Highly sensitive electrochemical detection of trace liquid peroxide explosives at a Prussian-blue 'artificial-peroxidase' modified electrode

A highly sensitive electrochemical assay of the peroxide-based explosives triacetone triperoxide (TATP) and hexamethylene triperoxide diamine (HMTD) at a Prussian-blue (PB) modified electrode is reported. The method involves photochemical degradation of the peroxide explosives and a low potential (0.0 V) electrocatalytic amperometric sensing of the generated hydrogen peroxide at the PB transducer and offers nanomolar detection limits following a short (15 s) irradiation times. The electrochemical sensing protocol should facilitate rapid field screening of peroxide explosives.     

Recent methods for the determination of peroxide-based explosives

In the last few years, the need to determine peroxide-based explosives in solid samples and air samples has resulted in the development of a series of new analytical methods for triacetonetriperoxide (TATP, acetone peroxide) and hexamethylenetriperoxidediamine (HMTD). In this review, after a short introduction describing the state of the art in the field, these new analytical methods are critically discussed. Particular emphasis is placed on spectroscopic and mass spectrometric methods as well as on chromatographic techniques with selective detection schemes. The potential of these methods to analyse unknown solid samples that might contain one or more of the explosives and to analyse peroxide-based explosives in air is evaluated.     

"One-step" simplified electrochemical sensing of TATP based on its acid treatment

A fast, simple and sensitive electrochemical method for sensing peroxide-based explosives based on their acid treatment is reported. The method relies on the high electrocatalytic activity of Prussian-blue (PB)-modified electrodes towards the acid-generated hydrogen peroxide in the harsh acidic medium (down to pH 0.3) used for releasing hydrogen peroxide. Such effective operation of PB electrochemical sensors in strongly acidic media eliminates the need for an additional neutralization step required in analogous peroxidase-based assays (due to acid-induced enzyme deactivation processes). Factors affecting the efficiency of the acid pre-treatment of triacetone triperoxide (TATP) have been examined and optimized to allow its sensitive measurement down to the 50 ng level within 60 s. Chronoamperometric detection of microgram amounts of solid TATP, following a one-minute acid mixing and placing a 20 microL droplet onto a disposable PB-modified screen-printed electrode is illustrated. Similar results were obtained for the peroxide explosive hexamethylene triperoxide diamine (HMTD). By greatly simplifying the analytical procedure, such an acid-operated "artificial peroxidase" electrocatalytic transducer holds great promise for designing "one-step", user-friendly, miniaturized, cost-effective devices for field screening of peroxide explosives.     

A quantitative chemiluminescent assay for analysis of peroxide-based explosives

A quantitative chemiluminescent method, enabling indirect identification of the peroxide-based explosives TATP (triacetone triperoxide) and HMTD (hexamethylene triperoxide diamine) has been developed. Treatment of these compounds with acidic solutions produced peroxides, which were transformed into radical derivatives by horseradish peroxidase (HRP) and then quantified by measuring the light emitted during their oxidation of luminol. The method was first developed in the microplate format and later optimized for a portable luminometer, to enable rapid application of the assay directly on site. When the portable luminometer was used each analysis took only 5–10 min. The method had good selectivity, sensitivity, and reproducibility; in the microplate format the limits of detection (LOD) and quantification (LOQ) were 40 and 50 ng mL⁻¹, respectively, for both TATP and HMTD. When the portable luminometer was used the LOD and LOQ were 50 and 100 ng mL⁻¹, respectively, for both compounds. Introduction of light emission-enhancing compounds did not improve the analytical performance of the assay. Imprecision (CV values) was always below 10%. Recovery varied rapidly with time, with an average value of 78% after 5 min. No false-positive result was detected on measurement of a variety of samples; this is an important feature for analysis on site. The method was applied both to contaminated materials and to fortified soil samples, simulating operational conditions.     

