Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Analytical and Bioanalytical Chemistry (v.364, #1-2)
Characterization of some functionalized RP-HPLC phases by the use of linear solvation energy relationships by Sabine Werlich; J. T. Andersson (pp. 3-14).
The linear solvation energy relationship equation developed by Abraham and coworkers was applied to the retention factors k of a series of 20 polar solutes on four chemically different RP-HPLC phases. Three of them were specially synthesized and are functionalized with ether, phenylsulfide or phenylsulfoxide groups. Their retention properties are compared with those of a nonpolar octadecylsiloxane (ODS) phase. The phase properties r, the excess molar refraction; s, the dipolarity; a and b, the hydrogen-bond basicity and acidity; and v, the cavity factor show significant differences on the four phases and are used here to suggest a classification of stationary phases based on the type of interactions that are important for the retention. The hydrophilic system properties r, s, a and b are the reason for different elution orders of a set of solutes on the four phases. The intrinsic hydrophobicity of the system, the v/A ratio (A is the surface coverage in μmol/m2), shows a dependence on the mobile phase composition as do the normalized phase properties r/v, s/v, a/v and b/v. Averaging the constants over a large span of mobile phase composition should be done very carefully. The LSER model is used to predict the elution order on the stationary phases for five phenols which show coelution on ODS. On the phenylsulfide phase they are resolved.
Solid diluted calibrants – a new concept for the preparation of standard solutions Part I: Principles and application to Cr (VI) by M. Krapp; B. Neidhart (pp. 15-21).
A novel concept involving the utilization of solid diluted calibrants (SDC) for the preparation of calibration and standard solutions for chemical analysis in the trace and ultra-trace concentration range is presented. This new method avoids the disadvantages of the conventional procedure which is primarily associated with the necessity for step-by-step dilution, and moreover, offers additional benefits. The principle and theoretical aspects of SDC are described. Using the example of an SDC for chromate (VI), the preparation process and characteristic features are described and the advantages and applicability of SDC are demonstrated.
Calibration of a planar differential CO2 probe by E. Lindner; Richard P. Buck (pp. 22-27).
The working mechanism of the differential CO2 sensor inherently contains several calibration problems. These difficulties are highlighted and some possibilities for eliminating them are discussed. Finally, a simple error analysis is shown for optimizing the composition of the standard solutions to be used for the calibration of the differential CO2 probe in blood electrolyte analyzers.
In-situ flow probe for improving the performance of electrochemical stripping analysis by J. Wang; Jianmin Lu; Doug MacDonald; Marcio A. Augelli (pp. 28-31).
Submersible flow probes, originally developed for in-situ electrochemical monitoring of trace metal contaminants, are used for minimizing common problems in stripping analysis, such as overlapping signals, intermetallic effects or ohmic distortions. These problems are alleviated via an internal delivery of an appropriate solution, containing a masking ligand, a third element, or a conductive matrix. Such attention to common problems, via in-situ manipulations of the collected metal, holds great promise for environmental and industrial applications. The coupling of fluid manipulations with the stripping sensor represents the first step towards the construction of miniaturised stripping analysers on a cable.
Use of the original silicone cladding of an optical fiber as a reagent-immobilization medium for intrinsic chemical sensors by Radislav A. Potyrailo; G. M. Hieftje (pp. 32-40).
