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Analytica Chimica Acta (v.611, #2)

Editorial Board (pp. co1).

Contents (pp. iii-iv).

Editorial Board (pp. i).

Determination of the different oxidation states of As and Sb by a new electrochemical hydride generator coupled with atomic fluorescence spectrometry by Wang-bing Zhang; Xin-an Yang (pp. 127-133).

A novel disk electrochemical hydride generator has been developed for the determination of As and Sb. Compared with the traditional thin-layer cell, the disk cell combined the advantages of quick assembly and easy operation. This electrochemical system for hydride generation in neutral buffer solutions has been studied for analytical usefulness in coupling with atomic fluorescence spectrometry. It was found that the use of neutral phosphate buffer solution could markedly increase the fluorescence intensity of As(III) and Sb(III) and reduce the impact of cathode erosion on the stability of signal intensity. At the same time, the fluorescence intensity of As(V) and Sb(V) were almost suppressed totally. The detection limits (3 σ) of 0.031μgL⁻¹ As(III) and 0.026μgL⁻¹ Sb(III) in aqueous solutions were obtained, respectively. The precisions ( n=11) for 20μgL⁻¹ As(III) and Sb(III) were 2.0% and 2.7%, respectively. The method was successfully applied for determination of different oxidation states of As and Sb in environmental samples.

Keywords: Electrochemical hydride generation; Disk electrolytic cell; Neutral electrolyte; Atomic fluorescence spectrometry; Arsenic; Antimony

Optimisation and critical evaluation of a collision cell technology ICP-MS system for the determination of arsenic in foodstuffs of animal origin by Vincent Dufailly; Laurent Noël; Thierry Guérin (pp. 134-142).

The determination of arsenic (⁷⁵As) was studied using an ICP-MS equipped with collision cell technology (CCT). Different mixtures of gases (He and H₂) were tested using HCl conditions and a He flow rate of 4mLmin⁻¹ was found to be suitable for the removal of the poly-atomic spectral interference [⁴⁰Ar³⁵Cl]⁺. Trueness of the optimised method has been evaluated in both standard and CCT modes on six certified reference materials in foodstuffs of animal origin and on three external proficiency testing schemes (FAPAS). The results obtained generally coincided with the certified values, except for CCT mode in some categories of samples (meat, mussels and milk powder), for which a positive bias on results was observed due to the formation of poly-atomic interferences within the collision cell. The main interferences were studied and their contributions estimated. [⁵⁸Fe¹⁶O¹H]⁺ and [⁷⁴Ge¹H]⁺ were the most significant interferences formed in the cell. Finally, different parameters (e.g. hexapole and quadrupole bias voltage, nebuliser gas flow) were optimised to try to attenuate these interferences.

Keywords: Inductively coupled plasma mass spectrometry; Collision cell; Foodstuffs; Arsenic; Interferences

Content uniformity determination of pharmaceutical tablets using five near-infrared reflectance spectrometers: A process analytical technology (PAT) approach using robust multivariate calibration transfer algorithms by Yusuf Sulub; Rosario LoBrutto; Richard Vivilecchia; Busolo Wa Wabuyele (pp. 143-150).

Near-infrared calibration models were developed for the determination of content uniformity of pharmaceutical tablets containing 29.4% drug load for two dosage strengths (X and Y). Both dosage strengths have a circular geometry and the only difference is the size and weight. Strength X samples weigh approximately 425mg with a diameter of 12mm while strength Y samples, weigh approximately 1700mg with a diameter of 20mm. Data used in this study were acquired from five NIR instruments manufactured by two different vendors. One of these spectrometers is a dispersive-based NIR system while the other four were Fourier transform (FT) based. The transferability of the optimized partial least-squares (PLS) calibration models developed on the primary instrument (A) located in a research facility was evaluated using spectral data acquired from secondary instruments B, C, D and E. Instruments B and E were located in the same research facility as spectrometer A while instruments C and D were located in a production facility 35miles away. The same set of tablet samples were used to acquire spectral data from all instruments. This scenario mimics the conventional pharmaceutical technology transfer from research and development to production. Direct cross-instrument prediction without standardization was performed between the primary and each secondary instrument to evaluate the robustness of the primary instrument calibration model. For the strength Y samples, this approach was successful for data acquired on instruments B, C, and D producing root mean square error of prediction (RMSEP) of 1.05, 1.05, and 1.22%, respectively. However for instrument E data, this approach was not successful producing an RMSEP value of 3.40%. A similar deterioration was observed for the strength X samples, with RMSEP values of 2.78, 5.54, 3.40, and 5.78% corresponding to spectral data acquired on instruments B, C, D, and E, respectively. To minimize the effect of instrument variability, calibration transfer techniques such as piecewise direct standardization (PDS) and wavelet hybrid direct standardization (WHDS) were used. The PDS approach, the RMSEP values for strength X samples were lowered to 1.22, 1.12, 1.19, and 1.08% for instruments B, C, D, and E, respectively. Similar improvements were obtained using the WHDS approach with RMSEP values of 1.36, 1.42, 1.36, and 0.98% corresponding to instruments B, C, D, and E, respectively.

