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Analytica Chimica Acta (v.570, #2)

Editorial Board (pp. co1).

Contents (pp. iii-iv).

Calendar of forthcoming meetings (pp. n3).

Contents (pp. iii-iv).

Calendar of forthcoming meetings (pp. n3).

Editorial Board (pp. co1).

Enzyme-amplified protein microarray and a fluidic renewable surface fluorescence immunoassay for botulinum neurotoxin detection using high-affinity recombinant antibodies by Susan M. Varnum; Marvin G. Warner; Brian Dockendorff; Norman C. Anheier Jr.; Jianlong Lou; James D. Marks; Leonard A. Smith; Michael J. Feldhaus; Jay W. Grate; Cynthia J. Bruckner-Lea (pp. 137-143).

Two immunoassay platforms were developed for either the sensitive or rapid detection of botulinum neurotoxin A (BoNT/A), using high-affinity recombinant monoclonal antibodies against the receptor binding domain of the heavy chain of BoNT/A. These antibodies also bind the same epitopes of the receptor binding domain present on a nontoxic recombinant heavy chain fragment used for assay development and testing in the current study. An enzyme-linked immunosorbent assay (ELISA) microarray using tyramide amplification for localized labeling was developed for the specific and sensitive detection of BoNT. This assay has the sensitivity to detect BoNT in buffer and blood plasma samples down to 14fM (1.4pgmL⁻¹). Three capture antibodies and one antibody combination were compared in the development of this assay. Using a selected pair from the same set of recombinant monoclonal antibodies, a renewable surface microcolumn sensor was developed for the rapid detection of BoNT/A in an automated fluidic system. The ELISA microarray assay, because of its sensitivity, offers a screening test with detection limits comparable to the mouse bioassay, with results available in hours instead of days. The renewable surface assay is less sensitive but much faster, providing results in less than 10min.

Keywords: Immunoassay; Protein microarray; Renewable microcolumn sensor; Monoclonal antibody; Botulinum neurotoxin A

Developing an electrochemical deoxyribonucleic acid (DNA) biosensor on the basis of human interleukine-2 gene using an electroactive label by M.H. Pournaghi-Azar; M.S. Hejazi; E. Alipour (pp. 144-150).

Development of an electrochemical DNA biosensor based on a human interleukine-2 (IL-2) gene probe, using a pencil graphite electrode (PGE) as transducer and methylene blue (MB) as electroactive label is described. The sensor relies on the immobilization of a 20-mer single stranded oligonucleotide probe (hIL-2) related to the IL-2 gene on the electrode. The hybridization between the probe and its complementary sequence (chIL-2) as the target was studied by square wave voltammetry (SWV) of MB accumulated on the PGE. In this approach the extent of hybridization is evaluated on the basis of the difference between SWV signals of MB accumulated on the probe-PGE and MB accumulated on the probe-target-PGE. Some hybridization experiments with non-complementary oligonucleotides were carried out to assess whether the suggested DNA sensor responds selectively to the target. Some experimental variables affecting the performance of the biosensor including: polishing of PGE, its electrochemical activation conditions (i.e., activation potential and activation time) and probe immobilization conditions on the electrodes (i.e., immobilization potential and time) were investigated and the optimum values of 1.80V and 300s for PGE activation, and −0.5V and 400s for the probe immobilization on the electrode were suggested.

Keywords: Deoxyribonucleic acid biosensor; Human interleukine-2 gene; Methylene blue; Pencil graphite electrode; Hybridization detection

Self-assembling gold nanoparticles on thiol-functionalized poly(styrene- co-acrylic acid) nanospheres for fabrication of a mediatorless biosensor by Shiyi Xu; Guoli Tu; Bo Peng; Xiaozu Han (pp. 151-157).

A novel strategy to construct a sensitive mediatorless sensor of H₂O₂ was described. At first, a cleaned gold electrode was immersed in thiol-functionalized poly(styrene- co-acrylic acid) (St- co-AA) nanosphere latex prepared by emulsifier-free emulsion polymerization St with AA and function with dithioglycol to assemble the nanospheres, then gold nanoparticles were chemisorbed onto the thiol groups and formed monolayers on the surface of poly(St- co-AA) nanospheres. Finally, horseradish peroxidase (HRP) was immobilized on the surface of the gold nanoparticles. The sensor displayed an excellent electrocatalytical response to reduction of H₂O₂ without the aid of an electron mediator. The biosensor showed a linear range of 8.0μmolL⁻¹–7.0mmolL⁻¹ with a detection limit of 4.0μmolL⁻¹. The biosensor retained more than 97.8% of its original activity after 60 days’ storage. Moreover, the studied biosensor exhibited good current reproducibility and good fabrication reproducibility.

