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Analytica Chimica Acta (v.565, #1)

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

Calendar of forthcoming meetings (pp. n1).

Contents (pp. v-vi).

Rapid response optical ion/gas sensors using dimer–monomer metalloporphyrin equilibrium in ultrathin polymeric films coated on waveguides by Youngjea Kang; Mark E. Meyerhoff (pp. 1-9).

Optical sensors with rapid response times (1–2s) toward solution phase chloride and gas phase amine species are described. The sensors are based on the incorporation of indium(III) octaethylporphyrin (In(III)[OEP]) within ultrathin polymeric films (<0.5μm) deposited via spin coating on a planar fused silica waveguide. The In(III)[OEP] forms a hydroxide ion bridged dimer when anion sites in the form of a lipophilic borate derivative (i.e., potassium tetrakis([3,5-bis(trifluoromethyl)phenyl]borate (KTFPB)) are added to the plasticized films. Selective chloride or amine extraction into the films results in a change in the optical absorption spectrum of the metalloporphyrin owing to ligation of these species to the In(III) center, forcing the formation of monomeric In(III)[OEP] species. These ligation reactions are completely reversible. The use of the waveguide sensing configuration enables very fast response times without loss in sensitivity since the optical pathlength is significant (e.g., absorbance is enhanced about 20 times even when 0.3μm thick film is employed). The fast response times of the sensors makes such devices potentially useful as detectors in flow-through analytical systems such as flow-injection analysis (FIA) or gas/liquid phase chromatography.

Keywords: Optical sensors; Chloride measurement; Amine sensor; Metalloporphyrin-based sensors; Optical waveguide

Application of gas-sensor array technology for detection and monitoring of growth of spoilage bacteria in milk: A model study by John Erik Haugen; Knut Rudi; Solveig Langsrud; Sylvia Bredholt (pp. 10-16).

The aim of this study was to develop a novel, rapid system for detection and monitoring of growth of undesirable bacteria in food using gas-sensor array technology. Three spoilage bacteria isolated from a cheese-processing hall were identified as Serratia marcescens, Serratia proteamacufans and Pseudomonas putida. The growth of these bacteria in milk was investigated using a commercial solid state based gas-sensor array system. On the basis of the temporal sensor readings of the pure cultures, bacterial growth could be monitored and the individual strains identified and followed throughout the complete growth cycle in both single and mixed culture. The gas-sensor signals could be used as early indicators of the onset of bacterial growth. Start detection of volatile bacterial metabolites coincided with the start of the exponential growth phase taking place around 7h after inoculation and corresponding to bacterial numbers of 10⁴ (cfu/ml). The results were confirmed by comparing the gas profiles with the cell counts and by headspace gas chromatography mass spectrometry (GC/MS) of volatile microbial metabolites. High correlation ( r>0.90, p<0.001) was found between the gas-sensor readings and major secondary volatile metabolites. Using the sensor readings, cell numbers of single strain cultures could be predicted with an error of less than 5%. The results show that it is possible to monitor growth of individual strains of spoilage bacteria in a mixed culture in milk on the basis of the type and amount of volatile compounds which they produce, using a gas-sensor array system. The system thus affords possibilities for further development for quick, more accurate and full scale determinations of shelf life, the design of spoilage indicators, rapid identification of undesired microorganisms and rapid measurements of spoilage.

Keywords: Gas-sensors; Detection; Spoilage bacteria; Milk

A vapor selectivity study of microsensor arrays employing various functionalized ligand protected gold nanoclusters by Chang-Yong Yang; Chi-Lin Li; Chia-Jung Lu (pp. 17-26).

We synthesized and tested four different monolayer protected gold nanoclusters (MPCs) as chemically selective interfaces for an organic vapor sensor array. The ligands chosen for capping the nano-Au particles and for selective organic vapor sorption were octanethiol, 2-naphthalenethiol, 2-benzothiazolethiol and 4-methoxythiolphenol. The same set of gold nanoclusters were tested on two different types of sensor platforms, a chemiresistor (CR) and a quartz crystal microbalance (QCM). The sensing properties of both sensor arrays were investigated with 10 organic vapors of various functional groups. Vapor sensing selectivity, dominated by the shell ligand structure of MPC, was demonstrated. The sensitivities of MPC coated CR are better than those of QCM sensors coated with the same material. The average CR/QCM amplification factors are range from 1.9 for 4-methoxythiolphenol MPC to 16.9 for octanethiol MPC. These differences in amplification factors indicate the functional group specific mechanisms for each vapor–MPC pair. The shell penetration mechanism of hydrogen-bonding vapor molecules into the 2-benzothiazolethiol capped MPC reduced the CR/QCM amplification factors. Strong attraction between MPC shell ligands can also reduce the magnitude of resistance changes during vapor sorption.

