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Analytical and Bioanalytical Chemistry (v.384, #2)

Organic thin-film transistors as analytical and bioanalytical sensors by Luisa Torsi (pp. 309-309).

Nanoscale organic and polymeric field-effect transistors as chemical sensors by Liang Wang; Daniel Fine; Deepak Sharma; Luisa Torsi; Ananth Dodabalapur (pp. 310-321).

This article reviews recently published work concerning improved understanding of, and advancements in, organic and polymer semiconductor vapor-phase chemical sensing. Thin-film transistor sensors ranging in size from hundreds of microns down to a few nanometers are discussed, with comparisons made of sensing responses recorded at these different channel-length scales. The vapor-sensing behavior of nanoscale organic transistors is different from that of large-scale devices, because electrical transport in a nanoscale organic thin-film transistor depends on its morphological structure and interface properties (for example injection barrier) which could be modulated by delivery of analyte. Materials used in nanoscale devices, for example nanoparticles, nanotubes, and nanowires, are also briefly summarized in an attempt to introduce other relevant nano-transducers.

Carbon nanotube transistors for biosensing applications by G. Gruner (pp. 322-335).

Electronic detection of biomolecules, although still in its early stages, is gradually emerging as an effective alternative to optical detection methods. We describe field effect transistor devices with carbon nanotube conducting channels that have been developed and used for biosensing and biodetection. Both transistors with single carbon nanotube conducting channels and devices with nanotube network conducting channels have been fabricated and their electronic characteristics examined. The devices readily respond to changes in the environment, and such effects have been examined using gas molecules and coatings with specific properties. Device operation in (conducting) buffer and in a dry environment—after buffer removal—is also discussed. Applications in the biosensing area are illustrated with three examples: the investigation of the interaction between devices and biomolecules, the electronic monitoring of biomolecular processes, and attempts to integrate cell membranes with active electronic devices.

Keywords: Carbon nanotube transistor; Nanoscale devices; Electronic detection; Bioelectronic integration; Cellectronics

Effect of morphology on organic thin film transistor sensors by Jason Locklin; Zhenan Bao (pp. 336-342).

This review provides a general introduction to organic field-effect transistors and their application as chemical sensors. Thin film transistor device performance is greatly affected by the molecular structure and morphology of the organic semiconductor layer. Various methods for organic semiconductor deposition are surveyed. Recent progress in the fabrication of organic thin film transistor sensors as well as the correlation between morphology and analyte response is discussed.

Keywords: Field effect transistor; Organic semiconductor; Chemical sensor; Biological sensor; Electrochemical sensors/Mass sensitive sensors; Semiconductor materials

Chemical and biological sensors based on organic thin-film transistors by Jeffrey T. Mabeck; George G. Malliaras (pp. 343-353).

The application of organic thin-film transistors (OTFTs) to chemical and biological sensing is reviewed. This review covers transistors that are based on the modulation of current through thin organic semiconducting films, and includes both field-effect and electrochemical transistors. The advantages of using OTFTs as sensors (including high sensitivity and selectivity) are described, and results are presented for sensing analytes in both gaseous and aqueous environments. The primary emphasis is on the major developments in the field of OTFT sensing over the last 5–10 years, but some earlier work is discussed briefly to provide a foundation.

Keywords: Gas sensors; Biosensors; Organic field-effect transistors; Microelectrochemical enzyme transistors

Organic thin-film transistors as transducers for (bio) analytical applications by Carmen Bartic; Gustaaf Borghs (pp. 354-365).

The use of organic thin-film transistors (OTFTs) in sensorics is relatively new. Although electronic noses, electronic textiles and disposable biochemical sensors appear to be viable applications for this type of devices, the benefits of the technology still have to be proven. This paper aims to provide a review of the recent advances in the area of chemically sensitive field-effect devices based on organic thin-film transistors (OTFTs), with emphasis on bioanalytical applications. Detection principle, device configuration, materials and fabrication processes as well as sensor performances will be discussed, with emphasis on the potential for implementation in real applications and the important challenges ahead.

Keywords: OTFTs; CHEMFETs; Conducting polymers; Bioanalytics

Phthalocyanine-based field-effect transistors as gas sensors by Marcel Bouvet (pp. 366-373).

In this review molecular field-effect transistors are described and compared with their gate-modified inorganic counterparts. The different processes involved in gas sensing are summarized. The advantages of transistors on resistors are demonstrated. The sensitivity of molecular field-effect transistors to strong oxidizing species, for example ozone, is detailed and compared with their sensitivity to humidity and volatile organic compounds. Application to ozone monitoring in urban atmospheres is also described.

