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Analytical and Bioanalytical Chemistry (v.378, #1)
Eurocurriculum II for Analytical Chemistry approved by the Division of Analytical Chemistry of FECS
by R. Salzer (pp. 28-32).
Teaching chemistry in Europe—a look at future developments
by J. Barbosa; J. Guiteras; G. Fonrodona (pp. 33-36).
Immunoaffinity capillary electrophoresis applications of clinical and pharmaceutical relevance
by Norberto A. Guzman (pp. 37-39).
Miniaturized liquid separation techniques in bioanalysis
by Lisa A. Holland; Jocelyn McKeon (pp. 40-42).
Real-time analysis on microarrays
by Frank F. Bier; Eva Ehrentreich-Förster; Peter M. Schmidt (pp. 52-53).
Towards total-consumption pneumatic liquid micro-sample-introduction systems in ICP spectrochemistry
by Jean-Michel Mermet; José-Luis Todolí (pp. 57-59).
Immunoanalytical detection of allergenic proteins in food
by R. Krska; E. Welzig; S. Baumgartner (pp. 63-65).
Ganglioside–liposome immunoassay for the detection of botulinum toxin by Soohyoun Ahn-Yoon; Thomas R. DeCory; Richard A. Durst (pp. 68-75).
A rapid and highly sensitive receptor immunoassay for botulinum toxin (BT) has been developed using ganglioside-incorporated liposomes. Botulism outbreaks are relatively rare, but their results can be very severe, usually leading to death from respiratory failure. To exert their toxicity, the biological toxins must first bind to receptors on the cell surface, and the trisialoganglioside GT1b has been identified as the cell receptor for BT. Therefore, in this study, GT1b was used to prepare the ganglioside–liposomes by spontaneous insertion into the phospholipid bilayer. In a sandwich-based, hybrid receptor immunoassay, BT is detected as a colored band on a nitrocellulose membrane strip, where BT bound to the GT1b-liposomes are captured by anti-BT antibodies immobilized in a band across the strip. The intensity of the colored band can be visually estimated, or measured by densitometry using computer software. The limit of detection (LOD) for BT in the lateral-flow assay system was 15 pg mL−1, which is comparable to the limits of detection achieved with the most sensitive assays previously reported. However, this rapid assay can be completed in less than 20 min. These results demonstrate that the sandwich assay using GT1b-liposomes for detection of BT is rapid and very sensitive, suggesting the possibility for detecting BT in field screening, simply and reliably, without the need for complex instrumentation.
Keywords: Botulinum toxin; Ganglioside; Liposomes; Ganglioside–liposomes; Immunoliposomes; Receptor immunoassay
Use of a gas-sensor array for detecting volatile organic compounds (VOC) in chemically induced cells by Patrizia Pasini; Nilesh Powar; Ricardo Gutierrez-Osuna; Sylvia Daunert; Aldo Roda (pp. 76-83).
An application of gas sensors for rapid bioanalysis is presented. An array of temperature-modulated semiconductor sensors was used to characterize the headspace above a cell culture. Recombinant Saccharomyces cerevisiae yeast cells, able to respond to 17β-estradiol by producing a reporter protein, were used as a model system. Yeast cells had the DNA sequence of the human estrogen receptor stably integrated into the genome, and contained expression plasmids carrying estrogen-responsive sequences and the reporter gene lac-Z, encoding the enzyme β-galactosidase. The sensor-response profiles showed small but noticeable discrimination between cell samples induced with 17β-estradiol and non-induced cell samples. The sensor array was capable of detecting changes in the volatile organic compound composition of the headspace above the cultured cells, which can be associated with metabolic changes induced by a chemical compound. This finding suggests the possibility of using cross-selective gas-sensor arrays for analysis of drugs or bioactive molecules through their interaction with cell systems, with the advantage of providing information on their bioavailability.
Keywords: Metal oxide sensors; Volatile organic compounds; Recombinant yeast cells; Chemically induced cells; 17β-Estradiol; Drug analysis
Target-selective ion-exchange media for highly hydrophilic compounds: a possible solution by use of the “interval immobilization technique” by Takuya Kubo; Nobuo Tanaka; Ken Hosoya (pp. 84-88).
