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Analytical and Bioanalytical Chemistry (v.388, #8)

Teaching chemometrics by Maria Cruz Ortiz (pp. 1557-1560).

is a permanent member of the staff of Analytical Chemistry in the University of Burgos (Faculty of Sciences). She does research and teaching on chemometrics. She is the head of an active research group, the Chemometrics and Qualimetrics group of the University of Burgos ( http://www.ubu.es/investig/grupos/cien_biotec/QA-4/index.htm ).

New plasma discharges for atomic spectrometry by J. A. C. Broekaert; N. Jakubowski (pp. 1561-1563).

is professor of analytical chemistry at the University of Hamburg. His research interests include analytical chemistry focussing on the development of atomic spectrometric problem-solving methods, especially in the field of environmental and material sciences Norbert Jakubowski is a senior scientist in ISAS. His research interests are related to the development of methods and instrumentation for plasma-based inorganic mass spectrometry, and their application in the material and bio-related sciences.

Microplasma-based atomic emission detectors for gas chromatography by M. Miclea; M. Okruss; K. Kunze; N. Ahlman; J. Franzke (pp. 1565-1572).

This paper is an update on the development of microplasmas as detectors for gas chromatography. Direct current (dc), alternating current (ac), and radio frequency (rf) microplasmas developed in recent years will be described with their significant analytical results, which mostly concern the detection of halogens and sulfur. New results will be added which employ a microhollow cathode discharge (MHCD) as excitation source. Emphasis will be given to this microplasma which has already been implemented as an element-selective detector for emission spectrometry and as ionization source for mass spectrometry. The possibility to use it as a multielement-selective detector for gas chromatography will be presented. A discussion of the published detection limits of all these microplasmas is given.

Keywords: Microplasmas; Emission; Spectrometry; Gas chromatography

Modifying argon glow discharges by hydrogen addition: effects on analytical characteristics of optical emission and mass spectrometry detection modes by A. Martín; A. Menéndez; R. Pereiro; N. Bordel; A. Sanz-Medel (pp. 1573-1582).

An overview of the effects produced by the presence of hydrogen in a glow discharge (GD), generated either in argon or in neon, is given. Extensive work related to the addition of hydrogen to GDs, coupled with optical emission spectrometry (OES) and mass spectrometry (MS), has been published in the last few years in an attempt to explain the processes involved in the discharge of mixed gases. Although numerous experimental results have already been explained theoretically, a complete understanding of the effects brought about by mixing hydrogen with argon (or another discharge inert gas) has not been reported yet. The use of theoretical models implemented using a computer has allowed the importance of some collisional and radiative processes in the inert gas plasma when hydrogen is present to be evaluated. This review shows, however, that both experimental work and theoretical work are still needed. The influence of small quantities of hydrogen on discharge parameters, such as electrical current or dc bias voltage, on crater shapes and on sputtering rates is thoroughly reviewed along with the effect on the analytical signals measured by OES and MS. Also, hydrogen-effect corrections needed to carry out proper calibrations for direct solid quantitative analyses are discussed. Figure Hydrogen induced changes in the Ar glow discharge reactions.

Keywords: Glow discharge–optical emission spectrometry; Glow discharge–mass spectrometry; Hydrogen mixtures; Sputtering rates; Collisional/radiative processes

Computer simulations of a dielectric barrier discharge used for analytical spectrometry by Tom Martens; Annemie Bogaerts; Wouter Brok; Jan van Dijk (pp. 1583-1594).

A model developed for a dielectric barrier discharge (DBD) in helium, used as a new spectroscopic source in analytical chemistry, is presented in this paper. The model is based on the fluid approach and describes the behavior of electrons, He⁺ and $${ ext{He}}^{ + }_{2} $$ ions, He metastable atoms, He atoms in higher excited levels, and He₂ dimers. The He ground-state atoms are regarded as background gas. The characteristic effect of charging/discharging of the dielectrics which cover both electrodes is also simulated. Typical results of the model include the distribution of potential inside the plasma (and the potential drop across the dielectrics), the electric current and gap voltage as a function of time for a given applied potential profile, the spatial and temporal number-density profiles of the different plasma species, and the relative contributions of the mechanisms of their production and loss. Figure Schematic diagram of the dielectric barrier discharge (left) and typical temporal profiles of voltage and current, as obtained from the simulations (right)

Keywords: Dielectric barrier discharge; Computer simulations; Modeling; Microplasma

Micromachined, planar-geometry, atmospheric-pressure, battery-operated microplasma devices (MPDs) on chips for analysis of microsamples of liquids, solids, or gases by optical-emission spectrometry by Vassili Karanassios; Kara Johnson; Andrea T. Smith (pp. 1595-1604).

Because of their desirable characteristics, for example small size, lightness, low power and gas consumption, and potential for portability, miniaturized plasma sources are receiving significant attention in the scientific literature. To take advantage of these characteristics we micromachined and fabricated new, planar-geometry, self-igniting, atmospheric-pressure microplasma devices (MPDs) on chips. These microplasmas required such low power for their operation they could be operated from a re-chargeable battery (of the type used in cordless power-tools). Despite their advantages, most miniaturized plasma sources reported in the literature have not performed well with liquid samples; analysis of powders or solids that can be converted to a powder (and processed and used as slurries) is even more difficult. To address these shortcomings we coupled an electrothermal, mini-in-torch vaporization (mini-ITV) “dry” sample-introduction system to the low-power planar microplasma devices we developed. In this preliminary investigation, absolute detection limits obtained from microsamples of single-element liquid standards and optical emission spectrometry with photomultiplier-tube detection and a spectral bandpass similar to that of portable, commercially available fiber-optic spectrometers were in the low-pg to ng range, for example 2 pg (for K) to 25 ng (for Pb). Mini-ITV also enabled (as far as we are aware, for the first time) measurement of analyte emission from microsamples of powdered solids (as slurries). In addition to the 3% H₂ in Ar mixtures, the ac-operated microplasmas were sustained by use of a variety of electrode materials and different plasma-support gases (e.g. Ar, He and 3% H₂ in He) thus indicating fabrication versatility and operational flexibility. Such flexibility has the potential to enable microplasmas to be tailored to analytical problems, and this is demonstrated by using a He MPD and chlorine emission measurements (837.594 nm) from gaseous microsamples as an example. Figure Cross-sectional view of a microplasma formed in a micromachined channel (typical channel dimensions: L=5 mm, W=1 mm, D=0.5 mm).

Keywords: Microplasmas; Spectroscopy instrumentation; Microsamples; Lab-on-a-chip; Microfluidics; Microfabrication

Introducing wet aerosols into the static high sensitivity ICP (SHIP) by Andy Scheffer; Carsten Engelhard; Michael Sperling; Wolfgang Buscher (pp. 1605-1613).

