Multivariate curve resolution–alternating least squares (MCR–ALS) analysis is proposed to solve chromatographic challenges during two-dimensional gas chromatography–time-of-flight mass spectrometry (GC?×?GC–TOFMS) analysis of complex samples, such as crude oil extract. In view of the fact that the MCR–ALS method is based on the fulfillment of the bilinear model assumption, three-way and four-way GC?×?GC–TOFMS data are preferably arranged in a column-wise superaugmented data matrix in which mass-to-charge ratios (m/z) are in its columns and the elution times in the second and first chromatographic columns are in its rows. Since m/z values are common for all measured spectra in all second-column modulations, unavoidable chromatographic challenges such as retention time shifts within and between GC?×?GC–TOFMS experiments are properly handled. In addition, baseline/background contributions can be modeled by adding extra components to the MCR–ALS model. Another outstanding aspect of MCR–ALS analysis is its extreme flexibility to consider all samples (standards, unknowns, and replicates) in a single superaugmented data matrix, allowing joint analysis. In this way, resolution, identification, and quantification results can be simultaneously obtained in a very fast and reliable way. The potential of MCR–ALS analysis is demonstrated in GC?×?GC–TOFMS analysis of a North Sea crude oil extract sample with relative errors in estimated concentrations of target compounds below 6.0 % and relative standard deviations lower than 7.0 %. The results obtained, along with reasonable values for the lack of fit of the MCR–ALS model and high values of the reversed match factor in mass spectra similarity searches, confirm the reliability of the proposed strategy for GC?×?GC–TOFMS data analysis. 相似文献
A specially designed micro-mixer made of silicon, calcium fluoride, and silicone with an optical transmission path of 8 μm has been used for mid-IR spectroscopy monitoring of mixing-induced chemical reactions in the low millisecond time regime. The basic principle of the proposed continuous-flow technique is to mix two liquids introduced in two times two alternatingly stacked layers through diffusion at the entrance of a 200 μm wide, 1 cm long micro-fluidic channel also serving as measurement area. By using this special, dedicated arrangement, diffusion lengths and hence the mixing times can be significantly shortened and the overall performance improved in comparison to previous systems and alternative methods. Measurements were carried out in transmission mode using an Fourier transform infrared (FTIR) microscope, recording spectra with spot sizes of 180?×?100 μm2 each at defined spots along this channel. Each of these spots corresponds to a specific reaction time: moving the measurement spot towards the entry yields shorter reaction times, moving it towards the channel’s end gives longer reaction times. This principle is generic in nature and provides a solution for accurate, chemically induced triggering of reactions requiring the mixing of two liquid reagents or reagent solutions. A typical experiment thus yields up to 85 time-coded data points, covering a time span from 1 to 80 ms at a total reagent consumption of only about 125 μL. Using the fast neutralization reaction of acetic acid with sodium hydroxide as a model, the time required for 90% mixing was determined to be around 4 ms. Additionally, first experiments on ubiquitin changing its secondary structure from native to “A-state” were carried out, illustrating the potential for time-resolved measurements of proteins in aqueous solutions.