Keywords: Thiol-functionalized poly(St-; co; -AA) nanospheres; Gold nanoparticles; HRP; Biosensors; Self-assembly

Bulk-modified modified screen-printing carbon electrodes with both lactate oxidase (LOD) and horseradish peroxide (HRP) for the determination ofl-lactate in flow injection analysis mode by Fouad Ghamouss; Sophie Ledru; Nadine Ruillé; Françoise Lantier; Mohammed Boujtita (pp. 158-164).

A screen-printed carbon electrode modified with both HRP and LOD (SPCE–HRP/LOD) has been developed for the determination ofl-lactate concentration in real samples. The resulting SPCE–HRP/LOD was prepared in a one-step procedure, and was then optimised as an amperometric biosensor operating at [0, −100]mV versus Ag/AgCl forl-lactate determination in flow injection mode. A significant improvement in the reproducibility (coefficient variation of about 10%) of the preparation of the biosensors was obtained when graphite powder was modified with LOD in the presence of HRP previously oxidised by periodate ion (IO₄⁻). Optimisation studies were performed by examining the effects of LOD loading, periodation step and rate of the binder on analytical performances of SPCE–HRP/LOD. The sensitivity of the optimised SPCE–HRP/LOD tol-lactate was 0.84nALμmol⁻¹ in a detection range between 10 and 180μMol. The possibility of using the developed biosensor to determinel-lactate concentrations in various dairy products was also evaluated.

Keywords: Biosensor; Screen-printed carbon electrode SPCE; HRP; Direct electron transfer; l; -Lactate

A biosensor based on graphite epoxy composite electrode for aspartame and ethanol detection by Ülkü Anik Kirgöz; Dilek Odaci; Suna Timur; Arben Merkoçi; Salvador Alegret; Nurgün Beşün; Azmi Telefoncu (pp. 165-169).

A gelatin membrane with carboxyl esterase and alcohol oxidase was subsequently integrated onto the surface of a graphite epoxy composite electrode (GECE). The developed biosensors showed linearity in the range of 2.5–400μM for aspartame and 2.5–25μM for ethanol with response times of 170 and 70s for each analyte, respectively. The resulting bienzyme biosensor was used for aspartame detection in diet coke samples and ethanol detection in beer and wine samples. From the obtained results, it can be concluded that the developed biosensor is a selective, practical and economic tool for aspartame and ethanol detection in real samples.

Keywords: Bienzyme biosensor; Aspartame; Ethanol; Graphite epoxy composite electrode (GECE)

A selective optical sensor for picric acid assay based on photopolymerization of 3-( N-methacryloyl) amino-9-ethylcarbazole by Yan-Jun Hu; Shu-Zhen Tan; Guo-Li Shen; Ru-Qin Yu (pp. 170-175).

A novel optical sensor based on covalent immobilization for picric acid assay has been described. To improve the stability of the sensor, a terminal double bond was attached to the fluorescent compound, 3-amino-9-ethylcarbazole (AEC), via methacryloyl chloride. The resultant compound, 3-( N-methacryloyl) amino-9-ethylcarbazole (MAEC) was copolymerized with 2-hydroxypropyl methacrylate on surface-modified quartz glass plates by UV irradiation. The resulting optical sensor (optode membrane) was used to determine picric acid based on fluorescence quenching. It shows a linear response toward picric acid in the concentration range of 9.33×10⁻⁸ to 9.33×10⁻⁵moll⁻¹, with rapid response, high stability and good selectivity to picric acid.

Keywords: Optical sensor; 3-(; N; -methacryloyl) amino-9-ethylcarbazole; Covalent immobilization; Fluorescence quenching; Picric acid

A selective optical sensor for picric acid assay based on photopolymerization of 3-( N-methacryloyl) amino-9-ethylcarbazole by Yan-Jun Hu; Shu-Zhen Tan; Guo-Li Shen; Ru-Qin Yu (pp. 170-175).

Keywords: Optical sensor; 3-(; N; -methacryloyl) amino-9-ethylcarbazole; Covalent immobilization; Fluorescence quenching; Picric acid

Potentiometric anion selectivity of polymer-membrane electrodes based on cobalt, chromium, and aluminum salens by Ibrahim H.A. Badr (pp. 176-185).