Keywords: Pharmaceutical analysis; Near-infrared; Content uniformity; Calibration transfer; Partial least-squares

Palladium nanoparticle decorated carbon ionic liquid electrode for highly efficient electrocatalytic oxidation and determination of hydrazine by Norouz Maleki; Afsaneh Safavi; Elahe Farjami; Fariba Tajabadi (pp. 151-155).

In this work arrays of palladium nanoparticles were synthesized on carbon ionic liquid electrode (CILE) (Pd/CILE), and the electrocatalytic oxidation of hydrazine was investigated using this electrode. Electrochemical oxidation of hydrazine in phosphate buffer (pH 7) was performed using cyclic voltammetry and square wave voltammetric techniques (SWV). Using the proposed electrode, a highly reproducible and well-defined peak was obtained for hydrazine at a very low potential of −0.02V versus Ag/AgCl. A linear dynamic range of 5–800μM with an experimental detection limit of 0.82μM was obtained. These results show that the proposed electrode displays better electrocatalytic activity compared to the previously reported palladium modified electrodes towards oxidation of hydrazine.

Keywords: Palladium arrays nanoparticles; Carbon ionic liquid electrode; Hydrazine; Electrocatalytic oxidation

Electrochemical detection of dopamine using arrays of liquid–liquid micro-interfaces created within micromachined silicon membranes by Alfonso Berduque; Raúl Zazpe; Damien W.M. Arrigan (pp. 156-162).

The detection of protonated dopamine by differential pulse voltammetry (DPV) and square wave voltammetry (SWV) at arrays of micro-interfaces between two immiscible electrolyte solutions (μITIES) is presented. Microfabricated porous silicon membranes (consisting of eight pores, 26.6μm in radius and 500μm pore–pore separation, in a hexagonal layout) were prepared by photolithographic and etching procedures. The membrane pores were fabricated with hydrophobic internal walls so that the organic phase filled the pores and created the liquid interface at the aqueous side of the membrane. These were used for harnessing the benefits of three-dimensional diffusion to the interface and for interface stabilisation. The liquid–liquid interface provides a simple method to overcome the major problem in the voltammetric detection of dopamine at solid electrodes due to the co-existence of ascorbate at higher concentrations. Selectivity for dopamine over ascorbate was achieved by the use of dibenzo-18-crown-6 (DB18C6) for the facilitated ion transfer of dopamine across the μITIES array. Under these conditions, the presence of ascorbate in excess did not interfere in the detection of dopamine and the lowest concentration detectable was ca. 0.5μM. In addition, the drawback of current signal saturation (non-linear increase of the peak current with the concentration of dopamine) observed at conventional (millimetre-sized) liquid–liquid interfaces was overcome using the microfabricated porous membranes.

Keywords: Dopamine; Voltammetry; Micro-interface; Interface between two immiscible electrolyte solutions

Application of head-space solid-phase microextraction coupled to comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry for the determination of multiple pesticide residues in tea samples by J. Schurek; T. Portolés; J. Hajslova; K. Riddellova; F. Hernández (pp. 163-172).