It is demonstrated that extended-length sensors can be fabricated by the direct immobilization of suitable reagents into the original cladding of a plastic-clad silica (PCS) optical fiber. This cladding, a copolymer of vinyl-terminated poly(dimethylsiloxane) and poly(dimethylmethylhydrosiloxane), is an attractive immobilization matrix for a wide variety of reagents and opens up new avenues of sensor design. Unlike fibers with custom-drawn cladding, the new approach offers greater photo- and thermal stability and permits immobilization of several reagents in adjacent sections of a single fiber. Further, compared to room-termperature vulcanizable (RTV) silicone films used often in optical point sensors, the silicone cladding of a PCS optical fiber offers a number of advantages, including a dynamic fluorescence quenching constant for an immobilized fluorophore that is up to 3.4 times higher, tolerance to aggressive environments (e.g. highly alkaline solutions), lower rates of indicator leaching, high uniformity, and applicability to extended-length sensing. The homogeneity of the microenvironment of the fiber cladding, its resistance to aggressive alkaline solutions, and its ability to transport water vapor were probed by introducing a variety of reagents into the cladding, including a fluorescent ruthenium complex and acid-base and solvatochromic indicators. The new sensor-fabrication approach should find wide application, including detection of neutral species in gases and dissolved in water, and for spatial analyte mapping over extended, remote areas.
Stabilized potentiometric solid-state polyion sensors using silver-calixarene complexes as additives within ion-exchanger-based polymeric films by Oliver Lutze; Ravi K. Meruva; Aaron Frielich; Narayanan Ramamurthy; Richard B. Brown; Robert Hower; M. E. Meyerhoff (pp. 41-47).
Novel solid-state sensors for biomedically important polyions (i.e., heparin and protamine) that exhibit significantly enhanced initial EMF stability are prepared by incorporation of lipophilic silver-calixarene complexes along with the required ion-exchangers within polymeric films. A dithioether of tertiary butyl calix[4]arene together with its silver complex are added to the polyion sensing membranes which are deposited on a silver-epoxy conductor of a solid-state transducer. The silver-complex serves as a reversible electron transfer agent between the organic polymer film and the underlying solid-state conductor, resulting in highly reproducible starting EMF values and improved initial signal stability. This approach is further employed to devise a heparin sensing cartridge for blood measurements based on a novel differential measurement mode. One sensor responds to heparin, while the second identical solid-state sensor serves as a pseudo reference electrode with all heparin present in the sample within this half-cell complexed by the addition of excess protamine. The cartridges are evaluated by monitoring heparin response in spiked dog blood using poly(vinyl chloride) (PVC) blends and fluorinated silicone rubber (Dow Corning RTV 730) films containing appropriate levels of ion-exchanger and Ag+-calixarene/free calixarene additives.
Long-lifetime based pH micro-optodes without oxygen interference by U. Kosch; I. Klimant; Otto S. Wolfbeis (pp. 48-53).
The first decay time-based fiber optic pH microsensors are presented which are without cross-sensitivity to molecular oxygen. They are based on radiationless energy transfer from the donor ruthenium(II)-tris(1,10-phenanthroline) to a pH-sensitive sulfonephthalein acceptor dye. The microsensors have decay times in the microsecond range, a fact that makes them compatible with existing devices designed for optical oxygen microsensing. The sensor tips have diameters of 20 to 30 μm. Outstanding features are the excellent mechanical stability and the inertness to quenching by oxygen. The dynamic range depends on the pKa of the selected pH indicator. The sensors were characterized with respect to the dynamic range, response, storage stability and photostability. A high resolution pH measurement in a marine sediment core serves as an example for its utility.
Sulfur based self-assembled monolayers (SAM’s) on piezoelectric crystals for immunosensor development by R. D. Vaughan; C. K. O’Sullivan; G. G. Guilbault (pp. 54-57).
Self-assembled monolayers (SAM’s) of different thiols and sulfides with various structures were tested. They were investigated as a method to covalently bind antibodies to the surface of piezoelectric crystals. A capture assay using a Mouse IgG test system was performed. All tests were performed in solution. The reduction in frequency observed as binding occurred was monitored in real time. The SAM’s were activated with 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide hydrochloride (EDC) and N-hydroxysulfosuccinimide (NHS) prior to antibody immobilisation. Ethanolamine was used to block any available activated sizes after antibody immobilisation. The potential of this technique for immunosensor development is demonstrated.
Acrylate polymer immobilisation of enzymes by E. A. H. Hall; J. Justin Gooding; Carl E. Hall; Nicolas Martens (pp. 58-65).
