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Analytica Chimica Acta (v.739, #)
Review on recent applications of the liquid waveguide capillary cell in flow based analysis techniques to enhance the sensitivity of spectroscopic detection methods by Ricardo N.M.J. Páscoa; Ildikó V. Tóth; António O.S.S. Rangel (pp. 1-13).
Display Omitted► Advances in application of liquid core waveguide capillary cell are summarised and critically discussed. ► Different flow strategies using the LWCC are presented. ► Practical advantages and limitations in application are pointed out.Incorporation of long path length liquid waveguide capillary cell (LWCC or LCW) into spectrometric detection systems can increase the sensitivity of these by orders of magnitude (up to 500 times), and consequently can reduce the detection limits. The combination of the long path length spectrophotometry with flow methodologies can provide analytical solutions for various challenges in the field of environmental, biochemical and food chemistry.In this present work, the analytical applications of the long capillary cells are summarised and critically discussed. A historical overview of the cell development is given; applications in different areas are presented and grouped by analyte type. Major improvements achieved based on the use of the LWCC in the analytical characteristics (like sensitivity and detection limit) are emphasised while some of the limitations are also discussed.
Keywords: Liquid core waveguide (LCW); Liquid waveguide capillary cell (LWCC); Spectrophotometric methods; Flow analysis; Long path-length spectrophotometry; Nanomolar detection limit
Single-drop microextraction as a powerful pretreatment tool for capillary electrophoresis: A review by Zeid A. ALOthman; Mohamed Dawod; Jihye Kim; Doo Soo Chung (pp. 14-24).
.Display Omitted► SDME is a convenient and powerful preconcentration and sample cleanup method for CE. ► SDME-CE has been applied to the analysis of target analytes in complex matrices. ► SDME-CE has been hyphenated with other on-line preconcentration techniques in CE.Single drop microextraction (SDME) is a convenient and powerful preconcentration and sample cleanup method for capillary electrophoresis (CE). In SDME, analytes are typically extracted from a sample donor solution into an acceptor drop hanging at the inlet tip of a capillary. The enriched drop is then introduced to the capillary for CE analysis. Since the volume of the acceptor drop can be as small as a few nanoliters, the consumption of solvents can be minimized and the preconcentration effect is enhanced. In addition, by covering the acceptor phase with an organic layer or by using an organic acceptor phase, inorganic ions such as salts in the sample solution can be blocked from entering the acceptor phase, providing desalting effects. Here, we describe the basic principles and instrumentation for SDME and its coupling with CE. We also review recent developments and applications of SDME-CE.
Keywords: Abbreviations; BGE; background electrolyte; C; 4; D; capacitively-coupled contactless conductivity detection; EOF; electroosmotic flow; LIF; laser-induced fluorescence; LLE; liquid–liquid extraction; LPME; liquid phase microextraction; LVSS; large volume sample stacking; LVSEP; large volume stacking using an electroosmotic flow pump; SDME; single drop microextraction; SPE; solid phase extraction; SPME; solid phase microextractionSingle drop microextraction; Electrophoresis; Preconcentration; Extraction
Zeolite A functionalized with copper nanoparticles and graphene oxide for simultaneous electrochemical determination of dopamine and ascorbic acid by Ping He; Wei Wang; Licheng Du; Faqin Dong; Yuequan Deng; Tinghong Zhang (pp. 25-30).