A demountable design of the static high sensitivity ICP (SHIP) for optical emission spectrometry is presented, and its use as an excitation source with the introduction of wet aerosols was investigated. Aerosols were produced by standard pneumatic sample introduction systems, namely a cross flow nebulizer, Meinhard nebulizer and PFA low flow nebulizer, which have been applied in conjunction with a double pass and a cyclonic spray chamber. The analytical capabilities of these sample introduction systems in combination with the SHIP system were evaluated with respect to the achieved sensitivity. It was found that a nebulizer tailored for low argon flow rates (0.3–0.5 L min⁻¹) is best suited for the low flow plasma (SHIP). An optimization of all gas flow rates of the SHIP system with the PFA low flow nebulizer was carried out in a two-dimensional way with the signal to background ratio (SBR) and the robustness as optimization target parameters. Optimum conditions for a torch model with 1-mm injector tube were 0.25 and 0.36 L min⁻¹ for the plasma gas and the nebulizer gas, respectively. A torch model with a 2-mm injector tube was optimized to 0.4 L min⁻¹ for the plasma gas and 0.44 L min⁻¹ for the nebulizer gas. In both cases the SHIP system saves approximately 95% of the argon consumed by conventional inductively coupled plasma systems. The limits of detection were found to be in the low microgram per litre range and below for many elements, which was quite comparable to those of the conventional setup. Furthermore, the short-term stability and the wash out behaviour of the SHIP were investigated. Direct comparison with the conventional setup indicated that no remarkable memory effects were caused by the closed design of the torch. The analysis of a NIST SRM 1643e (Trace Elements in Water) with the SHIP yielded recoveries of 97–103% for 13 elements, measured simultaneously. Photo of the SHIP-III during operation

Keywords: SHIP; Inductively coupled plasma; Optical emission spectrometry; Pneumatic nebulization; NIST SRM 1643e

Evaluation and application of argon and helium microstrip plasma for the determination of mercury by the cold vapor technique and optical emission spectrometry by Israel Jiménez Zapata; Pawel Pohl; Nicolas H. Bings; José A. C. Broekaert (pp. 1615-1623).

The suitability of a 2.45-GHz atmospheric pressure, low-power microwave microstrip plasma (MSP) operated with Ar and He for the determination of Hg by continuous-flow cold vapor (CV) generation, using SnCl₂/HCl as the reducing agent, and optical emission spectrometry (OES) using a small CCD spectrometer was studied. The areas of stability for a discharge in the Ar and in the He MSP enclosed in a cylindrical channel in a quartz wafer were investigated. The excitation temperatures as measured for discharge gas atoms (Ar I, He I), and the electron number densities at 35–40 W and 15–400 mL min⁻¹ were found to be at the order of 3,200–5,500 K and 0.8 × 10¹⁴–1.6 × 10¹⁴ cm⁻³, respectively. The relative intensity of the Hg I 253.6-nm line and the signal-to-background ratio as a function of the forward power (35–40 W) as well as of the flow rate of the working gas (15–400 mL min⁻¹) were evaluated and discussed. For the selected measurement conditions, the Ar MSP was established to have the lower detection limit for Hg (0.6 ng mL⁻¹) compared with the He MSP. The linearity range is up to 300 ng mL⁻¹ and the precision is on the order of 1–3%. With the optimized CV Ar MSP-OES method a determination of Hg in spiked domestic and natural waters at concentration levels of 20–100 μg L⁻¹ and an accuracy of 1–4% could be performed. In an NIST domestic sludge standard reference material, Hg (3.64 μg g⁻¹) could be determined with a relative standard deviation of 4% and an agreement better than 4%.

Keywords: Microwave microstrip plasma; Cold vapor generation; Mercury; Optical emission spectrometry

Amplification of noble gas ion lines in the afterglow of a pulsed hollow cathode discharge and possible benefit for analytical glow discharge mass spectrometry by A. Surmeian; C. Diplasu; A. Groza; M. Ganciu; P. Belenguer; A. Tempez; P. Chapon (pp. 1625-1629).

A high-current pulsed hollow cathode discharge was used to study the role of atomic and ionic metastables involved in ionization plasma processes. We observed the enhancement of the spectral emission lines of noble gas ions in the afterglow. A study of the processes that involve atomic and ionic metastables is of great interest since it should lead to a better understanding of and enhanced control over the ionization mechanisms crucial to analytical glow discharge mass spectrometry (GDMS) analysis. Figure Time profile of Ti, Ti⁺, and Ne⁺ spectral lines

Keywords: GDMS; Afterglow plasma; Metastable; Ionization processes

On the occasion of Professor Werner Engewald’s 70th birthday by Katja Dettmer (pp. 1631-1632).

Analysis of cysteine-containing proteins using precolumn derivatization with N-(2-ferroceneethyl)maleimide and liquid chromatography/electrochemistry/mass spectrometry by Bettina Seiwert; Uwe Karst (pp. 1633-1642).

N-(2-Ferroceneethyl)maleimide (FEM) is introduced as an electroactive derivatizing agent for thiol functionalities in proteins. Using appropriate reaction conditions, the derivatization is completed within five minutes and no unspecific labeling of free amino functions is observed. Liquid chromatography/electrochemistry/mass spectrometry was used to detect the reaction products. The reagent is a useful tool for determining the number of free thiol groups or the total number of free and disulfide-bound thiol groups in proteins. The electrochemical cell provides additional information, because the increase in mass spectrometric response upon electrochemical oxidation of the neutral ferrocene to the charged ferrocinium groups is monitored. The method was successfully applied to the analysis of native proteins and their tryptic digests.

Keywords: Cysteine; Proteins; Derivatization; N-(2-ferroceneethyl)maleimide; Liquid chromatography/mass spectrometry; Electrochemical conversion

Autism and urinary exogenous neuropeptides: development of an on-line SPE–HPLC–tandem mass spectrometry method to test the opioid excess theory by K. Dettmer; D. Hanna; P. Whetstone; R. Hansen; B. D. Hammock (pp. 1643-1651).

Autism is a complex neurodevelopmental disorder with unknown etiology. One hypothesis regarding etiology in autism is the “opioid peptide excess” theory that postulates that excessive amounts of exogenous opioid-like peptides derived from dietary proteins are detectable in urine and that these compounds may be pathophysiologically important in autism. A selective LC–MS/MS method was developed to analyze gliadinomorphin, β-casomorphin, deltorphin 1, and deltorphin 2 in urine. The method is based on on-line SPE extraction of the neuropeptides from urine, column switching, and subsequent HPLC analysis. A limit of detection of 0.25 ng/mL was achieved for all analytes. Analyte recovery rates from urine ranged between 78% and 94%, with relative standard deviations of 0.2–6.8%. The method was used to screen 69 urine samples from children with and without autism spectrum disorders for the occurrence of neuropeptides. The target neuropeptides were not detected above the detection limit in either sample set.

Keywords: Autism; Neuropeptides; β-Casomorphin; Gliadinomorphin; Opioid peptide excess theory; On-line SPE–HPLC–MS/MS

Characterization of sulfonated azo dyes and aromatic amines by pyrolysis gas chromatography/mass spectrometry by Astrid Rehorek; Alexander Plum (pp. 1653-1662).

