PNNL-13501 - Pacific Northwest National Laboratory

introduce low-volatility compounds into the gas phase for
transport across the membrane to the mass spectrometer.
Results and Accomplishments
• We successfully demonstrated laser desorption
membrane introduction ion trap mass spectroscopy
using polyaromatic hydrocarbons.
• Constructed a semiautomated field device for
acquiring filter samples.
• Adapted the membrane introduction ion trap mass
spectroscopy device for field deployment in Houston.
• Deployed the combined filter and real-time gas-phase
membrane introduction ion trap mass spectroscopy at
TX2000AQS in Houston.
A schematic of the membrane introduction ion trap mass
spectroscopy device for analysis of samples is shown in
Figure 1. Semivolatile organics, such as polyaromatic
hydrocarbons are placed into the gas phase by the laser
pulse, pass through the membrane, and are carried into the
mass spectrometer by a flow of helium. The instrument
deployed in Houston collected the particulates on a filter
for subsequent laboratory analysis. Three filter
combinations were used in order to check for
volatilization artifacts: Teflon, quartz, and
Vacuum
System
Modified Commercial
Ion Trap M ass Spec.
E-Gun
Membrane
Filter
Sample
Ion
Detector
Amp &
Signal
Proc.
Desorption Laser
Nd:YAG
Mass Spectrum
Data Acquisition
Figure 1. Schematic diagram of laser desorption membrane
ion trap mass system
Teflon followed by quartz. Each filter configuration was
exposed to sample air alternately for 10-minute intervals
over 4 hours. The air samples were passed directly
through the membrane for real-time analysis of the gasphase
organics. The semiautomated field device is shown
in Figure 2. A sample mass spectrum from Houston air is
shown in Figure 3. The major components were found to
be alkanes and alkenes by using the sequential mass
spectrum capabilities of the ion trap system. These MS-
MS scans also showed the presence of acetaldehyde. The
higher weight compounds were not conclusively
identified.
Figure 2. Schematic diagram of automated filter collection
system deployed in Houston
Counts
40 00
35 00
30 00
25 00
20 00
15 00
10 00
500
Mass Spectrum from Houston Air
0
35 55 75 95 1 15 1 35 1 55 1 75 1 95
Mass m/Z
Figure 3. Sample mass spectrum of Houston air
Analytical and Physical Chemistry 7