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Analytical and Bioanalytical Chemistry (v.377, #4)

2003, a very special year for Spanish chemistry by Luis A. Oro (pp. 587-587).

Do we need education in metrology in chemistry? by Ewa Bulska; Philip Taylor (pp. 588-589).

Derivatisation in gas chromatographic determination of acidic herbicides in aqueous environmental samples by Martyna Rompa; Ewa Kremer; Bogdan Zygmunt (pp. 590-599).

This paper reviews derivatisation processes applied in chromatographic determination of acidic herbicides (with carboxyl and phenol groups), mainly in aqueous environmental samples. The discussion focuses on the basic derivatisation reactions used to convert herbicides to derivatives to make them analysable by gas chromatography, and possibly to reduce detection limits and/or increase extraction recovery from aqueous samples. The reactions are transesterification, esterification, silylation, alkylation, and extractive and pyrolytic alkylation. The reagents used to conduct the reactions are numerous. Diazomethane is a very efficient methylation reagent but explosive and toxic. Methyl iodide also ensures rapid and efficient methylation. Benzyl bromide can be used directly in water but derivatisation yield is low and reproducibility is poor. Butyl chloroformate and dimethyl sulfite can also be used for derivatisation in water, and acetic anhydride can be used for in-situ derivatisation of phenolic herbicides. For increasing selectivity of GC detection pentafluorobenzyl bromide (for ECD) and (2-cyanethyl)dimethyl(diethylamino)silane (for NPD) have been applied. Very characteristic ions are produced in mass spectra if silyl groups are introduced, e.g. by using bis(trimethylsilyl)trifluoroacetamide. Tetramethylammonium, trimethylphenylammonium, tetraalkylammonium, and trimethylsulfonium hydroxides and salts can by used for derivatisation at elevated temperature in the GC injection port. Extractive alkylation is relatively efficient if tetraalkylammonium salts with long chain alkyl groups are used.

Keywords: Derivatisation; Acidic herbicides; Gas chromatography; Environmental samples

An integrated electrochemical fructose biosensor based on tetrathiafulvalene-modified self-assembled monolayers on gold electrodes by Susana Campuzano; Rocío Gálvez; María Pedrero; F. Javier Manuel de Villena; José M. Pingarrón (pp. 600-607).

An integrated amperometric fructose biosensor based on a gold electrode (AuE) modified with a self-assembled monolayer (SAM) of 3-mercaptopropionic acid (MPA) on which fructose dehydrogenase (FDH) and the mediator tetrathiafulvalene (TTF) are co-immobilized by cross-linking with glutaraldehyde is reported. Variables concerning the behavior of the biosensor were optimized by taking the slope value obtained for the fructose calibration plot in the 0.1–1.0 mM concentration range as a criterion of selection. At an applied potential of +0.20 V, a good repeatability of such slope values (RSD=6.7%, n=10) was obtained with no need to apply a cleaning or pretreatment procedure to the modified electrode. Moreover, results from five different TTF-FDH-MPA-AuEs yielded a RSD of 5.8%. The useful lifetime of one single biosensor was approximately 30 days, exhibiting a 93% of the original response on the 33rd day. A linear calibration graph was obtained for fructose over the 1.0×10⁻⁵–1.0×10⁻³ M range, with a limit of detection of 2.4×10⁻⁶ M. The effect of potential interferents was evaluated. The TTF-FDH-MPA-AuE also performed well in the flow-injection mode. The biosensor was used for the determination of fructose in real samples, and the results compared with those provided by using a commercial enzyme test kit.

Keywords: Self-assembled monolayers; Enzyme biosensors; Fructose

Amidine-based molecularly imprinted polymers—new sensitive elements for chiral chemosensors by Dirk Nopper; Olaf Lammershop; Günter Wulff; Günter Gauglitz (pp. 608-613).

Using the optical measurement technique reflectometric interference spectroscopy (RIfS), the interaction of molecularly imprinted polymers (imprinted with either (R,R)- or (S,S)-2,3-di-O-benzoyltartraric acid) with the corresponding templates and template antipodes were investigated. With these sensors chiral separation with a separation factor of 1.2 could be achieved whereas a reference polymer resulted in no separation. RIfS signals were of opposite sign for imprinted polymer layers containing phenylboronic acid binding site monomers.

Keywords: RIfS; Molecular imprinting; Sensors; Chiral separation

Fluorescence optosensors based on different transducers for the determination of polycyclic aromatic hydrocarbons in water by J. F. Fernández-Sánchez; A. Segura-Carretero; J. M. Costa-Fernández; N. Bordel; R. Pereiro; C. Cruces-Blanco; A. Sanz-Medel; A. Fernández-Gutiérrez (pp. 614-623).