Sixteen sulfonated and unsulfonated azo dyes as well as eleven sulfonated and unsulfonated aromatic amines were analyzed and qualitatively characterized by means of pyrolysis gas chromatography/mass spectrometry at different temperatures. Aniline and aminonaphthalene were found to be the dominant pyrolysis products of sulfonated aromatic amines and dyes. Azo dye and dye class specific key compounds such as benzidine, vinyl-p-base and 4-aminoazobenzene could be identified by pyrolysis gas chromatography/mass spectrometry of commercial acid, cationic, direct, reactive and solvent dyes. 500 °C was the optimal pyrolysis temperature for most of the pyrolyzed compounds. The method was applied to a dried sample of a textile wastewater concentrate from a dyeing process. Reactive azo dyes of the group of Remazol dyes and anthraquinone dyes could be identified as the major compounds of the sample. The finding of caprolactam (a printing additive) suggests that the wastewater contained effluent from a process of heat-activated printing with reactive dyes. p-Chloraniline, a banned aromatic amine, was identified. Chemical reduction of the wastewater sample prior to pyrolysis resulted in the release of volatile aromatic amines and aided the classification of several products of pyrolysis.

Keywords: Pyrolysis; GC–MS; Thermal extraction; Sulfonated azo dyes; Aromatic amines

Evaporative light scattering detection: trends in its analytical uses by R. Lucena; S. Cárdenas; M. Valcárcel (pp. 1663-1672).

Evaporative light scattering detection (ELSD) is widely recognized as a universal tool for liquid and supercritical chromatographies. In addition, this detection technique is fully compatible with continuous-flow systems. In fact, the combination of continuous non-chromatographic techniques and ELSD affords the design of simple, reliable systems for extracting qualitative information. This paper reviews instrumental innovations regarding the miniaturization of evaporative light scattering detectors and their uses in micro and capillary liquid chromatography; also, it discusses their increasingly important role in the development of vanguard configurations for sample screening and the determination of total indices without the need for chromatographic separation. Moreover, it compares them with other types of chromatographic detectors in terms of performance. Finally, the potential of ELSD for solving real-life analytical problems arising from the need to meet (bio)chemical information needs is illustrated with various selected applications. Figure New trends in evaporative light scattering detection: recent chromatographic uses and its role in vanguard/rearguard strategies

Keywords: Evaporative light scattering detection; Universal detectors; Liquid chromatography; Total indices; Vanguard/rearguard analytical strategies

Implantation of a glass capillary-based enzyme electrode in mouse hippocampal slices for monitoring of L-glutamate release by Takayuki Oka; Chihiro Tasaki; Hiromi Sezaki; Masao Sugawara (pp. 1673-1679).

A glass capillary-based enzyme electrode (tip size ≈10 μm) was implanted in the target neuronal region, i.e., dentate gyrus (DG) or cornu ammonis 1 (CA1), of acute brain slices at a depth of ≈10 μm from the slice surface in order to allow the monitoring of chemical stimulant-induced changes in L-glutamate levels. First, the sampling behavior of a glass capillary in a slice was investigated by visualizing the transport of a fluorescence dye. Then, the electrode was applied to real-time monitoring of L-glutamate release in acute hippocampal slices stimulated by surface application of a stimulant solution. The extracellular application of KCl (0.10 M) increased the glutamate levels in the DG and CA1 regions, respectively. The enhancement of L-glutamate concentration at DG was much larger than at CA1. The application of tetraethylammonium chloride (TEA) (25 mM) enhanced the L-glutamate level in the DG region and the enhanced level did not return to the initial value before TEA application even when washed with an artificial cerebrospinal fluid (ACSF). The usefulness of a surface-implanted capillary electrode for monitoring L-glutamate release in acute brain slices is discussed.

Keywords: Implanted glass capillary electrode; L-Glutamate; Mouse hippocampal slices; Interface chamber

Correlation between CMC and chromatographic index: simple and effective evaluation of the hydrophobic/hydrophilic balance of bile acids by Benedetto Natalini; Roccaldo Sardella; Emidio Camaioni; Antimo Gioiello; Roberto Pellicciari (pp. 1681-1688).

The discovery that bile acids are involved in the modulation of nuclear steroid receptors has prompted renewed interest in this field of research. Due to the nature of research in this field, a technique that enables simple and effective assessment of the hydrophobic/hydrophilic balance, thus improving and speeding up evaluations of the biological profiles of these compounds, is greatly needed. In this context, both CMC value determination and RP-HPLC mobility evaluation were explored as possible approaches. While the CMC was calculated using the noninvasive conductimetric method, the RP-HPLC mobility was assessed by measuring the retention factor at several mobile phase compositions and extrapolating back to the pure aqueous mobile phase. The correlation of the CMC with the derived chromatographic hydrophobic index ϕ ₀ was satisfactory. Figure Experimental versus predicted pCMC values

Keywords: Critical micellar concentration; Hydrophobicity index; Conductimetry; Noninvasive method

Contact angle measurements under thermodynamic equilibrium conditions by Carol Lages; Eduardo Méndez (pp. 1689-1692).

The precise control of the ambient humidity during contact angle measurements is needed to obtain stable and valid data. For a such purpose, a simple low-cost device was designed, and several modified surfaces relevant to biosensor design were studied. Static contact angle values for these surfaces are lower than advancing contact angles published for ambient conditions, indicating that thermodynamic equilibrium conditions are needed to avoid drop evaporation during the measurements.

Keywords: Biosensors; Biomaterials; Interface/surface analysis

Retention prediction of adrenoreceptor agonists and antagonists on unmodified silica phase in hydrophilic interaction chromatography by Noel S. Quiming; Nerissa L. Denola; Yoshihiro Saito; Kiyokatsu Jinno (pp. 1693-1706).

The development of retention prediction models for adrenoreceptor agonists and antagonists chromatographed on an unmodified silica stationary phase under the hydrophilic interaction chromatographic (HILIC) mode at three pH conditions (3.0, 4.0 and 5.0) is described. The models were derived using multiple linear regression (MLR) and an artificial neural network (ANN) using the logarithm of the retention factor (log k) as the dependent variable. In addition to the effects of the solute-related variables (molecular descriptors), the percentage of acetonitrile (%ACN) was also used as a predictor to gauge the influence of the mobile phase on the retention behavior of the analytes. Using stepwise MLR, the retention behavior of the studied compounds at pH 3.0 were satisfactorily described by a four-predictor model; the predictors being the %ACN, the logarithm of the partition coefficient (log D), the number of hydrogen bond acceptors (HBA), and the magnitude of the dipole moment (DipolMag). In addition to these four predictors, the total absolute atomic charge (TAAC) was found to be a significant predictor of retention at pH 4.0 and 5.0. Among the five descriptors, %ACN had the strongest effect on the retention, as indicated by its higher standardized coefficient than those obtained for the other four predictors. The inclusion of these four predictors which are related to the molecular properties of the compounds (log D, HBA, DipolMag, and TAAC) suggested that hydrophilic interactions, hydrogen bonding and ionic interactions are possible mechanisms by which analytes are retained on the studied system. The reliability and predictive ability of the derived MLR equations were tested using cross-validation and a test set which was not used when fitting the model. The models derived from MLR produced adequate fits, as proven by the high R ² values obtained for all calibration and training sets (0.9497 and above), and their good predictive power, as indicated by the high cross-validated q ² (0.9465 and above) and high R ² (0.9305 and above) values obtained for the test sets. ANN prediction models were also derived using the predictors derived from MLR as inputs and log k as output. A comparison of the models derived from both ANN and MLR revealed that the trained ANNs showed better predictive abilities than the MLR models, as indicated by their higher R 2 values and their lower root mean square error of predictions (RMSEP) for both training and test sets under all pH conditions. The derived models can be used as references and they provide a useful tool for method development and the optimization of chromatographic conditions for the separation of adrenoreceptor agonists and antagonists.

