Amperometric detection explosives

Hilmi and Luong [25] employed a gold working electrode, formed by electroless deposition onto the chip capillary outlet, for highly sensitive amperometric detection of nitroaromatic explosives [with a detection limit of 24 ppb trinitrotoluene (TNT)]. Analysis of a mixture of four explosives (TNT, 2,4-DNT,... 

Figure 13.5 Total and Individual measurements of nitroaromatic organic explosives using CE microchip with amperometric detection, based on rapid switching between flow injection and separation modes, respectively. (Reprinted in part with permission from [28]. Copyright 2002 American Chemical Society.)...

A dual electrochemical microchip detection system, based on the coupling of conductivity and amperometric detection schemes, was developed for simultaneous measurements of both nitroaromatic and ionic explosives [34], The microsystem relied on the combination of a contactless conductivity detector with an end-column thick-film carbon amperometric detector. Such ability to monitor both redox-active nitroaromatic and ionic explosives is demonstrated in Figure 13.7, which shows typical dual-detection electropherograms for a sample mixture containing the nitroaromatic explosives trinitrobenzene (TNB) (4), TNT (5), 2,4-DNB (6), and 2-Am-4,6-DNB (7), as well as the explosive-related ammonium... 

Amperometric detection is the preferred method for the analysis of nitroaromatic explosives on microchip devices since it offers up to three orders of magnitude higher sensitivity than indirect LIF and it has a great potential for miniaturization and integration on microchip platform. Presence of nitrogroup allows its cathodic reduction to form al-kylhydroxyamines. The reduction mechanism of polynitroaromatic compounds is complex and depends on the number of nitro groups,... 

Electrode surface fouling is a problem in amperometric detection on microfluidic platform. Wang et al. introduced boron-doped diamond electrode with highly stable response towards detection of explosives [23]. While thick-film carbon detector displayed a gradual decrease in... 

Other materials were also employed to construct electrodes for amperometric detection. For instance, a boron-doped diamond (BOD) electrode was used for amperometric detection of nitroaromatic explosives, organophosphate nerve agents, and phenols. The BOD electrode offers enhanced sensitivity, lower noise, negligible adsorption of organic compounds, and low sensitivity to oxygen [760], In addition, a copper particle-modified carbon composite electrode was used for amperometric detection of glucose in a PDMS chip [761]. 

Explosive residues containing 2,4,6-trinitrotoluene transformation products have been examined (Kleibohmer et al. 1993), and a range of explosives including TNT and related compounds, and nitra-mines analyzed using amperometric detection with a silver-on-gold electrode (Hilmi et al. 1999). 

Hilmi, A., J.H.T. Luong, and A.-L. Nguyen. 1999. Development of electrokinetic capillary electrophoresis equipped with amperometric detection for analysis of explosive compounds. Anal. Chem. 71 873-878. 

Our group and that of Luong have developed several effective CE/amperometric microchip protocols for detecting nitroaromatic explosives down to the ppb level [14,15]. Such amperometric detection relies on the application of a fixed (negative) potential at the working electrode, and monitoring the reduction current as a function of time. The current response thus generated reflects the concentration profiles of these explosives as they... 

Peroxide-based explosives, such as TATP, diacetone diperoxide (DADP), and hexamethylene triperoxide diamine (MHTD) can be detected using HPLC-DAD at 214 nm (see Figmes 11.5 and 11.6). Successful LC-MS/MS of explosives has been reported, as has the use of ion mobility and liquid chromatography with amperometric detection (Vigneau and Machuron-Mandard 2009 Hilmi et al. 1999 Ou et al. 2009 Meng et al. 2008). 

Besides the already cited metal ions, a large number of different chemical species have been investigated, such as amino acids [30], dmgs [121], explosives [129], inorganic ions (CP [120], SCN [34], etc.), and oxidizing species [130]. The amperometric detection of these species takes advantage of different mechanisms of interaction of the analyte with the tail group of the SAM, such as complexation, electrostatic [131] attraction or repulsion, hydrophobic interaction [121], formation of covalent bonds, or size exclusion effects [111]. 

