Dopant-Assisted Positive Photoionization Ion ... - ACS Publications

Subscriber access provided by George Washington University Libraries

Article

Dopant-Assisted Positive Photoionization Ion Mobility Spectrometry Coupled with Time-Resolved Thermal Desorption for On-site Detection of TATP and HMTD in Complex Matrices Dandan Jiang, Liying Peng, Meng Wen, Qinghua Zhou, Chuang Chen, Xin Wang, Wendong Chen, and Haiyang Li Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.5b04830 • Publication Date (Web): 31 Mar 2016 Downloaded from http://pubs.acs.org on April 5, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Analytical Chemistry is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analytical Chemistry

Dopant-Assisted Positive Photoionization Ion Mobility Spectrometry Coupled with Time-Resolved Thermal Desorption for On-site Detection of TATP and HMTD in Complex Matrices Dandan Jiang, †,‡ Liying Peng, †,‡ Meng Wen, †,‡ Qinghua Zhou, †,‡ Chuang Chen, † Xin Wang, † Wendong Chen, †,‡ Haiyang Li. †,* †

Key Laboratory of Separation Science for Analytical Chemistry, Dalian Institute of

Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning, 116023, People’s Republic of China ‡

Graduate University of Chinese Academy of Sciences, Beijing, 100049, People’s Republic of China

*E-mail: [email protected]. Fax: +86-411-84379517.

1

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT Peroxide explosives, such as triacetone triperoxide (TATP) and hexamethylene trioxide diamine (HMTD), were often used in the terrorist attacks due to their easy synthesis from readily starting materials. Therefore, an on-site detection method for TATP and HMTD is urgently needed. Herein, we developed a stand-alone dopant-assisted positive photoionization ion mobility spectrometry (DAPP-IMS) coupled with time-resolved thermal desorption introduction for rapid and sensitive detection of TATP and HMTD in complex matrices, such as white solids, soft drinks, and cosmetics. Acetone was chosen as the optimal dopant for better separation between reactant ion peaks and product ion peaks as well as higher sensitivity and the limits of detection (LODs) of TATP and HMTD standard samples were 23.3 ng and 0.2 ng, respectively. Explosives on the sampling swab were thermally desorbed and carried into the ionization region dynamically within 10 s, the maximum released concentration of TATP or HMTD could be time-resolved from the matrix interference owing to the different volatility. Furthermore, with the combination of the fast response thermal desorber (within 0.8 s) and the quick data acquisition software to DAPP-IMS, two-dimensional data related to drift time (TATP: 6.98 ms, K0 = 2.05 cm2 V-1 s-1; HMTD: 9.36 ms, K0 = 1.53 cm2 V-1 s-1) and desorption time was obtained for TATP and HMTD, which is beneficial for their identification in complex matrices.

2


Page 2 of 33

Page 3 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


INTRODUCTION Triacetone triperoxide (TATP) and hexamethylene trioxide diamine (HMTD)，as two common homemade peroxide explosives, have been used in the improvised explosives devices (IEDs) for the terrorist attacks in the last decade, due to their simple synthesis procedures with the easy-to-obtain materials. TATP, with the explosive power similar to that of 2,4,6-trinitrotoluene (TNT), is the dominant compound involved in these cases1,2. The nearest was the Paris attacks on November 13, 2015, in which TATP was the explosive used by the suicide bombers3. In 2009, underwear bomber also used TATP in his failed attempt to blow up a Northwest Airlines flight on Christmas Day. The most notable included the London Subway attacks in 2005 and the “Shoe Bomber” incident in 2001. Therefore, the on-site analysis techniques for the TATP and HMTD in real environment are in high demands. So far, different analysis methods have been developed to detect explosives, such as X-rays, neutron analysis, nuclear quadrupole resonance, colorimetric detection4,5, mass spectrometry (MS) with different ionization methods including atmospheric pressure chemical ionization (APCI), electrospray ionization (ESI), secondary electrospray ionization (SESI)6-8 and so on. However, unlike the conventional explosives such as TNT, pentaerythritol tetranitrate (PETN) and ammonium nitrate fuel oil (ANFO), TATP and HMTD contain no nitro groups and aromatic rings in their

