Electronic Supplementary Material for

Direct Analysis of Large Living Organism by Megavolt Electrostatic Ionization Mass Spectrometry

Kwan-Ming Ng, Ho-Wai Tang, Sin-Heng Man, Pui-Yuk Mak, Yi-Ching Choi, Melody Yee-Man Wong
Department of Chemistry, and State Key Laboratory of Synthetic Chemistry, The University of Hong Kong, Hong Kong, China

Correspondence to: Kwan-Ming Ng; e-mail:

Experimental Procedures and Materials

Chemicals, Solvent and Others

The explosives (2,4-ditnitrotoluene at >99.9% purity and 2,4,6-trinitrophenol at >99.0 % purity) and cocaine (> 97 % purity) standards were purchased from Sigma Aldrich (St. Louis, MO, USA). Toluene (AR grade) was purchased from VWR International (Radnor, PA, USA). Acetonitrile (HPLC grade) was purchased from Scharlab S.L. (Sentmenat, Barcelona, Spain). Water (HPLC grade) was purchased from RCI Labscan (Pathumwan, Bangkok, Thailand). Formic acid (ACS grade, > 98 % purity) was purchased from Sigma Aldrich.

Red wine (Vintage 2009, Reserve Shiraz, Jacob’s Creek, South Australia, Australia), mint flavored chewing gum (Airwaves, Wrigley, IL, USA) and painkiller tablet (each contain 500 mg acetaminophen, Panadol, GlaxoSmithKline, County Waterford, Ireland) were purchased from a local supermarket.

Mass Spectrometry

All mass spectrometric measurements were performed using a hybrid quadrupole-time-of-flight (Q-TOF) tandem mass spectrometer (Q-TOF Premier, Waters Micromass, Manchester, UK). The original ion extraction cone in the ion source was replaced by an extended ion source, which extended the mass spectrometer inlet away from the ion source block for easier sampling. The extended ion source was electrically grounded to prevent the accumulation of electrostatic charge. In addition, to prevent possible electrostatic damage, the mass spectrometer was shielded from electrical charges using several electrically grounded metal plates. Instrumental control and data acquisition were performed using MassLynx 4.1 system software (Waters Corporation, Milford, MA, USA).

The experimental settings of the mass spectrometer were as follows. Ions collected from the inlet would pass through an ion source block which was set at 80 °C. No pneumatic assistance, including cone gas or nebulising gas, was used. The sample cone voltage was set at 30 V. In TOF-MS experiment, the ions were guided through an argon-filled collision cell with collision energy of 2 eV for better ion transmission. For tandem mass spectrometry experiment, ions of interest would be selected by a quadrupole mass filter and then guided into the collision cell with collision energy from 2 – 14 eV (laboratory frame), depending on the extent of fragmentation of the respective analyte ion (except for [Toluene - H]+ which required a higher collision energy of 35 eV). The ions were then mass analyzed by a reflectron TOF mass analyzer and detected by a microchannel plate detector set at 2.1 kV. The mass resolving power of the TOF mass analyzer was tuned to ~6,500 (at m/z 304.1, Full-width at Half Maximum, FWHM). For the general TOF-MS experiments, the mass accuracy of the Q-TOF mass spectrometer was calibrated to be within 20 ppm (at m/z 304.1468) with an external calibration. For accurate mass measurement of volatile compounds in human breath gas, TOF-MS experiment was performed immediately after mass calibration, the mass accuracy was within 6 ppm (at m/z 90.9772). The vacuum pressure of the source, collision cell and TOF mass analyzer regions were 1.68, 6.22 × 10-3, 8.73 × 10-7 mbar respectively. In general, each TOF MS spectrum was a combination of 30 – 60 scan. The scan time for each scan was 1 s and the interscan time was 0.1 s. The acquisition mass range was m/z 10 – 1,000.

Electrostatic Generators

The positive (+0.2 megavolt) and negative (-0.4 megavolt) electrostatic potential were generated using two Van de Graaff generators (Science First, Yulee, FL, USA). The Van de Graaff generators used in all our experiments were the same type, but the model adopted for the positive ion mode study is different from that adopted for the negative ion mode study. The difference between the two models is size of the domes (that used for the accumulation of the electrostatic charge). Both domes (for the positive and negative electrostatic generators) are spherical in shape, but their diameters and circumferences are different. The circumferences of the domes used for the Van de Graaff generators generating positive electrostatic potential (+0.2 megavolt) and negative electrostatic potential (-0.4 megavolt) were 56.5 cm and 100.8 cm respectively. The diameters of the domes used for the Van de Graaff generators generating positive electrostatic potential (+ 0.2 megavolt) and negative electrostatic potential (-0.4 megavolt) were approximate 18.0 cm and 32.1 cm, respectively.

Direct Analysis of Explosives on Latex Glove

A laboratory latex glove was worn on a hand of a healthy individual, and then a small amount (< 1 mg) of the explosive compounds was deposited on the fingertip region of the glove. The individual was electrically floated to megavolt potential by putting one of his hand on the metal ball of the Van de Graaff generator for the gradual accumulation of charge for about 2 seconds, then the gloved hand of the individual was moved in front of (~ 8 cm away from) the extended inlet of the mass spectrometer. The Van de Graaff generator (with negative potential at 0.4 MV) was switched on only when the individual had put his hand on the metal ball. Ions of the explosives were readily detected upon the electrostatic charging of the individual. The individual was isolated from the surrounding to avoid charge leakage. A diagram showing the experimental setup is depicted in Figure 1.

Direct Analysis of Explosives and Flammable Solvent on Cloth/ Tissue Paper

Explosive powder/ a drop of toluene was deposited on a piece of cotton cloth/ tissue paper. The cloth/ paper was held by an individual, and then put in front of the mass spectrometer inlet after the individual was electrostatically charged by a Van de Graaff generator. Negative electrostatic potential was applied for the detection of explosives, and positive electrostatic potential was applied for the detection of toluene.

Direct Analysis of Cocaine on Bare Hand

The experimental procedure was essentially similar to that of the analysis of explosives on a glove, except that cocaine (< 0.5 mg) was deposited directly on the fingertip of an individual, and also a Van de Graaff generator which generated a positive electrostatic potential (0.2 MV) was employed.

Direct Analysis of Acetaminophen in Painkiller Tablet

The experimental procedure was essentially similar to that of the analysis of cocaine on bare hand, except that a painkiller tablet instead of powder was directly held by an individual, with the addition of 200 μL of an aqueous solution (containing 50% acetonitrile and 0.1 % formic acid) onto the tablet.

Direct Analysis of Human Breath after Drinking Red Wine and Chewing Mint Flavored Gum

For the analysis of human breath after drinking red wine, a healthy individual first drank a cup of red wine. After 3 minutes, breath gas of the individual was directed to the extended inlet via a glass tube (~ 20 cm long), and he was then electrostatically charged by a Van de Graaff generator generating a positive electrostatic potential (0.2 MV). The breath gas analysis of the individual after chewing the mint-flavored gum (for 5 minutes) was performed with the same procedure.

Direct Analysis of Normal Breath of Individuals

For the direct analysis normal breath of four healthy individuals, the procedure was essentially the same as that in the analysis of breath after drinking red wine, except that the breath of the individuals can be directed to the extended inlet of the mass spectrometer, without the intake of any special food or drink prior to analysis.

Supplementary Figures