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Analytica Chimica Acta (v.559, #2)

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

Calendar of forthcoming meetings (pp. n3).

Contents (pp. iii-iv).

Biosensor technology for detecting biological warfare agents: Recent progress and future trends by J. Justin Gooding (pp. 137-151).

This review paper outlines the important issues with regards to the development of biosensors for the monitoring of biological warfare agents (BWAs) starting with the basic components of biosensors and the features of BWAs, which are compatible with detection using biological recognition molecules. The advantages and limitations of biosensors are discussed followed by the current state of the art in biosensors for detecting BWAs. Finally the developments required to enable biosensors to become more effective at providing early warning of possible biological attack and advances towards these developments are covered.

Keywords: Biosensors; Biological agents; Affinity sensors; Bioweapon detection; Detect-to-protect

On-line microfluidic sensor integrated with an enzyme-modified pre-cell for the monitoring of paracetamol in pharmaceutical samples by Germ�n A. Messina; Irma E. De Vito; Julio Raba (pp. 152-158).

An on-line microfluidic sensing device with an enzyme-modified pre-cell coupled to an amperometric detector for the monitoring of paracetamol in pharmaceutical formulations is described. Horseradish peroxidase (HRP) [EC 1.11.1.7], immobilized on a 3μl pre-cell, in presence of hydrogen peroxide catalyses the oxidation of paracetamol to N-acetyl- p-benzoquinoneimine. The electrochemical reduction back to hydroquinone is detected on glassy carbon electrode surface at −0.10V. The recovery of paracetamol from 10 samples ranged from 99.00 to 101.10%. This method could be used to determine paracetamol concentration in the range 0.35–100μM ( r=0.997) with a limit of detection of 3.0×10⁻⁷M and a relative standard deviation was less than 4.1% ( n=8). The method was successfully applied for the processing of as many as 20 samples per hour of paracetamol in pharmaceutical formulations.

Keywords: Paracetamol; Glassy carbon; Biosensor; Horseradish peroxidase; FIA

A new thermal desorption solid-phase microextraction system for hand-held ion mobility spectrometry by Xinyu Liu; Sabatino Nacson; Alexander Grigoriev; Paul Lynds; Janusz Pawliszyn (pp. 159-165).

In this paper a new prototype of solid phase microextraction–ion mobility spectrometry (SPME–IMS) system was developed to effectively couple the extraction efficiency of SPME with the detection capability of IMS. The main component of this system was the transfer line/desorber, which was a low-thermal-mass (ca. 0.15g) silicosteel coatings stainless steel tube. The transfer line/desorber was designed to rapidly desorb and transfer the analytes extracted by SPME to IMS. A custom-made temperature controller with a proportional–integral–differential (PID) was used to maintain the temperature of the transfer line/desorber stable and avoid overheating or oscillating. The low thermal mass of this interface allowed it to be rapidly heated and cooled with much less electrical power and could substantially reduce the demand for high capacity batteries. The operational characteristics of this system were demonstrated through the analysis of camphor vapour. The precision of reduced mobility and the peak amplitude of camphor were good (R.S.D. 0.62%, n=10; R.S.D. 2.5%, n=10, respectively). SPME–IMS system was also shown to be capable of on-site measurement by monitoring the biogenic volatile organic compounds (BVOCs) emitted from eucalyptus citriodora leaves. In addition, this system was applied to quantitation of diazepam and cocaine in aqueous solution. Limits of detection were 10ng/mL for diazepam and 50ng/mL for cocaine with the reported experimental conditions. This SPME–IMS system exhibits considerable promise as a robust, simple, rapid, energy-saving fieldable approach for on-site analysis of analytes in various matrix.

Keywords: Ion mobility spectrometry (IMS); Solid phase microextraction–ion mobility spectrometry (SPME–IMS); On-site analysis; Membrane interface

Liquid-phase microextraction for sample preparation in analysis of unconjugated anabolic steroids in urine by Antti Leinonen; Katariina Vuorensola; Laura-Maria Lepola; Tiia Kuuranne; Tapio Kotiaho; Raimo A. Ketola; Risto Kostiainen (pp. 166-172).

