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Analytica Chimica Acta (v.599, #2)

Contents (pp. iii-iv).

Editorial Board (pp. co1).

Confirmation of lead aminocarboxylic complex formation using electrospray ionization mass spectrometry and speciation by anion-exchange chromatography coupled with ICP-MS by ZuLiang Chen; Gary Owens; Kwon-Rae Kim; Ravendra Naidu (pp. 163-169).

Inductively coupled plasma mass spectrometry (ICP-MS) and electrospray ionization mass spectrometry (ESI-MS) were used as complementary techniques to provide element and molecular information for aminocarboxylic lead species including [Pb(NTA)]¹⁻, [Pb(HEDTA)]¹⁻, [Pb(EDTA)]²⁻ and [Pb(DTPA)]³⁻. ESI-MS was used to initially confirm the formation of lead aminocarboxylic complexes in solution and subsequently anion-change chromatography coupled with ICP-MS was used to speciate these complexes using a mobile phase containing 30mM NH₄H₂PO₄ at pH of 8.0. However, [Pb(NTA)]¹⁻ was not observed during chromatographic separation due to its poor stability. The species [Pb(HEDTA)]¹⁻, [Pb(EDTA)]²⁻ and [Pb(DTPA)]³⁻ were separated within 15min with reasonable resolution and detection limits ranging from 0.05 to 0.2μgL⁻¹ with simple direct injection of sample. The proposed method was used to speciate aminocarboxylic lead complexes in soil solution.

Keywords: ESI-MS; IC–ICP-MS; Aminocarboxylic acid; Lead speciation; Soil solution

Microwave digestion—ICP-MS for elemental analysis in ambient airborne fine particulate matter: Rare earth elements and validation using a filter borne fine particle certified reference material by Pranav Kulkarni; Shankararaman Chellam; James B. Flanagan; R.K.M. Jayanty (pp. 170-176).

NIST standard reference material SRM 2783 was employed to validate a high temperature, high pressure, two-stage microwave assisted acid digestion procedure using HNO₃, HF and H₃BO₃ developed for the analysis of trace elements (including rare earths) in atmospheric fine particulate matter (PM_2.5) prior to inductively coupled plasma mass spectrometry (ICP-MS). This method quantitatively solubilized Na, Mg, Al, K, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sb, Cd, Cs, Ba, Pb, Th, U and several rare earth elements (REEs) (La, Ce, Pr, Nd, Gd, Dy, Er, Sm and Eu) from SRM 1648 and SRM 2783. A small amount of HF in the first stage was required to dissolve silicates necessitating the corresponding addition of H₃BO₃ in second stage to dissolve fluoride precipitates of Mg, La, Ce and Th. The optimized microwave dissolution—ICP-MS method detected Na, Mg, Al, K, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Cd, Mo, Sb, Cs, Ba, La, Ce, Pr, Nd, Sm, Gd, Pb, Th and U at trace to ultra-trace levels in ambient airborne fine particles from three sites in North Carolina. La to light lanthanide signature ratios suggested that soil and motor vehicles are the dominant REE sources in SRM 2783 and PM_2.5 samples collected during this study.

Keywords: Inductively coupled plasma mass spectrometry (ICP-MS); Microwave digestion; PM; _2.5; Standard reference material (SRM) 2783; Trace metals; Rare earth elements

Towards the development of a fossil bone geochemical standard: An inter-laboratory study by V. Chavagnac; J.A. Milton; D.R.H. Green; J. Breuer; O. Bruguier; D.E. Jacob; T. Jong; G.D. Kamenov; J. Le Huray; Y. Liu; M.R. Palmer; S. Pourtalès; I. Roduhskin; A. Soldati; C.N. Trueman; H. Yuan (pp. 177-190).