Keywords: Molecular materials; Phthalocyanine; Field-effect transistor; Sensor; Ozone; Nitrogen dioxide

Use of laser drilling in the manufacture of organic inverter circuits by Shingo Iba; Yusaku Kato; Tsuyoshi Sekitani; Hiroshi Kawaguchi; Takayasu Sakurai; Takao Someya (pp. 374-377).

Inverter circuits have been made by connecting two high-quality pentacene field-effect transistors. A uniform and pinhole-free 900 nm thick polyimide gate-insulating layer was formed on a flexible polyimide film with gold gate electrodes and partially removed by using a CO₂ laser drilling machine to make via holes and contact holes. Subsequent evaporation of the gold layer results in good electrical connection with a gold gate layer underneath the gate-insulating layer. By optimization of the settings of the CO₂ laser drilling machine, contact resistance can be reduced to as low as 3 Ω for 180 μm square electrodes. No degradation of the transport properties of the organic transistors was observed after the laser-drilling process. This study demonstrates the feasibility of using the laser drilling process for implementation of organic transistors in integrated circuits on flexible polymer films.

Keywords: Organic transistor; Laser drilling process; Inverter circuit; Pentacene

In vitro permeation of chromium species through porcine and human skin as determined by capillary electrophoresis–inductively coupled plasma–sector field mass spectrometry by Veerle Van Lierde; Cyrille C. Chéry; Nathalie Roche; Stan Monstrey; Luc Moens; Frank Vanhaecke (pp. 378-384).

Since the species that trigger chromium allergy are not yet known, it is important to gain more of an insight into the mechanism of chromium transport through the skin and into the relationship between chromium allergy and chromium species. In vitro permeation studies with porcine and human skin were performed using a Franz static diffusion cell. Investigations attempted to elucidate (i) which Cr compounds are able to permeate through skin, (ii) the influence the Cr concentration in the donor solution has on the Cr permeation, and (iii) the effect that the time of exposure to the donor solution has on Cr permeation. Capillary electrophoresis hyphenated to inductively coupled plasma–sector field mass spectrometry (CE–ICP–SFMS) was used to separate and quantify the Cr species in the receptor fluid. 50 mmol L⁻¹ phosphate buffer (pH 2.5) was used for CE separation, and two different electrophoretic runs were carried out (in the positive and negative modes). Pneumatic nebulization (PN)-ICP-SFMS was used in order to quantify the total amount of Cr absorbed by the skin after microwave-assisted acid digestion of the tissue. Cr(VI) was found to pass most easily through the skin. Nevertheless, Cr(VI) was also shown to be absorbed more efficiently by the skin than Cr(III), an observation attributed to a more pronounced rejection of the positively charged Cr(III) ions by the skin barrier. These results were in good agreement with in vitro permeation studies previously reported in the literature in which other analytical techniques were used. Differences observed in the permeation of Cr following the application of aqueous Cr donor solutions and Cr-containing simulated sweat donor solutions are also described.

Keywords: Chromium; CE–ICP–MS; Porcine skin; Human skin; Simulated sweat

Fabrication and characterization of stable ultrathin film micropatterns containing DNA and photosensitive polymer diazoresin by Bing Yu; Hai–Lin Cong; Hu–Wei Liu; Cong-Hua Lu; Fang Wei; Wei-Xiao Cao (pp. 385-390).

Stable, ultrathin DNA micropatterns were fabricated from photosensitive polymer diazoresin (DR) through a self-assembly technique. The micropatterns were achieved on LBL ultrathin film after UV exposure through a photomask. The patterns were characterized systematically with scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and fluorescence microscopy. All of the results indicate that the combined LBL self-assembly and photolithography technique is a promising method for constructing stable, well-defined micropatterns with a nanoscale thickness.

Keywords: DNA; Diazoresin; Self-assembly; Micropattern

Optimizing the analytical performance and construction of ion-selective electrodes with conducting polymer-based ion-to-electron transducers by Agata Michalska (pp. 391-406).

All-solid-state ion-selective electrodes that use a conducting polymer as the ion-to-electron transducer have emerged as one of the most promising classes of all-solid-state potentiometric sensors in recent years. This is largely because it has many analytical advantages, including high response stability, which is unique in the field of internal-solution-free ion-selective electrodes. This paper reviews the considerable progress that has been made in this area of sensing in recent years, in terms of detection limits, selectivity coefficients and novel construction methods.

