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Analytica Chimica Acta (v.566, #1)
Graphite impurities cause the observed ‘electrocatalysis’ seen at C60 modified glassy carbon electrodes in respect of the oxidation ofl-cysteine by Roohollah Torabi Kachoosangi; Craig E. Banks; Richard G. Compton (pp. 1-4).
The recently reported claims of electrocatalysis using C60 film modified glassy carbon electrodes [W.T. Tan, A.M. Bond, S.W. Ngooi, E.B. Lim, J.K. Goh, Anal. Chim. Acta 491 (2003) 181] for the oxidation ofl-cysteine are questioned. We show that C60 itself is not electrocatalytic at the potentials concerned but rather it is likely that graphite impurities in the C60 material used by Tan et al. that provide their observed ‘electrocatalysis’.
Keywords: C; 60; modified electrodes; Graphite impurities; l; -Cysteine; Electrocatalysis
A cobalt(II)-selective PVC membrane based on a Schiff base complex of N,N′-bis(salicylidene)-3,4-diaminotoluene by Vinod Kumar Gupta; Ashok Kumar Singh; Sameena Mehtab; Barkha Gupta (pp. 5-10).
A new PVC membrane electrode for Co2+ based on N,N′-bis(salicylidene)-3,4-diaminotoluene, an excellent neutral carrier, has been fabricated using sodium tetraphenylborate (NaTPB) as an anionic excluder and dioctylphthalte (DOP) as a solvent mediator. The electrode exhibits a linear potential response in the concentration range of 7.9×10−8 to 1.0×10−1M with a slope of 30±0.2mV per decade. The detection limit of the proposed sensor is 5.0×10−8M and it can be used over a period of 5 months. The proposed sensor revealed good selectivity over a wide variety of other cations including alkali, alkaline earth, heavy and transition metals and could be used in the pH range of 2.0–9.0. This electrode was successfully applied for the determination of Co2+in real samples and as an indicator electrode in potentiometric titration of cobalt ions.
Keywords: Cobalt-selective electrode; PVC membrane electrodes; Schiff base and potentiometric sensors
Amperometric biosensors based on two different enzyme systems and their use for glycerol determination in samples from biotechnological fermentation process by J. KatrlÃk; V. Mastihuba; I. VoÅ¡tiar; J. Å efÄ?oviÄ?ová; V. Å tefuca; P. Gemeiner (pp. 11-18).
Two amperometric enzyme biosensor systems, based on glycerol dehydrogenase/diaphorase (GDH/DP) and glycerol kinase/glycerol-3-phosphate oxidase/peroxidase (GK/GPOx/HRP), were developed and used for estimation of glycerol content in a complex biological fluids. Enzymes were immobilized on interchangeable membranes by PCS-prepolymer technique. Buffers containing ferricyanide/NAD+ or ferrocyanide/ATP were used for measurements with GDH/DP and GK/GPOx/HRP biosensor, respectively. FIA assay of glycerol biosensor was characterized by a linear range of 0.01–1 or 0.01–1.5mM glycerol, sensitivity of 6.02 or 1.42mA/Mcm2 and with signal loss of 40% after 90h or 30% after 16h during continuous operation at a sample throughput of 10 injections/h for GDH/DP or GK/GPOx/HRP biosensors, respectively. Both biosensors were successfully used for off-line monitoring of glycerol during microbial transformation of glycerol to 1,3-propanediol using an automatized flow-through system. The results were consistent with those obtained with HPLC. The stability of described biosensor systems was sufficient for monitoring and control of fermentation process within 24h. The storage stability of enzyme membranes was several months.
Keywords: Biosensor; FIA; Glycerol; 1,3-Propanediol; PCS; Biotechnology
Monitor adsorption of acetone vapor to a room temperature ionic liquid 1-octyl-3-methylimidazolium bromide by a langasite crystal resonator by Dazhong Shen; Xiaoyu Li; Qi Kang; Haiting Zhang; Yong Qi (pp. 19-28).