We prepared a crosslinked polymer as a separation and/or adsorption medium for CYN, as shown in Fig. 1. The polymers were evaluated by high-performance liquid chromatography (HPLC) and adsorption was examined under batch conditions. Results from detailed HPLC evaluation and measurement of the difference between the binding affinity for CYN and for other compounds showed the prepared polymer had specific recognition ability for CYN.
Keywords: Ion-exchange media; Highly hydrophilic compounds; Interval immobilization technique; Cylindrospermopsin (CYN); Cyanobacterium hepatotoxin
Enzyme stabilization strategies based on electrolytes and polyelectrolytes for biosensor applications by Nikolas A. Chaniotakis (pp. 89-95).
The achievements in the area of enzyme stabilization based on electrolytes, polyelectrolytes and polyols is reviewed, in the context of biosensor applications. Both the storage and operational stabilities of the biosensors can be improved using these stabilizers. The deactivation of the enzymes used for the development of biosensors from thermal shock, proteolytic degradation, and non-specific metal-catalyzed oxidation can be drastically reduced with the use of one or more of these stabilizers. It is attempted to deconvolute the effect of these additives on (a) the storage stability or shelf life, and (b) the operational stabilities of the biosensors. Even though there are a large number of techniques and reports dealing with enzyme stabilization, their application to biosensor technology is still very limited. It is thus concluded that the use of the existing enzyme stabilization techniques will have a drastic effect on the storage and operational stabilities of biosensors in the near future.
Keywords: Biosensor stabilization; Enzyme; Immobilization; Polyelectrolyte
Determination of ochratoxin A in foods: state-of-the-art and analytical challenges by Linda Monaci; Francesco Palmisano (pp. 96-103).
Ochratoxin A (OTA) can occur in a large variety of commodities (cereals, beans, groundnuts, spices, dried fruits, coffee, beer, wine) and, because of a carry-over effect, in milk, pig blood, liver, and kidney, and poultry meat from animals fed with contaminated feed. Because of the persistence of OTA in the food chain, exposure to the compound is a potential human health hazard. This has prompted adoption of regulatory limits in several countries which, in turn, implies the development of suitable validated and official analytical methods and rapid screening tests for cost-effective food control on a large scale. Liquid chromatography with fluorescence detection (LC–FLD), coupled with immunoaffinity column (IAC) clean-up, is the most widely employed analytical technique. LC coupled with electrospray-ionization mass spectrometry (MS) has detection limits comparable with those of LC–FLD and the selectivity of IAC can be achieved by tandem (MS–MS) or sequential (MS n ) detection. Synthetic counterparts to natural antibodies in the form of molecularly imprinted polymers seem a promising alternative to IAC for sample preparation. New analytical approaches to rapid, low-cost screening methods, for example those based on biosensors and dip-stick-like kits, are a direction in which innovation can be expected. Analytical methods for evaluation of the occurrence of OTA in foods, human exposure, and risk assessment are critically reviewed.
Keywords: Ochratoxin A; Food analysis; HPLC; Mass spectrometry; ELISA; SPME
Current strategies for electrochemical detection of DNA with solid electrodes by Patricia de-los-Santos-Álvarez; M. Jesús Lobo-Castañón; Arturo J. Miranda-Ordieres; Paulino Tuñón-Blanco (pp. 104-118).
A review of current strategies aimed at detecting nucleic acids (NA) using NA-modified solid electrodes reveals the versatility and potential of electrochemical detection in this field. What emerged at the beginning of 90s as a very promising detection system in DNA technology is now resulting in the first commercial devices. Many aspects of the experimental design, for example surface immobilisation and detection schemes, are outlined and evaluated. Although most approaches use hybridisation as the recognition reaction, those not based on hybridisation are also included. As is finally shown, great advances have been achieved, although further developments are required if electrochemical devices are to be suitable for routine measurement.
