Gillian M. Greenway

Occurrence, mechanisms and analytical applications of electrogenerated chemiluminescence. A review

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.

The use of a novel microreactor for high throughput continuous flow organic synthesis

Abstract The aim of this study was to investigate the performance characteristics of a flow injection microreactor with reference to both the chemistry and reactor design using a model system, the established synthesis of 4-cyanobiphenyl based on a modified Suzuki coupling of an aryl halide and an organoboron compound. The catalytic reaction was carried out in micro-channels (300 μm wide and 115 μm deep) etched into glass and sealed with a top plate. The mobility of the reagent solutions was achieved using electroosmotic flow (EOF) assisted by the incorporation of a microporous silica structure within the microreactor channels, which acted as both a micro-pump and an immobilisation technique for the catalyst bed (1.8% palladium on silica). The yield of 4-cyanobiphenyl was determined by GC–MS. The synthesis of 4-cyanobiphenyl at room temperature in a flow injection microreactor, using a supported catalyst, without the addition of a base gave a product yield of 67±7% ( n =6). This was achieved by injecting 4-bromobenzonitrile for 5 s, with a 25-s injection interval, into a continuous stream of phenylboronic acid. A series of injections were performed over a 25-min period and the product collected for analysis. Palladium contamination in the crude product was found to be in the range of 1.2–1.6 ppb, determined using ICP–MS, indicating a low leach rate from the immobilised catalyst. A conventional laboratory batch scale method was also performed for the same synthesis using the identical conditions as those used in the flow injection microreactor, with and without the addition of a base, at both room and elevated temperatures (75–80°C) in an inert atmosphere under reflux for 8 h. The product yield for the non-optimised bulk reaction was 10% (determined by GC–MS), significantly lower than with the flow injection microreactor illustrating the potential of microreactors for clean efficient synthesis.

Determination of L-ascorbic acid in fruit and vegetable juices by flow injection with immobilised ascorbate oxidase

Ascorbate oxidase was immobilised on cyanogen bromide activated-Sepharose 4B and incorporated in a flow-injection system with amperometric detection at a glassy carbon electrode at +0.6 V. On passage through the immobilised ascorbate oxidase a fraction of the L-ascorbic acid was converted into dehydroascorbic acid and the decrease in signal was measured. This could be directly related to the amount of L-ascorbic acid present. The calibration graph was linear over the range 0-400 ng ml(-1) with a correlation coefficient of 0.9994. The detection limit (2 sigma) in phosphate buffer (0.08 M, pH 5.5) was 4.0 ng ml(-1). The relative standard deviation for a 200 ng ml(-1) standard was 1.0% (n = 10) and the sampling throughput was 30 samples h(-1). The method was used for the simple and rapid determination of L-ascorbic acid in fruit and vegetable juice.

Electrogenerated chemiluminescent determination of codeine and related alkaloids and pharmaceuticals with tris(2,2′-bipyridine)ruthenium(II)

This work describes a novel and sensitive method for the determination of codeine, heroin, and dextromethorphan, using flow injection with electrogenerated chemiluminescence (ECL). The method is based on the ECL reaction of tris(2,2′-bipyridine)ruthenium(II)[Ru(bpy)22+] with tertiary amino groups. The factors affecting the determinations were investigated and possible reaction inhibitors, such as phenolic functional groups, were identified. Linear calibrations were obtained for signal (mV)versus concentration (µmol l–1) in the range 0.1–1.0 µmol l–1 with percentage relative standard deviations of less than 5%(n= 5). The 5σ limits of detection were calculated as 15, 45 and 44 nmol l–1 for codeine, heroin, and dextromethorphan, respectively.

Electrogenerated chemiluminescent determination of pyruvate using tris(2,2′-bipyridine)ruthenium(II)

A novel method for the sensitive and selective determination of pyruvate is presented, using an electrogenerated chemiluminescence (ECL) reaction of tris(2,2′-bipyridine)ruthenium(II) in the presence of cerium(III) nitrate, increasing the number and diversity of analytes currently detected by this ECL reaction. Various experimental conditions have been optimized, leading to a calibration over three-orders of magnitude of concentration, with a detection limit of 3.1 × 10–7 mol l–1(27 ppb). Simple methods have also been developed to suppress the interference effects of various compounds that are expected to be present in potential samples from fermentation media.