Metallo-salens of cobalt(II) (Co-Sal), chromium(III) (Cr-Sal), and aluminum(III) (Al-Sal) are used as the active ionophores within plasticized poly(vinyl chloride) membranes. It is shown that central metal–ion plays a critical role in directing the ionophore selectivity. Polymer-membrane electrodes based on Co-Sal, Cr-Sal, and Al-Sal are demonstrated to exhibit enhanced responses and selectivity toward nitrite/thiocyanate, thiocyanate, and fluoride anions, respectively. The improved anion selectivity of the three ionophore systems is shown to deviate significantly from the classical Hofmeister pattern that is based only on ion lipophilicity. For example, optimized membrane electrodes for nitrite ion based on Co-Sal exhibitlogKNitrite,Anionpot values of −5.22, −4.66, −4.48, −2.5 towards bromide, perchlorate, nitrate, and iodide anions, respectively. Optimized membrane electrodes based on Co-Sal and Cr-Sal show near-Nernstian responses towards nitrite (−57.9±0.9mV/decade) and thiocyanate (−56.9±0.8mV/decade), respectively, with fast response and recovery times. In contrast, Al-Sal based membrane electrodes respond to fluoride ion in a super-Nernstian (−70±3mV/decade) and nearly an irreversible mode. The operative response mechanism of Co-Sal, Cr-Sal, and Al-Sal membrane electrodes is examined using the effect of added ionic sites on the potentiometric response characteristics. It is demonstrated that addition of lipophilic anionic sites to membrane electrodes based on the utilized metallo-salens enhances the selectivity towards the primary ion, while addition of cationic sites resulted in Hofmeister selectivity patterns suggesting that the operative response mechanism is of the charged carrier type. Electron spin resonance (ESR) data indicates that Co(II) metal–ion center of Co-Sal ionophore undergoes oxidation to Co(III). This process leads to formation of a charged anion-carrier that is consistent with the response behavior obtained for Co-Sal based membrane electrodes.

Keywords: Anion sensors; Polymer-membrane electrodes; Salen complexes; Response mechanism

Potentiometric anion selectivity of polymer-membrane electrodes based on cobalt, chromium, and aluminum salens by Ibrahim H.A. Badr (pp. 176-185).

Keywords: Anion sensors; Polymer-membrane electrodes; Salen complexes; Response mechanism

Measuring quaternary ammonium cleaning agents with ion selective electrodes by Michael A. Plesha; Bernard J. Van Wie; James M. Mullin; David A. Kidwell (pp. 186-194).

Data for coated-wire, ion selective electrodes (ISEs) are presented for cationic surfactant ions found in common cleaners including benzyldimethyltetradecylammonium, benzyldimethyldodecylammonium, and benzyldimethylhexadecylammonium. The ion exchangers dinonylnaphthalene sulfonic acid, tetraphenyborate, and tetrakis(4-chlorophenyl)borate are examined, showing dinonylnaphthalene sulfonic acid to be the favored species. The ISEs exhibit approximately Nernstian behavior down to the 10⁻⁶M limit of detection with lifetimes in excess of 50 days when used continuously, and a shelf life of over 100 days. Reaching the upper detection limit at the critical micelle concentration requires use of polymeric-membrane reference electrodes including a new membrane cocktail, which allow response measurements of an order of magnitude higher than the traditional fritted-glass reference electrode. The surfactant ISEs show excellent selectivity over the common metal ions Na⁺, K⁺, Mg²⁺, Ca²⁺, and Cu²⁺ with selectivity coefficients less than 10^−5.3. The ISEs are also selective over the lower molecular weight quaternary ammonium ions tetradecyltrimethylammonium, dodecyltrimethylammonium, benzyldimethyl(2-hydroxyethyl)ammonium, and tetrabutylammonium with selectivity coefficients ranging from 10^−1.7 to 10^−5.5. Use of a single electrode to determine accurately the total cationic surfactant concentration in common cleaning solutions is accomplished with information about concentration dependent interferences and a modified Nikolsky–Eisenman model. Finally, quaternary ammonium surfactants have a deleterious effect on the measurements of pH and common ions like K⁺, Mg²⁺ and Ca²⁺ with polymeric ISEs. This makes it critical to include surfactant electrodes in a detector array when cleaning agents are present.

Keywords: Ion selective electrode; Surfactant; Quaternary ammonium ion; Selectivity; Polymeric reference electrode

Measuring quaternary ammonium cleaning agents with ion selective electrodes by Michael A. Plesha; Bernard J. Van Wie; James M. Mullin; David A. Kidwell (pp. 186-194).

Keywords: Ion selective electrode; Surfactant; Quaternary ammonium ion; Selectivity; Polymeric reference electrode

Refreshable mercury film silver based electrode for determination of chromium(VI) using catalytic adsorptive stripping voltammetry by Bogusław Baś (pp. 195-201).

