An automated dynamic headspace sampler coupled to a gas chromatograph/mass spectrometer was evaluated as an oxidative marker to determine hexanal content in vegetable oils. For the effective analysis, a cooled injection system (CIS) was used to focus and to introduce the hexanal desorbed from the Tenax TA. The temperature of the CIS was maintained at −60°C for 12 min before desorbing the hexanal. Hexanal was separated on a capillary column (DB-5, 0.25 mm × 60 m, 0.25 μm in film thickness) from 50 to 230°C, followed by mass spectrometer-selected ion monitoring analysis at m/z 56. The instrumental response to hexanal was highly linear from 10 ng mL−1 to 1 μg mL−1 (r2 = 0.9999). The relative standard deviation (RSD) of intra- and inter-day repeatability was acceptable, with values of less than 3.88 and 4.25%, respectively. The LOD and LOQ of hexanal were determined by gas chromatograph/mass spectrometer-selected ion monitoring to be 3.3 and 9.8 ng mL−1, respectively. The acid value, peroxide value and fatty acid composition revealed a good correlation with the hexanal concentration.
Enhanced indirect fluorescence detection with in-column optical-fiber LED-induced fluorescence (LED-IF) detection has been developed for the simultaneous separation and determination of p-nitrophenol, 2,4-dinitrophenol and trinitrophenol. The instrumental set-up is simple, cost-effective and the detection method is stable. Different experimental parameters have been studied. The optimum conditions were determined as: running buffer (pH 9.1) composed of 10 mM borate, 80 mM sodium dodecylsulfate and 0.18 μM fluorescein (as a background reagent); applied voltage of 15 kV; working temperature of 25.0°C. The limits of detection (S/N = 3) were 11, 18 and 16 μM for p-nitrophenol, 2,4-dinitrophenol and trinitrophenol, respectively. The nitrophenols were completely separated in 13 min and the number of theoretical plates for p-nitrophenol, 2,4-dinitrophenol and trinitrophenol were 8.1 × 106, 6.5 × 106 and 8.4 × 106, respectively. The RSDs (n = 6) for the migration time and the peak area were better than 0.85 and 0.91%, respectively. Our proposed method possesses the advantages of rapidness and good separation efficiency.
A novel hydrophilic stationary phase bonded with a zwitter-ionic polymer for HPLC was synthesized. The stationary phase, in combination with a mobile phase containing various salts, was evaluated for its ability to separate water-soluble compounds, such as nucleobases, nucleosides and glycosides. The retention of a large majority of the solutes, except for cytosine, was increased by adding anti-chaotropic ions to the mobile phase. These results suggested that the retention of solutes depended on the thickness of the hydration layer on the stationary phase. In the zwitter-ionic polymer adsorbent, the formation of the hydration layer and the ionicity of the zwitter-ionic group on the stationary phase will be controlled by the properties of the ions added to the mobile phase.
A quantitative analysis was developed for eight acidic and neutral preservatives in foods and daily necessities using the inline dialysis-IC combined with hydrophobic anion-exchange separation. The eight preservatives were dialyzed by inline dialysis and separated on a hydrophobic anion exchange column. Under the optimized separation conditions, the detection limits (S/N = 3) for the eight preservatives were from 0.08 to 0.66 mg L−1, moreover, a good linearity (R2 > 0.998) for each preservative was obtained in the range to 100 mg L−1. Although the dialysis rate of the neutral preservatives was not so high, a good repeatability (RSD, n = 8) of less than 1.5% for the eight preservatives was obtained. The inline dialysis-IC method was applied to the determination of the preservatives in foods and daily necessities. The preservatives were quantified without any interference. The proposed method will be useful for the determination of the preservatives in foods and daily necessities containing high concentration matrices.
Sample preparation is important for the isolation and concentration of desired trace components from complex matrices. Sample preparation is the most labor-intensive and error-prone process in analytical methodology, and greatly influences the reliable and accurate determination of analytes. The integration of sample preparation with various analytical instruments is most conveniently achieved by using microextraction techniques and/or microdevices. Solid-phase microextraction (SPME) is both simple and effective, enabling miniaturization, automation and high-throughput performance. Moreover, SPME has reduced analysis times, as well as the costs of solvents and disposal. This review describes current developments and future trends in novel SPME techniques, including fiber SPME, in-tube SPME and related new microextraction techniques. Especially innovative SPME approaches, including multi-well high-throughput sampling, ligand-receptor binding study for pharmacokinetics, direct in vivo sampling, chip-based microfluidic system, and new sampling techniques using intelligent carbon nanotube and temperature-response polymer in pharmaceutical and biomedical analysis are focused items.