Keywords: Conducting polymer; All-solid-state potentiometric sensors; Ion-to-electron transducers; Low detection limit; Selectivity

Label-free characterization of cell adhesion using reflectometric interference spectroscopy (RIfS) by Bernd P. Möhrle; Karsten Köhler; Jan Jaehrling; Roland Brock; Günter Gauglitz (pp. 407-413).

Reflectometric interference spectroscopy (RIfS) is a label-free, time-resolved technique for detecting interactions of molecules immobilized on a surface with ligands in solution. Here we show that RIfS also permits the detection of the adhesion of tissue culture cells to a functionalized surface in a flow system. Interactions of T cells with other leukocytes or epithelial cells of blood vessels are crucial steps in the regulating immune response and inflammatory reactions. Jurkat T cell leukemia cells rapidly attached to a transducer functionalized with a monoclonal antibody directed against the T cell receptor (TCR)/CD3 complex, followed by activation-dependent cell spreading. RIfS curves were obtained for the Jurkat derivative JCaM 1.6 (which lacks the key signaling protein Lck), cells preincubated with cytochalasin D (an inhibitor of actin polymerization), and for surfaces functionalized with an antibody directed against the coreceptor CD28. These curves differed with respect to the maximum signal and the initial slope of the increase in optical thickness. The testing of chemical inhibitors, cell surface molecules and gene products relevant to a key event in T cell immunity illustrates the potential of label-free techniques for the analysis of activation-dependent cell-surface contacts.

Keywords: Cell assay; Drug development; Reflectometric interference spectroscopy (RIfS); Label-free detection; T cell activation

Assembly of layer-by-layer films of heme proteins and single-walled carbon nanotubes: electrochemistry and electrocatalysis by Liyun Zhao; Hongyun Liu; Naifei Hu (pp. 414-422).

After being treated by mixed acids, single-walled carbon nanotubes (SWNTs) were shortened and had negatively charged groups on the surface. Positively charged hemoglobin or myoglobin at pH 5.0 was successfully assembled with SWNTs into layer-by-layer films on solid surfaces, designated as {SWNT/protein} n. While only those proteins in the first few bilayers closest to the electrode surface exhibited electroactivity, the {SWNT/protein} n films demonstrated a much higher fraction of electroactive proteins and better controllability in film construction compared with cast films of the proteins and carbon nanotubes. The proteins in the {SWNT/protein} n films retained their near-native structure at medium pH. The stable protein film electrode showed good electrocatalytic properties toward reduction of oxygen and hydrogen peroxide, demonstrating the potential application of the {SWNT/protein} n films as a new type of biosensor based on the direct electrochemistry of proteins without using mediators. Figure Cyclic voltammograms at 0.2 V s⁻¹ in pH 7.0 buffers with different number of bilayers (n) for layer-by-layer {single-walled carbon nanotube/hemoglobin} n films.

Keywords: Hemoglobin; Myoglobin; Single-walled carbon nanotube; Layer-by-layer assembly; Direct electrochemistry

Time-resolved chemiluminescent analysis of hydralazine in pharmaceuticals by José A. Murillo Pulgarín; Pablo Fernández López; Pilar Hoyas Nuño (pp. 423-430).

A new analytical method is proposed for determination of hydralazine (HZ) in pharmaceuticals—measurement of the chemiluminescence (CL) emitted after reaction with phosphoric-acidified KMnO₄. The novelty of this method is the recording of the whole CL–time profile. Such a recording is possible by use of a CL-detector operating in tandem which enables the reactants to be mixed in the measurement cell only and, therefore, the CL is reaction monitored from beginning. At the precise time the pump is stopped signal recording is triggered and so CL evolution is recorded completely. The optimum chemical conditions for the determination were 0.8 mol L⁻¹ formaldehyde, 0.3 mmol L⁻¹ KMnO₄, 4.0 mol L⁻¹ H₃PO₄, and a total flow of 0.37 mL s⁻¹. Two calibration graphs were plotted, CL intensity and area under the profile curve against HZ concentration. Exhaustive statistical analysis provided very interesting results, for example, accordance with Clayton’s theory, detection limit below 0.2 μg mL⁻¹, and linear calibration ranges from 0.2 to 5.0 μg mL⁻¹. This method was successfully applied to the determination of HZ in pharmaceuticals. Because they are usually formulated in association with diuretics and β-blockers, the method was used for analysis of HZ in pharmaceuticals that contained either HZ only or HZ with other hypotensive substances. Obtained and nominal content were approximately the same and experimental Student t values indicated there were no significant differences between the values.

Keywords: Hydralazine; Hydralazine hydrochloride; Apressinum; Time-resolved chemiluminescence

Electrochemical properties and square-wave voltammetric determination of pravastatin by Biljana Nigović (pp. 431-437).