A novel Cu-zeolite A/graphene-modified glassy carbon electrode was applied in the simultaneous electrochemical determination of dopamine (DA) and ascorbic acid (AA). The potential difference between the two oxidation peaks of DA and AA were over 200mV. The electrocatalytic oxidation currents of DA were linearly related to the corresponding concentration in the range of 1.0×10−7–1.9×10−5M.Display Omitted► Cu nanoparticles doped-zeolite A/graphene (CuZEA/RGO) modified electrode was prepared. ► The composites of CuZEA/RGO were prepared via reduction of Cu2+ functionalized zeolite A and graphene oxide in one pot. ► The modified electrode was presented for the simultaneous determination of DA and AA. ► The proposed electrode showed a higher electrocatalytic performance.A novel Cu-zeolite A/graphene modified glassy carbon electrode for the simultaneous electrochemical determination of dopamine (DA) and ascorbic acid (AA) has been described. The Cu-zeolite A/graphene composites were prepared using Cu2+ functionalized zeolite A and graphene oxide as the precursor, and subsequently reduced by chemical agents. The composites were characterized by X-ray diffraction, Fourier transform infrared spectra and scanning electron microscopy. Based on the Cu-zeolite A/graphene-modified electrode, the potential difference between the oxidation peaks of DA and AA was over 200mV, which was adequate for the simultaneous electrochemical determination of DA and AA. Also the proposed Cu-zeolite/graphene-modified electrode showed higher electrocatalytic performance than zeolite/graphene electrode or graphene-modified electrode. The electrocatalytic oxidation currents of DA and AA were linearly related to the corresponding concentration in the range of 1.0×10−7–1.9×10−5M for DA and 2.0×10−5–2.0×10−4M for AA. Detection limits (S/N=3) were estimated to be 4.1×10−8M for DA and 1.1×10−5M for AA, respectively.
Keywords: Dopamine; Ascorbic acid; Graphene; Cu doped zeolite A; Simultaneous electrochemical determination; Modified electrode
Electro membrane extraction of biological anions with ion chromatographic analysis by Tsze Yin Tan; Chanbasha Basheer; Kai Perng Ng; Hian Kee Lee (pp. 31-36).
. Schematic of (a) battery-operated electro membrane extraction, (b) proposed extraction mechanism and (c) selected target anions.Display Omitted► One-step battery-operated electro membrane extraction of anions from biological samples. ► Extraction performance was compared with liquid-phase microextraction. ► Simple and efficient analytical approach with low LODs, good linearity and repeatability.A simple and sensitive single step electro membrane extraction (EME) procedure was demonstrated for biological organic anions with determination by ion chromatography (IC). Nitrite, adipate, oxalate, iodide, fumarate, thiocyanate and perchlorate were extracted from aqueous donor solutions, across a supported liquid membrane (SLM) consisting of methanol impregnated in the walls of a porous polypropylene membrane bag and into an alkaline aqueous acceptor solution in the lumen of the propylene envelope by the application of potential of 12V applied across the SLM. The acceptor solution was analyzed by IC. Parameters affecting the extraction performance such as type of SLM, extraction time, pH of the donor and acceptor solution, and extraction voltage were studied. The most favorable EME conditions were methanol as the SLM, extraction time of 5min, pH of acceptor and sample solutions of 12 and 4, respectively, and a voltage of 12V. Portable 12V batteries were used in the study. Under these optimized conditions, all anions had enrichment factors ranging from 3.6 to 36.2 with relative standard deviations ( n=3) of between 6.6 and 17.5%. Good linearity ranging from 0.1 to 10μgmL−1 with coefficients of correlation ( r) of between 0.9981 and 0.9996 were obtained. The limits of detection of the EME-IC method were from 0.01 to 0.14μgmL−1. The developed methodology was applied to amniotic fluid samples to evaluate the feasibility of the method for real applications.
Keywords: Electro membrane extraction; Ion chromatography; Nitrite; Adipate; Oxalate; Iodide; Fumarate; Thiocyanate; Perchlorate; Portable battery
Evaluation of DGT techniques for measuring inorganic uranium species in natural waters: Interferences, deployment time and speciation by Geraldine S.C. Turner; Graham A. Mills; Peter R. Teasdale; Jonathan L. Burnett; Sean Amos; Gary R. Fones (pp. 37-46).