This paper presents the development of two optosensors for the determination of four polycyclic aromatic hydrocarbons (anthracene, benzo[a]pyrene, fluoranthene and benzo[b]fluoranthene) using a photomultiplier device and an intensified coupled charge device (ICCD) as optical transducers, respectively. These optosensors are based on the on-line immobilization of the analytes onto a non-ionic resin solid support (Amberlite XAD-4) in a continuous flow system, followed by the measurement of their native fluorescence. The determinations were performed using 15 mM H₂PO₄ ^-/HPO₄ ^2- buffer solution at pH 7 and 25% 1,4-dioxane. Detection limits were 6.4 and 9.3 for ANT, 3.3 and 2.5 for BbF, 1.4 and 13.2 for FLT, and 1.7 and 7.8 for BaP using optosensor 1 or 2, respectively. Relative standard deviations were 7.9 and 6.7 for ANT at 50 ng mL^-1, 3.5 and 7.4 for BbF at 60 ng mL^-1, 3.6 and 8.9 for FLT at 50 ng mL^-1, and 6.7 and 11.6 for BaP at 50 ng mL^-1 using optosensor 1 or 2, respectively. Finally, a critical comparison between the two configurations based on different transducers (photomultiplier and ICCD) for resolving and simultaneously determining mixtures of the polycyclic aromatic hydrocarbons under study in water samples (tap and mineral waters) were carried out.

Keywords: Fiber optic fluorescence sensors; Intensified charge coupled device; Polycyclic aromatic hydrocarbons; Water

Cholinesterase sensors based on screen-printed electrodes for detection of organophosphorus and carbamic pesticides by Alexey Ivanov; Gennady Evtugyn; Herman Budnikov; Francesco Ricci; Danila Moscone; Giuseppe Palleschi (pp. 624-631).

Cholinesterase sensors based on screen-printed electrodes modified with polyaniline, 7,7′,8,8′-tetracyanoquinodimethane (TCNQ), and Prussian blue have been developed and tested for detection of anticholinesterase pesticides in aqueous solution and in spiked grape juice. The influence of enzyme source and detection mode on biosensor performance was explored. It was shown that modification of the electrodes results in significant improvement of their analytical characteristics for pesticide determination. Thus, the slopes of the calibration curves obtained with modified electrodes were increased twofold and the detection limits of the pesticides were reduced by factors of 1.6 to 1.8 in comparison with the use of unmodified transducers. The biosensors developed make it possible to detect down to 2×10⁻⁸ mol L⁻¹ chloropyrifos-methyl, 5×10⁻⁸ mol L⁻¹ coumaphos, and 8×10⁻⁹ mol L⁻¹ carbofuran in aqueous solution and grape juice. The optimal conditions for grape juice pretreatment were determined to diminish interference from the sample matrix.

Keywords: Cholinesterase sensor; Biosensor; Pesticide detection; Grapes testing

A novel biosensing interfacial design produced by assembling nano-Au particles on amine-terminated plasma-polymerized films by Hua Wang; Cunchang Wang; Cunxi Lei; Zhaoyang Wu; Guoli Shen; Ruqin Yu (pp. 632-638).

A novel biosensing interfacial design strategy has, for the first time, been produced by assembling nano-Au particles on amine-terminated plasma-polymerized films (PPF). A quartz-crystal microbalance (QCM) as a model transducer was deposited with PPF of n-butylamine by use of a glow discharge and then treated with nano-Au particles. The kinetic assembly process and conditions were studied using the real-time-output device and the surface topology of the resulting crystal was characterized by atomic force microscopy (AFM) imaging. Based on analysis of the experimental data, including the association constant of Au–amine interaction, the assembly mechanism is considered to be partly or even mainly chemical adsorption. Moreover, immobilization of anti-human IgM antibody (IgM Ab), as an example, on the developed PPF-Au interface was investigated. It was found that antibody molecules immobilized by the proposed procedure had higher immunological activity than those immobilized by the conventional glutaraldehyde (GLU) cross-linking procedure or the direct gold-attachment procedure. The newly developed sensor had a better response, with a detection limit of IgM concentration as low as ~1.00 μg mL⁻¹. In particular, the extremely high stability of both PPF and nano-Au monolayer formulated allows the designed biosensing interface to withstand harsh regeneration treatment, making it reusable.

Keywords: Nano-Au particles; Plasma-polymerized film; Biosensing interfacial design; Piezoelectric immunosensor

Separation of the enantiomers of substituted dihydrofurocoumarins by HPLC using macrocyclic glycopeptide chiral stationary phases by Tom Ling Xiao; Roman V. Rozhkov; Richard C. Larock; Daniel W. Armstrong (pp. 639-654).

Enantiomer separations by HPLC using the macrocyclic glycopeptides teicoplanin (Chirobiotic T), teicoplanin aglycon (Chirobiotic TAG), and ristocetin A (Chirobiotic R) chiral stationary phases (CSP) have been achieved on a unique series of potentially biologically active racemic analogues of dihydrofurocoumarin. The macrocyclic glycopeptides have proven to be very selective for this class of compound. All of the 28 chiral analogues examined afforded baseline separation on at least one of the macrocyclic glycopeptide CSP. The teicoplanin CSP showed the broadest enantioselectivity with 24 of the compounds baseline separated. The TAG and the R CSP produced 23 and 14 baseline separations respectively. All three mobile phase modes, i.e. normal phase (NP), reversed phase (RP), and new polar organic modes (PO), have been evaluated. The NP mode proved to be most effective for the separation of chiral dihydrofurocoumarins on all CSP tested. In the reversed phase (RP) mode, all three CSP separated a similar number of compounds. It was observed that the structural characteristics of the analytes and steric effects are very important factors leading to chiral recognition. Hydrogen bonding was found to play a secondary role in chiral discrimination in the normal phase and polar organic modes. Hydrophobic interactions are important for chiral separation in the reversed-phase mode. Chromatographic retention data does not provide information on the absolute configuration of these chiral dihydrofurocoumarin derivatives. However, when coupled with circular dichroism using the exciton coupling chirality method, the enantiomer elution order and the absolute configuration of some chiral dihydrofurocoumarins were successfully determined.