Rapid arsenic speciation using ion pair LC-ICPMS with a monolithic silica column reveals increased urinary DMA excretion after ingestion of rice.

Rapid separation of arsenic species is described by application of a commercial monolithic silica column (Chromolith™). Arsenic species were separated within 3 min, greatly reducing the time required with conventional columns. The separation was achieved by ion-pair liquid chromatography using 2.5 mM tetrabutylammonium bromide, 10 mM phosphate buffer (pH 5.6) and 1.0% (v/v) methanol as the mobile phase. Detection limits of 0.107, 0.084, 0.120, 0.121 and 0.101 μg L−1 As for As(III), arsenobetaine (AsB), dimethylarsinate (DMA), monomethylarsonate (MMA) and As(V), respectively were achieved. The precision of the method, based upon analysis of 15 μg L−1 As, was better than 5.9% for all species. The technique was applied to the speciation analysis of urine and food samples in an ingestion experiment to investigate the effect of rice consumption on arsenic exposure in humans. For the first time this study reveals that ingestion of American long grain rice, which is widely consumed in the UK and purchased from a local supermarket, significantly increases the excretion of DMA in human urine. This is consistent with a recent study which reported that DMA was the predominant arsenic species in rice from the USA, which also happened to contain the highest mean arsenic level in the grain compared to rice grown in Bangladesh and India.1

Heavy metal speciation in the composting process

Composting is one of the more efficient and environment friendly methods of solid waste disposal and has many advantages when compared with landfill disposal on which the UK and Ireland are currently heavily dependent. Composting is a very complicated process involving intensive microbial activity and the detailed mechanisms of the process have yet to be fully understood. Metal speciation information can provide an insight into the metal-microbial interaction and would help in the evaluation of the quality of compost. This would facilitate the exploitation of composts in remediation of heavy metal contaminated land. In this work a systematic approach to metal speciation in compost has been taken by applying the three-step method for operationally defined metal speciation of soils and sediments, developed by the European Commissions Standards, Measurement and Testing Programme to monitor the change in metal speciation with time (up to 106 days) for four different waste composting processes. The results have shown that in general metals become less available for the first extraction step as the composting process proceeds. This implies that composting tends to redistribute the metals from more labile forms to more fixed forms which may explain why the application of composts could be useful for with heavy metal contaminated land. There are exceptions to this trend and in some cases, certain metals appear to behave differently depending on the source of the compost.

Interfacing microchip capillary electrophoresis with inductively coupled plasma mass spectrometry for chromium speciation

A microchip based electrophoresis separation system was interfaced with inductively coupled plasma mass spectrometry to provide rapid elemental speciation capabilities. The feasibility of this hyphenated method for elemental speciation was demonstrated by the on-line electrophoretic separation of CrIII and CrVI within 30 s using an 8 cm long separation channel etched in a glass base.

Relationship between structural attributes and observed electrogenerated chemiluminescence (ECL) activity of tertiary amines as potential analytes for the tris(2,2-bipyridine)ruthenium(II) ECL reaction. A review

The relationship between the structural attributes of various amine compounds and their observed electrogenerated chemiluminescence (ECL) activity with the tris(2,2-bipyridine)ruthenium(II) ECL reaction was examined, with a view to the determination of these compounds. This was carried out by first examining the reaction mechanism and then predicting the ECL activity of certain classes of compounds by considering the stability of intermediates, and drawing general conclusions by comparing the observations obtained by the authors and other workers. The molecular geometry and alternative anodic reactivity and their effect on ECL activity are discussed and results for the ECL activity of a range of local anaesthetics are presented.

The determination of food colours by HPLC with on-line dialysis for sample preparation

Abstract A simple method is reported for the determination of synthetic dyes in sugar rich foods. Extraction of the dyes is achieved with water at room temperature. The extract is then centrifuged or filtered prior to dialysis using an ASTED system. A portion of the dialysate is transferred directly to the HPLC column without further concentration, where adequate sensitivity is achieved for the determination of dyes in a range of foods. Samples studied include boiled sweets, fruit gums, lemon curd, jelly, blancmange and soft drinks.