Check out our New Publishers' Select for Free Articles

Analytical Methods (v.4, #5)

Front cover (pp. 1185-1185).

An automated method based on an optosensor included in a multisyringe flow injection system was developed for the determination of bromate in waters for human consumption. The optosensor was based on the formation of a colored radical cation after oxidation of chlorpromazine by bromate and its selective uptake in a mixed-mode cation exchanger sorbent (Discovery DSC-MCAX), placed on a flow-through spectrophotometric cell. In-line regeneration was attained by methanol + 5% (v/v) ammonia, fostering the application of the same sorbent portion up to 180 determinations. Parameters affecting the reaction development and uptake of the colored compound were studied and optimized, while in-line addition of sulfite (≥0.100 g L⁻¹) prevented interference from hypochlorite. The proposed methodology allowed the determination of bromate up to 50.0 μg L⁻¹, with 0.9 μg L⁻¹ as the limit of detection, meeting the requirements of current EU and USA legislation. Application to real drinking water samples was successful, with a mean recovery of 100.2 ± 2.8% for spiked levels of 5.0, 10.0 and 25.0 μg L⁻¹. Repeatability was good (RSD < 3.6%, n = 10) with a determination throughput of 8 h⁻¹, fostering the application to on-line control of water disinfection processes.

Inside front cover (pp. 1186-1186).

Mesoporous TiO2–graphene nanocomposites are fabricated in high yield via two successive steps: (1) hydrothermal hydrolysis of Ti(SO4)2 in an acidic suspension of graphene oxide to gain TiO2–graphene oxide nanocomposites; (2) UV-assisted photocatalytic reduction of graphene oxide to get the TiO2–graphene nanocomposites. The anatase TiO2 nanocrystals with a crystallite size of 10–20 nm are densely packed and supported on meshy graphene sheets with close interfacial contacts, which is confirmed by transmission electron microscopy (TEM) together with Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Although a low graphene loading (0–2 wt%) slightly influences the textural properties (including the crystallite size, specific surface areas, and pore volume etc.), the incorporation of graphene in TiO2–graphene nanocomposites greatly increases the adsorption capacity towards azo dyes such as MO and MB, which is possibly associated with their unique surface properties. Significantly, the incorporated graphene exerts combined effects on the adsorption and charge transfer dynamics in TiO2–graphene nanocomposites, which together endow them with good photocatalytic reactivity and tunable photocatalytic selectivity in decomposing MO and MB in aqueous solution.

Contents list (pp. 1187-1198).

Detection of unexpected contaminants in complex matrices such as food is fraught with challenges. Scientists undertaking targeted analysis will normally have sufficient time, well characterised methods at their disposal and adequate supplies of calibration standards and quality control materials. However, when faced with an unusual request, for example to rapidly detect compounds for which calibration standards are not readily available, a more generic approach may have to be used. Modern analytical approaches such as LC-UV-ToF have potential to undertake non-targeted analyses and an example is reported here in which selected mushroom toxins have been analysed and semi-quantitative measurements performed. A method was rapidly established for the detection and measurement of amatoxin and phallotoxin classes of oligo-peptide toxins in mushrooms using chromatography and time-of-flight (ToF) mass spectrometry and ultra-violet (UV)-semiquantitation techniques. Using authenticated mushrooms, a chromatographic profile for death cap mushrooms Amanita phalloides has been established and a consistent profile noted across five UK sampling sites. Representative specimens of A. muscaria, A. rubescens and A. citrina were found to be free of these specific 22 toxins (<ca. 1 mg kg⁻¹). We estimate that 80% of the mushroom toxicity is associated with the amatoxins and using our experimental data, we extrapolate that ingestion of a single A. phalloides mushroom could indeed prove fatal. The extraction and detection method can be used to determine the accidental or malicious adulteration of food with mushroom tissues containing, amatoxins and phallotoxins but the approach has wider applications for the detection of unexpected chemicals in complex matrices and in assessing their impact on food safety.

One-step facile synthesis of N-acetylglucosamine-functionalized gold nanoparticles for direct visual and light-scattering detection of lectin from wheat germ by Erqun Song; Jingrong Li; Hong Wei; Yang Song (pp. 1199-1201).

Here, we report the one-step synthesis of N-acetylglucosamine-functionalized gold nanoparticle (NAG–AuNP), which then served as a facile, economic, highly sensitive and selective sensor for the detection of lectin from wheat germ, based on colorimetric and resonance light scattering signals.

Mitochondrial-based voltammetric sensor for pesticides by Stephanie L. Maltzman; Shelley D. Minteer (pp. 1202-1206).

The mode of action of many pesticides is to inhibit electron transport chain complexes of the mitochondria of living cells. Therefore, this paper investigated whether mitochondrial modified electrodes could be utilized to electrochemically sense pesticides. This paper details the fabrication of a two electrode electrochemical cell utilizing a mitochondrial modified bioanode in pyruvate solution and an air-breathing platinum cathode. 2,4-Dichlorophenoxyacetic acid, atrazine, paraquat, parathion, and permethrin were studied as pesticides. Pesticide detection was performed by background subtracted linear scan voltammetry of the two-electrode mitochondrial biofuel cell before and after the addition of pesticide. Pesticides were shown to attenuate pyruvate bioelectrocatalysis for all pesticides studied. A concentration study was performed with atrazine and showed a sigmoidal inhibition response with concentration and the ability to detect concentrations at the EPA maximum contaminant level of 3 ppb.

On the stability of the silver/silver sulfate reference electrode by Matěj Velický; Kin Y. Tam; Robert A. W. Dryfe (pp. 1207-1211).

The preparation and application of a simple silver/silver sulfate reference electrode for an aqueous solution, which can be used as an alternative in chloride-free systems, is reported. The electrodes are prepared by galvanostatic oxidation of silver wire in sulfate solution: the potential stability with time is measured as a function of the current density and overall charge used in oxidation. The electrode potential is also measured in a wide concentration range of sulfate and chloride solutions and an explanation of the observed stability is presented. The range of optimal conditions, crucial for the correct electrode operation, is discussed.

Application of non-polar solvents to extractive electrospray ionization of 1-hydroxypyrene by Xue Li; Xiaowei Fang; Zhiqiang Yu; Guoying Sheng; Minghong Wu; Jiamo Fu; Feiyan Yan; Huanwen Chen (pp. 1212-1214).

