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Analytica Chimica Acta (v.698, #1-2)
Rapid monitoring of mono- and disaccharides in drinks, foodstuffs and foodstuff additives by capillary electrophoresis with contactless conductivity detection by Petr Tůma; Klára Málková; Eva Samcová; Karel Štulík (pp. 1-5).
Display Omitted► Small internal diameter of capillary. ► Electrophoretic separation of neutral saccharides in highly alkaline buffers. ► Contactless conductivity detection. ► Visualization of non-absorbing saccharides. ► Rapid food analysis.A capillary electrophoresis (CE) procedure with contactless conductivity detection (C4D) has been developed for monitoring of neutral mono- and disaccharides in drinks and foodstuffs. The separation of a mixture of seven neutral saccharides (glucose, fructose, galactose, mannose, ribose, sucrose and lactose) employed a quartz capillary, 5μm i.d., with an effective length of 18.3cm, and 75mM NaOH (pH 12.8) as the background electrolyte (BGE). The limit of detection (LOD) values obtained lied within a range from 0.4μmolL−1 for lactose to 0.9μmolL−1 for ribose, with a separation time shorter than 140s. The procedure was successfully applied to determinations of saccharides in fruit juices, Coca-Cola, milk, red and white wines, yoghurts, honey and a foodstuff additive.
Keywords: Abbreviations; C; 4; D; capacitively coupled contactless conductivity detection; PAD; pulsed amperometric detection; RID; refractive index detectionCapillary electrophoresis; Contactless conductivity detection; Food analysis; Saccharides
Dynamic reaction cell ICP-MS for determination of total As, Cr, Se and V in complex matrices: Still a challenge? A review by Sonia D’Ilio; Nicola Violante; Costanza Majorani; Francesco Petrucci (pp. 6-13).
Display Omitted► Trace elements determination may be hampered by atomic or polyatomic species. ► Different interference management systems have been introduced for their removal. ► The DRC™ technology uses a reaction gas to overcome these interferences. ► The paper is a review on analytical challenges for the assay of As, Cr, Se, V.Mass interferences, caused by atomic or polyatomic species and having the same mass/charge ratio of the analyte, can be a severe limit for a reliable assay of trace and ultratrace elements by ICP-MS. The DRC™ technology uses a reaction gas to overcome these interferences. Reactions of charge exchange, atom transfer, adduct formation, condensation and analyte association/condensation are the main mechanisms. Interfering ions tend to react with the gas exothermally, while, the analyte reacts endothermally.Selecting the most appropriate reaction gas in DRC-ICP-MS is the very critical point for the determination of strongly interfered elements. A careful evaluation of the reaction mechanisms and the chemistry involved are required. The DRC allows the use of different gases, among them, ammonia (NH3), methane (CH4), hydrogen (H2) and oxygen (O2) are the most known, but there are other potentially useful gases like nitrous oxide (N2O), nitrogen oxide (NO), carbon dioxide (CO2), fluoromethane (CH3F), sulphur hexafluoride (SF6) and carbon disulfide (CS2).This paper provides a review on the analytical challenges for a reliable assay of As, Cr, Se and V by DRC-ICP-MS and illustrates different approaches and mechanisms involved in the analysis of polymers, biological fluids (serum, urine and whole blood), rock, soil and particulate matter.
Keywords: DRC-ICP-MS; Interferences suppression; Reaction gases; Trace elements
Platinum–gold alloy nanoparticles and horseradish peroxidase functionalized nanocomposite as a trace label for ultrasensitive electrochemical detection of thrombin by Lijuan Bai; Ruo Yuan; Yaqin Chai; Yali Yuan; Li Mao; Yan Wang (pp. 14-19).
.Display Omitted► Use multifunctional single-walled carbon nanotubes (SWCNTs) for signal amplification. ► Combine the high sensitivity of enzymatic catalysis and the amplification of nanoparticles. ► Ultrasensitive electrochemical detection of thrombin.A novel tracer, platinum–gold alloy nanoparticles (Pt–AuNPs) and horseradish peroxidase (HRP) functionalized single-walled carbon nanotubes (SWCNTs) composite, is employed to label the secondary thrombin aptamer for constructing an ultrasensitive electrochemical aptasensor. Thionine, immobilized on functionalized SWCNTs, provides a pair of distinguished redox peak for electrochemical detection. Both the high-content Pt–AuNPs and HRP on SWCNTs amplify the electrochemical signal of thionine through electrocatalytic reduction of H2O2. Differential pulse voltammetry (DPV) is employed to detect thrombin with different concentrations. The reduction peak current is logarithmically related to the concentration of thrombin in an extremely wide range from 10fM to 5nM with a detection limit of 3.6fM. The dual signal amplification of Pt–AuNPs and HRP functionalized nanocomposite provides a promising way for ultrasensitive assay in electrochemical aptasensors.
