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Analytica Chimica Acta (v.554, #1-2)

Outside front cover - Editorial Board (pp. co1).

Contents (pp. v-vi).

Calendar of forthcoming meetings (pp. n1-n2).

Paid / MBP ad. aca_554_1_2_.pdf (pp. i).

Sequential injection analysis using electrochemical detection: A review by R. P�rez-Olmos; J.C. Soto; N. Z�rate; A.N. Ara�jo; M.C.B.S.M. Montenegro (pp. 1-16).

Nowadays a laboratory should be able to analyse a large number of samples in an accurate, reproducible, quick and economic way. As sequential injection analysis (SIA) is becoming an important tool for the automation of chemical procedures, this paper presents an overview of the principles of operation and applications of this emergent methodology using electrochemical detection. SIA systems developed to date present good characteristics for routine use and the electroanalytical methods proposed show adequate figures of merit. In addition, the results obtained are in good agreement with those furnished by the application of the reference methods.

Keywords: Sequential injection analysis; Electrochemical detection

Determination of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) in freshwaters by sequential injection spectrophotometry with on-line UV photo-oxidation by Orawan Tue-Ngeun; Richard C. Sandford; Jaroon Jakmunee; Kate Grudpan; Ian D. McKelvie; Paul J. Worsfold (pp. 17-24).

An automated sequential injection (SI) method for the determination of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) in freshwaters is presented. For DIC measurement on-line sample acidification (sulphuric acid, pH<2), converted DIC to CO₂ which subsequently diffused through a PTFE membrane into a basic, cresol red acceptor stream. The CO₂ increased the concentration of the acidic form of the cresol red indicator, with a resultant decrease in absorbance at 570nm being directly proportional to DIC concentration. DIC+DOC was determined after on-line sample irradiation (15W low power UV lamp) coupled with acid–peroxydisulfate digestion, with the subsequent detection of CO₂ as described above. DOC was determined by subtraction of DIC from (DIC+DOC). Analytical figures of merit were linear ranges of 0.05–5.0mgCL⁻¹ for both DIC and DIC+DOC, with typical R.S.D.s of less than 7% (0.05mgCL⁻¹–5.3% for DIC and 6.6% for DIC+DOC; 4.0mgCL⁻¹–2.6% for DIC and 2.4% for DIC+DOC, n=3) and an LOD (blank+3S.D.) of 0.05mgCL⁻¹. Sample throughput for the automated system was 8h⁻¹ for DIC and DOC with low reagent consumption (acid/peroxydisulfate 200μL per DIC+DOC analysis). A range of model carbon compounds and Tamar River (Plymouth, UK) samples were analysed for DIC and DOC and the results showed good agreement with a high temperature catalytic oxidation (HTCO) reference method ( t-test, P=0.05).

Keywords: Dissolved inorganic carbon; Dissolved organic carbon; UV photo-oxidation; Peroxydisulfate; Sequential injection; Freshwater

A sensitive procedure for the rapid determination of arsenic(III) by flow injection analysis and chemiluminescence detection by Sakchai Satienperakul; Terence J. Cardwell; Spas D. Kolev; Claire E. Lenehan; Neil W. Barnett (pp. 25-30).

A novel chemiluminescence flow injection procedure for the determination of As(III) in aqueous samples is described. The method involves injection of As(III) samples into a 1% (m/v) sodium hexametaphosphate in 0.02M H₂SO₄ carrier stream, which then merges at a Y-piece with a reagent stream consisting of potassium permanganate (5.0×10⁻⁵M) made up in the acidic sodium hexametaphosphate carrier solution. The chemiluminescence intensity of the resulting reaction mixture was measured at a photomultiplier tube operated at a voltage of 0.93kV. Under optimized conditions, the method is characterised by a linear range from 0.5 to 5.0μgl⁻¹, a detection limit of 0.3μgl⁻¹ and a sampling frequency of 150h⁻¹. The effects of common anionic and cationic interferences were investigated, and it was found that the only ions to cause serious interference were those which react with potassium permanganate, namely sulphide, iodide and ferrous.

Keywords: Flow injection; Chemiluminescence; Arsenic; Acidic potassium permanganate

An improved synthesis of disulfides linked β-cyclodextrin dimer and its analytical application for dequalinium chloride determination by spectrofluorimetry by Bo Tang; Hui-Ling Liang; Ke-Hua Xu; Zhen Mao; Xi-Feng Shi; Zhen-Zhen Chen (pp. 31-36).

An improved synthesis of β-cyclodextrin (β-CD) dimer, containing two β-CD moieties that are linked through their sides by disulfides was presented. The dimer was characterized by means of IR,¹H NMR and elemental analysis. The inclusion complexation behavior of β-cyclodextrin dimer with dequalinium chloride (DQC) was studied in an aqueous NH₄Ac–HAc buffer solution of pH 4.00 at room temperature by spectrofluorimetry. The apparent association constant of the complex was 1.67×10⁴lmol⁻¹, which showed higher affinity than native β-CD ( K_s=4.99×10²lmol⁻¹). Based on the significant enhancement of fluorescence intensity of DQC, a spectrofluorimetric method with high sensitivity and selectivity was developed for the determination of DQC in bulk aqueous solution in presence of β-CD dimer. The linear range was 6.38–1.60×10³ngml⁻¹with the detection limit 1.9ngml⁻¹. There was no interference from the excipients normally used in tablets and serum constituents. The proposed method was successfully applied to the determination of DQC in tablets and serum.