Ten international laboratories participated in an inter-laboratory comparison of a fossil bone composite with the objective of producing a matrix and structure-matched reference material for studies of the bio-mineralization of ancient fossil bone. We report the major and trace element compositions of the fossil bone composite, using in-situ method as well as various wet chemical digestion techniques.For major element concentrations, the intra-laboratory analytical precision (%RSD_r) ranges from 7 to 18%, with higher percentages for Ti and K. The %RSD_r are smaller than the inter-laboratory analytical precision (%RSD_R; <15–30%). Trace element concentrations vary by ∼5 orders of magnitude (0.1mgkg⁻¹ for Th to 10,000mgkg⁻¹ for Ba). The intra-laboratory analytical precision %RSD_r varies between 8 and 45%. The reproducibility values (%RSD_R) range from 13 to <50%, although extreme value >100% was found for the high field strength elements (Hf, Th, Zr, Nb). The rare earth element (REE) concentrations, which vary over 3 orders of magnitude, have %RSD_r and %RSD_R values at 8–15% and 20–32%, respectively. However, the REE patterns (which are very important for paleo-environmental, taphonomic and paleo-oceanographic analyses) are much more consistent.These data suggest that the complex and unpredictable nature of the mineralogical and chemical composition of fossil bone makes it difficult to set-up and calibrate analytical instruments using conventional standards, and may result in non-spectral matrix effects. We propose an analytical protocol that can be employed in future inter-laboratory studies to produce a certified fossil bone geochemical standard.

Keywords: Chemical composition; Biogenic phosphate; Reference material; Fossil bone/tooth

Dissolved inorganic carbon effect in the determination of arsenic and chromium in mineral waters by inductively coupled plasma-mass spectrometry by Maurizio Pettine; Barbara Casentini; Domenico Mastroianni; Silvio Capri (pp. 191-198).

The analysis of some Italian mineral waters by ICP-MS has revealed errors in the determination of As and Cr in natural effervescent or carbonated waters due to the presence of dissolved inorganic carbon (DIC). This leads to overestimate As and Cr in 1% (v/v) HNO₃ acidified samples, analysed within 1–2h after the acidification. The overestimation of As concentration is caused by matrix interferences producing a signal enhancement due to the presence of dissolved inorganic carbon. This effect is analogous to that observed in the presence of organic carbon and occurs at millimolar DIC levels. The overestimation of Cr concentration is due to the⁴⁰Ar¹²C⁺ species interfering with⁵²Cr⁺ despite the use of the octopole reaction system. The optimization of the He flow in the collision cell can solve the latter problem, but the required increase in the flow rate decreases the sensitivity of the ICP-MS technique. The observed effects in CO₂ rich mineral waters and artificial NaHCO₃ solutions suggest that 5–10mM DIC levels may affect the determination of As and Cr concentration in thermal waters, rivers, lakes and groundwaters.

Keywords: Inductively coupled plasma-mass spectrometry matrix interferences; Inorganic carbon signal enhancement; As and Cr analysis; Mineral and natural waters

The application and comparison of several chemometric methods of excitation–emission matrix spectra in studying the interactions of metal complexes with DNA by Fang Zhang; Qian-Qian Zhang; Wei-Guo Wang; Chen-Jian Zhu; Xiu-Lin Wang (pp. 199-208).

The interactions of fs DNA and two metal complexes [Cu(phen)SO₄]·2H₂O and [Ni(phen)SO₄]·2H₂O were explored by several chemometric methods, including parallel factor (PARAFAC), singular value decomposition-least squares (SVD-LS), and singular value decomposition-nonnegative least squares (SVD-NNLS) of excitation–emission matrix spectra (EEMs). The applications of SVD-LS and SVD-NNLS in this domain have been discussed. Rayleigh scatter part is avoided by ordered zero and reconstructed by linear interpolation. The importance of avoiding Rayleigh scatter has also been discussed. All the three methods do well in qualitative analysis. SVD-LS does best in present small changes of ethidium bromide (EB). In order to get accurate results, PARAFAC and SVD-NNLS can be utilized together in quantitative analysis. All the three chemometric methods indicate that the DNA binding modes of [Cu(phen)SO₄]·2H₂O are hydrogen bond effect and intercalation, while intercalation is the only DNA binding mode for [Ni(phen)SO₄]·2H₂O. These results are verified by the electronic absorption and emission fluorescence spectra. Just like PARAFAC, both SVD-LS and SVD-NNLS are proven to be convenient and convincing in studying the interactions between nucleic acids and complexes.