Keywords: Electrochemical aptasensor; Amplification; Functionalized single-walled carbon nanotubes; Thrombin
Comparing dissolved reactive phosphorus measured by DGT with ferrihydrite and titanium dioxide adsorbents: Anionic interferences, adsorbent capacity and deployment time by Jared G. Panther; Peter R. Teasdale; William W. Bennett; David T. Welsh; Huijun Zhao (pp. 20-26).
The accuracy of the DGT technique for the measurement of DRP in natural waters is dependent on the adsorbent, adsorbent capacity and deployment time.Display Omitted► Titanium dioxide based adsorbent (Metsorb) is superior to ferrihydrite adsorbent. ► Bicarbonate interferes with measurement of DRP by ferrihydrite-DGT but not Metsorb-DGT. ► Metsorb has a higher capacity and is more accurate than ferrihydrite. ► Accuracy of DGT measurements is dependent on adsorbent capacity and deployment time. ► Testing the performance of DGT over longer time periods is critical.Two adsorbents (Metsorb and ferrihydrite) used in binding layers with the diffusive gradients in a thin film technique were evaluated for the measurement of dissolved reactive phosphorous (DRP) in synthetic and natural waters. Possible interferences were investigated with Cl− (up to 1.35molL−1) and SO42− (up to 0.056molL−1) having no affect on either DGT binding layer, and HCO3− (up to 5.7mmolL−1) having no effect on Metsorb-DGT, over 4 days. However, HCO3− interfered with the ferrihydrite-DGT measurement at concentrations typical of many natural waters (≥0.7mmolL−1) after a deployment period of 1–2 days. The capacity of the Metsorb binding phase for DGT response was ∼37,000ngP, whereas the capacities of a low-mass (17.8mg of adsorbent per DGT sampler) and high-mass (29.2mg of adsorbent per DGT sampler) ferrihydrite binding phase were substantially lower (∼15,000ngP and ∼25,000ngP, low-mass and high-mass, respectively). Increasing the capacity of the ferrihydrite adsorbent allowed the ferrihydrite-DGT to be utilized for up to 3 days before interference by HCO3− was observed. Seawater deployments demonstrated that even high-capacity ferrihydrite-DGT devices underestimated the DRP concentration by 37%, whereas Metsorb-DGT measurements were accurate. The Metsorb-DGT is superior to the ferrihydrite-DGT for determining DRP over deployment times greater than 1 day and in waters with ≥0.7mmolL−1 HCO3−. Based on the experience obtained from this detailed validation process, the authors propose a number of key requirements that need to be considered when developing new DGT binding layers, with testing the performance over longer deployment times being critical.
Keywords: Diffusive gradients in a thin film; Metsorb; Iron hydroxide; Bicarbonate; Laboratory validation; Natural waters
Effective concentration difference model to study the effect of various factors on the effective diffusion coefficient in the dialysis membrane by Hong Chen; Ting Sun; Dianpeng Sui; Jia Dong (pp. 27-35).
Display Omitted► The effective diffusion coefficient is determined by the effective concentration difference across the dialysis membrane. ► The effective diffusion coefficient was affected by ionic strength, binding agent, ligands and Donnan potential. ► The determination of effective diffusion coefficient and its application should be in the same environment.Cellulose acetate dialysis membrane (CDM) has been used in the diffusive gradients in thin films (DGT) technique, where accurate diffusion coefficients are essential for the assessment of the concentrations of labile metal in solution. Effective concentration difference model (ECDM), based on the assumption that the effective diffusion coefficient of metal ion in the dialysis membrane is determined by the effective concentration difference (Δ Ce) across the dialysis membrane, is proposed and applied to study the effect of ionic strength, binding agent, ligands and Donnan potential on the effective diffusion coefficient. The effective diffusion coefficients of Cd2+ through the dialysis membrane immersed in receptor solutions with binding agent were almost the same as those in receptor solutions without binding agent at higher ionic strengths (0.01–1M) but much higher than those at lower ionic strengths (0.001–0.0001M). The effective diffusion coefficients of Cd2+ through the dialysis membrane immersed in deionized water receptor solutions with binding agent were not significantly different from those in synthetic receptor solutions (receptor solutions with various ionic strengths) with binding agent. The DGT-labile fractions were measured in synthetic solutions and natural waters, which indicated that the effective diffusion coefficients, through the dialysis membrane immersed in the deionized water solution with binding agent as receptor solution and in the spiked natural water as source solution, were more suitable for DGT application.