In this work, the responses of a Y-cut langasite crystal resonator (LCR) in liquid phases were investigated by an impedance analysis method. The resonant frequency ( fS) of the LCR decreases with increasing mass loading on the active surface of the resonator. The LCR can be operated at the resonant frequency that is down to about 60% of the fundamental frequency ( f0) under foreign mass loading. The frequency–mass coefficient of the Y-cut LCR is theoretically derived to be −1.282×10−6f02, which is supported by the experimental results. The resonant frequency of the LCR decreases linearly while its motional resistance ( Rm) increases linearly with increasing ( Ï?η)1/2, where η and Ï? are the viscosity and density of the liquid phase, respectively. The slopes of the plots of fS versus ( Ï?η)1/2 and Rm versus ( Ï?η)1/2 are related to the region of ( Ï?η)1/2 because of the influence of surface roughness of the LCR. The changes in viscodensity of a room temperature ionic liquid (RTIL), 1-octyl-3-methylimidazolium bromide ([C8MIM][Br]), were investigated in acetone vapor adsorption and ascending temperature processes by the LCR. The adsorption of acetone into [C8MIM][Br] causes a significantly drop in viscosity of the [C8MIM][Br] film, which induces an increase in fS and a decrease in Rm for the RTIL modified LCR. When the thickness of [C8MIM][Br] film is less than the decay distance of the thickness-shear wave, a mass effect model is observed in the early adsorption process. Based on the responses of the LCR, the viscodensity of the [C8MIM][Br] film as well as the adsorbed amounts of acetone into film were monitored in real time during the adsorption or desorption processes.
Keywords: Langasite; Ionic liquid; Adsorption; Viscosity
Ultrasound-assisted extraction technique for establishing selenium contents in breast cancer biopsies by Zeeman-electrothermal atomic absorption spectrometry using multi-injection by I. Lavilla; A. Mosquera; J. Millos; J. Cameselle; C. Bendicho (pp. 29-36).
A solid–liquid extraction method is developed to establish the contents of selenium in breast cancer biopsies. The method is based on the ultrasound-assisted extraction of selenium from pretreated biopsies prior to Se determination by atomic absorption spectrometry with longitudinal-Zeeman background correction. Fifty-one breast biopsies were collected from the Cies Hospital (Vigo, Spain), 32 of which correspond to tumor tissue and 19 to normal tissue (parenchyma). Difficulties arising from the samples analyzed, i.e. small samples mass (50–100mg), extremely low Se contents and sample texture modification including tissue hardening due to formaldehyde preservation are addressed and overcome. High intensity sonication using a probe together with addition of hydrogen peroxide succeeded in completely extracting Se from biopsies. The multiple injection technique was useful to tackle the low Se contents present in some biopsies. The detection limit was 25ngg−1 of Se and the precision, expressed as relative standard deviation, was less than 10%. Se contents ranged from 0.08 to 0.4μgg−1 for parenchyma samples and from 0.09 to 0.8μgg−1 for tumor samples. In general, Se levels in tumor biopsies were higher as compared with the adjacent normal tissue in 19 patients by a factor of up to 6. Analytical data confirmed Se accumulation in the breast tumors.
Keywords: Selenium; Breast cancer; Ultrasound assisted extraction; Biopsies; Zeeman-electrothermal atomic absorption spectrometry
Optimisation of microwave assisted digestion of sediments and determination of Sn and Hg by P. Navarro; J.C. Raposo; G. Arana; N. Etxebarria (pp. 37-44).