Keywords: Synthesis; β-Cyclodextrin dimer; Disulfides; Dequalinium chloride (DQC); Spectrofluorimetry

Simple and rapid determination of the active metabolite of nabumetone in biological fluids by heavy atom-induced room temperature phosphorescence by Jose A. Murillo Pulgar�n; Aurelia Ala��n Molina; Ignacio S�nchez-Ferrer Robles (pp. 37-42).

A simple, selective and sensitive heavy atom induced-room temperature phosphorimetric method is described for the determination of 6-methoxynaphthylacetic acid, main metabolite of nabumetone, in biological fluid. The phosphorescence signals are a consequence of intermolecular protection when analytes are, exclusively, in presence of heavy atom salt and sodium sulfite as an scavenger to minimize room temperature phosphorescence quenching. This technique enables us to determine analytes in complex matrices without the need for a tedious prior separation process.Optimized conditions for the determination were 0.12M TlNO₃. An amount of 0.025M sodium sulfite and pH 7.5 (adjusted with 0.1M sodium hydrogen phosphate-dihydrogen phosphate buffer solution). The delay time, gate time and time between flashes were 180, 1500μs, and 5ms, respectively.The maximum phosphorescence signal appeared instantly and the intensity was measured at λ_ex=328.4nm and λ_em=544.4nm. The response obtained was linearly dependent on concentration in the range of 20–1000ngmL⁻¹. The detection limit, according to error propagation theory, was 11.6ngmL⁻¹ and the detection limit as proposed by Clayton, was 17.4ngmL⁻¹. The repeatability was studied by using 10 solutions of 100 and 800ngmL⁻¹ of metabolite; if the theory of error propagation is assumed the relative error is 4.3 and 0.66%. The S.D. of replicates was found to be 2.2 and 11.0ngmL⁻¹. This method was successfully applied to the analysis of 6-methoxynaphthylacetic acid in human serum and urine.

Keywords: 6-Methoxynaphthylacetic acid; Biological fluids; Phosphorescence

Impedance spectral studies of self-assembly of alkanethiols with different chain lengths using different immobilization strategies on Au electrodes by Shinn-Jyh Ding; Bin-Wha Chang; Ching-Chou Wu; Min-Feng Lai; Hsien-Chang Chang (pp. 43-51).

Alkanethiols are commonly used self-assembly reagents in the preparation of modified electrode. In this study, self-assembled monolayers (SAMs) of alkanethiols with different chain lengths formed on gold electrode were mainly investigated by electrochemical impedance spectroscopy (EIS) in addition to cyclic voltammetry (CV). Two types of immobilization strategies applied to the electrode were also examined. The interfacial properties of all self-assembled electrodes were evaluated in the presence of Fe(CN)₆^3−/4− redox probe. A simple equivalent circuit model with a constant phase element was used to interpret the obtained impedance spectra. The results of cyclic voltammetry revealed that the voltammetric behavior of the redox probe was influenced by the electrode surface modification. The EIS data indicated that the formation of saturated SAMs on gold required at least 30min and more apparent differences occurred with immobilization time compared to that obtained by CV. Depending on the alkyl chain length of the SAMs, the electron-transfer resistance increased and the capacitance decreased. It was found a good linear relationship between inverse capacitance and chain length for carboxyl-terminated SAMs. To achieve a defect-free structure and/or close packing, the direct application method may provide a more effective, rapid, and facile self-assembly immobilization than immersion method from the viewpoint of the electron-transfer resistance.

Keywords: Self-assembly; Electrochemical impedance spectroscopy; Equivalent circuit; Cyclic voltammetry; Alkanethiol

Detection of Saccharomyces cerevisiae immobilized on self-assembled monolayer (SAM) of alkanethiolate using electrochemical impedance spectroscopy by Hui Chen; Chew Kiat Heng; Poenar Daniel Puiu; Xiao Dong Zhou; Ai Cheng Lee; Tit Meng Lim; Swee Ngin Tan (pp. 52-59).

The preparation of chemically functionalized self-assembled monolayer (SAM) surfaces is of great interest for applications in the immobilization of various bioactive species such as enzymes, DNA, whole cells, etc. In this paper, an electrochemical impedance biosensor for the rapid detection of Saccharomyces cerevisiae (yeast cells) was developed by immobilizing yeast cells on a gold surface modified with an alkanethiolate SAM. The patterns formed on the gold electrode surface after the assembly of 3-mercaptopropionic acid (MPA) monolayer and the immobilization of yeast cells were clearly observed from atomic force microscopy (AFM) and optical microscope, respectively. The electrochemical impedance spectroscopy (EIS) measurements were based on the charge-transfer kinetics of [Fe(CN)₆]^3−/4− redox couple. The SAM assembly and the subsequent immobilization of yeast cells on the gold electrodes greatly increased the electron-transfer resistance ( R_et) of the redox couple and decreased the double layer capacitance ( C_dl). A linear relationship between the R_et and logarithmic value of yeast concentrations was found in the range between 10² and 10⁸cfumL⁻¹.

Keywords: Saccharomyces cerevisiae; (yeast); Self-assembled monolayer (SAM); Electrochemical impedance spectroscopy (EIS)

Electrochemical deposition of 5,10,15,20-tetrakis-(4-sulphonatophenyl) porphyrin and its Co(II) derivative at a gold microelectrode array by Karolien De Wael; Annemie Adriaens; Eduard Temmerman (pp. 60-65).