Extractive electrospray ionization of 1-hydroxypyrene (1-OHP) is achieved by using non-polar solvents (e.g., benzene, toluene, xylene, pentane and hexane) as the primary ESI solvent. The extraction of 1-OHP from various polar sample solutions by a non-polar primary ESI solvent is identified and 1-OHP ionization efficiency strongly depends on the sample solution.

Direct labeling rolling circle amplification as a straightforward signal amplification technique for biodetection formats by Lena Linck; Edda Reiß; Frank Bier; Ute Resch-Genger (pp. 1215-1220).

Biodetection formats, such as DNA and antibody microarrays, are valuable tools in the life sciences, but for some applications, the detection limits are insufficient. A straightforward strategy to obtain signal amplification is the rolling circle amplification (RCA), an easy, isothermal, and enzymatic nucleic acid synthesis that has already been employed successfully to increase the signal yield for several single-analyte and multiplexing assays in conjunction with hybridization probes. Here, we systematically investigated the parameters responsible for the RCA driven signal amplification with fluorescent labels, such as the type of fluorophore chosen, labeling strategy, composition of reaction solution, and number of handling steps. In labeling strategies, post-synthetic labeling via a Cy3-hybridization probe was compared to the direct incorporation of fluorescent Cy3–dUTP and DY-555–dUTP into the nascent strand during synthesis. With our direct labeling protocol, the assay's runtime and handling steps could be reduced while the signal yield was increased. These features are very attractive for many detection formats but especially for point-of-care diagnostic kits that need to be simple enough to be performed by scientifically untrained personnel.

Proteinaceous binders identification in the works of art using ion-pairing free reversed-phase liquid chromatography coupled with tandem mass spectrometry by Bartłomiej Witkowski; Magdalena Biesaga; Tomasz Gierczak (pp. 1221-1228).

A simple, fast and reliable procedure for the proteinaceous binders identification in the works of art samples is presented. The procedure consisted of ammonia extraction in order to suppress pigment interferences, acidic hydrolysis and quantification of underivatized amino acids using reversed phase liquid chromatography coupled with electrospray tandem mass spectrometry (RP-LC–ESI-MS/MS). Fourteen underivatized amino acids were quantified without the addition of ion-pairing agents (IPA) using the multiple reaction monitoring (MRM) mode. The chromatographic separation was optimized by testing three C18 columns and three different eluent compositions. The optimal chromatographic resolution and the ionization efficiency were achieved with Symmetry C18 column and the eluent consisting of water with methanol. The amino acids composition of the proteins commonly found in the paint binding media, eggs, casein and animal glues, was determined. The procedure was tested using a set of naturally aged samples. Calculated detection and quantification limits indicated that the method is suitable for the analysis of protein binders in the paint micro-samples. Animal glues, casein and eggs were identified in the samples from 18^th and 19^th century paintings by Jacek Malczewski, while eggs and casein were detected in the mural painting samples from the 13^th century UNESCO-listed church of Yemrehanna Krestos. The LC/MS/MS based method of the protein binders identification described here can be used as an alternative for the approach based on the gas chromatography coupled with mass spectrometry (GC/MS).

Automated solid-phase spectrophotometric system for optosensing of bromate in drinking waters by Sara M. Oliveira; Hugo M. Oliveira; Marcela A. Segundo; António O. S. S. Rangel; José L. F. C. Lima; Víctor Cerdà (pp. 1229-1236).

Extensive grinding and pressurized extraction with water are key points for effective and species preserving extraction of arsenic from rice by Pradeep Alava; Tom Van de Wiele; Filip Tack; Gijs Du Laing (pp. 1237-1243).

An adequate sample preparation is an essential prerequisite for an accurate assessment of exposure to arsenic (As) upon consumption of contaminated rice. Firstly, a well-defined amount of As must be released from the matrix following sample extraction. Secondly, given the toxicological importance of As species, the sample extraction procedure must preserve As speciation. We evaluated the effectiveness of closed and open microwave digestion procedures to extract As from a certified reference sample of rice and 3 commercial rice matrices. In addition, we investigated to what extent rice grain particle size after grinding, the ratio of rice over extraction liquid, hold time and temperature affect the release of different arsenic (As) species (As^III, As^V, and DMA^V) from rice samples. Particle size was found to have a major influence on arsenic extraction. Extraction efficiency of As was decreased to 75% when rice was treated as whole grain compared to powdered form. Extraction efficiency using microwave digestion in closed vessels was better than using microwave digestion in open vessels when the particle size was larger than 0.5 mm. For powdered samples, extraction efficiencies using both methods were similar. However, less time (30 min) was needed for complete extraction using microwave digestion in closed vessels compared to using microwave digestion in open vessels (180 min). The highest extraction efficiency for closed microwave digestion was obtained with powdered rice in 80 °C water at a liquid/solid ratio of 10 and a hold time of 30 min. The use of closed or open vessels during microwave digestion was indifferent to the speciation pattern. Extraction efficiencies of individual As species are affected by particle size to the same extent as that of total As, except for As^III. We concluded that closed microwave digestion of powdered sample under the proposed conditions is the most successful technique for species-preserving quantitative extraction of As species from rice.

Phosphopeptide enrichment and fractionation by using Click OEG-CD matrix by Yanyan Zhao; Xiuling Li; Jingyu Yan; Zhimou Guo; Xinmiao Liang (pp. 1244-1251).

Reversible protein phosphorylation regulates many significant cellular processes. Identification of phosphorylation sites is vital to elucidate their biofunctions. To aid in phosphoproteome characterization, several selective enrichment methods have been developed, including immobilized metal-ion affinity chromatography (IMAC) and titanium dioxide (TiO2). However, the high pH elution step applied in these two methods, which tends to degrade phosphopeptides. In order to improve phosphopeptide enrichment efficiency, a hydrophilic interaction liquid chromatography (HILIC) based material, cyclodextrin (CD) bonded silica (Click OEG-CD), was synthesized in our group and applied to phosphopeptide enrichment and fractionation. Taking tryptic digest of standard protein α-casein as model sample, the performance of Click OEG-CD in phosphopeptide isolation was investigated. It was found that both the acetonitrile and salt concentrations in mobile phase influence the phosphopeptide enrichment selectivity of the matrix. Under optimized enrichment condition, Click OEG-CD has a similar phosphopeptide enrichment selectivity as commercial TiO2. Meanwhile, phosphopeptides with same charges could be fractionated according to hydrophilicity difference on Click OEG-CD under acetonitrile gradient. Different selectivity is proved with Click OEG-CD from conventional SAX. We demonstrate that Click OEG-CD is an efficient matrix in phosphopeptide enrichment and fractionation.

