Electrochemiluminescenct Detection Of Methamphetamine And-Free PDF

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Direct detection of amphetamine type stimulants ATS including methylamphetamine MA. in street samples and biological matrices without the need for pretreatment or extraction is a. great challenge for forensic drug analysis Electrochemical techniques such as. electrochemiluminescence ECL are promising tools for this area of analysis This. contribution focuses on the electrochemical and photochemical properties of Ru bpy 3 2. nafion composite films and their subsequent use for the detection of ATS in particular MA. Under optimised conditions the response linearly increased with the concentration over the. concentration range 50 pM MA 1 mM while an equivalent dynamic range was obtained. for amphetamine with a correlation coefficient of 0 9903 and 0 9948 respectively The ECL. signal was monitored at 620 nm representing the max for the Ru bpy 3 2 nafion composite. films This wavelength is shifted by approximately 15 nm compared to the photoexcited max. for the same system The modified films were formed by direct interaction with the electrode. surface without the need for surface modification or chain linkers This is a major advantage. for the fabrication of any sensor as it reduces the synthesis times resulting in more. economically and cheaper production costs This technique is simple rapid selective and. sensitive and shows potential for the high throughput quantitation of ATS as well as. possibilities for adaptation with other techniques such as FIA or LC systems. INTRODUCTION, Methamphetamine MA has received much attention as an amphetamine type stimulant. ATS drug that even in small amounts has a strong impact on the central nervous system. causing mental alertness and other symptoms 1 2 It has been used to treat obesity and. alcoholism but it can cause physiological and psychological effects such as increased heart. rate and blood pressure affecting body temperature attention and mood It has also been. reported as a widely abused drug in many areas of the world 3 4 As a result the determination. of MA has attracted much attention Many chromatographic methods have been utilised for. the identification and quantification of MA including gas chromatography GC 5 HPLC 6. GC MS 7 LC MS 8 solid phase microextraction capillary electrophoresis9 and capillary. electrophoresis electrochemical ECL 10 The demand for portable rapid and quantitative. methods for the determination and analysis of illicit substances have been highlighted as the. concerns over methamphetamine and amphetamine usage11 increase with growing concern. over the situation within Europe 12 Techniques which have the ability to street samples and. biological matrices without the need for pre treatment or extraction is a great challenge for. forensic drug analysis and this contribution will try to address this need through the. application of ECL to the analysis of amphetamine and methampethamine Current. chromatographic methods generally involve time consuming derivatisation steps13 15 and or. extraction methods for biological samples 16 In this study we present a simple and rapid ECL. method as proof of concept for the detection and analysis of amphetamine and. methamphetamine 17, ECL has been the subject of extensive study for the past three decades 18 22 The. production of light from intermediates generated during electrolysis occurs when the. energy liberated by reaction between the electrogenerated precursors is sufficient to. generate a product in an electronically excited form 23 Studies of inorganic ECL have. been dominated by transition metal complexes 24 25 particularly ruthenium poly pyridyl. species e g those of the general formula Ru L 32 e g where L 2 2 bipyridine 26 or. 4 7 diphenyl 1 10 phenanthroline 27 This is due to the attractive photophysical and. electrochemical properties that these compounds typically exhibit. ECL combines the inherent sensitivity selectivity and linear range advantages of. chemiluminescence methods with increased temporal and spatial control over the. chemiluminescent reaction making ECL a powerful analytical tool particularly when the. surface may be modified to tune the ECL properties Systems utilising both organic and. inorganic complexes have been developed 18 28 29 ECL usually involves the reaction of. electrogenerated species that react to form excited states usually via an energetic redox. reaction 18 Thus ECL can also be utilized to probe electron and energy transfer processes. at electrified interfaces 30 31 As such it has been used for the detection of alkylamines. NADH hydrazine amino acids biomolecules and a variety of pharmaceutical. compounds 24 32 38, For example one of the many applications of Ru bpy 3 2 ECL is the detection of amino. acids 34 and amine containing substances 35 36 A key advantage of ECL is that is offers the. possibility of detecting very low concentrations of amino acids i e sub nM with good. reproducibility by detecting