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Analytica Chimica Acta (v.551, #1-2)
Chiral separation of dansyl amino acids by PDMS microchip gel monolithic column electrochromatography with γ-cyclodextrin bonded in polyacrylamide by Hu-Lie Zeng; Hai-Fang Li; Jin-Ming Lin (pp. 1-8).
A polydimethylsiloxane (PDMS) microchip polyacrylamide (PAA) gel monolithic column for electrochromatography was prepared. A chiral recognizable molecule, γ-cyclodextrin (γ-CD) was immobilized firmly in the PAA gel in the microchannel through chemical bond. The PDMS microchannel was pretreated with 3-(trimethoxysilyl)-propyl methacrylate (Bind-Silane) before bonding PAA monolithic column, which was an anchor molecule to connect the PAA gel with PDMS inner wall in microchannel. The experiments demonstrated γ-CD was a perfect chiral selector for fluorescein isoihiocyanate (FITC) labeled dansyl amino acids (Dns-AAs), which showed well capability for chiral recognization in monolithic column electrochromatography. The mixture of two pairs of FITC-labeled Dns-AAs was separated absolutely in this new-style PDMS-based microfluidic device monolithic column within 100s in 36mm effective separation length, and the resolutions of the two pairs of optical isomers could reach 2.53 and 1.12, respectively. The condition of preparation PAA gel monolithic column for chiral separation was optimized by adjusting the concentration of allyl-γ-CD. The stability, transferring heat and optical characteristic of PDMS-based microfluidic device monolithic column were examined, respectively.
Keywords: PDMS microfluidic device; Monolithic column electrochromatography; γ-CD; Chiral separation; FITC-labeled Dns-amino acid
Development of a microfabricated impinger for on-chip gas phase sampling by Christopher A. Tipple; Matt Smith; Greg E. Collins (pp. 9-14).
The design and development of a glass fabricated microimpinger for gas phase sampling of hydrogen cyanide is described. Using standard glass microfabrication techniques, a microimpinger consisting of a gas sample inlet, gas delivery arms, and an extraction reservoir was used to extract dilute hydrogen cyanide vapor from a gas delivery system using a basic aqueous trapping buffer. A Teflon membrane was utilized for containing the liquid sample in the extraction reservoir. Extraction efficiency for sampling hydrogen cyanide was monitored by forming a fluorescent cyanide isoindole in the reaction of cyanide with naphthalene-2,3-dicarboxaldehyde and taurine. Experiments using a flow of 2mLmin−1 and a sampling time of 1min were used to measure cyanide vapors as low as 1.9mgm−3, with a calculated limit of detection of 0.486mgm−3. The effects of the vacuum flow rate and sampling time were also investigated.
Keywords: Impinger; Microchip; Hydrogen cyanide; Sampling
Equivalent circuit model and impedance analysis for the fine response characteristics to liquid viscodensity for a piezoelectric quartz crystal sensor with longitudinal wave effect by Dazhong Shen; Qi Kang; Minghui Huang; Haiting Zhang; Mengsu Yang (pp. 15-22).
In this work, the resonance behavior of a piezoelectric quartz crystal (PQC) operating in the thickness-shear model to solution viscodensity was investigated using the electroacoustic impedance analysis method. It was shown that a slight variation in liquid density caused unexpected large impedance responses of the PQC. The fine structures of the responses of the resonant frequency shift (Δ fS) and motional resistance ( Rm) as a function of the density ( Ï?) and viscosity ( η) of the liquid deviated from the linear relationships of Δ fS versus ( Ï?η)1/2 and Rm versus ( Ï?η)1/2. Detail analysis of the correlation between Δ fS and Rm versus ( Ï?η)1/2 showed periodic waveforms, revealing the presence of longitudinal wave. The properties of the longitudinal wave could be integrated with the thickness shear wave with a modified BVD equivalent circuit model. The validity of the equivalent circuit was supported by the experimental observations, and the fitting of experimental data with the equivalent circuit simulation was further improved with the consideration of the second and third harmonics of the longitudinal waves. While the longitudinal wave effect has been regarded as a source of error in the PQC measurements, our study demonstrated that it is possible to control the periodicity and intensity of the longitudinal wave and to generate additional information on the solution properties utilizing the longitudinal wave effect.
Keywords: Quartz crystal; Piezoelectric sensor; Liquid viscodensity; Longitudinal wave
Electrochemical biosensing of DNA with capture probe covalently immobilized onto glassy carbon surface by Huey Fang Teh; Haiqing Gong; Xian-Dui Dong; Xianting Zeng; Annie Lai Kuan Tan; Xinhao Yang; Swee Ngin Tan (pp. 23-29).
In this study, an electrochemical DNA biosensor was developed based on the recognition of target DNA by hybridization detection with immobilized capture synthesized 21-mer single-stranded deoxyribonucleic acid (ssDNA) capture probe on a chemically modified glassy carbon electrode (GCE). The capture probe was covalently attached through free amines on the DNA bases using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydrosulfosuccinimide (NHS) cross-linking reaction on a carboxylate-terminated 4-aminobenzoic acid (4-ABA) monolayer modified GCE. The covalent immobilized capture probe could selectively hybridize with its target DNA to form double-stranded DNA (dsDNA) on GCE surface. The aim of this work is to provide a well defined recognition interface for the detection of DNA. Square wave voltammetry (SWV) was used to monitor the hybridization reaction on the capture probe electrode. The decrease of the peak current of methylene blue (MB), an electroactive indicator, was observed upon hybridization of the probe with the target DNA. The peak current of MB was found to increase in the following order: hybrid-modified GCE, mismatch hybrid-modified GCE, non-complementary modified GCE. There is decrease of the reduction current of MB intercalator with increasing concentration of target DNA with the capture probe. Fabrication reproducibility for 3 independently made electrode was ca. 9.7%, measured at 10ng/μl of target DNA. The detection limit of the DNA biosensor was ca. 0.5ng/μl for target DNA.