Voltammetric procedures for trace metals analysis in polluted natural waters using homemade bare gold-disk microelectrodes of 25- and 125-μm diameters have been determined. In filtered seawater samples, square wave anodic stripping voltammetry (SWASV) with a frequency of 25 Hz is applied for analysis, whereas in unfiltered contaminated river samples, differential pulse anodic stripping voltammetry (DPASV) gave more reliable results. The peak potentials of the determined trace metals are shifted to more positive values compared to mercury drop or mercury-coated electrodes, with Zn always displaying 2 peaks, and Pb and Cd inversing their positions. For a deposition step of 120 s at ?1.1 V, without stirring, the 25-μm gold-disk microelectrode has a linear response for Cd, Cu, Mn, Pb and Zn from 0.2 μg L?1 (1 μg L?1 for Mn) to 20 μg L?1 (30 μg L?1 for Zn, Pb and 80 μg L?1 for Mn). Under the same analytical conditions, the 125-μm gold-disk microelectrode shows linear behaviour for Cd, Cu, Pb and Zn from 1 μg L?1 (5 μg L?1 for Cd) to 100 μg L?1 (200 μg L?1 for Pb). The sensitivity of the 25-μm electrode varied for different analytes from 0.23 (±0.5%, Mn) to 4.83 (±0.9%, Pb) nA L μmol?1, and sensitivity of the 125-μm electrode varied from 1.48 (±0.7%, Zn) to 58.53 (±1.1%, Pb nA L μmol?1. These microelectrodes have been validated for natural sample analysis by use in an on-site system to monitor Cu, Pb and Zn labile concentrations in the Deûle River (France), polluted by industrial activities. First results obtained on sediment core issued from the same location have shown the ability of this type of microelectrode for in situ measurements of Pb and Mn concentrations in anoxic sediments. 相似文献
A hybrid of reduced graphene oxide–palladium (RGO–Pd) nano- to submicron-scale particles was simultaneously chemically prepared using microwave irradiation. The electrochemical investigation of the resulting hybrid was achieved using cyclic voltammetry and differential pulse voltammetry. RGO–Pd had a higher current response than unmodified RGO toward the oxidation of morphine. Several factors that can affect the electrochemical response were studied, including accumulation time and potential, Pd loading, scan rate, and pH of electrolyte. At the optimum conditions, the concentration of morphine was determined using differential pulse voltammetry in a linear range from 0.34 to 12 μmol L?1 and from 14 to 100 μmol L?1, with detection limits of 12.95 nmol L?1 for the first range. The electrode had high sensitivity toward morphine oxidation in the presence of dopamine (DA) and of the interference compounds ascorbic acid (AA) and uric acid (UA). Electrochemical determination of morphine in a spiked urine sample was performed, and a low detection limit was obtained. Validation conditions including reproducibility, sensitivity, and recovery were evaluated successfully in the determination of morphine in diluted human urine.
Immunoglobulin Y (IgY) is derived from egg yolk and has been identified as a cheap and high-yield immunoreagent. The application of IgY in immunoassays for the detection of chemical contaminants in food samples has rarely been reported. In this work, we describe a rapid and sensitive fluorescence polarization immunoassay (FPIA) for valnemulin (VAL) using IgY which was produced using a previously prepared immunogen. Three fluorophore-labeled VAL tracers were synthesized and the sensitivity of the best tracer (VAL–DTAF) in the optimized FPIA with antibody IgY100 demonstrated an IC50 value of 12 ng mL?1 in buffer. After evaluation of several extraction procedures, acidified acetonitrile was selected to extract VAL from swine tissue. The recoveries of VAL in spiked swine tissue at three levels (50, 100, and 200 μg kg?1) were higher than 79 % with coefficients of variation (CVs) lower than 12 %. The limit of detection (LOD) of the FPIA in swine tissue was 26 μg kg?1 and was lower than the maximum residue limit (MRL) of VAL set by the European Union. The study showed that IgY could be a good substitute for IgG when developing a high-throughput assay for chemical residues.
A multi-residue method based on modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) sample preparation, followed by liquid chromatography tandem mass spectrometry (LC-MS/MS), was developed and validated for the determination of three selected fungicides (propiconazole, pyraclostrobin, and isopyrazam) in seven animal origin foods. The overall recoveries at the three spiking levels of 0.005, 0.05, and 0.5 mg kg?1 spanned between 72.3 and 101.4 % with relative standard deviation (RSD) values between 0.7 and 14.9 %. The method shows good linearity in the concentrations between 0.001 and 1 mg L?1 with the coefficient of determination (R2) value >0.99 for each target analyte. The limit of detections (LODs) for target analytes were between 0.04 and 1.26 μg kg?1, and the limit of quantifications (LOQs) were between 0.13 and 4.20 μg kg?1. The matrix effect for each individual compound was evaluated through the study of ratios of the areas obtained in solvent and matrix standards. The optimized method provided a negligible matrix effect for propiconazole within 20 %, whereas for pyraclostrobin and isopyrazam, the matrix effect was relatively significant with a maximum value of 49.8 %. The developed method has been successfully applied to the analysis of 210 animal origin samples obtained from 16 provinces of China. The results suggested that the developed method was satisfactory for trace analysis of three fungicides in animal origin foods.