The refreshable mercury film silver based electrode Hg(Ag)FE applied for determination of Cr(VI) traces using catalytic adsorptive striping voltammetry (CAdSV) will be presented. The film electrode is characterized by its very good surface reproducibility (not less than 2%) and long-term stability (1500–2000 measurement cycles). The mechanical refreshing of mercury film is realized in the specially constructed device, in a time shorter than 1–2s.In the paper, it will be proved that a mechanically weak hanging mercury drop electrode (HMDE) may be substituted by mercury film Hg(Ag)FE electrode with a surface area adjustable from 1.5 to 12mm². For the electrode surface 4mm² the detection limit obtained for Cr(VI) was 0.19nM, while the linearity range measured for a 20s accumulation time was between 0.5 and 50nM. The relative standard deviation (R.S.D.) in determination of Cr(VI) varied from 1 to 5%. The influence of the excess of Cr(III) on determination of Cr(VI) was analyzed using samples from the Dobczyce reservoir spiked with known amounts of Cr(VI) and Cr(III).

Keywords: Chromium speciation; Water analysis; Voltammetry; Silver amalgams; Mercury film electrodes; Hanging mercury drop electrode

Refreshable mercury film silver based electrode for determination of chromium(VI) using catalytic adsorptive stripping voltammetry by Bogusław Baś (pp. 195-201).

Keywords: Chromium speciation; Water analysis; Voltammetry; Silver amalgams; Mercury film electrodes; Hanging mercury drop electrode

Chemiluminescence from singlet oxygen under laminar flow condition in a micro-channel by Kazuhiko Tsukagoshi; Kazuaki Fukumoto; Keiichi Noda; Riichiro Nakajima; Kenichi Yamashita; Hideaki Maeda (pp. 202-206).

Singlet oxygen was generated by reaction of sodium hypochlorite and hydrogen peroxide in a micro-channel. The two reagent solutions were delivered into the micro-channel by syringe pumps, providing a laminar flow. Such a laminar flow forms a liquid–liquid interface instantly in a micro-channel, and then the interface collapses gradually through molecular diffusion with the residence times. The chemiluminescence from the singlet oxygen was emitted in the course of the collapse of the interface under laminar flow condition. The chemiluminescence intensity was observed continuously and stably in the micro-channel as long as the reagents were fed into the channel. We examined the features of the chemiluminescence emitted in the micro-channel by changing the flow rates of reagents and the detection points in the micro-channel. The data obtained were considered along with the residence times and diffusion lengths. We also examined the effects of antioxidants, such as sodium azide, histidine, nitroblue tetrazolium, and 2-propanol on the chemiluminescence intensity.

Keywords: Micro-reactor; Micro-channel; Chemiluminescence; Singlet oxygen; Laminar flow

A novel electrogenerated chemiluminescence sensor for pyrogallol with core-shell luminol-doped silica nanoparticles modified electrode by the self-assembled technique by Lili Zhang; Xingwang Zheng (pp. 207-213).

The core-shell luminol-doped SiO₂ nanoparticles were synthesized and immobilized on the surface of chitosan film coating graphite electrode by the self-assembled technique. Then, a novel electrogenerated chemiluminescence (ECL) sensor for pyrogallol was developed based on its ECL enhancing effect for the core-shell luminol-doped silica nanoparticles. The ECL analytical performances and the sensing mechanism of this ECL sensor for pyrogallol were investigated in detail. The corresponding results showed that: compared with the conventional ECL reaction procedures by luminol ECL reaction system, the electrochemical (EC) reaction of pyrogallol and its subsequent chemiluminescence (CL) reaction occurred in the different spatial region whilst offering a high efficiency to couple the EC with the CL reaction to form the ECL procedures. In this case, this new sensing scheme offered more potential to improve the analytical performances of the ECL reaction. Under the optimum experimental conditions, this ECL sensor showed less than 5% decrease in continuums over 100 times ECL measurements, the detection limit was 1.0×1.0⁻⁹mol/L for pyrogallol. The linear range extended from 3.0×10⁻⁹mol/L to 2.0×10⁻⁵mol/L for pyrogallol.

Keywords: Core-shell luminol-doped SiO; ₂; nanoparticle; ECL sensor; Self-assembled; Pyrogallol determination

Synthesis of water-soluble, ring-substituted squaraine dyes and their evaluation as fluorescent probes and labels by Anatoliy L. Tatarets; Irina A. Fedyunyayeva; Tatyana S. Dyubko; Yevgeniy A. Povrozin; Andrey O. Doroshenko; Ewald A. Terpetschnig; Leonid D. Patsenker (pp. 214-223).