3



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

structures. Thus, they have no significant absorption band in the ultraviolet region and do not exhibit fluorescence. The analytical methods for conventional explosives are not suitable for their detection9-11. In recent years, many techniques have been developed to analyze TATP and HMTD. IR and Raman are recognized as the classical tools for the identification of TATP and HMTD, but their quantitative ability is needed to be further improved12. Liquid chromatography (LC) with infrared detector has been reported to quantitative analysis of TATP and HMTD. However, infrared detection techniques are often time-consuming in sample preparation and are not appropriate for detection of trace amounts of explosives13. Mass spectrometry (MS) coupled with LC or gas chromatography (GC), was applied for sensitive detection of trace peroxide explosives, but the chromatographic separation increased the analysis time10,14. Although methods based on MS are very sensitive and can detect trace amounts of peroxide explosives, instruments are often expensive, bulky and inappropriate for on-site detection. The electrochemical device is small, portable, inexpensive, and chemiluminescent methods show good sensitivity and reproducibility, but the decomposition or derivatization of TATP and HMTD make them difficult to on-site detect TATP and HMTD in complex matrices15,16. Therefore, developing a new method for the rapid on-site detection of TATP and HMTD in complex matrices is highly demanded. Ion mobility spectrometry (IMS) is a gas-phase ion separation and detection technique, which differentiates ions in a uniform electric field based on their mobility 4


Page 4 of 33

Page 5 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


differences. With the attractive features of fast response, relative low cost and good portability, it has been used for the detection of conventional explosives, such as TNT, PETN and ANFO with strong electrophilic groups –NO2 and –ONO2, which are usually detected by negative ion molecules due to their large positive electron affinities17. However, the peroxide explosives, such as TATP and HMTD could be only detected in positive ion mode related to their high proton affinities18,19. Many studies on the ionization of TATP and HMTD have been reported, such as the choice of ionization mode and the attribution of product ions. Becotte et al. firstly reported the detection of TATP and HMTD by dual mode

63

Ni-IMS, suggesting that

TATP was more easily detected in the positive ion mode20. Buttigieg et al. detected TATP in toluene by 63Ni-IMS with the limit of detection (LOD) of 187 µg ml-1, and the product ion with K0 of 2.71 cm2 V-1 s-1 was found to be the protonated molecular ion (m/z = 223)21. Marr et al. found that TATP could be only detected in the positive ion mode, while HMTD could be detected in both positive and negative ion modes by using GC-IMS-MS with NH3 and CH2Cl2 as dopants, respectively. In their research, the product ion of TATP was identified to be [TATP+NH4]+ (m/z = 240, K0 = 1.36 cm2 V-1 s-1); the product ion of HMTD was attributed to [HMTD+H]+ (m/z = 209, K0 = 1.50 cm2 V-1 s-1) in the positive ion mode, while it was associated with fragment ions in negative ion mode22. In addition, Ewing et al. studied the atmospheric pressure chemical ionization of TATP in the presence of H3O+ and NH4+ reactant ions. Positive ionization with hydronium reactant ions produced only fragments of the TATP 5



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 33

molecule, with m/z of 91 for the most predominant ion species. Ionization with ammonium reactant ions produced an ammonia-TATP adduct at m/z 240. The reduced mobility value of this ion was constant at 1.36 cm2 V-1 s-1 across the temperature range from 60 to 140 oC18. Most of these methods were based on

63

Ni ionization

source, however, its radioactivity limits its application due to safety, environmental, and regulatory concerns. In recent years, nonradioactive ionization sources were also developed to detect TATP and HMTD. Hilton et al. used a commercial electrospray ionization-high resolution ion mobility spectrometry (ESI-HRIMS) to measure TATP in positive ion mode. The peak at 8.5 ms is consistent with the [TATP+Na]+ adduct, confirmed by preliminary HRIMS-MS data23. Nevertheless, due to the long sample pretreatment time and low detection sensitivity, they are unpractical for rapid on-site detection of TATP and HMTD in complex matrices. In addition, the poor separation capacity of IMS also restricted the detection of TATP and HMTD in complex matrices, which might cause false positives. Hence, more improvements are in demand for IMS to detect TATP and HMTD in real applications. Due to the advantage of non-radioactivity, photoionization source as an alternative ionization source for

63

Ni ionization source has been used to detect conventional

explosives. Negative-ion atmospheric pressure photoionization (APPI) has been reported as a powerful ionization technique for LC-MS analysis of explosives in water8,24. Song et al. have studied the APPI-MS response to a series of explosives. Toluene was used as the analyte solvent and the dopant25. Chen et al. developed a 6


Page 7 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


vacuum ultraviolet radiation induced (UVRI) negative ionization source based on photoelectric effect by irradiating the metal surface with a 10.0 eV VUV lamp. UVRI was proved to be a high efficiency ionization source for the detection of explosives26. Dopant-assisted negative photoionization ion mobility spectrometry (DANP-IMS) was developed by Cheng et al. to detect conventional explosives17,27. However, the investigation of a dopant-assisted positive photoionization source for the detection of TATP and HMTD was rare. Herein, we developed a new method based on dopant-assisted positive photoionization ion mobility spectrometry (DAPP-IMS) coupled with time-resolved thermal desorption introduction. With acetone as the dopant, the product ions of TATP and HMTD were analyzed and attributed. The sensitivity of TATP and HMTD was improved, realizing the detection of their standard samples at ng levels. For the volatility differences between TATP or HMTD and the matrix interference, we designed a fast response thermal desorber (within 0.8 s), in which the sample was desorbed dynamically and then introduced successively into IMS. At the same time, with a quick data acquisition software, two-dimensional data with respect to the drift time and the thermal desorption time of the rapid thermal desorption process of TATP and HMTD in the complex matrices was achieved, which provided detailed and comprehensive information for the accurate identification of target compounds in the complex matrices.