Keywords: Chemometric methods; Excitation–emission matrix spectra; Metal complex; DNA binding; Ethidium bromide

Simultaneous determination of iron and aluminium by differential kinetic spectrophotometric method and chemometrics by Yongnian Ni; Chunfang Huang; Serge Kokot (pp. 209-218).

A differential kinetic spectrophotometric method was researched and developed for the simultaneous determination of iron and aluminium in food samples. It was based on the direct reaction kinetics and spectrophotometry of these two metal ions with Chrome Azurol S (CAS) in ethylenediamine–hydrochloric acid buffer (pH 6.3). The results were interpreted with the use of chemometrics. The kinetic runs and the visible spectra of the complex formation reaction were studied between 540 and 750nm every 30s over a total period of 285s. A set of synthetic metal mixture samples was used to build calibrations models. These were based on the spectral and kinetic two-way data matrices, which were processed separately by the radial basis function-artificial neural network (global RBF-ANN) method. The prediction performance of these models was poorer than that from the combined kinetic-spectral three-way array, which was similarly processed by the same method (% relative prediction error (RPE_T)=5.6). These results demonstrate that improved predictions can be obtained from the data array, which has more information, and that appropriate chemometrics methods can enhance analytical performance of simple techniques such as spectrophotometry.Other chemometrics models were then applied: N-way partial least squares (NPLS), parallel factor analysis (PARAFAC), back propagation-artificial neural network (BP-ANN), single radial basis function-artificial neural network (RBF-ANN), and principal component neural network (PC-RBF-ANN). There was no substantial difference between the methods with the overall %RPE_T range being 5.0–5.8. These two values corresponded to the NPLS and BP-ANN models, respectively. The proposed method was applied for the determination of iron and aluminium in some commercial food samples with satisfactory results.

Keywords: Iron; Aluminium; Spectrophotometry; Kinetics; Chemometrics – PLS, ANN and PARAFAC

Bootstrap classification and point-based feature selection from age-staged mouse cerebellum tissues of matrix assisted laser desorption/ionization mass spectra using a fuzzy rule-building expert system by Peter B. Harrington; Claudine Laurent; Douglas F. Levinson; Pat Levitt; Sanford P. Markey (pp. 219-231).

A bootstrap method for point-based detection of candidate biomarker peaks has been developed from pattern classifiers. Point-based detection methods are advantageous in comparison to peak-based methods. Peak determination and selection are problematic when spectral peaks are not baseline resolved or on a varying baseline. The benefit of point-based detection is that peaks can be globally determined from the characteristic features of the entire data set (i.e., subsets of candidate points) as opposed to the traditional method of selecting peaks from individual spectra and then combining the peak list into a data set. The point-based method is demonstrated to be more effective and efficient using a synthetic data set when compared to using Mahalanobis distance for feature selection. In addition, probabilities that characterize the uniqueness of the peaks are determined.This method was applied for detecting peaks that characterize age-specific patterns of protein expression of developing and adult mouse cerebella from matrix assisted laser desorption/ionization (MALDI) mass spectrometry (MS) data. The mice comprised three age groups: 42 adults, 19 14-day-old pups, and 16 7-day-old pups. Three sequential spectra were obtained from each tissue section to yield 126, 57 and 48 spectra for adult, 14-day-old pup, and 7-day-old pup spectra, respectively. Each spectrum comprised 71,879 mass measurements in a range of 3.5–50kDa. A previous study revealed that 846 unique peaks were detected that were consistent for 50% of the mice in each age group (C. Laurent, D.F. Levinson, S.A. Schwartz, P.B. Harrington, S.P. Markey, R.M. Caprioli, P. Levitt, Direct profiling of the cerebellum by MALDI MS: a methodological study in postnatal and adult mouse, J. Neurosci. Res. 81 (2005) 613–621.).A fuzzy rule-building expert system (FuRES) was applied to investigate the correlation of age with features in the MS data. FuRES detected two outlier pup-14 spectra. Prediction was evaluated using 100 bootstrap samples of 2 Latin-partitions (i.e., 50:50 split between training and prediction set) of the mice. The spectra without the outliers yielded classification rates of 99.1±0.1%, 90.1±0.8%, and 97.0±0.6% for adults, 14-day-old pups, and 7-day-old pups, respectively. At a 95% level of significance, 100 bootstrap samples disclosed 35 adult and 21 pup distinguishing peaks for separating adults from pups; and 8 14-day-old and 15 7-day-old predictive peaks for separating 14-day-old pup from 7-day-old pup spectra. A compressed matrix comprising 40,393 points that were outside the 95% confidence intervals of one of the two FuRES discriminants was evaluated and the classification improved significantly for all classes. When peaks that satisfied a quality criterion were integrated, the 55 integrated peak areas furnished significantly improved classification for all classes: the selected peak areas furnished classification rates of 100%, 97.3±0.6%, and 97.4±0.3% for adult, 14-day-old pups, and 7-day-old pups using 100 bootstrap Latin partitions evaluations with the predictions averaged. When the bootstrap size was increased to 1000 samples, the results were not significantly affected. The FuRES predictions were consistent with those obtained by discriminant partial least squares (DPLS) classifications.