The electrochemical reduction and adsorptive voltammetric behaviour of pravastatin have been studied by means of cyclic and square-wave voltammetry at a hanging mercury-drop electrode in electrolytes of different pH. Within the entire pH range (2.0–9.0) in Britton–Robinson buffer, pravastatin gave rise to a single voltammetric peak in the potential interval from −1.22 to −1.44 V, depending on pravastatin concentration. It was found that the reduction of pravastatin proceeds via a relatively stable intermediate, which is transformed to the final electroinactive product by a coupled chemical reaction or can be re-oxidized back to pravastatin. The rate of chemical transformation is controlled by the proton concentration. The electrode mechanism has the properties of a surface redox reaction. A sensitive analytical method for trace analysis of pravastatin based on the adsorptive stripping technique has been developed. The calibration plot was linear in the range 8×10⁻⁸–5×10⁻⁷ mol L⁻¹. Application of the square-wave voltammetric method to determination of pravastatin in a pharmaceutical dosage form, without sample pretreatment, resulted in acceptable deviation from the stated concentration.

Keywords: Pravastatin; Square-wave voltammetry; Adsorptive stripping voltammetry; Hanging mercury-drop electrode; Pharmaceutical dosage forms

Determination of dibenzopyrenes in standard reference materials (SRM) 1649a, 1650, and 2975 using ultrasonically assisted extraction and LC–GC–MS by Christoffer Bergvall; Roger Westerholm (pp. 438-447).

A method has been developed for analysis of the highly potent polycyclic aromatic hydrocarbon (PAH) carcinogens dibenzo(a,l)pyrene, dibenzo(a,h)pyrene, and dibenzo(a,i)pyrene (molecular weight 302) present in small amounts in diesel and air particulate material. The method can also be used for analysis of the PAH benzo(a)pyrene, coronene, and perylene, for which reference and certified values are available for the standard reference materials used for validation of the method—SRM 1649a (urban dust) and SRM 2975 (diesel particulate matter). The only NIST values that have been published for these dibenzopyrene isomers in the analyzed SRM are reference values for dibenzo(a,i)pyrene and dibenzo(a,h)pyrene in SRM 1649a. The concentrations determined in the SRM were in good agreement with reported NIST-certified and reference values and other concentrations reported in the literature. Standard reference material 1650 (diesel particulate matter) was also analyzed. The method could not, however, be validated using this material because certification of SRM 1650 had expired. The method is based on ultrasonically assisted extraction of the particulate material, then silica SPE pre-separation and isolation, and, separation and detection by hyphenated LC–GC–MS. The method is relatively rapid and requires only approximately 1–5 mg SRM particulate material to identify and quantify the analytes. Low extraction recoveries for the analytes, in particular the dibenzopyrenes, when extracting diesel SRM 2975 and 1650 resulted, however, in the dibenzopyrenes being present in amounts near their limits of quantifications in these samples. The method’s limit of quantification (LOQ), based on analyses of SRM 1649a, is in the range 10–77 pg. By use of this method more than 25 potential PAH isomers with a molecular weight of 302 could be separated.

Keywords: PAH; Dibenzopyrenes; SRM 1649a; SRM 2975; SRM 1650; LC–GC–MS

Use of liquid chromatography quadrupole time-of-flight mass spectrometry in the elucidation of transformation products and metabolites of pesticides. Diazinon as a case study by María Ibáñez; Juan V. Sancho; Óscar J. Pozo; Félix Hernández (pp. 448-457).

Liquid chromatography (LC) coupled to hybrid quadrupole time-of-flight (QTOF) mass spectrometry (MS) is a useful analytical tool in the elucidation and confirmation of transformation products (TPs)/metabolites of pesticides with a wide range of polarity, in both environmental and biological samples. Firstly, the versatility of LC allows the determination of very distinct TPs/metabolites as chromatographic conditions can be easily changed and optimized depending on the analytical problem. Secondly, the mass accuracy provided by the TOF analyser allows the assignment of a highly probable empirical formula for each compound and the differentiation between nominal isobaric compounds. Finally, the possibility of performing MS/MS spectra with accurate mass measurements can been used for the final characterization of the TPs/metabolites detected and for the differentiation of isomeric compounds. In this study, the insecticide diazinon was used as model compound, and its photodegradation and metabolism have been investigated by LC-QTOF-MS. On one hand, environmental spiked water was irradiated with a mercury lamp for 9 days, sampling 3-mL aliquots approximately every 12 h. On the other hand, both in vitro and in vivo metabolism experiments were carried out with different substrate concentrations and incubation times. After centrifugation, and protein precipitation in the in vitro and in vivo studies, 50-μL aliquots of both environmental and biological samples were directly injected into the LC electrospray ionization QTOF system. The most important transformation processes were found to be hydrolysis of the ester moiety, hydroxylation in the aromatic ring or in one of the alkylic groups, oxidation of the sulfur atom on the P=S cleavage or a combination of these processes, with the highest number of compounds being found in the photodegradation study. Very polar compounds, such as diethyl phosphate and diethyl thiophosphate, were detected after direct injection of the aqueous sample, which was feasible owing to the characteristics of the LC. In MS mode, mass errors were below 3 mDa, leading to an empirical formula for each compound. MS/MS spectra with accurate mass were used for the final elucidation of the compounds detected.

