Jacqui L. Adcock

Advances in the use of acidic potassium permanganate as a chemiluminescence reagent: a review.

We review the analytical applications of acidic potassium permanganate chemiluminescence published since our previous comprehensive review in mid-2007 to early 2013. This includes a critical evaluation of evidence for the emitting species, the influence of additives such as polyphosphates, formaldehyde, sulfite, thiosulfate, lanthanide complexes and nanoparticles, the development of a generalized reaction mechanism, and the use of this chemistry in pharmaceutical, clinical, forensic, food science, agricultural and environmental applications.

Determination of selected neurotransmitter metabolites using monolithic column chromatography coupled with chemiluminescence detection

The oxidation of selected clinically important neurotransmitter metabolites with acidic potassium permanganate in the presence of polyphosphates evokes chemiluminescence of sufficient intensity to enable the sensitive determination of these species. Limits of detection for 5-hydroxyindole-3-acetic acid (5-HIAA), vanilmandelic acid (VMA; alpha,4-dihydroxy-3-methoxybenzeneacetic acid), 4-hydroxy-3-methoxyphenylglycol (MHPG), homovanillic acid (HVA, 4-hydroxy-3-methoxyphenylacetic acid) and 3,4-dihydroxyphenylacetic acid (DOPAC) were between 5x10(-9) and 4x10(-8)M, using flow-injection analysis methodology. In addition, we demonstrate the rapid determination of homovanillic acid and 5-hydroxyindole-3-acetic acid in human urine - without the need for extraction procedures - using monolithic column chromatography with chemiluminescence detection.

Selective concentration of EPA and DHA using Thermomyces lanuginosus lipase is due to fatty acid selectivity and not regioselectivity

The selectivity of anchovy oil hydrolysis was optimised for Thermomyces lanuginosus lipase, so that docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) were concentrated and partially separated from each other. Enzyme concentration and pH control were important factors for effective hydrolysis. Monitoring percent hydrolysis using capillary chromatography with flame ionisation detector (Iatroscan) and fatty acid selectivity using gas chromatography (GC) indicated that during hydrolysis DHA primarily remained on the glycerol backbone, while EPA was progressively removed. (13)C nuclear magnetic resonance (NMR) data showed that selectivity of hydrolysis was primarily due to fatty acid selectivity and not regioselectivity, with hydrolysis from both sn-1,3 and sn-2 sites being equally favoured.

Peak Modeling Approach to Accurate Assignment of First-Dimension Retention Times in Comprehensive Two-Dimensional Chromatography

Modeling of first-dimension retention of peaks based on modulation phase and period allows reliable prediction of the modulated peak distributions generated in the comprehensive two-dimensional chromatography experiment. By application of the inverse process, it is also possible to use the profile of the modulated peaks (their heights or areas) to predict the shape and parameters of the original input chromatographic band (retention time, standard deviation, area) for the primary column dimension. This allows an accurate derivation of the first-dimension retention time (RSD 0.02%) which is equal to that for the non-modulated experiment, rather than relying upon the retention time of the major modulated peak generated by the modulation process (RSD 0.16%). The latter metric can produce a retention time that differs by at least the modulation period employed in the experiment, which displays a discontinuity in the retention time vs modulation phase plot at the point of the 180 degrees out-of-phase modulation. In contrast, the new procedure proposed here gives a result that is essentially independent of modulation phase and period. This permits an accurate value to be assigned to the first-dimension retention. The proposed metric accounts for the time on the second-dimension, the phase of the distribution, and the hold-up time that the sampled solute is retained in the modulating interface. The approach may also be based on the largest three modulated peaks, rather than all modulated peaks. This simplifies the task of assigning the retention time with little loss of precision in band standard deviation or retention time, provided that these peaks are not all overloaded in the first or second dimension.

Emitting Species in Chemiluminescence Reactions with Acidic Potassium Permanganate: A Re-Evaluation Based on New Spectroscopic Evidence

The reaction of acidic potassium permanganate with a wide range of compounds is known to produce a broad red emission, and there is strong evidence for an excited manganese(II) emitting species. Nevertheless, numerous researchers have proposed other emitters for reactions with acidic potassium permanganate, particularly for systems where fluorescent compounds were present, either as enhancers or reaction products. We have examined many reactions of this type and found that, in most cases, the same red emission was produced. There were, however, some exceptions, including the oxidation of dihydralazine, certain thiols and sulphite (each in the presence of an enhancer).