A new method has been developed to detect 36 pesticides that may contaminate tea samples (green, black and fruit tea). The hyphenation of solid-phase microextraction in head-space mode with a comprehensive two-dimensional gas chromatography coupled with high-speed time-of-flight mass spectrometry (HS-SPME–GC×GC/TOF MS) proved to be a quick alternative to conventional GC/MS methodology which employs solvent-based extraction. The key parameters for controlling HS-SPME performance were optimized, including fiber coating type, temperature and absorption time settings and tea matrix modification by adding water. Quantification was carried out using matrix-matched calibration. The repeatability of measurements, expressed as relative standard deviation (R.S.D.), was less than 24% for all analytes. The limits of quantification ranged from 1 to 28μgkg⁻¹. The optimized method was applied to analyze real life samples obtained from a retail market. Results generated by the new SPME procedure and those obtained by using a conventional one involving ethyl acetate extraction and high-performance gel permeation chromatography (HPGPC) clean up agreed with each other for positive (containing residue) samples.

Keywords: Pesticides; Tea; Solid-phase microextraction; Comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry

Application of a new hybrid organic–inorganic monolithic column for efficient deoxyribonucleic acid purification by Shengbing Yu; Jing Geng; Ping Zhou; Jing Wang; Airong Feng; Xiangdong Chen; Hua Tong; Jiming Hu (pp. 173-181).

A new hybrid organic–inorganic monolithic column for efficient deoxyribonucleic acid (DNA) extraction was prepared in situ by polymerization of N-(β-aminoethyl)-γ-aminopropyltriethoxysilane (AEAPTES) and tetraethoxysilane (TEOS). The main extraction mechanism was based on the Coulombic force between DNA and the amino silica hybrid monolithic column. DNA extraction conditions, such as pH, ion concentration and type, and loading capacity, were optimized online by capillary electrophoresis with laser-induced fluorescence detection. Under optimal condition, a 6.0-cm monolithic column provided a capacity of 48ng DNA with an extraction efficiency of 74±6.3% ( X±RSD). The DNA extraction process on this monolithic column was carried out in a totally aqueous system for the successful purification of DNA and removal of proteins. The PBE2 plasmid could be extracted from Bacillus subtilis ( B. subtilis) crude lysate within 25min, and the purified DNA was suitable for the amplification of a target fragment by polymerase chain reaction. This study demonstrates a new attractive solid-phase support for DNA extraction to meet the increasingly miniaturized and automated trends of genetic analyses.

Keywords: Deoxyribonucleic acid purification; Solid-phase extraction; Monolithic column; N; -(β-Aminoethyl)-γ-aminopropyltriethoxysilane; Bacillus subtilis

An environmental friendly method for the automatic determination of hypochlorite in commercial products using multisyringe flow injection analysis by N. Ornelas Soto; B. Horstkotte; J.G. March; P.L. López de Alba; L. López Martínez; V. Cerdá Martín (pp. 182-186).

A multisyringe flow injection analysis system was used for the determination of hypochlorite in cleaning agents, by measurement of the native absorbance of hypochlorite at 292nm. The methodology was based on the selective decomposition of hypochlorite by a cobalt oxide catalyst giving chloride and oxygen. The difference of the absorbance of the sample before and after its pass through a cobalt oxide column was selected as analytical signal. As no further reagent was required this work can be considered as a contribution to environmental friendly analytical chemistry. The entire analytical procedure, including in-line sample dilution in three steps was automated by first, dilution in a stirred miniature vessel, second by dispersion and third by in-line addition of water using multisyringe flow injection technique. The dynamic concentration range was 0.04–0.78gL⁻¹ (relative standard deviation lower than 3%), where the extension of the hypochlorite decomposition was of 90±4%. The proposed method was successfully applied to the analysis of commercial cleaning products. The accuracy of the method was established by iodometric titration.

Keywords: Multisyringe flow injection analysis; Environmental friendly analytical chemistry; Hypochlorite determination

Rapid structural determination of modified pregnane glycosides from Cynanchum forrestii by liquid chromatography–diode-array detection/electrospray ionization multi-stage tandem mass spectrometry by Yue Liu; Jianbei Li; Shishan Yu; Zeper Abliz; Yunbao Liu; Jing Qu; Jing Liu; Youcai Hu (pp. 187-196).