Keywords: Diazinon; Liquid chromatography; Time-of-flight mass analyser; Tandem mass spectrometry; Pesticide transformation products; Pesticide metabolites

The analysis of seasonal air pollution pattern with application of neural networks by Marek Wesolowski; Bogdan Suchacz; Jan Halkiewicz (pp. 458-467).

Air pollution monitoring includes measuring the concentrations of air contaminants such as nitrogen dioxide, sulfur dioxide, some polycyclic aromatic hydrocarbons(PAHs), suspended particulate matter (PM) and tar substances. The purpose of this study was to determine the possibility of using artificial neural networks for identification of any patterns occurring during heating and nonheating seasons. The samples included in the study were collected over a period of 5 years (1997–2001) in the area of the city of Gdansk and the levels of pollutants measured in the samples collected were used as inputs to two different types of neural networks: multilayer perceptron (MLP) and self-organizing map (SOM). The MLP was used as a tool to predict in what heating season a certain sample was collected, and the SOM was applied for mapping all samples to recognize any similarities between them. This study also presents the comparison between two projection methods—linear (principal component analysis, PCA) and nonlinear (SOM)—in extracting valuable information from multidimensional environmental data. In the research the MLP model with 13-12-1 topology was developed and successfully trained for classification of air samples from different seasons. The sensitivity analysis on the inputs to the MLP indicated benz[α]anthracene, benzo[α]pyrene, PM₁, SO₂, tar substances and PM₁₀ as the most distinctive variables, while PCA pointed to PAHs and PM₁.

Keywords: Urban air contaminants; Multilayer perceptron; Self-organizing map; Artificial neural networks; Principal component analysis

Double-layer Tedlar bags: a means to limit humidity evolution of air samples and to dry humid air samples by Stephane Cariou; Jean-Michel Guillot (pp. 468-474).

Tedlar bags, which are widely used to collect air samples, especially VOCs and odorous atmospheres, can allow humidity to diffuse when relative humidity levels differ between the inside and outside. Starting with dry air inside the bag and humid air outside, we monitored equilibrium times under several conditions showing the evolution and influence of collected volumes and exposed surfaces. A double-film Tedlar bag was made, to limit the impact of external humidity on a sample at low humidity level. With the addition of a drying agent between both films, the evolution of humidity of a sample can be stopped for several hours. When a VOC mixture was monitored in a humid atmosphere, humidity was decreased but no significant evolution of VOC concentrations was observed.

Keywords: Tedlar bags; Air sampling; Humidity; Sample evolution; VOC

Analysis of trace levels of pesticides in rainwater using SPME and GC–tandem mass spectrometry by Anne Scheyer; Stéphane Morville; Philippe Mirabel; Maurice Millet (pp. 475-487).

A multiresidue method using gas chromatography coupled to ion trap tandem mass spectrometry (GC–ITD–MS/MS) associated with solid phase microextraction (SPME) was developed for the analysis of 20 pesticides commonly used in the Alsace region in rainwater samples. Since the pesticides were expected to be present at very low concentrations and in complex matrices, the analytical method used was both highly selective and sensitive. Therefore, fibers coated with polyacrylate (PA), polydimethylsiloxane (PDMS) and polydimethylsiloxane-divinylbenzene (PDMS-DVB) were tested, and the parameters affecting the precision and accuracy of the SPME method were investigated and optimized. These parameters include the type of fiber, the adsorption time, the effect of salt, and the extraction temperature. The PDMS fiber was the most polyvalent for the extractions of the different pesticides studied. Detection limits of between 5 and 500 ng L⁻¹, depending on the compounds under study (except for those which could not be analyzed: captan and mevinphos), were obtained with this analytical procedure. This method was applied to the analysis of rainwater samples collected simultaneously on a weekly basis at one rural and one urban site between March 2002 and July 2003. While some of the 20 pesticides analyzed were constantly detected (such as lindane and atrazine), a strong temporal variability was observed for some of the others (including alachlor, metolachlor, atrazine).