The determination of Sn by flow injection–hydride generation–quartz furnace atomic absorption spectrometric (FI–HG–QFAAS) was optimised following different experimental designs. The best conditions were: 0.2% HCl (v/v), 0.5% NaBH4 (w/v) and the furnace temperature 875°C. Under those conditions, the limit of detection was 0.17ngdm−3 and a precision of 5.3% was obtained. One of the aims of this work was to optimise the closed vessel microwave assisted digestion (MAD) of sediments for the determination of Sn and Hg in the same extract using the analytical conditions previously optimised for Sn in the FI–QFAAS. The optimisation of the MAD of sediments was accomplished following a D-optimal design, including the composition of the HCl–HNO3 mixture, the pressure and irradiation time. However, we could not determine tin in the extracts due to the formation of foams, the optimisation of the digestion conditions were taken from the FI–cold vapour (CV)–QFAAS measurements of mercury. The optimum conditions were: 2.1bar of pressure during 10min of irradiation and two local optima composition of the acid mixtures: 80% HCl–20% HNO3 and 60% H2O–20% HCl–20% HNO3. The determination of mercury in sediments was validated with the CRM-580. In order to determine Sn in sediments the solutions from the same D-optimal design were analysed using an ICP-MS and the digestion conditions were optimised for Sn and for other 8 metals. In this case the same optimal conditions were obtained (2.1bar and 10min) but different acid mixture composition 20% HCl–80% HNO3. The determination of Sn and the other metals in sediments was validated using two other CRMs (PACS-2 and SGR-1).
Keywords: Microwave assisted digestion; Tin; Mercury; Metals; Sediments
Phase-resolved detection in ion-mobility spectrometry by Andrew W. Szumlas; Gary M. Hieftje (pp. 45-54).
Throughput has been improved in an ion-mobility spectrometer by means of continuous ion-beam modulation and phase-resolved detection. Conventional ion-mobility spectrometry (IMS) utilizes brief packets of ions for separation in the gas phase. In contrast, this preliminary report outlines a new detection method based on phase resolution and involves monitoring the ion signal continuously, which raises the duty cycle of the instrument from approximately 1% (conventional IMS) to 50%. The greater duty cycle is shown to improve signal-to-noise ratios (S/N). However, the higher S/N levels did not translate into higher sensitivity values when calibration plots were constructed. It is demonstrated that even analytes with small differences in drift times can be modulated at frequencies that maximize the measured phase differences between ions. Phase-resolved signals can be processed with a Fourier transform and chemometric data reduction to simplify identification of the analyte from its phase spectra.
Keywords: Enhanced resolution; Higher sensitivity; Fourier transform; Ion-mobility spectrometry; Phase resolution
Cytokine assay on a cellular chip by combining collagen gel embedded culture with scanning electrochemical microscopy by Shigenobu Kasai; Hitoshi Shiku; Yu-suke Torisawa; Kuniaki Nagamine; Tomoyuki Yasukawa; Toshiaki Watanabe; Tomokazu Matsue (pp. 55-59).
A novel cytokine assay has been designed using a cellular chip by combining a collagen gel embedded cell culture technique with scanning electrochemical microscopy–enzyme linked immunosorbent assay (SECM–ELISA). An array of cell–collagen gel mixture (2μL) was spotted on an antibody-coated chip and incubated for 0.5–24h. The very small trace amounts of cytokines produced by the activated leukocytes on the chip were effectively entrapped within the collagen gel matrix, and these were collected with the immobilized antibodies on the chip. The chip was further treated with horseradish peroxidase (HRP)-labeled antibodies via the sandwich method after removing the cell–collagen gel spots from the chip. Scanning electrochemical microscopy (SECM) was used to quantitatively evaluate the cytokines from the activated leukocytes produced on the chip, and the SECM images were obtained to visualize the position and concentration of IL-1β secreted from THP-1 and HL-60 cell lines at concentration levels of 10–350pgmL−1. Based on the chemiluminescence method, the sensitivity of the cytokine assay system in combination with SECM–ELISA is comparable to that of the marketed cytokine assay kit; further, the sample volume required for a single assay is drastically reduced.
Keywords: SECM-cytokine assay; Collagen cell chip; IL-1β; THP-1; HL-60
Predicting the performance of molecularly imprinted polymers: Selective extraction of caffeine by molecularly imprinted solid phase extraction by Keith Farrington; Edmond Magner; Fiona Regan (pp. 60-68).