A rotating disk electrode analysis of pin-holes in polymer membrane coverings is described and the results correlated with the performance of the polymers when used as immobilisation matrices for enzymes in amperometric biosensors. The polymer family chosen for study is that of the acrylates and two preparations are considered via bulk polymerisation and emulsion polymerisation. In the latter case PVA present in the polymerisation may form ‘diffusion channels’ in the deposited film. For the bulk polymers it is found that better signal response is obtained for pin-hole rich polymers, leading to the conclusion that transport of analyte/measurand is through the pin-holes. A pin-hole free polymer can be produced by inclusion of plasticiser or producing polymers with more ‘elastic’ properties (e.g. lower Tg). However, these polymers show poor permeability to analyte/measurand. The emulsion polymers can be produced with another component, e.g. PVA which may create diffusion channels. Polymers which show pin-hole behaviour in this class have hole-diffusion properties which are different to solution and comparable to a PVA ‘solution’. This approach may provide a means of optimising both immobilisation polymer matrix and diffusion channels for a biosensor, although the underlying correlation to permeability was found to be the pin-hole population rather than the hydrophilic-hydrophobic balance.
Recessed microelectrode array for a micro flow-through system allowing on-line multianalyte determination in vivo by R. Lenigk; H. Zhu; Tai-Chin Lo; Reinhard Renneberg (pp. 66-71).
Using CMOS-compatible processes, a microelectrode system for use in a micro flow-through cell was manufactured. The electrode was specially designed to enable multianalyte determination with immobilized oxidase enzymes and combines minimal flow dependency with a very small dead volume (< 1 μL) of the cell. This allows biomedical applications like measurements of glucose and lactate in interstitial fluid, which can be collected by ultrafiltration. Besides a 3-electrode system with 4 individually addressable platinum working electrodes, the sensor contains 2 electrodes that measure the conductivity of the sample as well as a Pt thermoresistor to measure the temperature. The temperature dependence in enzyme reactions can thus be controlled during on-line measurements. The 4 working electrodes comprise multielectrode arrays, each comprising 192 micro-holes with a diameter of 3.6 μm. They are arranged symmetrically around the central counter electrode, which is surrounded by a circular Ag/AgCl reference electrode. Between the array and the reference electrode are the loops of the Pt thermoresistor. The thermoresistor is electrically insulated from the measurement solution by a Si3N4 layer.A method for the pretreatment of platinum thin-film electrodes that increases the reversibility of the electrode process is described. The chemical modification of the working electrodes by electropolymerization of a resorcinol/1,3-diaminobenzene mixture enables interference-free measurement in blood and plasma as well as protection against electrode fouling.
Direct analysis of tantalum powders by electrothermal vaporization inductively coupled plasma atomic emission spectrometry by K.-C. Friese; V. Krivan (pp. 72-78).
A direct inductively coupled plasma atomic emission method for the determination of Ag, Al, As, Ca, Cd, Co, Cu, Fe, Ga, K, Li, Mg, Na and Pb in high-purity tantalum powders has been developed. The electrothermal vaporization technique using a modified longitudinally-heated Grün-ETAAS furnace with sample introduction on a platform and an automated sampling workstation provided the possibility of in situ analyte-matrix separation, freedom of blank, and applicability to routine analysis. Hard- and software were modified to allow signal recording and data processing independent of the spectrometer software. The extent of spectral interferences by Ta-emission at the analyte wavelengths used was determined and the analyte signals of each sample run were automatically corrected. Limits of detection ranging from 5 ng/g (Ag, Cu) to 250 ng/g (K, Pb) were obtained using optimized furnace and spectrometer conditions. The method was applied to the analysis of two tantalum samples and the results for Cu, Fe, K, Mg and Na were compared with those obtained by liquid and solid-samping ETAAS, showing satisfactory agreement.