Keywords: Electrochemical detection of NA; DNA-modified electrodes; Electrochemical mutation detection
Highly parallel dispensing of chemical and biological reagents by Bas de Heij; Martina Daub; Oliver Gutmann; Remigius Niekrawietz; Hermann Sandmaier; Roland Zengerle (pp. 119-122).
We present a technology for the highly parallel dispensing of a multitude of reagents. It allows one to dispense up to 96 different reagents simultaneously in a fixed array, in a volume range of 100 pL up to several nL. The pitch of the dispensed droplets can be as small as 500 µm. All channels are fired simultaneously, giving an unprecedented throughput. The system was originally developed for the high-throughput fabrication of microarrays, but can easily be adopted for other applications such as highly parallel filling of nanotiterplates. Based on our standard configuration we achieved droplets with 125-µm in-flight diameter (1.2 nL) with a CV of <1%.
Keywords: Microarrays; Biochips; Dispenser; Nanotiter plates; Microfluidics; Non-contact printing
Determination of Cr(VI) in ambient airborne particulate matter by a species-preserving scrubber-sampling technique by Detlef Metze; Helmut Herzog; Bernhard Gosciniak; Dieter Gladtke; Norbert Jakubowski (pp. 123-128).
Airborne particulate matter has been sampled at a location close to a metallurgical plant in North-Rhine-Westphalia, Germany, and first results on the chromium(VI) content in the collected dust are presented. A special procedure using a scrubber as sampling device was used to preserve Cr(VI) during the sampling procedure. The scrubber solution which consisted of 0.1 mol L−1 TRIS-buffer solution was adjusted to a slightly alkaline pH of 8.6 to reduce the oxidation potential of Cr(VI) and to avoid possible oxidation of Cr(III) to Cr(VI), for example by oxygen (or ozone at ambient concentrations). After sampling Cr(VI) was pre-concentrated on an anion-exchange material and eluted with aqueous 0.6 mol L−1 sodium perchlorate solution. After elution, a species-selective complex of Cr(VI) with diphenylcarbazide (DPC) was prepared; this was extracted into n-hexanol and quantified by UV–visible spectrophotometry. A detection limit of 0.9 ng m−3 for Cr(VI) in ambient aerosols can be achieved with this method.
Keywords: Speciation; Hexavalent chromium; Ambient aerosols
Iodine concentration in different human brain parts by E. Andrási; Cs. Bélavári; V. Stibilj; M. Dermelj; D. Gawlik (pp. 129-133).
Iodine is one of the most important essential elements as demonstrated by the fact that its deficiency can cause goitre. Nevertheless, quantitative data on its concentration in biological materials, especially in the human brain, are scarce. There is therefore a demand for accurate and reliable information on iodine in these types of samples. The purpose of the present work was to determine the concentration of total iodine in some control human brain parts by rapid radiochemical neutron activation analysis. Our second goal was to determine I distribution between lipid fraction and in brain tissue without lipid by applying two types of solvent extraction methods. The results were checked by the analysis of biological standard reference materials with certified or literature values for iodine and good agreement was found.
Keywords: Iodine; Human brain; Radiochemical neutron activation
Determination, by dynamic surface-tension analysis, of the molar mass of proteins denatured in guanidine thiocyanate by Wes W. C. Quigley; Emilia Bramanti; Bethany A. Staggemeier; Keith E. Miller; Abdul Nabi; Kristen J. Skogerboe; Robert E. Synovec (pp. 134-143).