A rational design approach was taken to the planning and synthesis of a molecularly imprinted polymer capable of extracting caffeine (the template molecule) from a standard solution of caffeine and further from a food sample containing caffeine. Data from NMR titration experiments in conjunction with a molecular modelling approach was used in predicting the relative ratios of template to functional monomer and furthermore determined both the choice of solvent (porogen) and the amount used for the study. In addition the molecular modelling program yielded information regarding the thermodynamic stability of the pre-polymerisation complex. Post-polymerisation analysis of the polymer itself by analysis of the pore size distribution by BET yielded significant information regarding the nature of the size and distribution of the pores within the polymer matrix. Here is proposed a stepwise procedure for the development and testing of a molecularly imprinted polymer using a well-studied compound—caffeine as a model system. It is shown that both the physical characteristics of a molecularly imprinted polymer (MIP) and the analysis of the pre-polymerisation complex can yield vital information, which can predict how well a given MIP will perform.
Keywords: Molecular imprinting; Rational design; Pore size distribution; Molecular modelling; Solid phase extraction; Caffeine
Ion imprinted polymer based ion-selective electrode for the trace determination of dysprosium(III) ions by K. Prasad; R. Kala; T. Prasada Rao; G.R.K. Naidu (pp. 69-74).
Ion-selective electrode (ISE) was designed by dispersing the dysprosium(III) IIP particles in 2-nitrophenyloctyl ether plasticizer and then embedded in polyvinyl chloride matrix. The ISE shows a Nernstian response for dysprosium(III) over a wide concentration range (8.0×10−6 to 1.0×10−1M) with a slope of 21.7mV per decade. The limit of detection was 2×10−6M. This sensor has a very fast response time (∼10s) and offers high selectivity compared to conventional chemical sensors towards dysprosium(III) with respect to several alkali, alkaline earth and transition metal ions as the selectivity is 10–100-fold better. The sensor was used for determination of dysprosium(III) ions by potentiometric (EDTA) titration and has been successfully demonstrated for the determination of fluoride in mouth wash solution.
Keywords: Ion imprinted polymer particles; Ion-selective electrode; Dysprosium(III); Fluoride; Mouthwash
The properties of calibration errors in the analysis of reduced sulfur compounds by the combination of a loop injection system and gas chromatography with pulsed flame photometric detection by Ki-Hyun Kim (pp. 75-80).
In order to evaluate the extent of analytical biases involved in the GC calibration, we conducted a series of experiments to examine the calibration methods of trace gas components. For the purpose of this comparative study, gaseous standards of reduced sulfur compounds (RSC) including hydrogen sulfide (H2S), methanethiol (CH3SH), dimethyl sulfide (DMS), carbon disulfide (CS2), and dimethyl disulfide (DMDS) were calibrated by the combination of a GC/PFPD technique and a loop-injection method. In the course of this study, two different types of calibration methods were tested and compared: incremental-injection of a given standard with the fixed standard concentration (FSC) versus injection of multiple standards (with different concentrations) at the fixed standard volume (FSV). In the case of the FSV calibration, a notable increase in the GC sensitivity is apparent with decreasing loop size (or injection volume). For instance, the calibration slope for RSC obtained using a 10μl loop system was approximately three times higher than that for a 250μl one. However, the results obtained by the FSC method exhibit much poorer sensitivity than its counterpart with slight differences in their sensitivities across different standard concentrations (due to such factors as the matrix effect from varying injection volumes). Thus, the overall results of this study confirm that the detailed characterization of the selected calibration method (e.g., the use of FSV approach relative to FSC) is of primary significance to perform an accurate quantification of trace gases.
Keywords: GC; PFPD; Hydrogen sulfide; Reduced sulfur compounds; Atmospheric
Properties of a genetic algorithm extended by a random self-learning operator and asymmetric mutations: A convergence study for a task of powder-pattern indexing by Wojciech Paszkowicz (pp. 81-98).