Keywords: Pesticides; SPME; Rainwater; GC–MS/MS

Naked eye detection of cadmium using inorganic–organic hybrid mesoporous material by Tatineni Balaji; Manickam Sasidharan; Hideyuki Matsunaga (pp. 488-494).

A novel and low-cost optical sensor for the naked eye detection of Cd²⁺in aqueous media based on mesoporous silica containing 4-(2-pyridylazo)resorcinol (PAR) as a probe molecule anchored by N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride (TMAC) was prepared. The effects of various factors such as pH, solvent volume, temperature, reaction time, amount of the material, and the presence of various ions were studied in order to optimize operating conditions. The detection was based on the color change of PAR from orange-yellow to purple as a result of complexation with Cd²⁺. The intensity of the Cd-PAR complex varies linearly with the Cd²⁺concentration, from zero to 1.78×10⁻⁷mol dm⁻³. The detection and quantification limits for the method when determining Cd²⁺ were 1.75×10⁻⁸and 5.77×10⁻⁸ mol dm⁻³, respectively, with a correlation coefficient of 0.99. Good chemical stability of the material was observed for a period of five months. The developed sensor was applied to the analysis of various industrial effluents and tap water samples.

Keywords: Inorganic–organic hybrid material; Optical sensor; Cadmium; 4-(2-pyridylazo)resorcinol; Industrial effluents

Determination of TOCl, TOBr and TOI in drinking water by pyrolysis and off-line ion chromatography by Guanghui Hua; David A. Reckhow (pp. 495-504).

The objective of this research was to determine the optimum total organic halogen (TOX) protocol for use with ion chromatographic (IC) detection to analyze total organic chlorine (TOCl), bromine (TOBr), and iodine (TOI) in drinking water simultaneously. Two commercial analyzers (one using a pure O₂ carrier and one using O₂/CO₂ mixture) and three commercially available activated carbons (two coconut-based and one bituminous coal-based) were examined in this study. Results showed that the pyrolytic analyzer using pure O₂ and off-line IC combined with a standard TOX carbon (coconut-based) achieved the most complete recovery of TOCl, TOBr and TOI for both model compounds and real samples. There was no obvious difference between the two analyzers when used in microcoulometric detection mode. The TOX method is moderately sensitive to nitrate rinse volume. The monohaloacetic acids were partly washed out during sample preparation. This problem was solved by a modified nitrate rinsing solution.

Keywords: TOX; TOCl; TOBr; TOI; Pyrolysis; Ion chromatography

Determination of pharmaceuticals in environmental waters by liquid chromatography/electrospray ionization/tandem mass spectrometry by Chunyan Hao; Linda Lissemore; Bick Nguyen; Sonya Kleywegt; Paul Yang; Keith Solomon (pp. 505-513).

A high-performance liquid chromatography/electrospray ionization/tandem mass spectrometry (LC/MS-MS) method was developed, validated and used to characterize pharmaceutical inputs in the Grand River watershed, Ontario, Canada. Twenty-seven antibiotics and neutral pharmaceuticals were extracted from aqueous environmental samples in a single step using ¹³C₆-labeled sulfamethazine phenyl as a method surrogate and analyzed by LC/MS-MS. Method detection limits were in the range of 20–1,400 ng/L for the compounds of interest with recoveries from 51 to 130%. Using this method, pharmaceutical profiles in tributaries flowing into the Grand River were investigated using samples collected from seven agricultural sites and one urban site. Quality control data collected during the 5-month field study period showed good method performance. Concentrations of pharmaceuticals in source water with heavy agricultural input and surface waters downstream with urban inputs were determined to examine the effect of agricultural and urban inputs to surface water quality. Only human prescription drugs were found from urban site samples taken at both high-flow (spring and fall) and low-flow (summer) events in 2003, indicating minimal agricultural input. We also found for the first time the presence of the ionophore monensin in the environment as well as the occurrence of the human prescription drug carbamazepine in surface waters receiving primarily agricultural inputs. Possible causes and analytical solutions for some poor recoveries are discussed with respect to extraction pH, total organic carbon and metal ions in the water samples. The ability to extract 27 pharmaceuticals in a single solid-phase extraction step from diverse environmental matrices such as agricultural tile drain, tributary and surface water samples, followed by a single LC/MS-MS analysis, enabled the effective delivery of quality data.