The applicability of in-vial two-phase liquid-phase microextraction (LPME) in porous hollow polypropylene fiber was studied for the sample preparation of unconjugated anabolic steroids in urine. Four different anabolic steroids – metabolites of fluoxymesterone, 4-chlorodehydromethyltestosterone, stanozolol and danazol – were used as test compounds and methyltestosterone as an internal standard. A standard two-phase LPME method for use with liquid chromatography/mass spectrometry (LC/MS) was set up and the influence of different parameters, including the nature of organic solvent, extraction time, salting-out and temperature, on the LPME process was investigated. Taking advantage of the preliminary studies, a novel two-phase LPME method utilizing simultaneous in-fiber silylation was developed and validated for gas chromatographic/mass spectrometric (GC/MS) analysis of a danazol metabolite in urine. In all, LPME allowed a very straightforward, simple and selective way to prepare urine samples for steroid analysis, being most suitable for hydrophobic steroids. The LPME method with in-fiber derivatization for GC/MS analysis exhibited high sensitivity, repeatability and linearity and enabled simultaneous filtration, extraction, enrichment and derivatization of the analyte from urine matrix without any other steps in sample pretreatment.

Keywords: Liquid-phase microextraction; Hollow fibers; Extraction techniques; Derivatization; Anabolic steroids; Liquid chromatography; Gas chromatography; Mass spectrometry

Ultrasonic solvent extraction of organochlorine pesticides from soil by Ali Tor; Mehmet Emin Aydin; Senar �zcan (pp. 173-180).

Ultrasonic solvent extraction of the organochlorine pesticides (OCP) including α-, β-, γ- and Δ-hexachlorocyclohexane (HCH), heptachlor, aldrin, o, p′-DDE, dieldrin, p, p′-DDE, p, p′-DDT, methoxychlor, mirex from soil is reported. The extraction procedure was optimized with regard to the solvent type, amount of solvent, duration of sonication and number of extraction steps. Determination of pesticides was carried out by gas chromatography (GC) equipped with electron capture detection (ECD). Twice ultrasonic extraction using 25mL of a mixture of petroleum ether and acetone (1/1v/v) for 20min of sonication showed satisfactory extraction efficiency. Recoveries of pesticides from fortified soil samples are over 88% for three different fortification levels between 15 and 200μgkg⁻¹, and relative standard deviations of the recoveries are generally below 6%. Real soil samples were analyzed for OCP residues by optimized ultrasonic solvent extraction and shake-flask as well as soxhlet extraction technique. Investigated all extraction methods showed comparable extraction efficiencies. Optimized ultrasonic solvent extraction is the most rapid procedure because the use of time in ultrasonic extraction was considerably reduced compared to shake-flask and soxhlet extraction.

Keywords: Soil; Ultrasonic solvent extraction; Organochlorine pesticides; Environmental analysis

Synergistic flotation of U(VI)–alizarin complex with some diamines followed by spectrophotometric determination of U(VI) using 4,4′-diaminophenylmethane by Mohammad Saeid Hosseini; Heidar Raissi; Hamid Reza Yavari (pp. 181-185).

In this work, synergistic flotation of U(VI)–alizarin complex at the presence of some diamine compounds was firstly investigated by the spectrophotometric method. The flotation process was carried out on aliquots of 100ml of U(VI) solutions containing alizarin and the diamine at pH of 5.00 using n-heptane. The floated layer was then dissolved in acetonitrile and its absorbance was measured. Since the synergistic effect of 4,4′-diaminophenylmethane (dapm) was much more than the others, it was used for the determination of U(VI) by this method. Beer's law was obeyed ( λ_max=591nm) in the range of 5×10⁻⁷ to 1×10⁻⁵moll⁻¹ with the apparent molar absorptivity of 1.12×10⁶lmol⁻¹cm⁻¹, and a correlation coefficient of 0.9991. The detection limit ( n=7) was 1×10⁻⁷moll⁻¹, and the R.S.D. ( n=7) obtained for 4×10⁻⁶moll⁻¹ of U(VI) was 2.23%. Except that only a few analogous cations, which could be masked by EDTA, no interference was observed at the presence of various conventional ions, even at high concentrations. The reliability and applicability of the method were confirmed using some geological standard reference materials and spiked synthetic water samples, respectively.