In situ field deployment of DGT devices – manganese dioxide (▪) best suited for sea water monitoring (a) up to 7 days and Metsorb (▪) best suited for fresh water monitoring (b) of inorganic uranium species up to 7 days.Display Omitted► The adsorbents Chelex-100, Metsorb and MnO2 were investigated for use with DGT. ► All three adsorbents performed well in low ionic strength solutions. ► MnO2 resin was found to be the most suitable for marine deployments. ► DGT is able to measure isotopic ratios of U down to concentrations of 0.1μgL−1. ► DGT underestimated U concentrations by at least 50% if the DBL was not taken into account.Three adsorbents (Chelex-100, manganese dioxide [MnO2] and Metsorb), used as binding layers with the diffusive gradient in thin film (DGT) technique, were evaluated for the measurement of inorganic uranium species in synthetic and natural waters. Uranium (U) was found to be quantitatively accumulated in solution (10–100μgL−1) by all three adsorbents (uptake efficiencies of 80–99%) with elution efficiencies of 80% (Chelex-100), 84% (MnO2) and 83% (Metsorb). Consistent uptake occurred over pH (5–9), with only MnO2 affected by pH<5, and ionic strength (0.001–1molL−1 NaNO3) ranges typical of natural waters, including seawater. DGT validation experiments (5 days) gave linear mass uptake over time ( R2≥0.97) for all three adsorbents in low ionic strength solution (0.01M NaNO3). Validation experiments in artificial sea water gave linear mass uptake for Metsorb ( R2≥0.9954) up to 12h and MnO2 ( R2≥0.9259) up to 24h. Chelex-100 demonstrated no linear mass uptake in artificial sea water after 8h. Possible interferences were investigated with SO42− (0.02–200mgL−1) having little affect on any of the three DGT binding layers. PO43− additions (5μgL−1–5mgL−1) interfered by forming anionic uranyl phosphate complexes that Chelex-100 was unable to accumulate, or by directly competing with the uranyl species for binding sites, as with MnO2 and the Metsorb. HCO3− (0.1–500mgL−1) additions formed anionic species which interfered with the performance of the Chelex-100 and the MnO2, and the Ca2+ (0.1–500mgL−1) had the affect of forming labile calcium uranyl species which aided uptake of U by all three resins. DGT field deployments in sea water (Southampton Water, UK) gave a linear mass uptake of U over time with Metsorb and MnO2 (4 days). Field deployments in fresh water (River Lambourn, UK) gave linear uptake for up to 7 and 4 days for Metsorb and MnO2 respectively. Field deployment of the Metsorb-DGT samplers with various diffusive layer thicknesses (0.015–0.175cm) allowed accurate measurements of the diffusive boundary layer (DBL) and allowed DBL corrected concentrations to be determined. This DBL-corrected U concentration was half that determined when the effect of the DBL was not considered. The ability of the DGT devices to measure U isotopic ratios with no isotopic fractionation was shown by all three resins, thereby proving the usefulness of the technique for environmental monitoring purposes.
Keywords: Diffusive gradients in thin films; Uranium; Chelex-100; Manganese dioxide; Metsorb; Titanium dioxide; Natural waters
A quantitative liquid chromatography tandem mass spectrometry method for metabolomic analysis of Plasmodium falciparum lipid related metabolites by S. Vo Duy; S. Besteiro; L. Berry; C. Perigaud; F. Bressolle; H.J. Vial; I. Lefebvre-Tournier (pp. 47-55).
Display Omitted► Plasmodium falciparum is the causative agent of malaria. ► Two analytical techniques using LC/MS/MS developed. ► 35 compounds were quantified. ► The methods were validated and applied to determine intracellular concentrations of metabolites. Plasmodium falciparum is the causative agent of malaria, a deadly infectious disease for which treatments are scarce and drug-resistant parasites are now increasingly found. A comprehensive method of identifying and quantifying metabolites of this intracellular parasite could expand the arsenal of tools to understand its biology, and be used to develop new treatments against the disease. Here, we present two methods based on liquid chromatography tandem mass spectrometry for reliable measurement of water-soluble metabolites involved in phospholipid biosynthesis, as well as several other metabolites that reflect the metabolic status of the parasite including amino acids, carboxylic acids, energy-related carbohydrates, and nucleotides. A total of 35 compounds was quantified. In the first method, polar compounds were retained by hydrophilic interaction chromatography (amino column) and detected in negative mode using succinic acid-13C4 and fluorovaline as internal standards. In the second method, separations were carried out using reverse phase (C18) ion-pair liquid chromatography, with heptafluorobutyric acid as a volatile ion pairing reagent in positive detection mode, using d9-choline and 4-aminobutanol as internal standards. Standard curves were performed in P. falciparum-infected and uninfected red blood cells using standard addition method ( r2>0.99). The intra- and inter-day accuracy and precision as well as the extraction recovery of each compound were determined. The lower limit of quantitation varied from 50pmol to 100fmol/3×107cells. These methods were validated and successfully applied to determine intracellular concentrations of metabolites from uninfected host RBCs and isolated Plasmodium parasites.
