with a linearity range from 5 pg L^?1 to 10 ng L^?1, and the limit of detection (LOD) was 1.72 pg L^?1. Real samples of Larimichthys polyactis, collected from the East China Sea, were analyzed. Recovery was from 82 % to 112 %, and the coefficient of variation (CV) was acceptable. The results were compared with GC–ECD, revealing that the method would be acceptable for providing rapid, semi-quantitative, and reliable test results for making environmental decisions.

A 3-D open-framework material with intrinsic chiral topology used as a stationary phase in gas chromatography

Compared with liquid chromatography and capillary electrophoresis, the diversity of gas chromatography chiral stationary phases is rather limited. Here, we report the fabrication of Co(d-Cam)_1/2(bdc)_1/2(tmdpy) (d-Cam?=?d-camphoric acid; bdc?=?1,4-benzenedicarboxylate; tmdpy?=?4,4′-trimethylenedipyridine)-coated open tubular columns for high-resolution gas chromatographic separation of compounds. The Co(d-Cam)_1/2(bdc)_1/2(tmdpy) compound possesses a 3-D framework containing enantiopure building blocks embedded in intrinsically chiral topological nets. In this study, two fused-silica open tubular columns with different inner diameters and lengths, including column A (30 m?×?530 μm i.d.) and column B (2 m?×?75 μm i.d.), were prepared by a dynamic coating method using Co-(d-Cam)_1/2(bdc)_1/2(tmdpy) as the stationary phase. The chromatographic properties of the two columns were investigated using n-dodecane as the test compound at 120 °C. The number of theoretical plates (plates/m) of the two metal–organic framework columns was 1,450 and 3,100, respectively. The separation properties were evaluated using racemates, isomers, alkanes, alcohols, and Grob's test mixture. The limit of detection and limit of quantification were found to be 0.125 and 0.417 ng for citronellal enantiomers, respectively. Repeatability (n?=?6) showed lower than 0.25 % relative standard deviation (RSD) for retention times and lower than 2.2 % RSD for corrected peak areas. The experimental results showed that the stationary phase has excellent selectivity and also possesses good recognition ability toward these organic compounds, especially chiral compounds.

Preconcentration of ultra-trace amounts of iron and antimony using ion pair solid phase extraction with modified multi-walled carbon nanotubes

Ion pair solid phase extraction was applied to the simultaneous preconcentration of iron and antimony. The ion pairs consisting of FeCl₄ ^? or SbCl₄ ^? anions and the benzyldimethyltetradecyl ammonium cation were formed on the surface of multi-walled carbon nanotubes, then eluted with nitric acid, and the elements finally quantified by ETAAS. The adsorption capacities of the impregnated MWCNTs are 9.2 mg g^?1 for iron and 27.5 mg g^?1 for antimony. The following analytical figures of merit were determined for iron and antimony, respectively: Enrichment factors of 210 and 230, assay precisions of ±5.3 % and ±4.8 %, linear calibration plots from 0.7 to 9.4 and 13.0 to 190 ng L^?1, and detection limits of 0.17 and 3.5 ng L^?1. The method was applied to the determination of iron and antimony in human hair, synthetic sample, and to the certified reference materials gold ore (MA-1b) and trace elements in water (SRM 1643d).

In-situ decorated gold nanoparticles on polyaniline with enhanced electrocatalysis toward dopamine

Gold nanoparticles were in-situ decorated on top of a polyaniline film (GNPs–PANI) via the direct electroreduction of the adsorbed AuCl ₄ ^- ions on a glassy carbon electrode that previously was coated with PANI by electropolymerization. The GNPs–PANI composite and the performance of the resultant sensors were investigated in some detail. The sensor was applied to the oxidation of dopamine (DA) with improved catalytic activity. Its catalytic current showed wide linear response toward dopamine ranging from 3 to 115 μM, with a low detection limit of 0.8 μM (S/N=3). In addition, the sensor exhibits easy-operation, fast response to dopamine, as well as excellent reproducibility and stability.

Solvent extraction of europium trifluoromethanesulfonate into nitrobenzene by using three electroneutral receptors

From extraction experiments and $ \gamma $ -activity measurements, the extraction constants corresponding to the general equilibrium Eu³⁺(aq) + 3 A^?(aq) + L(nb) $ \Leftrightarrow $ EuL³⁺(nb) + 3A^?(nb) taking place in the two-phase water–nitrobenzene system ( $ {\text{A}}^{ - } = {\text{CF}}_{ 3} {\text{SO}}_{3}^{ - } $ ; L = electroneutral receptors denoted by 1, 2, and 3 – see Scheme 1; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Further, the stability constants of the EuL³⁺ complexes in nitrobenzene saturated with water were calculated; they were found to increase in the series of 3 < 2 < 1.

Reinvestigation of the Structure of Protonated Lysine Dimer

To better understand inconsistencies between the predicted infrared (IR) spectra of previously suggested isomers of Lys₂H⁺ reported by Wu et al. (J. Am. Soc. Mass Spectrom. 22:1651–1659, 18) and the experimental IR photon dissociation (IRPD) spectrum obtained by Oh et al. (J. Am. Chem. Soc. 127:4076–4083, 4), the structure of Lys₂H⁺ was reinvestigated using IRPD spectroscopy in the extended region 2700–3700 cm^?1 and theoretical calculations. The new experimental IRPD spectrum is in good agreement with Oh’s spectrum in the corresponding wavelength range. Based on calculations at the MP2/6-311++G(d,p)//B3LYP/6-311++G(d,p) and MP2/6-31?+?G(d,p)//MP2/6-31?+?G(d,p) levels, a new salt-bridged isomer, ZW1, was found to be the most stable isomer; it is more energetically favored than the previously suggested charge-solvated isomer LL-CS01 by 10 or 26 kJ mol^?1. Although the calculated IR spectrum of ZW1 is in good agreement with the experimental one in the range 2700–3700 cm^?1, it is in poor agreement with the previous IRPD spectrum in the range 1000–1900 cm^?1. This investigation shows that the intermolecular interactions inside the dimer are more complex than previously supposed. It is possible that both salt-bridged and charge-solvated isomers of Lys₂H⁺ are stable in the gas phase, and the isomers generated during ionization are sensitive to the experimental conditions.