Simultaneous UV/Vis spectroscopy and surface enhanced Raman scattering of nanoparticle formation and aggregation in levitated droplets by Jonas Schenk; Lisa Tröbs; Franziska Emmerling; Janina Kneipp; Ulrich Panne; Merwe Albrecht (pp. 1252-1258).

The formation and growth of hydroxylamine reduced silver nanoparticles were investigated by simultaneous Raman and UV/Vis spectroscopy coupled to an acoustic levitator as a sample holder. Based on the UV/Vis spectra, a two step particle formation mechanism with fast initial formation and adjacent coalescence can be proposed for the reduction of silver nitrate with hydroxylamine. The presence of the analyte adenine during particle formation resulted in differences in the adenine SERS signature compared to experiments, where adenine was added after particle synthesis. It was possible to monitor the adenine and sodium chloride induced aggregation of the nanoparticles and its dynamics based on both the extinction spectra and the SERS data. Correlating the information from the extinction spectra with the SERS intensity, the maximum SERS signals were observed at maximum extinction of the aggregated nanoparticle solution at the Raman excitation wavelength.

Colorimetric detection of Cr³⁺ using tripolyphosphate modified gold nanoparticles in aqueous solutions by Junwei Xin; Lijing Miao; Shougang Chen; Aiguo Wu (pp. 1259-1264).

A sensitive and selective colorimetric assay method for the detection of Cr³⁺ has been developed using tripolyphosphate functionalized gold nanoparticles (P3O10⁵⁻–AuNPs). Infrared (IR) spectra and energy dispersive X-ray spectroscopy (EDS) confirmed that tripolyphosphates capped on the surfaces of gold nanoparticles (AuNPs). Gold nanoparticles were prepared by reducing HAuCl4 with sodium borohydride (NaBH4) in the presence of sodium tripolyphosphate (Na5P3O10). Upon exposure to Cr³⁺, the color of the gold nanoparticle solution changed from red to violet, which was in response to the surface plasmon absorption of dispersed and aggregated nanoparticles. The P3O10⁵⁻–AuNPs were bound by Cr³⁺ and showed excellent selectivity compared to other ions (Hg²⁺, Fe³⁺, Cr⁶⁺, Mn²⁺, Cd²⁺, Ni²⁺, Pb²⁺, Ba²⁺, Co²⁺, Cu²⁺, Ca²⁺, Mg²⁺, Zn²⁺, Al³⁺, Na⁺, Cl⁻, SO4²⁻, PO4³⁻, CO3²⁻, NO3⁻, and all of the above interfering ions with the exception of Cr³⁺) and had a detection limit of 10⁻⁷ M by the naked eye in this way. Most importantly, the P3O10⁵⁻–AuNPs can be stored at room temperature over half a year. In addition, the P3O10⁵⁻–AuNPs were also used to detect Cr³⁺ in real environmental water samples, with low interference.

Identification of microbial volatile organic compounds (MVOCs) emitted from fungal isolates found on cinematographic film by Gavin D. Bingley; Joanna Verran; Lindsey J. Munro; Craig E. Banks (pp. 1265-1271).

We report the detection of microbial contamination and growth of cinematographic film utilising headspace solid phase micro-extraction coupled with Gas Chromatography–Mass Spectrometry. Microbial Volatile Organic Compounds (MVOCs) are produced only when the mould is actively growing on the cine film. Over 150 volatile compounds were detected from 16 fungal isolates, with over 40 being common to 2 or more isolates. It was found that 1-octen-3ol was produced from 13 of the isolates analysed, 3-octanone from 10 of the isolates and 3-octanol from 4 isolates. These three key chemical markers are indicative of viable fungal growth on cinematographic film precluding the need for traditional microbiology laboratory culture methods. Such an approach would prevent valuable historical footage from being discarded due to health and safety concerns regarding spore inhalation, and would enable safe handling.

Platinum screen printed electrodes for the electroanalytical sensing of hydrazine and hydrogen peroxide by Jonathan P. Metters; Fang Tan; Rashid O. Kadara; Craig E. Banks (pp. 1272-1277).

We report the fabrication of platinum screen printed electrodes which are electrochemically characterised and evaluated as to their potential analytical application towards the sensing of hydrazine and hydrogen peroxide. In the case of hydrazine a linear range of 50 to 500 μM is possible with a limit of detection (3σ) of 0.15 μM achievable using cyclic voltammetry which can be reduced to 0.12 μM using chronoamperometry. The novelty of these platinum screen printed electrodes is highlighted in that the platinum on the screen printed electrode surface resides as an oxide, which is favourable for the electrochemical oxidation of hydrazine, which need to be formed via extensive potential cycling when using a traditional platinum electrode hence the platinum screen printed sensors alleviate these requirements. The electroanalytical reduction of hydrogen peroxide is shown to be feasible with a linear range over 100 and 1000 μM with a limit of detection (3σ) of 0.14 μM which is competitive with other reported analytical protocols.

Underway determination of dissolved inorganic carbon in estuarine waters by gas-diffusion flow analysis with C⁴D detection by Somkid Pencharee; Peter A. Faber; Peter S. Ellis; Perran Cook; Janpen Intaraprasert; Kate Grudpan; Ian D. McKelvie (pp. 1278-1283).

