Quiz3 Flashcards
If one uses FAAS and an air-acetylene flame, one needs to be aware of the fact that if the most intense lenda to measure the element of interest is in the ultraviolett region, the flame itself will absorb light of this lenda. To rectify this situation one way either chose a different lenda which is ____ and ____ or one may chose a different ____.
less sensitive
>230nm
oxidant fuel mixture
In GAAS, the utilization of a transversely heated graphite tube/furnace instead of a conventional one offers one important advantage: during the atomization step, the ____ of atoms at the ____ is precluded , which will ____ the detection limit.
condensation
cooler ends of the tube
decrease
In terms of the detection limits that can be obtained with FAAS for many elements (eg. Cd), they are about the same than those that can be achieved for the same element by ICP-AES. The major limitation of FAAS, however, is that ____ can be measured, whereas ICP-AES allows to measure ____, which is why the latter is ____.
only single elements
multiple elements
most widely used
An ICP cannot be used instead of a flame to conduct an atomic absorption experiment because the number of analyte atoms in the ____ is too small because of the ____ of the ICP.
ground state
high temperature
True/False: In GFAAS it is sometimes useful to add a matrix modifier to the sample (in the graphite tube) in order to decrease the volatility of the analyte.
True
One advantage of the hydride technique is that for certain elements (eg. As), it provides even lower detection limits than GFAAS. This is because the analyte is ____ from the ____ and the generated volatile analyte molecules (eg. AsH3) are decomposed into atoms in a heated quartz cell.
separated
matrix
If one wants to use atomic emission spectroscopy (AES) for quantitative measurements, one should avoid ___ as the atomization source because small changes of its ____ will dramatically affect the ____. This problem is virtually eliminated if one uses an ____ as the atomization source.
a flame
temperature
emission light intensity
ICP
If one wants to characterize an unknown sample by mass spectrometry, one needs to first desorb the sample molecules into the gas-phase, then generate ions, accelerate the latter in an electric field and separate the ions according to their ____ and finally detect them.
mass to charge ratio
If one wants to determine the molecular mass ion M+ of an unknown compound by MS, one should use ____, because this generally results in ____ of the molecule of interest.
chemical ionization
In the context of using an ICP as an atomizer, the utilization of an ultrasonic nebulizer (instead of a pneumatic nebulizer) decreases the detection limit of many chemical elements by ~1 order of magnitude. This is attributed to the increased ____ of the analyte into the plasma.
mass transfer
If one has detected an ion with an m/z of 84 with a MS and one wants to distinguish whether this species corresponds to C5H8O+ = 85.05696 or C6H12+ = 84.09335, the ____ of the spectrometer must be increased.
resolving power
Short answer: identify and briefly explain the four major advantages of graphite furnace atomic absorption spectrometry (GFAAS) compared to flame atomic absorption spectrometry (FAAS)?
- less sample requirement
- higher sensitivity -> lower detection limit, longer “residue” time
- higher temperature, less spectral interference
- can increase sample injection times to decrease detection limit (pre-[])
- can analyze solid sample
