Chemistry Reference
In-Depth Information
Answer:
Since limited sample is available for analysis, GC-MS would
be used, diacetylmorphine and other opium alkaloids such as
morphine and codeine.
2.
The barbiturates butalbital and secobarbital were analysed by GC-MS
and two peaks were found with similar retention times. On further
mass spectrometric analysis, both peaks were found to have princi-
pal ions of 167 and 168 Da. How would you identify which peak was
which compound?
Answer:
Pure standards of both barbiturates would be analysed
separately and the retention times would be compared to those
found in the mixture analysed.
3.
Which derivatising reagent would you choose to use with the follow-
ing analytes?
CH
3
CH
3
N
OH
O
NH
2
OH
O
H
3
C
H
3
C
O
O
C
5
H
11
HO
CH
3
OH
O
(a)
(b)
(c)
Answer:
(a) BSA or MSTFA, (b) HFBA or other acylating agent, (c)
MSTFA or BSTFA.
4.
In our toxicology example (Section 8.3.6), Proadifen was used as an
internal standard and was added to the blood sample prior to the
extraction step. What is the purpose of an internal standard?
Answer:
An internal standard is added to the sample prior to extraction
for comparison of signal from the analyte. This is used to establish
how much analyte is extracted (efficiency of extraction). Internal
standards are especially useful for analyses where the quantity of
sample analysed or the instrument response varies slightly from
run to run for reasons that are out of the analyst's control.
5.
Although Proadifen was used in our example, it is best to use a deu-
terated analogue of the analyte(s) under investigation. Why?
Answer:
An isotopically labelled version of the analyte(s) is best to
use since this compound is chemically similar and therefore will
have a similar (or the same) retention time but is not likely to be
present in the sample being analysed.
6.
In GC-MS the most abundant ion is not always the molecular ion.
Why?
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