APCI explosives

Various mass spectrometer configurations have been used for the detection of explosives, such as ion traps, quadrupoles and time-of flight mass analyzers and combinations as MS/MS systems. The ionization method is usually APCI with corona discharge [24, 25]. An example is given in Figure 20, which shows the schematic diagram of an explosive mass spectrometer detector [25]. It is based on an ion trap mass analyzer, an APCI source with corona discharge and a counter-flow introduction (CFI) system. The direction of the sample gas flow introduced into the ion source is opposite to that of the ion flow produced by the ion source. 

Peroxide explosives are potent explosives that can be made starting from common and easy to obtain raw materials. The analysis of triacetone triperoxide (TATP) and hexamethylenetriper-oxidediamine (HMTD) was successfully carried out by HPLC-APCI-MS in a powder sample as well as in post-blast extracts originating from a forensic case [134]. After RP separation on a C18 column using a methanohwater (75 25 v/v) mobile phase containing ammonium acetate (2.5mM) at a 0.4mL/min flow rate, detection was carried out in positive ion mode. MS-MS analysis of [TATPh-NH4]+ and [HMTD - H]+ as precursor ions was necessary in order to achieve the required sensitivity in the analysis of postblast extracts (LOD 0.8 and 0.08 ng on column, respectively). 

A commercial explosive trace detection system, Hitachi DS-120E, based on a quadrupole mass spectrometer was built [7], Ionization is carried out by corona discharge and APCI. Sampling is carried out by wiping surfaces on suspicious objects for traces of explosives. The wipe sheet is inserted into the detection system, where it is heated in order to desorb the trace explosives into the ion source. Analysis time is 5-10 s. 

The desorption of explosives from the passes was achieved by short wave infrared radiation. The vapors produced were drawn into a triple quadrupole mass spectrometer (MS/MS) and were monitored in the selected reaction monitoring (SRM). Ionization is carried out by corona discharge, followed by APCI. Ions formed from most explosives are M, [M-H]-, and adduct ions. One of these ions is selected to pass into the collision cell, to react with molecules of nitrogen, as a result of which a series of product ions are formed. In the SRM mode, one precursor ion and one product ion are chosen for each compound. The first and third quadruples are adjusted in order to enable SRM transition between these two ions. 

Both normal phase [53] and reversed phase [54] HPLC methods have been used for the separation of diterpene alkaloids. Reversed phase HPLC coupled to APCI mass spectrometry has been used for the analysis of diterpene alkaloids of Aconitum spp. [64,65] and normal phase HPLC conditions [53] have been successfully used with APCI-MS for the detection of diterpene alkaloids in Delphinium species [56]. However, caution should be observed in the use of APCI sources with some normal phase HPLC solvents such as hexane, to ensure no oxygen is introduced into the system producing a possible explosive mixture in the API source. 

The great advantage of APPI is that it can be used to ionize nonpolar classes of compounds such as alkanes, alkenes, and aromatics that are not ionized by ESI or APCI and it can be interfaced with normal-phase chromatography,49 51 where the corona discharge (APCI) and the high-voltage discharge (ESI) present a potential explosion hazard. 

Mass spectrometry (MS) has become one of the most important analytical tools employed in the analysis of pharmaceuticals. This can most likely be attributed to the availability of new instrumentation and ionization techniques that can be used to help solve difficult bioanalytical problems associated with this field (1-8). Perhaps the best illustration of this occurrence is the development of electrospray (ESI) and related atmospheric-pressure ionization (API) techniques, ion-spray (nebulizer-assisted API), turbo ionspray (thermally assisted API), and atmospheric pressure chemical ionization (APCI nebulization coupled with corona discharge), for use in drug disposition studies. The terms ESI and ionspray tend to be used interchangeably in the literature. For the purpose of this review, the term API will be used to describe both ESI and ionspray. In recent years there has been an unprecedented explosion in the use of instrumentation dedicated to API/MS (4,6,8-14). API-based ionization techniques have now become the method of choice for the analysis of pharmaceuticals and their metabolites. This has made thermospray (TSP), the predominant LC/MS technique during the 1980s, obsolete (15). Numerous reports describing the utility of API/MS for pharmaceutical analysis have appeared in the literature over the last decade (7). The... 

Figure 13.15 LC-MS interface ionization mechanism diagrams, (a) coulomb explosion in ESI droplets and (b) reactions leading to molecular ion in APCI. (Adapted with permission from Applied Biosystems/MDS Sciex.)...

Xu, X., van de Craats, A.M., Kok, E.M., de Bruyn, P. (2004) Trace analysis of peroxide explosives by high performance liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry (HPLC-APCI-MS/ MS) for forensic applications. /. Forensic Sci., 49(6), 1230-1236. 

LC-MS is another widely used analytical method for the analysis of explosives. Several articles review LC-MS for explosives analysis [150-152], In particular, Wnon and his coworkers have significantly contributed to the development of explosives analysis by LC-MS. Zhao and Yinon identified nitrate ester explosives by LC-MS using both ESI and APCI [153], In both ionization studies, postcoluran additives are introduced to increase specificity and sensitivity of the product ions produced by the explosives pentaerythritol tetranitrate (PETN), nitroglycerin (NG), and ethylene glycol dinitrate (EGDN) to form stable adduct ions (as shown in Figure... 

Various ionization sources are employed in the analysis of explosives by MS. APCI is used with GC-MS, LC-MS, and LC-MS/MS systems for explosives analysis [200-204] this source is chosen because lower LOD can be found with APCI over El sources. However, El remains the ionization source used most often in GC-MS analyses of explosives [12,134-137,139-143,205], DESI, desorption atmospheric pressure chemical ionization (DAPCI), and direct analysis in real time (DART) sources are used to detect explosives, including emerging explosive threats like TATP and as part of field-deployable MS systems [163,206-209],... 

For the ion source and the mass spectrometer, atmospheric pressure chemical ionization (APCI) with an ion trap mass spectrometer (ITMS) is mainly used. The ion source and the mass spectrometer used in our laboratory for detection of explosives are described below. 

APCI is a well-known technique for ionizing explosive molecules. A high voltage of about -2 kV is applied to a needle electrode to produce a negative corona discharge. The typical ionization process of the explosive molecules (M) consists of two steps ... 

To detect explosives with higher vapor pressure such as 2,6-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT), and glycerol trinitrate (NG), vapors from the explosives are directly introduced into the ion source by a pump. Figure 21.7 shows a prototype of a vapor detector. A flexible tube is connected to the APCI ion source. The end of the tube is moved toward objects to be checked such as hands, clothes, and luggage. The sample vapor is collected by the flexible tube and introduced into the APCI ion source. The temperature of the inner... 

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