A new zinc-layered hydroxide-L-phenylalanate (ZLH-LP)-modified multiwalled carbon nanotube (MWCNT) was prepared as a new material of paste electrode for the detection of paracetamol (PCM) in 1.0?×?10?1 M phosphate buffer solution and at pH 7.5. The electrochemical characterization of the MWCNTs/ZLH-LP paste electrode was characterized by square wave voltammetry, electrochemical impedance spectroscopy, and cyclic voltammetry while the morphology properties of the MWCNTs, ZLH-LP, and MWCNTs/ZLH-LP were investigated using transmission electron microscopy and scanning electron microscopy. Under optimized conditions, the MWCNTs/ZLH-LP paste electrode demonstrated an excellent electrocatalytic activity towards oxidation of PCM in the linear responses’ ranges from 7.0?×?10?7 M to 1.0?×?10?4 M (correlation coefficient, 0.996) with the limit of detection obtained at 8.3?×?10?8 M. As a conclusion, the MWCNTs/ZLH-LP paste electrode revealed good repeatability, reproducibility, and stability, and was found to be applicable for use in pharmaceutical tablet samples.
This paper describes the development of a biosensor for the detection of anti-hemagglutinin antibodies against the influenza virus hemagglutinin. The steps of biosensor fabrications are as follows: (i) creation of a mixed layer containing the thiol derivative of dipyrromethene and 4-mercapto-1-butanol, (ii) complexation of Cu(II) ions, (iii) oriented immobilization of the recombinant histidine-tagged hemagglutinin, and (iv) filling free spaces with bovine serum albumin. The interactions between recombinants hemagglutinin from the highly pathogenic avian influenza virus type H5N1 and anti-hemagglutinin H5 monoclonal antibodies were explored with Osteryoung square-wave voltammetry. The biosensor displayed a good detection limit of 2.4 pg/mL, quantification limit of 7.2 pg/mL, and dynamic range from 4.0 to 100.0 pg/mL in buffer. In addition, this analytical device was applied for the detection of antibodies in hen sera from individuals vaccinated and non-vaccinated against the avian influenza virus type H5N1. The limit of detection for the assay was the dilution of sera 1: 7?×?106, which is about 200 times better than the enzyme-linked immunosorbent assay.
A simple, low-cost, and efficient online focusing method that combines a dynamic pH junction and sweeping by capillary electrophoresis with polymer solutions was developed and optimized for the simultaneous determination of benzoic acid (BA) and sorbic acid (SA). A sample solution consisting of 2.5 mM phosphate at pH 3.0 and a buffer solution containing 15 mM tetraborate (pH 9.2), 40 mM sodium dodecyl sulfate, and 0.100 % (w/v) poly(ethylene oxide) were utilized to realize dynamic pH junction–sweeping for BA and SA. Under the optimized conditions, the entire analysis process was completed in 7 min, and a 900-fold sensitivity enhancement was achieved with limits of detection (S/N?=?3) as low as 8.2 and 6.1 nM for BA and SA, respectively. The linear ranges were between 20 nM and 20 μM for BA and 20 nM and 10 μM for SA, with correlation coefficients greater than 0.992. The recoveries of the proposed method ranged from 90 to 113 %. These satisfactory results indicate that this method has the potential to be an effective analytical tool for the rapid screening of BA and SA in different food products.
