Showing papers in "Analyst in 1994"
TL;DR: A method was developed that permits the determination of numerous variants of microcystins by a single procedure, and involves filtration to separate cyanobacterial cells from water, allowing intracellular and extracellular toxin levels to be assessed.
Abstract: Increasing concern over the presence of microcystins (cyanobacterial/blue–green algal hepatotoxins) in water supplies has emphasized the need for a suitable analytical method. As many microcystins are known to exist, a method was developed that permits the determination of numerous variants by a single procedure. The method involves filtration to separate cyanobacterial cells from water, allowing intracellular and extracellular toxin levels to be assessed. The cellular components of the samples are extracted repeatedly in methanol, which was found to be the most versatile solvent tested for the extraction of microcystins. The efficiency of this extraction procedure was found to be independent of cell biomass. The filtered water was subjected to trace enrichment using a C18 solid-phase extraction cartridge, followed by identification and determination by photodiode-array high-performance liquid chromatography. The procedure was assessed using four water samples (two raw and two treated) spiked with a mixture of five microcystins and the cyanobacterial hepatotoxin nedularin. Recoveries of all but one microcystin were found to be good when spiked with concentrations as low as 250 ng l–1. The linearity and precision of the experimental procedure were assessed for five microcystins and nodularin. The proposed method permits rapid sample processing and determination of several microcystins.
638 citations
TL;DR: Values for NSP provide a good marker for a diet rich in fruit, vegetables and high-extraction cereal products associated with health and recommended in dietary guidelines.
Abstract: Methods for the measurement of dietary fibre as non-starch polysaccharides (NSP) are described. A common enzymic removal of starch and acid hydrolysis of the NSP to their constituent sugars are followed by one of three alternative techniques, gas–liquid chromatography, high-performance liquid chromatography or spectrophotometry, for measurement of the released sugars. The results obtained by the three methods are in good agreement for a wide range of raw and processed foods. NSP compose approximately 90% of the plant cell-wall material and are therefore a good index of this material. Values for NSP therefore provide a good marker for a diet rich in fruit, vegetables and high-extraction cereal products associated with health and recommended in dietary guidelines. Values for total, soluble and insoluble NSP may be obtained with any of the end-point techniques, and the detailed information obtained from the chromatographic methods is useful in studies of the relationship between the intakes of various types of NSP and health. The causes of some potential interferences in the spectrophotometric assay, especially from processed foods, have been identified and eliminated. The rapid spectrophotometric version is suitable for food labelling purposes and for quality control, and the changes described have made it more robust.
454 citations
TL;DR: In this paper, a spreadsheet method for the calculation of standard deviations based on the general formula for error propagation is presented, without violating the condition of mutual independence, with substantial time gain and with no risk of calculating errors.
Abstract: A quick and universally applicable spreadsheet method is outlined for the calculation of standard deviations based on the general formula for error propagation: “graphic omitted” With this method, standard deviations are calculated numerically without violating the condition of mutual independence, with a substantial time gain and with no risk of calculating errors. Satterthwaite's approximation of the degrees of freedom is a logical extension of the technique with which confidence intervals can be easily established. Direct insight is obtained about the separate contributions of the different error sources.
439 citations
TL;DR: In this paper, the authors show that a particular experimental set-up can be calibrated for the inner filter effect from the absorption and fluorescence excitation spectra of a suitable standard.
Abstract: Recorded fluorescence intensity is in general not proportional to sample concentration owing to absorption of the incident and emitted light passing through the sample to and from the point inside the cell where the emission is detected. This well known inner-filter effect depends on sample absorption and on instrument geometry, and is usually significant even in samples with rather low absorption (the error is about 8% at an absorbance of 0.06 in a 1 cm square cell). In this work we show that a particular experimental set-up can be calibrated for the inner-filter effect from the absorption and fluorescence excitation spectra of a suitable standard. The calibration takes only a few minutes and provides correction with sufficient accuracy for most practical situations.
350 citations
TL;DR: In this paper, the occurrence, mechanisms, and practicalities of the electrogeneration of chemiluminescence are described with reference to applications in analytical chemistry, and the general theory of electron transfer excitation mechanisms is discussed with respect to organic reactions in aprotic media, and extended to include inorganic complexes and clusters.