A drop-based dynamic surface-tension detector (DSTD) has been used to study the dynamic surface tension behavior of proteins denatured in guanidine thiocyanate (GndSCN). The dynamic surface tension at the air–liquid interface is obtained by measuring the internal pressure of drops that grow and detach at a specified rate. In the method the sample of interest is injected and subsequently flows to the DSTD-sensing capillary tip. For this work, a novel DSTD calibration procedure utilizing two distinct mobile phases is applied. Here, the mobile phases are aqueous with different constituents, for example GndSCN and phosphate buffer, either added or omitted. The dual-mobile phase calibration procedure gives the analyst the capability of making protein measurements in a GndSCN–phosphate buffer mobile phase, while measuring a calibration standard in another mobile phase, such as water, in which the surface tension of the calibration standard is readily available. Results are presented with drop volumes of either 2 μL (i.e. 2-s drops) or 7 μL (i.e. 7-s drops) for proteins varying in molar mass from 12,000 to 330,000 g mol−1. We demonstrate that the DSTD can be used to determine the molar mass of proteins denatured in GndSCN. The method applies a regime where the denatured protein is detected by surface-active properties, and selectivity with regard to molar mass is contained in the dynamic component of the DSTD signal. The dynamic surface pressure signals of the denatured proteins suggest that diffusion plays a large role in the kinetics of the surface activity. The limit of detection for the denatured proteins studied ranged from 3 mg L−1 to 14 mg L−1. The DSTD, coupled with the novel dual-mobile phase calibration procedure, can be used to investigate the fundamental properties of proteins. Insight into the behavior at the air–liquid interface for native and denatured proteins is achieved; this is a novel tool for studying protein denaturation, complementary to other common approaches such as spectroscopy and calorimetry. Furthermore, the reported method could be widely applied to the study of effects on the interfacial properties of proteins after a variety of chemical and physical modifications that are possible with the dual-mobile phase calibration procedure.
Keywords: Dynamic surface tension; Denature; Guanidine thiocyanate; Molar mass; Protein; Surface activity
Liquid chromatographic method for the determination of enantiomeric composition of amphetamine and methamphetamine in hair samples by Karen W. Phinney; Lane C. Sander (pp. 144-149).
Interest in hair analysis as an alternative or complementary approach to urinalysis for drug abuse detection has grown in recent years. Hair analysis can be particularly advantageous for drugs such as amphetamine and methamphetamine that are rapidly excreted. Confirmation of abuse of these stimulants is complicated by the fact that some forms are found in legitimate medications. Examination of the enantiomeric composition of amphetamine and methamphetamine in hair samples can provide valuable assistance in interpreting drug testing results. In this work, we developed a liquid chromatographic method for the separation of amphetamine and methamphetamine enantiomers isolated from human hair samples. The drug enantiomers were separated on a chiral stationary phase after derivatization with an achiral fluorescent agent. The methodology was evaluated with a Standard Reference Material that contained several drugs of abuse including amphetamine and methamphetamine.
Keywords: Amphetamines; Chiral separations; Drugs of abuse; Enantiomers; Hair analysis
Headspace solid-phase microextraction (HS-SPME): a microscale sampling technique for determination of monoterpene hydrocarbons in coniferous needles by gas chromatography/mass spectrometry (GC/MS) by I. Chvílíčková; V. Kubáň (pp. 150-158).
A headspace solid-phase microextraction (HS-SPME) technique has been applied for the microscale sampling (single needle for Picea omorica, two needles of Picea abies) of volatile monoterpene hydrocarbons (MTHs) from conifer needles. A simple device consisting of a closed headspace vial equipped with an integral cutting device was used for the collection, homogenisation, and HS-SPME sampling. The highly sensitive gas chromatographic/mass spectrometric (GC/MS) analyses (LODs in tenths of ng g−1 FW were obtained for 3×S/N criteria) of individual needles confirmed the space distribution of MTHs in different parts of a single sprout (base, centre, apex) and among the left, central and right sprout of a whorl. The highest concentrations of MTHs were found in the apical (leading) sprout (S) of a whorl. The serious increase of MTHs content near the base of the left (SNL) sprout and nearly zero concentrations in the central parts of both the side sprouts of P. abies corresponded to the morphology of the whorl. On the other hand, similar concentrations of MTHs were found in the apex of the side (SNL and SNR) sprouts. The distributions of MTHs obtained after HS-SPME and solvent extraction followed the similar trends for both species. HS-SPME is more suitable for the evaluation of distribution of volatiles in microscale experiments due to the more precise separation of needles into correct categories and elimination of “averaging” effects of the larger quantities of needles needed for the solvent extraction. The precision was improved by one order of magnitude due to the reduction of uncontrolled losses of volatile species during the sample treatment.