Genetic algorithms represent a powerful global-optimisation tool applicable in solving tasks of high complexity in science, technology, medicine, communication, etc. The usual genetic-algorithm calculation scheme is extended here by introduction of a quadratic self-learning operator, which performs a partial local search for randomly selected representatives of the population. This operator is aimed as a minor deterministic contribution to the (stochastic) genetic search. The population representing the trial solutions is split into two equal subpopulations allowed to exhibit different mutation rates (so called asymmetric mutation). The convergence is studied in detail exploiting a crystallographic-test example of indexing of powder diffraction data of orthorhombic lithium copper oxide, varying such parameters as mutation rates and the learning rate. It is shown through the averaged (over the subpopulation) fitness behaviour, how the genetic diversity in the population depends on the mutation rate of the given subpopulation. Conditions and algorithm parameter values favourable for convergence in the framework of proposed approach are discussed using the results for the mentioned example. Further data are studied with a somewhat modified algorithm using periodically varying mutation rates and a problem-specific operator. The chance of finding the global optimum and the convergence speed are observed to be strongly influenced by the effective mutation level and on the self-learning level. The optimal values of these two parameters are about 6 and 5%, respectively. The periodic changes of mutation rate are found to improve the explorative abilities of the algorithm. The results of the study confirm that the applied methodology leads to improvement of the classical genetic algorithm and, therefore, it is expected to be helpful in constructing of algorithms permitting to solve similar tasks of higher complexity.
Keywords: Abbreviations; DPF; dynamic penalty function; GA; genetic algorithm; HGA; hybrid genetic algorithm; LCO; lithium copper oxide; LM; local minimum; MGA; mixed genetic algorithm; OFN; objective function; RGA; reduced genetic algorithm; SL; self learningDiffraction pattern; Genetic algorithm; Indexing; Self-learning; Male driven evolution; Mutation; Operator; Premature convergence
Simultaneous measurement of trace monoadenosine and diadenosine monophosphate in biomimicking prebiotic synthesis using high-performance liquid chromatography with ultraviolet detection and electrospray ionization mass spectrometry characterization by Hongxia Liu; Canfang Zhao; Jiansha Lu; Mian Liu; Shusheng Zhang; Yuyang Jiang; Yufen Zhao (pp. 99-108).
The method for simultaneous separation and determination of trace monoadenosine and diadenosine monophosphate (i.e. 2′-AMP, 3′-AMP, 5′-AMP and 3′–5′ ApA) in biomimicking prebiotic synthesis was developed using high-performance liquid chromatography (HPLC) with ultraviolet (UV) detection and electrospray ionization mass spectrometry (ESI-MS) identification. The separation was performed on a Supelco C18 column with a gradient elution (solvent A: 10mM NH4Ac aqueous solution; solvent B: MeOH). The flow rate was set at 1.0ml/min. The quantitative determination was achieved by HPLC with UV detection at 260nm. The linearity ranged from 0.5 to 100μg/ml for each nucleotide. The limits of detection (LODs) for the four nucleotides were less than 0.30μg/ml. The recovery ranged from 95.2 to 100.7%. The intra-day relative standard deviations (RSDs) of the retention times were between 0.7 and 1.1%. Both full-scan ESI-MS and -MS2 for the four nucleotides under both positive and negative polarity were carried out and the possible cleavage pathways of them were depicted. The specific ions, [AMP+H]+ at m/ z 348 and [ApA+H]+ at m/ z 597, were chosen to characterize the four nucleotides in biomimicking prebiotic synthesis between N-( O, O-diisopropyl) phosphoryl amino acid (Dipp-aa) and adenosine. Using the proposed HPLC/UV/ESI-MS method, the concentration of 2′-AMP, 3′-AMP, 5′-AMP and 3′–5′ ApA in the biomimicking prebiotic synthesis samples were determined.
Keywords: N; -phosphoryl amino acid; Adenosine; Adenosine monophosphate; Diadenosine monophosphate; High-performance liquid chromatography; Electrospray ionization mass spectrometry
High-performance liquid chromatography with fluorescence detection for aqueous analysis of nanogram-level N-nitrosodimethylamine by Woosuk Cha; Peter Fox; Brijesh Nalinakumari (pp. 109-116).