Various separation processes have been integrated in microfluidics, such as capillary electrophoresis and chromatography, on a microchip. However, it is extremely difficult to separate a complicated biological system by conventional methods. Here, we report on a feasible structure and the culture condition of human renal proximal tubule epithelial cells (RPTECs), with the aim to construct a bioartificial renal tubule on a chip. Glass microchips and a polycarbonate membrane were sealed with no leakage after a surface modification. Furthermore, matrigel was selected as an optimized extracellular matrix (ECM) for cell-proliferation on the membrane. After culturing for 5 days, RPTECs reached confluent in the chip-membrane structure, which was confirmed by nuclei staining. So far, we have constructed the basic structure and cell proliferation circumstance for the future demonstration of the RPTECs separating function. This separation microdevice has promising potential to be applied as both a unit of a circulation cell culture system and a research platform of cell biology.
Sodium permanganate, sodium picrate (NaPic), Bu4NPic, Me4NPic, and Et4NPic were extracted at an ionic strength of 2 × 10−5 to 0.08 mol dm−3 and 25°C from water (w)-phases into the organic (o)-ones, 1,2-dichloroethane (DCE) and nitrobenzene (NB). Thereby, apparent distribution constants (KD,±) of the anions (A−) or the cations (M+) and ion-pair formation ones (KMAorg) of the univalent salts (MA) in the o-phases were determined at 25°C, where KD,± = ([A−]o[M+]o/[A−][M+])1/2 = (KD,AKD,M)1/2 and KMAorg = [MA]o/[M+]o[A−]o. Also, the Kex and KD,MA values with A− = Pic−, MnO4− were estimated from the relations Kex (= [MA]o/[M+][A−]) = KMAorg(KD,±)2 and = KMAKD,MA, respectively. Standard potentials (Δφtr0) for ion transfers at the w/DCE and w/NB interfaces were evaluated from the log KD,A or log KD,M values by assuming the relations KD,Pic = KD,Et4N and = KD,Me4N, respectively. The thus-obtained Δφtr0 values, especially for the w/DCE system, were in good agreement with the values based on the extra-thermodynamic assumption for Ph4As+ and BPh4− transfers at the interfaces. In the present extraction systems, the ion-pair formation of MA in the w- and o-phases was less effective in the determination of their distribution constants into the two o-phases.
This paper describes a facile and effective method to synthesize gold nanoflowers (AuNFs) by a controllable electrodeposition method induced by a L-cysteamine (L-Cys) monolayer self-assembled on the surface of a gold electrode. The AuNFs/L-Cys/Au electrodes were characterized by field emission scanning electron microscopy (FE-SEM), cyclic voltammetry, and AC impedance spectroscopy methods. This obtained AuNFs/L-Cys/Au electrode exhibits excellent electrocatalytic activity towards the oxidation of dopamine (DA) due to the synergistic effect of AuNFs and a L-Cys monolayer. Differential pulse voltammetry (DPV) experiment results show that the oxidation peak of DA is separated from the oxidation peaks of ascorbic acid (AA) and uric acid (UA), which can be used to detect DA in the presence of AA and UA, and the results are satisfactory.
The present work describes the construction of a new modified graphite-multiwall carbon nanotube paste electrode by casting the appropriate mixture of tetraheptylammonium iodide-iodine as a new modifier. The modified paste electrode was used for the determination of ascorbic acid (AA) in a phosphate buffer solution (pH 2.0). When compared to activated carbon, a graphite and multiwall carbon nanotube paste electrode containing a new modifier, the proposed modified paste electrode not only shifted the oxidation potential of AA towards a less-positive potential but also enhanced its oxidation peak current. Further, the oxidation of AA was highly stable at the modified paste electrode. The optimum analytical conditions were sought. The current response of AA increases linearly while increasing its concentration from 5.6 × 10−5 to 1.2 × 10−2 M with a correlation coefficient of 0.9991; the detection limit (3σ) was found to be of 3.6 × 10−5 M. The present modified paste electrode was also successfully used for the determination of AA in the presence of common interference compounds. The present modified electrode was successfully demonstrated towards the determination of AA in pharmaceutical and food samples.