Keywords: HPLC; Macrocyclic glycopeptide; Chiral stationary phases; Enantiomer separation; Dihydrofurocoumarin

Quantitative determination of saturated oligogalacturonic acids in enzymatic digests of polygalacturonic acid, pectin and carrot pomace by on-line LC-ESI-MS by Thomas Stoll; Andreas Schieber; Reinhold Carle (pp. 655-659).

A method for the quantitative determination of oligogalacturonic acids (OGAs) by on-line high-performance liquid chromatographic (HPLC) separation and mass spectrometric detection via an electrospray interface (ESI-MS) without additional desalting steps was developed. Saturated OGAs up to a degree of polymerization (dp) of 3 were quantified by comparison with reference compounds. The calibration plots showed high linearity (R ²>0.99), and the detection limits for dp 1, 2, and 3 were 11, 28, and 6 ng per injection, respectively. Non- and partially methyl-esterified OGAs with a dp of 3 and 4 were calculated semi-quantitatively as dp 3. The analytical system was used for the quantification of OGAs of digests obtained by incubation of polygalacturonic acid, pectin, and carrot pomace with commercial enzyme preparations. Furthermore, methyl-esterified OGAs up to a dp of 12 containing up to 4 methyl esters were detected in a pectin digest.

Keywords: Oligogalacturonic acids; HPLC; Electrospray-ionization mass spectrometry; Carrot pomace; Pectin; Polygalacturonic acid

A flow-injection ultrafiltration sampling chemiluminescence system for on-line determination of drug–protein interaction by Zhouping Wang; Zhujun Zhang; Zhifeng Fu; Yan Xiong; Xiao Zhang (pp. 660-665).

A flow-injection ultrafiltration sampling chemiluminescence system for on-line determination of cimetidine–bovine serum albumin (BSA) interaction is proposed in this paper. Cimetidine can be oxidized by N-bromosuccinimide (NBS) and sensitized by fluorescein to produce high chemiluminescence emission in basic media. The concentration of cimetidine is linear with the CL intensity in the range 3×10⁻⁷–1×10⁻⁴ mol L⁻¹ with a detection limit of 1×10⁻⁷ mol L⁻¹ (3σ). The drug and protein were mixed in different molar ratios in 0.067 mol L⁻¹ phosphate buffer, pH 7.4, and incubated at 37 °C in a water bath. The ultrafiltration probe was utilized to sample the mixed solution at a flow rate of 5 µL min⁻¹. The data obtained by the proposed ultrafiltration flow-injection chemiluminescence method was analyzed with Scrathard analysis and a Klotz plot. The estimated association constant (K) and the number of the binding site (n) on one molecule of BSA by Scrathard analysis and Klotz plot were 3.15×10⁴ L mol⁻¹ and 0.95, 3.25×10⁴ L mol⁻¹ and 0.92, respectively. The proposed system proved that flow-injection chemiluminescence analysis coupled with on-line ultrafiltration sampling is a simple and reliable technique for the study of drug–protein interaction.

Keywords: Chemiluminescence analysis; Ultrafiltration sampling; Cimetidine; Bovine serum albumin

Analysis of meso-2,3-dimercaptosuccinic acid in human urine by capillary electrophoresis using direct injection by Xiaofeng Zhu; Susan Z. Lever (pp. 666-669).

meso-2,3-Dimercaptosuccinic acid (meso-DMSA) is an effective chelating agent for the treatment of lead poisoning. We have developed a capillary electrophoresis (CE) method to monitor the urinary excretion of meso-DMSA in human beings. The urine sample was directly injected for analysis in CE without the requirement of solid-phase extraction (SPE). The meso-DMSA was detected in 20 mM borate buffer (pH 8.3) using a 60-cm length bare fused-silica capillary (75-μm ID, 52.5-cm effective length). The meso-DMSA can be extensively biotransformed during metabolism, and no meso-DMSA in urine samples was found in our studies. Any metabolized meso-DMSA can be successfully converted to free meso-DMSA by chemical reduction with dithiothreitol (DTT). In addition, samples were also treated with ethylenediaminetetraacetic acid (EDTA) to transchelate any meso-DMSA that is coordinated with metal ions present in the urine samples. The total amount of meso-DMSA present as these chemical forms was quantified after chemical reduction and addition of EDTA. The detection limit of meso-DMSA was about 50 μM, the RSD of peak area and migration time of meso-DMSA were 4–8% and less than 1%, respectively.

Keywords: meso-DMSA; Urine; Capillary electrophoresis; Direct injection

Identification of selenium species in urine by ion-pairing HPLC–ICP–MS using laboratory-synthesized standards by Kazimierz Wrobel; Katarzyna Wrobel; Sasi S. Kannamkumarath; Joseph A. Caruso (pp. 670-674).