Keywords: Fuzzy rule-building expert system; Matrix assisted laser desorption/ionization; Mass spectrometry; Bootstrap Latin-partitions; Mouse (; Mus musculus domesticus; ); Cerebellum tissue; Biomarker

Use of different artificial neural networks to resolve binary blends of monocultivar Italian olive oils by Federico Marini; Antonio L. Magrì; Remo Bucci; Andrea D. Magrì (pp. 232-240).

The problem of authenticating extra virgin olive oil varieties is particularly important from the standpoint of quality control. After having shown in our previous works the possibility of discriminating oils from a single variety using chemometrics, in this study a combination of two different neural networks architectures was employed for the resolution of simulated binary blends of oils from different cultivars. In particular, a Kohonen self-organizing map was used to select the samples to include in the training, test and validation sets, needed to operate the successive calibration stage, which has been carried out by means of several multilayer feed-forward neural networks.The optimal model resulted in a validation Q² in the range 0.91–0.96 (10 data sets), corresponding to an average prediction error of about 5–7.5%, which appeared significantly better than in the case of random or Kennard–Stone selection.

Keywords: Extra virgin olive oil; Chemometrics; Artificial neural networks; Back-propagation algorithm; Kohonen self-organizing maps

Spectrophotometric investigation of the effect of β-cyclodextrin on the intramolecular cyclization reaction of catecholamines using rank annihilation factor analysis by Abbas Afkhami; Lida Khalafi (pp. 241-248).

The catalytic effect of β-cyclodextrin (β-CD) on the intramolecular cyclization reaction of catecholamines dopamine, methyldopa and levodopa after their oxidation with periodate was investigated spectrophotometrically using rank annihilation factor analysis (RAFA). The method was based on the effect of β-CD concentration on the intramolecular cyclization reaction of the investigated catecholamines after their oxidation with potassium periodate. In order to perform RAFA, concentration profiles were calculated by optimizing the value of formation constant. The rank of original data matrix can be reduced by one by annihilating the information of the cyclization reaction in the absence of β-CD. The rate constant for the reactions in the presence and absence of β-CD was also determined. The best estimation of rate constant in the presence of β-CD reduces the rank of the system to zero (noise level). The method was evaluated using synthetic data as well as experimental data and good results were obtained.

Keywords: Catecholamine; Cyclodextrin; Cyclization; Reaction rate; Stability constant

Anodic stripping voltammetry at a new type of disposable bismuth-plated carbon paste mini-electrodes by L. Baldrianova; I. Svancara; S. Sotiropoulos (pp. 249-255).