The fragmentation behaviors of the two types of modified pregnane glycosides from Cynanchum forrestii were investigated by positive ion electrospray ionization multi-stage tandem mass spectrometry equipped with an ion trap analyzer. The spectral data further illuminated the predominance of ESI-MSⁿ technique on the identification of pregnane glycosides, especially of two sorts of modified pregnane glycosides with aglycone skeletons of 13,14:14,15-disecopregnane-type and 14,15-secopregnane-type, which differed in the presence of the characteristic [M−46+Na]⁺ ion. For sugar residues, the fragment ions were analyzed and some possible fragmentation pathways were proposed, especially for 3-demethyl-2-deoxythevetose, the glycosidic cleavage reaction was easier to occur than those of other sugar units in its moiety. The natures and differences of the pregnane cores, and the types and linked sequences of sugar residues were illustrated. According to these conclusions, eight new pregnane glycosides in the fraction of Cynanchum forrestii were structurally elucidated by HPLC/HRMS and HPLC–DAD/ESI-MSⁿ techniques. Results of the present studies can benefit the rapid identification and structural determination of analogous constituents in crude plant extracts.

Keywords: Cynanchum forrestii; 13,14:14,15-Disecopregnane glycosides; 14,15-Secopregnane glycosides; High-performance liquid chromatography–diode-array detection/electrospray ionization tandem mass spectrometry

A fluorescent chemosensor for calcium with excellent storage stability in water by Huarui He; Kenneth Jenkins; Chao Lin (pp. 197-204).

This article describes the design, synthesis and characterization of an optical sensor suitable for practical measurement of ionized calcium in serum and whole blood samples. The key to the development of this sensor is the identification of a chemically very stable, nitrogen-containing, calcium selective ionophore, coupled with a fluorophore having the correct spectral and electron accepting properties. The slope of the sensor is about 34%/mM in the typical clinically significant range of 0.32–2.2mM. This sensor has been implemented into the disposable cartridge, used for commercially available OPTI CCA analyzer with precision better than ±0.02mM (1S.D.). The sensor displays excellent stability against hydrolysis and oxidation, leading to less than 0.02mM measurement error after 9 months of wet storage at room temperature, up to 30°C.

Keywords: Fluoroionophore; Optical sensor; Calcium indicator

Stimuli-responsive hydrogel–silver nanoparticles composite for development of localized surface plasmon resonance-based optical biosensor by Tatsuro Endo; Ryuzoh Ikeda; Yasuko Yanagida; Takeshi Hatsuzawa (pp. 205-211).

In this paper, the development of a localized surface plasmon resonance (LSPR)-based optical enzyme biosensor using stimuli-responsive hydrogel–silver nanoparticles composite is described. This optical enzyme biosensor was constructed by immobilizing glucose oxidase (GOx) into the stimuli-responsive hydrogel. When a sample solution such as glucose was applied to the surface of this optical enzyme biosensor, the interparticle distances of the silver nanoparticles present in the stimuli-responsive hydrogel were increased, and thus the absorbance strength of the LSPR was decreased. Furthermore, hydrogen peroxide, which was produced by the enzymatic reaction, induced the degradation of highly clustered silver nanoparticles by the decomposition of hydrogen peroxide. Hence, a drastic LSPR absorbance change, which depends on the glucose concentrations, could be observed. On the basis of the abovementioned mechanism, the characterization of the LSPR-based optical enzyme biosensor was carried out. It was found that the LSPR-based optical enzyme biosensor could be used to specifically determine glucose concentrations. Furthermore, the detection limit of this biosensor was 10pM. Therefore, this LSPR-based optical enzyme biosensor has the potential to be applied in cost-effective, highly simplified, and highly sensitive test kits for medical applications.

Keywords: Biosensor; Stimuli-responsive hydrogel; Localized surface plasmon resonance (LSPR); Silver nanoparticles

Nonaqueous capillary electrophoresis with laser-induced fluorescence detection: A case study of comparison with aqueous media by Lei Zhou; Weiping Wang; Shumin Wang; Yang Hui; Zhi Luo; Zhide Hu (pp. 212-219).