7



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

EXPERIMENTAL SECTION Apparatus Fig. 1(a) shows the schematic diagram of the DAPP-IMS used in this study. A commercial low-pressure dc-discharge 10.0 eV Kr lamp (Cathodeon Ltd., Cambridge, U.K.) with MgF2 window was used as the ultraviolet light source. The IMS cell was operating at 120 oC. The reaction region and the drift region was 25 mm and 77 mm long, respectively. The electric field for the drift tube was 377 V cm-1. The length of acquisition time for ion mobility spectrum was 15 ms, then an output spectrum was obtained by averaging five initial IMS spectrum, so 12 averaged spectrum could be recorded within one second. The IMS clean air, purified and filtrated by activated carbon, silica gel, and 13X molecular sieves, was used as the carrier and drift gas. The moisture level of the air was kept below 1 ppm. The flow rate for the dopant carrier gas was kept at 50 mL min-1 while the sample carrier gas and drift gas were controlled at 200 and 600 mL min-1, respectively. Thermal Desorber In order to get the entire thermal desorption process of TATP and HMTD in the complex matrices, we designed a fast response thermal desorber (within 0.8 s). The sample of TATP (vapor pressure: 7.87 Pa, 25 oC) and HMTD (vapor pressure: 0.027 Pa, 25 oC) 25,31 was vaporized in the thermal desorber and then introduced into IMS, as shown in Fig. 1(b). The thermal desorber was made of stainless steel and controlled 8


Page 8 of 33

Page 9 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


by a step motor to open or close. It also equipped with a heating rod and a digital temperature controller (AI-518, UDINA). The temperature of the desorber was kept at 120 oC. In the sampling process, the step motor was descended to open the inlet, then inserted the sampling thin swab, with a thickness of 0.2 mm, into the thermal desorption chamber. At the same time, the step motor was ascended to close the inlet, which could be rapidly closed at the instant of inserting the sampling swab within 0.8 s. The sampling thin swab was push tightly against the stainless steel and was then heated rapidly. The heating process was a contact and rapid temperature rising process, during which the sample of TATP and HMTD was dynamically desorbed out from the sampling swab surface. The sample carrier gas continuously passed through the thermal desorption chamber while carried the sample vapor into the ionization region for analysis. The system was designed to minimize desorption times with the intention to separate different compounds before IMS based on their different volatilities. The ion mobility spectrum at different thermal desorption time was recorded by the quick data acquisition software. Thus, the drift time/desorption time two-dimensional data with respect to the drift time and the thermal desorption time could be constructed. Sample preparation and introduction All the samples used in the experiment were of analytical grade. Toluene, acetone, 2-butanone, hydrogen peroxide (30%), phosphoric acid (85%) and sulfuric acid (98%) were purchased from Kermel Chemicals Co., Ltd. (Tianjin, China). 2-pentanone was

9



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

purchased from TCI (Wellesley Hills, MA). Hexamethylenetetramine was purchased from Alfa Aesar (Ward Hill, MA, USA). The sugar, peach juice, green tea, cola, hand cream and perfume, were purchased from local grocery stores. TATP and HMTD were synthesized in our laboratory as described in the literature1,28. Stock solutions of 1000 µg mL-1 of TATP and HMTD were prepared by direct dissolving appropriate amount of fresh solids in acetone solvent. Samples of lower concentrations were obtained by the consecutive dilution method. 1% TATP and 0.01% HMTD in sugar was obtained by mixing solid TATP and HMTD with sugar, respectively. 1000 µg mL-1 TATP and 300 µg mL-1 HMTD in peach juice was prepared by dissolving solid TATP and HMTD directly in peach juice, respectively. Hand cream and perfume were dissolved in acetone firstly to obtain 10 mg mL-1 hand cream solution and 0.1% perfume solution, and then 500 µg mL-1 TATP in hand cream solution and 30 µg mL-1 HMTD in perfume solution was obtained by directly dissolving solid TATP and HMTD, respectively. Fresh samples were prepared for each experiment. All the samples were stored in a refrigerator at 4 oC to avoid decomposition. 1 µL of sample solution was first deposited on the sampling swabs (Teflon-coated fiberglass), and then inserted into the thermal desorber after the solvent was evaporated. Each sample was analyzed for 5 times. Safety note TATP and HMTD are very sensitive to explosions when present as a dry solid. They 10