Figure An online focusing strategy combining dynamic pH junction and sweeping for sensitive determination of benzoic and sorbic acid in food products using capillary electrophoresis wit polymer solutions
Laser electrospray mass spectrometry (LEMS) measurement of the dissociation constant (Kd) for hen egg white lysozyme (HEWL) and N,N′,N″-triacetylchitotriose (NAG3) revealed an apparent Kd value of 313.2?±?25.9 μM for the ligand titration method. Similar measurements for N,N′,N″,N″’-tetraacetylchitotetraose (NAG4) revealed an apparent Kd of 249.3?±?13.6 μM. An electrospray ionization mass spectrometry (ESI-MS) experiment determined a Kd value of 9.8?±?0.6 μM. In a second LEMS approach, a calibrated measurement was used to determine a Kd value of 6.8?±?1.5 μM for NAG3. The capture efficiency of LEMS was measured to be 3.6?±?1.8% and is defined as the fraction of LEMS sample detected after merging with the ESI plume. When the dilution is factored into the ligand titration measurement, the adjusted Kd value was 11.3 μM for NAG3 and 9.0 μM for NAG4. The calibration method for measuring Kd developed in this study can be applied to solutions containing unknown analyte concentrations.
This research work was executed to determine chemical composition, anti-oxidant and anti-microbial potential of the essential oils extracted from the leaves and stem of Daphne mucronata Royle. From leaves and stem oils fifty-one different constituents were identified through GC/MS examination. The antioxidant potential evaluated through DPPH free radical scavenging activity and %-inhibition of peroxidation in linoleic acid system. The stem’s essential oil showed the good antioxidant activity as compared to leaves essential oil. Results of Antimicrobial activity revealed that both stem and leaves oils showed strong activity against Candida albicans with large inhibition zone (22.2?±?0.01, 18.9?±?0.20 mm) and lowest MIC values (0.98?±?0.005, 2.44?±?0.002 mg/mL) respectively. Leaves essential was also active against Escherichia coli with inhibition zone of 8.88?±?0.01 mm and MIC values of 11.2?±?0.40 mg/mL. These results suggested that the plant’s essential oils would be a potential cradle for the natural product based antimicrobial as well as antioxidant agents.
We report on a small (20?×?10 mm) micromachined device for the detection of gases in micro-gas chromatography (GC). It incorporates a micro-discharge across a 20-μm gap, and a remote electrode in the micro cavity that generates an electrical signal corresponding to the photo-ionization of gaseous analytes in a stream of carrier gas. Multi-component mixtures were detected and the results compared to those obtained with a flame ionization detector. The minimum detectable limit is 350 pg.μL?1 of n-octane in air when applying a 1.4 mW discharge. The combination of wet etching of glass (as used for microfluidic channels) with a lift-off process for detector electrodes by a robust batch process results in a universal, non-destructive, and sensitive microdetector for micro-GC.
A stir foam composed of graphene oxide, poly(ethylene glycol) and natural latex (GO-PEG-NL) was prepared for use in micro-solid phase extraction sorbent of preservative agents and antioxidants from cosmetic products. The extracted analytes were quantified by GC-MS. Under the optimized conditions, the calibration plots are linear in the concentration ranges between 5.0 μg·L?1 to 1.0 mg·L?1 for benzoic acid, of 10.0 μg·L?1 to 1.0 mg·L?1 for 2-methyl-3-isothiazolinone (MI), and between 1.0 μg·L?1 and 1.0 mg·L?1 for both 3-tert-butyl-4-hydroxyanisole (BHA) and 2,6-di-tert-butyl-p-hydroxytoluene (BHT). The LODs are 1.0 μg·L?1 for benzoic acid, 5.0 μg·L?1 for MI and 0.5 μg·L?1 for both BHA and BHT. The stir-foam can be easily prepared, is inexpensive and well reproducible (RSDs <3%, for n?=?6). It can be re-used for up to 12 times after which extraction efficiency has dropped to 90%. The method was successfully applied to the determination of preservatives and antioxidants in cosmetic samples. Recoveries from spiked samples ranged between 94.5?±?2.1% and 99.8?±?1.8%.