Keywords: Adrenoreceptor agonists/antagonists; Artificial neural network; Hydrophilic interaction chromatography; Multiple linear regression; Quantitative structure–retention relationships

On-line NMR detection of microgram quantities of heparin-derived oligosaccharides and their structure elucidation by microcoil NMR by Albert K. Korir; Cynthia K. Larive (pp. 1707-1716).

The isolation and purification of sufficient quantities of heparin-derived oligosaccharides for characterization by NMR is a tedious and time-consuming process. In addition, the structural complexity and microheterogeneity of heparin makes its characterization a challenging task. The improved mass-sensitivity of microcoil NMR probe technology makes this technique well suited for characterization of mass-limited heparin-derived oligosaccharides. Although microcoil probes have poorer concentration sensitivity than conventional NMR probes, this limitation can be overcome by coupling capillary isotachophoresis (cITP) with on-line microcoil NMR detection (cITP-NMR). Strategies to improve the sensitivity of on-line NMR detection through changes in probe design and in the cITP-NMR experimental protocol are discussed. These improvements in sensitivity allow acquisition of cITP-NMR survey spectra facilitating tentative identification of unknown oligosaccharides. Complete structure elucidation for microgram quantities of the purified material can be carried out through acquisition of 2D NMR spectra using a CapNMR microcoil probe. Survey NMR spectrum obtained by cITP-NMR using a second-generation probe (the microcoil of which is shown) facilitates tentative identification of unknown oligosaccharides (e.g., the heparin-derived tetrasaccharide illustrated)

Keywords: Heparin; Microcoil; NMR; Capillary isotachophoresis; Glycosaminoglycans; Structure elucidation

A comprehensive chemoselective and enantioselective 2D-HPLC set-up for fast enantiomer analysis of a multicomponent mixture of derivatized amino acids by T. Welsch; C. Schmidtkunz; B. Müller; F. Meier; M. Chlup; A. Köhne; M. Lämmerhofer; W. Lindner (pp. 1717-1724).

A feasibility study on the fast enantioselective two-dimensional HPLC separation of racemic amino acid derivatives is presented. The method involves the on-line coupling of a narrow-bore C18 RP column in the first dimension to a short enantioselective column based on nonporous 1.5 μm particles modified with quinidine carbamate as chiral selector in the second dimension. Conceptually, the system was designed to enable both time-controlled repeated transfer of fractions of the eluate and detector-controlled transfer of selected fractions from column 1 to column 2. To avoid volume overloading of the second chiral column, a narrow-bore reversed phase column was installed in the first dimension. Due to the fast (less than 1.5 minutes) enantiomer separation that occurs in the second dimension, the overall analysis time for the two-dimensional separation of a mixture of nine racemic 3,5-dinitrobenzoyl amino acids was optimized at 16 minutes.

Keywords: Comprehensive two-dimensional high-performance liquid chromatography; Reversed phase separation; Enantioselective separation; 3,5-Dinitrobenzoyl amino acids; Chiral stationary phase; O-9-(tert-butylcarbamoyl) quinidine; Nonporous silica; Sub-2-μm particles

Metal-coated fused silica fibers as a support for immobilized compounds yielding a volatile analyte (C₂H₄) by A. Naganowska-Nowak; P. Konieczka; J. F. Biernat; J. Szczygelska-Tao; A. Przyjazny; J. Namieśnik (pp. 1725-1731).

This paper presents the results of investigations of chemically modified fibers comprising an immobilized compound that yields ethene as the analyte in generated standard gaseous mixtures. Prior to chemical modification, the fibers were coated with a thin aluminum layer to improve their mechanical strength. Commercially available Al-coated fibers were used in this work. During thermal decomposition of the immobilized compound, reproducible quantities of the analyte per unit fiber length were obtained for all the investigated fibers (fiber diameter (μm)/outside diameter (μm) of the Al-coated fiber = 110/146, 220/300, and 660/830), amounting to 0.685 ± 0.032, 0.8300 ± 0.0081, and 1.092 ± 0.010 ng cm⁻¹, respectively. The proposed procedure can be used successfully for the generation of measured component of matrix-free reference materials.

Keywords: Metal-coated fused silica fibers; Reference materials; Matrix-free reference materials; Thermal decomposition process; Immobilized compounds

Metabolism of ¹⁴C-labelled and non-labelled sulfadiazine after administration to pigs by Marc Lamshöft; Premasis Sukul; Sebastian Zühlke; Michael Spiteller (pp. 1733-1745).

The behaviour of sulfadiazine (SDZ) and its metabolites was investigated by administering the ¹⁴C-labelled veterinary drug to fattening pigs. The excretion kinetics were determined after daily collection of manure. Two known metabolites, N-acetylsulfadiazine and 4-hydroxysulfadiazine, and two hitherto unidentified minor metabolites were recovered. Various mass spectrometric techniques such as parent, product ion scans and accurate mass measurement were used. The new compounds were identified as N-formylsulfadiazine (For-SDZ) and N-acetyl-4-hydroxysulfadiazine (Ac-4-OH-SDZ). The identification of SDZ, Ac-SDZ and For-SDZ was confirmed by comparison of the spectroscopic and chromatographic data of the synthesized authentic references. The identification of the hydroxylated compounds 4-OH-SDZ and Ac-4-OH-SDZ was performed by MSⁿ, and accurate mass measurements. Only 4% of the administered radioactivity remained in the pig after ten days and SDZ accounted for 44% of the 96% radioactivity excreted. More than 93% of the labelled compounds were detected and identified in the manure. The key analytical problem, namely a high concentration of matrix in sample extracts, was overcome by advanced measurement techniques and with the use of a suitable internal standard. The mean recoveries for all compounds were ≥96%. Linearity was established over a concentration range of 0.5 to 10,000 μg kg⁻¹ manure with a correlation coefficient ≥0.99. The same experiment was carried out simultaneously with non-labelled SDZ to obtain manure for outdoor soil experiments.

Keywords: Bioanalytical methods; Drug monitoring; Drug screening; HPLC; Mass spectrometry/ICP-MS; Radiochemical methods

Genotyping of single nucleotide polymorphisms by primer extension reaction and a dual-analyte bio/chemiluminometric assay by Jessica Konstantou; Penelope C. Ioannou; Theodore K. Christopoulos (pp. 1747-1754).

Primer extension reaction (PEXT) is the most widely used approach to genotyping of single nucleotide polymorphisms (SNP). It is based on the high accuracy of nucleotide incorporation by the DNA polymerase. We propose a dual-analyte bio/chemiluminometric method for the simultaneous detection of the PEXT reaction products of the normal and mutant allele in a high sample-throughput format. PCR-amplified DNA fragments that span the SNP of interest are subjected to two PEXT reactions using normal and mutant primers in the presence of digoxigenin-dUTP and biotin-dUTP. Both primers contain a d(A)₃₀ segment at the 5′-end but differ in the final nucleotide at the 3′-end. Under optimized conditions only the primer that is perfectly complementary with the interrogated DNA will be extended by DNA polymerase and lead to a digoxigenin- or biotin-labeled product. The products of the PEXT reactions are mixed, denatured, and captured in microtiter wells through hybridization with immobilized oligo(dT) strands. Detection is performed by adding a mixture of antidigoxigenin–alkaline phosphatase (ALP) conjugate and a streptavidin–aequorin conjugate. The flash-type bioluminescent reaction of aequorin is triggered by the addition of Ca²⁺. ALP is then measured by adding the appropriate chemiluminogenic substrate. The method was evaluated by genotyping two SNPs of the human mannose-binding lectin gene (MBL2) and one SNP of the cytochrome P450 gene CYP2D6. Patient genotypes showed 100% concordance with direct DNA sequencing data.