Page 10 of 33

Page 11 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


should be handled carefully with appropriate precautions and should be dissolved in acetone as soon as synthesis, and stored in the refrigerator. In this work, TATP and HMTD were synthesized no more than 100 mg each time to reduce the risk of spontaneous explosions. Calculations The reduced mobility K0 (cm2 V-1 s-1) of analytes can be calculated by eq. (1), where K0a is the reduced mobility of analyte, tds and tda are the drift time of the standard and the analyte, respectively. In this work, DMMP ([DMMP]2H+ ) with a reduced mobility K0s of 1.40 cm2 V-1 s-1 and a drift time tds of 10.22 ms was used as the standard29. K0a = K0s × (tds / tda)

(1)

RESULTS AND DISCUSSION Optimization of dopants for DAPP-IMS In order to improve the sensitivity and selectivity, the dopant was optimized to produce strong and stable reactant ions to react with TATP and HMTD via charge transfer or proton transfer reaction. The response for both TATP and HMTD should be strong, meanwhile the separation between the product ion peaks (PIPs) and the reactant ion peaks (RIPs) should be good enough. Aromatics and ketones are commonly used as dopants, because of their low ionization energy (IE) and high ionization efficiency30. Therefore, in this work, aromatics, such as toluene (IE: 8.8 eV,

11



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

PA: 784 kJ mol-1), and ketones including acetone (IE: 9.7 eV, PA: 812 kJ mol-1), 2-butanone (IE: 9.5 eV, PA: 827 kJ mol-1) and 2-pentanone (IE: 9.3 eV, PA: 832 kJ mol-1) were tested for optimal dopants. The ion mobility spectra of these dopants were shown in Fig. 2, from which we can see all these dopants can form strong, stable and single RIPs, while the K0 of 2.07 cm2 V-1 s-1, 1.84 cm2 V-1 s-1, 1.66 cm2 V-1 s-1 and 1.50 cm2 V-1 s-1 were observed for toluene, acetone, 2-butanone and 2-pentanone, respectively, The signal intensities of acetone and 2-butanone were relatively higher due to their lower IE and higher ionization efficiency31. When the 400 µg mL-1 TATP and 20 µg mL-1 HMTD were detected using these four kinds of dopant, the ion mobility spectra of TATP and HMTD could be obtained as shown in Fig.2. From Fig. 2(a), we learned that with toluene as dopant, the PIPs of TATP and HMTD appeared at 2.15 cm2 V-1 s-1 and 1.55 cm2 V-1 s-1, respectively. When ketones were used as dopants, the PIPs of TATP and HMTD were observed at 2.05 cm2 V-1 s-1 and 1.53 cm2 V-1 s-1, respectively, which were different from those obtained with toluene as dopant. This observation might be caused by the different ionization mechanism, that is, TATP and HMTD might be ionized through the charge transfer reaction with toluene, while they might be ionized through proton transfer reaction with ketones30. Under the typical working condition of the current IMS apparatus, two adjacent peaks cloud be well separated when the difference of their reduced mobilities, ∆K0, is

12


Page 12 of 33

Page 13 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


higher than 0.16 cm2 V-1 s-1. The reduced mobilities and their differences between RIPs produced from the four kinds of dopants, and the PIPs of TATP or HMTD were listed in Table 1. From Table 1, we can see that with toluene as dopant, the ∆K0RIP-HMTD reached to 0.52 cm2 V-1 s-1, demonstrating the good separation efficiency for HMTD, while ∆K0TATP-RIP of 0.08 cm2 V-1 s-1 indicated the difficulty in identifying the PIP of TATP from RIP. Thus, toluene was not a good dopant for the detection of both TATP and HMTD. When acetone was chosen as dopant, the ∆K0TATP-RIP of 0.21 cm2 V-1 s-1 and ∆K0RIP- HMTD of 0.31 cm2 V-1 s-1 were obtained for TATP and HMTD, respectively, which indicated the sufficient peak to peak resolution for both TATP and HMTD as well as the feasibility of acetone as the dopant. Meanwhile, the ∆K0TATP-RIP was achieved at 0.39 cm2 V-1 s-1 and 0.55 cm2 V-1 s-1 for 2-butanone and 2-pentanone, respectively, while the ∆K0RIP- HMTD was successively obtained at 0.13 cm2 V-1 s-1 and 0.03 cm2 V-1 s-1. Both of them demonstrated the good separation efficiency for TATP but poor separation efficiency for HMTD. Therefore, 2-butanone and 2-pentanone was not a perfect choice as the dopant for the detection. Additionally, since the residue acetone solvent in the samples would react with the dopant and generate interference peaks, the IMS spectra of TATP and HMTD with toluene, 2-butanone and 2-pentanone as dopants were complicated, further hampering their identification and lowering the sensitivity. For these reasons, acetone was chosen as the optimal dopant for the rest analysis of both TATP and HMTD. Furthermore, acetone has been utilized as dopant by Cheng et al. to detect conventional explosives by using dopant-assisted 13