both the current and light responses Most detection systems. involve the solution phase detection of amino acids or amine containing substances by ECL. and flow injection analysis FIA 37 However changes in the micro environment of solution. based analysis including changes in viscosity temperature ion strength and pH can. influence the resultant ECL For example Jackson et al 37 demonstrated that Ru bpy 3 3. generated in situ undergoes a chemiluminescent reaction with free amino acids In agreement. with previous studies the chemiluminescence was maximized at pH values near the pKa of. the N terminal amine site 34 Similar results were obtained for ATS when electrochemically. analysed in solution phase approaches 35 36, There are several disadvantages to using solution phase reactants including loss of signal due. to diffusion of the ECL reagent out of the detection zone the limited ability to repeatedly. electrochemically cycle an individual luminophore and high reagent consumption To. overcome these problems considerable effort has been invested in immobilizing the. Ru bpy 3 2 reagent on an electrode 34 37 This kind of reagentless ECL sensor can avoid. external addition of reagents and can also overcome the limitation of reagent consumption. since the Ru bpy 3 3 is regenerated in situ, In this study we report on the electrochemical photophysical and.
electrochemiluminescent properties of Ru bpy 3 2 Nafion composite films modified on. glassy carbon electrodes The surface coverage of the complex about 7 5 x10 9 mol cm 1. which is consistent with that expected for a composite film The Ru2 3 couple is. electrochemically reversible and the surface coverage is very stable over extended periods. under voltammetric cycling Significantly emission is observed from the modified. electrodes following photoexcitation or reaction of the electrochemically generated Ru 3. species with MA This work has shown that the ruthenium composite film is suitable for. the use in ECL detection of MA and could be extremely helpful in the development of. portable quantitative systems for the detection of ATS over a forensically relevant linear. range minimizing the requirement for sample preparation Ideally this system could be. used in combination to exploit this technology for a variety of illicit substances and this is. an are in which future work would focus,EXPERIMENTAL SECTION. Materials All the materials were purchased from Sigma Aldrich and were used as received. with the exception of the interferent starch BDN Laboratory Supplies and the high purity. methoal Fluka The controlled substances MA and amphetamine were purchased from. Sigma Aldrich in their salt forms All concnentrations of these controlled ATS are quoted as. free base concentrations, Methods Working electrodes were prepared by polishing with alumina 1 0 m 0 3 m. on a felt pad followed by sonication in distilled deionized water for 30 min Where. appropriate working electrodes were modified by applying a drop 15 L of an ethanolic. solution of the Ru bpy 3 2 Nafion film to the electrode surface Stock solutions of Nafion. Ru bpy 3 2 were prepared by dissolving 1 mg of Ru bpy 3 2 in 2 mL methanol Then 200. L of this solution was diluted in 1 8 mL of methanol and 200 L of Nafion 5 w v mixture. of low molecular weight alcohols was added The mediator was found to precipitate at. higher concentrations The modified electrodes were then allowed to dry in the dark for 10 to. 12 hours The surface coverage was determined by graphical integration of background. corrected cyclic voltammograms 5 mV s 1 In all cases the surface coverage were. typically 7 5 x10 9 mol cm 1 All solutions were deoxygenated using nitrogen or argon prior. to measurement, Electrochemical experiments were performed in a standard electrochemical cell using a CH. instruments Memphis TN model 602E potentiostat Cyclic Voltammetry experiments were. carried out using a 3 mm diameter glassy carbon working electrode in a conventional three. electrode assembly using a platinum flag as the counter electrode Potentials were measured. versus a standard Ag AgCl aqueous reference electrode 3M KCL Measurements involving. simultaneous detection of light and current utilised a CH instrument model 602E connected. to a Hamamatsu H6780 20 PMT powered at 600 V During the experiments the cell was. kept in a light tight box in a specially designed holder where the working electrode was. positioned directly opposite to the fibre optic bundle the other end of which was coupled to. the PMT Emission spectra were recorded on a Cary Eclipse Fluorescence Spectrophotometer. with an excitation and emission slits of 5 nm 800 V PDA power and a scan rate of 120. nm min All other reagents used were of analytical grade and all solutions were prepared in. milli Q water 18 m cm,RESULTS AND DISCUSSION, Electrochemical properties of the glassy carbon electrode modified with the composite film. containing Ru bpy 3 3 in Nafion, The electrochemical behaviour of the Ru bpy 3 2 when surface confined within a nafion.