Keywords: Pharmaceuticals and personal care products; Solid-phase extraction; Antibiotics; Electrospray ionization; Liquid chromatography/tandem mass spectrometry

Effect of surface coverage on the conformation and mobility of C₁₈-modified silica gels by Gokulakrishnan Srinivasan; Lane C. Sander; Klaus Müller (pp. 514-524).

C₁₈-modified silica gels with surface coverages of 2 to 8.2 μmol m⁻², were prepared by different synthetic pathways and characterized by Fourier Transform infrared spectroscopy (FTIR), solid-state nuclear magnetic resonance (NMR) spectroscopy, and chromatographic measurements. The effects of temperature and bonding density on the conformational order of C₁₈-modified silica gels were studied in detail by FTIR spectroscopy. The silane functionality and degree of cross-linking of silane ligands on the silica surface were evaluated by ²⁹Si cross-polarization magic-angle spinning (CP/MAS) NMR and the structural order and mobility of the alkyl chains were investigated by ¹³C CP/MAS NMR spectroscopy. CH₂ symmetric and anti-symmetric stretching bands and CH₂ wagging bands were used as IR probes to monitor the conformational order and flexibility of the alkyl chains in the C₁₈ phases. Qualitative information about the conformational order was obtained from frequency shifts of the CH₂ symmetric and anti-symmetric stretching bands. The relative amounts of kink/gauche–trans–gauche, double-gauche, and end–gauche conformers in the alkyl chains were determined by analysis of CH₂ wagging bands. These results indicate that surface coverage plays a dominant role in the conformational order of C₁₈-modified silica gels. The FTIR and NMR data are discussed in the context of the chromatographic shape-selectivity differences.

Keywords: C₁₈-modified silica gels; Surface coverage; NMR; FTIR; Conformational order; Mobility

Quantitative analysis of the Ge concentration in a SiGe quantum well: comparison of low-energy RBS and SIMS measurements by D. Krecar; M. Rosner; M. Draxler; P. Bauer; H. Hutter (pp. 525-530).

The germanium concentration and the position and thickness of the quantum well in molecular beam epitaxy (MBE)-grown SiGe were quantitatively analyzed via low-energy Rutherford backscattering (RBS) and secondary ion mass spectrometry (SIMS). In these samples, the concentrations of Si and Ge were assumed to be constant, except for the quantum well, where the germanium concentration was lower. The thickness of the analyzed quantum well was about 12 nm and it was situated at a depth of about 60 nm below the surface. A dip showed up in the RBS spectra due to the lower germanium concentration in the quantum well, and this was evaluated. Good depth resolution was required in order to obtain quantitative results, and this was obtained by choosing a primary energy of 500 keV and a tilt angle of 51° with respect to the surface normal. Quantitative information was deduced from the raw data by comparing it with SIMNRA simulated spectra. The SIMS measurements were performed with oxygen primary ions. Given the response function of the SIMS instrument (the SIMS depth profile of the germanium delta (δ) layer), and using the forward convolution (point-to-point convolution) model, it is possible to determine the germanium concentration and the thickness of the analyzed quantum well from the raw SIMS data. The aim of this work was to compare the results obtained via RBS and SIMS and to show their potential for use in the semiconductor and microelectronics industry. The detection of trace elements (here the doping element antimony) that could not be evaluated with RBS in low-energy mode is also demonstrated using SIMS instead.

Keywords: Secondary ion mass spectrometry SIMS (68.49.Sf, 82.80.Ms); Low energy Rutherford backscattering RBS (82.80.Yc); Quantum well (73.21.Fg); Ge δ layer (68.18.-g, 68.47.Pe); Convolution (02.60.Ed)

A new continuous calibration method for inductively coupled plasma spectrometry by E. Paredes; S. E. Maestre; J. L. Todolí (pp. 531-541).