Abstract: The occurrence, mechanisms, and practicalities of the electrogeneration of chemiluminescence are described with reference to applications in analytical chemistry. The general theory of electron transfer excitation mechanisms is discussed with respect to organic reactions in aprotic media, and extended to include inorganic complexes and clusters. Analytical applications are classified according to the excitation mechanism, i.e., organic and inorganic systems, established chemiluminescence reactions initiated electrochemically, and cathodic luminescence at semiconductor electrodes.
270 citations
255 citations
TL;DR: In this paper, an examination of the practice of derivatizing organic compounds such as fatty acids, sterols and amino acids in relation to subsequent analysis via gas chromatography-combustion-isotope ratio mass spectrometry is presented.
Abstract: An examination of the practice of derivatizing organic compounds such as fatty acids, sterols and amino acids in relation to subsequent analysis via gas chromatography–combustion–isotope ratio mass spectrometry is presented. Fractionation processes, such as kinetic isotope effects, which cause a deviation in the measured stable carbon isotope ratios (δ-values) of derivatized compounds from simple mass balance considerations are examined. Particular attention is paid to reactions that proceed by the cleavage of a carbon-containing bond and reactions that are likely to have kinetic isotope effects associated with them, such as acetylation and diazotization. Isotope fractionation processes other than those which are kinetic based are also discussed, as is the additional imprecision of the calculation of the δ-values of sample compounds inherent when derivative carbon is added. Failure to take this imprecision into account when comparing δ-values could lead to erroneous conclusions with respect to the magnitude of kinetic isotope effects caused by derivative reactions.
219 citations
TL;DR: In this paper, the advantages and disadvantages of microelectrode voltammetry have been discussed, and the advantages of using micro-electrodes in a wide range of electrochemically exotic media are discussed.
Abstract: Traditionally, electroanalytical studies employing voltammetric techniques with conventionally sized solid electrodes (e.g., 1–5 mm radius disc) have been applied in a relatively small range of conducting solvent (electrolyte) media under transient (time-dependent) conditions. In this review it is emphasized that many of the limitations associated with the use of conventional voltammetric electrodes have either been removed or greatly minimized via the use of microelectrodes (e.g., ⩽25 µm radius disc). A major feature of microelectrode voltammetry is the ready access to near steady-state conditions (radial diffusion) where the influence of the ohmic (iR) drop is considerably reduced relative to that associated with the transient response (linear diffusion). Additionally, under near steady-state conditions, electrochemically derived charging current terms are negligible. Consequently, provided that the difficulties in fabricating and maintaining microelectrodes with high quality seals and electrical contacts can be overcome, then close to the analytically ideal response may be achieved with simple two-electrode (microelectrode and reference electrode) instrumental configurations and applied d.c. waveforms. The need for more complicated potentiostatic forms of instrumentation and relatively sophisticated pulse, square-wave or alternating current techniques is, therefore, reduced. In order to emphasize the wide range of electrochemically exotic media that are now voltammetrically accessible via the use of microelectrodes, representative studies without deliberately added electrolyte (dilute electrolyte), in high resistance organic solvents such as toluene and heptane, in supercritical fluids, at very low temperatures and in the gaseous and solid-state phases are reviewed. Additionally, the very small physical size of a microelectrode sensing element enables their use in precise locations as is often required when monitoring biologically important molecules in single cells or in situations where high spatial resolution is required. Other advantages related to the small physical size of microelectrodes are also reviewed, although it is noted that the determination of oxygen in muscle tissue with a microelectrode was first reported more than 50 years ago, so that in one sense microelectrode voltammetry is not fundamentally new. The review concludes with a discussion of the advantages and disadvantages of microelectrode voltammetry.
179 citations
TL;DR: In this paper, all-solid-state ion-selective electrodes were prepared by using poly(3-octylthiophene)(POT) as solid contact material.