Keywords: Monoterpene hydrocarbons; Extraction methods; HS-SPME; Solid-phase microextraction; Solvent extraction; Gas chromatography; Mass spectrometry
A comparative study of mid-infrared diffuse reflection (DR) and attenuated total reflection (ATR) spectroscopy for the detection of fungal infection on RWA2-corn by Gregor Kos; Rudolf Krska; Hans Lohninger; Peter R. Griffiths (pp. 159-166).
An investigation into the rapid detection of mycotoxin-producing fungi on corn by two mid-infrared spectroscopic techniques was undertaken. Corn samples from a single genotype (RWA2, blanks, and contaminated with Fusarium graminearum) were ground, sieved and, after appropriate sample preparation, subjected to mid-infrared spectroscopy using two different accessories (diffuse reflection and attenuated total reflection). The measured spectra were evaluated with principal component analysis (PCA) and the blank and contaminated samples were classified by cluster analysis. Reference data for fungal metabolites were obtained with conventional methods. After extraction and clean-up, each sample was analyzed for the toxin deoxynivalenol (DON) by gas chromatography with electron capture detection (GC-ECD) and ergosterol (a parameter for the total fungal biomass) by high-performance liquid chromatography with diode array detection (HPLC-DAD). The concentration ranges for contaminated samples were 880–3600 μg/kg for ergosterol and 300–2600 μg/kg for DON. Classification efficiency was 100% for ATR spectra. DR spectra did not show as obvious a clustering of contaminated and blank samples. Results and trends were also observed in single spectra plots. Quantification using a PLS1 regression algorithm showed good correlation with DON reference data, but a rather high standard error of prediction (SEP) with 600 μg/kg (DR) and 490 μg/kg (ATR), respectively, for ergosterol. Comparing measurement procedures and results showed advantages for the ATR technique, mainly owing to its ease of use and the easier interpretation of results that were better with respect to classification and quantification.
Keywords: Attenuated total reflection; Diffuse reflection; Mid-infrared spectroscopy; Comparison study; Cereals; Mycotoxins
Speciation of sulfur in individual aerosol particles from work places by wavelength-dispersive electron-probe microanalysis by B. L. W. Höflich; S. Weinbruch; H. M. Ortner (pp. 167-170).
The oxidation state of sulfur has been determined by measuring the energy shift of the S K α line by wavelength-dispersive electron-probe microanalysis. On flat polished samples the energy shift between sulfate (S+6) and sulfide (S-2) was 1.3 eV, in good agreement with previous literature data. The observed energy shift of the S K α line is dominated by the change of the valence state of sulfur—the effects of co-ordination geometry and nearest neighbours are small. The relationship between the energy shift of the S K α line and the oxidation number of sulfur is linear, to a first approximation. The effect of particle geometry on the position of the S K α line is usually small and introduces an error of approximately half an oxidation number. The apparent sulfur valence states observed for individual aerosol particles from work places in a nickel refinery are highly variable and most probably result from different mixtures of the two end-members sulfide and sulfate.
Keywords: Speciation of sulfur; Aerosol particles; Work place air; Wavelength-dispersive electron-probe microanalysis
Elemental fingerprint analysis of barley (Hordeum vulgare) using inductively coupled plasma mass spectrometry, isotope-ratio mass spectrometry, and multivariate statistics by Søren Husted; Birgitte F. Mikkelsen; Jacob Jensen; Niels Erik Nielsen (pp. 171-182).