A series of ring-substituted squaraines absorbing and emitting in the red and NIR spectral region was synthesized and their spectral and photophysical properties (quantum yields, fluorescence lifetimes) and photostabilities were measured and compared to Cy5, a commonly used fluorescent label. The absorption maxima in aqueous media were found to be between 628 and 667nm and the emission maxima are between 642 and 685nm. Squaraine dyes exhibit high extinction coefficients (163,000–265,000M⁻¹cm⁻¹) and lower quantum yields (2–7%) in aqueous buffer but high quantum yields (up to 45%) and long fluorescence lifetimes (up to 3.3ns) in presence of BSA. Dicyanomethylene- and thio-substituted squaraines exhibit an additional absorption around 400nm with extinction coefficients between 21,500 and 44,500M⁻¹cm⁻¹. These dyes are excitable not only with red but also with blue diode lasers or light emitting diodes. Due to the favourable spectral and photophysical properties these dyes can be used as fluorescent probes and labels for intensity- and fluorescence lifetime-based biomedical applications.

Keywords: Probes; Labels; Squaraines; Fluorescence assay; Fluorescence lifetimes

On-line dynamic fractionation and automatic determination of inorganic phosphorus in environmental solid substrates exploiting sequential injection microcolumn extraction and flow injection analysis by Janya Buanuam; Manuel Miró; Elo Harald Hansen; Juwadee Shiowatana (pp. 224-231).

Sequential injection microcolumn extraction (SI-MCE) based on the implementation of a soil-containing microcartridge as external reactor in a sequential injection network is, for the first time, proposed for dynamic fractionation of macronutrients in environmental solids, as exemplified by the partitioning of inorganic phosphorus in agricultural soils. The on-line fractionation method capitalises on the accurate metering and sequential exposure of the various extractants to the solid sample by application of programmable flow as precisely coordinated by a syringe pump.Three different soil phase associations for phosphorus, that is, exchangeable, Al- and Fe-bound, and Ca-bound fractions, were elucidated by accommodation in the flow manifold of the three steps of the Hieltjes–Lijklema (HL) scheme involving the use of 1.0M NH₄Cl, 0.1M NaOH and 0.5M HCl, respectively, as sequential leaching reagents. The precise timing and versatility of SI for tailoring various operational extraction modes were utilized for investigating the extractability and the extent of phosphorus re-distribution for variable partitioning times.Automatic spectrophotometric determination of soluble reactive phosphorus in soil extracts was performed by a flow injection (FI) analyser based on the Molybdenum Blue (MB) chemistry. The 3 σ detection limit was 0.02mgPL⁻¹ while the linear dynamic range extended up to 20mgPL⁻¹ regardless of the extracting media. Despite the variable chemical composition of the HL extracts, a single FI set-up was assembled with no need for either manifold re-configuration or modification of chemical composition of reagents.The mobilization of trace elements, such as Cd, often present in grazed pastures as a result of the application of phosphate fertilizers, was also explored in the HL fractions by electrothermal atomic absorption spectrometry.

Keywords: Sequential injection; Dynamic fractionation; Inorganic phosphorus; Soil

A novel spectrophotometric method for batch and flow injection determination of sulfite in beverages by Saad S.M. Hassan; Mohamed S.A. Hamza; Ayman H.K. Mohamed (pp. 232-239).

A novel spectrophotometric assay method for batch and flow injection determination of sulfite in beverages is described. The method involves a reaction with diaquacobyrinic acid heptamethyl ester (diaquacobester, DACbs) in acetate buffer of pH 3 to form a highly stable sulfite cobester complex (SO₃Cbs). In the absence of sulfite, the reagent displays three absorption maxima at 349, 409 and 525nm. Addition of sulfite is associated with the development of a new absorption band at 313nm, an increase in the intensity of the band at 425nm and a decrease in the absorbance of the bands at 349 and 525nm. Variations of the absorptions at 313, 349, 425 and 525nm are linearly proportional to sulfite concentrations over the range of 0.05–25μgml⁻¹with a detection limit of 0.01–0.2μgml⁻¹. Negligible interferences are caused by most common ions. Validation of the method according to the quality assurance standards shows suitability for quality control assessment of sulfite in complex matrices without prior treatment. The method has the advantages of high selectivity, good sensitivity, fast reaction, high stability of the reagent and reaction product and absorbance measurements at four different wavelengths in the same run. The method is successfully applied to determine the sulfite contents of some beverages. The results compare fairly well with data obtained using the standard method.