Abstract: All-solid-state ion-selective electrodes were prepared by using poly(3-octylthiophene)(POT) as solid contact material. A film of POT (thickness approximately 0.25 µm) was deposited on a solid substrate (platinum, gold or glassy carbon) by electrochemical polymerization of 3-octylthiophene. The POT layer was subsequently coated with an ion-selective membrane (ISM) to produce a solid-contact ion-selective electrode (SCISE), SCISEs for several ions (Li+, Ca2+ and Cl–) were prepared and investigated. The compositions of the ion-selective membranes were the same as normally used for the same ions in poly(vinyl chloride)(PVC)-based ion-selective electrodes (ISEs) with internal filling solution. The potentiometric response of the SCISEs was studied and compared with that of coated-wire electrodes (CWEs) prepared by coating the bare substrate with the same ion-selective membrane. The potentiometric slopes, limits of detection and response times of the SCISEs were similar to those of the corresponding CWEs, but the long-term stability of the potential was different for the two type of electrodes. The SCISEs exhibited a more stable electrode potential than the corresponding CWEs. However, the stability of the SCISEs was found to be influenced by the substrate material and this was studied in detail for the Ca-SCISE and Ca-CWE. For comparison, a Ca-ISE with internal filling solution was also used. By using glassy carbon as the substrate it was possible to obtain a Ca-SCISE exhibiting a standard potential that was almost as stable (ESCISE= 259.3 ± 1.3 mV, drift = 0.23 mV d–1) as for the conventional Ca-ISE (EISE= 61.4 ± 0.5 mV, drift = 0.16 mV d–) and significantly more stable than for the Ca-CWE, during a time period of 8 d. The most stable Ca-CWE, prepared by using glassy carbon as substrate, showed a potential drift of –3.8 mV d–1(ECWE= 269.6 ± 10.2 mV) during testing for 8 d. Electrochemical impedance spectrometry was used to understand the charge-transfer mechanisms of the different types of ion-selective electrodes studied. The impedance response of the electrodes was modelled by equivalent electrical circuits.
156 citations
TL;DR: In this article, the applications of chemically modified electrodes (CMEs) to the determination of trace amounts of metals and organic analytes are discussed, and the common feature of the CMEs reviewed is that prior to the voltammetric determination step the analyte is collected or accumulated onto the electrode.
Abstract: The applications of chemically modified electrodes (CMEs) to the determination of trace amounts of metals and organic analytes are discussed. The common feature of the CMEs reviewed is that prior to the voltammetric determination step the analyte is collected or accumulated onto the electrode. The accumulation step serves to preconcentrate the analytes from dilute solution, making their determination easier. It is analogous to the preconcentration step employed in stripping voltammetry at conventional electrodes. Trace analytes can be accumulated in several ways: ion-exchange, complexation, bioaccumulation, covalent attachment, and hydrophobic interaction accumulation schemes are discussed. Uses of CMEs in speciation analysis are outlined, and modified mercury-film electrodes and mercury films based on CMEs are discussed. Examples of the use of CMEs in the determination of trace metals [e.g., copper(II), lead(II), mercury(II), and silver(I) ions] and organic compounds are given.
154 citations
TL;DR: The use of low-volume (7 ml) Teflon vessels and microwave heating is described for the digestion of three marine biological tissues representing a mollusc, a fish and a crustacean.
Abstract: The use of low-volume (7 ml) Teflon vessels and microwave heating is described for the digestion of three marine biological tissues representing a mollusc, a fish and a crustacean. Freeze-dried samples (<0.1 g dry mass) and 1 ml of nitric acid were placed in 7 ml screw-topped Teflon vessels and treated using a programmed three-stage digestion. The first two stages were kept consistent (600 W, 2 min; 0 W, 2 min) and the third stage was varied from 150 to 450 W over 15–60 min to find the optimum microwave digestion conditions. Trace elements were determined using flame atomic absorption spectrometry, or electrothermal atomic absorption spectrometry when analysing samples containing very low concentrations of cadmium. Quantitative recoveries of copper, zinc and cadmium were obtained from the five marine reference materials under the following conditions: 600 W, 2 mins; 0 W, 2 min; 450 W, 45 mins.