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

negative photoionization (DANP-IMS)17,27. It is also beneficial for the simultaneously detection of conventional organic explosives and inorganic explosives in negative ion mode and peroxide explosives of TATP and HMTD in positive ion mode by fast switching of ion mode. Qualitative and Quantitative Analysis of TATP and HMTD Standard Samples To identify the reactant ions and the product ions of TATP and HMTD, these ions were analyzed by a homemade ion trap mass spectrometer (ITMS), as the typical mass spectra were displayed in Fig. 3. The reactant ions with K0 of 1.86 cm2 V-1 s-1 were attributed to [CH3COCH3]2H+ (m/z = 117)32, while the product ions of TATP with K0 of 2.06 cm2 V-1 s-1 were assigned to [(CH3)2C(O)OO]H+ (m/z = 91), originated from the fragmentation of molecular ions, which corresponded to the reported value of 2.14 cm2 V-1 s-1 in reference18,33. Moreover, the product ions of HMTD with K0 of 1.53 cm2 V-1 s-1 were contributed to the protonated molecular ions [HMTD+H]+ (m/z = 209), which was assistance with the reported value of 1.50 cm2 V-1 s-1 in references10,22. By the real-time tracking of the maximum peak intensity, the response curves and the linear calibration curves of TATP and HMTD standard samples were obtained (see Fig. S-1 in the Supporting Information). The quantitative results of TATP and HMTD were listed in Table S-1 (see the Supporting Information). The linear response range of TATP and HMTD was 80-800 ng and 5-50 ng, with LODs (S/N = 3) of 23.3 ng and 14


Page 14 of 33

Page 15 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.2 ng for TATP and HMTD, respectively. The performance of DAPP-IMS comparison with the reported techniques for the detection of TATP and HMTD were listed in Table 2, from which we can see that IR and Raman were mainly qualitative analysis techniques. Although the LODs of GC and LC/MS could achieve to ng and pg levels, the analysis time was relatively long. The LODs of electrochemical, chemiluminescent and

63

Ni-IMS were relatively high

at µg even mg levels. While for DAPP-IMS, the LODs of TATP and HMTD standard samples reached to ng levels. So the sensitivity of DAPP-IMS was comparible to these techniques, while its analysis time was shortened to 10 s, which made it more suitable for the rapid detection of TATP and HMTD. Time-Resolved Thermal Desorption for Elimination of the Matrix Interference Although the pure TATP and HMTD could be detected readily, it was difficult to detect TATP and HMTD in the realistic environment, which were usually concealed in complex matrices, such as white solids, soft drinks and cosmetics. The ion mobility spectrum of HMTD in 0.1% perfume I solution was more complicated compared to the ion mobility spectrum of HMTD standard sample as shown in Fig. 4. Hence, it was rather difficult to identify the PIP of HMTD from the PIPs of the perfume interference. Moreover, the signal intensity of 30 µg mL-1 HMTD reduced from 906 mV to 164 mV, indicating that the detection sensitivity was seriously reduced. In order to solve this problem, we tentatively recorded the thermal desorption 15



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

profiles of 30 µg mL-1 HMTD and perfume interference peak 1 and interference peak 2, as shown in Fig. 5. From these profiles, we found that perfume interference desorbed faster than HMTD. The perfume interference reached to the maximum signal intensity at 0.91 s and 1.25 s, while HMTD reached to the maximum signal intensity of 867 mV at 4.54 s, where the perfume interference had been almost disappeared completely. It might be due to the lower volatility of HMTD than that of perfume interference. Therefore, based on the different volatility between the target compounds TATP or HMTD and the matrix interference, the maximum released concentration of TATP or HMTD could be time-resolved from the matrix interference during the fast thermal desorption process, which could improve the selectivity and the detection sensitivity greatly by minimizing competitive ionization from the interference. TATP and HMTD in the form of white solid powder might be concealed in white solids, such as sugar. As shown in Fig. 6 (a), no interfere peak from the sugar was observed due to the low desorption temperature of the desorber, which was kept at 120 oC. The two-dimensional ion mobility spectra of the 1% TATP and 0.01% HMTD in sugar was obtained, as shown in Fig. 6(d) and Fig. 7(a). Compared with the drift time/desorption time two-dimensional spectra of the sugar matrix, TATP and HMTD could be easily detected in the sugar with the characteristic drift time of 6.98 ms and 9.36 ms, as the same as the standard samples. Due to the different volatility, TATP reached to the maximum signal intensity at 1 s and desorbed completely within 4 s, 16