Keywords: Gold nanoparticles; Volatile organic compounds (VOCs); Chemiresister; Vapor sensor

An interference-free first generation alcohol biosensor based on a gold electrode modified by an overoxidised non-conducting polypyrrole film by Donatella Carelli; Diego Centonze; Angelo De Giglio; Maurizio Quinto; Pier Giorgio Zambonin (pp. 27-35).

An interference-free first generation alcohol biosensor based on alcohol oxidase immobilized, by glutaraldehyde co-crosslinking with bovine serum albumin, on a perm-selective electropolymerized film modified gold electrode is described. The use, in place of platinum, of a gold electrode, properly conditioned by an electrochemical pre-treatment, allowed the elimination of the electrode fouling and of the interference caused by the direct alcohol oxidation at the electrode surface. The efficiency of overoxidized polypyrrole and poly- ortho-phenylendiamine as anti-interferent perm-selective films towards the most common electroactive interferents was also investigated.The low response time and the fabrication procedure employed in this study allowed the use of the biosensor in a flow injection system equipped with a conventional thin-layer electrochemical cell.The biosensor showed a high sensitivity, a good stability and a complete suppression of electroactive interferences in operational conditions. Biosensor performances were tested by the rapid determination of the alcohol content in just diluted wine samples and the results compared well with those obtained with the classical method of distillation.

Keywords: Amperometric biosensors; Alcohol oxidase; Alcohols; Perm-selective films; Gold electrode; Flow injection analysis (FIA)

Tris(2-ethylhexyl)phosphine oxide as an effective solvent mediator for constructing a serotonin-selective membrane electrode by Keisuke Ueda; Rei Yonemoto; Keiko Komagoe; Kazufumi Masuda; Nobumitsu Hanioka; Shizuo Narimatsu; Takashi Katsu (pp. 36-41).

A series of solvent mediators containing a phosphoryl (PO) group, such as tris(2-ethylhexyl)phosphate, bis(2-ethylhexyl) 2-ethylhexylphosphonate, 2-ethylhexyl bis(2-ethylhexyl)phosphinate, and tris(2-ethylhexyl)phosphine oxide, were used to construct serotonin-selective membrane electrodes. We found that replacing the alkoxy groups attached to phosphorus atoms in PO groups with alkyl groups strengthened the response of the electrode to serotonin, suppressing remarkably interference from inorganic cations, such as Na⁺. Thus, an electrode combining tris(2-ethylhexyl)phosphine oxide with an ion-exchanger, sodium tetrakis[3,5-bis(2-methoxyhexafluoro-2-propyl)phenyl]borate, gave a detection limit of 9×10⁻⁶M with a slope of 55.2mV per concentration decade in physiological saline containing 150mM NaCl and 10mM NaH₂PO₄/Na₂HPO₄ (pH 7.4). This is the best detection limit of any serotonin-selective electrode developed to date. The selectivity of this electrode for serotonin was over 10³ times that for inorganic cations, such as Na⁺ and K⁺, and lipophilic quaternary ammonium ions, such as acetylcholine and (C₂H₅)₄N⁺. Using the electrode, we measured the amount of serotonin released from platelets and found that the results agreed well with those obtained by a conventional fluorimetric assay of serotonin.

Keywords: Ion-selective electrode; Serotonin determination; Tris(2-ethylhexyl)phosphine oxide; Solvent mediator; Platelet; Potentiometry

Optical sensor materials for the detection of amines in organic solvents by Anja Gräfe; Karsten Haupt; Gerhard J. Mohr (pp. 42-47).