TL;DR: In this article, a modified form of the Nikolskii-Eisenman equation is proposed in which the power dependence of the interfering ion activity is removed, and selectivity is determined for polyvinyl chloride membrane electrodes (Na+, K+, Ca2+ and NH4+) in terms of constants rather than conventional coefficients.
Abstract: A modified form of the Nikolskii–Eisenman equation is proposed in which the power dependence of the interfering ion activity is removed. Selectivity is determined for poly(vinyl chloride) membrane electrodes (Na+, K+, Ca2+ and NH4+) in terms of constants (which are valid only for the particular experimental design and conditions used) rather than conventional coefficients. These constants and other electrode parameters, such as cell constant and slope, are measured by means of an ion-selective array approach coupled with flow injection. Each electrode in the array is characterized by means of a fractional factorial calibration design and simplex optimization of the electrode parameters. The applicability of the resulting values for these parameters is demonstrated through the determination of unknowns by direct solution of the system of modified Nikolskii–Eisenman equations describing the array response. The approach is suitable for use in real-time monitoring applications where batch calibration techniques cannot easily be implemented.
TL;DR: Isotope ratio monitoring gas chromatography-mass spectrometry (irm GC-MS) was used to determine the δ13C values of individual compounds present in organic residues preserved in archaeological potsherds.
Abstract: Isotope ratio monitoring gas chromatography–mass spectrometry (irm GC–MS) was used to determine the δ13C values of individual compounds present in organic residues preserved in archaeological potsherds. The lipid fractions of the preserved organic residues were extracted from potsherds recovered from excavations performed as part of the Raunds Area Project, Northamptonshire, UK. The lipid extracts were analysed by high temperature GC and GC–MS. The leaf wax of a contemporary wild-type Brassica was also extracted and analysed for comparative purposes. Prior to irm GC–MS analysis, lipid extracts were fractionated; alkane and ketone fractions were obtained from the wild-type Brassica leaf wax, the total lipid extracts of two of the potsherds, and an archaeological soil sample using small-scale flash chromatography. The δ13C values obtained for the samples were consistent with the individual lipids investigated being of C3 plant origin. These data support the hypothesis that the lipids preserved in the potsherds were derived from a Brassica species such as cabbage. These results confirm the potential value of irm GC–MS to derive stable isotope ratios for individual lipid species of archaeological interest, and, more specifically, the potential for application of the technique to palaeodietary investigations.
TL;DR: In this article, the authors focus on current developments and future prospects in developing electrochemical stripping methodologies for on-site monitoring of trace metals, focusing on the replacement of bulky electrodes and cumbersome cells with self-contained test strips.
Abstract: This paper focuses on current developments and future prospects in developing electrochemical stripping methodologies for on-site monitoring of trace metals. Particular attention is given to the replacement of bulky electrodes and cumbersome cells with self-contained test strips. Coupled with a greatly simplified stripping operation and the introduction of high-quality, user-friendly, compact instruments, such innovative disposable metal sensors should accelerate the realization of decentralized clinical and environmental testing of toxic metals. Other stripping-based tools for in situ monitoring, including automated flow systems or remote indwelling electrodes, offer the option of continuous environmental surveillance. Recent examples, including in-office tests for blood lead levels and field screening of contaminated nuclear energy sites, will be discussed.
TL;DR: These factors combine to make the simultaneous determination of alpha-, beta-, gamma-, and delta-tocopherol, cis and trans isomers of retinol, and total carotenes by HPLC a practical technique for routine quality control and chemical and nutritional research applications.
Abstract: In the present study we describe a high-performance liquid chromatographic method for the simultaneous determination of alpha-, beta-, gamma- and delta-tocopherol, cis and trans isomers of retinol, and total carotenes in different Italian cheeses. The method involves sample extraction and saponification followed by normal-phase high-performance liquid chromatography (HPLC). Monitoring of the absorbance and fluorescence is achieved using a programmable spectrophotometer and a programmable spectrofluorometer connected in series. The proposed method, which has the advantage of being able to evaluate simultaneously the fat-soluble vitamins considered by us in this work, has been applied to some Italian cheeses (Percorino romano, Taleggio, Provolone, and Caciotta) and milk samples (cows', goats', and sheep milk). The HPLC analytical procedure provides excellent reproducibility of results and is less subject to interferences from the sample matrix than wet chemical techniques. These factors combine to make the simultaneous determination of alpha-, beta-, gamma-, and delta-tocopherol, cis and trans isomers of retinol, and total carotenes by HPLC a practical technique for routine quality control and chemical and nutritional research applications.