Keywords: DNA; Covalent immobilization; GCE
Long-lived solid state perchlorate ion selective sensor based on doped poly(3,4-ethylenedioxythiophene) (PEDOT) films by Tatyana A. Bendikov; Thomas C. Harmon (pp. 30-36).
This work describes the development and fabrication of stable potentiometric solid state sensors for the perchlorate ion (ClO4−) based on doped poly(3,4-ethylenedioxythiophene) (PEDOT) films. PEDOT, one of the most promising conducting polymers, is extremely stable in its oxidized state. Using PEDOT(ClO4−) films as sensing material in ion selective electrodes presents a unique opportunity to create sensors having a longer lifetime compared to analogous sensors, such as those created using doped polypyrrole. Over the 8 month period of this study, the PEDOT(ClO4−) sensors exhibited a stable, linear response spanning at least five orders of magnitude in concentration (1M to 1×10−5M perchlorate) with near-Nernstian slopes approaching −59mV/decade of ClO4− concentration and a limit of detection of 5×10−6M. Carbon fibers and pencil leads were employed as alternative and inexpensive substrates for EDOT polymerization, addressing problems with the sensor's form (miniature size, flexibility) and cost.
Keywords: Perchlorate solid state sensor; PEDOT; Potentiometry; Carbon fibers; Pencil leads
Zirconium(IV)-salophens as fluoride-selective ionophores in polymeric membrane electrodes by Å?ukasz Górski; Agnieszka Saniewska; PaweÅ‚ Parzuchowski; Mark E. Meyerhoff; Elżbieta Malinowska (pp. 37-44).
The feasibility of using Zr(IV)-salophens as ionophores to prepare anion-selective polymeric membrane electrodes is examined. It is shown that electrodes formulated with these compounds exhibit greatly enhanced selectivity towards fluoride anion (as compared to a classical quaternary ammonium anion-exchanger) when introduced into plasticized PVC films containing lipophilic anionic site additives. Electrodes constructed with optimal membrane compositions exhibit the following selectivity pattern: F−>ClO4−>SCN−>NO3−>Br−>Cl−. For these electrodes, near-Nernstian and rapid potentiometric fluoride responses are observed. It is shown that the optimal response to fluoride occurs when the sample solution is buffered in the range of pH 4.5–6.0. At present, the response lifetime of the proposed electrodes is limited to 14 days due to fast deterioration of fluoride response with time. This phenomenon is ascribed to the decomposition of the ionophore within the polymeric membrane phase of the electrode in contact with the aqueous test solution.
Keywords: Fluoride-selective sensors; Zr(IV)-salophens; Potentiometry
Rubeanic acid as novel carrier in construction of selective membrane sensor for La(III) by A.K. Jain; A.K. Singh; Sameena Mehtab; Puja Saxena (pp. 45-50).
A new polyvinylchloride-based membrane of rubeanic acid as an ion carrier was fabricated using oleic acid as lipophilic additive. The best performance was exhibited by the membrane having composition rubeanic acid:PVC:OA: o-NPOE as 5:180:18:208 (w/w). The sensor exhibited a Nernstian response for La3+ over a wide concentration range of 3.2×10−8 to 1.0×10−2M with a detection limit of 2.5×10−8M. It showed response time of less than 15s and could be used for 5 months without any significant divergence. The proposed membrane sensor revealed good selectivity for La3+ over a wide variety of other metal ions and can be used in a pH range of 3.5–9.5 and in mixtures containing up to 30% (v/v) non-aqueous content. It was successfully used as an indicator electrode in the potentiometric titration of La(III) against EDTA.
Keywords: Rubeanic acid; La(III)-selective electrode; Membrane sensor; Potentiometry
Glucose oxidase-β-galactosidase hybrid biosensor based on glassy carbon electrode modified with mercury for lactose determination by Tüge Göktuğ; Mustafa Kemal Sezgintürk; Erhan Dinçkaya (pp. 51-56).
An amperometric biosensor prepared by immobilization of β-galactosidase and glucose oxidase (GOD) onto a glassy carbon electrode coated with mercury thin film for lactose has been developed. The enzymes were immobilized by gelatin and glutaraldehyde onto mercury thin film electrode easily. The chronoamperometric detection of lactose was carried out at −0.2V (versus Ag/AgCl) in 0.05M citrate buffer (pH 5.5). Optimum pH and temperature, and thermal stability were investigated. Interference effects of some sugars and repeatability of the biosensor were also studied. The response to lactose was found to be linear range between 1×10−4 and 3.5×10−3M. The biosensor was applied to the determination of lactose in milk samples and the results obtained with the biosensor were validated by Somogyi–Nelson method.
Keywords: Lactose; Mercury thin film electrodes; Hybrid biosensors; Chronoamperometry
Development of disk ultramicroelectrodes based on low melting or softening point metal fibers by low temperature plasma enhanced chemical vapor deposition by Mingzhi Zhu; Zhuangde Jiang; Weixuan Jing (pp. 57-64).