Abundance ratios of mercury isotopes by 6s6p3P1-intermediate state excitation with resonance ionization mass spectrometry by P. Bisling; J. Dederichs; B. Neidhart; C. Weitkamp (pp. 79-86).
The isotope-selective excitation of mercury via the 6s6p 3 P 1 intermediate state excitation is studied with two-color resonance ionization mass spectrometry to determine abundance ratios of stable mercury isotopes. Lifetime, isotopic shifts, and hyperfine structure (HFS) splittings are measured. Atomic hyperfine interaction constants are determined. Line strengths of the ten components of the 6s 2 1S0→ 6s6p 3 P 1 transition are used for isotope ratio determinations. Ion signal intensities of even-mass components directly give the isotopic abundance, in contrast to the odd-mass components, for which the sum of the HFS components results in an anomalously high response for the isotopic abundance. The laser bandwidth dependence of the excitation and population probabilities of magnetic HFS sublevels due to linear polarization of the radiation are discussed. These considerations yield reasonable values for the apparent odd-mass isotope abundance.
Determination of ruthenium in photographic emulsions – development and comparison of different sample treatments and mass spectrometric methods by Petra Krystek; K. G. Heumann (pp. 87-90).
Different sample treatment procedures were combined with inductively coupled plasma mass spectrometry (ICP-MS) and negative thermal ionisation mass spectrometry (NTI-MS) for the determination of ruthenium traces in photographic emulsions. Dissolution of the samples in concentrated ammonia solution was used in connection with ICP-MS by external calibration, which has the advantage of a simple sample preparation technique but introduces high amounts of the silver matrix into the mass spectrometer. On the other hand, isotope dilution mass spectrometry (IDMS) with an enriched 99Ru spike solution was applied for ICP-MS and NTI-MS measurements, respectively, in connection with a significant reduction of the matrix by AgCl precipitation. In these cases loss of ruthenium by the AgCl precipitate has no effect on the analytical result. The results of the different methods agreed usually well analysing ruthenium traces in the range of 0.1–10 μg per gram emulsion. The detection limits obtained were 4 ng/g for ICP-IDMS, 20 ng/g for NTI-IDMS, and 15 ng/g for ICP-MS with external calibration. Differences in the results between the different methods could mainly be attributed to sample inhomogeneities. ICP-IDMS with silver matrix reduction by AgCl precipitation is recommended as a routine method, NTI-IDMS with the corresponding sample treatment as a calibration method.
EI- and NCI-mass spectrometry of arylalkyl nitrates and their occurrence in urban air by Stefan Woidich; O. Froescheis; O. Luxenhofer; Karlheinz Ballschmiter (pp. 91-99).
The overall probability of the formation of arylalkyl nitrates is low in comparison to alkyl nitrates. However, measurable amounts of arylalkyl nitrates are found in traffic influenced air. It is reported here an analytical protocol based on high-volume sampling, adsorption liquid chromatography as a step in sample preparation, and high-resolution gas chromatography with electron ionization mass selective detection (HRGC/EI-MSD) as well as high-resolution gas chromatography with negative chemical ionization mass selective detection (HRGC/NCI (methane)-MSD) for the determination of arylalkyl nitrates as atmospheric constituents in urban air. The synthesis of arylalkyl nitrates as reference compounds is described. The arylalkyl nitrates can be selectively detected by the fragments M-46 (M-NO2) and M-48 (M-NO2-2H) in HRGC/NCI(methane)-MSD. In EI(70 EV)-MSD the dominating ions are at 46, 77, 91 and 105 u, which correspond to the NO2 + and the phenyl, benzyl, and ethylbenzene fragments, respectively. The molecular ions are missing in (NCI-methane)-MSD and are of medium intensity in EI-MSD. Phenylethyl and phenylpropyl nitrates elute in GC in the range of n-octyl to n-dodecyl nitrate. The following arylalkyl nitrates have been identified in urban air: Benzyl nitrate (PhC1) and the three xylyl nitrates (M-PhC1), phenylethyl-1-nitrate (1Ph1C2), phenylethyl-2-nitrate (1Ph2C2), phenyl-n-propyl-1-nitrate (1Ph1C3), and phenyl-n-propyl-2-nitrate (1Ph2C3). Benzyl nitrate is the dominating compound in this group and is found at levels of 10–300 ng/m3 in urban air.