TL;DR: A new biocomposite, based on the incorporation of the enzyme tyrosinase into a graphite-epoxy resin matrix, was used for the effective biosensing of phenolic compounds and offers convenient quantification for various phenolic substrates.
Abstract: A new biocomposite, based on the incorporation of the enzyme tyrosinase into a graphite-epoxy resin matrix, was used for the effective biosensing of phenolic compounds. The enzyme retains its bioactivity on confinement in the epoxy resin environment. This renewable (polishable) and rigid bioprobe offers convenient quantification for various phenolic substrates. The fast response (steady-state time = 25 s) accrues from the close proximity of the enzyme and graphite sites. The influence of various experimental variables was explored for optimum biosensing performance. Flow-injection monitoring of phenolic compounds at a rate of 50 samples h–1 yielded a detection limit of 1×10–6 mol l–1 and a relative standard deviation of 1.4%(n= 40).
TL;DR: Methods of antibody immobilization on crystals and several applications are reported including microgravimetric immunoassays, microbial toxins and other contaminants.
Abstract: The development of piezoelectric (PZ) devices as immunosensors is reviewed. The recent advances in sensor design have stimulated great interest in PZ technology and facilitated diverse applications in a variety of matrices. Methods of antibody immobilization on crystals and several applications are reported including microgravimetric immunoassays, microbial toxins and other contaminants.
TL;DR: In this article, the electrochemical behavior of thiocholine at screen-printed carbon electrodes chemically modified with cobalt phthalocyanine was investigated, and the optimum potential for amperometric studies was found to be + 0.1 V.
Abstract: Cyclic voltammetry was used to investigate the electrochemical behaviour of thiocholine at screen-printed carbon electrodes chemically modified with cobalt phthalocyanine. Cyclic voltammograms exhibited one anodic peak (Ia) and two cathodic peaks (Ic and IIc) in the potential range –0.8–+0.3 V between pH 5.0 and 12.0. Peak Ia is considered to result from the electrocatalytic oxidation of the thiol moiety to produce the corresponding disulfide; peak Ic is likely to be the electrocatalytic reduction of the disulfide back to the original thiol species. Peak IIc is probably due to a reduction process occurring in the macrocyclic phthalocyanine molecule. Hydrodynamic voltammetry was performed in 0.05 mol dm–3 phosphate buffer (pH 8.0) containing thiocholine; one well-defined anodic wave was obtained. From this, the optimum potential for amperometric studies was found to be +0.1 V. Calibration studies were performed using amperometry in stirred solution; a linear response was obtained over the range 5.0 × 10–7–4.8 × 10–5 mol dm–3. It should be possible to use these screen-printed electrodes as the basis of a pesticide sensor.
TL;DR: In this paper, it is proposed that the catalytically active species are surface-bound oxyruthenium groups, and that the latter mediate substrate oxidation via a process of cyclic heterogeneous redox catalysis.
Abstract: The oxidation of glucose at RuO2–carbon paste composite electrodes in alkaline solution was examined. It is proposed that the catalytically active species are surface-bound oxyruthenium groups, and that the latter mediate substrate oxidation via a process of cyclic heterogeneous redox catalysis. The latter process can be described in terms of a Michaelis–Menten mechanism involving the formation of a substrate–catalyst complex which subsequently decomposes to form product and pre-catalyst; the latter can subsequently be regenerated electrochemically. Hence the oxyruthenium surface groups operate as inorganic enzyme analogues.
TL;DR: In this paper, three time-resolved infrared (TRIR) spectrometers are described based on a line-tunable CO laser, a continuously tunable semiconductor diode laser and a modified and adapted dispersive IR spectrometer with Nernst glower.