A new optical polymer-based sensor was developed, which is able to recognize amines in organic solvents with high sensitivity. Thin polymer membranes were prepared and investigated, which contain a chromogenic functional dye (reactand) that shows a significant colour change during a reversible chemical reaction with the analyte. For that purpose the azo dye 4-trifluoroacetyl-4′-[ N-(methacryloxyethyl)- N-(ethyl)amino]-azobenzene (CR-465) was synthesized, which contains a trifluoroacetyl moiety (receptor for interaction with amines) and in addition, a polymerizable methacrylate group. The methacrylate group links the dye covalently to the polymer matrix and the receptor recognizes the analyte via covalent binding. For immobilisation of the dye cross-linked methacrylate polymers with different composition were used. The highly cross-linked polymer network was stable against most organic solvents and exhibited enhanced stability against mechanical strain compared to plasticized PVC. The sensitivity of the reaction between the analyte and the dye was tailored by the choice of the solvent in which the analysis of the sensor layer was performed, with equilibrium constants for 1-butylamine ranging from 80 to 2000M⁻¹ in chloroform and DMSO, respectively. In toluene as the solvent, sensor layers typically exhibited equilibrium constants of 100M⁻¹ for 1-butylamine, 1300M⁻¹ for 1,4-diaminobutane and 20,000M⁻¹ for tris-(2-aminoethyl)amine. We have also investigated the cross-linked sensor layers with respect to molecular imprinting and did not find any enhancement in selectivity through imprinting in the presence of different analyte molecules.

Keywords: Trifluoroacetyl dyes; Amines; Molecular imprinting

Tris(2,2′-bipyridyl)ruthenium(II) electrogenerated chemiluminescence sensor based on carbon nantube dispersed in sol–gel-derived titania–Nafion composite films by Han Nim Choi; Ja-Young Lee; Young-Ku Lyu; Won-Yong Lee (pp. 48-55).

A highly sensitive and stable tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) electrogenerated chemiluminescence (ECL) sensor was developed based on carbon nanotube (CNT) dispersed in mesoporous composite films of sol–gel titania and perfluorosulfonated ionomer (Nafion). Single-wall (SWCNT) and multi-wall carbon nanotubes (MWCNT) can be easily dispersed in the titania–Nafion composite solution. The hydrophobic CNT in the titania–Nafion composite films coated on a glassy carbon electrode certainly increased the amount of Ru(bpy)₃²⁺ immobilized in the ECL sensor by adsorption of Ru(bpy)₃²⁺ onto CNT surface, the electrocatalytic activity towards the oxidation of hydrophobic analytes, and the electronic conductivity of the composite films. Therefore, the present ECL sensor based on the CNT–titania–Nafion showed improved ECL sensitivity for tripropylamine (TPA) compared to the ECL sensors based on both titania–Nafion composite films without CNT and pure Nafion films. The present Ru(bpy)₃²⁺ ECL sensor based on the MWCNT–titania––Nafion composite gave a linear response ( R²=0.999) for TPA concentration from 50nM to 1.0mM with a remarkable detection limit (S/N=3) of 10nM while the ECL sensors based on titania–Nafion composite without MWCNT, pure Nafion films, and MWCNT–Nafion composite gave a detection limit of 0.1μM, 1μM, and 50nM, respectively. The present ECL sensor showed outstanding long-term stability (no signal loss for 4 months).

Keywords: Electrogenerated chemiluminescence; Ru(bpy); ₃; ²⁺; Sol–gel; Titania–Nafion composite film; Carbon nanotube

The effects of solvent preoxidation on inhibited chemiluminescence of pyrogallol oxidation in flow injection analysis and liquid chromatography by George Z. Tsogas; Dimosthenis L. Giokas; Athanasios G. Vlessidis; Nicholaos P. Evmiridis (pp. 56-62).

A new extension of chemiluminescence technique using pre-oxidation of a carrier solvent before the conventional inhibited chemiluminescence detection is presented in this study. The method is based on the modification of the oxidation chemistry of pyrogallol upon contact with a flow stream consisting of an organic solvent in mixture with an aqueous solution of a soft oxidant. The final response was found to depend on the kind of solvent and the oxidant/pre-oxidant mixture employed for the oxidation of pyrogallol and the solvent, respectively. By selecting the appropriate combination two detection modalities with increased sensitivity can be achieved. The first is based on the enhancement of the analytes signal through intensification of their scavenging effect on pyrogallol oxidation and the second on the enhancement of signal above the emission induced during the pyrogallol oxidation. Various combinations of organic solvents, oxidizing and pre-oxidizing mixtures were examined for their response in inhibited chemiluminescence measurements yielding very interesting results. The analytical utility of this new technique to the improvement of previous analytical methods as well as to the development of new procedures employing flow injection analysis is demonstrated. Furthermore, the application of the proposed method in combination with liquid chromatographic analysis is also presented.