Hilmi et al. demonstrated a CE chip with direct amperometric detection for five nitroaromatic explosives, including trinitrotoluene (TNT), in ground water and soil extracts. The microfluidic device achieved rapid separation and detection of explosive compounds with LODs of 100-200 pg/L. 

Boron-doped diamond presents another attractive material with low and stable background current and noise over a wide potential range, corrosion resistance, high thermal conductivity, and high current densities. Usually no mechanical or electrochemical pretreatment of BDD film electrode is needed. Therefore, BDD film electrodes find use also in the area of environmental analysis for organic explosive determinations. BDD-based electrochemical detector allowed, e.g., amperometric detection of 2,4,6-trinitrotoluene, 1,3-dinitrobenzene, and 2,4-dinitrotoluene over the 200-1,400 ppb range, with detection limits at the 100 ppb level. ... 

Amperometric detection is useful for fast flow injection analysis or HPLC of explosives in complicated environmental matrices which can be demonstrated by the analysis of the mixture of 14 standard explosives with detection limit around 0.2 pg mL ... 

Barek J, Fischer J, Wang J (2011) Voltammetric and amperometric detection of nitrated explosives (a review). In Kalcher K, MeteUca R, Svancara 1 et al (eds) Sensing in electroanalysis, vol 6. University Press Centre, Pardubice, pp 139-147... 

Dual Amperometric/Conductivity Detection for Simultaneous Monitoring of Ionic and Organic Explosives... 

Figure 13.7 Electropherograms showing the simultaneous measurement of low- and high-energy explosives as recorded with the (a) conductivity and (b) amperometric detectors. Analytes, ammonium (1), methylammonium (2), sodium (3), TNB (4), TNT (5), 2,4-DNB (6), and 2-Am-4,6-DNB (7), system peak (SP). Explosive concentration, 2 mM (1,2,3) and 15 ppm (4,5,6,7). Conditions MES/His buffer (20 mM, pH 6.1) containing 15 mM lithium dodecyl sulfate as the run buffer separation field strength, +250 V/cm injection field strength, +250 V/cm for 2 s detection at 200 kHz, (a) 5 Vp p and at (b) —0.5 V. (Reprinted in part with permission from [34]. Copyright 2002 American Chemical Society.)...

There can be found good reviews on conventional and microchip capillary electrophoresis in forensic/security analysis [4 7] in the literature. The aim of this chapter is to overview the progress which has been made towards the development of portable microfluidic device for on-site and fast detection of nitrated explosives and to describe the major developments in this field (summarized details on analytical methods for microchip determination of nitroaromatic explosives can be found in Table 35.2). The corresponding practical protocol for measurements of explosives on microfluidic device with amperometric detector is described in Procedure 49 (see CD accompanying this book). 

Preliminary results are presented for the use of cyclic voltammetiy as a method for pattern recognition. The current at eight potentials of a cyclic voltammgramm was analyzed and these values served as a simulation of eight amperometric sensors. It is shown that on the basis of this procedure, different explosives and apple juices are easily distinguished by the use of one electrode alone These results clearly show that cyclic voltammetry could easily be used for a so called electronic tongue. In the future it is planned to use cyclic voltammetry as a method in combination with different sensor methods and also for the vapour detection. 

Meiilainen PT (1990) A differential paramagnetic sensor for breath-by-breath oximetry. J Clin Monit 6(l) 65-73 Messer H, Zinevich A, Alpert P (2006) Environmental monitoring by wireless communication networks. Science 312 713 Miller JB (2001) Catalytic sensors for monitoring explosive atmospheres. IEEE Sensors J 1(1) 88—93 Miura N, Ono M, Shimanzoe K, Yamazoe N (1998a) A compact solid-state amperometric sensor for detection of NOj... 

Growing requirements for safety and environmental controls has led to the development of voltammetric and amperometric methods for determination of explosives described in this chapter. Further development can be envisaged, especially in the field of nano-material-based electrochemical devices for detection of explosives, namely at graphene, carbon nanotubes, nanoparticles, and nanoporous materials, and composites of these materials. Electrochemical sensors offer rapid, sensitive, inexpensive, and reliable detection of explosive materials in any conceivable scenario. Coupling these attractive properties with the portable nature of electrochemical devices facilitates a wide range of decentralized applications. 

---