Abstract: Three time-resolved infrared (TRIR) spectrometers are described These instruments are based on (i) a line-tunable CO laser (2000–1550 cm–1), (ii) a continuously tunable semiconductor diode laser (approximately 2250–1900 cm–1) and (iii) a modified and adapted dispersive IR spectrometer with Nernst glower (or globar) which, in principle, could cover all of the mid-IR region The spectrometers differ in their inherent signal-to-noise ratio and their response Although the ultimate performance can be achieved with the CO laser, the instruments are complementary, each with its own advantages The performances of the three TRIR spectrometers were compared in a number of applications in organometallic photochemistry, including the IR detection of molecules in electronically excited states, the kinetic behaviour of intermediates in the reaction of (η5-C5H5)M(CO)4 compounds (M = V, Nb and Ta), an IR study of the photochemical reaction of CpMn(CO)3 within polyethylene film and solvent interactions in supercritical xenon solution and the detection of W(CO)5Xe
TL;DR: In this article, the pros and cons of advanced electroanalytical techniques versus modern atomic absorption spectrometric, inductively coupled plasma atomic emission spectrum analyzer and inductive coupled plasma mass analyzer are discussed.
Abstract: The challenge for the chemical industry in the 1990s and beyond is: (i) innovation and profitability, and (ii) environmental protection and safety. This is also true for analyses in which the needs are for simple, reliable and viable techniques. Analyses are costly, running costs especially can be very high. There are still too many poor quality analyses. The task of the analytical chemist is to choose the most appropriate procedure in order that the desired information about the particular material of interest can be provided. The pros and cons of advanced electroanalytical techniques versus modern atomic absorption spectrometric, inductively coupled plasma atomic emission spectrometric and inductively coupled plasma mass spectrometric methods commonly in use in industrial and technical laboratories are discussed. The features that make electroanalytical methods competitive techniques are: the very large useful concentration range (from 1 to 10–10 mol l–1 and less for inorganic, organometallic and organic species), the larger linear ranges than many commonly used instrumental techniques, the ability to assay dissolved and solid samples, the ability to speciate on the basis of complex lability and to distinguish between different states of valency, and the immunity of the matrix to samples with high ionic content, etc. These are illustrated by practical examples in this work. However, the still limited commercial availability of highly automated electroanalytical instrumentation is a serious limitation for the large-scale routine use of these methods in the industrial and control laboratory.
TL;DR: In this article, a potentiometric ion-selective electrode based on a solid conducting poly(pyrrole) contact and neutral carrier tri-n-dodecylamine membrane was developed.
Abstract: A potentiometric ion-selective electrode based on a solid conducting poly(pyrrole) contact and neutral carrier tri-n-dodecylamine membrane was developed. The effect of the poly(pyrrole) doping anion on the characteristic of the sensor is presented and discussed. The ion-selective H+ sensitive electrode with a solid poly(pyrrole) contact is characterized by having a good stability over both short and long periods of time. Selectivity coefficients for this electrode are slightly better than those for internal solution electrodes. Stability is also improved especially when compared with coated wire type electrodes. Responses are fast and nearly Nernstian within the pH range 2–12. All solid-state sensors with plastic tri-n-dodecylamine were used for pH determinations in blood serum.
TL;DR: In this paper, fuel particles from Chernobyl were investigated with respect to structure using scanning electron microscopy and composition using X-ray microanalysis and γ-, β- and α-spectrometry.
Abstract: Fuel particles released during the accident at the Chernobyl reactor (1986) and during the operation at the Windscale (UK) pile (1952–57) were investigated with respect to structure using scanning electron microscopy and composition using X-ray microanalysis and γ-, β- and α-spectrometry. Particles from Chernobyl released at a relatively high temperature have in general a compact crystalline-like structure with a relatively uniform surface layer of uranium. Aggregates consisting of small-sized (1–2 µm) spherical uranium granulates were also identified. These granulates were similar to particles identified in Norway. About 25% of the particles investigated were covered by lead, which is attributed to a release during the last stage of the accident. Particles from Windscale released under low-temperature conditions have a flake-like layered structure, varying in size (10–250 µm) and activity levels. Thus the travelling distance for these particles may be substantially longer than previously anticipated for spheres. The surfaces of these particles were also composed of uranium. The mobility of radionuclides associated with fuel particles of different structure is believed at least initially to be low when compared with those associated with condensed particles or with ionic tracers. However, mobilization of especially 90Sr due to weathering of hot particles should be expected in the years to come.