Keywords: Inhibited chemiluminescence; Pyrogallol; Pre-oxidative chemiluminescence; Flow injection analysis; Liquid chromatography

Fractionation of potentially toxic elements in urban soils from five European cities by means of a harmonised sequential extraction procedure by Christine M. Davidson; Graham J. Urquhart; Franco Ajmone-Marsan; Mattia Biasioli; Armando da Costa Duarte; Encarnación Díaz-Barrientos; Helena Gr�?man; Iain Hossack; Andrew S. Hursthouse; Luis Madrid; Sonia Rodrigues; Marko Zupan (pp. 63-72).

The revised (four-step) BCR sequential extraction procedure has been applied to fractionate the chromium, copper, iron, manganese, nickel, lead and zinc contents in urban soil samples from public-access areas in five European cities. A preliminary inter-laboratory comparison was conducted and showed that data obtained by different laboratories participating in the study were sufficiently harmonious for comparisons to be made between cities and land types (e.g. parks, roadside, riverbanks, etc.). Analyte recoveries by sequential extraction, with respect to direct aqua regia digestion, were generally acceptable (100±15%). Iron, nickel and, at most sites, chromium were found mainly in association with the residual phase of the soil matrix. Copper was present in the reducible, oxidisable and residual fractions, whilst zinc was found in all four sequential extracts. Manganese was strongly associated with reducible material as, in some cities, was lead. This is of concern because high lead concentrations were present in some soils (>500mgkg⁻¹) and the potential exists for remobilisation under reducing conditions. As would be expected, extractable metal contents were generally highest in older, more heavily industrialised cities. Copper, lead and zinc showed marked (and often correlated) variations in concentrations between sites within the same city whereas manganese and, especially, iron, did not. No overall relationships were, however, found between analyte concentrations and land use, nor between analyte partitioning and land use.

Keywords: Potentially toxic elements; Potentially toxic metals; Urban soil; Sequential extraction

Determination of mercury in polluted soils surrounding a chlor-alkali plant by Anna Bernaus; Xavier Gaona; Derk van Ree; Manuel Valiente (pp. 73-80).

Soil samples collected in the surroundings of a chlor-alkali plant in the Netherlands were characterised by synchrotron-based techniques and conventional analytical procedures, in order to evaluate the environmental impact of Hg emissions and other heavy metals present in these locations. Analysis of total metal content by inductively coupled plasma-optical spectroscopy (ICP-OES) revealed a heterogeneous contamination of Hg, with concentrations ranging from 4.3 to 1150μgg⁻¹. In addition, significant concentrations of Cu, Ni, Pb, Zn, Mn and principally Fe were also identified within the studied samples. Direct determination of mercury species by X-ray absorption near edge spectroscopy (XANES) showed inorganic Hg compounds to prevail in all soils, being Cinnabar (HgS_red) and Corderoite (Hg₃S₂Cl₂) the main species. Nevertheless, more soluble mercury compounds, such as HgO and HgSO₄, have been also identified in significant proportion (from 6 to 20% of total mercury content), indicating a potential risk of mercury mobilisation. On the other hand, the application of sequential extraction schemes (SES) revealed large portions of weakly available Hg extracted in the residual fraction, while Hg associated to the exchangeable phase amounts as much as 19% of total Hg, thus, supporting the results obtained by XANES.Finally, synchrotron-based micro X-ray fluorescence (μ-XRF) was applied to identify qualitative trends on elemental associations in sample particles through a systematic mapping of its surface. In this concern, results show a well-defined correlation between Hg and Cu/Ni in the analysed particles. On the other hand, an absence of correlation between Hg and several other elements (Fe, Ti, Ca, Zn, Mn and S) was also observed. These effects have been attributed to chemical and physical interactions of mercury species on both enriched particles and sample matrices.

Keywords: Soil mercury speciation; Chlor-alkali plant; Mercury mobility; X-ray absorption near edge spectroscopy (XANES); Micro X-ray fluorescence (μ-XRF); Sequential extraction schemes

Investigation of four digestion procedures for multi-element determination of toxic and nutrient elements in legumes by inductively coupled plasma-optical emission spectrometry by Awad A. Momen; George A. Zachariadis; Aristidis N. Anthemidis; John A. Stratis (pp. 81-88).