Page 16 of 33

Page 17 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


while HMTD started to desorb after 2 s and reached to its maximum signal intensity at 4.5 s. TATP and HMTD could be concealed in soft drinks carried by the terrorists, so 1000 µg mL-1 TATP and 300 µg mL-1 HMTD in peach juice were tested, as shown in Fig. 6(e) and Fig. 7(b). Compared with the drift time/desorption time two-dimensional spectra of the peach juice matrix as shown in Fig. 6 (b), TATP and HMTD were detected at their characteristic drift time of 6.98 ms and 9.36 ms, respectively. The characteristic desorption time of TATP and HMTD were 1.2 s and 3.5 s, which was time-resolved from the peach juice interference with the thermal desorption time of 2.4 s and 1 s, respectively. The starting thermal desorption time of TATP and HMTD in liquid matrix were a bit later than that in solid matrix, which might be related to the evaporation of the water. TATP and HMTD could persist on the hands or clothes of the terrorists or criminal suspects in transit, cosmetics such as hand cream and perfume might be the potential interference for the detection of TATP and HMTD. Hence, 500 µg mL-1 TATP in hand cream I and 30 µg mL-1 HMTD in 0.1% perfume I were detected, and their two-dimensional spectra were displayed in Fig. 6(e) and Fig. 7(c). Compared with the drift time/desorption time two-dimensional spectra of the hand cream matrix as shown in Fig. 6 (c), TATP was detected at the drift time of 6.98 ms, which was the same as that in other matrices. TATP started to desorb at the instant of sampling and reached to

17



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

the maximum concentration at 0.2 s, almost desorbed completely within 2 s, while the hand cream desorbed after TATP and reached to the maximum signal intensity at 3.4 s and 5.2 s, respectively. HMTD was detected in the perfume matrix at the drift time of 9.36 ms, and it desorbed to the maximum signal intensity at 5.1 s, which was time-resolved from the perfume interference at 0.7 s and 1.3 s. HMTD with lower volatility desorbed slower than the perfume interference. In addition, TATP and HMTD were also detected in other common soft drinks and cosmetics. The drift time/desorption time two-dimensional spectra of 1000 µg mL-1 TATP in cola, green tea and 500 µg mL-1 TATP in hand cream II were shown in Fig. S-3. The product ion peak of TATP in these matrices was detected at the drift time of 6.98 ms as well. Due to the different volatility, TATP was desorbed completely within 3 s or so, earlier than the most interferents in cola, green tea and hand cream II. Also, the ion peak of 300 µg mL-1 HMTD in cola, green tea and 30 µg mL-1 HMTD in 0.1% perfume II was detected at the drift time of 9.36 ms, as shown in Fig. S-4. Different from TATP, the majority of HMTD was desorbed later than most other substances in the three matrices. According to the difference of desorption time, TATP and HMTD could be resolved from the complex matrices. CONCLUSIONS In this work, a dopant-assisted positive photoionization ion mobility spectrometer (DAPP-IMS) with time-resolved thermal desorption introduction was constructed for 18


Page 18 of 33

Page 19 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


on-site detection of TATP and HMTD in complex matrices. With acetone as the dopant, the limits of detection (LODs) reached to ng levels for TATP and HMTD standard samples. With the combination of the fast response thermal desorber (within 0.8 s) and the quick data acquisition software, rapid on-site detection (less than 10 s) was achieved for TATP and HMTD in complex matrices, such as white solids, soft drinks and cosmetics. According to the differences of volatility between the TATP or HMTD and matrix interference, the drift time/desorption time two-dimensional spectrum could be obtained, which help to identify TATP and HMTD in complex matrices. The addition of time-resolved dynamic thermal desorption to IMS improved the trace analysis capability through better resolution and reduced detection saturation. Compared with other techniques, DAPP-IMS shows great potential for the detection of TATP and HMTD in complex matrices. Under the guarantee of the sensitivity at ng levels, DAPP-IMS could shorten the analysis time to 10 s. It is a powerful method to identify the target compounds in complex matrices. ASSOCIATED CONTENT Supporting Information

Additional information as noted in text. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author 19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