An enzymatic-fluorimetric method for monitoring of ethanol in ambient air by M. Schilling; G. Voigt; T. Tavares; D. Klockow (pp. 100-105).
A method is described for the continuous monitoring of ethanol in ambient air. The system consists of a scrubber coil for enrichment of the analyte from air in an aqueous solution and a directly connected fluorescence detector. Because of using a reagent solution containing alcohol dehydrogenase (ADH) and nicotinamide adenine dinucleotide (NAD+) for absorption, ethanol can react directly with ADH and NAD+ during air sampling, producing NADH, which can be measured by fluorescence detection. The influence of reagent concentrations, gas flow rate and scrubber solution flow rate on the performance of the instrument was tested. Possible ozone interferences can be avoided by placing a KI coated filter in front of the scrubber inlet. The response time of the system was found to be 2.3 min and the detection limit about 1 ppbV. The applicability of the developed method was demonstrated during a field campaign in Brazil.
At-line SPE–GC–MS of micropollutants in water using the PrepStation by Th. Hankemeier; P. C. Steketee; J. J. Vreuls; U. A. Th. Brinkman (pp. 106-112).
An automated at-line SPE–GC–MS system for the determination of micropollutants in aqueous samples, which is based on the PrepStation and uses large-volume on-column injections, has been redesigned. A cartridge made from stainless steel and polychlorotrifluoroethylene and a 2-needle system was constructed which allow the determination of micropollutants at the low ng/L level without interferences from impurities extracted from the septa of the vials or the commercial cartridges. No time-consuming pre-cleaning of the cartridges or septa is required. The SPE sample extract (300 μL) is transferred from the sample preparation module to the autosampler of the GC–MS and 50 or 100 μL are injected. The analytical characteristics of the integrated procedure such as analyte recovery (typically 80–105%) and repeatability (RSDs, 2–9%), were satisfactory. Several micropollutants were detected in (unfiltered) river water at the 0.2–400 ng/L level using full-scan MS acquisition. The system proved to be robust during the analysis of more than 100 tap and river water samples.
Characterization of a monoclonal TNT-antibody by measurement of the cross-reactivities of nitroaromatic compounds by Anne Zeck; M. G. Weller; Reinhard Niessner (pp. 113-120).
The characterization of a commercially available monoclonal antibody directed against the explosive 2,4,6-trinitrotoluene (TNT) is reported. The cross-reactivities of various nitroaromatic compounds have been determined by competitive enzyme-linked immunosorbent assay (ELISA). Byproducts and metabolites of TNT were examined as well as the azo dye Disperse Blue 79 and its major metabolites (2-bromo-4,6-dinitroaniline and 2-chloro-4,6-dinitroaniline, respectively). By investigation of the cross-reactivities of different spacer derivatives of TNT it could be demonstrated that the bridge-recognition of the antibody is not very pronounced. N-(2,4,6-Trinitrophenyl)-methylamine shows the highest cross-reactivity (240%) of the examined compounds. Additionally, affinity constants of several nitroaromatic compounds have been determined. The affinity constant of TNT has been calculated to 1.3 × 109 L/mol from the minimal midpoint (IC50 value) of the standard curve. The detection limit achieved for TNT was 0.06 μg/L; the midpoint of the optimized assay was 0.34 μg/L.
The application of the phase transition in nematic liquid crystals for the optical detection of volatile organic compounds by B. Drapp; D. Pauluth; J. Krause; G. Gauglitz (pp. 121-127).