Inductively coupled plasma mass spectrometry (ICP–MS) and isotope-ratio mass spectrometry (IR-MS) have been used to examine the multi-elemental composition and 15N/14N and 13C/12C isotope ratios of three spring barley (Hordeum vulgare) genotypes (Orthega, Barke, and Bartok) grown in three typical Danish agricultural soils (North Jutland, West Jutland, and East Zealand) differing in soil fertility. The aim of the study was to examine whether it was possible to generate a unique elemental fingerprint of individual barley genotypes irrespective of the elemental imprint plants had received from soils differing in fertility and agricultural practice. Multivariate statistics were used to analyze the elemental fingerprints of the barley genotypes at different times during a full growing season from early tillering to full maturity of the barley grains. Initially, 36 elements were analyzed in the plant samples but this number was subsequently reduced to 15 elements: B, Ba, C, Ca, Cu, Fe, K, Mg, Mn, N, Na, P, S, Sr, and Zn. These elements exceeded the limit of detection (LOD) for all genotypes, soil types, and plant growth stages and for these elements the accuracy was better than 90% compared with apple leaf certified reference material (CRM). Principal component analysis (PCA) separated multi-elemental data in accordance with soil type when plants of similar physiological age were compared, whereas this separation disappeared if plants of all ages were compared simultaneously. Isotope ratios (δ15N) of plants also proved to be a highly accurate property for classification of samples according to soil type. In contrast, the differences in δ13C were too small to enable such classification. The differences in δ15N among soils were so pronounced that separation of samples according to the physiological age of plants became redundant. However, δ15N and the multi-elemental analysis revealed no differences between the three barley genotypes, indicating that the influence of soil chemistry and possibly also climate and agricultural practice was too large to allow an unique elemental fingerprint for the genotypes. This finding was substantiated by analyzing the multi-elemental composition of grain from two additional genotypes (Otira and Barthos) grown at the north and east locations, respectively. PCA showed not only that the elemental fingerprints of these two genotypes were similar to those of the others, but also that the soil in which the plant had been growing could be accurately predicted on the basis of the PCA scores from the genotypes Orthega, Barke, and Bartok. Similar conclusions could be drawn using δ15N data.
Keywords: Cultvars; Geographic origin; Elemental fingerprint analysis; Multi-element analysis; ICP–MS; IR-MS; Principal component analysis
Determination of cannabinoids in hemp food products by use of headspace solid-phase microextraction and gas chromatography–mass spectrometry by Dirk W. Lachenmeier; Lars Kroener; Frank Musshoff; Burkhard Madea (pp. 183-189).
A fully automated procedure using alkaline hydrolysis and headspace solid-phase microextraction (HS-SPME), followed by on-fiber derivatization and gas chromatographic–mass spectrometric (GC–MS) detection has been developed for determination of cannabinoids in hemp food samples. After addition of a deuterated internal standard, the sample was hydrolyzed with sodium hydroxide and submitted to direct HS-SPME. After absorption of analytes for on-fiber derivatization, the fiber was placed directly into the headspace of a second vial containing N-methyl-N-trimethylsilyltrifluoroacetamide (MSTFA), before GC–MS analysis. Linearity was good for Δ 9-tetrahydrocannabinol (THC), cannabidiol, and cannabinol; regression coefficients were greater than 0.99. Depending on the characteristics of the matrix the detection limits obtained ranged between 0.01 and 0.17 mg kg−1 and the precision between 0.4 and 11.8%. In comparison with conventional liquid–liquid extraction this automated HS-SPME–GC–MS procedure is substantially faster. It is easy to perform, solvent-free, and sample quantities are minimal, yet it maintains the same sensitivity and reproducibility. The applicability was demonstrated by analysis of 30 hemp food samples. Cannabinoids were detected in all of the samples and it was possible to differentiate between drug-type and fiber-type Cannabis sativa L. In comparison with other studies relatively low THC concentrations between 0.01 and 15.53 mg kg−1 were determined.
Keywords: Cannabinoids; Hemp food; Tetrahydrocannabinol (THC); Solid-phase microextraction (SPME); Gas chromatography (GC); Mass spectrometry (MS)
Headspace SPME followed by GC/PFPD for the analysis of malodorous sulfur compounds in liquid industrial effluents by François Lestremau; Valérie Desauziers; Jean-Louis Fanlo (pp. 190-196).