A new type of disposable carbon paste mini-electrodes (CPmEs), with dimensions in the 50–300μm range, have been fabricated by heat-shrinking the end-tip of plastic micropipette tips and filling them with carbon paste. The CPmEs have been characterized by microscopic and electrochemical means and tested as substrates for in situ plated Bi film electrodes (BiF–CPmEs), used in the determination of heavy metals by square wave anodic stripping voltammetry (SWASV). It was found that this new class of CPmEs combines the advantages of carbon paste electrodes (readily renewable surface and high surface area) with those of near-microelectrode behaviour (no stirring or electrolyte excess needed). During SWASV experiments in unstirred Pb(II) and Cd(II) solutions well-shaped stripping peaks were obtained whose height varied linearly with analyte concentration in the wide 1×10⁻⁸ to 10⁻⁶M range, both in acetate buffer and unbuffered solutions. Under optimal conditions detection limits of 8×10⁻¹⁰ and 1.3×10⁻⁹M were achieved for Pb(II) and Cd(II), respectively and in a trial application, these metal ions have been determined in a spiked tap water sample using a BiF–CPmE.

Keywords: Bismuth film electrodes; Microelectrodes; Carbon paste electrodes; Anodic stripping voltammetry

Purity of potassium hydrogen phthalate, determination with precision coulometric and volumetric titration–A comparison by Sebastian Recknagel; Martin Breitenbach; Joachim Pautz; Detlef Lück (pp. 256-263).

The mass fraction of potassium hydrogen phthalate (KHP) from a specific batch was certified as an acidimetric standard. Two different analytical methods on a metrological level were used to carry out certification analysis: precision constant current coulometric and volumetric titration with NaOH. It could be shown that with a commercial automatic titration system in combination with a reliable software for the end-point detection it is possible to produce equivalent results with the same accuracy in comparison to a definite method handled by a fundamental apparatus for traceable precision coulometry. Prerequisite for titrations are that a high number of single measurement are applied which are calibrated with a high precision certified reference material.

Keywords: Potassium hydrogen phthalate; Precision constant current coulometry; Volumetric titration; Certified reference material

Assessment of elemental mobility in soil using a fluidised bed approach with on-line ICP-MS analysis by Michael Philip Beeston; Hylke Jan Glass; Johannes Teun van Elteren; Zdenka Šlejkovec (pp. 264-270).

A new method has been developed to analyse the mobility of elements within soils employing counter-current flow soil contacting in a fluidised bed (FB) column. This method alleviates the problem of irreproducible peaks suffered by state-of-the-art micro-column techniques as a result of particle compaction. Reproducible extraction profiles are produced through the leaching of soil with a linear gradient of 0.05molL⁻¹ ammonium sulphate to 0.11molL⁻¹ acetic acid using a high pressure liquid chromatography (HPLC) quaternary pump, and the continuous monitoring of the elements in the leachate with inductively coupled plasma mass spectrometry (ICP-MS). Quantification of the procedure is achieved with an external flow injection (FI) calibration method.Flow rate and FB column length were investigated as critical parameters to the efficiency of the extraction methodology. It was found that an increase in the column length from 10 to 20cm using a flow rate of 0.15mLmin⁻¹ produced the same increase in extracted elemental concentration as an increase in flow rate from 0.15 to 0.30mLmin⁻¹. In both examples, the increase in the concentration of elements leached from the soil may be ascribed to the increase in the concentration gradient between the solid and liquid.The exhaustive nature of the technique defines the maximum leachable concentration within the operationally defined leaching parameters of the exchangeable phase, providing a more accurate assessment of the risk associated with the elements in the soil for the phase providing the greatest risk to the environment.The multi-elemental high sensitivity nature of the on-line detector provides an accurate determination of the associations present between the elements in the soil, and the identification of multiple phases within the exchangeable phase through the presence of multiple peaks in the extraction profiles. It is possible through the deconvolution of these extraction profiles that the concentration corresponding to the peaks identified can be defined.

Keywords: Counter-current flow; Extraction profile; Exchangeable phase; Exhaustive extraction

Study on the resonance Rayleigh scattering spectra of the interactions of palladium (II)–cephalosporins chelates with 4,5-dibromofluorescein and their analytical applications by Shenghui Fu; Zhongfang Liu; Shaopu Liu; Jangtao Liu; Aoer Yi (pp. 271-278).