Keywords: Synergistic flotation; Spectrophotometry; Uranium determination; Alizarin; Diamine

Behaviour of triazine herbicides and their hydroxylated and dealkylated metabolites on a propazine-imprinted polymer by R. Carabias-Mart�nez; E. Rodr�guez-Gonzalo; E. Herrero-Hern�ndez (pp. 186-194).

A molecularly imprinted polymer (MIP) obtained by precipitation polymerization with methacrylic acid as functional monomer and propazine as template was tested as a sorbent for the solid phase extraction of chloro- and methylthio-triazines and some of their dealkylated and hydroxylated metabolites. In order to confirm the interaction between the functional monomer and the template,¹H NMR (CD₂Cl₂) analyses were made. It was observed that the hydrogen and/or nitrogen of the amino group of the propazine were involved in the formation of hydrogen bonds with the functional monomer.The possibilities offered by the propazine-MIP for the extraction of triazine and derivatives were studied in organic and aqueous media and different types of behaviour were observed. From organic medium, selective extractions of chloro- and methylthio-triazines were obtained after optimization of the extraction process, with recoveries higher than 75% in both cases. However, the hydroxylated metabolites were not retained on the propazine-MIP in organic medium.In aqueous medium, the chloro-triazines and the dealkylated chloro-metabolites were retained on the propazine-MIP by specific interactions, the recoveries obtained being a function of their polarity. Regarding the hydroxylated metabolites, these are retained on the propazine-MIP through non-specific hydrogen-bridge interactions. The methylthio-triazines undergo poor molecular recognition in this medium.

Keywords: Molecularly imprinted polymers; Precipitation polymerization; Triazine herbicides; Dealkylated and hydroxylated metabolites

Detection of paracetamol by capillary electrophoresis with chemiluminescence detection by Shulin Zhao; Wenling Bai; Hongyan Yuan; Dan Xiao (pp. 195-199).

Indirect detection of paracetamol was accomplished using a capillary electrophoresis–chemiluminescence (CE–CL) detection system, which was based on its inhibitory effect on a luminol-potassium hexacyanoferrate(III) (K₃[Fe(CN)₆]) CL reaction. Paracetamol migrated in the separation capillary, where it mixed with luminol included in the running buffer. The separation capillary outlet was inserted into the reaction capillary to reach the detection window. A four-way plexiglass joint held the separation capillary and the reaction capillary in place. K₃[Fe(CN)₆] solution was siphoned into a tee and flowed down to the detection window. CL was observed at the tip of the separation capillary outlet. The CL reaction of K₃[Fe(CN)₆] oxidized luminol was employed to provide the high and constant background. Since paracetamol inhibits the CL reaction, an inverted paracetamol peak can be detected, and the degree of CL suppression is proportional to the paracetamol concentration. Maximum CL signal was observed with an electrophoretic buffer of 30mM sodium borate (pH 9.4) containing 0.5mM luminol and an oxidizer solution of 0.8mM K₃[Fe(CN)₆] in 100mM NaOH solution. Under the optimal conditions, a linear range from 6.6×10⁻¹⁰ to 6.6×10⁻⁸M ( r=0.9999), and a detection limit of 5.6×10⁻¹⁰M (signal-to-noise ratio=3) for paracetamol were achieved. The relative standard deviation (R.S.D.) of the peak area for 5.0×10⁻⁹M of paracetamol ( n=11) was 2.9%. The applicability of the method for the analysis of pharmaceutical and biological samples was examined.

