Page 287 - Advances in Forensic Applications of Mass Spectrometry - Jehuda Yinon

1522_book.fm Page 258 Thursday, November 13, 2003 9:58 AM

[2M+75] - 524.4
100
95
90
85
80
75
70
65
Relative abundance 55
60

50
45
40
35 [M+75] - 299.7
30
25
[2M+59] -
20
[M+59] -
15 [2M+35] -
[M+45] -
10 283.7 484.4 508.4
269.8
5
0
200 250 300 350 400 450 500 550 600 650 700 750 800
m/z
Figure 6.16 ESI mass spectrum of C 3 -RDX. (From Gapeev, A., Sigman, M.
13
and Yinon, J., LC/MS of explosives: RDX adduct ions, Rap. Comm. Mass Spec-
trom., 17, 943, 2003. © John Wiley & Sons Ltd. Reproduced with permission).
–
–
–
[2M + 37] , [2M + 59] ,and [2M + 75] indeed contain two RDX molecules,
and that RDX decomposition plays no role in ion formation in the ESI source.
The most abundant ions in the RDX concentration range of 25 ppb to
–
–
10 ppm were found to be [2M + 75] and [M + 75] . Lower RDX concen-
–
–
trations lead to lower [2M + 75] /[M + 75] ion ratios. At higher RDX
–
concentrations, formation of the [2M + 75] dimer becomes more favorable,
–
–
so that the [2M + 75] /[M + 75] ratio increases.
–
The elemental composition of the ion at m/z 297, [M + 75] , was deter-
– 43
mined by FT-ICR to be [RDX + C H O ] . Glycolic (hydroxyacetic) acid,
2
3
3
–
CH (OH)COOH, having an anion at [M – H] , fits that elemental compo-
2
sition and was found to be an impurity at 8 ppm level in the methanol (HPLC
44
grade) of the mobile phase. The elemental composition of the ion at m/z
–
– 43
267, [M + 45] , was determined by FT-ICR to be [RDX + HCOO] . Formate
impurity in the methanol (HPLC grade) of the mobile phase, at an upper
level of 100 ppm, was found to be the origin of this adduct ion. 44
–
The elemental composition of the ion at m/z 281, [M + 59] , was deter-
mined by FT-ICR to be [RDX + C H O ] –.43 Acetate impurity in the methanol
3
2
2
(HPLC grade) of the mobile phase, at an upper level of 60 ppm was found
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