* E-mail: [email protected]. Fax: +86-411-84379517. Notes The authors declare no competing financial interest. ACKNOWLEDGEMENTS This work is partially supported by the NSF of China (21177124), the National High-Tech Research and Development Plan (No.2014AA06A507), the National Special Fund for the Development of Major Research Equipment and Instrument (Grants 2011YQ05006904). REFERENCES (1)

Dubnikova, F.; Kosloff, R.; Almog, J.; Zeiri, Y.; Boese, R.; Itzhaky, H.; Alt, A.;

Keinan, E. J. Am. Chem. Soc. 2005, 127, 1146 - 1159. (2)

Mullen, C.; Huestis, D.; Coggiola, M.; Oser, H. International Journal of Mass

Spectrometry 2006, 252, 69-72. (3) http://www.nydailynews.com/news/world/paris-suicide-bombers-tatp-homemade-expl osive-article-1.2435082 2015. (4)

Yinon, J. Trends in Analytical Chemistry 2002, 21.

(5)

Singh, S.; Singh, M. Signal Processing 2003, 83, 31–55.

(6)

Martinez-Lozano, P.; Rus, J.; Fernandez de la Mora, G.; Hernandez, M.;

Fernandez de la Mora, J. Journal of the American Society for Mass Spectrometry 2009, 20


Page 20 of 33

Page 21 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


20, 287-294. (7)

Vidal-de-Miguel, G.; Macia, M.; Pinacho, P.; Blanco, J. Anal. Chem. 2012, 84,

8475-8479. (8)

Badjagbo, K.; Sauvé, S. Critical Reviews in Analytical Chemistry 2012, 42,

257-271. (9)

Cotte-Rodriguez, I.; Hernandez-Soto, H.; Chen, H.; Cooks, R. G. Anal. Chem.

2008, 80, 1512-1519. (10)

Crowson, A.; Beardah, M. S. The Analyst 2001, 126, 1689-1693.

(11)

Schulte-Ladbeck, R.; Kolla, P.; Karst, U. Anal. Chem. 2003, 75, 731-735.

(12)

Pena, A. J.; Pacheco-Londono, L.; Figueroa, J.; Rivera-Montalvo, L. A.;

Roman-Velazquez, F. R.; Hernandez-Rivera, S. P. In Sensors, and Command, Control, Communications, and Intelligence, Carapezza, E. M., Ed., 2005, pp 347-358. (13)

Schulte-Ladbeck, R.; Edelmann, A.; Quinta, G.; Lendl, B.; Karst, U. Anal.

Chem. 2006, 78, 8150-8155. (14)

Kende, A.; Lebics, F.; Eke, Z.; Torkos, K. Microchimica Acta 2008, 163,

335-338. (15)

Laine, D. F.; Cheng, I. F. Microchemical Journal 2009, 91, 125-128.

(16)

Mahbub, P.; Zakaria, P.; Guijt, R.; Macka, M.; Dicinoski, G.; Breadmore, M.;

Nesterenko, P. N. Talanta 2015, 143, 191-197. (17)

Cheng, S.; Dou, J.; Wang, W.; Chen, C.; Hua, L.; Zhou, Q.; Hou, K.; Li, J.; Li,

H. Anal. Chem. 2013, 85, 319-326. 21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(18)

Ewing, R. G.; Waltman, M. J.; Atkinson, D. A. Anal. Chem. 2011, 83,

4838-4844. (19)

Burks, R. M.; Hage, D. S. Anal. Bioanal. Chem. 2009, 395, 301-313.

(20)

McGann, W. J.; Goedecke, K.; Becotte-Haigh, P.; Neves, J.; Jenkins, A. Int. J.

Ion Mobil. Spectrom. 2001, 4, 144-147. (21)

Buttigieg, G. A.; Knight, A. K.; Denson, S.; Pommier, C.; Bonner Denton, M.

Forensic Science International 2003, 135, 53-59. (22)

Marr, A. J.; Groves, D. M. Int. J. Ion Mobil. Spectrom. 2003, 6, 59-61.

(23)

Hilton, C. K.; Krueger, C. A.; Midey, A. J.; Osgood, M.; Wu, J.; Wu, C.