Keywords: Chemiluminescence; Capillary electrophoresis; Paracetamol

Preconcentration and determination of nicosulfuron, thifensulfuron-methyl and metsulfuron-methyl in water samples using carbon nanotubes packed cartridge in combination with high performance liquid chromatography by Qingxiang Zhou; Weidong Wang; Junping Xiao (pp. 200-206).

A new procedure was described with multiwalled carbon nanotubes as solid phase extraction packing material for the trace analysis of nicosulfuron, thifensulfuron and metsulfuron-methyl in water samples. The possible parameters influencing the enrichment were optimized and the optimal conditions were as followed: eluent, sample pH, flow rate and sample volume were acetonitrile containing 1% acetic acid, pH 3, 8mLmin⁻¹ and 500mL, respectively. Under the optimal chromatographic separation and SPE conditions, the linear range, detection limit (S/N=3) and precision (R.S.D., n=6) were 0.04–40ngmL⁻¹, 6.8ngL⁻¹ and 2.5% for nicosulfuron, 0.04–40ngmL⁻¹, 11.2ngL⁻¹ and 5.4% for thifensulfuron, 0.02–20ngmL⁻¹, 5.9ngL⁻¹, 2.1% for metsulfuron-methyl, respectively. The established method was well employed to determine nicosulfuron, thifensulfuron and metsulfuron-methyl in tap water, seawater, reservoir water and well water samples, and satisfactory results were obtained, the spiked recoveries in the range of 87.2–100.7%, 96.5–105.6% and 83.7–111.1% for them each, respectively.

Keywords: Multiwalled carbon nanotubes; Sulfonylurea herbicides; Enrichment

Determination of acrylamide in foodstuffs by liquid chromatography ion-trap tandem mass-spectrometry using an improved clean-up procedure by E. Bermudo; E. Moyano; L. Puignou; M.T. Galceran (pp. 207-214).

The present paper describes an analytical method based on liquid chromatography coupled to tandem mass-spectrometry (LC–MS/MS) for the determination of acrylamide in foodstuffs. Atmospheric pressure chemical ionization (APCI) as ionization source and an ion-trap (LCQ) analyzer were used, and to the best of our knowledge, this hyphenated technique has not ever been employed to this purpose. In order to obtain clean extracts an improved purification procedure based on the coupling of two highly cross-linked polystyrene–divinylbenzene polymeric sorbents: Strata-X-C and ENV+, was also developed. High recoveries (85%) and good reproducibility (relative standard deviation of 12%) were obtained using the two solid-phase extraction cartridges in combination. One hundred percent water as mobile phase was used for the LC separation. The obtained figures of merit showed detection limits of 250pg for standards and 45ng/g for samples, and run-to-run and day-to-day precisions of 3.3 and 8%, respectively. Acrylamide (AA) was determined in several of the most frequently eaten carbohydrate-rich foodstuffs commercialized in Spain such as potato crisps and chips, biscuits, crisp breads, pastry, dried fruits, chocolates and coffee. For the first time, a typical pastry product called as “churros�? and highly consumed in Spain was also studied. Some of the products tested such as french fries frozen or “churros�? were household cooked. Acrylamide was determined in the selected food commodities using the developed analytical methodology. A commonly used method by liquid chromatography coupled to tandem mass-spectrometry with a triple quadrupole as mass analyzer (LC–QqQ–MS/MS) was also applied in order to validate the analytical results. Different levels of acrylamide were obtained and pastry and dried fruits showed the lower levels (<20ng/g). Potato chips and french fries gave values of the order of 500–9250ng/g.

Keywords: Acrylamide; Food; SPE; LC–MS/MS

Reversed-phase high-performance liquid chromatography applied to the determination of soybean proteins in commercial heat-processed meat products by M� Concepci�n Garc�a; Mar Dom�nguez; Carmen Garc�a-Ruiz; M� Luisa Marina (pp. 215-220).