A procedure of insulating the low melting or softening point metal fibers for preparing disk ultramicroelectrodes (UMEs) is presented that employs low temperature plasma enhanced chemical vapor deposition (PECVD) technique. Specially, the development of Au disk UME is described. The 25μm diameter Au fibers are concentrically coated by PECVD with an insulating layer of silicon nitride thin film that is performed with lower PECVD electrode temperature of 340±10°C. The silicon nitride thin films are found to be free of microcracks and characterized with excellent adhesion at the silicon nitride thin film–Au interfaces by scanning electron microscopy measurements. The corrosion resistance is investigated on exposure to the normal saline that indicates the fabricated disk UMEs can be used as the disposable basal electrodes. Prior to the electrochemical experiments the surgical scissors are used to produce tip surfaces. The electrochemical responses are sigmoidal in shape at different scan rates and indicate that the fabricated disk electrodes exhibit electrochemical response of UMEs. The data of cyclic voltammetry show that the diffusion-limited steady-state current of the electrode tip produced by the surgical scissors is too large for a 25μm diameter disk electrode, so a polishing machine should be specifically developed to produce the electrode active surface for the quantitative analyses of disk UMEs with small overall size based on PECVD technique.
Keywords: Disk ultramicroelectrodes; Low temperature PECVD; Silicon nitride thin films; Au fibers
Pseudopolarography of lead (II) in sediment and in interstitial water measured with a solid microelectrode by Ivanka Pižeta; Gabriel Billon; Dario Omanović; Vlado Cuculić; Cédric Garnier; Jean-Claude Fischer (pp. 65-72).
Pseudopolarograms of lead (II) constructed from the voltammograms measured in situ in the sediment and in the interstitial water by using an Ir solid microelectrode with a thin mercury film have shown as a kind of fingerprints of the sample. Despite shortcomings when compared to measurements with the mercury drop electrode and in model solutions, the measurement procedure was adapted for enough signal repeatability, avoiding to a reasonable extent the memory effect and electrode surface blocking. To make the best use of the information available, besides the classical pseudopolarograms, i.e. besides the dependence of the peak-height on the deposition potential, it is necessary to analyze the peak-area, the peak-position and the half-peak width versus deposition potential, and combine them with the knowledge from various theoretical and model situations. They have shown to contain interesting information about speciation. This information is not always unambiguous, it is often semi-quantitative, and cannot be reached by other methods, however, in combination with other methods it could be useful for the characterization of the sample solution. Pseudopolarograms of lead (II) in different liquid fractions of the sediment were measured and compared, the electrode sensitivity varying from 4 to 20nA/μmolL−1 of lead (II). The differences in half-wave potentials recorded were ranging up to 0.6V and those in the slopes of pseudopolarograms were three-fold, having interesting relationships with the peak potentials of single voltammetric curves.
Keywords: Pseudopolarography; Ir solid microelectrode; Sediment; Interstitial water; Speciation; Lead (II)
Homogeneous assay based on low quantum yield Sm(III)-donor and anti-Stokes’ shift time-resolved fluorescence resonance energy-transfer measurement by Ville Laitala; Ilkka Hemmilä (pp. 73-78).
Non-overlapping fluorescence resonance energy-transfer (nFRET) is a highly sensitive, time-resolved, assay technology. It utilizes lanthanide chelates as donors together with non-overlapping acceptor fluorophores, which have their absorption maximum energetically at a higher level than the emittive transitions of the donor. In this report the nFRET was studied using a low quantum yield Sm(III)-chelate as the donor in a homogeneous dF508-DNA hybridization assay. Despite the low quantum yield, Sm(III) could function as an efficient donor in nFRET, which resulted in strong energy-transfer induced acceptor emission in the assay. Further, the induced acceptor emission of the assay showed non-Förster-type decay characteristics and allowed the sensitive anti-Stokes’ shift FRET measurement, in which the induced acceptor emission was measured at a wavelength region shorter than the main emittive transitions of the donor. The detection limit for the dF508 DNA-target was 12.0pM (S/B=2). The assay sensitivity was surprisingly similar with the corresponding Eu-based nFRET-assay, despite the approximately 90-fold lower quantum yield of the Sm-donor. The results confirm the exceptional properties of the nFRET induced acceptor signal and support the theory of energy-transfer taking place from the excited energy levels above the emittive energy level of the lanthanide donor. We conclude that nFRET-technique is well suited for highly sensitive DNA assays and that the assay sensitivity is not limited by the emittive quantum yield of the donor.
Keywords: FRET; Energy-transfer; Lanthanide; Time-resolved; Anti-Stokes’; Homogeneous
Study on the enhancement of electrochemiluminescence of luminol–H2O2 system by sulphonated cobalt(II) phthalocyanine by Yingying Su; Jian Wang; Guonan Chen (pp. 79-84).
The main aim of this paper is to explore a new label for electrochemiluminescence (ECL) bioassays. Tetra-substituted sulphonated cobalt(II) (CoTSPc) acting as a mimetic peroxidase of horseradish peroxidase was first found to be able to catalyze the ECL reaction of luminol–H2O2 at a glass carbon electrode. CoTSPc also retained its ECL catalytic activity when it was conjugated to BSA. Moreover, the enhanced ECL intensity of the luminol–H2O2 system at pH 7.4 was proportional to the amount of target bovine serum albumin (BSA). The spectrum characteristics of CoTSPc–BSA conjugate was examined. The effects of the pH, reaction medium of the solution, the concentration of luminal, H2O2 and the electrochemical scanning mode were also investigated. Although refinements in the technique are still necessary before it can be used in practice, a new ECL probe for protein, CoTSPc, has been preliminarily developed.
Keywords: Electrochemiluminesence; Tetra-substituted sulphonated cobalt(II) phthalocyanine; Bovine serum albumin
Development of chemiluminescence detection of gold nanoparticles in biological conjugates for immunoassay by Zheng-Ping Li; Yu-Cong Wang; Cheng-Hui Liu; Yan-Kun Li (pp. 85-91).