Keywords: Metabolomics; Plasmodium falciparum; Liquid chromatography tandem mass-spectrometry; Phospholipid
A strategy for efficient discovery of new natural compounds by integrating orthogonal column chromatography and liquid chromatography/mass spectrometry analysis: Its application in Panax ginseng, Panax quinquefolium and Panax notoginseng to characterize 437 potential new ginsenosides by Wen-zhi Yang; Min Ye; Xue Qiao; Chun-fang Liu; Wen-juan Miao; Tao Bo; Hai-yan Tao; De-an Guo (pp. 56-66).
Display Omitted► Orthogonal MCI and silica gel separation achieved enrichment of minor ginsenosides. ► LC–(±)ESI-MS n analysis offered complementary structure information of ginsenosides. ► 623 ginsenosides including 437 new ones were identified from three Panax species. ► LC/MS guided isolation of P. ginseng yielded two new ginsenosides. ► NMR analysis of two new ginsenosides was consistent with LC/MS analysis.To discover new natural compounds from herbal medicines tends to be more and more difficult. In this paper, a strategy integrating orthogonal column chromatography and liquid chromatography/mass spectrometry (LC/MS) analysis was proposed, and was applied for rapid discovery of new ginsenosides from Panax ginseng (PG), Panax quinquefolium (PQ), and Panax notoginseng (PN). The ginsenosides extracts were fractionated by MCI gel×silica gel orthogonal column chromatography. The fractions were then separated on a C18 HPLC column, eluted with a three-component mobile phase (CH3CN/CH3OH/3mM CH3COONH4H2O), and detected by electrospray ionization tandem mass spectrometry. The structures of unknown ginsenosides were elucidated by analyzing negative and positive ion mass spectra, which provided complementary information on the sapogenins and oligosaccharide chains, respectively. A total of 623 comprising 437 potential new ginsenosides were characterized from the ethanol extracts of PG, PQ and PN. New acylations, diversified saccharide chains and C-17 side chains constituted novelty of the newly identified ginsenosides. An interpretation guideline was proposed for structural characterization of unknown ginsenosides by LC/MS. To confirm reliability of this strategy, two targeted unknown trace ginsenosides were obtained in pure form by LC/MS-guided isolation. Based on extensive NMR spectroscopic analysis and other techniques, they were identified as 3- O-[6- O-( E)-butenoyl- β-d-glucopyranosyl(1,2)- β-d-glucopyranosyl]-20( S)-protopanaxadiol-20- O- β-d-glucopyranosyl(1,6)- β-d-glucopyranoside (named ginsenoside IV) and 3- O- β-d-glucopyranosyl(1,2)- β-d-glucopyranosyl-3 β,12 β,20( S),24( R)-tetra hydroxy-dammar-25-ene-20- O- β-d-glucopyranosyl(1,6)- β-d-glucopyranoside (ginsenoside V), respectively. The fully established structures were consistent with the MS-oriented structural elucidation. This study expanded our understanding on ginsenosides of Panax species, and the proposed strategy was proved efficient and reliable in the discovery of new minor compounds from herbal extracts.
Keywords: Natural compounds discovery; Ginsenoside; Panax; species; Orthogonal chromatography; Liquid chromatography coupled with mass spectrometry
De novo analysis of electron impact mass spectra using fragmentation trees by Franziska Hufsky; Martin Rempt; Florian Rasche; Georg Pohnert; Sebastian Böcker (pp. 67-76).