In pH 2.8–3.8 BR buffer medium, the third generation cephalosporin antibiotics (TGCs) such as ceftazidime (CZD), ceftriaxone (CTRX), cefoperazone (CPZ), and cefotaxime (CFTM) react with palladium(II) (Pd(II)) to form 1:2 yellowish-brown cationic chelates, which further react with 4, 5-dibromofluorescein (DBF) to form 1:3 brown ion-association complexes. As a result, not only the spectra of absorption and fluorescence are changed, but also the resonance Rayleigh scattering (RRS) is enhanced greatly and the new RRS spectra are observed. The four TGCs products have similar spectral characteristics and their maximum RRS wavelengths are all located at 291nm. The quantitative determination ranges and the detection limits of the four TGCs are 0.0065–1.0μgmL⁻¹ and 2.0ngmL⁻¹ for CZD, 0.0070–1.1μgmL⁻¹ and 2.2ngmL⁻¹ for CTRX, 0.0090–1.6μgmL⁻¹ and 2.7ngmL⁻¹ for CPZ, and 0.014–2.2μgmL⁻¹ and 4.2ngmL⁻¹ for CFTM, respectively. The optimum conditions of the reactions and the effects of foreign substances are investigated, and the composition of ion-association complexes is discussed also. Based on the ion-association reaction, a highly sensitive, simple and rapid method has been proposed to the determination of TGCs.

Keywords: Resonance Rayleigh scattering; Cephalosporins; Palladium(II); 4,5-Dibromofluorescein

Light scattering sensing detection of pathogens based on the molecular recognition of immunoglobulin with cell wall-associated protein A by Zhong De Liu; Shao Fen Chen; Cheng Zhi Huang; Shu Jun Zhen; Qie Gen Liao (pp. 279-286).

In this contribution, we report a rapid optical detection method of pathogens using Staphylococcus aureus ( S. aureus) as the model analyte based on the molecular recognition of immunoglobulin with cell wall-associated Protein A (SpA). It was found that the molecular recognition of human immunoglobulin (IgG) with protein A on the cell wall of S. aureus on glass slide sensing area could result in strong surface enhanced light scattering (SELS) signals, and the SELS intensity (Δ I) increases proportionally with the concentration of S. aureus over the range of 2.5×10⁵–1.0×10⁸CFUmL⁻¹ with right angle light scattering (RALS) signals detection mode. In order to identify the solid support based molecular recognition between IgG with SpA, we also employed water-soluble CdS quantum dots (CdS-QDs) as a fluorescent marker for IgG by immobilizing the IgG onto the surfaces of CdS-QDs through covalent binding in order to generate recognition probes for SpA on the cell wall of S. aureus. Consequently, the fluorescent method also showed that the detection for pathogens with solid supports is reliable based on the molecular recognition of IgG with SpA.

Keywords: Surface enhanced light scattering; Molecular recognition; Staphylococcus aureus; CdS quantum dots

Catalytic activity of iron hexacyanoosmate(II) towards hydrogen peroxide and nicotinamide adenine dinucleotide and its use in amperometric biosensors by Petr Kotzian; Tereza Janků; Kurt Kalcher; Karel Vytřas (pp. 287-293).