Association interaction and voltammetric determination of 1-aminopyrene and 1-hydroxypyrene at cyclodextrin and DNA based electrochemical sensors

The aim of this work was voltammetric determination of 1-aminopyrene and 1-hydroxypyrene using carbon paste electrodes modified with cyclodextrin derivatives and double stranded deoxyribonucleic acid (dsDNA). The detection schemes based on a preconcentration and differential pulse voltammetric (DPV) determination at beta-cyclodextrin and gamma-cyclodextrin modified carbon paste electrode (beta-CD/CPE, gamma-CD/CPE), neutral beta-cyclodextrin polymer and carboxymethyl-beta-cyclodextrin polymer modified screen-printed electrode (beta-CDP/SPE, beta-CDPA/SPE) and dsDNA modified screen-printed electrode (DNA/SPE) are proposed for the trace determination of studied analytes within the concentration range from 2 x 10(-8) to 4 x 10(-7) mol dm(-3) and from 2 x 10(-7) to 4 x 10(-6) mol dm(-3) with the limits of quantification down to 10(-8) mol dm(-3). Depending on pH, 1-aminopyrene interacts with both surface attached CD and DNA by electrostatic bonds and supramolecular complexation while 1-hydroxypyrene associates with the CD hosts via complexation. The 1-aminopyrene interaction with dsDNA was confirmed by fluorimetric measurements in the solution phase using a competing DNA-TO-PRO-3 dye complex. In addition, the effect of temperature on this association was investigated using an electrically heated DNA-modified carbon paste electrode (DNA/CPE).     

Cathodic stripping voltammetry of the anticancer agent 5-fluorouracil and determination in urine

Cathodic stripping voltammetry was used to determine 5-fluorouracil (5-FU) in the presence of traces of Cu(II). It was found that the addition of 5 x 10(-9) mol dm(-3) Cu(II) to the measurement cell greatly enhanced the peak current of the adsorbed molecule. Different parameters were tested to optimize the conditions for the determination of 5-FU. The adsorbed form is reduced irreversibly. It was observed that by controlling the deposition potential, the technique could be directed to the determination of Cu(II) or the drug. The linear range was from 5 x 10(-9) to 6 x 10(-8) mol dm(-3) for 5-FU and from 6 x 10(-9) to 5 x 10(-8) mol dm(-3) for Cu(II). Detection limits of 4.6 x 10(-10) and 5 x 10(-10) mol dm(-3) were obtained for 5-FU and Cu(II), respectively. The method was applied to urine and molecules or ions which may interfere were studied.     

Selective determination of hydrogen peroxide by adduct formation with a dinuclear iron(III) complex and flow injection analysis/tandem mass spectrometry

A highly selective method for the determination of hydrogen peroxide is presented. In a flow injection analysis (FIA) instrument, the analyte is brought into contact with a dinuclear heptadentate iron(III) complex. The formation of the peroxide adduct is quantified using electrospray tandem mass spectrometry (ESI-MS/MS). Selected reaction monitoring (SRM) based on the transition from the triply charged peroxide adduct with m/z = 251.2 to the triply charged fragment ion of m/z = 240.5 is performed. The limit of detection for hydrogen peroxide is 10(-7) mol dm(-3), limit of quantification is 3 x 10(-7) mol dm(-3), and a linear range of 2.5 decades starting at the limit of quantification is observed.     

过氧化物模拟酶催化的苯基荧光酮氧化反应及其分析应用

在ＮＨ４Ｃｌ－ＮＨ４ＯＨ缓冲介质中，氯化血红素（Ｈｅｍｉｎ）有显著的过氧化物模拟酶活性，催化过程化氢氧化苯基荧光酮褪色。本文探讨了反应机理，比较Ｈｅｍｉｎ与天然酶催化性能，考察反应条件和共存物质影响，从而提出测定Ｈｅｍｉｎ和过氧化氢的高灵敏分光光度法，线性范围分别为０￣３．０×１０＾－８ｍｏｌ／Ｌ和０￣１．２×１０＾５ｍｏｌ／Ｌ；检测限（３σ）分别为１．８×１０＾－１０ｍｏｌ／Ｌ和１．４×１０＾７     