Keywords: Spectrophotometry; Diaquacobyrinic acid heptamethylester (daquacobester); Sulfite determination; Flow injection analysis; Beverages

A novel spectrophotometric method for batch and flow injection determination of sulfite in beverages by Saad S.M. Hassan; Mohamed S.A. Hamza; Ayman H.K. Mohamed (pp. 232-239).

Keywords: Spectrophotometry; Diaquacobyrinic acid heptamethylester (daquacobester); Sulfite determination; Flow injection analysis; Beverages

Monodisperse porous polymer particles with polyionic ligands for ion exchange separation of proteins by Ender Unsal; Taşkın Irmak; Elifnaz Durusoy; Mürvet Tuncel; Ali Tuncel (pp. 240-248).

A new “grafting to�? strategy was proposed for the preparation of polymer based ion exchange supports carrying polymeric ligands in the form of weak or strong ion exchangers. Monodisperse porous poly(glycidyl methacrylate-co-ethylene dimethacrylate), poly(GMA-co-EDM) particles 5.9μm in size were synthesized by “modified seeded polymerization�?. Poly(2,3-dihydroxypropyl methacrylate-co-ethylene dimethacrylate), poly(DHPM-co-EDM) particles were then obtained by the acidic hydrolysis of poly(GMA-co-EDM) particles. The hydroxyl functionalized beads were treated with 3-(trimethoxysilyl)propyl methacrylate to have covalently linked methacrylate groups on the particle surface. The selected monomers carrying weak or strong ionizable groups (2-acrylamido-2-methyl-1-propane sulfonic acid, AMPS; 2-dimethylaminoethylmethacrylate, DMAEM and N-[3-(dimethylamino)propyl] methacrylamide, DMAPM) were subsequently grafted onto the particles via immobilized methacrylate groups. The final polymer based materials with polyionic ligands were tried as chromatographic packing in the separation of proteins by ion exchange chromatography. The proteins were successfully separated both in the anion and cation exchange mode with higher column yields with respect to the previously proposed materials. The plate heights obtained for poly(AMPS) and poly(DMAEM) grafted poly(DHPM-co-EDM) particles by using proteins as the analytes were 80 and 200μm, respectively. Additionally, the plate height exhibited no significant increase with the increasing linear flow rate in the range of 1–20cm/min. The most important property of the proposed strategy is to be applicable for the synthesis of any type of ion exchanger both in the strong and weak form.

Keywords: Ion exchange chromatography; High-performance liquid chromatography; Protein separation; Monodisperse porous particles; Chromatographic packing; Glycidyl methacrylate; Ethylene dimethacrylate

Monodisperse porous polymer particles with polyionic ligands for ion exchange separation of proteins by Ender Unsal; Taşkın Irmak; Elifnaz Durusoy; Mürvet Tuncel; Ali Tuncel (pp. 240-248).

A new “grafting to” strategy was proposed for the preparation of polymer based ion exchange supports carrying polymeric ligands in the form of weak or strong ion exchangers. Monodisperse porous poly(glycidyl methacrylate-co-ethylene dimethacrylate), poly(GMA-co-EDM) particles 5.9μm in size were synthesized by “modified seeded polymerization”. Poly(2,3-dihydroxypropyl methacrylate-co-ethylene dimethacrylate), poly(DHPM-co-EDM) particles were then obtained by the acidic hydrolysis of poly(GMA-co-EDM) particles. The hydroxyl functionalized beads were treated with 3-(trimethoxysilyl)propyl methacrylate to have covalently linked methacrylate groups on the particle surface. The selected monomers carrying weak or strong ionizable groups (2-acrylamido-2-methyl-1-propane sulfonic acid, AMPS; 2-dimethylaminoethylmethacrylate, DMAEM and N-[3-(dimethylamino)propyl] methacrylamide, DMAPM) were subsequently grafted onto the particles via immobilized methacrylate groups. The final polymer based materials with polyionic ligands were tried as chromatographic packing in the separation of proteins by ion exchange chromatography. The proteins were successfully separated both in the anion and cation exchange mode with higher column yields with respect to the previously proposed materials. The plate heights obtained for poly(AMPS) and poly(DMAEM) grafted poly(DHPM-co-EDM) particles by using proteins as the analytes were 80 and 200μm, respectively. Additionally, the plate height exhibited no significant increase with the increasing linear flow rate in the range of 1–20cm/min. The most important property of the proposed strategy is to be applicable for the synthesis of any type of ion exchanger both in the strong and weak form.

Geographical classification of wine and olive oil by means of classification and influence matrix analysis (CAIMAN) by Davide Ballabio; Andrea Mauri; Roberto Todeschini; Susanna Buratti (pp. 249-258).