Comparison of homoleptic and heteroleptic 2,2′-bipyridine and 1,10-phenanthroline ruthenium complexes as chemiluminescence and electrochemiluminescence reagents in aqueous solution

We have conducted a comprehensive comparative study of Ru(bipy)(3)(2+), Ru(bipy)(2)(phen)(2+), Ru(bipy)(phen)(2)(2+), and Ru(phen)(3)(2+) as chemiluminescence and electrochemiluminescence (ECL) reagents, to address several previous conflicting observations and gain a greater insight into their potential for chemical analysis. Clear trends were observed in many of their spectroscopic and electrochemical properties, but the relative chemiluminescence or ECL intensity with a range of analytes/co-reactants is complicated by the contribution of numerous (sometimes opposing) factors. Significantly, the reversibility of cyclic voltammetric responses for the complexes decreased as the number of phenanthroline ligands was increased, due to the lower stability of their ruthenium(III) form in the aqueous solvent. This trend was also evident over a longer timescale when the ruthenium(III) form was spectrophotometrically monitored after chemical oxidation of the ruthenium(II) complexes. In general, the greater stability of Ru(bipy)(3)(3+) resulted in lower blank signals, although this effect was less pronounced with ECL, where the reagent is oxidised in the presence of the co-reactants. Nevertheless, this shows the need to compare signal-to-blank ratios or detection limits, rather than the more common comparisons of overall signal intensity for different ruthenium complexes. Furthermore, our results support previous observations that, compared to Ru(bipy)(3)(2+), Ru(phen)(3)(2+) provides greater ECL and chemiluminescence intensities with oxalate, which in some circumstances translates to superior detection limits, but they do not support the subsequent generalised notion that Ru(phen)(3)(2+) is a more sensitive reagent than Ru(bipy)(3)(2+) for all analytes.

Precision milled flow-cells for chemiluminescence detection

Novel flow-cells with integrated confluence points and reaction channels designed for efficient mixing of fast chemiluminescence systems were constructed by machining opposing sides of a polymer chip and sealing the channels with transparent epoxy-acetate films. A hole drilled through the chip provided the conduit from the confluence point on one side to the centre of the reaction zone on the other side, allowing rapid presentation of the reacting mixture to the photodetector. The effectiveness of each flow-cell was evaluated by comparing the chemiluminescence intensity using flow injection analysis methodology, and examining the distribution of light emanating from the reaction zone (captured by photography in a dark room) when the reactants were continuously merged. Although previously reported chemiluminescence detectors constructed by machining channels into polymers have almost exclusively been prepared using transparent materials, we obtained far greater emission intensities using an opaque white chip with a thin transparent seal, which minimised the loss of light through surfaces not exposed to the photomultiplier tube. Furthermore, this approach enabled the exploration of reactor designs that could not be incorporated in traditional coiled-tubing flow-cells.

Any old radical won't do: An EPR study of the selective excitation and quenching mechanisms of [Ru(bipy)3]2+ chemiluminescence and electrochemiluminescence

[Ru(bipy)] chemiluminescence: The mechanisms governing the selectivity of the luminescence of the [Ru(bipy)] complex (bipy=2,2′-bipyridyl) were investigated using continuous flow EPR spectroscopy. The radical intermediates of substrates thought to evoke or quench the emission from this reagent were characterized in the light-producing pathway.

Chemiluminescence spectra for the oxidation of sulphite in the presence of fluorescent and non-fluorescent enhancers

The spectral distribution of chemiluminescence provides key evidence in the elucidation of the reaction mechanism and emitting species. We have collected chemiluminescence spectra for the oxidation of sodium sulphite and captopril in the presence of a range of fluorescent and non-fluorescent enhancers. This evidence was used to evaluate several previously proposed light-producing pathways, and revealed some new approaches to enhance the chemiluminescent oxidation of sulphite and thiol compounds. Chemiluminescence reactions between sulphite and permanganate produce two potential emitters: one derived from the oxidation of sulphite (in some cases via energy transfer to a more efficient luminophore) and another derived from the reduction of permanganate. This second light-producing pathway is rarely considered in discussions on the chemiluminescent oxidation of sulphite, but can make a significant contribution to the overall emission. Non-fluorescent enhancers of sulphite chemiluminescence result in several distinct spectral distributions and, contrary to previous postulation, these reactions are unlikely to lead to the same emitting species. Non-fluorescent enhancers of sulphite chemiluminescence can also significantly increase the weak emission from the oxidation of thiol compounds such as captopril.

Chemiluminescence detectors for liquid chromatography

In this tutorial we describe the construction of chemiluminescence detectors for high performance liquid chromatography (HPLC), comprising the components required to deliver the chemiluminescence reagent, a coiled-tubing flow cell, photomultiplier tube and detector housing, and various options for data acquisition. We also discuss two state-of-the-art commercially available chemiluminescence detectors for HPLC and other flow analysis methodology.