Page 277 - Advances in Forensic Applications of Mass Spectrometry - Jehuda Yinon

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NO 2 NO 2

N CH 2 N
N NO CH CH
CH 2 2 2 2
O N N CH 2 N N
2
CH 2 N O N CH 2 NO 2
2
NO 2
HMX RDX

Scheme 5

much greater than that of TNT. 1,20, 28 Its melting point is 204˚C. It is most
soluble in dimethyl sulfoxide (41 g/100 g at 25˚ C), in dimethyl formamide
(37 g/100 g at 25˚C), and in acetone (8.3 g/100 g at 25˚C), and it is slightly
soluble in water (6 mg/100 g at 25˚C). Its vapor pressure at 25˚C is 4.6 ¥ 10 –9
Torr. The industrial product may contain traces of HMX, up to 9% depending
on the manufacturing process. RDX is never handled pure and dry because
of the danger of accidental explosion. Following production, it is immediately
incorporated into formulations or desensitized with an additive. RDX is a
component in explosive mixtures, especially plastic explosives (such as C-4
and Semtex).
Electrospray ionization coupled to tandem mass spectrometry was used
for the analysis of a series of explosives, including RDX and HMX (Scheme
5). 21,32 Analyses were performed with a Perkin–Elmer Sciex API III-PLUS
triple quadrupole mass spectrometer with electrospray ionization. Standard
solutions of RDX and HMX were made in acetonitrile–water (50:50), con-
taining 2 mM of ammonium acetate. The solutions were introduced directly
into the ion source by means of a syringe pump at a flow rate of 5 ml/min.
The major ion in the mass spectrum of RDX was at m/z 281, interpreted
as [M + CH COO] , the additive originating from the ammonium acetate.
–
3
The MS/MS spectrum of this ion produced ions at m/z 46 [NO ] (base peak)
–
2
and at m/z 59, due to the acetate.
Another negative-ion ESI-MS study of explosives used a PE-Sciex API
100 LC/MS system. RDX and HMX were injected into an eluent consisting
33
of methanol–water (75:25) and 5 mM ammonium acetate, producing major
–
[M + CH COO] ions.The mass spectrum of HMX also showed a major ion
3
[M + CH COO] at m/z 355.
–
3
In a study to enhance ESI intensities, 22,23 several additives were tested
with a series of explosives, including RDX and HMX. Mobile phase of meth-
anol–water (50:50) with 1 mM ammonium nitrate as additive produced best
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