This paper describes the fabrication and surface modification of gold microelectrode array structures. The modification is done by continuous cycling of the electrode array in a pH 12 buffer solution containing 8.01mmolL⁻¹ 5,10,15,20-tetrakis-(4-sulphonatophenyl)porphyrin tetrasodium salt (H₂TSPor). Incorporation of gold ions in the ligand during the potential cycling of the gold electrode is assumed. Only ring processes appear in the current potential curves, which do not change with scan number, indicating a fast adsorption. A second modification was performed through the electrodeposition of 5,10,15,20-tetrakis-(4-sulphonatophenyl)porphyrin Co(II) (CoTSPor) at a gold micro-electrode array.

Keywords: Surface modification; Porphyrins; Microelectrode array; Gold electrode; Electrocatalysis

Copper–palladium alloy nanoparticle plated electrodes for the electrocatalytic determination of hydrazine by Chih-Chio Yang; Annamalai Senthil Kumar; Ming-Chih Kuo; Shu-Hua Chien; Jyh-Myng Zen (pp. 66-73).

The preparation of copper–palladium alloy nanoparticle plated screen-printed carbon electrodes (SPE/Cu–Pd) and their use for the electrocatalytic determination of hydrazine in pH 7.4 phosphate buffer solution is described. X-ray photoelectron spectroscopic study indicates that the SPE/Cu–Pd prepared by successive electrochemical deposition of Cu and Pd is possessed of strong perturbed electronic interaction with a high Pd/Cu atomic ratio. Flow injection analysis of hydrazine using the SPE/Cu–Pd shows a linear detection range of 2–100μM at an applied potential of +0.2V versus Ag/AgCl with a current sensitivity and relative standard deviation of 0.21μA/μM and 1.86%, respectively. The detection limit (S/N=3) was 270nM. Quantitative detection of hydrazine in cigarette tobacco was further demonstrated using the proposed electrode.

Keywords: Copper; Palladium; Alloy; Nanoparticle; Hydrazine; Screen-printed electrode

Electrochemistry of nicotinamide adenine dinucleotide (reduced) at heated platinum electrodes by Carolin Lau; Gerd-Uwe Flechsig; Peter Gr�ndler; Joseph Wang (pp. 74-78).

This paper reports on the electrochemical behavior and determination of nicotinamide adenine dinucleotide reduced (NADH) at indirectly electrically heated platinum electrodes. At room temperature, a surface fouling can be observed during voltammetric and amperometric measurements, whereas a slight electrode heating during the measurements greatly minimizes such electrode passivation. This is illustrated by repetitive cyclic and square-wave voltammetric scans as well as using amperometry. The effect of electrode temperature and NADH concentration is evaluated. Amperometric calibration data exhibit a 10-fold higher sensitivity upon elevating the electrode temperature from 22 to 75�C. Furthermore, the amperometric response at the hot Pt-electrode is very stable, with 86% of the initial activity remaining after 20min stirring of 5mM NADH (compared to 32% under cold conditions). This represents the first example of using heated electrodes for minimizing surface fouling effects. The ability of heated Pt-electrodes to promote the NADH electron-transfer reaction suggests great promise for dehydrogenase-based amperometric biosensors.

Keywords: NADH; Heated platinum electrode; Hot-wire; LTCC; Surface fouling

Characterization of the composition of bovine urine and its effect on the electrochemical analysis of the model mediator, p-aminophenol by Mamun Jamal; Mark A. Crowe; Edmond Magner (pp. 79-85).

The reliable identification of compounds such as illegal growth promoters in cattle is generally based on expensive gas chromatography–mass spectrophotometric analysis in urine, a method that does not allow on a large-scale screening. The use of simple, semi-quantitative electrochemical biosensors may provide a means of screening for the presence of compounds such as illegal growth promoters. Before such sensors can be utilised, it is necessary to understand which factors influence the response of an electrochemical sensor in bovine urine. The concentration range of protein (0.01–0.04%), uric acid (0.5–0.65mM), xanthine (0.02–0.12mM) and ascorbic acid (0.1–0.95mM) in 26 individual urine samples were determined. Using p-aminophenol ( p-AP) as a model system, the electrochemical response increased by 5% in the presence of 6.0mM uric acid, by 10% on the addition of 0.2mM xanthine and by 22% in the presence of 1.0mM ascorbic acid. Exposing urine to air and light for 75min eliminated interference from ascorbic acid. Addition of Cu²⁺ (10μM) reduced the time required to 34min. Binding of species such as growth promoters to proteins may be disrupted by the addition of 8-anilino-1-naphthalene sulphonic acid (ANS) to the urine samples. Addition of 10μM ANS did not affect the limit of detection of p-AP. The pH of fresh bovine urine samples was monitored over the period 7 to 192h after collection and ranged from 8.00 to 8.77. The pH of lyophilised urine samples ranged from 8.24 to 9.60. Amperometry was the most sensitive method among a range of electrochemical techniques in the detection of p-AP with a limit of detection (LOD) in urine of 1.0μgmL⁻¹ (10μM) on a glassy carbon electrode.

Keywords: Electrochemical biosensors; Urine matrix effects; p; -Aminophenol; Interferents

Determination of trace tin by catalytic adsorptive cathodic stripping voltammetry by Yi-Heng Li; Hui Long; Fang-Qin Zhou (pp. 86-91).