High-performance liquid chromatography (HPLC) and fluorescence derivatization were applied for a nanogram-level N-nitrosodimethylamine (NDMA) analysis of water samples. For the analysis of N-nitrosodimethylamine, samples were first denitrosated by a mixed solution of hydrobromic acid and acetic acid to produce dimethylamine, which was derivatized with dansyl chloride for HPLC fluorescence detection. Fluorescence detection was optimized with excitation and emission wavelengths of 340 and 530nm, respectively. pH adjustment after denitrosation was necessary to maximize fluorescence intensity with pHs in the range of 9–12. A dansyl chloride concentration of 500mgl−1 was found to be optimal for measuring a fluorescence signal. An instrumental detection limit of 0.1ng of NDMA was possible with fluorescence derivatization. The NDMA in water samples was extracted by continuous solid-phase extraction using Ambersorb 572. Although the determination of NDMA was variable at lower concentrations (less than 200ngl−1), it was observed that the NDMA detection limit with this method could be lowered to a concentration of 10ngl−1. Another benefit of this method can be found in its selectivity for NDMA. Unlike gas chromatographic (GC) methods, this method generates a distinct peak for NDMA without interference even in the complex matrix of wastewater effluents. The HPLC with fluorescence derivatization method may be applicable for determining NDMA in water and wastewater samples for various research purposes and for screening environmental samples.
Keywords: N; -Nitrosodimethylamine (NDMA); HPLC; Fluorescence derivatization; Denitrosation; Dansyl chloride; Wastewater
Validation of two analytical methods for the determination of ochratoxin A by reversed-phased high-performance liquid chromatography coupled to fluorescence detection in musts and sweet wines from Andalusia by MarÃa Jesús Hernández; M. Valme GarcÃa-Moreno; Enrique Durán; Dominico Guillén; Carmelo G. Barroso (pp. 117-121).
Some Spanish sweet wines are made from raisins, grapes dried by direct exposure to the sun after picking. This drying process can encourage ochratoxin A (OTA) formation. OTA is a mycotoxin formed by several fungi. It has been linked to nephropathy in humans, and may have a long half-life in humans. The aim of this study is to develop and to apply two procedures for the analysis of OTA in grape musts (during the raisining process) and sweet wines, respectively. Reversed-phase high-performance liquid chromatography (RP-HPLC) coupled to fluorescence detection (FLD) was employed in both analytical methods. In grape must, the method involves the direct injection of the sample in a HPLC-FLD system without any kind of prior clean-up procedure. The complexity of the sweet wine samples requires a solid-phase extraction (SPE) clean-up on a C18 column which enables the OTA to be isolated from the matrix. The methods used were statistically validated. The validation also included the comparison of the slopes of the curve obtained with standards and the regression curves obtained by the addition of a standard. Two different studies of standard additions were conducted. One method was validated without sample preparation and it was applied to must samples. The other method was validated with SPE extraction and it was applied to sweet wine samples. Recovery was always better than 89.69%. The limit of detection (S/N=3) and limit of quantification (S/N=10) were established at 0.22 and 0.77μgl−1, respectively. In general, the analytical data obtained provided good results at the sub-μgl−1 concentration level.
Keywords: Ochratoxin A; Sweet wine; Grape must; Solid-phase extraction; Direct injection; Reversed-phased high-performance liquid chromatography coupled to fluorescence detection
2,2′:6′,2″-Terpyridine[hydroxypropyl-β-cyclodextrin] 1:3 complex used as chelating agent for the determination of iron with a sensitive, selective and fast liquid chromatographic method by Panos Mytides; Stavroula Rozou; Dimitra Benaki; Ekaterini Antoniadou-Vyza (pp. 122-129).