The development and evaluation of a gas diffusion flow analysis system for the underway determination of dissolved inorganic carbon in marine and estuarine waters is described. Carbon dioxide produced when sample is injected into an acidic donor stream, diffuses through an efficient hollow fibre microporous membrane into an acceptor stream of ultrapure water, where the resultant changes in electrical conductivity are detected using a contactless capacitively coupled conductivity detector (C⁴D). The optimal parameters for the construction and operation of the C⁴D system are reported. Under field operational conditions, the flow analysis method had a linear calibration range for DIC of 0.2–10 mM, a limit of detection of 0.12 mM, repeatability of 0.46% RSD (n = 9 at 6 mM), a sample throughput of 90 h⁻¹ and excellent correlation with comparative analyses (R² = 0.9951, n = 16). The system was used to perform >250 determinations of DIC measurements underway during a short cruise on the Yarra River estuary, which demonstrated that DIC was conservative over much of the salinity gradient, with the exception of the low salinity region which exhibited the effects of respiratory CO2 and other DIC inputs. The results illustrate the advantages of the use of rapid flow analysis techniques for chemical mapping in transient environments like estuaries.

A fast graphical similarity algorithm for pattern recognition for data from a voltammetric electronic tongue by Hua-Mao Gu; Jin-Qin Shi; Xun Wang; Shao-Ping Deng (pp. 1284-1291).

Multi-sensor arrays have been applied more and more extensively in various fields, especially in the electrochemical industry. Among them, cross-sensitive multi-sensor arrays (e.g. electronic tongues and electronic noses) are the most popular ones. Taking advantage of the cross-sensitive response of voltammetric electronic tongues, a unique fast approach for variable reduction and pattern recognition is proposed in this paper based on a set of well-designed graphical similarity principles. It translates the measurement data of electronic tongues into a net graph containing rich pattern information, and then compares the similarity between the graphs on the levels of topology, geometric shape, and geometric size respectively and finally gives the corresponding similarity distances between the samples for pattern recognition.

Highly sensitive and selective fiber-optic modal interferometric sensor for detecting trace mercury ion in aqueous solution by Mingjie Yin; Bobo Gu; Jinwen Qian; A. Ping Zhang; Quanfu An; Sailing He (pp. 1292-1297).

A novel type of fiber-optic mercury ion (Hg²⁺) sensor was prepared by coating poly (N-ethyl-4-vinylpyridinium chloride) (P4VP·HCl) and poly (sodium-p-styrenesulfonate) (PSS) ultrathin film on the surface of a thin-core fiber modal interferometer (TCFMI) with layer-by-layer (LbL) electrostatic self-assembly method. The fabricated TCFMI Hg²⁺ sensor exhibits a high selectivity to Hg²⁺ and its detection limit and response time are 10⁻⁹ M and 30 s, respectively. The LbL electrostatic self-assembly process is monitored with a quartz crystal microbalance (QCM) and UV–vis spectroscopy for film growth. Atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) were used to characterize the morphology of the ultrathin film. Both demonstrated nanoporous film, which is helpful in shortening the response time of the TCFMI Hg²⁺ sensor.

Application of liquid chromatography coupled to time-of-flight mass spectrometry separation for rapid assessment of toxins in Amanita mushrooms by Don Brian Clarke; Antony S. Lloyd; Paul Robb (pp. 1298-1309).

An oligonucleotide-based label-free fluorescent sensor: highly sensitive and selective detection of Hg²⁺ in aqueous samples by Yamin Luo; Peng Wu; Jing Hu; Shaopan He; Xiandeng Hou; Kailai Xu (pp. 1310-1314).

A highly sensitive and selective detection method for mercury(ii) in aqueous samples was developed based on the use of an oligonucleotide-based label-free fluorescent probe. The novel design was composed of two oligonucleotides with partially complementary sequences and the label-free dye ethidium bromide (EB). The fluorescence signal was very low when EB was free in water solution. However, the fluorescence signal increased by nearly 15 times when the DNA duplex was present. This dsDNA–EB system was used as a fluorescent sensor for Hg²⁺. The presence of Hg²⁺ led to the release of EB from the grooves of dsDNA and the fluorescence intensity was quenched. In this investigation, the optimal concentrations of dsDNA and EB were 0.285 μM and 0.9 μM, respectively. The calibration curve was linear in the range of 30 to 120 nM for Hg²⁺ (R² = 0.992), with a detection limit of 9.5 nM. The method was simple and convenient, and this sensor also provided potential applications for developing aptasensors.

Application of an integrated LC-UV-MS-NMR platform to the identification of secondary metabolites from cell cultures: benzophenanthridine alkaloids from elicited Eschscholzia californica (california poppy) cell cultures by Rose M. Gathungu; John T. Oldham; Susan S. Bird; Carolyn W. T. Lee-Parsons; Paul Vouros; Roger Kautz (pp. 1315-1325).

Plant cell and tissue cultures are a scalable and controllable alternative to whole plants for obtaining natural products of medical relevance. Cultures can be optimized for high yields of desired metabolites using rapid profiling assays such as HPLC. We describe an approach to establishing a rapid assay for profiling cell culture expression systems using a novel microscale LC-UV-MS-NMR platform, designed to acquire both MS and NMR each at their optimal sensitivity, by using nanosplitter MS from 4 mm analytical HPLC columns, and offline microdroplet NMR. The approach is demonstrated in the analysis of elicited Eschscholzia californica cell cultures induced with purified yeast extract to produce benzophenanthridine alkaloids. Preliminary HPLC-UV provides an overview of the changes in the production of alkaloids with time after elicitation. At the time point corresponding to the production of the most alkaloids, the integrated LC-MS-microcoil NMR platform is used for structural identification of extracted alkaloids. Eight benzophenanthridine alkaloids were identified at the sub-microgram level. This paper demonstrates the utility of the nanosplitter LC-MS/microdroplet NMR platform when establishing cell culture expression systems.

Whole cell based amperometric sensor with relative selectivity for zinc ions by Jasminder Singh; Susheel K. Mittal (pp. 1326-1331).

A whole cell based amperometric biosensor was fabricated using unicellular microalgae Chlorella sp. as the biocatalyst, entrapped in a polymeric membrane directly interfaced to the surface of a platinum electrode for the detection of bioavailable heavy metal ions like zinc, copper, cadmium, cobalt and nickel with a life time of 7 days. The proposed system is sensitive to a lower concentration range of 10⁻⁹ M of nickel ions, 10⁻¹⁰ M of cadmium and cobalt ions, 10⁻¹¹ M of copper and zinc ions. The amperometric biosensor responds to heavy metal ions with a relative selectivity in the order: Zn²⁺ > Cu²⁺ > Cd²⁺ > Co²⁺ > Ni²⁺. The proposed analytical method has been validated with atomic absorption spectroscopy for heavy metal detection in real time samples.