Graphical abstract A stir foam was prepared from graphene oxide, poly(ethylene glycol) and natural latex (GO-PEG-NL) and is shown to be a most viable sorbent for the microextraction of trace amounts of preservative agents and antioxidants from cosmetic products.
We describe a chemical exfoliation method for the preparation of MoS2 nanosheets. The nanosheets were incorporated into poly(3,4-ethylenedioxythiophene) (PEDOT) by electrodeposition on a glassy carbon electrode (GCE) to form a nanocomposite. The modified GCE is shown to enable simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA). Due to the synergistic effect of MoS2 and PEDOT, this electrode displays better properties in terms of electrocatalytic oxidation of AA, DA and UA than pure PEDOT, which is illustrated by cyclic voltammetry and differential pulse voltammetry (DPV). Under optimum conditions and at pH 7.4, the respective sensitivities and best working potentials are as follows: AA: 1.20 A?mM?1?m?2, 30 mV; DA: 36.40 A?mM?1?m?2, 210 mV; UA: 105.17 A?mM?1?m?2, 350 mV. The calculated detection limits for AA, DA and UA are 5.83 μM, 0.52 μM and 0.95 μM, respectively. The modified electrode was applied to the detection of the three species in human urine samples and gave satisfactory results.
Graphical abstract MoS2 nanosheets were prepared by a facile chemical exfoliation method. MoS2 and poly(3,4-ethylenedioxythiophene) nanocomposite modified glassy carbon electrodes were fabricated, which are shown to enable simultaneous determination of ascorbic acid, dopamine and uric acid with high sensitivity and selectivity.
A sensing device was constructed for the amperometric determination of nitrite. It is based on the use of titanium dioxide (TiO2) nanotubes template with natural fibers and carrying hemin acting as the electron mediator. A glassy carbon electrode (GCE) was modified with the hemin/TNT nanocomposite. The electrochemical response to nitrite was characterized by impedance spectroscopy and cyclic voltammetry. An amperometric study, performed at a working potential of + 0.75 V (vs. Ag/AgCl), showed the sensor to enable determination of nitrite with a linear response in the 0.6 to 130 μM concentration range and with a 59 nM limit of detection. Corresponding studies by differential study voltammetry (Ep?=?0.75 V) exhibited a linear range from 0.6?×?10?6 to 7.3?×?10?5 M with a limit of detection of 84 nM. The sensing device was applied to the determination of nitrite in spiked tap and lake water samples.
Graphical abstract Natural fibers templated synthesis of TNT immobilized hemin as electron transfer mediator for quantitative detection of nitrite with detection limit of 59 nM and good electrochemical sensitivity and the method can be used for quantitative determination of nitrite in water samples.
Disposable screen-printed carbon arrays modified with gold nanoparticles (AuNPs) are described. The AuNP-modified screen-printed carbon arrays, designated as AuNP-SPCE arrays, were characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The AuNP-SPCE arrays display excellent electrocatalytic activity towards lead and copper. Two well-defined and fully resolved anodic stripping peaks, at 20 mV for Pb(II) and at 370 mV for Cu(II), both vs. Ag/AgCl, can be seen. Square wave anodic stripping voltammetry was used to simultaneously analyze Pb(II) and Cu(II) in their binary mixtures in tap water. The linear working range for Pb(II) extends from 10 μg.L?1 to 100 μg.L?1 with a sensitivity of 5.94 μA.μg?1.L.cm?2. The respective data for Cu(II) are a working range from 10 μg.L?1 to 150 μg.L?1 with a sensitivity of 3.52 μA.μg?1.L.cm?2. The limits of detection (based on 3× the baseline noise) are 2.1 ng.L?1 and 1.4 ng.L?1, respectively. In our perception, this array is particularly attractive because Pb(II) and Cu(II) can be determined at rather low working potentials which makes the method fairly selective in that it is not significantly interfered by other electroactive species that require higher reduction potentials.