By using human immunoglobulin G (IgG), goat-anti-human IgG and rabbit-anti-goat IgG-functionalized gold nanoparticles as an immunoassay model, a chemiluminescence (CL) detection of gold nanoparticles in biological conjugates has been developed. The assay is based on the sandwich-type immunoreaction coupled with CL reaction of AuCl4−–luminol–H2O2 system. The AuCl4−, which is the dissolving product of the gold nanoparticles labeled to the rabbit-anti-goat IgG, served as an analyte in the CL reaction for the indirect measurement of goat-anti-human IgG. The chemiluminescence intensity is proportional to the logarithm of the concentration of goat-anti-human IgG in the range of 5ngml−1 to 10μgml−1 and the detection limit (3 σ) is 1.5ngml−1. This method has been successfully applied to the determination of goat-anti-human IgG immune serum samples. As a new chemiluminescence detection method, it shows significant potential for the determination of biological analytes by labeling nanoparticles.
Keywords: Chemiluminescence; Immunoassay; Gold nanoparticle; Sandwich-type immunoreaction
Direct sub-ppt detection of the endocrine disruptor ethinylestradiol in water with a chemiluminescence enzyme-linked immunosorbent assay by Christian Schneider; Heinz F. Schöler; Rudolf J. Schneider (pp. 92-97).
A chemiluminescence ELISA for the direct detection of ethinylestradiol (EE2) in water at sub-ppt levels was developed and validated. At a signal-to-noise ratio of three the detection limit is 0.2±0.1ngL−1, at a ratio of 10 the LOQ is found to be 1.4±0.8ngL−1. Based on a conservatively calculated precision profile the analytical working range is established from 0.8 to 100ngL−1. The ELISA was tested in four different matrices, including surface water and effluent of sewage treatment plants. All measurements were validated using an LC–MS/MS method. Typical results were consistent in both methods below 1ngL−1. Using this chemiluminescence ELISA facilitates for the first time the direct detection of EE2 at ecotoxicologically relevant concentrations.
Keywords: Abbreviations; PBS; phosphate buffered saline; TBS; tris buffered saline; ELISA; enzyme-linked immunosorbent assay; CLEIA; chemiluminescence enzyme immunoassay; CMO; carboxymethyloxime; EE2; 17α-ethinylestradiol; POD; horseradish peroxidase; STP; sewage treatment plant; CV; coefficient of variation; LOD; limit of detectionChemiluminescence; ELISA; Ethinylestradiol; Sub-ppt concentrations; Direct measurement; Optimization
Acousto-optic tunable filter-surface plasmon resonance immunosensor for fibronectin by Yuan Tian; Yanhua Chen; Daqian Song; Xia Liu; Shuyun Bi; Xin Zhou; Yanbo Cao; Hanqi Zhang (pp. 98-104).
An acousto-optic tunable filter-surface plasmon resonance (AOTF-SPR) immunosensor based on wavelength-modulation was applied to detect fibronectin by direct, sandwich and colloidal Au-enhanced immunoassay. The design of the wavelength-modulation AOTF-SPR immunosensor is based on fixing the incident angle of light and measuring the reflected intensity of light in the wavelength range spanning 440–790nm. Fibronectin was determined in the concentration range 2.5–30, 0.5–30, and 0.25–30μg/mL for direct, sandwich and colloidal Au-enhanced immunoassay, respectively. The results demonstrate that AOTF-SPR biosensor can be applied to direct and enhanced immunoassay of biomolecule.
Keywords: AOTF; SPR; Immunosensor; Enhanced immunoassay; Fibronectin
Monoclonal antibody-based competitive assay for the sensitive detection of coeliac disease toxic prolamins by M.C. Bermudo Redondo; P.B. Griffin; M. Garzon Ransanz; H.J. Ellis; P.J. Ciclitira; C.K. O'Sullivan (pp. 105-114).
Current immunosorbent assays for gluten detection suffer from a number of drawbacks including lack of specificity (e.g. cross-reaction with coeliac disease non-toxic prolamins, detection of total gluten and not specifically coeliac disease toxic gluten) and an inability to detect quantitatively hydrolysates and prolamins present in rye, barley and, possibly, oats. Additionally, the extraction methods employed involve the use of strong reducing agents that are not compatible with enzyme-linked immunosorbent assay. This work reports on the development of a novel competition assay based on the use of a monoclonal antibody raised against a 19-mer peptide recognised in vivo to be coeliac disease toxic. This assay is specific to those cereal prolamins that exacerbate coeliac disease, is capable of the detection of hydrolysate forms and is compatible with typical extraction agents. The optimal assay format is highly sensitive with a detection limit of 0.128ppm and good reproducibility is obtained with intra-plate and inter-plate relative standard deviation of 3.21% ( n=6) and 3.57% ( n=3) being obtained, respectively. The reported system is the first of several systems under development that aim to address the drawbacks that current assays suffer and meet the sensitivity requirements outlined by the World Health Organisation and Codex Alimentarius.