This study focused on the detection/identification of possible selenium metabolites in human urine. Organoselenium compounds not commercially unavailable were synthesized and characterized by electrospray mass spectrometry. Separation of selenomethionine, methylselenomethionine, trimethylselonium, selenoethionine, and selenoadenosylmethionine was achieved by ion-pairing HPLC with a mobile phase of 2 mmol L⁻¹ hexanesulfonic acid, 0.4% acetic acid, 0.2% triethanolamine (pH 2.5), and 5% methanol. The column effluent was introduced on-line to inductively coupled plasma–mass spectrometry for selenium-specific detection (⁷⁷Se and ⁷⁸Se). For selenium speciation in urine, solid-phase extraction was carried out using C₁₈ cartridges modified with hexanesulfonic acid. Selective retention of cationic species was observed from acidified urine (perchloric acid, pH 2.0). After elution with methanol, evaporation, and dissolution in the mobile phase, the sample was introduced to the HPLC–ICP–MS system and the chromatographic peaks were assigned by adding standards. The species identified in urine were selenomethionine, trimethylselonium ion, and selenoadenosylmethionine. The last species was detected for the first time and our results suggest that selenomethionine might enter the metabolic pathway of its sulfur analog in the activated methylation cycle.

Keywords: Ion-pairing HPLC–ICP–MS; Laboratory-synthesized standards; Human urine; Metabolites; Selenium species

Simple and sensitive assay for nucleic acids by use of the resonance light-scattering technique with copper phthalocyanine tetrasulfonic acid in the presence of cetyltrimethylammonium bromide by Yongxin Li; Yuqin Wu; Jinlong Chen; Changqin Zhu; Lun Wang; Sujuang Zhuo; Danhua Zhao (pp. 675-680).

On the basis of enhancement of resonance light scattering (RLS) of copper phthalocyanine tetrasulfonic acid (CuTSPc) by nucleic acids and cetyltrimethylammonium bromide (CTMAB) under suitable conditions, a new RLS method for determination of nucleic acids in aqueous solutions has been developed. At pH 9.80–10.95 and ionic strength 0.01 mol L⁻¹ (NaCl), the interaction of copper phthalocyanine tetrasulfonic acid with nucleic acids in the presence of cetyltrimethylammonium bromide results in enhanced RLS signals at 282.0 nm, 383.6 nm, and 616.2 nm in the enhanced regions. It was found that the enhanced RLS intensity at 383.6 nm was proportional to the concentration of nucleic acids within suitable ranges. The limits of detection were 10.6 ng mL⁻¹ for fish sperm DNA and 32.4 ng mL⁻¹ for calf thymus DNA when the concentration of copper phthalocyanine tetrasulfonic acid was 2.0×10⁻⁶ mol L⁻¹. This method is rapid, simple and sensitive. In addition, the reagents used are relatively inexpensive, stable, and easily synthesised. The method can be applied to the determination of nucleic acids in the presence of coexisting substances, and we have applied it to the determination of DNA in synthetic samples, with satisfactory results.

Keywords: Copper phthalocyanine tetrasulfonic acid; Cetyltrimethylammonium bromide; Nucleic acids; Resonance light scattering

Determination of trace europium by use of the new fluorescence system europium–sparfloxacin–1,10-phenanthroline–sodium dodecyl sulfate by Wei Jiang; Yudao Ma; Wenyuan Zhao; Yu Feng; Naixing Wang; Zhikun Si (pp. 681-684).

A new lanthanide-sensitized luminescence system: europium–sparfloxacin–1,10-phenanthroline–sodium dodecyl sulfate has been discovered. The spectrofluorimetric properties of the system were studied. The effect of experimental conditions on the fluorescence intensity was defined. Under the optimum conditions, the fluorescence intensity of the system is a linear function of the concentration of europium in the range 5.0×10⁻⁹–1.0×10⁻⁶ mol L⁻¹ and the detection limit is 1.0×10⁻¹⁰ mol L⁻¹. The system was used for the determination of trace amounts of europium in rare earth samples with satisfactory results.

Keywords: Fluorescence; Europium; Sparfloxacin

Development of analytical procedures for determination of total chromium by quadrupole ICP–MS and high-resolution ICP–MS, and hexavalent chromium by HPLC–ICP–MS, in different materials used in the automotive industry by F. Séby; M. Gagean; H. Garraud; A. Castetbon; O. F. X. Donard (pp. 685-694).

A European directive was recently adopted limiting the use of hazardous substances such as Pb, Hg, Cd, and Cr(VI) in vehicle manufacturing. From July 2003 a maximum of 2 g Cr(VI) will be authorised per vehicle in corrosion-preventing coatings of key components. As no standardised procedures are available to check if produced vehicles are in agreement with this directive, the objective of this work was to develop analytical procedures for total chromium and Cr(VI) determination in these materials. The first step of this study was to optimise digestion procedures for total chromium determination in plastic and metallic materials by inductively coupled plasma mass spectrometry (ICP–MS). High resolution (HR) ICP–MS was used to examine the influence of polyatomic interferences on the detection of the ⁵²Cr⁺ and ⁵³Cr⁺ isotopes. If there was strong interference with m/z 52 for plastic materials, it was possible to use quadrupole ICP–MS for m/z 53 if digestions were performed with HNO₃+H₂O₂. This mixture was also necessary for digestion of chromium from metallic materials. Extraction procedures in alkaline medium (NH₄ ⁺/NH₃ buffer solution at pH 8.9) assisted by sonication were developed for determining Cr(VI) in four different corrosion-preventing coatings by HPLC–ICP–MS. After optimisation and validation with the only solid reference material certified for its Cr(VI) content (BCR 545; welding dusts), the efficiency of this extraction procedure for screw coatings was compared with that described in the EN ISO 3613 standard generally used in routine laboratories. For coatings comprising zinc and aluminium passivated in depth with chromium oxides the extraction procedure developed herein enabled determination of higher Cr(VI) concentrations. This was also observed for the screw covered with a chromium passivant layer on zinc–nickel. For coating comprising a chromium passivant layer on alkaline zinc the standardized extraction procedure was more efficient. In the case of painted metallic plate, because of a reactive matrix towards Cr(VI), its extraction without degradation was difficult to perform.