Polarographic study of acrolein and its determination by flow injection with amperometric detection at a mercury electrode

A study of the electrochemical behavior of acrolein at a dropping mercury electrode using different polarographic techniques is described. Theoretical studies of the reversibility of the wave of acrolein were carried out using two different polarographic techniques: direct current tast and differential pulse. Differential pulse polarography may be used to determine acrolein concentration in a Britton-Robinson buffer solution of pH 10 in the ranges 2 x 10(-7)10(-8) and 5 x 10(-8)-10(-4) mol dm(-3) and a coefficient of variation of 1.7% for a concentration of 10(-5)mol dm(-3). A flow injection method with amperometric detection at a potential of -1.4V using a mercury electrode is also described. Before each injection, any drop hanging from the tip of the capillary needs to be dislodged and a new electrode drop dispensed; three different drop sizes were tested. A linear relationship between peak intensity and acrolein concentration was obtained in the range 10(-5)-10(-7) mol dm(-3), with a detection limit of 9.8 x 10(-8) mol dm(-) 3 and a coefficient of variation of 2.9% for a 2 x 10(-7) mol dm(-3) concentration. Several organic and inorganic species were tested in order to ascertain whether they interfered with the signal for acrolein. The proposed methods were applied to the determination of acrolein in seawater samples.     

Flow-injection determination of trace amounts of dopamine by chemiluminescence detection

A flow-injection analysis (FIA) for the determination of dopamine has been developed. The method is based on the inhibition effect of dopamine on the iron(II)-induced chemiluminescence (CL) of 10,10'-dimethyl-9,9'-biacridinium dinitrate (lucigenin). The presence of a non-ionic surfactant, polyoxyethylene (23) lauryl ether (Brij 35), caused an increase in the inhibition effect. The present method allows the determination of dopamine over the range 1x10(-8)-2x10(-7) mol dm(-3). The relative standard deviation was 0.7% for eight determinations of 6x10(-8) mol dm(-3) dopamine. The detection limit (S/N=3) was 2x10(-9) mol dm(-3) with the sampling rate of 40 samples h(-1). The effect of other catecholamines and compounds of similar structure on the lucigenin CL reaction was studied: quinone, hydroquinone, norepinephrine, pyrocatechol and l-dopa suppressed the CL intensity.     

Simultaneous determination of trace amounts of cadmium, nickel and cobalt in water samples by adsorptive voltammetry using ammonium 2-amino-cyclopentene dithiocarboxylate as a chelating agent

This paper reports the use of an adsorptive voltammetric technique for the simultaneous detection of Cd(II), Ni(II) and Co(II) using ammonium 2-amino-cyclopente dithiocarboxylate as a selective complexing agent. Scans containing three resolved peaks corresponding to these metals were obtained in synthetic and real samples. The reduction current peaks of the metals that were distinctly separated by 200 mV or more, allowing their determination over a wide range of concentrations. These metals can be quantified at concentrations above 1.33x10(-8) mol dm(-3) Cd(II), 8.51x10(-9) mol dm(-3) Ni(II) and 3.39x10(-10) mol dm(-3) Co(II). The influence of pH, ligand concentration, scan rate, accumulations time and applied potential was investigated. The R.S.D. at a concentration level of 1.78x10(-7) mol dm(-3) of Cd(II), 3.40x10(-7) mol dm(-3) and Ni(II) and 1.7x10(-9) mol dm(-3) of Co(II) was 2.5% for Cd(II), 2.7% for Ni(II) and 3.3% for Co(II). The method was applied to various water samples.     

Simple method of paroxetine determination using a single channel FIA with no in-line reaction process.