Keywords: Single nucleotide polymorphisms; Genotyping; (Bio)Chemiluminescence; High throughput; Dual analyte assay

Analysis of tensides in complex samples with comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry by Jane Hübner; Rahil Taheri; David Melchior; Hans-Willi Kling; Siegmar Gäb; Oliver J. Schmitz (pp. 1755-1762).

Multidimensional gas-chromatographical analysis of various tensides of natural or synthetic origin in cosmetic products is demonstrated. Comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry allows the qualitative and quantitative determination of alkyl polyglucosides (AG), fatty alcohol ethoxylates (FAEO), fatty alcohol sulfates (FAS), fatty alcohol ether sulfates (FAES) and cocamidopropyl betaines (CAPB) in shower gel and cleaning agents. The samples were aliquoted in two parts. The first part was silylated, diluted and analysed; then, in order to detect anionic tensides (FAES, FAS) too, the second aliquot was hydrolysed before being silylated for analysis. Because of their amphoteric character, the betaines can only be analysed by gas chromatography after thermal decomposition in the injector, which leads to the corresponding amidoamines among other products.

Keywords: GC×GC; Comprehensive two-dimensional GC; Tenside; Alkyl polyglycoside; FAEO; FAES; FAS; Betaine

Analysis of glutathione in supernatants and lysates of a human proximal tubular cell line from perfusion culture upon intoxication with cadmium chloride by HPLC and LC-ESI-MS by Hans Hahn; Christian W. Huck; Matthias Rainer; Muhammad Najam-ul-Haq; Rania Bakry; Thomas Abberger; Paul Jennings; Walter Pfaller; Günther K. Bonn (pp. 1763-1769).

A simple and highly effective reversed-phase (RP) high-performance liquid chromatography (HPLC) method is described for analysing glutathione (GSH) and glutathione disulfide (GSSG) in out-flowing supernatants and lysates of perfusion cell cultures of human kidney cells (HK-2 cells) continuously exposed to cadmium chloride (CdCl₂), which is a well-known nephrotoxin. The developed linear liquid chromatographic gradient employs monolithic poly(styrene-co-divinylbenzene) (PS/DVB) as a stationary phase and is adaptable for coupling to mass spectrometry via an electrospray ionisation interface (LC-ESI/MS), which is carried out in case of co-eluting peaks. This study presents a quantitative assay of glutathione over the time of experiment and cell lysates at the end of the experiment. The assay of out-flowing supernatants has the potential to be applied as an online assay in high time resolution. Glutathione (reduced and oxidised, GSH and GSSG) is chosen as an indicator for toxic effects in the cultured cells. In principle it is possible to show the concentration of glutathione as a function of time in an investigation of exposure of the HK-2 cell line to CdCl₂. In addition to glutathione analysis, well-established assays of cell death such as enzyme release and cell viability are performed to obtain information about the number of living cells. Toxicity of 5 μM CdCl₂ is manifested in all of the assays applied. Fast (<7 min) and highly reproducible (max. aberration 4.7%) determination of glutathione could be achieved.

Keywords: Glutathione; HPLC; LC-ESI-MS; Perfusion cell culture

Determination of sub-ppb reserpine by an optosensing device based on photochemically induced fluorescence by Javier López-Flores; María L. Fernández-de Córdova; Antonio Molina-Díaz (pp. 1771-1777).

A flow injection–solid-phase spectroscopy (FI-SPS) system implemented with photochemically induced fluorescence (PIF) is described for the rapid and very sensitive determination of reserpine in biological fluids and pharmaceutical formulations. An intensively fluorescent photoproduct is in-line generated, retained on C₁₈ silica gel in the detection area and monitored at 394/489 nm (λ _ex/λ _em). After the establishment of the appropriate working variables, the system is calibrated at two different injection volumes, 100 and 800 μL, achieving detection limits of 0.33 and 0.05 ng mL⁻¹, respectively. The RSD for reserpine at 2 ng mL⁻¹ (800 μL) was 1.5% (n = 10). The sampling rates were 46 and 43 h⁻¹ for each injection volume, respectively. The potential interference of some common species coexisting with reserpine in the analysed samples was also studied. The procedure was successfully applied to commercial formulations, urine and serum without any previous treatment of samples. Recoveries ranged from 94.9 to 100.2%.

Keywords: Flow-through optosensor; Photochemically induced fluorescence; Reserpine; Serum; Urine; Pharmaceuticals

A simple and rapid method for simultaneous determination of benzoic and sorbic acids in food using in-tube solid-phase microextraction coupled with high-performance liquid chromatography by Yi Wen; Ying Wang; Yu-Qi Feng (pp. 1779-1787).

A simple, rapid and sensitive on-line method for the simultaneous determination of benzoic and sorbic acids in food was developed by coupling in-tube solid-phase microextraction (SPME) to high-performance liquid chromatography (HPLC) with UV detection. The diethylamine-modified poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolithic capillary selected as the extraction medium exhibited a high extraction capability towards benzoic and sorbic acids. To obtain optimum extraction performance, several in-tube SPME parameters were investigated, including pH value, inorganic salt, and the organic solvent content of the sample matrix. After simple dilution with 0.02 mol/L phosphate solution (pH 4.0), carbonated drink, juice drink, sauce and jam samples could be directly injected for extraction. For succade samples, a small amount of acetonitrile was required to extract analytes prior to dilution and subsequent extraction. The linearity of the method was investigated over a concentration range of 5–20000 ng/mL for both analytes, and the correlation coefficients (R ² values) were higher than 0.999. The detection limits for benzoic and sorbic acids were 1.2 and 0.9 ng/mL, respectively. The method reproducibility was tested by evaluating the intra- and interday precisions; relative standard deviations of less than 4.4 and 9.9%, respectively, were obtained. Recoveries of compounds from spiked food samples ranged from 84.4 to 106%. The developed method was shown to be suitable for the routine monitoring of benzoic and sorbic acids in various types of food samples.

Keywords: Benzoic and sorbic acids; Food; In-tube solid-phase microextraction; High-performance liquid chromatography; Diethylamine-modified poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolithic capillary

Optimization of a sensitive method for the determination of nitro musk fragrances in waters by solid-phase microextraction and gas chromatography with micro electron capture detection using factorial experimental design by Maria Polo; Carmen Garcia-Jares; Maria Llompart; Rafael Cela (pp. 1789-1798).