A reversed-phase chromatographic method has been developed and optimised in order to detect and quantitate soybean proteins in commercial heat-processed meat products. The optimised conditions consisted of a linear binary gradient tetrahydrofurane–water–0.05% trifluoroacetic acid at a flow rate of 1mL/min. Meat products were defatted with acetone and soybean proteins were extracted with a buffered solution at pH 9.60. The injection of this extract into the chromatographic system enabled the detection of soybean proteins in heat-processed meat products in about 12min. The method enabled the detection and quantitation of additions of 0.38% (w/w) and 0.63% (w/w), respectively, of soybean proteins (related to 10g of initial product). The method has been proven to be precise with relative standard deviations (R.S.D.) for repeatability, intermediate precision, and internal reproducibility lower to 7.0%. Recoveries obtained for spiked meat products were close to 100% and no matrix interferences were observed. The application of the method to commercial heat-processed meat products in whose formulation soybean proteins were present yielded soybean protein contents ranging from 0.90% to 1.54%, below the maximum levels established by regulations.

Keywords: Soybean proteins; Heat-processed meat products; High-performance liquid chromatography

Inverse gas chromatographic and chemometric tools for determination of interactions between the components of polymeric composition by A. Voelkel; K. Milczewska; K. H�berger (pp. 221-226).

Compositions of polymers (polyethylene and polyuretane) and fillers (initial silica and silicas modified with: N-2-aminoethyl-3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxy-silane, 3-merkaptopropyltrimethoxysilane, octyltriethoxysilane) were examined by inverse gas chromatography at 383K. Small amounts of the following test solutes were injected to achieve the infinite dilution conditions: pentane, hexane, heptane, octane, nonane, dichloromethane, chloroform, carbon tetrachloride and 1,2-dichloroethane.The retention times for these test solutes were determined and Flory–Huggins parameters were calculated. Flory–Huggins parameters characterize interactions between components:χ12∞ – between composition and the test solute andχ′23 – between polymer and filler in the composition.Values of both physicochemical parameters characterizing the examined materials were arranged in a matrix form: in the rows the compositions were enumerated at different temperatures whereas the columns contained the test solutes. After standardization the input matrix was subjected to principal component analysis. Three principal components explain more than 93% of the total variance in the data. Almost all test solutes carry very similar information. Therefore, it is justified to eliminate most of them from the series of test solutes.

Keywords: Polymer–filler interactions; Flory–Huggins parameter; Inverse gas chromatography; Principal component analysis; Modified fillers; Chemometrics

In situ silylation for the multicomponent analysis of canola oil by-products by gas chromatography–mass spectrometry by Armando A. Durant; Marie-Jos�e Dumont; Suresh S. Narine (pp. 227-233).

In this study, a simple method for the determination of free fatty acids, phytosterols, tocopherols, mono and diglycerides present in canola oil deodorizer distillate (DD) and soapstock samples was developed. Analytes were derivatized “in situ �? using a mixture of hexamethyldisilazane (HMDS), pyridine and trifluoroacetic acid; separated by gas chromatography (GC) with mass spectrometry (MS) for final detection. Two drying procedures were evaluated for drying deodorizer distillate samples before derivatization: freeze drying and drying at 100°C for 24h. The use of high temperatures caused the degradation of tocopherols and phytosterols, while lyophilization did not affect the substances negatively. The chromatographic conditions used in this work allow for the separation and quantification of oleic, linoleic and linolenic acids, monoolein and monolinolein in both samples, and brassicasterol and α-tocopherol in deodorizer distillate samples. MS provided an accurate identification for the compounds which were at very low concentrations (>0.09%). Oleic acid was the most abundant compound in both samples. Deodorizer distillate was an important source of tocopherols which were not detected in the soapstock samples.

Keywords: Canola oil; Soapstock; Deodorizer distillate; Silylation; GC–MS

Preparation, characterization and evaluation of water-solublel-cysteine-capped-CdS nanoparticles as fluorescence probe for detection of Hg(II) in aqueous solution by Zhao-Xia Cai; Hong Yang; Yi Zhang; Xiu-Ping Yan (pp. 234-239).