A new calibration method was developed and applied to inductively coupled plasma atomic emission spectrometry. External calibration was performed as follows. A container was filled with a given volume of deionized (V _p) water. Then a concentrated standard was introduced at a controlled rate (Q _e) into the tank by means of a peristaltic pump. The resulting solution was stirred throughout the experiment. Simultaneously, the solution inside the tank was pumped from the vessel to the plasma at a given rate (Q _s). The signal was continuously recorded. The variation of the concentration of the solution leaving the tank with time was determined by applying a basic equation of stirred tanks. The representation of the emission intensity versus the time and the further conversion of the time scale into a concentration scale gave rise to the calibration line. The best results in terms of linearity were achieved for V _p=15 cm³, Q _e=0.6–0.75 ml min⁻¹ and Q _s=1–1.2 ml min⁻¹. Graphs with more than 40 standards were obtained within about 10 min. The results found were not statistically different from those afforded by the conventional calibration method. In addition, the new method was faster and supplied better linearity and precision than the conventional one. Another advantage of the stirred tank was that procedures such as dynamic calibration and standard additions could be easily and quickly applied, thus shortening the analysis time. A complete analysis following these procedures based on the measurement of 30 standards took about 5 min. Several synthetic as well as certified samples (i.e., bovine liver, mussel tissue and powdered milk) were analyzed with the stirred tank by applying four different calibration methodologies (i.e., external calibration, internal calibration, standard additions and a combination of internal standardization and standard additions), with the combination of internal standardization and standard additions being the method that provided the best results. The element concentrations obtained were not significantly different from the actual or certified values.

Keywords: Stirred tank; Continuous calibration; Standard addition; Inductively coupled plasma atomic emission spectrometry

Estrogen-active nonylphenols from an isomer-specific viewpoint: a systematic numbering system and future trends by Klaus Guenther; Einhard Kleist; Bjoern Thiele (pp. 542-546).

4-Nonylphenols (NPs) are very important environmentally relevant substances. They are persistent, toxic, endocrine-disrupting chemicals that are priority hazardous substances of the EU Water Framework Directive. NPs are degradation products of 4-nonylphenol ethoxylates (NPEs), a widely used group of nonionic surfactants. The technical synthesis of NP leads to a complex mixture of NPs consisting of isomeric compounds that have different branched nonyl side chains. It has recently become clear that an isomer-specific view is absolutely necessary when it comes to correctly evaluating the biological effects of NPs and their behavior in the environment, including degradation processes. To rationalize the identification of individual NP isomers in scientific studies, we have developed a numbering system for all possible NP isomers that follows the IUPAC rules of substituent characterization in alkylphenols. The 211 possible constitutional isomers of NP are numbered according to a hierarchical and logical system. In the future, multidimensional coupling systems—for example GC×GC-TOF-MS—will be needed to study these highly complex class of substances.

Ultraviolet photolysis of urine for suppression of color quenching prior to liquid scintillation counting of tritium by Yoko Watanabe; Jun Kuwabara (pp. 547-550).

In order to reduce the color quenching in the measurement of tritium in urine by liquid scintillation counting , UV irradiation was applied to decompose the organic substances in the sample. Urine was decolorized under UV irradiation in the presence of hydrogen peroxide. As a result, color quenching was considerably suppressed and higher counting efficiency of tritium was obtained. This UV treatment made it possible to increase the urine content in the sample from 2 to 40% (v/v) without significant decrease of counting efficiency. Either higher sensitivity or shorter analysis time was achieved in the tritium measurement by the augmentation of urine content. When the measurement time was 30 min, the detection limit of tritium defined as 3s was 0.03 Bq/ml. At the expense of some sensitivity (set at a detection limit of 0.3 Bq/ml), the measurement time was shortened to 0.5 min. These results will make a great improvement to routine tritium monitoring as well as to emergency monitoring in mass tritium exposure.

Keywords: UV photolysis; Liquid scintillation counter; Tritium; Color quenching; Rapid analysis

Development and optimization of a method for analysis of the products from the transesterification of dimethyl carbonate and phenol by Ai-Hua Xing; Min-Qing Zhang; Zhi-Min He; Jian-Ping Zhang (pp. 551-554).

A high-purity sample of methyl phenyl carbonate (MPC) was obtained by developing a novel reaction route followed by a series of separation and purification procedures. Identification and quantification of the MPC sample (98.32%) was performed by a gas chromatography–mass spectrometry and Karl Fisher titration. The laboratory-prepared MPC was then used as a standard to optimize quantitative analysis of the products synthesized by transesterification of dimethyl carbonate and phenol. The advantage of the improved method was that MPC can be quantified directly rather than being calculated by subtracting the yield of diphenyl carbonate (DPC) and by-product anisole from the conversion of dimethyl carbonate (DMC). The resulting method was validated for linearity, precision, accuracy, detection limit, and quantification limit. With the improved method, simultaneous accurate quantification of DMC, MPC, DPC, phenol, and anisole in the transesterification products can be achieved. This enables evaluation of the activity and selectivity of different catalysts and control of the reaction processes.

Keywords: Transesterification; Methyl phenyl carbonate; Internal standard; Gas chromatography

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Analytical and Bioanalytical Chemistry (v.384, #2)

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Analytical and Bioanalytical Chemistry (v.384, #2)