Display Omitted► We present a method for de novo analysis of accurate mass EI mass spectra of small molecules. ► This method identifies the molecular ion and thus the molecular formula where the molecular ion is present in the spectrum. ► Fragmentation trees are constructed by automated signal extraction and evaluation. ► These trees explain relevant fragmentation reactions. ► This method will be very helpful in the automated analysis of unknown metabolites.The automated fragmentation analysis of high resolution EI mass spectra based on a fragmentation tree algorithm is introduced. Fragmentation trees are constructed from EI spectra by automated signal extraction and evaluation. These trees explain relevant fragmentation reactions and assign molecular formulas to fragments. The method enables the identification of the molecular ion and the molecular formula of a metabolite if the molecular ion is present in the spectrum. These identifications are independent of existing library knowledge and, thus, support assignment and structural elucidation of unknown compounds. The method works even if the molecular ion is of very low abundance or hidden under contaminants with higher masses. We apply the algorithm to a selection of 50 derivatized and underivatized metabolites and demonstrate that in 78% of cases the molecular ion can be correctly assigned. The automatically constructed fragmentation trees correspond very well to published mechanisms and allow the assignment of specific relevant fragments and fragmentation pathways even in the most complex EI-spectra in our dataset. This method will be very helpful in the automated analysis of metabolites that are not included in common libraries and it thus has the potential to support the explorative character of metabolomics studies.
Keywords: Metabolomics; GC–MS; Computational mass spectrometry; Molecular formula identification; Fragmentation trees
Development of an automatic multi-channel ink-jet ejection chemiluminescence system and its application to the determination of horseradish peroxidase by Fengming Chen; Zhen Lin; Yongzan Zheng; Hulie Zeng; Hizuru Nakajima; Katsumi Uchiyama; Jin-Ming Lin (pp. 77-82).
An automatic multi-channel ink-jet ejection chemiluminescence system.Display Omitted► Automatic multi-channel ink-jet ejection chemiluminescence. ► Determination of horseradish peroxidase. ► Horseradish peroxidase–protein conjugates.In this work, an automatic multi-channel ink-jet for chemiluminescence (CL) analysis was developed. The four-channel ink-jet device was controlled by a home-made circuit. Differing from the classic flow injection CL, the whole procedure for CL analysis was automatically completed on a hydrophobic glass side. CL reaction of luminal and hydrogen peroxide for the determination of horseradish peroxidase (HRP) was selected as an application to automatic CL analysis platform. All solutions delivered by different channels were precisely ejected to the same position of the glass slide for the CL analysis. The consumption of reaction solution was reduced to nanoliter level. The whole CL analysis could be completed in less than 4min, which was benefited from the prompt solution mixing in small size of droplet. The CL intensity increased linearly with HRP concentration in the range from 0.01 to 0.5μgmL−1. The limit of detection (LOD) (S/N=3) was 0.005μgmL−1. Finally, the automatic CL system could also be used for the detection of HRP in HRP–protein conjugates, which showed its practical application in immunoassay.
Keywords: Ink-jet; Chemiluminescence; Horseradish peroxidase; Multi-channel device
Detecting solution pH changes using poly ( N-isopropylacrylamide)- co-acrylic acid microgel-based etalon modified quartz crystal microbalances by Kai C.C. Johnson; Francisco Mendez; Michael J. Serpe (pp. 83-88).
Display Omitted► Color tunable materials on a QCM crystal can detect solution pH changes. ► Sensitivity of 1.3×10−8M [H+]Hz−1 is achieved over a 2pH unit range. ► Detection limit of 390nM [H+] was realized.Poly ( N-isopropylacrylamide)- co-acrylic acid (pNIPAm- co-AAc) microgel-based etalons have been shown to have visible color and unique spectral properties, which both depend on solution temperature and pH. In this investigation, pNIPAm- co-AAc microgel-based etalons were fabricated on the Au electrode of a quartz crystal microbalance (QCM), and the resonant frequency of the QCM monitored as a function of temperature, at pH 3.0. Furthermore, the resonant frequency at either pH 3.0 or 7.0 was monitored while keeping the solution temperature constant at various temperatures. In all cases, when the solution temperature was below the collapse transition for the microgels (∼32°C), the resonant frequency at pH 3.0 was lower than at pH 7.0, which we attribute to the film transitioning from a deswollen to swollen state, respectively. It was observed that the magnitude of the resonant frequency change increased as the solution temperature approached the collapse temperature for the microgels. The overall sensitivity to pH was determined to be 1.3×10−8M [H+]Hz−1 and a theoretical detection limit of 390nM was obtained. This sensitivity will be exploited further for future biosensing applications.