Keywords: Abbreviations; ELISA; enzyme-linked immunosorbent assay; CD; coeliac disease; PWG; Prolamin Working Group; ALP; alkaline phosphatase; p; NPP; p; -nitrophenyl phosphate; HRP; horse radish peroxidase; TMB; tetramethyl benzidine; SATA; N; -succinimidyl-; S; -acetylthioacetate; PBS; phosphate buffered saline; BSA; bovine serum albumin; R.S.D.; relative standard deviation; HMW; high molecular weight; LMW; low molecular weight; DTT; dithiothreitol; WHO/FAO; World Health Organisation/Food and Agriculture Organisation; MAb; monoclonal antibody; SDS-PAGE; sodium dodecyl sulphate polyacrylamide gel electrophoresisCoeliac disease; Prolamin; Competitive ELISA; In vivo toxicity
Design and preparation of novel antibody system and application for the determination of heroin metabolites in urine by capillary electrophoresis by Xiao-Hua Qi; Jian-Qiu Mi; Xin-Xiang Zhang; Wen-Bao Chang (pp. 115-123).
A novel multi-target antibody to morphine and derivatives was induced by designed morphine-3-site substituted and the polyclonal antibody was prepared with immunizing rabbits. A simple, specific and accurate method for the determination of morphine and related compounds, codeine, acetylcodeine, 6-monoacetylmorphine and morphine-3-glucuronide in urine of heroin abusers, has been developed using the multi-target immunoaffinity column (IAC) prior to capillary electrophoresis separation. The analytes were extracted from the urine of drug addicts with the column, which was made by coupling CNBr-activated Sepharose 4B and multi-target polyclonal antibodies. The analytes of interest were extracted with a methanol/water mixture in one step. Baseline separation of these analogs was achieved by CE using β-cyclodextrin as additive and they were monitored at 214nm. The assay presented very good reproducibility and precision with the recovery and detection limit between 91–105% and 10–20ng/mL based on S/N=2, respectively. The inter-day and intra-day variation, capacity and elution conditions of the immunoaffinity column were also discussed. The metabolites in five heroin addicts’ urine were measured by the present method. The experimental results indicated that the combination of IAC and CE was a useful technique for determination of heroin metabolites from urine samples.
Keywords: Multi-target; Antibody; Immunoaffinity column (IAC); Heroin; Metabolites; Capillary electrophoresis (CE)
Fast screening of total flavonols in wines, tea-infusions and tomato juice by flow injection/adsorptive stripping voltammetry by George J. Volikakis; Constantinos E. Efstathiou (pp. 124-131).
A novel approach for a fast screening of total flavonols (quercetin, kaempferol, myricetin) in wines, tea-infusions and tomato juice using adsorptive stripping voltammetry in a flow injection system is described. The proposed method is based on the property of flavonols to be pre-concentrated on carbon paste electrodes where diphenylether is used as the pasting liquid. The samples are subjected to an acid hydrolysis step and 1mL sample of the diluted hydrolysate is injected in the flow injection apparatus. After 2min pre-concentration period (under reciprocated flow) the electrode is washed with Britton–Robinson buffer, pH 5 solution and an anodic voltammetric scan is applied to produce an anodic current peak (analytical signal). The lower determination limits for kaempferol, quercetin and myricetin in pure aqueous solutions were 20, 9 and 25μgL−1. Mixtures of flavonols resulted into a single anodic peak, which can be used for the calculation of the total flavonols concentration expressed in terms of “quercetin equivalent�. The measurement throughput was about 13h−1 and the overall reproducibility of measurements was 3–6%. The total concentration of quercetin equivalent in eight tested samples was found in the range 3–60mgL−1 and the results compare favorably with those obtained by an LC procedure.
Keywords: Flavonols; Adsorptive stripping voltammetry; Carbon paste electrode; Flow injection analysis
A contactless conductivity detection cell for flow injection analysis: Determination of total inorganic carbon by Zuzana HoherÄ?áková; FrantiÅ¡ek Opekar (pp. 132-136).
New, very simple cells for contactless conductivity detection have been designed and tested in flow injection analysis. The cells consist of two insulated wire electrodes placed inside a PTFE tubing at a close mutual distance and oriented either across the tube or along the tube axis; the detection takes place within the space limited by the two electrodes. The electrodes are insulated by a 5μm thick film of a polyimide (the dielectric). The electrodes with thin film of dielectric represent capacitors with higher capacitance which allows a higher ac current to flow between the electrodes, as compared to contactless conductivity cells used, e.g., in capillary electrophoresis, and the measuring sensitivity is thus enhanced. The cells were tested on the determination of total inorganic carbon in model water samples by the flow injection analysis combined with a gas diffusion separation. A concentration range from 0.01 to 1mmoll−1 NaHCO3 was tested with a linear dynamic range of up to 0.1mmoll−1. Detection limits of 0.6 and 6μmoll−1 with RSD values of 4.1 and 4% were obtained for detectors with the electrodes placed axially and across the tube, respectively. A throughput of 15 samples per hour was attained under an experimental procedure used. The analytical parameters were compared with those obtained using a contactless conductivity cell with tubular electrodes placed outside the PTFE tubing.
Keywords: Contactless conductivity detector; Insulated wire electrodes; Gas-diffusion separation; Flow injection analysis; Total inorganic carbon
Serum protein profiling using surfactant-aided matrix-assisted laser desorption/ionization mass spectrometry by Rama Tummala; Patrick A. Limbach (pp. 137-141).
It has been shown previously that sodium dodecyl sulfate (SDS) can be used at its critical micellar concentration to increase the number of peptides detected in a peptide mixture by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Here we demonstrate that, in a similar fashion, preparation of peptides and low molecular weight proteins from serum using SDS micelles improves the information content in MALDI-MS. In particular, the addition of SDS yielded a 30% increase in the number and a 50% increase in the abundance of low molecular weight (<6000Da) analytes. C18 ziptips and C18 magnetic beads were used as pre-cleaning steps for comparative analysis and it was found that magnetic beads were more suitable for pre-cleaning prior to combining the eluent with SDS. The non-ionic surfactant n-octyl-β-d-glucopyrinoside yielded improved ion abundances of peptides with masses above 6000Da, although these increases are less dramatic than those found with SDS. These results demonstrate that surfactant-aided MALDI-MS can lead to an increase in the amount of information obtained from complex mixtures of peptides/proteins. Such improvements may prove advantageous for applications such as those focused on protein profiling.