International Journal of Mass Spectrometry 2010, 298, 64-71. (24)

Crescenzi, C.; Albinana, J.; Carlsson, H.; Holmgren, E.; Batlle, R. Journal of

Chromatography A 2007, 1153, 186-193. (25)

Song, L.; Wellman, A. D.; Yao, H.; Bartmess, J. E. Journal of the American

Society for Mass Spectrometry 2007, 18, 1789-1798. (26)

Chen, C.; Dong, C.; Du, Y. Z.; Cheng, S. S.; Han, F. L.; Li, L.; Wang, W. G.;

Hou, K. Y.; Li, H. Y. Anal. Chem. 2010, 82, 4151-4157. (27)

Cheng, S.; Wang, W.; Zhou, Q.; Chen, C.; Peng, L.; Hua, L.; Li, Y.; Hou, K.; Li,

H. Anal. Chem. 2014. (28)

Schaefer, W. P.; Fourkas, J. T.; Tiemann, B. G. J. Am. Chem. Soc. 1985, 107,

2461-2463. (29)

Viitanen, A. K.; Mauriala, T.; Mattila, T.; Adamov, A.; Pedersen, C. S.; Makela, 22


Page 22 of 33

Page 23 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


J. M.; Marjamaki, M.; Sysoev, A.; Keskinen, J.; Kotiaho, T. Talanta 2008, 76, 1218-1223. (30)

Nazarov, E. G.; Miller, R. A.; Eiceman, G. A.; Stone, J. A. Anal. Chem. 2006,

78, 4553-4563. (31)

Adam, T.; Zimmermann, R. Anal. Bioanal. Chem. 2007, 389, 1941-1951.

(32)

Vautz, W.; Bödeker, B.; Baumbach, J. I.; Bader, S.; Westhoff, M.; Perl, T.

International Journal for Ion Mobility Spectrometry 2009, 12, 47-57. (33)

Sigman, M. E.; Clark, C. D.; Fidler, R.; Geiger, C. L.; Clausen, C. A. Rapid

Communications in Mass Spectrometry 2006, 20, 2851-2857. (34)

Oxley, J. C.; Smith, J. L.; Kirschenbaum, L. J.; Marimganti, S.; Vadlamannati,

S. J. Forensic. Sci. 2008, 53, 690-693.

23



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 1. Schematic diagram of (a) the dopant-assisted positive photoionization ion mobility spectrometer coupled with the fast thermal desorber; (b) the time-resolved thermal desorption process of TATP and HMTD in complex matrices.

24


Page 24 of 33

Page 25 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. Ion mobility spectra of the reactant ion, 400 µg mL-1 TATP, and 20 µg mL-1 HMTD with (a) toluene, (b) acetone, (c) 2-butanone and (d) 2-pentanone as dopant. (“＊” marks the product ion peaks originated from the acetone solvent.)

25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 3. Mass spectra of 400 µg mL-1 TATP and 20 µg mL-1 HMTD with acetone as dopant.

26


Page 26 of 33

Page 27 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. Ion mobility spectra of (a) 30 µg mL-1 HMTD；(b) 30 µg mL-1 HMTD in 0.1% perfume I.

27



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 5. Dynamic thermal desorption profiles of 30 µg mL-1 HMTD in 0.1% perfume I.

28


Page 28 of 33

Page 29 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 6. Drift time/desorption time two-dimensional spectra of (a) sugar, (b) peach juice, (c) hand cream I, (d) 1% TATP in sugar, (e) 1000 µg mL-1 TATP in peach juice, and (f) 500 µg mL-1 TATP in hand cream I.

29



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 7. Drift time/desorption time two-dimensional spectra of (a) 0.01% HMTD in sugar (b) 300 µg mL-1 HMTD in peach juice, and (c) 30 µg mL-1 HMTD in 0.1% perfume I.

30


Page 30 of 33

Page 31 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1. The reduced mobilities and their differences of RIP, TATP and HMTD with toluene, acetone, 2-butanone and 2-pentanone as dopants.

Dopant

Toluene Acetone 2-Butanone 2-Pentanone

K0 RIP

2.07

1.84

1.66

1.50

K0 TATP

2.15

2.05

2.05

2.05

1.55

1.53

1.53

1.53

0.08

0.21

0.39

0.55

0.52

0.31

0.13

0.03

HMTD

K0 ∆K0TATP-RIP ∆K0RIP- HMTD

31



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 33

Table 2. Comparison of different techniques for the detection of TATP and HMTD.

Detection technique

TATP/HMTD

LODs

Reference

IR/Raman HPLC-IR SPME GC-MS

TATP; HMTD TATP; HMTD TATP model samples (20 min)

Qualitative 1 mM; 0.5 mM 5 ng

12

LC-MS

HMTD in acetone (30 min)

20 pg

10

Electrochemical Chemiluminescent 63 Ni-IMS

HMTD (＞1 min) TATP; HMTD (1.5 min -3 min) TATP in toluene

3×10-5 M

15 16

IMS

TATP in hair

DAPP-IMS

TATP in acetone HMTD in acetone (10 s)

0.5 µM 187 µg mL-1 1.9 µg (E-mode) 0.8 µg (N-mode) 23.3 ng 0.2 ng

32


13 14

21 34

Present work

Page 33 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


for TOC only

33


Dopant-Assisted Positive Photoionization Ion ... - ACS Publications

Recommend Documents