TL;DR: The evolution of this field and perennial issues concerning these sensors are reviewed from the author's perspective in this article, where the authors present a survey of the field of field effect transistors.
Abstract: Ion sensitive field-effect transistors have been researched for over twenty years. Several hundred papers have been written about them and they are beginning to appear on the commercial market. The evolution of this field and perennial issues concerning these sensors are reviewed from the author's perspective.
TL;DR: In this article, a method and apparatus for the detection of hydrazine, monomethylhydrazine and 1,1-dimethylhydrazines in air (or other gas medium) or in an aqueous solution is presented.
Abstract: A method and apparatus for the detection of hydrazine, monomethylhydrazine, 1,1-dimethylhydrazine in air (or other gas medium) or in an aqueous solution. The detection is accomplished by introducing a stream of air, or other gas medium, or aqueous solution suspected of containing hydrazine, monomethylhydrazine, 1,1-dimethylhydrazine or mixtures thereof into a pH controlled reagent solution containing an aromatic dicarboxaldehyde to react with the hydrazine, monomethylhydrazine, 1,1-dimethylhydrazine or mixtures thereof, respectively, and by exposing the reacted reagent solution to an excitation wavelength range and monitoring an emission from the exposed reagent solution at an emission wavelength range to detect the presence of a hydrazine derivative, monomethylhydrazine derivative, 1,1-dimethylhydrazine derivative, or mixtures thereof (i.e. a derivative formed by the reaction between hydrazine, monomethylhydrazine, 1,1-dimethylhydrazine and the aromatic dicarboxaldehyde) indicating the presence of hydrazine, monomethylhydrazine, 1,1-dimethylhydrazine or mixtures thereof within the stream of air or other gas medium or aqueous solution.
TL;DR: In this article, an array of closely spaced interdigitated microelectrodes was applied to the sensitive detection of reversible redox couples, where the measurement is based on the redox cyclization between the adjacent microband electrodes of the IDA, when both the respective oxidation and reduction potential are applied at the electrode pairs.
Abstract: An array of closely spaced interdigitated microelectrodes was applied to the sensitive detection of reversible redox couples. The measurement is based on the redox cyclization between the adjacent microband electrodes of the interdigitated array (IDA), when both the respective oxidation and reduction potential are applied at the electrode pairs. The multiple oxidation and reduction result in an increased generation of current. The steady-state current of mediators, such as phenazine methosulfate, hexacyanoferrate(II), pyrocatechol, benzoquinone and p-aminophenol, was amplified by a factor of 10–20 compared with the current of single electrodes. The high collection efficiency enabled this signal amplification rate to be obtained. The detection limit for p-aminophenol was 100 nmol l–1. The IDA sensor was applied to the determination of alkaline phosphatase and β-galactosidase activity by detecting enzymatically generated p-aminophenol.
TL;DR: A method was developed to determine the flavanols prodelphinidin B3, procyanidinB3, (+)-catechin, and (-)-epicatechin by high-performance liquid chromatography, using dual-channel electrochemical detection, which offered improved sensitivity and selectivity compared with ultraviolet detection.
Abstract: A method was developed to determine the flavanols prodelphinidin B3, procyanidin B3, (+)-catechin, and (–)-epicatechin by high-performance liquid chromatography, using dual-channel electrochemical detection. This method was especially suited to the direct analysis of beer samples and to analysis of acetone extracts of barley samples, and was capable of determining proanthocyanidins and catechins at levels of 0.1–5.0 mg l–1. The use of dual-channel electrochemical detection also enabled unambiguous peak identification by measurement of collection efficiencies. This method offered improved sensitivity and selectivity compared with ultraviolet detection, and sample preparation procedures were greatly simplified. The method was applied to the comparison of stabilized and unstabilized lagers, and to the analysis of different barley varieties grown in Ireland.