Water-solublel-cysteine-capped-CdS nanoparticles were prepared in aqueous solution at room temperature through a straightforward one-pot process by using safe and low-cost inorganic salts as precursors, and characterized by transmission electron microscopy, X-ray diffraction spectrometry, Fourier transform infrared spectrometry, spectrofluorometry and ultraviolet–visible spectrometry. The preparedl-cysteine-capped-CdS nanoparticles were evaluated as fluorescence probe for Hg(II) detection. The fluorescence quenching of thel-cysteine-capped-CdS nanoparticles depended on the concentration and pH of Hg(II) solution. Maximum fluorescence quenching was observed at pH 7.4 with the excitation and emission wavelengths of 360nm and 495nm, respectively. Quenching of its fluorescence due to Hg(II) at the 20nmoll⁻¹level was unaffected by the presence of 5×10⁶-fold excesses of Na(I) and K(I), 5×10⁵-fold excesses of Mg(II), 5×10⁴-fold excesses of Ca(II), 500-fold excesses of Al(III), 91-fold excesses of Mn(II), 23.5-fold excesses of Pb(II), 25-fold excesses of Fe(III), 25-fold excesses of Ag(I), 8.5-fold excesses of Ni(II) and 5-fold excesses of Cu(II). Under optimal conditions, the quenched fluorescence intensity increased linearly with the concentration of Hg(II) ranging from 16nmoll⁻¹ to 112nmoll⁻¹. The limit of detection for Hg(II) was 2.4nmoll⁻¹. The developed method was applied to the detection of trace Hg(II) in aqueous solutions.

Keywords: Nanoparticles; Fluorescence probe; Mercury

Determination of phenol in the presence of its principal degradation products in water during a TiO₂-photocatalytic degradation process by three-dimensional excitation–emission matrix fluorescence and parallel factor analysis by M.V. Bosco; M. Garrido; M.S. Larrechi (pp. 240-247).

This paper describes a simple and rapid way of monitoring a photocatalytic degradation of phenol in aqueous suspensions of TiO₂. A three-way analytical methodology based on fluorescence excitation–emission matrix (EEM) and parallel factor analysis (PARAFAC) was developed to resolve the species present in the reaction mixture and quantify the concentration of phenol and its principal degradation products throughout the degradation. Parameters such as core consistency, fit% and correlation coefficients between recovered and pure spectra were used to determine the appropriate number of factors for the PARAFAC model. The accuracy of the model was evaluated by the root mean square error of prediction (RMSEP). Using a four-factors PARAFAC model, phenol, hydroquinone, resorcinol and catechol, were satisfactorily determined. The proposed method is an interesting alternative to the traditional techniques normally used for monitoring degradation reactions.

Keywords: Phenol; PARAFAC model; Photodegradation reactions; Fluorescence; Excitation–emission matrix

At-line determination of formaldehyde in bioprocesses by sequential injection analysis by Burkhard Horstkotte; Elisabeth Werner; Stefan Wiedemeier; Olaf Elsholz; V�ctor Cerd�; Reiner Luttmann (pp. 248-256).

A sequential injection analysis (SIA) method for the at-line determination of formaldehyde in a cultivation process of Pichia pastoris is presented. A genetically modified yeast strain was used for cultivation processes wherein methanol feed induced the production of the recombinant protein 1-3del I-TAC. Recurring measurements of culture medium, its blank and including standard addition were performed with Nash reagent using an automated syringe device and photometric detection. The apparatus was coupled via a laboratory-made flow-through adapter to a continuous filtered and cell-medium flow from the bioreactor. At-line monitoring of formaldehyde was performed at two cultivations, each of 250h during fed-batch phases with glycerol and methanol as carbon sources. High reliability, robustness and reproducibility of the method, the software and the instrumentation as well as the high selectivity of the reaction were demonstrated.

Keywords: Formaldehyde; Yeast cultivation; At-line bioprocess monitoring; Sequential injection analysis

Development of a fast and non-destructive procedure for characterizing and distinguishing original and fake euro notes by A. Vila; N. Ferrer; J. Mantec�n; D. Bret�n; J.F. Garc�a (pp. 257-263).