Keywords: Total chromium; Hexavalent chromium; Vehicle materials

Determination of alcohol content in beverages using short-wave near-infrared spectroscopy and temperature correction by transfer calibration procedures by Fernando D. Barboza; Ronei J. Poppi (pp. 695-701).

This paper reports the utilization of short-wave near-infrared (SW-NIR) transmission spectroscopy for rapid and conclusive analysis of alcoholic content (% v/v) in beverages. This spectral region is interesting because common visible diode array spectrometers can be utilized, reducing time and costs in comparison with traditional near-infrared or mid-infrared instruments. A correction of external temperature influence is necessary, and for this purposes two calibration transfer procedures were compared: piecewise direct standardization (PDS) and orthogonal signal correction (OSC). The RMSEP found for the alcoholic content model at 20 °C was 0.13% v/v and, after application of transfer calibration procedures at other temperatures (15, 25, 30 and 35 °C) using the model built at 20 °C, errors of the same order of magnitude were obtained.

Keywords: Short-wave near-infrared; Alcoholic content; Multivariate calibration; Calibration transfer, ; Piecewise direct standardization; Orthogonal signal correction

Isolation of free phenolic compounds from arboreal leaves by use of the Florisil/C₁₈ system by Jadwiga Jaroszyńska (pp. 702-708).

In studies of the phenolic compounds present in leaves and needles, GC and GC–MS have so far been applied only sporadically. This is probably because of the greater difficulties encountered in preparing the samples for this method than those used for liquid chromatography. When preparing a sample for gas chromatography the analyst is faced with two difficult stages—separation of the compound from the matrix without losses (stage 1) so that the final sample can be derivatized to make it suitable for analysis on a non-polar capillary column of the gas chromatograph (stage 2). This paper presents a procedure for extraction of phenolic compounds from the matrix by means of a Florisil/C₁₈ sorbent system and their analysis by GC. After passage through the adsorbents the recovery ranges from 32% for ferulic acid to 88% for gentisic acid. It was found that this extraction method and the GC analysis are very precise (particularly for samples of a mass <1 g) and can be used for quantification. The high-precision quantification of 15 phenolic acids, shikimic acid, and six other compounds present in pine needles has been achieved. The conditions used for GC analysis and construction of calibration curves for quantitative determination are given.

Keywords: Phenolic acids; Shikimic acid; SPE; Florisil; Plant sample

Spectrophotometric determination of manganese with derivatives of 1,3,3-trimethyl-2-[3-(1,3,3-trimethyl-1,3-H-indol-2-ylidene)propenyl]-3H-indolium by Ioseph S. Balogh; Vasil Andruch; Mária Kovács (pp. 709-714).

A new, simple, rapid, and sensitive spectrophotometric method has been developed for the determination of manganese in sewage. The method is based on the reaction of manganese with derivatives of 1,3,3-trimethyl-2-[3-(1,3,3-trimethyl-1,3-H-indol-2-ylidene)propenyl]-3H-indolium to form a colored ion associate with a sensitive absorption maximum at 560 nm. The appropriate reaction conditions have been established: pH 8.5–10.0, 1.25–2.3×10⁻³ mol L⁻¹ 1-nitroso-2-naphthol, and 1.6–2.4×10⁻⁴ mol L⁻¹ dye reagent. Beer's law is obeyed for manganese concentrations up to 4.2 mg L⁻¹. The limit of detection is 0.01 mg L⁻¹ Mn²⁺; the molar absorptivity of the ion associate was 7.5×10⁴ L mol⁻¹ cm⁻¹. The effect of various foreign ions was examined. A reaction mechanism is suggested. The developed procedure was tested for determination of manganese in sewage with satisfactory precision and accuracy.

Keywords: Manganese; Carbocyanine dye; Spectrophotometry

A systematic approach for optimisation of supercritical-fluid extraction of polycyclic aromatic hydrocarbons from earthworms by Ronald Hoogerbrugge; Alida A. M. Stolker; Arjan Barendregt; Elbert A. Hogendoorn (pp. 715-722).

A systematic approach using a mathematical model as an alternative to time-consuming empirical optimisation of a supercritical-fluid extraction (SFE) procedure is presented. The model was applied to the extraction of 15 polycyclic aromatic hydrocarbons (PAH). The selected fat-containing matrix is the earthworm used in ecotoxicological absorption studies. Settings for optimal recovery were established for the important parameters (temperature, pressure, amount of trapping sorbent, flow, and dynamic extraction time) using a D-optimal experimental design (including quadratic terms and interactions). The recoveries were modelled using a two sigmoid-model with parameters for each of the individual PAH. The main objective was to optimise the conditions for 15 PAH congeners by maximisation of the lowest recovery. The results show that for some parameters, e.g. the amount of sorbent material, optimal conditions are identical for all PAH. For other parameters, e.g. extraction time, the optimum is PAH dependent. The advantage of this optimisation procedure is that, within three days of analysis (73 experiments), optimised extraction conditions for the extraction of the set of 15 PAH were found but also optimum conditions for specific subsets can be extracted from the collected data for specific subsets.