Hydrogen peroxide and nicotinamide adenine dinucleotide (NADH) may be determined amperometrically using screen-printed electrodes chemically modified with iron(III) hexacyanoosmate(II) (Osmium purple) in flow injection analysis (FIA). The determination is based on the exploitation of catalytic currents resulting from the oxidation/reduction of the modifier. The performance of the sensor was characterized and optimized by controlling several operational parameters (applied potential, pH and flow rate of the phosphate buffer). Comparison has been made with analogous complexes of ruthenium (Ruthenium purple) and iron (Prussian blue). Taking into account the sensitivity and stability of corresponding sensors, the best results were obtained with the use of Osmium purple. The sensor exhibited a linear increase of the amperometric signal with the concentration of hydrogen peroxide in the range of 0.1–100mgL⁻¹ with a detection limit (evaluated as 3 σ) of 0.024mgL⁻¹ with a R.S.D. 1.5% for 10mgL⁻¹ H₂O₂ under optimized flow rate of 0.4mLmin⁻¹ in 0.1M phosphate buffer carrier (pH 6) and a working potential of +0.15V versus Ag/AgCl. Afterwards, a biological recognition element – either glucose oxidase or ethanol dehydrogenase – was incorporated to achieve a sensor facilitating the determination of glucose or ethanol, respectively. The glucose sensor gave linearity between current and concentration in the range from 1 to 250mgL⁻¹ with a R.S.D. 2.4% for 100mgL⁻¹ glucose, detection limit 0.02mgL⁻¹ (3 σ) and retained its original activity after 3 weeks when stored at 6°C. Optimal parameters in the determination of ethanol were selected as: applied potential +0.45V versus Ag/AgCl, flow rate 0.2mLmin⁻¹ in 0.1M phosphate buffer carrier (pH 7). Different structural designs of the ethanol sensor were tested and linearity obtained was up to 1000mgL⁻¹ with a maximum R.S.D. of 5.1%. Applications in food analysis were also examined.

Keywords: Screen-printed electrodes; Biosensor; Osmium purple; Ruthenium purple; Prussian blue; Hydrogen peroxide; Glucose; Ethanol; Flow injection analysis

A stoichiometric imprinted chelating resin for selective recognition of copper(II) ions in aqueous media by Mojtaba Shamsipur; Javad Fasihi; Alireza Khanchi; Rahim Hassani; Kamal Alizadeh; Hosna Shamsipur (pp. 294-301).

This work reports the preparation of a new copper(II) ion-imprinted polymer (IIP) material, using 5,6;14,15-dibenzo-1,4-dioxa-8,12-diazacyclopentadecane-5,14-diene (DBDA15C4) and 2-vinylpyridine (VP) as a non-vinylated chelating agent and a functional vinyl monomer, respectively. The Cu²⁺ ion can form stable complexes with DBDA15C4 and VP. The stoichiometries of Cu²⁺–DBDA15C4 and ternary Cu²⁺–DBDA15C4-VP complexes were elucidated using conductometric and spectrophotometric methods, and found to be Cu²⁺(DBDA15C4), Cu²⁺(DBDA15C4)₂ and Cu²⁺(DBDA15C4)(VP)₂. The results obtained from solution studies were also supported by ab initio theoretical calculations. The resulting ternary complex Cu²⁺(DBDA15C4)(VP)₂ was copolymerized with ethyleneglycoldimethacrylate, as a cross-linking monomer, via bulk polymerization method. The imprinted copper ion was removed from the polymeric matrix by 0.1M HNO₃. The Cu²⁺-imprinted polymer particles were characterized by IR spectroscopy and elemental analysis. Optimum pH range for rebinding of Cu²⁺ on the IIP and equilibrium binding time were 7.0–7.5 and 45min, respectively. Sorbent capacity and enrichment factor for Cu²⁺ were obtained as 75.3±1.9μmolg⁻¹ and 100, respectively. In selectivity study, it was found that imprinting results in increased affinity of the material toward Cu²⁺ ion over other competitor metal ions with the same charge and close ionic radius. The prepared IIPs were repeatedly used and regenerated for five times without a significant decrease in polymer binding affinities.

Keywords: Ion-imprinted polymer; Cu; ²⁺; Aza-crown; 2-Vinylpyridine; Bulk polymerization; Inductively coupled plasma-atomic emission spectrometry

Validated stability-indicating densitometric thin-layer chromatography: Application to stress degradation studies of minocycline by Nilu Jain; Gaurav Kumar Jain; Farhan Jalees Ahmad; Roop Krishen Khar (pp. 302-309).