A flow-injection analysis (FIA) of paroxetine hydrochloride (PRX), a selective serotonin reuptake inhibitor (SSRI) currently used as an antidepressant drug, is described. A 0.1 mol dm(-3) acetate buffer at pH 3.07 was found to be thebest solvent. The analyte was detected at 293 nm. The calibration equation was linear over the range of 1.07 x 10(-6) to 5.35 x 10(-6) mol dm(-3). The limit of detection (LOD) and the limit of quantitation (LOQ) were 3.2 x 10(-7) and 9.5 x 10(-7) mol dm(-3), respectively. The proposed method was applied to the determination of PRX in pharmaceutical preparations. The results were compared with those obtained by a conventional batchwise UV-spectrophotometry.     

Voltammetric determination of niclosamide at a glassy carbon electrode

A very sensitive and selective procedure was developed for the determination of niclosamide based on square-wave voltammetry at a glassy carbon electrode. Cyclic voltammetry was used to investigate the electrochemical reduction of niclosamide at a glassy carbon electrode. Niclosamide was first irreversibly reduced from NO2 to NHOH at -0.659 V in aqueous buffer solution of pH 8.5. Reversible and well defined peaks at -0.164 V and -0.195 V (vs. Ag/AgCl) were obtained that are responsible for two electron peaks between NHOH and NO. Following optimisation of the voltammetric parameters, pH and reproducibility, a linear calibration curve over the range 5 x 10(-8)-1 x 10(-6) mol dm(-3) was achieved. The detection limit was found to be 2.05 x 10(-8) mol dm(-3) niclosamide. For eight successive determinations of 5 x 10(-7) mol dm(-3) niclosamide, a relative standard deviation of 2.4% was obtained. This voltammetric method was applied to the direct determination of niclosamide in tablets. The results of the analysis suggest that the proposed method has promise for the routine determination of niclosamide in the products examined.     

Investigation of the reaction of copper(I) with 2,9-dimethyl-1,10-phenanthroline at trace level by thermal lensing

The stability constants for copper(I) chelate with 2,9-dimethyl-1,10-phenanthroline are determined by thermal lensing, and the advantages over spectrophotometric determination of stability constants are shown. Changes in the photometric reaction when moving from the microgram to the nanogram level of reactants are discussed. The conditions for the thermal-lens determination of copper are optimized. The limit of detection of copper is 3x10(-8) mol dm(-3), and the linear calibration range 1x10(-7)-1x10(-5) mol dm(-3).     

Turn-on fluorescence detection of H2O2 and TATP

Peroxide-based explosives, like triacetone triperoxide (TATP), are important targets for detection because of their broad use in improvised explosives but pose challenges. We report a highly sensitive turn-on fluorescence detection for H2O2 and organic peroxides, including TATP. The detection strategy relies on oxidative deboronation to unmask H2Salen, which subsequently binds Zn(2+) to form fluorescent Zn(Salen). Sensitivity is excellent, with detection limits below 10 nM for H2O2, TATP, and benzoyl peroxide. In addition, acid treatment is necessary to sense TATP, suggesting the potential to discriminate between H2O2 and TATP based upon minimal sample pretreatment.     

Incorporation of horseradish peroxidase in a Kieselguhr membrane and the application to a mediator-free hydrogen peroxide sensor.

Horseradish peroxidase was incorporated in a kieselguhr membrane. The electron-transfer process of the enzyme was examined by cyclic voltammetry. It was observed that the electron-transfer reactivity of horseradish peroxidase was greatly enhanced, and that direct electrochemistry was accordingly feasible. Using the merits of the direct electron-transfer reactivity of horseradish peroxidase and its specific enzymatic catalysis towards hydrogen peroxide, an unmediated hydrogen peroxide biosensor was constructed. The calibration plot of this hydrogen peroxide sensor was linear in the range of 2.0 x 10(-6) mol/L - 6.5 x 10(-4) mol/L. The relative standard deviation was 4.1% for 6 successive determinations at a concentration of 1.0 x 10(-4) mol/L. The detection limit was 1.0 x 10(-6) mol/L.     

