Environmental Engineering Reference
In-Depth Information
applications.of.and.images.from.AFM.for.nanotechnology.are.available.on.instru-
ment.manufacturers'.websites.[18,.19].
5.1.2  C OmpOsitiOnal  a nalysis
...  single Particle Mass spectrometer
Mass.spectrometry.forms.the.basis.of.several.U.S..EPA.methods.for.environmental.
sample. analysis. on. a. bulk. basis,. providing. chemical. composition. data. on. an. ele-
mental.level.for.metals,.and.on.a.molecular.level.for.organics..Mass.spectrometry.
also. applies. to. the. analysis. of. single. particles. on. a. real-time. basis,. although. the.
instrumentation.has.major. differences. from.mass.spectrometers. used.in.U.S..EPA.
method.analyses..The.single.particle.mass.spectrometer,.irst.developed.in.the.1970s.
for. atmospheric. aerosol. research,. analyzes. particles. from. a. continuous. air. stream.
drawn.directly.into.the.ion.source..Both.organic.and.inorganic.constituents.can.be.
detected. and. identiied.. The. instrument. has. been. widely. used. for. air. monitoring.
studies.of.particles.with.aerodynamic.diameters.in.the.low.micron.range.[20,.21],.but.
the.technology.has.been.extended.now.to.the.nanoparticle.range.
Most.current.single.particle.mass.spectrometers.are.time-of-light.instruments,.
with.some.that.can.detect.and.analyze.particles.down.to.3.nm.in.diameter.[22]..As.
a.solid.particulate.or.droplet.suspended.in.the.air.stream.enters.the.source.region.of.
the.mass.spectrometer,.a.pulsed.laser.beam.desorbs.and.ionizes.the.particle.compo-
nents;.immediately.afterward,.a.pulsed.electric.ield.accelerates.all.ions.of.the.same.
charge.to.the.same.energy,.after.which,.depending.on.their.mass.and.charge,.they.
“ly”. at. different. velocities. to. a. charged. detector.. Both. positive. and. negative. ions.
can.be.detected.in.some.time-of-light.instruments..These.instruments.can.be.ield-
deployed.and.have.been.used.in.upper.atmospheric.studies.[23].and.for.on-site.ambi-
ent. air. monitoring. [24].. Of. the. nanomaterials. speciically. discussed. in. this. topic,.
fullerene.is.the.only.one.for.which.detection.by.single.particle.mass.spectrometry.
has.been.reported.[25].
A. recent. modiication. to. the. technology. adds. particle. size. measurement. prior.
to.the.introduction.of.the.particle.into.the.mass.spectrometer.source..These.instru-
ments,. called. aerosol. time-of-light. mass. spectrometers. (ATOFMS). [26],. employ.
two. distinct. time-of-light. technologies.. One. determines. particle. size;. the. other.
determines. particle. chemical. composition.. As. a. particle. enters. the. instrument,. a.
supersonic. expansion. of. the. carrier. gas. accelerates. the. particle. to. terminal. veloc-
ity..Because.smaller.particles.reach.a.higher. velocity.than.the.larger.particles,.the.
aerodynamic.diameter.can.be.calculated.from.the.time.it.takes.the.particle.to.travel.
between. two. lasers.. As. the. particle. passes. the. second. laser. and. enters. the. mass.
spectrometer. source,. the. high-intensity. laser. of. the. source. is. triggered. to. hit. the.
particle. and. desorb. and. ionize. particle. constituents.. These. instruments. have. been.
used. for. nanoparticle. emission. studies. from. vehicle. emissions. [27]. as. well. as. for.
atmospheric.studies.[23].
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