Electrocatalytic oxidation of captopril on a vinylferrocene modified carbon nanotubes paste electrode by Ali A. Ensafi; Malihe Monsef; B. Rezaei; Hassan Karimi-Maleh (pp. 1332-1338).

The study of electrochemical behavior and determination of captopril, as an angiotensin-converting enzyme inhibitor using a vinylferrocene modified multiwalled carbon nanotubes paste electrode (VFMCNTPE) is reported. The cyclic voltammetric results indicate that the VFMCNTPE system can remarkably enhance electrocatalytic activity toward the oxidation of captopril in aqueous buffer solution pH 8.0. Under the best experimental conditions selected, the calibration curve for captopril was linear in the concentration range from 0.2 to 400 μmol L⁻¹ and a detection limit of 0.08 μmol L⁻¹ was obtained. The influence of pH and potential interfering substances on the determination of captopril were studied. Electrochemical impedance spectroscopy was used to study the charge transfer properties at the electrode–solution interface. Finally, the sensor was examined as a selective, simple, and precise new electrochemical sensor for the determination of captopril in real samples, such as drugs and urine. Satisfactory results were obtained.

Discrimination and identification of different amines by pattern recognition of kinetic spectral data by Masoumeh Hasani; Fereshteh Emami (pp. 1339-1349).

This study represents detection and differentiation of primary, secondary, tertiary, aliphatic and aromatic as well as linear and branched amines using kinetic absorption spectra and multivariate analysis. The approach utilizes the electron donor-acceptor (EDA) complex formation between amines (as electron donors) and iodine (as electron acceptor) in chloroform solution. The criteria for discrimination were shape and intensity of the time dependent spectra of the amine–iodine systems as well as the kinetics of the process. It was found that the time-dependent absorption spectra of the complex formed between different amines and iodine are sufficiently diverse to provide a signature for each of the amines used. Pattern recognition methods including principal component analysis (PCA), linear discriminate analysis (LDA) and quadratic discriminate analysis (QDA) were used to analyze the response patterns. Multidimensional spectral identification of a collection of 27 amines was successfully performed. The method was successful even for the identification of amines having close structural similarity.

A supersensitive sensor for rutin detection based on multi-walled carbon nanotubes and gold nanoparticles modified carbon paste electrodes by Jing Zhou; Kai Zhang; Jie Liu; Ge Song; Baoxian Ye (pp. 1350-1356).

A new voltammetric sensor was designed by covering a layer of gold nanoparticles (AuNPs) on a carbon paste electrode that was pre-mixed in some multi-walled carbon nanotubes (MWCNT). This sensor exhibited super sensitive detection of the electroactive flavonoid rutin due to the large surface area and good conductivity of MWCNT and AuNPs. Cyclic voltammetry curves at various scan rates and pH were recorded to investigate the redox properties of rutin. Further experiments demonstrated that the oxidative peaks increased linearly with rutin concentrations in the ranges of 4.0 × 10⁻¹⁰ to 1.0 × 10⁻⁸ mol L⁻¹ and 2.0 × 10⁻⁸ to 1.0 × 10⁻⁶ mol L⁻¹ with a limit of detection of 4.0 × 10⁻¹¹ mol L⁻¹. The method was successfully applied to detect rutin in medicine tablets with satisfactory results.

Surfactant-assisted dispersive liquid–liquid microextraction followed by high-performance liquid chromatography for determination of amphetamine and methamphetamine in urine samples by Mohammad Saber Tehrani; Mohammad Hadi Givianrad; Nasibeh Mahoor (pp. 1357-1364).

A novel surfactant-assisted dispersive liquid–liquid microextraction (SADLLME) based on solidification of floating organic drop (SFO) combined with high-performance liquid chromatography-ultraviolet detection (HPLC-UV) has been proposed for extraction and determination of amphetamine (AM) and methamphetamine (MA) in urine samples. 1-undecanol and sodium dodecyl sulfate (SDS) were used as extracting solvent and disperser, respectively. Face-centered central composite design (FCCCD) was used for optimization of several factors affecting extraction recovery. The optimal conditions were pH = 6.4, volume of extracting solvent V = 31.0 μL, 0.08 CMC as surfactant concentration, and the amount of NaCl for ionic strength was 0.3% (W/V). The limits of detection (LODs, S/N = 3) of the extraction method were 2 for AM and 3 μg L⁻¹ for MA, with the enrichment factors (EFs) of 56 and 48 folds, respectively. The relative standard deviation (RSD %) for n = 3 was below 5.6% and a good linearity (R² > 0.991) in the range of 10–2000 μg L⁻¹ was observed. The application feasibility of SFO-SADLLME-HPLC-UV in real sample was investigated by analyzing different real samples and satisfactory results were obtained.

Determination of copper(ii) and cadmium(ii) based on ternary CuInS2 quantum dots by Siyu Liu; Yanyi Li; Xingguang Su (pp. 1365-1370).

Water-soluble CuInS2 ternary quantum dots (QDs) capped by mercaptopropionic acid (MPA) were directly synthesized in aqueous solution, and were then applied to the detection of Cu²⁺ and Cd²⁺ ions. The ternary QDs exhibited obvious photoluminescence (PL) quenching in the presence of Cu²⁺ and marked enhancement in the presence of Cd²⁺ respectively. Other physiological cations such as K⁺, Ca²⁺ Mg²⁺ and Zn²⁺ had no effect on the PL intensity under similar conditions. The detection limits were 0.1 µmol L⁻¹ for Cu²⁺ and 0.19 µmol L⁻¹ for Cd²⁺. The fluorescence quenching of the ternary CuInS2 QDs by Cu²⁺ could be explained by the reduction of Cu²⁺ to Cu⁺ on the surface of the QDs, whereas the fluorescence enhancement by Cd²⁺ was attributed to activation of surface states. Ternary QDs modified by sufficient Cd²⁺ showed enhanced sensitivity for Cu²⁺ determination compared with unmodified QDs, and a detection limit of 0.037 µmol L⁻¹ was obtained for Cu²⁺. Utilizing the property that Cu²⁺ can be easily removed by addition of iodide, we could eliminate the interference of Cu²⁺ on the Cd²⁺ detection. To the best of our knowledge, this is the first report on the selective detection of Cu²⁺ and Cd²⁺ by quenching and enhancing the fluorescence of the near-infrared CuInS2 QDs in aqueous solution. This novel method has been successfully applied to the detection of trace Cu²⁺ and Cd²⁺ in real water samples with satisfactory results.