Headspace SPME was used to analyse malodorous sulfur compounds in liquid industrial effluents. A pulsed flame photometric detector (PFPD) was selected for a specific and sensitive analysis. Two fibres, PDMS/Dvb and PDMS/Carboxen, which are particularly convenient for extracting small and volatile molecules were tested. To compare these fibres, both sensitivity and artefact formation were considered. The PDMS/Carboxen fibre showed the lower limits of detection and moreover the least artefact formation yields. It was therefore selected and headspace SPME extraction conditions were optimised. Limits of detection of the target compounds evaluated were 12–31 ng L−1 and repeatability was around 7%. Due to the adsorption mechanism involved, extraction is strongly influenced by the sample matrix and the low affinity compounds can suffer displacement effects. To investigate the occurrence of this phenomenon, two sampling times corresponding to non-equilibrium (5 min) and equilibrium conditions (60 min) were investigated. An external calibration was carried out by using standard solutions for both sampling times. The developed procedure was then compared to the standard addition method on a real industrial effluent. The results obtained from the two methods and for the two extraction times were in good agreement, demonstrating that even a long sampling time can be used. Therefore, the simple and timesaving external calibration was defined as relevant for an accurate quantification of sulfur compounds by headspace SPME.
Keywords: SPME; Sulfur compounds; Liquid effluent; Headspace
Determination of a flame retardant hydrolysis product in human urine by SPE and LC–MS. Comparison of molecularly imprinted solid-phase extraction with a mixed-mode anion exchanger by Kristina Möller; Carlo Crescenzi; Ulrika Nilsson (pp. 197-204).
Diphenyl phosphate is a hydrolysis product and possible metabolite of the flame retardant and plasticiser additive triphenyl phosphate. A molecularly imprinted polymer solid-phase extraction (MISPE) method for extracting diphenyl phosphate from aqueous solutions has been developed and compared with SPE using a commercially available mixed-mode anion exchanger. The imprinted polymer was prepared using 2-vinylpyridine (2-Vpy) as the functional monomer, ethylene glycol dimethacrylate (EGDMA) as the cross-linker, and a structural analogue of the analyte as the template molecule. The imprinted polymer was evaluated for use as a SPE sorbent, in tests with both aqueous standards and spiked urine samples, by comparing recovery and breakthrough data obtained using the imprinted form of the polymer and a non-imprinted form (NIP). Extraction from aqueous solutions resulted in more than 80% recovery. Adsorption by the molecularly imprinted polymer (MIP) was non-selective , but selectivity was achieved by selective desorption in the wash steps. Diphenyl phosphate could also be selectively extracted from urine samples, although the urine matrix reduced the capacity of the MISPE cartridges. Recoveries from urine extraction were higher than 70%. It was important to control pH during sample loading. The MISPE method was found to yield a less complex LC–ESI–MS chromatogram of the urine extracts compared with the mixed-mode anion-exchanger method. An LC–ESI–MS method using a Hypercarb LC column with a graphitised carbon stationary phase was also evaluated for organophosphate diesters. LC–ESI–MS using negative-ion detection in selected ion monitoring (SIM) mode was shown to be linear for diphenyl phosphate in the range 0.08–20 ng μL−1.
Keywords: Molecularly imprinted polymers; Solid-phase extraction; Urine samples; LC–MS; Organophosphate esters
The effect of resin particle size on the rate of ion release: interactions in mixed bed systems by A. Torrado; M. Valiente (pp. 205-213).