A solid-phase microextraction method (SPME) followed by gas chromatography with micro electron capture detection for determining trace levels of nitro musk fragrances in residual waters was optimized. Four nitro musks, musk xylene, musk moskene, musk tibetene and musk ketone, were selected for the optimization of the method. Factors affecting the extraction process were studied using a multivariate approach. Two extraction modes (direct SPME and headspace SPME) were tried at different extraction temperatures using two fiber coatings [Carboxen–polydimethylsiloxane (CAR/PDMS) and polydimethylsiloxane–divinylbenzene (PDMS/DVB)] selected among five commercial tested fibers. Sample agitation and the salting-out effect were also factors studied. The main effects and interactions between the factors were studied for all the target compounds. An extraction temperature of 100 °C and sampling the headspace over the sample, using either CAR/PDMS or PDMS/DVB as fiber coatings, were found to be the experimental conditions that led to a more effective extraction. High sensitivity, with detection limits in the low nanogram per liter range, and good linearity and repeatability were achieved for all nitro musks. Since the method proposed performed well for real samples, it was applied to different water samples, including wastewater and sewage, in which some of the target compounds (musk xylene and musk ketone) were detected and quantified. Figure Stardardized Pareto charts for the main effects and interactions

Keywords: Nitro musk fragrances; Solid-phase microextraction; Gas chromatography–micro electron capture detection; Water analysis; Factorial design

Spectroscopic and electrochemical studies of cocaine–opioid interactions by Jorge M. P. J. Garrido; M. Paula M. Marques; Artur M. S. Silva; Tice R. A. Macedo; Ana M. Oliveira-Brett; Fernanda Borges (pp. 1799-1808).

The drugs of abuse cocaine (C), heroin (H), and morphine (M) have been studied to enable understanding of the occurrence of cocaine–opioid interactions at a molecular level. Electrochemical, Raman, and NMR studies of the free drugs and their mixtures were used to study drug–drug interactions. The results were analyzed using data obtained from quantum-mechanical calculations. For the cocaine–morphine mixture (C–MH), formation of a binary complex was detected; this involved the 3-phenolic group and the heterocyclic oxygen of morphine and the carbonyl oxygen and the methyl protons of cocaine’s methyl ester group. NMR studies conducted simultaneously also revealed C–MH binding geometry consistent with theoretical predictions and with electrochemical and vibrational spectroscopy results. These results provide evidence for the occurrence of a cocaine–morphine interaction, both in the solid state and in solution, particularly for the hydrochloride form. A slight interaction, in solution, was also detected by NMR for the cocaine–heroin mixture. Figure "Schematic representation of the proposed model for cocaine:morphine salt interaction"

Keywords: Cocaine; Opioids; Drug–drug interaction; Electrochemistry; Molecular spectroscopy

Quasi-simultaneous determination of antioxidative activities against superoxide anion and nitric oxide by a combination of sequential injection analysis and flow injection analysis with chemiluminescence detection by Aoi Miyamoto; Kuniko Nakamura; Naoya Kishikawa; Yoshihito Ohba; Kenichiro Nakashima; Naotaka Kuroda (pp. 1809-1814).

A method that combines sequential injection analysis (SIA), flow injection analysis and chemiluminescence (CL) detection was developed for the quasi-simultaneous determination of antioxidative activities against superoxide anion $$ {left( {{ ext{O}}^{ - }_{2} } ight)} $$ and nitric oxide (NO). The antioxidative activity was expressed as the decrease in luminol CL intensity caused by the quenching of $${ ext{O}}^{ - }_{2} $$ or NO by an antioxidant. The SIA system consisted of two syringe pumps, two selection valves, two holding coils, an HPLC pump to deliver luminol solution, and a CL detector. Operation of the syringe pumps and multiport valves was controlled automatically using a personal computer with appropriate software. A hypoxanthine (HX)-xanthine oxidase (XOD) system was used for the generation of $${ ext{O}}^{ - }_{2} $$ , and (±)-(E)-4-methyl-2-[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hexenamide (NOR1) was employed as NO donor agent. The repeatability of the method was evaluated with 35.2 μg ml⁻¹ L-ascorbic acid, and the relative standard deviations (RSD) of the antioxidative activities were less than 3.8%. The quasi-simultaneous determination of the antioxidative activities in one sample was completed within 2.0 min. The antioxidative activities of some antioxidants and commercially available supplements containing certain antioxidants were successfully determined using this system. The proposed system is rapid and reproducible, and thus may be useful for the screening of functional foods, supplements and pharmaceutical formulations that exhibit antioxidative activity. Figure The system that utilizes a combination of SIA and FIA with CL for the quasi-simultaneous determination of antioxidative activity against a NO and b $${ ext{O}}_{{{ ext{2}}^{ - } }} $$ . SP1, 2: syringe pump, HC1, 2: holding coil, MV1, 2: multi-port valve, P: pump, D: chemiluminescence detector, I: integrator, M1, 2: mixing tee, NOR1: (±)-(E)-4-methyl-2-[(E)- hydroxyimino]-5-nitro-6-methoxy-3-hexenamide, HX: hypoxanthine, XOD: xanthine oxidase.

Keywords: Sequential injection analysis; Antioxidative activity; Chemiluminescence; Superoxide anion; Nitric oxide

Determination of D- and L-amino acids produced by cyanobacteria using gas chromatography on Chirasil-Val after derivatization with pentafluoropropyl chloroformate by Helena Zahradníčková; Petr Hušek; Petr Šimek; Petr Hartvich; Blahoslav Maršálek; Ivan Holoubek (pp. 1815-1822).

A rapid and simple method was developed for the determination of free amino acids (AAs) released from cyanobacteria. The procedure involves trapping of AAs from the centrifuged cyanobacterial culture fluid on a cation-exchange resin, their release together with the resin by direct treatment with the reaction medium, followed by immediate derivatization with a corresponding chloroformate. The extractive alkylation transfers the analytes into an organic phase, an aliquot of which is subjected to GC analysis. Identification and quantification of AAs was performed by GC/MS and GC/FID, respectively, using propyl chloroformate (PCF) as the derivatization reagent. For chiral analysis, the cyanobacteria extracts were treated with 2,2,3,3,3-pentafluoropropyl chloroformate (PFPCF) to create more volatile analytes. Separation of the AA enantiomers was accomplished on a Chirasil-Val capillary column and the D/L enantiomeric ratios were determined. AAs of cyanobacteria are considered to be important for the assessment of energy flow in an aquatic food web, nutrition value of cyanobacteria in a food web and for cell–cell communication within cyanobacteria. The highest levels of AAs were found in the summer period at the beginning of the season (July). In the September and October samples, the amount of AAs was lower, the number of D-AAs decreased and the D/L ratio was higher than in the July sample. Based on the obtained results it can be assumed that young populations excrete AAs in higher concentrations and a different composition compared to actively growing populations. Figure PFPCF derivatization scheme

Keywords: D, L-Amino acids; GC; Chiral separation; Chloroformates; Cyanobacteria

Study of the influence of water matrix components on admicellar sorbents by Amalia García-Prieto; Loreto Lunar; Soledad Rubio; Dolores Pérez-Bendito (pp. 1823-1830).