Keywords: Diffusive gradients in thin films; Effective diffusion coefficient; Effective concentration difference model; Dialysis membrane; Cd; 2+
Comparison of surfactant-assisted shotgun methods using acid-labile surfactants and sodium dodecyl sulfate for membrane proteome analysis by Fang Wu; Difei Sun; Nan Wang; Yan Gong; Liang Li (pp. 36-43).
Three surfactant-assisted shotgun methods using acid labile surfactants, sodium-3-[(2-methyl-2-undecyl-1,3-dioxolan-4-yl)-methoxyl]-1-propanesulfonate (RapiGest) and 3-[3-(1,1-bisalkyloxyethyl)pyridin-1-yl]propane-1-sulfonate (PPS), and sodium dodecyl sulfate (SDS) were investigated for their applicability to membrane proteome analysis. It is shown that RapiGest is a preferred reagent for handling membrane proteomes of Escherichia coli and MCF7 cells for liquid chromatography tandem mass spectrometry (LC MS/MS) analysis of tryptic digests. The RapiGest method allowed identification of more peptides and proteins than the SDS and PPS methods and there was no apparent bias for the type of peptides and proteins identified by the RapiGest and SDS methods, while a slightly higher proportion of hydrophilic peptides and proteins were identified by the PPS method. The performance of the SDS and PPS methods is similar in terms of the numbers of peptides and proteins identified. Since the SDS method required the removal of SDS using a technique such as strong-cation exchange (SCX), we further investigated the effect of SCX on sample loss through analyzing the digest of an enriched E. coli membrane fraction as well as a standard protein, bovine serum albumin (BSA). The results showed that extensive sample loss (as much as 62%) was encountered during the SCX cleaning step. We then applied the RapiGest method in combination with two-dimensional LC MS/MS to characterize the E. coli membrane proteome. In total, 1626 unique proteins (5799 unique peptides) were identified with a peptide false discovery rate of 2.4%. About 60% of the identified proteins with known cellular locations were found to be membrane proteins. Among them, about 75% were integral membrane proteins. This work represents one of the most comprehensive profiles of E. coli membrane proteome generated by a proteomic technique.
Keywords: Shotgun proteome analysis; Membrane proteome; Surfactants; Sodium dodecyl sulfate; Acid-labile surfactant; Liquid chromatography/mass spectrometry; Proteomics
Cross-talk-free simultaneous fluoroimmunoassay of two biomarkers based on dual-color quantum dots by Zhijuan Cao; Huan Li; Choiwan Lau; Yuhao Zhang (pp. 44-50).
Display Omitted► A new cross-talk-free duplex fluoroimmunoassay for cancer related biomarkers was developed using multiple QD as detection elements with the LOD of 0.625ng/mL. ► A fast homogeneous immunoreaction as well as a simple heterogeneous separation process was achieved by the coupling of the submicrometer-sized polystyrene microspheres as the carrier and the 96-well filter plate as the reaction and separation container. ► This new approach could also be extended to detect other biomarkers relating to other cancers, such as alpha fetoprotein and prostate specific antigen associated with liver cancer and prostrate cancer, etc.In this article, we demonstrate the fabrication and simultaneous fluorescent detection of two biomarkers related to lung cancer. Polystyrene microspheres (PSM) were introduced as biomolecular immobilizing carriers and a 96-well filter plate was used as the separation platform. The whole experiment could be effectively carried out in a homogeneous system, as exemplified by the detection of carcinoembryonic antigen (CEA) and neuron specific enolase (NSE). First, two capture antibodies for CEA and NSE were immobilized on the PSM surface. Next, they reacted successively with two antigens and two modified detection antibodies. Finally, these two biomarkers could be recognized by streptavidin-conjugated quantum dots (QD) and goat-anti-FITC conjugated QD with a detection limit of 0.625ngmL−1, which was lower than the clinical cut-off level. The protocol showed good precision within 6.36% and good recovery in the range of 90.86–105.02%. Compared with several other assay formats reported previously, our new technique is competitive or even better. Furthermore, the immunosensor was successfully illustrated in 20 serum samples. Overall, this new immunoassay offers a promising alternative for the detection of biomarkers related to cancer diseases, taking advantage of simplicity, specificity, sensitivity and cost-efficiency.
Keywords: Simultaneous detection; Two biomarkers; Polystyrene microspheres; Quantum dots; Cross-talk-free
Development and validation of a fast monoclonal based disequilibrium enzyme-linked immunosorbent assay for the detection of triphenylmethane dyes and their metabolites in fish by Michalina Oplatowska; Lisa Connolly; Paul Stevenson; Sara Stead; Christopher T. Elliott (pp. 51-60).