Keywords: Experimental design; PAH; SFE; Optimisation; Microcontaminants; Multi-method

A comparison of sequential extraction techniques for determining arsenic fractionation in synthetic mineral mixtures by M. Mihaljevič; M. Poňavič; V. Ettler; O. Šebek (pp. 723-729).

The sequential extraction methods according to Tessier et al. [1], Borovec et al. [2], Zhang and Moore [3] and Hall et al. [4] have been tested for their suitability for arsenic fractionation in samples of artificially prepared mineral mixtures. Mixtures containing different amounts of As-containing phases were prepared so that their compositions corresponded to weathering products on As-bearing ore deposits. A comparison of different procedures on simple mineral mixtures containing calcium arsenate (CaHAsO₄·H₂O), As-bearing goethite (FeOOH) and arsenopyrite (FeAsS) showed that only the results of the Hall method satisfactorily correspond to the expected arsenic distribution. A detailed verification of the Hall method was subsequently carried out on most complex synthetic mineral mixtures with varying amounts of As-containing kaolinite and carbonate, calcium arsenate, As-bearing goethite and arsenopyrite. The results confirm that the Hall method cannot be fully employed for an accurate As speciation but may be applied for a route identification of As distribution between "labile", "medium-labile" and "residual" forms in heavily polluted soils.

Keywords: Arsenic; Fractionation; Sequential extraction; Synthetic mineral mixtures

Flow injection on-line ultrasound-assisted extraction of iron in meat samples coupled to a flame atomic absorption spectrometric system by A. Moreno-Cid; M. C. Yebra; S. Cancela; R. M. Cespón (pp. 730-734).

Iron was extracted on-line from solid meat samples by a simple and rapid continuous ultrasound-assisted extraction system (CUES). The CUES is connected to a flow injection manifold, which allows the on-line flame atomic absorption spectrometric determination of iron. A Plakett–Burman design was used for the optimisation of the CUES. The method achieved a total sampling frequency of 11 samples per hour with a relative standard deviation for the complete procedure of 0.4%. The detection limit was 0.6 μg g⁻¹ (dry mass) for a sample amount of 30 mg. Accurate results were obtained by measuring the certified reference materials BCR-186 (pig kidney) and BCR-184 (bovine muscle). The analytical procedure was applied to different real meat samples with satisfactory results.

Keywords: Continuous ultrasound-assisted extraction system; Flame atomic absorption spectrometry; Iron determination; Meat samples

Use of solid-phase extraction to eliminate interferences in the determination of mercury by flow-injection CV AAS by Agnieszka Krata; Krystyna Pyrzyńska; Ewa Bulska (pp. 735-739).

Solid-phase extraction with two-step elution has been developed for effective elimination of copper and iron interference with mercury determination by flow-injection cold vapour atomic absorption spectrometry (CV AAS). Sodium tetrahydroborate(III) was used as reducing agent. Cation-exchanger Dowex 50Wx4 was applied for the sorption of mercury and both interfering ions. In the first step elution of Cu(II) and Fe(III) was performed using 0.5 mol L⁻¹ KF solution. Then mercury was eluted with 0.1% thiourea in 8% HCl. The detection limit (3δ) for Hg(II) was 27 ng L⁻¹. The expanded uncertainty estimated for the whole procedure was about 6%. The accuracy of the proposed method was evaluated by determination of the recovery of known amount of mercury added to mineral, spring, and tap waters, and by analysis of a certified reference material BCR-144R (sewage sludge).

Keywords: Mercury; CV AAS; Interferences; Solid-phase extraction

Bromate assay in water by inductively coupled plasma mass spectrometry combined with solid-phase extraction cartridges by Qiantao Cai; Zhong-Xian Guo; Chunhai Yu; Wei Zhang; Zhaoguang Yang (pp. 740-748).

Based on selective sorption of bromide, bromoacetic acids (BAA) and bromomethanes on solid-phase extraction (SPE) cartridges, a sensitive and convenient method was developed for the determination of bromate in waters by inductively coupled plasma mass spectrometry (ICP–MS). Dionex OnGuard Ag and reversed-phase (RP) cartridges were tested for retention characteristics for bromide, BAA and bromomethanes. When a sample acidified with nitric acid was passed through an RP cartridge, BAA and bromomethanes were retained, afterwards bromide was absorbed as a precipitate of silver bromide and bromate was unretained when the nearly neutral sample passed a combination of Ag and H cartridges. After SPE pretreatment the recovery of bromate was 96–106%, and bromide remaining in the aqueous phase was found to be less than 0.06 μg L⁻¹ when the original bromide concentrations were less than 5 mg L⁻¹. Effectiveness of stacked Ag and H cartridges in removing bromide from chloride-containing samples was also examined. Common cations and other anions did not interfere with bromate determination. The detection limit for bromate is 57 ng L⁻¹. This method has been applied to analyse waters from various sources, and the recovery of the spiked bromate was in the range of 92–107%.

Keywords: Bromate; ICP–MS; Solid-phase extraction; Water analysis

Comparative study of extraction techniques for determination of garlic flavor components by gas chromatography–mass spectrometry by Sun-Neo Lee; Nam-Sun Kim; Dong-Sun Lee (pp. 749-756).