Classification and influence matrix analysis (CAIMAN) is a new classification method, recently proposed and based on the influence matrix (also called leverage matrix). Depending on the purposes of the classification analysis, CAIMAN can be used in three outlines: (1) D-CAIMAN is a discriminant classification method, (2) M-CAIMAN is a class modelling method allowing a sample to be classified, not classified at all, or assigned to more than one class (confused) and (3) A-CAIMAN deals with the asymmetric case, where only a reference class needs to be modelled.In this work, the geographic classification of samples of wine and olive oil has been carried out by means of CAIMAN and its results compared with discriminant analysis, by focusing great attention on the model predictive capabilities. The geographic characterization has been carried out on three different datasets: extra virgin olive oils produced in a small area, with a “protected denomination of origin�? label, wines with different denominations of origin, but produced in enclosed geographical areas, and olive oils belonging to different production areas.Final results seem to indicate that the application of CAIMAN to the geographical origin identification offers several advantages: first, it shows – on an average basis – good performances; second, it is able to deal in a simple way classification problems related to tipicity, authenticity, and uniqueness characterization, which are of increasing interest in food quality issues.

Keywords: Classification; Leverage; Olive oil; Wine; Sensitivity; Specificity; Discriminant analysis

Classification and influence matrix analysis (CAIMAN) is a new classification method, recently proposed and based on the influence matrix (also called leverage matrix). Depending on the purposes of the classification analysis, CAIMAN can be used in three outlines: (1) D-CAIMAN is a discriminant classification method, (2) M-CAIMAN is a class modelling method allowing a sample to be classified, not classified at all, or assigned to more than one class (confused) and (3) A-CAIMAN deals with the asymmetric case, where only a reference class needs to be modelled.In this work, the geographic classification of samples of wine and olive oil has been carried out by means of CAIMAN and its results compared with discriminant analysis, by focusing great attention on the model predictive capabilities. The geographic characterization has been carried out on three different datasets: extra virgin olive oils produced in a small area, with a “protected denomination of origin” label, wines with different denominations of origin, but produced in enclosed geographical areas, and olive oils belonging to different production areas.Final results seem to indicate that the application of CAIMAN to the geographical origin identification offers several advantages: first, it shows – on an average basis – good performances; second, it is able to deal in a simple way classification problems related to tipicity, authenticity, and uniqueness characterization, which are of increasing interest in food quality issues.

Keywords: Classification; Leverage; Olive oil; Wine; Sensitivity; Specificity; Discriminant analysis

On-line monitoring of μg/L levels of haloacetic acids using ion chromatography with post-column nicotinamide reaction and fluorescence detection by Paul S. Simone Jr.; Greg T. Anderson; Gary L. Emmert (pp. 259-266).

A method for measuring the concentrations of the five regulated haloacetic acids (HAA5) in drinking water is reported. This method uses ion chromatography to separate HAA5 species, followed by post-column reaction with nicotinamide and detection of the fluorescent products. The result of method detection limit, accuracy, precision, linearity and interference studies are reported. The on-line monitoring method is compared directly to USEPA 552.3 in Memphis drinking water. Though not meant to replace the USEPA 552.3 for compliance monitoring, the proposed method does offer attractive alternatives considering the ease of automation and application of on-line monitoring directly from drinking water distribution systems.

Keywords: Haloacetic acids (HAA5); Drinking water; Water analysis; Ion chromatography; On-line monitoring; Disinfection by-products

Determination of selectivity differences for basic compounds in gradient reverse phase high performance liquid chromatography under high pH conditions by partial least squares modelling by Emilia Fornal; Phil Borman; Christopher Luscombe (pp. 267-276).

The retention behaviour of compounds in a chromatographic system is believed to be multivariate by nature, i.e. many physico-chemical properties of an analyte can influence its retention. Principal component analysis (PCA) and partial least squares (PLS) can therefore be particularly useful tools for visualising, exploring and modelling the complex interactions between solutes and the mobile and stationary phase. PCA allows the relationships between compounds (the observations) and their retention parameters (the variables) to be visualised in usually just two or three dimensions. PLS can be used to model quantitative structure-retention relationships (QSRRs) and may lead to better understanding of retention and selectivity changes in chromatographic systems.The objective of the study was to investigate the chromatographic behaviour of basic compounds under optimised gradient conditions using octadecyl high performance liquid chromatography (HPLC) columns designed for high pH separations. Three pharmaceutical mixtures were analysed by linear gradient reverse phase HPLC (RP-HPLC) at high pH using ammonia as a pH modifier, and methanol and/or acetonitrile as the organic modifier. The separations were carried out on three octadecyl columns: Waters XTerra MS C18, Agilent Zorbax Extend C18 and Thermo Hypersil-Keystone BetaBasic-18. Multivariate PCA and PLS modelling were employed to explore and explain the differences in selectivity between the chromatographic systems studied when the basic compounds were analysed under the high pH conditions. The interactions between the analytes and the mobile–stationary phases were described by relating the compound molecular descriptors with the selectivity of each chromatographic system. The selectivity differences between the chromatographic systems were identified.