A highly sensitive and selective catalytic adsorptive cathodic striping procedure for the determination of trace tin is presented. The method is based on adsorptive accumulation of the Sn(IV)–3,4-dihydroxybenzoic acid (DHBA) complex onto a hanging mercury drop electrode, followed by reduction of the adsorbed species. The reduction current is enhanced catalytically by vanadium(IV). The optimal experimental conditions include the use of 0.10M formate buffer (pH 3.1), 8.0×10⁻⁵M DHBA, 3.0×10⁻³M V(IV), an accumulation potential of −0.30V (versus SCE), an accumulation time of 60s, a scan rate of 200mV/s and a second-order derivative linear scan mode. The peak current is proportional to the concentration of tin over the range of 0.01–40μg/L, and the detection limit is 0.005μg/L for a 60s adsorption time. The proposed method was applied to the determination of tin in canned food, human hair and waste water samples with satisfactory results.

Keywords: Catalytic adsorptive stripping voltammetry; Tin; 3,4-Dihydroxybenzoic acid; Vanadium

A high performance glucose biosensor enhanced via nanosized SiO₂ by Haipeng Yang; Yongfa Zhu (pp. 92-97).

A series of monodispersed nano-SiO₂ film enhanced glucose biosensors with different thickness were fabricated by using dip-coating method. The suitable thickness of nanosized SiO₂ film provided optimal environment for glucose oxidase to retain its bioactivity. A key factor to fabricate high sensitivity glucose biosensor was to enlarge the enzyme loading on the surface. The high surface area of the small nanosized SiO₂ particles in the thick film increased the surface enzyme loading, resulting in the high performance of the biosensor. But if the film is too thick, the performance of the sensor would decrease because the mass transfer of glucose and H₂O₂ became difficulty. The electrochemical response of glucose with the 800nm SiO₂-biosensor revealed a linear behavior in the range of 0.005–2.5mM glucose in pH 7.2 phosphate buffer solution. Such a glucose biosensor held its sensitivity as high as 71.1μAmM⁻¹cm⁻² and its detection limit as low as 0.3μM. The good sensor-to-sensor reproducibility also indicates the simpleness and practicability of this kind of biosensor.

Keywords: Glucose biosensor; Monodispersed nano-SiO; ₂; Glucose oxidase; Immobilization; Film

Improved free chlorine amperometric sensor chip for drinking water applications by F. Javier Del Campo; Olga Ordeig; F. Javier Mu�oz (pp. 98-104).

This paper outlines the advantages of using gold cathodes, in comparison to platinum ones, combined with a series of potential steps that keep the electrode active longer times. A working potential of 0.150V versus Ag/AgCl (3MKCl) allows the amperometric determination of free chlorine over the pH range most likely to be found in drinking waters. This pH window spans from pH 5 up to pH 8. The importance of pH and how it can influence the amperometric response inside and outside this narrow pH window is discussed.

Keywords: Hypochlorite; Amperometry; Voltammetry; Drinking water; On-chip electrodes

Taste sensing with cellophane phosphate membrane by Sarmishtha Majumdar; Basudam Adhikari (pp. 105-112).

There are reports of taste sensor fabrication by incorporation of lipids in a PVC membrane. Such lipid-based sensors were used to evaluate the senses of tastes such as sourness, saltiness, sweetness, bitterness and umami by measuring the membrane potential using Ag/AgCl electrodes. We have measured the senses of above five basic tastes with a functionalized polymer membrane without using any lipid. Commercial cellophane membrane was reacted with POCl₃ for conversion to cellophane phosphate. FT-IR spectroscopy and XRD analysis were done to get an idea about the structure and the morphology of the membranes. The sensor characteristics like temporal stability, response stability, response to different taste substances, and reproducibility of sensing performance were studied using both cellophane and cellophane phosphate membranes. The sensor devices prepared with these membranes showed distinct response patterns in terms of membrane potentials for different taste substances. Both the membranes showed reproducible response patterns with a temporal stability of 30min in 1mM KCl solution and a stable response for 5min in 1mM solution of each of the taste substances such as HCl for sourness, NaCl for saltiness, sucrose for sweetness, quinine hydrochloride (Q-HCl) for bitterness and monosodium glutamate (MSG) for umami. The concentration threshold values of these membranes were compared with the human threshold values for the above taste substances. Both the membranes responded to lower threshold concentrations than the human detection limits. The membranes also showed characteristic response patterns for organic and mineral acids. Sensor device prepared with cellophane phosphate membrane has excellent shelf life.

Keywords: Taste sensor; Taste substances; Cellophane; Functionalized polymer

Validation of a dynamic ammonium extraction technique for the determination of¹⁵N at enriched abundances by Cristina Diaconu; Natacha Brion; Marc Elskens; Willy Baeyens (pp. 113-122).