A simple and reliable multi-element procedure for determination of essential (Cr, Cu, Fe, Mg, Mn, Zn) and toxic (Al, Cd, Pb) elements in legumes by inductively coupled plasma-optical emission spectrometry (ICP-OES) was developed. In this contribution, four different digestion procedures were thoroughly investigated and accurately evaluated with respect to their affect on the analysis of legumes. These included wet digestion with HNO₃/H₂SO₄ and HNO₃/H₂SO₄/H₂O₂, and dry ashing with Mg(NO₃)₂ and Mg(NO₃)₂/HNO₃. Two calibrations (aqueous standard and standard addition) procedures were studied, and proved that standard addition was preferable for all analytes. ICP-OES operating parameters, such as radio-frequency (RF) incident power, sample uptake flow rate and nebulizer argon gas flow rate were optimized. The precision as repeatability, expressed as relative standard deviation (R.S.D.) for aqueous standard containing 250μgl⁻¹ of each analyte was in the range1.5–8.0%. The accuracy, expressed as relative error was generally varied in the range of 0.5–10% for all analytes, while the quantification limits were lower than 2.5μgg⁻¹. Although, acceptable results were obtained from all developed procedures, wet digestion method with HNO₃/H₂SO₄/H₂O₂ is recommended for better recovery. The good agreement between measured and certified concentrations with respect to IAEA-331 and IAEA-359 (CRM's supplied by IAEA, International Atomic Energy Agency) indicates that the developed analytical method is well suited for determination of toxic and nutrient elements in legumes and possibly similar matrices.

Keywords: Sample digestion; Multi-element determination; Toxic and nutrient elements; Legumes; Inductively coupled plasma-optical emission spectrometry (ICP-OES)

Determination of C10-chloroalkane residues in fish matrices by short column gas chromatography/electron capture negative ion low resolution mass spectrometry applying single pure and representative synthesised chlorodecanes as standards by Florence Beaume; Mehmet Coelhan; Harun Parlar (pp. 89-96).

A new chlorodecane (CD) standard was developed consisting of five single compounds with 5–9 Cl-atoms, with which it was possible to determine chlorodecane residues in fish matrices from different countries using short column gas chromatography/electron capture negative ion low resolution mass spectrometry (SCGC/ECNI-LRMS). The concentrations found were between 4.8 and 30.2ng/g fat. Pentachlorodecanes could not be detected in all samples. For an evaluation of the new CD-standard, the fish matrices were also quantified by several other polychlorinated decane (CP10) standards with different chlorine grade: 50, 55, 63.5, 65, and 70%. The concentrations found differed unsurprisingly considerable among the applied standards. Considering only these CP10:50–70% standards that showed the highest similarity in peak patterns with the fish samples, the differences in observed chlorodecane concentrations between these standards and the new CD-standard were low, varying only 1–16%. The CP10:50–70% standards were further quantified with the new CD-standard (chlorine content, 58.2%) with neglectable observed differences to the CP10:60, 63.5, and 65% standards. Highest differences were observed to the CP10:50, 55, and 70% standards. By this work, the quantification of eco-toxicologically relevant C10-chloroparaffins using the new CD-standard has led to reproducible and reliable results, which indicates further that these compounds are still a concerning class of substances in environmental fish samples.

Keywords: Chloroparaffins; Chlorodecanes; Residue analysis; Fish samples; Short column gas chromatography (GC)

Food safety evaluation: Detection and confirmation of chloramphenicol in milk by high performance liquid chromatography-tandem mass spectrometry by Rebecca S. Nicolich; Eduardo Werneck-Barroso; Marlice A. Sípoli Marques (pp. 97-102).

A simple and rapid procedure for extraction of chloramphenicol (CAP) in milk and analysis by high-performance liquid chromatography coupled with quadrupole mass spectrometry in tandem was developed. The method consisted of one step of liquid–liquid extraction using ethyl acetate and acidified water (10mmolL⁻¹ formic acid) and HPLC-MS/MS detection. CAP-D5 was used as internal standard. The method was validated according to Commission Decision 2002/657/EC. The calibration curves were linear, with typical r² values higher than 0.98. Absolute recovery of CAP from milk proved to be more than 95%, however CAP-D5 absolute recovery was 75%. The method was accurate and reproducible, being successfully applied to the monitoring of CAP in milk samples obtained from the Brazilian market. Decision limit (CCα) was 0.05ngmL⁻¹ and detection capability (CCβ) was 0.09ngmL⁻¹.