Keywords: Reverse phase high pH liquid chromatography; Pharmaceutical analysis; Principal component analysis; Partial least squares analysis; Selectivity differences between chromatographic systems

Determination of lanthanides by source excited energy dispersive X-ray fluorescence (EDXRF) method after preconcentration with ammonium pyrrolidine dithiocarbamate (APDC) by Visnja Orescanin; Luka Mikelic; Vibor Roje; Stipe Lulic (pp. 277-282).

A new analytical procedure for determination of lanthanides in environmental samples after chemical separation from major matrix elements on DOWEX 50W-X8 resin followed by preconcentration with chelating agent ammonium pyrrolidine dithiocarbamate (APDC) and analyses of thin targets by energy dispersive X-ray fluorescence (EDXRF) method using¹⁰⁹Cd as the source of excitation was presented. Characteristic Lα X-ray lines of the lanthanides were used for calculations of the net peak area and mass concentrations. The influence of pH value of the solution and addition of organic matter on the complexation was investigated. Percentage of recovery of each lanthanide after separation on DOWEX 50W-X8 resin was also determined. Accuracy of the method was tested on standard reference materials and real environmental samples (red mud material). For that purpose samples of standard reference materials and red mud were prepared as thick targets and directly analyzed (without the separation step) by EDXRF method using²⁴¹Am as the excitation source. In that case lanthanides concentrations were determined over their characteristic Kα X-ray lines and results were compared with those obtained after separation/preconcentration step described above. Results showed that selected lanthanides made stable complexes with APDC in the alkaline medium with the maximum recovery at pH=8. The presence of organic matter slightly modified the complexation by means of somewhat higher recovery percentage at pH lower than 7 and approx. 20% lower recovery at pH higher than 7.Recovery of the elements after separation on DOWEX 50W-X8 resin and preconcentration with APDC at pH=8 varied from 91.4% (Pr) to only 24.9% in the case of Dy.Concentrations of lanthanides measured in standard reference material and environmental samples of red mud after microwave digestion, separation on DOWEX 50W-X8 resin, preconcentration with APDC at pH=8 and recalculation on the percentage of recovery were in good agreement with certified values in the case of SRM as well as with the concentrations obtained by direct determination over Kα lines using²⁴¹Am excitation source in the case of red mud leading to the conclusion that presented method was applicable for the determination of lanthanides in real environmental samples.

Keywords: Lanthanides; Preconcentration; APDC; EDXRF

Digital image-based titrations by Edvaldo da Nobrega Gaiao; Valdomiro Lacerda Martins; Wellington da Silva Lyra; Luciano Farias de Almeida; Edvan Cirino da Silva; Mário César Ugulino Araújo (pp. 283-290).

The exploitation of digital images obtained from a CCD camera (WebCam) as a novel instrumental detection technique for titration is proposed for the first time. Named of digital image-based (DIB) titration, it also requires, as a traditional titration (for example, spectrophotometric, potentiometric, conductimetric), a discontinuity in titration curves where there is an end point, which is associated to the chemical equivalence condition. The monitored signal in the DIB titration is a RGB-based value that is calculated, for each digital image, by using a proposed procedure based on the red, green, and blue colour system. The DIB titration was applied to determine HCl and H₃PO₄ in aqueous solutions and total alkalinity in mineral and tap waters. Its results were compared to the spectrophotometric (SPEC) titration and, by applying the paired t-test, no statistic difference between the results of both methods was verified at the 95% confidence level. Identical standard deviations were obtained by both titrations in the determinations of HCl and H₃PO₄, with a slightly better precision for DIB titration in the determinations of total alkalinity. The DIB titration shows to be an efficient and promising tool for quantitative chemical analysis and, as it employs an inexpensive device (WebCam) as analytical detector, it offers an economically viable alternative to titrations that need instrumental detection.

Keywords: Digital images; RGB colour system; DIB titration; Alkalinity; Waters analysis

Author index (pp. 291-293).

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Analytica Chimica Acta (v.570, #2)

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Analytica Chimica Acta (v.570, #2)