Since the introduction of the euro as the common currency in most of the countries of the European Union, the production of counterfeit banknotes has increased steadily. The European Central Bank has distributed information on a systematic procedure to distinguish genuine notes from counterfeits based on the look, feel and tilt of the notes. Counterfeits, however, have remained difficult to detect. In order to improve such detection, a procedure based on the analysis of several areas of euro notes using microscope ATR-infrared spectroscopy is proposed. This procedure is fast, robust and non-destructive and it can be applied in situ. The present study is focused on the denomination most frequently falsified, the 50€ note, but 100€ notes were also analysed. The inter- and intra-bank reproducibility of the original notes was also evaluated. Results indicate that characteristics of the spectra depend mainly on the area of the note studied and, furthermore, these characteristics do not change with the nominal value of the notes. Counterfeit banknotes were also analysed and were clearly distinguished from authentic notes in all cases. Unlike genuine notes, the spectra of fakes are the same in all areas of the note analysed.

Keywords: Notebanks; Counterfeits; Artistic prints, Artworks; Original versus fakes discrimination; ATR infrared spectroscopy

Application of two-dimensional J-resolved nuclear magnetic resonance spectroscopy to differentiation of beer by Alfi Khatib; Erica G. Wilson; Hye Kyong Kim; Alfons W.M. Lefeber; Cornelis Erkelens; Young Hae Choi; Robert Verpoorte (pp. 264-270).

A number of ingredients in beer that directly or indirectly affect its quality require an unbiased wide-spectrum analytical method that allows for the determination of a wide array of compounds for its efficient control.¹H nuclear magnetic resonance (NMR) spectroscopy is a method that clearly meets this description as the broad range of compounds in beer is detectable. However, the resulting congestion of signals added to the low resolution of¹H NMR spectra makes the identification of individual components very difficult. Among two-dimensional (2D) NMR techniques that increase the resolution, J-resolved NMR spectra were successfully applied to the analysis of 2-butanol extracts of beer as overlapping signals in¹H NMR spectra were fully resolved by the additional axis of the coupling constant. Principal component analysis based on the projected J-resolved NMR spectra showed a clear separation between all of the six brands of pilsner beer evaluated in this study. The compounds responsible for the differentiation were identified by 2D NMR spectra including correlated spectroscopy and heteronuclear multiple bond correlation spectra together with J-resolved spectra. They were identified as nucleic acid derivatives (adenine, uridine and xanthine), amino acids (tyrosine and proline), organic acid (succinic and lactic acid), alcohol (tyrosol and isopropanol), cholines and carbohydrates.

Keywords: Beer analysis; Nuclear magnetic resonance spectroscopy; Two-dimensional; J; -resolved spectroscopy; Principal component analysis

PARAFAC and PARAFAC2 calibration models for antihypertensor Nifedipine quantification by Jo�o M.M. Leit�o; Joaquim C.G. Esteves da Silva (pp. 271-280).

Two-way data structures were obtained by acquiring UV–vis spectra as function of the time of the alkaline hydrolysis reaction of the antihypertensor Nifedipine in dimethylsulfoxide (DMSO). Sets of three-way data structures were obtained from the analysis of solutions with different concentrations of Nifedipine generated by standard additions to DMSO, Nifedipine standard and a pharmaceutical formulation. PARAFAC and PARAFAC2 methods were used in the analysis of these multi-way data structures and calibration models were developed for Nifedipine quantification in pharmaceutical formulations. For all the three-way data structures a better model fit was found with the PARAFAC2 suggesting that the experimental data sets have deviations from trilinearity. The best concentrations estimations were found with the PARAFAC2 model in the analysis of a [concentration×time (s)×wavelength (nm)] three-way data structure which allows the quantification of Nifedipine in pharmaceutical formulations.

Keywords: Antihypertensor Nifedipine; PARAFAC; PARAFAC2; Calibration models; Alkaline hydrolysis; UV–vis spectroscopy

Author Index (pp. 281-283).

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Analytica Chimica Acta (v.559, #2)