A diffusion method for extracting ammonium from marine, estuarine and fresh waters for¹⁵N/¹⁴N isotopic ratio determinations at enriched level was developed and validated. The method is based on the conversion of NH₄⁺ to NH₃ gas under alkaline conditions, diffusion of NH₃ out of the solution to the headspace, NH₃ trapping on an acidified GF/D glass fiber filter, and subsequent¹⁵N/¹⁴N isotope ratio determination with mass spectrometry. The diffusion period necessary to extract sufficient N in order to accurately measure the atom%¹⁵N was reduced to less than 15h by bubbling the sample with a carrier gas (Air) at room temperature. The technique uses 250mL sample volume and enables accurate atom%¹⁵N measurements in NH₄⁺ pools as small as 1.25μM. A standard operating procedure for ammonium extraction is given involving method performance criteria, such as accuracy, precision, detection limit, quantification limit and robustness. The efficiency of the NH₄⁺ extraction ranged from 40 to 100%. The quantification limit of the method was estimated at around 0.26μmol% N, for an initial¹⁵N abundance of ∼1%. The within-laboratory reproducibility amounted to 0.03atom%¹⁵N. It was shown that the recovery rate obtained after extraction of the certified reference material (CRM: IAEA-311) solution falls within the 95% confidence interval of the certified values. By applying the developed method to fortified natural water samples of different conductivities, the atom%¹⁵N determinations were precise and accurate for α=1–5%.

Keywords: ¹⁵; N; Ammonium; Diffusion; Method; Mass spectrometry

Effects of deuterium in octopole reaction and collision cell ICP-MS on detection of selenium in extracellular fluids by Yasumitsu Ogra; Kazuya Ishiwata; Kazuo T. Suzuki (pp. 123-129).

Inductively coupled plasma-mass spectrometry (ICP-MS) equipped with a reaction/collision cell has been successfully used for dissociating polyatomic interferences. Hydrogen (H₂) is one of the most effective and frequently used reaction/collision gases. However, the H₂ reaction produces interference in the detection of selenium (Se) in bromine (Br)-containing samples, such as extracellular fluids. In this study, deuterium (D₂) was evaluated for possible use as a reaction gas instead of H₂. Although Se concentration in serum and urine was over-estimated in the H₂ reaction mode, it was determined accurately in the D₂ one. In speciation analyses, the background counts at m/ z 77, 78 and 80 were reduced and the signal-to-noise (S/N) ratios were improved by either the H₂ or the D₂ reaction. The⁷⁹Br¹H⁺ and⁸¹Br¹H⁺ interferences appearing at m/ z 80 and 82, respectively, were decreased by changing from the H₂ reaction mode to the D₂ one. Thus, D₂ was effective in dissociating polyatomic interferences and removing Br interferences during Se determination and speciation, suggesting that the D₂ reaction mode is useful for selenometallomics, particularly in samples containing Br, such as serum, urine and cell culture medium.

Keywords: Selenium; ICP-MS; Reaction/collision; Deuterium; Bromine; Speciation

Size characterization of manganese species from liver extracts using size exclusion chromatography inductively coupled plasma mass spectrometry by Mercedes Quintana; Alkisti D. Klouda; Maria Ochsenk�hn-Petropoulou; Bernhard Michalke (pp. 130-135).

Increased Mn levels are known to damage the central nervous system, resulting in motoric abnormalities and psychic disorder and finally resulting even in symptoms similar to Parkinson's disease. Monomethyl-Mn-pentadienyl-tricarbonyl is used as anti-knock agent and consequently Mn compounds are exhausted into air from automobiles. With additional inhalative Mn exposure, finally an Mn overflow of the liver is known, resulting in increased Mn transport to other organs, predominantly to the brain. Specific Mn-species then seem to be generated in liver, however, their speciation is still not investigated. This paper focuses on experiments to get more information on Mn species with respect to a size characterization of the Mn species in liver. Liver extracts were analyzed using a mass calibrated size exclusion chromatography (SEC) column being coupled to inductively coupled plasma mass spectrometry (ICP-MS) detection. As an important prerequisite, the stability of Mn species in the liver extracts during storage was investigated as well. It turned out that short term storage of the extract (under Ar atmosphere) at 4°C seems to be best suited. Storage for several days even at −20°C demonstrated already considerable changes in species pattern. Further investigations focused on improvements in detection during hyphenation using dynamic reaction cell (DRC) technology for Mn detection. The signal to noise (S/N) ratio was increased up to a factor of 15 when using DRC technology compared to conventional ICP-MS without DRC. The analysis of liver extracts with a mass calibrated SEC column coupled to inductively coupled plasma-dynamic reaction cell-mass spectrometry (ICP-DRC-MS) showed Mn associated to ca. 36% to a peak covering a mass range 100–260kDa, approximately 9% was found in a peak having the mass range 37–77kDa, 46% in a peak having the mass range 13–36kDa and ca. 7% in the low molecular mass (LMM) range.

Keywords: Mn; Speciation; Size exclusion chromatography; Liver extract; Inductively coupled plasma mass spectrometry (ICP-MS); Dynamic reaction cell

Chronocultural sorting of archaeological bronze objects using laser-induced breakdown spectrometry by F.J. Fortes; M. Cort�s; M.D. Sim�n; L.M. Cabal�n; J.J. Laserna (pp. 136-143).

This work discusses the capability of laser-induced breakdown spectrometry (LIBS) for characterization and cataloging of metallic objects belonging to the Bronze and Iron Ages. A set of 37 metallic objects from different locations of the South East of Iberian Peninsula has been sorted according to their metal content. Arsenic concentration in metallic objects has been found a key factor for distinguishing between Bronze and Iron Ages objects, allowing the chronocultural sorting of each piece. For this study, a pulsed Q-switched Nd:YAG laser was used to generate a microplasma onto the sample surface. To quantify and catalogue these metallic objects, calibration curves for copper, arsenic, tin, lead and iron were established. The quantitative results demonstrate that the chronological sorting carried out by LIBS matches agreeably with archaeological dating criteria.