A simple, low toxic, sensitive strategy based on the localized surface plasmon resonance light scattering (LSPR-LS) properties of silver nanoparticles (AgNPs) is introduced for the detection of gallic acid (GA). It was found that the silver ammonium complex, [Ag(NH3)2]+(aq), could be reduced in the alkaline medium by GA at room temperature; this reaction formed dispersed AgNPs. Transmission electron microscopy analyses were performed to ascertain the formation of AgNPs. UV-visible spectra revealed the localized surface plasmon resonance (LSPR) absorption at 410 nm corresponding to the LSPR of AgNPs. On these basis, we could quantify the GA concentration in the range of 4 × 10−7 – 5 × 10−6 mol L−1 in the optimized experimental conditions. This method was used for determining the concentration of GA in artificial samples with satisfactory results. The detailed mechanism underlying this special phenomenon was elucidated.
A reversed-phase dispersive liquid–liquid microextraction (RP-DLLME) method coupled to HPLC was developed for the extraction of hydroxytyrosol (HTy) and tyrosol (Ty) from virgin olive oil. In this first application of the RP-DLLME method to non-polar samples, the phenolic compounds were directly extracted into an aqueous micro-drop, which could be injected into a chromatography column without any further pretreatment. A glass test tube with lengthened conical bottom was fitted inside a centrifuge tube in this work for more efficient withdrawal of the sedimented phase with a microsyringe. The volumes of water and ethyl acetate, the pH of water and the centrifuge time as four effective parameters on the extraction were optimized by a central composite design (response surface) method. Five replicated analyses under the optimized conditions (i.e., 0.2 mL ethyl acetate as disperser and 100 μL water at pH 11 as the extraction solvent) resulted in recoveries of 104.3 and 97.6%, and relative standard deviations of 5.75 and 4.57 for HTy and Ty, respectively. The detection limit of the method (3σ) was 0.043 mg L−1 for HTy and 0.032 mg L−1 for Ty. The method was successfully applied to the determination of HTy and Ty in five olive oil samples.
In anion-exchange chromatography using a high-concentration eluent and high-capacity ion-exchange resin, the effect of the countercation contained in the eluent was investigated. Cadmium(II) and zinc(II) ions were examined as additives in an aqueous potassium chloride eluent. The addition of these cations resulted in a reversed elution order of bromide and nitrate, as compared with conventional anion-exchange chromatography. The separation factor for these two anions increased as the cadmium concentration in the eluent was increased. Zinc(II) ion was also effective, but a relatively high concentration was necessary.
Determination methods of halide ions (X− = F−, Cl−, Br− and I−) by electrospray ionization mass spectrometry (ESIMS) were developed, where negative ions of the ternary complexes of group-13 elements, nitrilotriacetic acid (NTA), and halides were measured. In particular, these halides were simultaneously determined by measuring [InX(nta)]−, and the limits of detection (LODs) were 1.1 μmol dm−3 for F−, 0.32 μmol dm−3 for Cl−, 3.8 nmol dm−3 for Br−, and 1.6 nmol dm−3 for I−, respectively. This approach was extended to the determination of CN−, where the ternary complex of CuII, CN− and 4-(2-pyridylazo)resorcinol (PAR), i.e., [63CuII(CN)(par)]− (m/z 302) was measured. The LOD for CN− was 20 nmol dm−3.
We established a confluent cardiomyocyte culture method using an 800-μm diameter cylindrical microchannel in this report. This was realized by introducing cardiomyocytes 2 times before and after turning over a microchip. The optimum condition was starting the flowing medium 2.0 h after seeding and flowing the medium at 1.0 μL/min. By applying this technology to a cardiomyocyte-based spherical heart pump device, one may develop self-fluid regulated devices that could be applied for implantable or circulation analysis device on a chip.