Keywords: MALDI-TOF MS; SDS; Critical micelle concentration (CMC); Biomarkers; Proteomics; Protein profiling
Determination of phthalate esters in sewage by hemimicelles-based solid-phase extraction and liquid chromatography–mass spectrometry by Francisco José López-Jiménez; Soledad Rubio; Dolores Pérez-Bendito (pp. 142-149).
Hemimicelles-based solid-phase extraction was proposed for the concentration of high volume commodity phthalates from wastewater samples prior to their separation and quantitation by liquid chromatography/atmospheric pressure chemical ionization in positive mode, ion trap mass spectrometry. Di-(2-ethylhexyl) phthalate (DEHP), butyl benzyl phthalate (BBP) and di- n-butyl phthalate (DBP) were concentrated on hemimicelles of sodium dodecyl sulphate (SDS) produced on alumina on the basis of hydrophobic interactions. The recovery of the target compounds was found quantitative under a wide range of experimental conditions (15–255mgSDSg−1 alumina, pH 2–6 and sample loading volume up to 1L). Concentration factors of 2500 were achieved by SPE of 0.5L of sewage samples. The method detection limits found for BBP, DBP and DEHP were 7, 15 and 16pg, respectively. The relative standard deviation ranged from 2 to 5%, which indicated good method precision. The approach developed was applied to the determination of phthalates in raw and treated sewage samples.
Keywords: Phthalate esters; Sewage; Hemimicelles; Solid-phase extraction; Liquid chromatography; Mass spectrometry
Determination of acrylamide in infant cereal-based foods by isotope dilution liquid chromatography coupled with electrospray ionization tandem mass spectrometry by Yu Zhang; Jingjing Jiao; Yiping Ren; Xiaoqin Wu; Ying Zhang (pp. 150-158).
Isotope dilution liquid chromatography coupled with electrospray ionization tandem mass spectrometry (LC–MS/MS) was successfully applied to the quantification of acrylamide (2-propene-amide) in infant rice cereals (with nutrients) and other cereal-based foods (fastfood nutrient cake, teething cookie, hi-protein milk wheat and vegetable teething rusk). The method included defatting with petroleum ether, extraction with 2M aqueous solution of sodium chloride, further liquid–liquid extraction with ethyl acetate and clean-up by solid-phase extraction (SPE) with OASIS HLB 6cc cartridges. Acrylamide was detected with an Atlantis dC18 5μm; 210mm×1.5mm column using 10% methanol/0.1% formic acid in water as mobile phase. The analytical method in the present study was well validated and good results were obtained with respect to repeatability (R.S.D.<6.5%) and recovery (87–96%) which fulfilled the requirements defined by European Union (EU) legislation. The acrylamide levels in infant rice cereals and other cereal-based foods were 3.3–37.1μgkg−1 and 10.9–1568.9μgkg−1, respectively. This validated method might need to be modified under some special conditions. For instance, an additional deproteinating step should be operated during the sample treatment process as for the analysis of some protein-rich infant cereals.
Keywords: Infant cereal-based foods; Acrylamide; Liquid chromatography–tandem mass spectroscopy
Validation of LC–MS electrospray ionisation method for quantitation of haloperidol in human plasma and its application to bioequivalence study by Sonu Sundd Singh; Kuldeep Sharma (pp. 159-167).
In the present investigation, a new sensitive LC/MS electrospray ionisation mass spectrometric method has been developed for the quantitation of haloperidol—an antipsychotic drug, in human plasma. The method was developed with the objective of accurately measuring the concentration of haloperidol in the plasma of human subjects enrolled in the bioequivalence study of haloperidol (5mg) tablets of M/s. Cadila Health Care Ltd. India versus 5mg haloperidol tablets of Geneva Pharma USA. The sample purification and pre-concentration was performed by liquid–liquid extraction (LLE) using duloxetine as internal standard. The chromatographic separation was achieved using an isocratic mobile phase containing 1.0mM ammonium acetate pH 3.0 and acetonitrile (70:30, v/v) flowing through Xterra MS C18 100mm×2.1mm, 3.5μm analytical column, at a flow rate of 0.2ml/min. The lower limit of quantitation (LLOQ) of 70.0pg/ml was achieved using mass spectrometric detection in positive mode. The ion signals of m/ z 375.9 and 297.9 were measured for haloperidol and internal standard, respectively. An exhaustive pre-study method validation was performed in accordance with USFDA guidelines. The standard curves were linear in the concentration range of 70.0pg/ml to 14.0ng/ml with mean correlation coefficient of 0.998. The method was successfully applied to the bioequivalence study of haloperidol in healthy human male volunteers.
Keywords: Method validation; Bioequivalence; Haloperidol
Determination of sulfonamides in honey by liquid chromatography–tandem mass spectrometry by Thomas S. Thompson; Donald K. Noot (pp. 168-176).
A simple and rapid analytical method was developed for the determination of residues of seven sulfonamide antibiotics in honey. Sample preparation consisted of acid hydrolysis to release sugar-bound sulfonamides. After filtration, acidified honey solutions were injected directly into a liquid chromatograph–tandem mass spectrometer (LC–MS/MS) system. Using gradient elution programming, analyte extraction and sample cleanup were automated. A six-port valve system was utilized to divert eluent from the extraction column into the MS/MS after the bulk of the honey matrix had been selectively removed. Minimal contamination of the MS source chamber was observed even after the injection of over 600 honey samples. Using internal standard quantitation, excellent accuracy and good precision were obtained. The method detection limits for the sulfonamides studied were found to range from 0.5 to 2μgkg−1.