A simple, stability-indicating high-performance thin-layer liquid chromatographic (HPTLC) method for analysis of minocycline was developed and validated. The densitometric analysis was carried out at 345nm using methanol–acetonitrile–isopropyl alcohol–water (5:4:0.5:0.5, v/v/v/v) as mobile phase.The method employed TLC aluminium plates pre-coated with silica gel 60F-254 as the stationary phase. To achieve good result, plates were sprayed with a 10% (w/v) solution of disodium ethylene diaminetetraacetic acid (EDTA), the pH of which was adjusted to 9.0. Compact spots of minocycline were found at R_f=0.30±0.02. For proposed procedure, linearity ( r=0.9997), limit of detection (3.7ngspot⁻¹), recovery (99.23–100.16%), and precision (% R.S.D.≤0.364) was found to be satisfactory. The drug undergoes acidic and basic degradation, oxidation and photodegradation. All the peaks of degradation products were well resolved from the pure drug with significantly different R_f values. The acidic and alkaline degradation kinetics of minocycline, evaluated using this method, is found to be of first order.

Keywords: Minocycline; High-performance thin-layer chromatography; Stress degradation; Stability-indicating

Electrophoresis mobility shift assay and biosensor used in studying the interaction between bleomycin A5 and DNA by Yanbin Liu; Fan Wu; Guolin Zou (pp. 310-314).

DNA is the potential target of numerous drugs utilized widely in clinical cancer therapy. Here we employed bleomycin A5, with its deactivated form as contrast, to investigate the interaction between small pharmaceutical and DNA. Electrophoresis mobility shift assay (EMSA) which is a common technique used in studying specific interactions between DNA and proteins is applied in visualizing the binding of bleomycin A5 with DNA intuitively. More accurate association equilibrium constant for native and deactivated bleomycin A5 to DNA achieved on biosensor IAsys AUTO⁺ is 1.25×10⁴ and 1.3×10³M⁻¹, respectively. With combination of EMSA and biosensor, a qualitative and quantitative method is described, which can be extended to studying the binding of most small molecules with targeting DNA and serves as a powerful tool in designing and screening for novel drugs.

Keywords: Bleomycin; Electrophoresis mobility shift assay; Biosensor; Deoxyribonucleic acid

Iron-chelating agents never suppress Fenton reaction but participate in quenching spin-trapped radicals by Li Linxiang; Yoshihiro Abe; Kiyotada Kanagawa; Tomoko Shoji; Tadahiko Mashino; Masataka Mochizuki; Miho Tanaka; Naoki Miyata (pp. 315-319).

Hydroxyl radical formation by Fenton reaction in the presence of an iron-chelating agent such as EDTA was traced by two different assay methods; an electron spin resonance (ESR) spin-trapping method with 5,5-dimethyl-1-pyrroline N-oxide (DMPO), and high Performance liquid chromatography (HPLC)-fluorescence detection with terephthalic acid (TPA), a fluorescent probe for hydroxyl radicals. From the ESR spin-trapping measurement, it was observed that EDTA seemed to suppress hydroxyl radical formation with the increase of its concentration. On the other hand, hydroxyl radical formation by Fenton reaction was not affected by EDTA monitored by HPLC assay. Similar inconsistent effects of other iron-chelating agents such as nitrylotriacetic acid (NTA), diethylenetriamine penta acetic acid (DTPA), oxalate and citrate were also observed. On the addition of EDTA solution to the reaction mixture 10min after the Fenton reaction started, when hydroxyl radical formation should have almost ceased but the ESR signal of DMPO-OH radicals could be detected, it was observed that the DMPO-OH signal disappeared rapidly. With the simultaneous addition of Fe(II) solution and EDTA after the Fenton reaction ceased, the DMPO-OH signal disappeared more rapidly. The results indicated that these chelating agents should enhance the quenching of [DMPO-OH] radicals by Fe(II), but they did not suppress Fenton reaction by forming chelates with iron ions.

Keywords: Electron spin resonance; 5,5-Dimethyl-1-pyrroline; N; -oxide; Hydroxyl radical; Fenton reaction; Ethylenediamine tetraacetic acid

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Analytica Chimica Acta (v.599, #2)