Display Omitted► Monoclonal antibody to triphenylmethane dyes was generated for the first time. ► The antibody was used for the development of a fast disequilibrium ELISA. ► The method was validated for the detection of a range of dyes in fish. ► The assay can be used for fish screening for the presence of Malachite Green and related compounds.Malachite Green (MG), Crystal Violet (CV) and Brilliant Green (BG) are antibacterial, antifungal and antiparasitic agents that have been used for treatment and prevention of diseases in fish. These dyes are metabolized into reduced leuco forms (LMG, LCV, LBG) that can be present in fish muscles for a long period. Due to the carcinogenic properties they are banned for use in fish for human consumption in many countries including the European Union and the United States. HPLC and LC–MS techniques are generally used for the detection of these compounds and their metabolites in fish. This study presents the development of a fast enzyme-linked immunosorbent assay (ELISA) method as an alternative for screening purposes. A first monoclonal cell line producing antibodies to MG was generated using a hybridoma technique. The antibody had good cross-reactivates with related chromatic forms of triphenylmethane dyes such as CV, BG, Methyl Green, Methyl Violet and Victoria Blue R. The monoclonal antibody (mAb) was used to develop a fast (20min) disequilibrium ELISA screening method for the detection of triphenylmethanes in fish. By introducing an oxidation step with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) during sample extraction the assay was also used to detect the presence of the reduced metabolites of triphenylmethanes. The detection capability of the assay was 1ngg−1 for MG, LMG, CV, LCV and BG which was below the minimum required performance limit (MRPL) for the detection method of total MG (sum of MG and LMG) set by the Commission Decision 2004/25/EC (2ngg−1). The mean recoveries for fish samples spiked at 0.5 MRPL and MRPL levels with MG and LMG were between 74.9 and 117.0% and inter- and intra-assay coefficients of variation between 4.7 and 25.7%. The validated method allows the analysis of a batch of 20 samples in two to three hours. Additionally, this procedure is substantially faster than other ELISA methods developed for MG/LMG thus far. The stable and efficient monoclonal cell line obtained is an unlimited source of sensitive and specific antibody to MG and other triphenylmethanes.
Keywords: Monoclonal antibody; Malachite Green; Crystal Violet; Brilliant Green; Fish; Enzyme-linked immunosorbent assay
Imprinted sol–gel electrochemical sensor for the determination of benzylpenicillin based on Fe3O4@SiO2/multi-walled carbon nanotubes-chitosans nanocomposite film modified carbon electrode by Yufang Hu; Jiaxing Li; Zhaohui Zhang; Huabin Zhang; Lijuan Luo; Shouzhuo Yao (pp. 61-68).
. A novel imprinted sol–gel electrochemical sensor based on Fe3O4@SiO2–MWNTs–CTS nanocomposite film and a thin MIP film has been developed on a carbon electrode.Display Omitted► A novel imprinted sol-gel electrochemical sensor based on Fe3O4@SiO2–MWNTs–CTS nanocomposites has been developed. ► Fe3O4@SiO2–MWNTs–CTS nanocomposites act as “electronic wires” to enhance the electron transfer. ► The inherent specificity of the MIPs brings about highly selectivity. The imprinted sensor detects benzylpenicillin in real samples successfully.Herein, a novel imprinted sol–gel electrochemical sensor based on multi-walled carbon nanotubes (MWNTs) doped with chitosan film on a carbon electrode has been developed. Prior to doped, the MWNTs have been decorated with Fe3O4 nanoparticles which have been coated uniformly with SiO2 layer. The characterization of imprinted sensor has been carried out by X-ray diffraction and scanning electron microscopy. The performance of the proposed imprinted sensor has been investigated using cyclic voltammetry and differential pulse voltammetry. The imprinted sensor offers a fast response and sensitive benzylpenicillin quantification. The fabricated benzylpenicillin imprinted sensor exhibits a linear response from 5.0×10−8 to 1.0×10−3molL−1 with a detection limit of 1.5×10−9molL−1. For samples analysis, perfect recoveries of the imprinted sensor for benzylpenicillin indicated that the imprinted sensor was able to detect benzylpenicillin in real samples successfully.