The aim of the present study is to evaluate the influence of resin particle sizes on the rate of ions release from a mixture of ion-exchange resins (named NMTD) which supplies calcium, fluoride, and phosphate ions as the main mineral content, and to elucidate the different phenomena taking place through the related ion-exchange process. The final goal of the study, related to dental application (enamel restoration), is to limit the particle size range, since the rate of ion release is a key parameter in the successful achievement of such objective. Weak-type ion-exchange resins, loaded with the appropriate ions, were ground and sieved into granulometric fractions of bead diameters of 0.1–0.075, 0.075–0.063, and 0.063–0.05 mm. Particle size was controlled by a laser diffraction particle distribution analyzer. The experiments on the kinetics of ions release were carried out under batch conditions in artificial saliva desorption solution thermostatized at 37 °C. The release of Ca2+ and F− was determined by corresponding ion-selective electrodes automatically controlled, whereas H2PO4 − was measured spectrophotometrically by the inductively coupled plasma–optical emission technique (ICP-OES). The results of this study show that the process of ion-exchange for the different particle size fractions of resins is critical for the study of the kinetics release of the ions immobilized in the corresponding mixed bed polymeric matrices. In fact, despite the apparent narrow range of particle sizes of the mixed bed systems studied, appreciable differences in the rate of ions release are obtained. Since the ion release rate is depending on the contact surface, an increase of factor of 2 in particle size represents an increase of an order of magnitude of the resin contact surface due to the resin porosity. In this concern, it has been observed that the rate of ions release increases when particle size decreases. The interactions occurring during the ion release from the mixed bed resins (containing calcium-, fluoride-, and phosphate-loaded resins) can be interpreted by the following phenomena: H2PO4 −, which hardly modifies its rate of release in the presence of Ca2+ and F− in the mixture, promotes a considerable increase in the rate of Ca2+ release due to the formation of a calcium dihydrogen phosphate soluble complex. F− also produces an acceleration in the rate of Ca2+ release due to the formation of solid CaF2 on the surface of cationic resin particles, which in contrast leads to a decrease in the rate of F− release.
Keywords: Kinetics release; Particle size; Ion-exchange; Calcium; Phosphate; Fluoride
Analytical control of photocatalytic treatments: degradation of a sulfonated azo dye by A. Bianco Prevot; A. Basso; C. Baiocchi; M. Pazzi; G. Marcí; V. Augugliaro; L. Palmisano; E. Pramauro (pp. 214-220).
The degradation of Methyl Orange (C14H14N3SO3Na), chosen as a model sulfonated azo dye, was investigated in aqueous solutions containing suspended polycrystalline TiO2 particles under irradiation with simulated sunlight. The dye disappearance and the formation of the mineralization end products were monitored; the formation of the main transient intermediates was also examined in detail. Particular attention was devoted to the identification and to the evolution of fragments retaining the chromophoric group. The comparison of data coming from various analytical techniques led to a possible reaction mechanism for the degradation process, giving insight into an aspect of the treatment which has not been considered in previous studies.
Keywords: Photocatalytic degradation; Decolourisation; Azo dyes; Methyl Orange; Analysis
Statistical analysis of the impact of spectral correlation on observed formation constants from UV–visible spectroscopic measurements by Günther Meinrath; Stefan Lis; Zbigniew Piskula (pp. 221-226).
Information retrieved from UV–visible spectroscopic data by application of a self-modelling factor analysis algorithm showed apparently systematically shifted thermodynamic properties for the same chemical system as a function of spectral slit widths. This empirical observation triggered a systematic investigation into the likely effects of residual and spectral correlation on the numerical results from quantitative spectroscopic investigations. If slit width was a nuisance factor it would reduce the comparability of information evaluated from spectroscopic data. The influence of spectral slit width was investigated by simulation, i.e. by generating and evaluating synthetic spectra with known properties. The simulations showed that increasing spectral correlation may introduce bias into factor analysis evaluations. By evaluation of the complete measurement uncertainty budget using threshold bootstrap target factor (TB CAT) analysis, the apparent shifts are insignificant relative to the total width of the quantity’s measurement uncertainty. Increasing the slit widths causes some systematic effects, for example broadening of the registered spectral bands and reduction of spectral noise, because of higher light intensity passing to the detector. Hence, the observed systematic shifts in mean values might be caused by some latent correlation. As a general conclusion, slit width does not affect bias. However, the simulations show that spectral correlation and residual correlation may cause bias. Residual correlation can be taken into account by computer-intensive statistical methods, for example moving block or threshold bootstrap analysis. Spectral correlation is a property of the chemical system under study and cannot be manipulated. As a major result, evidence is given showing that stronger spectral correlation (r<−0.7) causes non-negligible bias in the evaluated thermodynamic information from such a system.
Keywords: Complete measurement uncertainty budget; Spectral correlation; Residual correlation; Factor analysis; UV–visible absorption spectroscopy; Chemometrics