Keywords: Laser-induced breakdown spectrometry; Archaeometallurgy; Bronzes; Quantitative analysis; Chronocultural sorting; Cluster analysis

Evaluation of a C18 hybrid stationary phase using high-temperature chromatography by Y. Liu; N. Grinberg; K.C. Thompson; R.M. Wenslow; U.D. Neue; D. Morrison; T.H. Walter; J.E. O’Gara; K.D. Wyndham (pp. 144-151).

Alkyl benzenes and aromatic alcohols were used as model analytes in a chromatographic separation on a new type of hybrid C18 stationary phase. The stationary phase was characterized from the point of view of its interaction with the mentioned analytes. The thermodynamic parameters such as Δ H° and Δ S° showed that there are very few differences in the interactions of the alkyl benzenes and aromatic alcohols with the stationary phase in the temperature interval from 150 to 200°C. A temperature study in the range from 30 to 200°C using toluene as an analyte revealed that the van’t Hoff plot is non-linear. Differential scanning calorimetry studies on this stationary phase indicated a phase transition at ∼90°C. Studies on the influence of organic modifier concentrations indicated that the retention of the analytes at 150°C varied linearly with the volume fraction of acetonitrile in the mobile phase. At 150°C the van Deemter plot showed that a minimum was reached for the reduced plate height at ∼1.6mL/min which was constant up to 5mL/min. A 1-month stability study of the column using pure water as a mobile phase, at 200°C indicated that analyte retention factor changed by 10% during this period of time.

Keywords: Alkyl benzenes; Aromatic alcohols; High-temperature chromatography; Thermodynamics; van Deemter plot; Hybrid stationary phase

Effect of chiral additive on formation of cellulose triacetate chiral stationary phase in HPLC by Li-Ming Yuan; Zhi-Gang Xu; Ping Ai; Yin-Xia Chang; A.K.M. Fakhrul Azam (pp. 152-155).

Cellulose triacetate, an chiral polymer that has been widely used in chiral recognition in high performance liquid chromatography, and also used in membrane science such as reverse osmosis, microfiltrtion and ultrafiltration, was coated on silica gel as stationary phase for HPLC and the pores of membrane were created by chiral additive (+)-di-O,O′- p-toluyl-d-tartarric acid, (+)-1-phenyl-1,2-ethanediol and (+)-l-mandelic acid, respectively. The results show that those stationary phases not only can separate extensively racemates, but also can resolve the chiral additive. This is a report, for the first time, that the chiral additive was used in formation of chiral stationary phase of optically active polymer. This work indicates that some optically active polymers, which have been used for chiral resolution, could soon become very attractive as new chiral stationary phase having a predictable chiral selectivity advantage.

Keywords: Chiral additive; Chiral recognition; Cellulose triacetate; HPLC

Enantiomeric separation of 8 hydroxy, 10 carboxylic and 6 dansyl amino acids by mono(6-amino-6-deoxy)-β-cyclodextrin in capillary electrophoresis by Weihua Tang; I. Wayan Muderawan; Siu-Choon Ng; Hardy Sze On Chan (pp. 156-162).

The enantioseparation of a wide spectrum of anionic analytes was successfully performed by using mono(6-amino-6-deoxy)-β-cyclodextrin (β-CD-NH₂). The effects of buffer pH and selector concentration on migration time and resolution of analytes were studied in detail. Good results were obtained for the chiral separations of hydroxy and carboxylic acids. A clear maximum in selectivity was found for most analytes. The introduced positive charge can greatly improve the chiral recognition ability of β-CD-NH₂ towards anionic analytes. The binding constants of eight analytes with β-CD-NH₂ were determined and suited well with the mobility difference model (by Wren). Moreover, a standard mixture of five acids was baseline separated within 23min.

Keywords: Enantioseparation; Cationic β-cyclodextrin; Capillary electrophoresis; Mono(6-amino-6-deoxy)-β-cyclodextrin; Binding constants

Theoretical characterization of McReynolds’ constants by Róbert Rajkó; Tamás Körtvélyesi; Krisztina Sebők-Nagy; Miklós Görgényi (pp. 163-171).

The properties of McReynolds’ constants were studied by a detailed statistical/chemometric analysis. The electronic structure, geometries and hydrophobicity of the McReynolds’ test compounds (benzene, 1-butanol, 2-pentanone, 1-nitropropane, pyridine, 2-methyl-2-pentanol, 1-iodobutane, 2-octyne, 1,4-dioxane and cis-hidrindane) were calculated at the level of PM3 semiempirical quantum chemical method and empirical formulas. The predominant pattern was revealed using cluster and principal component analyses (CA and PCA). Dependence of McReynolds’ constants on the calculated chemical descriptors was modeled by multiple linear regression (MLR) with stepwise selections, principal component regression (PCR) and partial least-square regression (PLSR). A novel statistical approach was developed for case-and-variable selection using the PCR and PLSR methods for characterizing and modeling the polarity of 25 gas chromatography (GC) stationary phases (phthalates, adipates, sebacates, phosphates, citrates and nitrils). Highest occupied molecular orbital energy, dipole moment, averaged isotropic polarizability and the apolar solvent accessible surface area; and energy of the lowest unoccupied molecular orbital and total solvent accessible surface area were suitable to describe the McReynolds’ constants based on the results obtained using Q² and adjusted- Q². Six of the 10 test compounds were found to be sufficient for the description of the polarity of the columns studied.