Keywords: Chloramphenicol; Antibiotic; Food control; High performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS)

Microwave-assisted extraction of polybrominated diphenyl ethers and polychlorinated naphthalenes concentrated on semipermeable membrane devices by V. Yusà; A. Pastor; M. de la Guardia (pp. 103-111).

Microwave-assisted extraction (MAE) has been evaluated as an alternative to dialysis for the extraction of polybrominated diphenyl ethers (PBDEs) and polychlorinated naphthalenes (PCNs) sampled by semipermeable membrane devices (SPMDs), using gas chromatography coupled to tandem mass spectrometry (GC–MS–MS).For MAE optimization a two level full factorial design 2³, plus a centre point, which involves 11 randomized runs was used. The results showed that the temperature had a significant influence on the extraction of the nine PBDEs and four PCNs tested. Also, the solvent volume had a positive influence on the extraction of PBDEs and PCNs, but only in latter compounds, it achieves statistical significance. The time had only statistical significance for the most volatile specie studied, PCN-54. The selected MAE conditions (60mL of hexane–acetone, 1:1 (v/v), 85°C, 1min, two cycles) lead to recoveries between 72 and 91% for PBDEs and between 96 and 103% for PCNs. The applicability of the MAE extraction was tested in field SPMDs deployed for 20 days in a sewage treatment plant.The MAE method developed is about 300 times faster than the conventional dialysis and remarkably reduces the solvent consumption.

Keywords: Semipermeable membrane device (SPMD); Microwave-assisted extraction (MAE); Polybrominated diphenyl ethers; Polychlorinated naphthalenes

A simple approach to the prediction of electrophoretic mobilities of diverse organic acids by Yiyu Cheng; Hua Yuan (pp. 112-120).

Based on the principle of separation by capillary electrophoresis, three simple molecular structural descriptors, the number of acid groups (NG), number of atoms (NA) and molecular weight (MW) were employed to model the molecular structure–electrophoretic mobility relationship with the general form of μ₀= aNG/( bNA^k+ cMW^k), where the value of k ranges from 1/3 to 2/3 depending on the magnitude of molecular weight. The absolute electrophoretic mobilities ( μ₀) of three diverse data sets including carboxylic acids, sulfonic acids and peptides were investigated. Each data set was randomly divided into a training set for model generation and a test set for prediction test. The absolute average relative deviations (AARD and AARD_P) of the training set and the test set are 7.21% and 7.53% for data set 1, 1.99% and 1.96% for data set 2, 3.25% and 3.95% for data set 3, respectively. Compared to the quantitative structure–mobility relationship (QSMR) models reported in the literature, the approach proposed in this study is much simpler in terms of the calculation of structural descriptors and the interpretation of the physicochemical meaning of the models.

Keywords: Electrophoretic mobility; Quantitative structure–mobility relationship (QSMR); Carboxylic acids; Sulfonic acids; Peptides

Characterisation of lignosulphonates and kraft lignin by hydrophobic interaction chromatography by Dag Ekeberg; Kristin Sandersen Gretland; Jonas Gustafsson; Svein Magne Bråten; Guro Elise Fredheim (pp. 121-128).

To characterise the polymeric properties of processed lignins, a new method has been developed using hydrophobic interaction chromatography (HIC). This method separates the lignin polymers into fractions based on differences in hydrophobicity using low pressure liquid chromatography (LPLC). The hydrophobic column material consists of monodisperse polystyrene/divinylbenzene beads. An elution gradient was prepared monitoring the electrolyte concentration and pH. Citric acid buffer, containing ammonium sulphate that promotes adsorption to the column material, was used as mobile phase in a step-wise gradient together with ethanol (20/80% (v/v) ethanol/water, pH 12) and isopropanol (40/60% (v/v) isopropanol/water, pH 12). Depending on eluent composition, the degree of elution was 94% or higher. With the HIC method developed, lignosulphonates and kraft lignins were separated into seven distinctive peaks according to hydrophobicity.

Keywords: Lignosulphonate; Kraft lignin; Hydrophobic interaction chromatography (HIC); LPLC

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Analytica Chimica Acta (v.565, #1)