Several sampling techniques based on steam distillation (SD), simultaneous distillation and solvent extraction (SDE), solid-phase trapping solvent extraction (SPTE), and headspace solid-phase microextraction (HS-SPME) have been compared for the determination of Korean garlic flavor components by gas chromatography–mass spectrometry (GC–MS). Diallyl disulfide (57.88%), allyl sulfide (23.59%), and diallyl trisulfide (11.40%) were found to be the predominant flavor components of garlic samples extracted by SDE whereas these components were at levels of 89.77%, 2.43%, and 3.89% when the same sample was extracted by SD, 97.77%, 0.17%, and 0.10% by SPTE, and 97.85%, 0.01%, and 0.01% by HS-SPME using the 50/30-μm divinyl benzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fiber. Thermal degradation of components such as allyl methyl sulfide, dimethyl disulfide, and thiirane were observed for SDE and SD but not for SPTE or HS-SPME. HS-SPME had several advantages compared with SD, SDE, and SPTE—rapid solvent-free extraction, no apparent thermal degradation, less laborious manipulation, and less sample requirement. Five different fiber coatings were evaluated to select a suitable fiber for HS-SPME of garlic flavor components. DVB/CAR/PDMS was most efficient among the five types of fiber investigated.

Keywords: Garlic; Flavor; GC–MS; Solid-phase trapping solvent extraction (SPTE); Headspace-solid-phase microextraction (HS-SPME); Simultaneous distillation and solvent extraction (SDE); Steam distillation (SD)

Synthesis and applications of poly(acrylp-aminobenzenesulfonamideamidine-p-aminobenzenesulfonylamide) chelating fiber for pre-concentrating and separating trace Bi(III), Hg(III), Au(III) and Pd(IV) from solution samples by Xijun Chang; Yuman Wang; Ran Zhao (pp. 757-762).

Poly(acrylp-aminobenzenesulfonamideamidine-p-aminobenzenesulfonylamide) chelating fiber containing "S", "N", and "O" elements was synthesized from polyacrylonitrile fiber and p-aminobenzene sulfonamide and used to enrich and separate trace Bi(III), Hg(III), Au(III), and Pd(IV) ions from wastewater and ore sample solution. The enrichment acidity, flow rate, elution conditions, reuse, interference ions, saturated adsorption capacity, constant of adsorption rate, analytical accuracy, and actual samples on chelating fiber were investigated by means of inductively coupled plasma optical emission spectrometry (ICP-OES) with satisfactory results. Solutions of 100 ng mL⁻¹ of Bi(III), Hg(III), Au(III), and Pd(IV) ions can be enriched quantitatively by this chelating fiber at a rate of 1.0 mL min⁻¹ at pH 4 and desorbed quantitatively with 20 mL of 0.25 M HCl and 2% CS(NH₂)₂ solution at 50 °C (with recovery ≥97%). When the chelating fiber was reused for 20 times, the recoveries of the analyzed ions enriched by the fiber were still over 95% (except for Hg(III)). One thousand-fold excesses of Mn²⁺, Ca²⁺, Zn²⁺, Mg²⁺, Fe³⁺, Cu²⁺, Ni²⁺, Al³⁺, and Ba²⁺ ions and thousands-fold excesses of Na⁺and K⁺ cause little interference in the pre-concentration and determination of the analyzed ions. The saturated adsorption capacity of Bi(III), Hg(III), Au(III), and Pd(IV) was 4.850×10⁻⁴, 3.235×10⁻⁴, 2.807×10⁻⁴, and 3.386×10⁻⁴ mol g⁻¹, respectively. The constants of adsorption rate were 0.409 min⁻¹ for Bi, 0.122 min⁻¹ for Hg, 0.039 min⁻¹ for Au, and 0.080 min⁻¹for Pd. The relative standard deviations (RSDs) for the enrichment and determination of 10 ng mL⁻¹ Bi(III), Hg(III), Au(III), and Pd(IV) were lower than 2.3%. The results obtained for these ions in actual samples by this method were basically in agreement with the given values with average errors of less than 1.0%. FT-IR spectra shows that the existence of –SO₂–Ar, –H₂N–Ar, O=C–NH–, HN=C–NH–, and –HN–SO₂ functional groups are verified in the chelating fiber. From the FT-IR spectroscopy, we can see that Hg(III), Au(III), and Pd(IV) are mainly combined with nitrogen and sulfur (or oxygen), and Bi(III) is mainly combined with nitrogen (or oxygen) of the groups to form a chelating complex.

Determination of lead and cadmium using a polycyclodextrin-modified carbon paste electrode with anodic stripping voltammetry by Gabriela Roa; M. T. Ramírez-Silva; M. A. Romero-Romo; Laura Galicia (pp. 763-769).

This work reports the use of α and β-cyclodextrin-modified carbon paste electrodes (CPE_α-CD and CPE_β-CD) to determine simultaneously Pb(II) and Cd(II) by means of the electrochemical technique known as anodic stripping voltammetry (ASV). Both modified electrodes displayed good resolution of the oxidation peaks of the said metals. Statistic analysis of the results strongly suggests that the CPE_β-CDexhibited a better analytical response that the CPE_α-CD, while the detection limits obtained for Pb(II) were 6.3×10⁻⁷ M for the CPE_α-CD and 7.14×10⁻⁷ M for the CPE_β-CD, whereas for Cd(II) they were 2.51×10⁻⁶ M for the CPE_α-CD and 2.03×10⁻⁶ M for the CPE_β-CD.