Keywords: Imprinted electrochemical sensor; Multi-walled carbon nanotubes; Fe; 3; O; 4; nanoparticles; Benzylpenicillin
High temperature liquid chromatography hyphenated with ESI-MS and ICP-MS detection for the structural characterization and quantification of halogen containing drug metabolites by Jon S.B. de Vlieger; Mark J.N. Giezen; David Falck; Cornelis Tump; Fred van Heuveln; Martin Giera; Jeroen Kool; Henk Lingeman; Jaap Wieling; Maarten Honing; Hubertus Irth; Wilfried M.A. Niessen (pp. 69-76).
Display Omitted► Hyphenation of high temperature liquid chromatography to ICP-MS and ESI-MS. ► Structural characterization of kinase inhibitor metabolites with high resolution MS n experiments. ► Quantification of drug metabolites with ICP-MS based on Iodine detection. ► Significant changes in ESI-MS response after small structural changes.In this paper we describe the hyphenation of high temperature liquid chromatography with ICP-MS and ESI-MS for the characterization of halogen containing drug metabolites. The use of temperature gradients up to 200°C enabled the separation of metabolites with low organic modifier content. This specific property allowed the use of detection methods that suffer from (significant) changes in analyte response factors as a function of the organic modifier content such as ICP-MS. Metabolites of two kinase inhibitors (SB-203580-Iodo and MAPK inhibitor VIII) produced by bacterial cytochrome P450 BM3 mutants and human liver microsomes were identified based on high resolution MS n data. Quantification was done using their normalized and elemental specific response in the ICP-MS. The importance of these kinds of quantification strategies is stressed by the observation that the difference of the position of one oxygen atom in a structure can greatly affect its response in ESI-MS and UV detection.
Keywords: High temperature liquid chromatography; Kinase inhibitors; ESI-MS; ICP-MS; Drug metabolism; Hyphenation
Characterization of drug-lysozyme conjugates by sheathless capillary electrophoresis–time-of-flight mass spectrometry by R. Haselberg; S. Harmsen; M.E.M. Dolman; G.J. de Jong; R.J. Kok; G.W. Somsen (pp. 77-83).
Display Omitted► We use sheathless CE–TOF-MS to characterize drug-protein conjugates. ► Sheathless interfacing allows detection of the conjugates in the nM-range. ► Efficient CE separation of highly related conjugate products is obtained. ► TOF-MS permits reliable assignment of separated compounds. ► CE–MS allows determination drug loading values and drug-protein stoichiometry.Drug-protein conjugates have been widely used for the cell-specific targeting of drugs to cells that can bind and internalize the proteinaceous carrier. For renal drug targeting, lysozyme (LZM) can be used as an effective carrier that accumulates in proximal tubular cells. We used capillary electrophoresis–time-of-flight mass spectrometry (CE–TOF-MS) for the characterization of different drug-LZM conjugates. A recently developed prototype porous tip sprayer was employed for sheathless electrospray ionization (ESI) CE–MS interfacing. In order to prevent adsorption of LZM conjugates to the capillary wall, a positively charged polyethylenimine capillary coating was used in combination with a low-pH background electrolyte. Drug-LZM products had been prepared by first coupling BOC-l-methionine hydroxysuccinimide ester (BOCmet) to lysine residues of LZM followed by conjugation with the kinase inhibitors LY364947, erlotinib, or Y27632 via a platinum(II)-based linker. CE–TOF-MS of each preparation showed narrow symmetrical peaks for the various reaction products demonstrating that drug-LZM conjugates remained stable during the CE analysis and subsequent ESI. Components observed in the drug-LZM products were assigned based on their relative migration times and on molecular mass as obtained by TOF-MS. The TOF-MS data obtained for the individual components revealed that the preparations contained LZM carrying one or two drug molecules, next to unmodified and BOCmet-modified LZM. Based on relative peak areas (assuming an equimolar response for each component) a quantitative conjugate profile could be derived for every preparation leading to drug loading values of 0.4–0.6mol drug per mole protein.
Keywords: Abbreviations; BGE; background electrolyte; BOCmet; BOC-; l; -methionine; BPE; base-peak electropherogram; CE; capillary electrophoresis; EIE; extracted-ion electropherogram; ESI; electrospray ionization; LC; liquic chromatography; LZM; lysozyme; MS; mass spectrometry; TOF; time-of-flightCapillary electrophoresis; Electrospray ionization; Mass spectrometry; Drug-protein conjugates; Sheathless interfacing
Erratum to “Micro near infrared spectroscopy (MicroNIRS) based on on-line enrichment: Determination of trace copper in water using glycidyl methacrylate-based monolithic material” [Anal. Chim. Acta 670 (2010) 39–43]
by Guiping Chen; Yuan Mei; Wei Tao; Cheng Zhang; Huirong Tang; Jibran Iqbal; Yiping Du (pp. 84-84).