Keywords: Polarity; McReynolds’ constants; Stationary phases; Gas chromatography; Quantum chemical method; Principal component analysis; Principal component regression; Partial least-square regression; Case and variable selection

Flow-injection pulse amperometric detection based on ion transfer across a water-plasticized polymeric membrane interface for the determination of verapamil by J.A. Ortu�o; C. S�nchez-Pedre�o; A. Gil (pp. 172-176).

A flow-injection pulse amperometric method for determining verapamil, based on ion transfer across a plasticized poly(vinyl chloride) (PVC) membrane, was developed. A four-electrode potentiostat with ohmic drop compensation was used, while a flow-through cell incorporated the four-electrode and the membrane, which contained tetraphenylpyridinium tetraphenylborate. The influence of the applied potential and of the flow-injection variables on the determination of verapamil was studied. In the selected conditions, a linear relationship between current peak height and verapamil concentration over a range of 5×10⁻⁶ to 1×10⁻⁴M verapamil was found. Good repeatability and between-day reproducibility were obtained. Some common ions and pharmaceutical excipients did not interfere. The method proposed has been applied satisfactorily to the determination of verapamil in pharmaceuticals and human urine.

Keywords: Interface between two immiscible electrolyte solutions; Pulse amperometry; Plasticized polymeric membrane; Verapamil determination; Flow-injection analysis

Fast determination of p K_a values of reverse transcriptase inhibitor drugs for AIDS treatment by using pH-gradient flow-injection analysis and multivariate curve resolution by Antonio Checa; V�ctor Gonz�lez Soto; Santiago Hern�ndez-Cassou; Javier Saurina (pp. 177-183).

This paper aims at the characterization of acid–base properties of nucleoside analogs using a pH-gradient flow injection -diode array detector (FI-DAD) system and further data analysis with multivariate curve resolution. Drugs selected comprise nucleoside reverse transcriptase inhibitors (NRTIs) extensively used in AIDS treatment, including zidovudine (AZT), didanosine (ddl), stavudine (d4T) and zalcitabine (ddC). The FI system consists of a two-channel manifold in which the sample injection into an acid carrier is responsible of the generation of a pH gradient. A first step is focused on an accurate calibration of the pH-gradient shape inside the FI peak using nucleoside analogs of known p K_a values as standard compounds. The pH gradient in the FI peak is estimated from the concentration profiles of standard compounds. In a second step, the pH-gradient profile is exploited for a rapid estimation of unknown p K_a values of test drugs. Various approaches for calculating p K_a values are evaluated using the peak front or peak tail gradient ranges. As a result, overall errors in p K_a estimations are lower than 2.5%.

Keywords: AIDS drugs; p; K; _a; values; pH gradient; Flow-injection analysis; Multivariate curve resolution

Spectrophotometric determination of amoxicillin by reaction with N, N-dimethyl- p-phenylenediamine and potassium hexacyanoferrate(III) by Mouayed Q. Al-Abachi; Hind Haddi; Anas M. Al-Abachi (pp. 184-189).

A batch and flow injection analysis (FIA) spectrophotometric methods have been developed for the determination of amoxicillin (AMX) in aqueous solution and in pharmaceutical preparations. The methods are based on the reaction of AMX with N, N-dimethyl- p-phenylenediamine in the presence of potassium hexacyanoferrate(III) in alkaline medium. The water soluble blue colour product was measured at λ_max 660nm. Linearity was observed from 20 to 400 and 100 to 700μg AMX in a final volume of 10ml (i.e. 2–40 and 10–700μgml⁻¹ AMX) with detection limits of 0.637 and 4.90μgml⁻¹ AMX by batch and FIA procedure respectively. The effect of chemical and physical parameters have been carefully considered and the proposed procedures were successfully applied to the determination of AMX in pharmaceutical formulations.

Keywords: Spectrophotometric; Amoxicillin; Potassium hexacyanoferrate(III); Flow injection analysis

Pitfalls and solution for simultaneous determination of estrone and 17α-ethinylestradiol by gas chromatography–mass spectrometry after derivatization with N, O-bis(trimethylsilyl)trifluoroacetamide by Kai Zhang; Yuegang Zuo (pp. 190-196).

A procedure for the simultaneous determination of both natural and synthetic estrogenic steroids (estrone and 17α-ethynylestradiol) in water is described. Analytes were derivatized with N, O-bis(trimethylsilyl)trifluoroacetamide (BSTFA)+trimethylchlorosilane (TMCS) in pyridine solution and determined by GC–MS. The effects of solvent, temperature, and reaction time on the derivatization of EE2 were investigated in order to prevent the formation of undesired multiple derivatization products and conversion of trimethylsilyl (TMS) derivatives of EE2 formed to their respective El derivatives reported in previous studies. The identity and mechanism of formation of multiple derivatives have been discussed. A new silylation mixture (BSTFA:TMCS:pyridine=49.5:05:50, v/v/v) was employed to overcome these pitfalls and generate a single product of di-TMS derivative of EE2. In the presence of pyridine, variations in reaction temperature (25–80°C) and time (30min versus 60min) did not significantly affect the derivatization efficiency and stability of the di-TMS derivative of EE2 formed. A good linearity of response in the concentration range from 1.0 to 800μg/mL estrogens with a coefficient R²>0.996 at 50°C for quantitative analysis was also achieved.