Keywords: Poly (; N; -isopropylacrylamide) microgels; Color tunable materials; Quartz crystal microbalance; Stimuli responsive polymers; Sensing
A sensitive microextraction by packed sorbent-based methodology combined with ultra-high pressure liquid chromatography as a powerful technique for analysis of biologically active flavonols in wines by Catarina L. Silva; João L. Gonçalves; José S. Câmara (pp. 89-98).
Display Omitted► An innovative methodology to pre-concentrate bioactive flavonols, MEPS. ► Rapid screening for analysis of biological active flavonols in wines. ► MEPS reduced the sample volume and the time necessary for the analysis. ► Limits the consumption of organic solvents thus also reducing the testing cost. ► Good results were obtained in terms of selectivity, precision, sensitivity and accuracy.A new approach based on microextraction by packed sorbent (MEPS) and reversed-phase high-throughput ultra high pressure liquid chromatography (UHPLC) method that uses a gradient elution and diode array detection to quantitate three biologically active flavonols in wines, myricetin, quercetin, and kaempferol, is described. In addition to performing routine experiments to establish the validity of the assay to internationally accepted criteria (selectivity, linearity, sensitivity, precision, accuracy), experiments are included to assess the effect of the important experimental parameters such as the type of sorbent material (C2, C8, C18, SIL, and C8/SCX), number of extraction cycles (extract-discard), elution volume, sample volume, and ethanol content, on the MEPS performance. The optimal conditions of MEPS extraction were obtained using C8 sorbent and small sample volumes (250μL) in five extraction cycle and in a short time period (about 5min for the entire sample preparation step). Under optimized conditions, excellent linearity(Rvalues2>0.9963), limits of detection of 0.006μgmL−1 (quercetin) to 0.013μgmL−1 (myricetin) and precision within 0.5–3.1% were observed for the target flavonols. The average recoveries of myricetin, quercetin and kaempferol for real samples were 83.0–97.7% with relative standard deviation (RSD, %) lower than 1.6%. The results obtained showed that the most abundant flavonol in the analyzed samples was myricetin (5.8±3.7μgmL−1). Quercetin (0.97±0.41μgmL−1) and kaempferol (0.66±0.24μgmL−1) were found in a lower concentration.The optimized MEPSC8 method was compared with a reverse-phase solid-phase extraction (SPE) procedure using as sorbent a macroporous copolymer made from a balanced ratio of two monomers, the lipophilic divinylbenzene and the hydrophilic N-vinylpyrrolidone (Oasis HLB) were used as reference. MEPSC8 approach offers an attractive alternative for analysis of flavonols in wines, providing a number of advantages including highest extraction efficiency (from 85.9±0.9% to 92.1±0.5%) in the shortest extraction time with low solvent consumption, fast sample throughput, more environmentally friendly and easy to perform.
Keywords: Wines; Flavonols; Microextraction by packed sorbent; Solid phase extraction; Ultra high pressure liquid chromatography
A data treatment method for detecting fluorescence anisotropy peaks in capillary electropherograms by Ryan A. Picou; Indu Kheterpal; S. Douglass Gilman (pp. 99-103).
Display Omitted► We explain the absence of fluorescence anisotropy peaks for capillary separations. ► We developed a method to visualize fluorescence anisotropy peaks for separations. ► This method was applied to a separation of amyloid beta peptide aggregates.A data treatment method is presented to detect fluorescence anisotropy (FA) peaks in capillary electrophoresis electropherograms. The data treatment method converts plots of fluorescence anisotropy vs. time that contain no peaks that are distinguishable from the noise of the anisotropy background into plots that show distinct fluorescence anisotropy peaks. The method was demonstrated using laser-induced fluorescence anisotropy data from individual Aβ (1–42) aggregates separated using capillary electrophoresis. Applying this data treatment method enabled the detection of anisotropy peaks for individual Aβ aggregate fluorescence peaks that were not observed prior to the data treatment method. The data treatment method is not specifically designed for Aβ aggregate analysis or capillary electrophoresis, and it should be applicable to other applications and other separation methods with FA detection.
Keywords: Fluorescence anisotropy; Data treatment; Capillary electrophoresis; Amyloid beta peptide