In the present work, 2,2′:6′,2″-Terpyridine (terpy), a substance with very poor aqueous solubility, was dissolved in water, after formation of its inclusion complex with hydroxypropyl-β-cyclodextrin (HPβCD), in a 1:3 stoichiometry. The obtained [terpy:(HPβCD)3] supramolecule, with enhanced aqueous solubility, enables its usage as a reagent at RP-LC methods. It was found that, terpy after inclusion complexation retains unaffected the ability of binding to Fe2+. It was also observed that, the stable, reddish-purple [Fe(terpy)]2+ complex was formed quantitatively in a wide pH range (2–9). Subsequently, iron as active substance or impurity in a drug product, can be determined through UV–vis measurements of [Fe(terpy)2]2+. Speed, sensitivity and selectivity are the most important features of the isocratic RP-LC method, developed to determine iron in pharmaceutical formulations. The duration of the chromatographic separation was less than 4.0min. The method was linear, precise and accurate from 0.17 to 2.2mgl−1 of iron and the detection limit was found to be 5μgl−1. The absorbance at 318 and 552nm allowed the quantitation of Fe (II) and Fe (III) after reduction, as well as of total Fe (II+III). Moreover, there were no interferences from Fe3+, Ni2+, Co2+ or Cu2+.
Keywords: Iron; Liquid chromatography; NMR; Cyclodextrin complex; 2,2′:6′,2″-Terpyridine; Chelate agent
Contributions of cationic and elemental gold on roughened gold substrates to surface-enhanced Raman scattering by Chung-Chin Yu; Yu-Chuan Liu (pp. 130-135).
In this work, the contributions of cationic and elemental gold on roughened gold substrates to surface-enhanced Raman scattering (SERS) of polypyrrole (PPy) films were first investigated. First, a gold substrate was roughened by a triangular wave oxidation–reduction cycle (ORC) in an aqueous solution containing 0.1M KCl. Then, the roughened gold substrate was further reduced by applying a cathodic potential for a fixed time to control the quantity of unreduced cationic Au on the roughened Au substrate. The result indicates that the content of cationic Au is responsible for the improved SERS of PPy electrodeposited on this roughened Au substrate. This phenomenon can be attributed to the interfacial charge transfer from PPy to the roughened Au substrate by the aid of cationic Au.
Keywords: Surface-enhanced Raman scattering; Polypyrrole; Cationic Au
Study of the influence of silver nanoparticles on the second-order scattering and the fluorescence of the complexes of Tb(III) with quinolones and determination of the quinolones by Fen Ding; Huichun Zhao; Linpei Jin; Dong Zheng (pp. 136-143).
Quinolones (Qs) can form the complex with Tb(III) ion, and the intramolecular energy transfer from Qs to Tb(III) takes place when excited. And thus the characteristic fluorescence of Tb(III) ion was enhanced and the maximum fluorescence peak locates at 545nm. The second-order scattering (SOS) peak at 545nm also appears for the Tb(III)–Qs complexes with the exciting wavelength of 274nm. When the silver nanoparticles were added to the Tb(III)–Qs system, the luminescence intensity at 545nm greatly increased. And the relative intensity is proportional to the amount of Qs. Based on this phenomenon, a novel method for determination of quinolones has been developed by using a common spectrofluorometer to measure the intensity of fluorescence and SOS. The luminescence intensity is greatly enhanced by silver nanoparticles in the pH range 5.5–6.2. The calibration graphs for pipemidic acid (PPA) and lomefloxacin (LMFX) are linear in the range 2.0×10−10 to 1.0×10−5 and 1.0×10−9 to 1.0×10−5molL−1, respectively. The limits of detection are 4.7×10−11molL−1 for PPA and 1.1×10−10molL−1 for LMFX. The method was applied satisfactorily to the determination of the two quinolones (Qs) in tablet, capsule, urine and serum samples. The experimental results showed that it is the certain size and certain concentration of silver nanoparticles that can greatly enhance the fluorescence -SOS intensity.
Keywords: Quinolones; Silver nanoparticles; Second-order scattering; Fluorescence