Rapid determination of four tobacco specific nitrosamines in burley tobacco by near-infrared spectroscopy by Yanjun Ma; Ruoshi Bai; Guorong Du; Li Ma; Aijun He; Na Li; Xiaoli Yi; Wensheng Cai; Jun Zhou; Xueguang Shao (pp. 1371-1376).

Indirect modeling of trace components in real samples by use of near-infrared spectroscopy (NIRS) has gained much interest, because it may provide a rapid way for analyzing the industrial or agricultural products. Coupling near-infrared diffusive reflectance spectroscopy and chemometric techniques, a method for rapid analysis of four tobacco specific N-nitrosamines (TSNAs) and their total content is studied in this work. For optimization of the models, techniques for spectral preprocessing and variable selection are adopted and compared. It is found that to remove the varying background and correction of the multiplicative scattering effect in the spectra is important in modeling, also variable selection can significantly improve the models. For validation of the models, the TSNA contents of independent test samples and tobacco leaves harvested in different years were predicted. Consistent results were obtained between the reference contents by GC/TEA analysis and those predicted. Although the relative errors for some low content samples are not satisfactory, the method is a practical alternative for industrial analysis due to the non-destructive and rapid nature of the method.

Electrochemical behavior and analytical detection of insulin on pretreated nanocarbon black electrode surface by Chaozhong Guo; Changguo Chen; Zhongli Luo; Lin Chen (pp. 1377-1382).

This work takes advantage of electrochemically anodic pretreated carbon paste electrode modified with acetylene black nanocarbon particles (AB/CPE), a new and high-sensitive analytical method for insulin was put forward. Modern voltammetric testing techniques were used for primarily investigating the redox electrochemical characterization of Fe(CN)6^3−/4− and electrochemical behavior of insulin on nanocarbon electrode surface. At the same time, a plausible mechanism was also proposed to provide insights into understanding how to facilitate the electron transfer between insulin biomolecule and electrode surface. The results have shown that the pretreated AB/CPE represented high accumulation efficiency to insulin and promoted its direct electron transfer rate owing to the presence of nanocarbon particles and anodic pretreatment. It is found that insulin exhibited a very sensitive anodic peak at 0.47 V on the pretreated AB/CPE, and its peak current was increased about six times more than that on the pretreated carbon paste electrode (CPE). A linear relationship between the anodic peak current and the concentration of insulin from 20 to 1000 nM and a limit of detection as low as 5 nM were obtained using the pretreated AB/CPE. Attracting attention, the proposed method was applied to the realistic samples successfully and showed good recovery and reproducibility.

LC-MS method for determining the activity of semicarbazide-sensitive amine oxidase in rodents by Lin Wang; Yongqian Zhang; Shengyuan Xiao; Gaofei Hu; Baoquan Che; Hong Qing; Yujuan Li; Lixia Zhuang; Yulin Deng (pp. 1383-1388).

Semicarbazide-sensitive amine oxidase (SSAO) is present in various mammalian tissues and in blood plasma. Elevation of SSAO activity is linked to vascular disorders associated with pathological conditions such as diabetic complications, heart failure and vascular dementia. In the present paper, a high performance liquid chromatography electrospray ionization mass spectrometry (HPLC-ESI-MS) method is developed to determine the SSAO activity. Methylamine is used as physiological substrate for the enzyme activity assay of SSAO. Formaldehyde, the enzymatic reaction product, was derivatized by dopamine, and separated by a silica-based pentafluorophenyl column. The calibration curve was linear over the range of 0.03–4.00 μM of formaldehyde concentration, with 0.03 μM the lower limit of quantification (LOQ). The inter-day and intra-day precisions ranged from 2.2% to 7.9% and 4.4% to 9.2% respectively for each quality control sample of formaldehyde at 0.06, 0.50, and 2.00 μM. The accuracy ranged from 96.0% to 111.5%. The limit of detection (LOD) for serum SSAO activity was 1 nmol h⁻¹ mg⁻¹ protein. The method was successfully applied for the determination of SSAO activity in both mouse serum and rat tissues. SSAO activity of the serum in diabetes mice was significantly increased compared with the control and was inhibited by 2-bromoethylamine in vivo. The levels of SSAO activity in rat lung, spleen, aorta, kidney and brain tissues were significantly decreased by semicarbazide in vitro.

Extracellular metabolites play a dominant role in near-infrared spectroscopic quantification of bacteria at food-safety level concentrations by Yuriko Nakakimura; Maria Vassileva; Todor Stoyanchev; Kaoru Nakai; Ro Osawa; Junichi Kawano; Roumiana Tsenkova (pp. 1389-1394).

Near infrared spectroscopy (NIRS) is a promising new tool for quick and accurate bacterial quantification in water-rich samples like food. However, we still do not know what this spectroscopic method takes into account in order to measure bacterial counts at food safety limits. This study tries to identify which part of the bacterial culture has a more significant impact on spectral models for bacterial quantification in an aqueous environment. Two type strains of E. coli and S. aureus were evaluated, at a concentration range 0.1–8 log10 CFU. Spectra from bacterial cells, separated by filtration, and extracellular metabolites were acquired separately and then combined in a reciprocal ratio in order to identify the spectral combination that would provide the best partial least squares quantification model for each strain. Spectral data were evaluated in the first wavelength overtone region of water 1300–1600 nm. The best model was achieved at a cells : extracellular metabolites spectral combination ratio of 40 : 60 for the E. coli strain and 20 : 80 for the S. aureus strain. While the best ratio was different for each species, extracellular metabolite spectra had a consistent significantly higher impact on PLS models. It can be concluded that species-specific extracellular metabolite spectra give more valuable information on bacterial quantification, and it is the spectral detection of changes in extracellular water conformations, due to extracellular bacterial metabolites, that represents the most significant factor for successful bacterial quantification. Finding out that bacteria influence the water matrix is an important step in understanding the mechanism of NIRS detection of low bacterial concentrations.