It is demonstrated that optical transducers can take advantage from the outstanding optical properties of nematic liquid crystals. The measurements point out that the birefringence and the phase transition of a liquid crystal can be exploited for the threshold sensing. For that purpose a device consisting of an orientated liquid crystalline film between two crossed polarizers was used. The nematic liquid crystal was also used as a sensitive coating material on an integrated optical Mach-Zehnder interferometer. The calibration experiments were carried out with volatile organic solvents and different calibration curves were measured for meta-xylene and para-xylene.
Modified cyclodextrines as mass-sensitive coatings for solvent vapour detection by F. L. Dickert; Ulrich Geiger; Karin Weber (pp. 128-132).
Advances in robustness, selectivity and sensitivity in organic solvent vapour detection can be achieved by the application of β-cyclodextrines as coatings for mass sensitive chemical sensors. Linking the cyclodextrines with e.g. diiodooctane combines the molecular recognition capabilities of host-guest chemistry with the high stability of polymeric layers. Special increase in selectivity is achieved with anhydro cyclodextrines, since their flattened conus is adapted to benzene derivatives as can also be shown by computer modelling. Furthermore methylation elongates the cavity, guaranteeing an optimised engulfing of the analytes. In this way even a differentiation between p- and m-xylene vapours and a QMB detection limit of some μL/L is possible.
Microwave induced plasma atomic emission spectrometry: a suitable detection system for the determination of volatile halocarbons by Sofie Slaets; Frank Laturnus; F. C. Adams (pp. 133-140).
Microwave induced plasma atomic emission spectrometry (MIP-AES), a highly sensitive detection system for organometal compounds, was coupled to an automated purge and trap gas chromatographic system for the determination of volatile halogenated hydrocarbons in environmental water samples. Optimisation of the parameters affecting the injection and detection system led to relative detection limits from 1 to 14 ng · L–1 for chlorine- and bromine-compounds and from 10 to 75 ng · L–1 for iodine-compounds, on basis of a 10 mL sample volume. A comparison of the analytical characteristics between atomic emission detection (AED) and electron capture detection (ECD) showed a lower sensitivity of the atomic emission detector for halocarbons, but the detection thresholds are low enough to use the method for the determination of volatile halocarbons in trace level concentrations. The ability of the atomic emission detector provides increased selectivity for monitoring individual halogenated compounds under simplified and rapid chromatographic conditions, within a total analysis time of only 30 min. The method was applied with gas chromatographic separation for the analysis of sea water samples. Concentrations for the different elements between 0.05 and 15.28 μg · L–1 were determined.
Disturbance of the determination of aldehydes and ketones: Structural elucidation of degradation products derived from the reaction of 2,4-dinitrophenylhydrazine (DNPH) with ozone by S. Achatz; Gabor Lörinci; Norbert Hertkorn; Istvan Gebefügi; Antonius Kettrup (pp. 141-146).
None of the reaction products of ozone and DNPH immobilized on solid phase support have been identified yet. However, they can interfere with the determination of carbonyl compounds in ozone containing air when analysis is performed by sampling and derivatization with DNPH coated silica cartridges. To elucidate the structure of these compounds, DNPH silica cartridges were treated with synthetic air containing defined concentrations of ozone and eluted with acetonitrile. The products were characterized by HPLC-UV/Vis and nuclear magnetic resonance (NMR) spectroscopy. Three of the degradation products were identified as 2,4-dinitrophenol, 2,4-dinitroaniline and 1,3-dinitrobenzene. The identification was confirmed by comparison with commercially available standard compounds. The other elutable products were characterized as substituted aromatic compounds. The formation of all characterized products is consistent with a radical mechanism which has been previously discussed in the literature.
Purge and trap/thermal desorption device for the determination of dimethylselenide and dimethyldiselenide by M. Beatriz de la Calle-Guntiñas; Frank Laturnus; F. C. Adams (pp. 147-153).