Keywords: Sulfonamides; Sulfathiazole; Honey; Residues; Liquid chromatograph–tandem mass spectrometer
Development of a rapid liquid chromatography tandem mass spectrometry method for the determination of lisinopril, applicable for a bioequivalence study, employing a 96-well format solid phase extraction protocol by Constantinos Kousoulos; Georgia Tsatsou; Yannis Dotsikas; Yannis L. Loukas (pp. 177-183).
A rapid liquid chromatography/tandem mass spectrometry (LC/MS-MS) method was developed for the determination of lisinopril in human plasma. Lisinopril and the internal standard enalaprilat (IS) were extracted from human plasma by semi-automated solid phase extraction (SPE) using a 96-well format extraction plate. Initially, a 1:1 plasma: acetonitrile (ACN) mixture was prepared and vortexed to achieve protein precipitation. After centrifugation, an aliquot of the supernatant water/ACN solvent mixture was evaporated. The residue was dissolved in a certain volume of a reconstitution solution, which was passed through the extraction plate and the eluent was analyzed by combined reversed phase liquid chromatography tandem mass spectrometry with positive ion electrospray ionization using multiple reactions monitoring (MRM). The method was proved to be sensitive and specific for both drugs and its statistical evaluation revealed excellent linearity for the range of concentrations 2.0–200.0ngmL−1 and very good accuracy, and inter- and intraday precisions. The proposed method enables the rapid and reliable determination of lisinopril in pharmacokinetic or bioequivalence studies after per os administration of 20mg tablet formulations of lisinopril and it was applied in such study from our laboratory.
Keywords: Lisinopril; Bioequivalence; 96-Well format tubes; Electrospray
A rapid method for determination and confirmation of the thyreostats in milk and urine by matrix solid-phase dispersion and gas chromatography–mass spectrometry by Qiong-Hui Zou; Yuan Liu; Meng-Xia Xie; Jie Han; Lei Zhang (pp. 184-191).
A rapid and simple method for determination and confirmation of the thyreostats in milk and urine has been developed. The samples were extracted and purified by matrix solid-phase dispersion (MSPD) with silica gel as the solid support, and the thyreostats including tapazole, 2-thiouracil, 6-methyl-2-thiouracil, 6-propyl-2-thiouracil and 6-phenyl-2-thiouracil have been separated and detected by gas chromatography–mass spectrometry in selected ion mode with dimethylthiouracil as internal standard after derivatization with pentafluorobenzylbromide and N-methyl- N-(trimethylsilyl)-trifluoroacetamide. The derivatization reaction was conducted in a strong basic condition, which can improve the derivatization yields of the thyreostats in the presence of the matrix. The relative abundances of the selected ions in the chromatograms of the derivatives were stable and consistent, and can be used for the confirmatory purpose. The average recoveries of the five thyreostatic compounds in milk and urine were above 70% in most cases with the relative standard deviations between 2.1 and 7.9%. The limit of detection was 0.0016μgg−1 for the thyreostats except for that of tapazole, which was 0.004μgg−1.
Keywords: Thyreostats; Matrix solid-phase dispersion; Gas chromatography–mass spectrometry; Milk; Urine
Determination of methylmercury and mercury(II) in a marine ecosystem using solid-phase microextraction gas chromatography-mass spectrometry by S. Mishra; R.M. Tripathi; S. Bhalke; V.K. Shukla; V.D. Puranik (pp. 192-198).
A solvent free solid-phase microextraction (SPME) method has been developed to determine methyl mercury and Hg(II) in sediment, seawater and biota samples from TTC area (Mumbai, India) using gas chromatograph-mass spectrometer (GC-MS). The analytical method consists of phenylation with Na[B(C6H5)4], simultaneous solid-phase microextraction of the derivatives, followed by a final GC-MS analysis. Experimental design methodology was used for optimization of important process parameter, like SPME fiber coating (nature and thickness), extraction time, extraction temperature, and pH. After extraction, the fiber is directly injected to the injector port of GC for desorption, separation and quantification. The absolute detection limits obtained for methylmercury and inorganic mercury were 0.02 and 0.05ng as Hg, respectively. Standard reference materials were analyzed for validation of the methodology. The total mercury content in different matrices was determined using hydride generation atomic adsorption spectrometry (HG-AAS).
Keywords: SPME; GC-MS; Mercury speciation; Methyl mercury; HG-AAS
The new concept of hyphenated analytical system: Simultaneous determination of inorganic arsenic(III), arsenic(V), selenium(IV) and selenium(VI) by high performance liquid chromatography–hydride generation–( fast sequential) atomic absorption spectrometry during single analysis by P. Niedzielski (pp. 199-206).
The paper presents a new conception of determination of inorganic speciation forms of arsenic: As(III) and As(V) as well selenium Se(IV) and Se(VI) by means of the high performance liquid chromatography hyphenated with a detection by the atomic absorption spectrometry with hydride generation (HPLC–HG–AAS). The application of optimization procedure conditions of chromatographic separation of arsenic and selenium speciation forms (using anion-exchange Supelco LC-SAX1 column and phosphate buffer at pH 5.40 as a mobile phase) as well as the use of the atomic absorption spectrometry as a detector, which enables work in fast sequential mode, allowed to develop original detection methodology of simultaneous determination of arsenic As(III), As(V) and selenium Se(IV) and Se(VI) speciation forms within a 220s single analysis. The obtained detection limits were 7.8ngmL−1 for As(III); 12.0ngmL−1 for As(V); 2.4ngmL−1 for Se(IV) and 18.6ngmL−1 for Se(VI) and precision 10.5%, 12.1%, 14.2% and 17.3%, respectively, for 100ngmL−1. The described method was used for ground water analysis.