A novel method based on separation by nonaqueous capillary electrophoresis (NACE) combined with laser-induced fluorescence (LIF) detection was developed and compared with classic aqueous modes of electrophoresis in terms of resolution of solutes of interest and sensitivity of the fluorescence detection. Catecholamines derivatized with 4-chloro-7-nitro-2,1,3-benzoxadiazole (NBD-Cl) were chosen as test analytes for their subtle fluorescence properties. In aqueous systems, capillary zone electrophoresis (CZE) was not suitable for the analysis of test analytes due to complete fluorescence quenching of NBD-labeled catecholamines in neat aqueous buffer. The addition of micelles or microemulsion droplets into aqueous running buffer can dramatically improve the fluorescence response, and the enhancement seems to be comparable for micellar electrokinetic chromatography (MEKC) and microemulsion electrokinetic chromatography (MEEKC). As another alternative, NACE separation was advantageous when performing the analysis under the optimum separation condition of 20mM sodium tetraborate, 20mM sodium dodecyl sulfate (SDS), 0.1% (v/v) glacial acetic acid, 20% (v/v) acetonitrile (ACN) in methanol medium after derivatization in ACN/dimethyl sulfoxide (DMSO) (3:2, v/v) mixed aprotic solvents containing 20mM ammonium acetate. Compared with derivatization and separation in aqueous media, NACE–LIF procedure was proved to be superior, providing high sensitivity and short migration time. Under respective optimum conditions, the NACE procedure offered the best fluorescence response with 5–24 folds enhancement for catecholamines compared to aqueous procedures. In addition, the mechanisms of derivatization and separation in nonaqueous media were elucidated in detail.

Keywords: Aprotic solvent derivatization; Nonaqueous capillary electrophoresis; Laser-induced fluorescence; Catecholamine; 4-Chloro-7-nitro-2,1,3-benzoxadiazole

A solid-phase extraction and size-exclusion liquid chromatographic method for polyethylene glycol 25 p-aminobenzoic acid determination in urine: Validation for urinary excretion studies of users of sunscreens by A. Balaguer; A. Chisvert; A. Salvador; M. Herraez; O. Diez (pp. 220-225).

No previous publications about percutaneous absorption of polyethylene glycol 25 p-aminobenzoic acid (PEG-25 PABA) have been found in the literature and the expected levels to be found in human urine after sunscreens use are unknown. The method proposed here is suitable to determine PEG-25 PABA in the urine of sunscreens users in order to carry out studies on body accumulation/excretion. It is based on solid-phase extraction (SPE) with size-exclusion liquid chromatography determination. Solid-phase extraction allows the analyte to be retained and subsequently eluted for a clean-up, using a silica-based cartridge. The size-exclusion liquid chromatography of the eluted allows the rest of matrix interferences to be avoided. Fluorescence intensity was measured at λ_em=350nm ( λ_exc=300nm). The sensitivity of the proposed method is in the order of 450±5mLng⁻¹ and the detection limit (3S y/_x/b) in the measured solutions is in the order of 13ngmL⁻¹, that is 2.6ngmL⁻¹ in urine samples. The method enables PEG-25 PABA to be determined in both, spiked and unspiked human urine samples. Results obtained for spiked human urine samples (11–100ngmL⁻¹) demonstrated the accuracy of the method. The mean relative standard deviation of the results was in the order of 3–10%. Three volunteers applied a sunscreen lotion containing a 8% PEG-25 PABA sunscreen cream and their urinary excretion was controlled from the moment of application until the excreted amounts were no longer detectable.

Keywords: Polyethylene glycol 25; p; -aminobenzoic acid; Ultraviolet filter; Sunscreen; Urine; Solid-phase extraction; Size-exclusion liquid chromatography; Fluorescence detection

Optimising cell temperature and dispersion field strength for the screening for putrescine and cadaverine with thermal desorption-gas chromatography–differential mobility spectrometry by M. Ali Awan; I. Fleet; C.L. Paul Thomas (pp. 226-232).

Biogenic amines, and putrescine and cadaverine in particular, have significant importance in the area of food quality monitoring, and are also potentially important markers of infection, for cancer, diabetes, arthritis and cystic fibrosis. A thermal desorption-gas chromatograph-heated differential mobility spectrometer was constructed and the significant effect of interactions between cell temperature and dispersion field strength on the observed responses studied. The experiment design was a Box–Wilson central composite design (CCD) over the levels of 10–24kVcm⁻¹ for dispersion field strength and 100–130°C for cell temperature. The optimum values were estimated to be 16.22kVcm⁻¹ and 116°C for putrescine and 14.78kVcm⁻¹ and 112°C for cadaverine, respectively with an ammonia dopant at 19mgm⁻³.An amine test atmosphere generator was constructed and produced stable concentrations of putrescine (7mgm⁻³) and cadaverine (4mgm⁻³) vapours at 50±0.5°C. Tenax TA–Carbotrap adsorbent tubes were used to sample putrescine and cadaverine vapour standards and a linear response function over the range of sample masses 5–20ng was obtained at 15.0kVcm⁻¹ 115°C, with a R² of 0.99 for both putrescine and cadaverine. The sample mass at the limit of detection was estimated to be 3ng for putrescine and cadaverine. Preliminary data from sampling the headspace of chicken meat revealed a 62% increase in the recovered masses of putrescine from 0.84 to 1.36ng in the sampled air.