Keywords: 17α-Ethynylestradiol (EE2); Estrone (E1); Derivatization; Gas chromatography–mass spectrometry; Steroids; Water chemistry

Investigation of solid-phase microextraction efficiency using pencil lead fiber for in vitro and in vivo sampling of defensive volatiles from insect's scent gland by Dj. Djozan; T. Baheri; R. Farshbaf; Sh. Azhari (pp. 197-201).

A new in vitro and in vivo solid-phase microextraction (SPME) sampling method using pencil lead fiber coupled with gas chromatography was developed for a fast, easy and reliable monitoring and recognition of volatile defensive chemical of scent gland of Graphosoma Lineatum (L.) ( Heteroptera Pentatomidae). The efficiency of three methods: (1) in vitro surgical sampling and direct injection in GC analysis known as a classical method, (2) in vitro surgical sampling, SPME/GC analysis and (3) in vivo SPME/GC method were investigated. The efficiency and reliability of homemade pencil lead fiber was evaluated and compared by commercial polydimethylsiloxane (PDMS) fiber. Some effective and experimental parameters, such as extraction time, chromatographic conditions were examined and optimized. The obtained results reveal that the in vivo SPME/GC is much better than in vitro pentane extraction of volatile compounds followed by either headspace SPME or direct injection and GC analysis. From the results obtained, for the studied chemicals, the extraction capacity of pencil lead fiber is about 1000-fold more than commercial PDMS fiber.

Keywords: Insect's scent gland; Volatile defensive compounds; In vitro sampling; In vivo sampling; SPME; Pencil lead fiber; Gas chromatography

Determination of azide in biological fluids by use of electron paramagnetic resonance by Kayoko Minakata; Osamu Suzuki (pp. 202-206).

A simple and sensitive method has been developed for the determination of azide ion (N₃⁻) in biological fluids and beverages. The procedure was based on the formation of a ternary complex Cu(N₃)₂(4-methylpyridine)_x in benzene, followed by its detection by electron paramagnetic resonance. The complex in benzene showed a characteristic four-peak hyperfine structure with a g-value of 2.115 at room temperature. Cu²⁺ reacted with N₃⁻ most strongly among common metals found in biological fluids. Several anions and metal ions in biological fluids did not interfere with the determination of N₃⁻ in the presence of large amounts of Cu²⁺ and oxidants. In the present method, N₃⁻ at the concentration from 5μM to 2mM in 100μl solution could be determined with the detection limit of 20ng. The recoveries were more than 95% for N₃⁻ added to 100μl of blood, urine, milk and beverages at 200μM. Our method is recommendable because it takes less than 10min to determine N₃⁻ and the produced complex is quite stable.

Keywords: Azide; Electron paramagnetic resonance; Copper; Blood; Urine

Application of infrared spectroscopy and multivariate quality-control methods in PVC manufacturing by Lidia Maria Bodecchi; Marina Cocchi; Marcello Malagoli; Matteo Manfredini; Andrea Marchetti (pp. 207-217).

This work aims at exploring the potentiality of the Fourier transform IR spectroscopy (FTIR) to study the effects that can be generated on plastic materials based on poly(vinyl chloride) (PVC) used for extra-corporal medical disposables, after industrial processes such as extrusion, sterilization and conservation. In particular, FTIR equipped with a single attenuated total reflection accessory (ATR) mounted on an infrared microscope (Mic-IR) has been used. At the same time, this paper proposes a quality-control method for semi-finished blood circuits’ components, based on the chemometric evaluation of surface-selective spectroscopic signals, i.e. Mic-IR/ATR spectra. Results suggest that IR spectroscopic technique coupled with a multivariate approach might represent a simple and powerful method for quality control of industrial processes.

Keywords: PVC; Industrial manufacturing; FTIR/ATR; Quality-control method; Multivariate control charts; 3-way PCA

Determination of alpha-naphthol by an oscillating chemical reaction using the analyte pulse perturbation technique by Wu Yang; Kanjun Sun; Weilian Lv; Lili Bo; Xiaoyan He; Nan Suo; Jinzhang Gao (pp. 218-223).

An analytical method for the determination of alpha-naphthol (α-NP) is proposed by the sequential perturbation caused by different amounts of alpha-naphthol on the oscillating chemical system involving the Cu(II)-catalyzed oscillating reaction between hydrogen peroxide and sodium thiocyanate in an alkaline medium with the aid of continuous-flow stirred tank reactor (CSTR). The method relies on the linear relationship between the changes in the oscillation amplitude of the chemical system and the concentration of alpha-naphthol. The use of the analyte pulse perturbation technique permits sequential determinations in the same oscillating system owing to the expeditiousness with which the steady state is regained after each perturbation. The calibration curve obeys a linear equation very well when the concentration of alpha-naphthol is over the range 0.034–530umol/L ( r=0.9991). Influences of temperature, injection points, flow rate and reaction variables on the oscillating system are investigated in detail and the possible mechanism of action of alpha-naphthol to the chemical oscillating system is also discussed. The method has been successfully used for the determination of α-naphthol in carbaryl hydrolysates.

Keywords: Alpha-naphthol; Oscillating chemical system; Analyte pulse perturbation

Author Index (pp. 224-226).

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Analytica Chimica Acta (v.554, #1-2)