film on a GC electrode was examined using cyclic voltammetry Figure 1 shows the. typical voltammetric behaviour of the ruthenium modified electrode in 0 1 M H2SO4 The. surface coverages were determined by graphical integration of background corrected. cyclic voltammograms 5 mV s 1 and were typically about 7 5 x10 9 mol cm 1 which is. consistent with that expected for a composite film 24 25 27 The anodic and cathodic peaks. corresponding to the Ru 2 3 couple are clearly visible at 1125 mV and 1075 mV. respectively The formal potential E is within 25 mV of that found for the complex. dissolved in acetonitrile where the working electrode is a platinum microdisk 17 This. observation indicates that the electron density of the metal centre does not change. significantly upon surface immobilisation and that the composite film is highly solvated. In addition the peak to peak separation between anodic and cathodic waves is close to. zero at low scan rates the full width at half maximum FWHM is close to the. theoretically value of 59 mV and the peak current varies linearly with the square root of. the scan rate as can be seen in Figure 1 Consistent with an electrochemically reversible. reaction involving a surface confined reactant the inset of Figure 1 shows that the peak current. increases linearly with increasing scan rate for both oxidation and reduction processes. This behavior is consistent with semi infinite linear diffusion and under these conditions the. response can be described by the Randles Sev ik Equation. ip 2 65x105n3 2ADct 1 2C 1, where n is the number of electrons transferred A is the area of the working electrode DCT is. the diffusion coefficient and C is the concentration of the redox centers 38 The concentration. of ruthenium centers within the composite film has been determined from density. measurements in non swelling solvents as 0 8 M Thus Equation 1 allows DCT to be. estimated for both the oxidation and reduction processes of the Ru2 3 couple within the. composite film The DCT was calculated to be 2 1 0 7 x 10 11 cm2s 1 to be which is consistent. with previous studies for similarly modified electrodes 20 21 24 25 38 Based on these DCT values. it is possible to predict the regeneration rates of the Ru3 species within each film according. to the equation 39, where is the minimum dry thickness and using DCT calculated from equation 2 which. indicates the time taken to fully oxidise the film and regenerate the Ru3 mediating centres. was 15 s for the composite film Generally faster regeneration rates are indicative of a. larger and faster ECL intensity with a subsequent decrease in detection limits 39 However. these times are sufficient for the detection of methamphetamine. ECL detection of methamphetamine One of the key objectives of this work was to investigate. whether the ability of a ruthenium nafion composite film to produce an ECL response upon. interaction with methamphetamine Figure 2 shows the ECL response for the RuNafion. composite films upon interaction with MA For the detection of amino acids and structurally. similar chemicals such as MA the electrogenerated Ru bpy 3 3 has been shown to undergo. a mediated oxidation reaction with the amino acids moieties Significantly the. chemiluminescent intensity is maximised at pH values near the pKa of the N terminal amine. site34 36 41 Experimental evidence in support of this mechanism has shown that the overall. reaction efficiency depends strongly on the pH at which. for the fabrication of any sensor as it reduces the synthesis times resulting in more economically and cheaper production costs This technique is simple rapid selective and sensitive and shows potential for the high throughput quantitation of ATS as well as possibilities for adaptation with other techniques such as FIA or LC systems INTRODUCTION Methamphetamine MA has received much

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