Keywords: Speciation analysis; HPLC–HG–AAS; On-line pre-reduction; Arsenic; Selenium; Ground water
A rapid acid digestion method with ICP-MS detection for the determination of selenium in dry sediments by J. Pinho; J. Canário; R. Cesário; C. Vale (pp. 207-212).
Selenium (Se) is an essential element to organisms with the following peculiarity: at low concentrations anomalies are observed due to the specific biochemical changes, and at higher concentrations it becomes a toxic element. The interval of essential concentrations is in general very narrow. This dual Se behaviour has stimulated the development of numerous analytical methods for its determination in environmental and biological samples.The baseline concentration of Se in sediments is low (0.05μgg−1), meaning that very sensitive analytical methods with low detection limits are required. We developed a simple and rapid method based on a pre-treatment/digestion of dry sediment samples with aqua-regia and HCl and quantification by ICP-MS using82Se. Obtained and certified Se concentrations for international certified reference materials MESS-1, MESS-2, BCSS-1 and 1646a, showed no statistically differences ( α=0.05) between obtained and certified values. Low detection limits (approximately 0.03μgg−1), good repeatability (<1.5%) and recoveries (98–103%) made this method a useful tool for rapid selenium analyses in dry sediments. This method was applied to 50 surface sediments collected in the Tagus estuary giving a rapid image of the distribution of total selenium concentrations in the estuary.
Keywords: Selenium; Analytical method; Estuarine sediments; ICP-MS; Tagus estuary
An investigation on the cation-exchange and Lewis-base interactions of a n-octadecylphosphonic acid-modified magnesia–zirconia stationary phase by Hai-Bo He; Yu-Qi Feng; Shi-Lu Da; Zhong-Hua Wang (pp. 213-221).
The cation-exchange and Lewis-base interactions of a n-octadecylphosphonic acid-modified magnesia–zirconia (C18PZM) stationary phase have been studied in greater detail than previous studies, which are characterized by the chromatography of some basic drugs of high p Ka and some hard Lewis base analytes, respectively. The effect of mobile phase constituents such as pH, type of buffer and buffer concentration on the surface chemistry properties on C18PZM are elucidated. The results show that at an intermediate pH, the cation-exchange sites are due to both the chemisorbed phosphonate and the adsorbed buffer anion, i.e. acetate, at the hard Lewis acid sites on the C18PZM phase; at high pH, the cation-exchange interactions mainly result from the chemisorbed phosphonate rather than the inherent zirconol groups. The chromatography of the hard Lewis base analytes indicates that a strong Lewis acid–base interaction still exists on C18PZM even in the presence of Lewis base buffer (such as acetate or phosphate) in the mobile phase or a high-pH eluents is used. Moreover, the chemisorbed n-octadecylphosphonic acid (C18P) is found to slowly bleed out of the C18PZM column when exposed to a phosphate buffer. As expected, the resulting mobile-phase phosphate modified C18PZM column (p-C18PZM) exhibits significantly stronger cation-exchange interactions towards the test basic solutes than the “original� C18PZM column. And the p-C18PZM column demonstrates a tremendous improvement on the chromatography of the Lewis base analytes over the “original� C18PZM column. An approach designed to overcome the Lewis acid sites problem by attaching methylphosphonic acid (MPA) onto the C18PZM column, however, is not successful in improving the chromatography of the troublesome Lewis base solutes.
Keywords: n; -Octadecylphosphonic acid modification; Magnesia–zirconia; Cation-exchange and Lewis-base interactions
Kinetic spectrophotometric methods for determination of trimetazidine dihydrochloride by Ibrahim A. Darwish (pp. 222-231).
Four simple and sensitive kinetic spectrophotometric methods (I–IV) for the determination of trimetazidine dihydrochloride (TRMZ) have been developed. Method I was based on the oxidation of the drug with alkaline KMnO4 producing green manganate species. Method II was based on the formation of colored condensation product between TRMZ and 4-chloro-7-nitrobenzofurazan (NBD-Cl). Method III was based on reaction of TRMZ and with 1,2-naphthoquinone-4-sulphonic acid sodium salt (NQS) forming orange colored product. Method IV was based on the formation of a violet charge-transfer complex between trimetazidine base and p-chloranil ( pCL). These reactions were followed spectrophotometrically by measuring the rate of color development at 610, 475, 485 and 560nm for the reactions with KMnO4, NBD-Cl, NQS, and pCL, respectively. The variables affecting the reactions were carefully investigated and the conditions were optimized. The stoichiometries of the reactions were determined, and the reactions pathways were postulated. The initial rate and fixed time methods were utilized for constructing the calibration graphs for the determination of TRMZ concentration. The assays limits of detection were 0.2–2.5μgml−1. The analytical performance of the methods, in terms of accuracy and precision, were statistically validated; the results were satisfactory. The methods have been successfully applied to the determination of TRMZ in commercial pharmaceutical formulations. Statistical comparison of the results with the reference method showed excellent agreement and proved that no significant difference in the accuracy and precision.
Keywords: Trimetazidine; Initial rate method; Fixed time method; Kinetic spectrophotometry; Pharmaceutical analysis