A method is described for the determination of dimethylselenide and dimethyldiselenide using a purge-and-trap/thermal desorption device (PT/TD) coupled to a capillary column gas chromatograph with a six-way Valco valve. The system is constructed in such a way that it allows also on-column injections of the volatile compounds in organic solvents for external calibration purposes without the need to disassemble the PT/TD. The influence of the purge flow, purge time and volume of sample, on the purge efficiency of the PT system is studied. Desorption time and temperature are optimised for the TD mode of operation. Atomic absorption spectrometry (AAS) and flame photometric detection (FPD) have been used for the final determination of the volatile compounds. The figures of merit achieved with both detectors are reported.
Application of dual-step potential on single screen-printed modified carbon paste electrodes for detection of amino acids and proteins by Priyabrata Sarkar; A. P. F. Turner (pp. 154-159).
A novel screen-printed biosensor for protein and amino acid (AA) estimation is reported. A rhodinised carbon paste working electrode (WE) was used in the three-electrode configuration. Bromine was generated by the electrolysis of an acidic potassium bromide electrolyte on the working electrode when poised at an appropriate potential. The consumption of bromine by the protein and amino acid was then measured at a lower potential. This sensor was used to detect most of the amino acids and some common proteins. The method is highly sensitive and can even detect L- and D- proline which give no response with enzyme electrodes. This sensor has also been used to detect protein/amino acid in fruit juice, milk, and urine. The unique feature of the sensor is that it does not require any reagent/chemical other than buffer. No surface treatment or modification of the WE is necessary and hence the sensor is stable for the lifetime of the basic screen-printed electrode, which is about a year. A very small amount of analyte (10 μL) is required for direct detection. The sensor is inexpensive and disposable and may also be used for continuous-flow systems. This sensor may have useful application in process monitoring and control during the production of amino acids.
Immobilized metal-ion affinity chromatography of peptides on metalloporphyrin stationary phases by Magdalena Biesaga; Jowita Orska; Dariusz Fiertek; J. Izdebski; M. Trojanowicz (pp. 160-164).
The retention of selected dipeptides and tripeptides containing tyrosine was examined. As stationary phase an aminopropylated silica gel loaded with covalently linked tetraphenylporphyrin was used. The effect of metalization of porphyrin with Cu(II) and Zn(II) on retention was investigated. The observed separation is based on a mixed mechanism involving π-π and hydrophobic interactions as well as complex formation between immobilized metal ions and peptides. A satisfactory separation was demonstrated for C-peptide and bovine insulin. The possibility of separation of various insulins was also investigated.
Towards immunoassay in whole blood: separationless sandwich-type electrochemical immunoassay based on in-situ generation of the substrate of the labeling enzyme by Charles N. Campbell; Thierry de Lumley-Woodyear; A. Heller (pp. 165-169).
An 18 minute separationless amperometric ELISA-type sandwich immunoassay, utilizing only stable reagents and having no washing steps is described. The platform for the assay was an electron conducting redox hydrogel on a vitreous carbon electrode. Avidin and choline oxidase were co-immobilized on the redox hydrogel and the biotinylated antibody to the antigen to be assayed (the biotin-labeled F(ab′)2 fragment of goat anti-rabbit IgG) was bound to the gel. When the antigen (goat anti-rabbit IgG) was present in the analyzed solution, then its binding to the immobilized antibody made the electrode receptive to the complementary peroxidase-labeled antibody (horseradish peroxidase-labeled F(ab′)2 fragment of goat anti-rabbit IgG). Its binding resulted in electrical contact (“wiring”) of the horseradish peroxidase label to the redox hydrogel, and converted the non-catalytic hydrogel into an electrocatalyst for the reduction of hydrogen peroxide to water at –0.07 V (SCE) and resulted in the flow of a cathodic current. The electroreduced hydrogen peroxide was not added to the solution and was therefore not significantly accessible to hydrogen peroxide decomposing agents such as catalase. Instead, it was generated within the coating of the electrode through reacting dissolved choline with oxygen. This reaction was catalyzed by the immobilized choline oxidase. The reaction centers of choline oxidase, unlike those of horseradish peroxidase, are not connected to the electrode by the redox hydrogel.