Graphical abstract Fabrication, characterization and electrochemical behavior of gold nanoparticles modified screen-printed carbon arrays towards lead and copper in tap water.
This study aims at evaluating the capabilities of synchrotron radiation micro X-ray fluorescence spectrometry (SR micro-XRF) for qualitative and semi-quantitative elemental mapping of the distribution of actinides in human tissues originating from individuals with documented occupational exposure. The investigated lymph node tissues were provided by the United States Transuranium and Uranium Registries (USTUR) and were analyzed following appropriate sample pre-treatment. Semi-quantitative results were obtained via calibration by external standards and demonstrated that the uranium concentration level in the detected actinide hot spots reaches more than 100 μg/g. For the plutonium hot spots, concentration levels up to 31 μg/g were found. As illustrated by this case study on these unique samples, SR micro-XRF has a high potential for this type of elemental bio-imaging owing to its high sensitivity, high spatial resolution, and non-destructive character.
Graphical Abstract SR micro-XRF study of the distribution of actinitides in human tissues. Left Location of the U-contaminated tissue sample in the human body. Middle U distribution derived from the high resolution SR micro-XRF scan on the tissue sample, indication of five U hot spots. Right Detail of the point measurement spectrum of U hot spot 3, intense U-Lα fluorescence peak located at 13.6 keV.
The authors describe the preparation of a molecularly imprinted polymer (MIP) film on the surface of electrodeposited hollow nickel nanospheres (hNiNS), and the use of this nanocomposite in an electrochemical sensor for dopamine (DA). The use of the 3-dimensional hNiNS as a support material enlarges the sensing area and conductivity, while the MIP film warrants improved selectivity for DA. Quantification based on the “MIP/gate effect” was performed by employing hexacyanoferrate as the electrochemical probe. Scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy were applied to characterize the sensor materials. The electropolymerization condition such as pH value, functional monomer and ratio of template to monomer were optimized. By using dopamine (DA) as a model analyte, the sensor, if operated at 0.1 V vs. SCE, has fairly low detection limit of 1.7?×?10?14 M (at an S/N ratio of 3), two wide assay ranges of 5?×?10?14 to 1?×?10?12 M and 1?×?10?12 to 5?×?10?11 M, and superb selectivity.
Graphical Abstract An electrochemical sensor platform with a novel composite film composed of hollow nickel nanospheres (hNiNS) and molecularly imprinted polymer (MIP) was developed via a facile double-elecrodeposition method. The synergistic effects of hNiNS and MIP guarantee the ultrahigh sensitivity (down to 10?2 ppt) and selectivity of the sensor.
This work demonstrates the feasibility of ultra-trace determination of halogens in biological samples by inductively coupled plasma mass spectrometry (ICP-MS) after decomposition by microwave-induced combustion (MIC). The conventional MIC method was improved to allow the combustion of samples with mass higher than that used in previous works in order to achieve better limits of detection (LODs). The applicability of the proposed method for ultra-trace determination of bromine and iodine in organic samples was demonstrated here using honey. It was possible to decompose up to 1000 mg of honey using microcrystalline cellulose as a combustion aid and polyethylene film for sample wrapping. After combustion, analytes were absorbed using 50 mmol L?1 NH4OH and recoveries for Br and I were between 99 and 104 %, and relative standard deviations were lower than 5 %. Microwave-assisted alkaline dissolution (MA-AD) was also evaluated for honey sample preparation using NH4OH or tetramethylammonium hydroxide solutions. However, the LODs for the MA-AD method were unsuitable because the high carbon content in digests required a dilution step prior to the analysis by ICP-MS. The LODs obtained by MIC were improved from 1143 to 34 ng g?1 for Br and from 571 to 6.0 ng g?1 for I, when compared to the MA-AD method. Furthermore, it was possible to decompose up to eight samples simultaneously in 30 min (including the cooling step) with very low reagent consumption and consequently lower generation of effluents, making MIC method well suited for routine ultra-trace determination of Br and I in honey.
