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Unformatted text preview: response Combination results in 3-D data providing both
quantitative and qualitative information. time One critical aspect of GC-MS and LCMS is the interface.
Both chromatographic approaches
have relatively large flows.
GC - 1 - 50 ml / min
LC - 0.1 - 5 ml / min
- 50-5000 ml/min as a gas
The mass spec requires a vacuum of
about 10-5 - 10-6 torr - gas phase. flow from chromatograph Simplest approach
would be to split
the flow. MS waste Only allow what
the MS can handle
to actually enter. This can result in only 1/1000
or less of the sample to enter
the MS - not good for trace work from
MS Vacuum source Most popular approach when
packed columns must be used.
Based on concept that larger
molecules will diffuse more
slowly so more will reach the
MS entry jet.
Relative simple and inexpensive
approach. He in
liner He out
to MS flow restrictor Somewhat similar to a jet separator. The MS pulls in
about 1 ml/min through the flow restrictor.
If column flow is above that - excess is vented.
If flow is <1 ml/min, He from external source is pulled in.
Best for sources that have flows close to 1 ml/min like
capillary columns. end of
column MS ionization
If we limit interface
to capillary columns,
the MS can actually
use all column effluent. Now that we have an interface, how do we
justify have a detector that costs more
than the chromatograph?
This is not a course in MS so we’ll limit our
discussion to using the MS as a
I’m assuming you know the basics of MS
instrumentation and interpretation. If your scan rate is too high, you don’t obtain enough
scans to properly define your peak. This results in a loss
in precision. Maximum sensitivity and precision is
obtained under conditions when
minimum qualitative information is
We need some way to maximize both
types of information
- Do multiple runs
- Target compound analysis A simple approach to obtain both
quantitative and qualitative analysis.
Works best if you are only dealing with
a limited number of analytes.
You also want to have an isotope
labeled internal standard. Example
Analysis of a drug in urine response 145
214 time 142
internal standard Sample vapor
jet • Sample is heated and allowed to
rapidly expand into a vacuum.
• Solvent is quickly pulled from
component drops and a ‘static’
charge is produced. MS column • Charged particles enter into the
MS via a skimmer. to vacuum heaters high voltage A charge is transferred to the droplets. nitrogen from LC They are then sprayed into a vacuum
chamber where the volatile solvent is
‘pulled off’. to MS nitrogen At some point, sample ions are ejected
from the drop and enter the MS. to vacuum Thermospray and Electrospray both result in
a solvent mist that is electrostatically
charged. e- e- e- e- As the drops are pulled towards the skimmer,
solvent is evaporated. e- From
Analyzer ee- This increases the charge density, causes
the drop to further disperse and ultimately
transfer the charge to the analyte. e- e- ee- Evaporation ee- e- eee- ee- e- e- e- e- e- ee- ee- e- ee- ee- e- ee- ee- ee- e- e- e- e- ee- ee- ee- ee- e- e- e- e- e- e- e- e- e- e- Breakup e- ee- ee- e- ee- interferometer injection port IR
FTIR GC Two types of data are produced
IR spectra for each scan
Full FT transformation of data is slow where as
GS calculation is fast - it only results in one
point per scan.
This permits real time display of your data. This approach relies on doing plasma
emission on your sample.
Hewlett-Packard offers a small
plasma emission detector based on
a microwave plasma source.
Relative expensive and sensitivity is
very dependent on element and
lines used vent holographic
grating reagent and
sorter column movable
photodiode array plasma
water out • Produces emission spectra for each
• A reagent gas may be needed to insure
proper atomization and excitation.
• Can obtain elemental analysis and
• Limited at this point - can only look at a
limited number of lines (due to small
range of photodiode). condensing mirror ...
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- Fall '10