Chromium(III) ion-selective electrode based on 4-dimethylaminoazobenzene

A PVC-based membrane of 4-dimethylaminoazobenzene reveals a Nernstian potentiometric response (with slope of 19.5+/-0.6 mV/decade and a correlation coefficient of 0.999) for Cr(III) over a wide concentration range (1.66 x 10(-6)-1.0 x10(-2) mol dm(-3)). The potential of this electrode is independent of pH in the range of 3.0-5.5. It has a fast response time of about 10 s and was used for a period of 3 months with good reproducibility. The detection limits of this membrane electrode was 8 x 10(-7) M. the proposed electrode has been used as an indicator electrode in the potentiometric titration of Cr(III) with EDTA. This sensor exhibits a very good selectivities for Cr(III) over a wide variety of metal ions.     

Spectrophotometric and direct-reading methods for the analysis of gas phase peroxyacetic acid

A new method for the determination of peroxyacetic acid (PAA) in gas phase samples is described. It is based on the oxidation of ABTS (2,2'-azino-bis(3-ethylbenzothiazoline)-6-sulfonate) by PAA with formation of a radical cation which is characterized by four strong absorption maxima between 405 nm and 810 nm. These allow for sensitive spectrophotometric determination of the peracid. The selectivity of the method towards hydrogen peroxide is strongly dependent on the sampling method used. Impinger sampling and sampling based on the use of coated solid sorbents (test tubes) was performed. Limits of detection are 10(-8) mol, limits of quantification are 5 x 10(-8) mol, the linear range consists of 1.5 concentration decades in both cases. Using ABTS-coated test tubes above 1 x 10(-7) mol, direct reading of the results is possible and may be used as rapid screening method for the PAA concentration.     

Synthesis of functionalized CdTe/CdS QDs for spectrofluorimetric detection of BSA

Luminescent quantum dots (QDs)-semiconductor nanocrystals are a promising alternative to organic dyes for fluorescence-based applications. We have developed procedures to use CdS to encapsulate CdTe and synthesize a new kind of functionalized CdTe/CdS QDs for the quantitative and selective determination of bovine serum albumin (BSA). Maximum fluorescence intensity was produced at pH 6.83, with excitation and emission wavelengths at 336 and 524 nm, respectively. Under optimal conditions, the straight line equation: DeltaF=6.84+62.29C (10(-6) mol dm(-3)) was found between the relative fluorescence intensity and the concentration of BSA in the range of 0-1.2 x 10(-6) mol dm(-3), and the limit of detection was 5.4 x 10(-8) mol dm(-3). Based on this approach, a novel quantitative method for the determination of BSA is presented in this paper.     

Homogeneous liquid-liquid extraction method for spectrofluorimetric determination of chlorophyll a

A new homogeneous liquid-liquid extraction using a fluorocarbon ionic surfactant, Zonyl FSA (FSA), having a diethylthioether group as a spacer between the perfluoroalkyl group and carboxyl group has been developed. In this FSA method, the phase separation phenomena were observed at mild pH (below pH 6). Moreover, by using this extraction method as a preconcentration, a highly sensitive spectrofluorometric determination of chlorophyll a was established. The results for the standard chlorophyll a were as follows. The concentration factor (V(w)/V(o)) was 200 (water phase, V(w), 20 cm(3), water-immiscible phase, V(o), 100 mul), the distribution ratio, log D, was 4.85, the extraction percentage, E, was 99.7%, and the procedure time was approximately 30 min. The calibration curve was linear in the concentration range 2 x 10(-11)-3 x 10(-7) mol dm(-3) and the detection limit (S/N=3) was 1 x 10(-11) mol dm(-3). The relative standard deviation was 0.72% for 10(-8) mol dm(-3) (five determinations).