Hemimicelle-based and/or admicelle-based solid-phase extraction (SPE) has recently been proved to be a fruitful strategy for the extraction and concentration of a wide variety of organic pollutants. This research focus on the effect of river and wastewater matrix components on the adsorption of sodium dodecyl sulfate (SDS) onto alumina, which is the most-used sorbent in hemimicelle-based and/or admicelle-based SPE, and we discuss the analytical consequences of the modifications observed. The effect of electrolytes (0.1 M NaCl), precipitating agents (127 and 333 mg L⁻¹ CaCl₂) and major organic components in wastewater (19.8 mg L⁻¹ carbohydrates, proteins and fats and 10 mg L⁻¹ linear alkylbenzene sulfonates (LAS) and rivers (8 mg L⁻¹ humic acid) on the SDS adsorption isotherm was investigated. Also, the global effect of matrix components was assessed using a river sample. Three types of sorbents were considered (hemimicelles, mixed hemimicelles/admicelles and admicelles). Electrolytes were found to compete with surfactant molecules for charge surface sites in the early part of the hemimicellar region; precipitating agents yield insoluble salts with the aqueous surfactant in equilibrium with admicelle-based sorbents; and organic matter did not have any influence at all. The matrix component concentrations investigated were above the usual range present in rivers and wastewater, which makes this study applicable to a wide number of environmental water samples. From the results obtained, simple rules were established to prevent and detect matrix-induced surfactant adsorption modifications, which permits us to know, a priori, the suitability of these sorbents for a specific application and allows the development of more straightforward and robust methods.

Keywords: Hemimicelles; Admicelles; Solid-phase extraction; Environmental water samples; Matrix interferences

Spectral elucidation of the acid metabolites of the four geometric isomers of trifloxystrobin by Kaushik Banerjee; Axel Patrick Ligon; Michael Spiteller (pp. 1831-1838).

Four geometric isomers of trifloxystrobin (TFS)—namely EE, EZ, ZE, and ZZ—were hydrolyzed by 0.05 M NaOH, resulting in four corresponding acid metabolites. These compounds—namely EE-, EZ-, ZE-, and ZZ-acids—were purified by preparative HPLC and authentically characterized by a combination of infrared, Raman, GC–MS, LC–MS/MS, and NMR spectroscopies. The spectra were found to be very characteristic of the individual isomers, and so they could be used to distinguish the isomers from each other. The detailed spectral features of the individual isomers are presented and compared. EE-acid was identified as being the major metabolite of TFS in soil, which indicates that hydrolysis is the principal route of degradation of TFS. This finding further justifies the importance of the present study in relation to assessing the risk associated with the release of TFS into the environment.

Keywords: Trifloxystrobin; Hydrolysis; HPLC; IR; Raman; NMR; Mass spectroscopy

Exploiting flow injection system with mini-immunoaffinity chromatographic column for chondroitin sulfate proteoglycans assay by Supaporn Kradtap Hartwell; Kanokphan Pathanon; Duriya Fongmoon; Prachya Kongtawelert; Kate Grudpan (pp. 1839-1846).

A flow injection (FI) system with a mini-immunoaffinity chromatographic column was used to perform on-line assays of specific proteoglycans. The 300-μL mini-column contained beads coupled with monoclonal antibodies against the specific sulfation pattern of chondroitin sulfate proteoglycans, which have been reported to be a potential biomarker for cancer. The amount of these proteoglycans present was estimated indirectly from their protein content using the Bradford assay, which is an alternative to a direct carbohydrate assay. The system developed was tested by assaying for chondroitin sulfate proteoglycans in sera from patients with various cancers and comparing the results to those obtained for sera from healthy people. The results indicated that this approach could be used as a cost-effective alternative system for determining the amount of these specific biomarker proteoglycans. The column could be reused at least 90 times, with each run consisting of 200 μL of serum sample diluted twofold; an analysis rate of 30 min per run was achieved, as compared to 4 h for a batch procedure.

Keywords: Flow injection; Immunoaffinity; Proteoglycans; Chromatographic column; Chondroitin sulfate; Cancers

Comparison of two different solvents employed for pressurised fluid extraction of stevioside from Stevia rebaudiana: methanol versus water by Jaroslav Pól; Elena Varaďová Ostrá; Pavel Karásek; Michal Roth; Karolínka Benešová; Pavla Kotlaříková; Josef Čáslavský (pp. 1847-1857).

Pressurised fluid extraction using water or methanol was employed for the extraction of stevioside from Stevia rebaudiana Bertoni. The extraction method was optimised in terms of temperature and duration of the static or the dynamic step. Extracts were analysed by liquid chromatography followed by UV and mass-spectrometric (MS) detections. Thermal degradation of stevioside was the same in both solvents within the range 70–160 °C. Methanol showed better extraction ability for isolation of stevioside from Stevia rebaudiana leaves than water within the range 110–160 °C. However, water represents the green alternative to methanol. The limit of detection of stevioside in the extract analysed was 30 ng for UV detection and 2 ng for MS detection.

Keywords: Pressurised fluid extraction; Liquid chromatography; Mass spectrometry; Stevia rebaudiana ; Stevioside

Sequential (step-by-step) detection, identification and quantitation of extra virgin olive oil adulteration by chemometric treatment of chromatographic profiles by F. Priego Capote; J. Ruiz Jiménez; M. D. Luque de Castro (pp. 1859-1865).

An analytical method for the sequential detection, identification and quantitation of extra virgin olive oil adulteration with four edible vegetable oils — sunflower, corn, peanut and coconut oils — is proposed. The only data required for this method are the results obtained from an analysis of the lipid fraction by gas chromatography–mass spectrometry. A total number of 566 samples (pure oils and samples of adulterated olive oil) were used to develop the chemometric models, which were designed to accomplish, step-by-step, the three aims of the method: to detect whether an olive oil sample is adulterated, to identify the type of adulterant used in the fraud, and to determine how much aldulterant is in the sample. Qualitative analysis was carried out via two chemometric approaches — soft independent modelling of class analogy (SIMCA) and K nearest neighbours (KNN) — both approaches exhibited prediction abilities that were always higher than 91% for adulterant detection and 88% for type of adulterant identification. Quantitative analysis was based on partial least squares regression (PLSR), which yielded R ² values of >0.90 for calibration and validation sets and thus made it possible to determine adulteration with excellent precision according to the Shenk criteria.

Keywords: Extra virgin olive oil; Adulteration; Chemometrics; Chromatographic profiles; Qualitative analysis; Quantitative analysis

Tripodal chelating ligand-based sensor for selective determination of Zn(II) in biological and environmental samples by Ashok Kumar Singh; Sameena Mehtab; Udai P. Singh; Vaibhave Aggarwal (pp. 1867-1876).

Potassium hydrotris(N-tert-butyl-2-thioimidazolyl)borate [KTt^t-Bu] and potassium hydrotris(3-tert-butyl-5-isopropyl-l-pyrazolyl)borate [KTp^t-Bu,i-Pr] have been synthesized and evaluated as ionophores for preparation of a poly(vinyl chloride) (PVC) membrane sensor for Zn(II) ions. The effect of different plasticizers, viz. benzyl acetate (BA), dioctyl phthalate (DOP), dibutyl phthalate (DBP), tributyl phosphate (TBP), and o-nitrophenyl octyl ether (o-NPOE), and the anion excluders sodium tetraphenylborate (NaTPB), potassium tetrakis(p-chlorophenyl)borate (KTpClPB), and oleic acid (OA) were studied to improve the performance of the membrane sensor. The best performance was obtained from a sensor with a of [KTt^t-Bu] membrane of composition (mg): [KTt^t-Bu] (15), PVC (150), DBP (275), and NaTPB (4). This sensor had a Nernstian response (slope, 29.4 ± 0.2 mV decade of activity) for Zn²⁺ ions over a wide concentration range (1.4 × 10⁻⁷ to 1.0 × 10⁻¹ mol L⁻¹) with a limit of detection of 9.5 × 10⁻⁸ mol L⁻¹. It had a relatively fast response time (12 s) and could be used for 3 months without substantial change of the potential. The membrane sensor had very good selectivity for Zn²⁺ ions over a wide variety of other cations and could be used in a working pH range of 3.5–7.8. The sensor was also found to work satisfactorily in partially non-aqueous media and could be successfully used for estimation of zinc at trace levels in biological and environmental samples.