Capillary enzyme immunoassay with electrochemical detection for determining indole-3-acetic acid in tomato embryos by Hongying Gao; Tongbo Jiang; William R. Heineman; H. Brian Halsall; John L. Caruso (pp. 170-174).
An amperometric immunoassay for indole-3-acetic acid (IAA) in tomato embryos was developed. The antibody against IAA was covalently bound to the chemically modified inner surface of a 22 μL silica capillary. The competitive binding of methylated IAA and an IAA alkaline phosphatase conjugate for a limited amount of antibody was accomplished in the silica capillary in 20 min. The enzymatic product p-aminophenol, produced from p-aminophenyl phosphate, was determined by flow injection analysis with amperometric detection. A detection limit for IAA of 3 pg/μL was obtained. The average concentration of IAA in mature embryos measured by this method is 0.37 ± 0.03 μg/g. Although isotope dilution GC-SIM-MS can achieve the same detection limit, the sample analysis is not feasible in such a complicated matrix and further purification and separation are required.
Detection of drug – tissue interactions using biosensors by David R. Coon; G. A. Rechnitz (pp. 175-178).
Neuronal biosensors are employed to assess the effect of selected anti-HIV drugs on nerve tissue. Preliminary experimental results show that Zalcitabine and Didanosine produce interference in neural function and suggest a correlation with clinically observed neuropathy. Zidovudine (AZT) produced no observable effect.
New enzyme sensors for morphine and codeine based on morphine dehydrogenase and laccase by Christian G. Bauer; Andrea Kühn; Nenad Gajovic; Olga Skorobogatko; Peter-John Holt; Neil C. Bruce; Alexander Makower; Christopher R. Lowe; Frieder W. Scheller (pp. 179-183).
Two new enzymatic methods have been developed to quantify morphine and codeine simultaneously in a flow injection system (FIA). The first enzyme sensor for morphine or codeine is based on immobilizing morphine dehydrogenase (MDH) and salicylate hydroxylase (SHL) on top of a Clark-type oxygen electrode. Morphine or codeine oxidation by MDH leads to a consumption of oxygen by SHL via the production of NADPH. This decreases the oxygen current of the Clark electrode. Concentrations of codeine and morphine are detected between 2 and 1000 μM and between 5 and 1000 μM, respectively. The second enzyme sensor for morphine is based on laccase (LACC) and PQQ-dependent glucose dehydrogenase (GDH) immobilized at a Clark oxygen electrode. Morphine is oxidized by laccase under consumption of oxygen and regenerated by glucose dehydrogenase. Since laccase cannot oxidize codeine, this sensor is selective for morphine. Morphine is detected between 32 nM and 100 μM. Both sensors can be operated simultaneously in one flow system (FIA) giving two signals without the requirement for a separation step. This rapid and technically simple method allows discrimination between morphine and codeine in less than 1 min after injection. The sampling rate for quantitative measurements is 20 h–1. The method has been applied to the quantitative analysis of codeine or morphine in drugs.
Flow injection analysis of hydrogen peroxide in disinfectants by Diedrich Harms; Roberto Than; Bernt Krebs; U. Karst (pp. 184-188).
A flow injection analysis (FIA) method for the automated determination of hydrogen peroxide in the presence of even stronger oxidants is presented based on the immediate formation of a colored adduct between hydrogen peroxide and a dinuclear iron(III) complex. A reagent stream with the complex and a carrier stream into which the sample is injected are combined in a low dead volume mixing tee. A reaction coil provides for a reaction time of 7 s, after which detection is performed using UV/ vis spectroscopy at 575 nm. Major advantages of the method are the simple experimental setup and the high selectivity even towards stronger oxidants. Real samples have been investigated and the method has been validated using independent techniques including microplate spectrophotometry and HPLC.