A novel partial least squares weighting Gaussian process algorithm and its application to near infrared spectroscopy data mining problems by Kai Song; Tuopeng Tong; Fang Wu; Ze Zhang (pp. 1395-1400).

A new partial least squares (PLS) weighting Gaussian process (PWGP) algorithm is proposed to improve the regression performance of Gaussian process (GP), an outstanding kernel-based machine learning method, on high dimensional data with small sample size, especially near-infrared (NIR) spectroscopy. Important indexes of original variables are firstly calculated according to their contributions to the PLS regression model. After being weighted by these important indexes, new values of the observations are input into GP algorithm for further regression analysis. Relying on the PLS based weighting technique, important variables could be highlighted by their relatively large index values. Consequently “information saturation” phenomenon could be successfully overcome. Most importantly, unlike other weighting methods, there is no need to have prior knowledge in order to optimize any factors or parameters, thus the PWGP method is especially suitable for regression problems of “black-box” systems. Applications of the proposed method on three NIR spectroscopy dataset, which are widely used as test data, strongly confirmed that the predictive performance of PWGP is superior to other approaches.

A simple and rapid microwave-assisted extraction method using polypropylene tubes for the determination of total mercury in environmental samples by flow injection chemical vapour generation inductively coupled plasma mass spectrometry (FI-CVG-ICP-MS) by M. V. Balarama Krishna; K. Chandrasekaran; D. Karunasagar (pp. 1401-1409).

Presented here is the development of a simple, rapid and cost-effective microwave-assisted extraction (MAE) method using closed polypropylene tubes (PP) and a domestic microwave oven for the determination of total mercury in a wide variety of environmental samples (coal, coal-fly ash, sediments and sludges). Extraction of mercury was achieved using microwave energy with a mixture of HNO3–thiourea as extractant for subsequent determination by flow injection chemical vapour generation inductively coupled plasma mass spectrometry (FI-CVG-ICP-MS). Two types of reference materials certified for mercury; Coal fly ash NIST-1633b and estuarine sediment ERM-CC-580 were taken to optimize extraction parameters such as microwave power, extraction time and sample amount for the quantitative recovery of mercury. The supernatant obtained upon centrifugation was used for analysis. Quantitative recoveries of mercury were obtained using 30% HNO3–0.02% thio-urea mixture with 30 s irradiation time at a microwave power of >640 W for 500 mg sample weight. The results obtained here were in good agreement with the certified values with an overall precision of better than 5% in all the cases. The limit of detection of the proposed method in conjunction with FI-CVG-ICP-MS was obtained to be 0.9 ng g⁻¹. A closed-microwave extraction procedure based on US EPA method (3051A) was used for the determination of mercury for comparison purposes. The optimized MAE procedure was successfully applied to real samples.

A dispersive liquid–liquid microextraction procedure for UV-Vis spectrophotometric determination of chromium(vi) in water samples by Michal Alexovič; Ioseph S. Balogh; Jana Škrlíková; Vasil Andruch (pp. 1410-1414).

A novel and simple procedure for chromium determination has been developed. The method is based on the reaction of chromium(vi) with dimethylindocarbocyanine dye reagent (DIC) in an acidic medium and in the presence of chloride ions, followed by dispersive liquid–liquid microextraction of the formed ion associate into the organic phase containing a mixture of toluene (extraction solvent), carbon tetrachloride (auxiliary solvent) and acetonitrile (dispersive solvent) in a ratio of 1 : 1 : 2 (v : v : v) and subsequent UV-VIS detection at 550 nm. The calibration plot was linear in the range 0.10–0.52 mg L⁻¹ of chromium. The limit of detection calculated based on 3s and limit of quantification calculated based on 10s is 0.03 mg L⁻¹ and 0.07 mg L⁻¹. The method was applied to the determination of chromium(vi) in spiked water samples.

Multiwalled carbon nanotube paste electrode as an easy, inexpensive and highly selective sensor for voltammetric determination of Risperidone by Abbas Afkhami; Hamed Ghaedi (pp. 1415-1420).

A carbon paste electrode (CPE) modified with multi-walled carbon nanotube (MWCNT) was proposed for determination of Risperidone (Risp). The method was based on adsorptive accumulation of the Risp on to paste electrode, followed by reduction of the accumulated species by voltammetric scan. The parameters influencing the peak current were optimized. Under the optimum conditions, the electrode established linear response over a wide range of Risp concentrations (0.04 to 10 μmol L⁻¹), the detection limit was 0.012 μmol L⁻¹ (after 150 s accumulation). The method was applied to the determination of Risp in a pharmaceutical preparation and in human serum samples, and satisfactory results were obtained.

A hydrogen peroxide sensor based on the nanocomposites of poly(brilliant cresyl blue) and single walled-carbon nanotubes by Hua-Jun Liu; Dong-Wei Yang; Hui-Hong Liu (pp. 1421-1426).

A poly(brilliant cresyl blue) (PBCB) functionalized single walled-carbon nanotube (SWCNT) modified glassy carbon electrode (PBCB/SWCNT/GCE) is fabricated by electropolymerization. The electrocatalytic activity of the PBCB/SWCNT/GCE towards the reduction of hydrogen peroxide is then investigated. The electrode shows high sensitivity [4.1 nA (μM) ⁻¹] to the electrocatalytic reduction of H2O2 at an applied potential of −0.30 V (vs. SCE). Important practical advantages such as a fast response time (within 5 s), a low detection limit (0.12 μM), wide linear dynamic range (4.9 × 10⁻⁷ to 2.3 × 10⁻⁴ M, R² = 0.994) and stability (remains ∼93% of its original activity after 30 days) are achieved with the PBCB/SWCNT/GCE. Further, the presence of probable interferences such as glucose, ascorbic acid, dopamine and uric acid does not interfere during the detection of H2O2. The application of the sensor to determine H2O2 in tap water with recovery values of 96% to 102% shows the sensor is suitable for routine analysis.

A novel ion-selective membrane electrode for the determination of duloxetine by Reda A. Ammar; Haleema Otaif; Abdulrhman Al-Warthan (pp. 1427-1431).