Keywords: Zinc-selective sensor; PVC membrane; Potassium hydrotris(N-tert-butyl-2-thioimidazolyl)borate; Potassium hydrotris(3-tert-butyl-5-isopropyl-l-pyrazolyl) borate; Ion-selective membrane sensors

Development of a reference solution for the pH of seawater by Enrico Prenesti; Enzo Ferrara; Silvia Berto; Paola Fisicaro; Pier Giuseppe Daniele (pp. 1877-1883).

A method that uses a Harned cell to perform potentiometric pH measurements has been optimized and applied to an aqueous solution of simulated seawater that contains sodium perchlorate, sodium sulfate, sodium hydrogen carbonate and boric acid and has an ionic strength I of 0.57 mol kg⁻¹. The standard metrological approach developed for the measurement of pH in low ionic strength aqueous solutions was maintained, but a few modifications were necessary, and measurement procedures and calculations were modified ad hoc from those adopted in conventional protocols. When determining the standard potential of the cell, E°, NaClO₄ salt was added to a 0.01 mol/kg HCl solution to attain the same ionic strength as the test solution and to investigate possible specific effects related to the high levels and the nature of the background electrolyte. An appropriate value of γ _±HCl (0.737) was then selected from the literature, based on a realistic value for I. Finally, in order to convert the acidity function at zero chloride molality into pH, a suitable value of γ _Cl (0.929) was calculated. As a result, we obtained pH = 8.18 (T = 25 °C) with an associated expanded uncertainty U = 0.01 (coverage factor k = 2). The aim was to establish a sound basis for the pH measurement of seawater by identifying the critical points of the experimental and theoretical procedure, and to discuss further possible developments that would be useful for achieving a reference solution.

Keywords: pH measurement; Electroanalytical methods; Ionic strength; Activity coefficients; Harned cell

Non-destructive assessment of parchment deterioration by optical methods by Bella Dolgin; Valery Bulatov; Israel Schechter (pp. 1885-1896).

A non-destructive and non-invasive method for quantitative characterization of parchment deterioration, based on spectral measurements, is proposed. Deterioration due to both natural aging (ancient parchments) and artificial aging (achieved by means of controlled UV irradiation and temperature treatment) was investigated. The effect of aging on parchment native fluorescence was correlated with its deterioration condition. Aging causes fluorescence intensity drop, spectral shift of the main peak, and an overall change in the fluorescence spectral features. Digital color imaging analysis based on visible reflectance from the parchment surface was also applied, and the correspondent color components (RGB) were successively correlated with the state of parchment deterioration/aging. The fluorescence and color imaging data were validated by analysis of historical parchments, aged between 50 and 2000 years and covering a large variety of states of deterioration. The samples were independently assessed by traditional microscopy methods. We conclude that the proposed optical method qualifies well as a non-destructive tool for rapid assessment of the stage of parchment deterioration.

Keywords: Parchment; Aging; Fluorescence; Digital imaging; Optical methods

Time-resolved fluorescence spectroscopy and imaging of proteinaceous binders used in paintings by Austin Nevin; Daniela Comelli; Gianluca Valentini; Demetrios Anglos; Aviva Burnstock; Sharon Cather; Rinaldo Cubeddu (pp. 1897-1905).

The differentiation of proteins commonly found as binding media in paintings is presented based on spectrally resolved and time-resolved laser-induced fluorescence (LIF) and total emission spectroscopy. Proteins from eggs and animal glue were analysed with pulsed laser excitation at 248 nm (KrF excimer) and 355 nm (third harmonic of Nd:YAG) for spectrally resolved measurements, and at 337 nm (N₂) and 405 nm (N₂ pumped dye laser) for spectrally resolved lifetime measurements and fluorescence lifetime imaging (FLIM). Total emission spectra of binding media are used for the interpretation of LIF spectra. Time-resolved techniques become decisive with excitation at longer wavelengths as fluorescence lifetime permits the discrimination amongst binding media, despite minimal spectral differences; spectrally resolved measurements of fluorescence lifetime have maximum differences between the binding media examined using excitation at 337 nm, with maximum observed fluorescence at 410 nm. FLIM, which measures the average lifetime of the emissions detected, can also differentiate between media, is non-invasive and is potentially advantageous for the analysis of paintings. Figure The fluorescence of solid ox glue extracted from collagen can be visualised in this Total Fluorescence Spectrum; three different peaks from multiple fluorophores are present and allow the discrimination between collagen- and non-collagen proteinaceous binding media found in paintings

Keywords: Proteins; Fluorescence; Lifetime; Laser-induced fluorescence; Fluorescence lifetime imaging; Binding media; Paintings

Voltammetric detection of paraquat pesticide on a phthalocyanine-based pyrolitic graphite electrode by Ilanna C. Lopes; Djenaine De Souza; Sergio A. S. Machado; Auro A. Tanaka (pp. 1907-1914).

This work describes the application of an ordinary pyrolitic graphite electrode modified by metallophthalocyanine allied to square wave voltammetry for the study of the electrochemical behavior of the herbicide paraquat and the development of a method for its analytical determination in natural water samples. Preliminary experiments indicated that the best responses, considering the intensities of the current and voltammetric profile for the paraquat reduction process, were obtained when the electrode modified by cobalt phthalocyanine was employed, which had a better catalytic activity as a result of this modification compared with that for an unmodified electrode and electrodes modified by iron, manganese and the acid form of the phthalocyanines. Studies of the concentration of cobalt phthalocyanine and the adsorption time showed that 1.0 × 10⁻⁴ mol L⁻¹ cobalt phthalocyanine with an adsorption time of 10 min was sufficient to obtain reliability and stability of modification for employment in the development of the electroanalytical procedure for paraquat determination in natural water samples. The variation in pH of a 0.10 mol L⁻¹ Britton–Robinson buffer solution and the square wave parameters indicated that the best conditions to reduce paraquat were pH 7.0, a frequency of 100 s⁻¹, a scan increment of 2 mV and a square wave amplitude of 50 mV. Under such conditions, the variation of paraquat concentrations from 5.00 × 10⁻⁷ to 2.91 × 10⁻⁵ mol L⁻¹ showed a linear relation, with detection and quantification limits of 26.53 and 88.23 μg L⁻¹; those values were lower than the maximum limits for drinking water permitted by the Brazilian Environmental Council (100 μg L⁻¹), indicating that the method could be employed to analyze paraquat in drinking water samples.

Keywords: Cobalt phthalocyanine; Pyrolitic graphite; Paraquat; Square wave voltammetry; Natural sample water

2008 Bunsen–Kirchhoff Award for Analytical Spectroscopy (pp. 1915-1915).

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Analytical and Bioanalytical Chemistry (v.388, #8)