Keywords: Putrescine; Cadaverine; Biogenic amines; Thermal desorption; Gas chromatography; Differential mobility spectrometry; Central composite design; Optimisation; Food screening

Advanced tip design for liquid phase vibration mode atomic force microscopy by Hiroshi Muramatsu; Yuji Yamamoto; Masatsugu Shigeno; Yoshiharu Shirakawabe; Akira Inoue; Woo-Sik Kim; Seung Jin Kim; Sang-Mok Chang; Jong Min Kim (pp. 233-238).

We have fabricated polymer tips for atomic force microscopy in order to elucidate the effects of tip length and shape on cantilever vibration damping in liquids. The vibration damping is investigated by measuring the vibration amplitude of cantilevers as a function of tip–sample distance. The cantilever with a short tip provides a higher damping effect over long tip–sample distances. When the vibration amplitude was rescaled to show the effect of the cantilever width on oscillation damping, the vibration amplitude of cantilevers with various tip lengths was similarly obtained in a long distance range over 50μm. This similarity is explained by an acoustic damping model in which an acoustic wave is generated by the cantilever. Finally, the results indicate a cantilever with a sufficiently long tip compared to the cantilever width can dramatically reduce the long-range damping effect in a liquid environment.

Keywords: Atomic force microscopy; Polymeric tip; Long tip; Tip design; Oscillation damping; Optimal tip length

Evaluating a Cumaean Sibyl: Domenichino or later? A multi analytical approach by Sister Daniilia; Elpida Minopoulou; Konstantinos S. Andrikopoulos; Ioannis Karapanagiotis; Gerasimos A. Kourouklis (pp. 239-249).

The purpose of this study is to clarify important details about a Cumaean Sibyl painting that is preserved in a private collection. This work, bearing neither signature nor date, has never undergone conservation. It was executed after Domenichino's Cumaean Sibyl, a work known to have been used as a model by many 18th century painters.Investigation of the anonymous artist's painting technique and identification of its constituent materials were facilitated by employing optical microscopy (OM), scanning electron microscopy (SEM/EDS), FTIR and microRaman spectroscopies and high performance liquid chromatography with diode array detection (HPLC-DAD). The painter's palette comprised lead white, yellow ochre, lead-antimonate yellow (Naples yellow), cinnabar, cochineal lake, madder lake, haematite, Prussian blue and carbon black.The detection of Prussian blue (synthesized in 1704 and widely used as artist's pigment after 1750) was decisive in establishing the work's authenticity for, as such, it cannot be attributed either to Domenico Zampieri (1581–1641) or to his apprentices. In addition, the identification of Naples yellow, which prevailed in the period from 1750 to 1850, supports this statement. Nevertheless, its elaborate painting technique strongly suggests an artist greatly influenced by the Renaissance masters. A comparison of its stylistic features with those of the Cumaean Sibyl of Angelica Kauffmann (1741–1807), a prolific 18th century artist known to have studied and to have copied Domenichino's Sibyl, reveals significant similarities between the two in composition and palette. The unsigned Sibyl, therefore, could well be by Kauffmann.

Keywords: Cumaean Sibyl; Domenichino; Kauffmann; Renaissance; Optical and scanning electron microscopy; Vibrational spectroscopies; Liquid chromatography

Erratum to “Composite planar electrode for sensing electrochemical oxygen demand” [Anal. Chim. Acta 607 (2008) 176–182] by Jahir Orozco; César Fernández-Sánchez; Ernest Mendoza; Mireia Baeza; Francisco Céspedes; Cecilia Jiménez-Jorquera (pp. 250-250).

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Analytica Chimica Acta (v.611, #2)

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Analytica Chimica Acta (v.611, #2)