A novel duloxetine ion-selective poly(vinyl chloride) membrane electrode based on the ion-pair complex of duloxetine with phosphomolybdic acid was prepared with diocyl phthalate as a plasticizer. The electrode exhibits a linear response with a slope of 56.9 mV decade^¬1 of duloxetine concentration at 25 ± 0.1 °C for the optimum electrode prepared with a membrane consisting of 10.0% ion pairs. The electrode response was not sensitive to pH changes from 4.30–8.35 and was not affected by possible interfering species such as common inorganic cations, sugars and amino acids. It has a relatively fast response time less than (15 s) and the lifetime was about 2 months during which it could be used without any measurable divergence. The electrode was successfully used for the potentiometric determination of duloxetine hydrochloride both in pure solutions and in pharmaceutical preparations.

Determination of glucose in human serum based on an onion primary cuticula biosensor immobilized glucose oxidase by Wenjuan Jia; Wenjuan Liu; Yan Zhang; Miao Cui; Shaomin Shuang; Chuan Dong; Martin M. F. Choi (pp. 1432-1437).

A glucose biosensor based on onion primary cuticula immobilized glucose oxidase has been developed. The glucose concentration was quantified by the decrease of dissolved oxygen. The effects of enzyme loading, pH, temperature, buffer concentration and interference have been studied in detail. The biosensor showed a wide linear relationship with a concentration range of 20 μM–1.1 mM, a fast response time (70 s), good repeatability (2.8%, n = 10) and satisfactory reproducibility (0.91%, n = 3). The biosensor retained 90% of its initial response after 3 months at 25 °C. The apparent Michaelis-Menten constant Km was estimated to be 0.042 mM, which revealed higher biological affinity to glucose. The proposed biosensor method has been successfully applied to the determination of glucose concentration in human blood serum and obtained results were agreement with the colorimetric assay kit. The recoveries of proposed method are 95.2–106.3%.

Manganese modified CdTe/CdS quantum dots as a highly selective probe to detect trace copper element in beer samples by Fangdi Wei; Hailin Yu; Miao Hu; Guanhong Xu; Zheng Cai; Jing Yang; Lei Li; Qin Hu (pp. 1438-1444).

This paper describes the investigation of manganese modified CdTe/CdS quantum dots as a fluorescence probe for trace copper detection. Manganese modified CdTe/CdS quantum dots were prepared in aqueous solution and were characterized by ultraviolet-visible absorbance, fluorescence spectra, transmission electron microscopy and X-ray diffraction. The as-synthesized manganese modified CdTe/CdS QDs presented a high photoluminescence quantum yield of 84%. The functionalized nanoparticles were used as a fluorescence probe for Cu²⁺. The interference study demonstrated that the normal foreign ions, such as Na⁺, Mg²⁺, Al³⁺et al., had very low interference for the detection of Cu²⁺, and the calibration plot of F⁰/F versus concentration of Cu²⁺ was linear in the range of 5.0 × 10⁻⁹ to 5.0 × 10⁻⁷ mol L⁻¹ with a correlation coefficient of 0.9991. The ultrasensitive fluorescence probe built was directly applied to the detection of trace copper element in beer samples with satisfactory results.

Electrochemical behavior of phenacetin on CdSe microspheres modified glassy carbon electrode and its simultaneous determination with paracetamol and 4-aminophenol by Huanshun Yin; Xiaomeng Meng; Zhenning Xu; Lijian Chen; Shiyun Ai (pp. 1445-1451).

A selective and sensitive electrochemistry method was developed for the determination of phenacetin on CdSe microspheres modified glassy carbon electrode (GCE). The electrode exhibited an effectively catalytic response to the oxidation of phenacetin, which was testified by the increased oxidation peak current and the decreased oxidation peak potential compared with the bare GCE. The scan rate investigation demonstrated that the electrochemical oxidation was an adsorption-controlled process in the range from 20 to 500 mV s⁻¹. Under optimal determination conditions, the oxidation peak current of phenacetin was proportional to its concentration in the range of 0.5 to 800 μM. The limit of detection was estimated to be 0.1 μM (S/N = 3). The developed method showed good reproducibility, acceptable stability and excellent anti-interference performance. The fabricated electrode was successfully used to determine phenacetin in pharmaceutical formulation samples.

Sequential injection system exploring the standard addition method for phosphate determination in high salinity samples: interstitial, transitional and coastal waters by Raquel Beatriz Ribeiro Mesquita; Inês Carvalho Santos; Adriano Agostinho Bordalo; António Osmaro Santos Silva Rangel (pp. 1452-1457).

A sequential injection system for phosphate determination within a wide concentration range was developed for water samples with high salinity levels. The determination is based on molybdenum blue chemistry using the standard addition quantification method. The detection system included a multi-reflective flow cell coupled to a light emitting diode, enabling the minimization of the schlieren effect. The developed system gave a LOD of 0.3 μmol P L⁻¹ and LOQ of 1.1 μmol P L⁻¹ with a sample consumption of 125 μL. A determination rate of about 30 h⁻¹ was obtained, and the developed method was effectively applied to interstitial, transitional and coastal waters.

Back matter (pp. 1458-1458).

The mobility of copper ions and redox reactions of Cu at the interface with SiO2 being directly attributed to the resistive switching effect have been studied by cyclic voltammetry (CV). The electrode kinetics of the Cu^z+/Cu redox reactions were analyzed suggesting the formation of both Cu⁺ and Cu²⁺ species. The ion mobility shows an unexpected strong dependence on the ion concentration indicating ion–ion interactions typical for concentrated solution conditions. Based on the standard reduction potentials for Cu^z+/Cu we identified partial electrochemical redox reactions during oxidation and reduction. The results contribute to a detailed understanding of the resistive switching effect in Cu/SiO2/Pt cells and provide insight into electrochemically assisted diffusion of metal cations in oxides in general.

Back cover (pp. 1459-1460).

Suspended graphene has been studied by STM for the first time. Atomic resolution on mono- and bi-layer graphene samples has been obtained after ridding the graphene surface of contamination via high-temperature annealing. Static local corrugations (ripples) have been observed on both types of structures.

Sections

Personal tools

Analytical Methods (v.4, #5)

Sections

Personal tools

Local resources

Analytical Methods (v.4, #5)