Lecture 7 - Explosions 7 Flashcards
what functional group within explosive is useful for detecting them and why
the nitro groups - NO2
these functional groups are often found in everyday items
how does a thermal energy analyser detect explosive compounds
the explosive material undergoes a pyrolysis reaction to form NO radical
then reacts with ozone where it becomes excited NO2
then it decays to its ground states and releases a wavelength of light = characteristic
give 5 advantages of using TEA analyser to detect explosive compounds
good LOD (sensitive) - picogram range
simple to use and maintain
fast - approx. 10min run time
reliable - can do lots of samples quickly
gives robust evidence (no known false positives)
what advantage of TEA analysers make them competitive with mass spectrometry
the good LOD (sensitivity) but the mass spec fragmentation patterns can sometimes be hard to understand so this is where TEA is better
how does the analysis using TEA analysers work
the same experiment is repeated with three different columns
if all three columns indicate the presence of an explosive the analysis is considered trustworthy
what is also added to the columns in TEA analysis to help with the detection of explosive compounds
TEA positive compound i.e reference compounds that have different retention times to known explosives and taggants commonly used
these different retention times are achieved by having other functional groups as well as the NO2 to shift the retention time slightly
these reference compounds need to have high purity and are run before running the analyte
what three columns are used in TEA analysis
BP1 = the non polar one
BPS = the slightly polar one
CPSIL19 = the polar one (not actually that polar but more polar than the others)
what compounds will be detected in TEA analysis
those with NO2 groups
why would TATP not be clearly detected using TEA analysis
as it doesn’t have nitro groups
what can be calculated from the spectrum produced in TEA analysis to validate an explosives identity
retention time of the analyte and the reference compound
why must two standard be run before running the sample
as if these retention times are different the analysis can not be called robustwqha
what is the % difference in retention time for the analyte and standard in the UK to be able to confirm the identity of the explosive
less than 0.5%
what is the order of running samples for TEA analysis
standard
blank
sample
standard
all of the above are also run alongside an internal standard
calculate % retention time difference
repeat with the other two column types
what is the equation used to quantify the amount of an explosive based on TEA spectrum
mass of sample injected = mass of standard injected x (peak area sample/ peak area of standard)
total mass = mass injected x (total sample volume/volume injected)
how to tell the difference between IR and raman spectra
raman goes up from x axis
IR comes down the the top to bottom
what is the problem with using TEA analysis for explosives and so what elese is needed
they wont detect explosive compounds that don’t have nitro groups - there aren’t many of these but one example is TATP
therefore we need other complimentary analyses