Keywords: Cyclodextrins; Carbon paste electrode; Anodic stripping voltammetry; Lead; Cadmium

Anodic stripping voltammetric determination of mercury using multi-walled carbon nanotubes film coated glassy carbon electrode by Hongchao Yi (pp. 770-774).

An electrochemical method for the determination of trace levels of mercury based on a multi-walled carbon nanotubes (MWNT) film coated glassy carbon electrode (GCE) is described. In 0.1 mol L⁻¹ HCl solution containing 0.02 mol L⁻¹ KI, Hg²⁺ was firstly preconcentrated at the MWNT film and then reduced at −0.60 V. During the anodic potential sweep, reduced mercury was oxidized, and then a sensitive and well-defined stripping peak at about −0.20 V appeared. Under identical conditions, a MWNT film coated GCE greatly enhances the stripping peak current of mercury in contrast to a bare GCE. Low concentrations of I⁻ remarkably improve the determining sensitivity, since this increases the accumulation efficiency of Hg²⁺ at the MWNT film coated GCE. The stripping peak current is proportional to the concentration of Hg²⁺ over the range 8×10⁻¹⁰–5×10⁻⁷ mol L⁻¹. The lowest detectable concentration of Hg²⁺ is 2×10⁻¹⁰ mol L⁻¹ at 5 min accumulation. The relative standard deviation (RSD) at 1×10⁻⁸ mol L⁻¹ Hg²⁺ was about 6% (n=10). By using this proposed method, Hg²⁺ in some water samples was determined, and the results were compared with those obtained by atomic absorption spectrometry (AAS). The two results are similar, suggesting that the MWNT-film coated GCE has great potential in practical analysis.

Keywords: Multi-walled carbon nanotubes; Mercury; Determination; Chemically modified electrode; Anodic stripping voltammetry

The uncertainty of atomic mass fractions in a molecule by Veronika R. Meyer (pp. 775-778).

The mass fraction of a certain atom species in a molecule is needed for the calculation of the result of some chemical analyses. Common examples are gravimetric determinations (e.g., the sulfur concentration in a sample that can be obtained from the mass of precipitated barium sulfate). A similar problem is encountered when a reference solution of an ion is prepared by dissolution of a salt. This paper presents how the uncertainty of the mass fraction is calculated from the uncertainties of the atomic weights as published by IUPAC. The value is needed for the determination of the combined standard uncertainty of the analysis. Some calculated examples illustrate the mathematical considerations presented in the paper.

Keywords: Measurement uncertainty; Atomic mass fraction; Atomic weights; Atomic weight uncertainty; Gravimetric analysis

Measurements of sulfur in oil using a pressurised wet digestion technique in open vessels and isotope dilution mass spectrometry by Markus Ostermann; Peter Kettisch; Dorit Becker; Jochen Vogl (pp. 779-783).

Graz University of Technology has developed a new technique for digesting samples using the well-established high-pressure asher (HPA) from Anton Paar GmbH (Graz, Austria). The digestion is performed in semi-open vessels inside a pressurised autoclave. The new HPA equipment consists of a liner for the autoclave, special sample racks and 30-mL digestion vessels made of quartz, covered with PTFE stoppers. The Laboratory for Isotope Dilution and Nuclear Analysis of the Federal Institute for Materials Research and Testing (BAM, Berlin) tested this new equipment in order to assess its usability for the decomposition of larger sample amounts of gas oils for the measurement of sulfur. Several experiments were carried out using the new sample decomposition technique. In order to test the recovery of the new digestion method, a gas oil material with known sulfur content was chosen, quantified by the validated conventional closed vessel HPA digestion in combination with thermal ionisation mass spectrometry. Isotope dilution mass spectrometry has been applied as analytical method in this investigation. The gas oil was spiked with an isotopic spike material, which is enriched in ³⁴S, and was then wet digested in the HPA. The oxidized sulfur of the dried samples was reduced to H₂S and precipitated as As₂S₃. The sulfur was measured as arsenic monosulfide (AsS⁺). The mass content of sulfur in the gas oil tested is 453.5 mg kg⁻¹. Recovery tests for increasing masses of gas oils indicate that the recovery using the new measurement technique decreases with increasing mass of gas oil. Results were obtained for approximately 0.3 g sample weight and had less overlap with the result of the old HPA method within the stated uncertainties. At approximately 0.5 g sample weight the yield decreases to about 97% and at approximately 1.0 g sample weight to about 87%. In comparison with the conventional closed vessel HPA digestion, the new technique shows no clear advantages for the certification of the sulfur content in gas oil other than a more convenient handling. The total uncertainty of the sulfur mass fractions (k=2) is about 1.5%. Repeated determination of the oil samples show a relative standard deviation of about 0.8% and indicate that the analytical procedure is robust and reproducible. The demonstrated reproducibility allows the establishment of correction factors for the yield, which in turn enables higher sample masses for routine work. The blank level (0.26×10^-6 g) was within the range of the conventional closed HPA digestion procedure·(0.28×10^-6 g). Cross contamination could not be detected. In terms of trace metal analysis a good applicability and more advantages over the conventional closed vessel HPA digestion can be assumed.

Keywords: Wet digestion; Open vessel digestion; Sulfur in oil; Reference materials; TIMS; IDMS

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Analytical and Bioanalytical Chemistry (v.377, #4)

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Analytical and Bioanalytical Chemistry (v.377, #4)