Supplementary Information
On-site Rapid Detection of Trace Non-volatile
Inorganic Explosives by Stand-alone Ion
Mobility Spectrometry via Acid-enhanced
Evaporization
Liying Peng1, 2, Lei Hua1, Weiguo Wang1, Qinghua Zhou1, 2, and Haiyang Li*, 1
1
Key Laboratory of Separation Science for Analytical Chemistry, Dalian Institute of
Chemical Physics, Chinese Academy of Sciences, Dalian, 116023, People’s Republic
of China
2
University of Chinese Academy of Sciences, Beijing, 100049, People’s Republic of
China
*E-mail: [email protected]. Fax: +86-411-84379517.
SI 1. Influence of different acids on the analysis
Since the common strong acids such as sulphuric acid (H2SO4), hydrochloric acid
(HCl) generally form many ion patterns in their background ion mobility spectra and
would interfere the analysis. Hence, we chose other weak acids such as acetic acid
(CH3COOH) and boric acid (H3BO3) to perform the acidification process. Ion
mobility spectra of KNO3 obtained in the existence of H3BO3 and CH3COOH were
depicted in Fig. S1. From Fig. S1 (a), ion patterns such as K0 at 2.15 and 1.82
cm2V-1s-1 were obtained for H3BO3, while only product ion with K0 of 2.05 cm2V-1s-1
was observed for KNO3 in the existence of H3BO3. The ion pattern of H3BO3 overlap
with the ion peak of KNO3 with K0 of 2.18 cm2V-1s-1 and it would interfere the
identification of KNO3. Additionally, when CH3COOH was used for acidification, ion
peak with K0 of 2.11 cm2V-1s-1 was appeared for CH3COOH, but no reponse was
obtained for KNO3, as seen in Figure S1(b). Hence, compared with the perfect
sensitivity and simple background of H3PO4 little interfering the analysis, the
common weak acids such as CH3COOH and H3BO3 was not suitable for the analysis.
Furthermore, the effect of concentration of H3PO4 on the sensitivity was also studied
and the results were presented in Fig. S2. The signal intensities of oxidizers sharply
increased with the H3PO4 concentration growing up, and then gradually reached to the
maximum as the H3PO4 concentration more than 0.03%.
Supplementary Figure S1. Ion mobility spectra of KNO3 obtained in the existence of (a) boric
acid (H3BO3) and (b) acetic acid (CH3COOH).
Supplementary Figure S2. The profile of signal intensities of inorganic oxidizers to H3PO4
concentration.
SI 2. Atmospheric pressure negative ionization time-of-flight mass spectra
(TOF-MS)
In mass spectrometry experiments, part of IMS including the ionization source and
reaction region was connected directly to TOF mass spectrometer to identify the
reactant ions as well as inorganic explosive product ions formed in them. And zero air
was divided into purified gas (500 mL/min) and carrier gas (500 mL/min) via two
mass flow controllers and there was no drift gas. So only the purified air flow the 63Ni
source and the pollution and acid corrosion of 63Ni source could be avoided.
Supplementary Figure S3. Schematic of atmospheric pressure negative ionization time-of-flight
mass spectra (TOF-MS).
SI 3. Ion mobility spectra of HNO3 and HClO4
Trace HNO3 and HCIO4 were directly detected and the ion mobility spectra were
demonstrated in Fig. S4 (The absence of HCIO3 arises from its instability and the
difficulty to be acquired). From the spectra, two ion peaks at K0 of 2.18 and 2.05 cm2
V-1s-1 were observed for HNO3 while ion peaks at K0 of 2.15 and 1.77 cm2 V-1s-1 were
found for HCIO4. Furthermore, compared with the low vapour pressure (10-4 Pa or
less) of typical explosive compounds, the vapour pressure of 1.07 (20 oC) and 0.9 kPa
(25 oC) for HNO3 and HCIO4, respectively reveals that they are easy to be vaporized
into gaseous phase. [1]
Supplementary Figure S4. Ion mobility spectra of HNO3 and HClO4 obtained without H3PO4.
SI 4. Ion mobility spectra of TNT and RDX
The commercial TNT and RDX were detected by IMS in the existence of H3PO4, and
the ion mobility spectra were shown in Fig. S5. Product ion peak at K0 of 1.54 cm2
V-1s-1 was observed obviously for TNT, while the product ion peaks at K0 of 1.65,
1.53 and 1.44 cm2 V-1s-1 were acquired for RDX.
Supplementary Figure S5. Ion mobility spectra of 5 ng TNT and 10 ng RDX obtained with
H3PO4.
SI 5. Ion mobility spectra obtained without acidification
The commercial firecracker and black powder were detected directly by IMS, and the
ion mobility spectra were shown in Fig. S6. From the ion mobility spectra, product
ion peak of S at K0 of 2.21 cm2 V-1s-1 was observed obviously for firecracker and
black powder.
Supplementary Figure S6. Ion mobility spectra of firecracker and black powder obtained without
H3PO4 acidification.
SI 6. Ion mobility spectra of KNO3/sugar, KClO3/sugar, KClO4/sugar
The sugar are always used as fuel for an inorganic explosive and 20 ng KNO3/sugar
(4:1), 50 ng KClO3/sugar (4:1) and 600 ng KClO4/sugar (3:2) were measured by this
current method, as depicted in Fig. S7. From the ion mobility spectra, characteristic
ions of KNO3, KClO3 and KClO4 were distinctly observed for KNO3/sugar,
KClO3/sugar and KClO4/sugar, respectively.
Supplementary Figure S7. Ion mobility spectra of 20 ng KNO3/sugar (4:1), 50 ng KClO3/sugar
(4:1) and 600 ng KClO4/sugar (3:2) obtained with H3PO4.
SI 7. References
[1] http://www.chemicalbook.com/ProductIndex_EN.aspx.