Download APRIL95

April 1995
[1]
T. Smith-Palmer
(a)
Draw a box diagram for a SFC instrument.
[2]
(b)
Label each box with a specific part.
e.g. don't just write detector, give a particular type.
[1]
(c)
What is the general principle behind any form of chromatography?
[3]
(d) Describe the separation principle applicable for the set-up column you have in your
diagram.
[1]
(e)
What is the mobile phase? (Suggest a typical one).
[2]
(f)
What characteristics of it can be varied?
[2]
(g)
Why does one want to vary the mobile phase?
[3]
(h)
Describe the advantages (with reasons) of SFC as compared to GC and HPLC.
[3]
(i)
Describe the operating principles of the detector you chose in (b).
[10]
1.
Chemistry 360
2.
Write a short magazine article for a ‘Popular' Science magazine entitled
EITHER
‘Capillary Electrophoresis - a growing field in separation science'
OR
‘Mass Spectroscopy - the ultimate detector for chromatographic applications'
[25] 3.
(i)
Do 5 (five) of the following: (Answer in note form where appropriate)
You have a mixture which you suspect contains Uranium and Thorium salts.
It is suggested that these ions can be separated from the other metal ions present in the
mixture by some form of chromatography, by means of their ability to form anionic
complexes with nitrate.
(a)
(b)
(c)
0
Elaborate on a suitable method.
When separated, Uranium can be distinguished from thorium because over several
weeks of monitoring the radioactivity is increasing in one spot, decreasing in
another.
Which spot is which, and why?
Will the amount of radioactivity keep on increasing? Normally we talk of
radioactive decay. Explain.
Chemistry 360 - April 1995 - T. Smith-Palmer
(ii)
Page 2
"Frequently for analytical instrumental methods, there are equations which can be derived
which relate a measured parameter to the concentration of a particular species. For
example, the ilkovic equation. Often the proportionality is rather complicated, and so the
best thing to do is to eliminate the need for its use."
What does this mean and how would we eliminate the need to use the derived
relationship?
(iii)
You have an unknown mix of organic compounds that you wish to analyse by gc. You
have been told it is some kind of petroleum extract, and you expect it is volatile enough to
analyse by gc.
(a)
(b)
(c)
Suggest - with reasons - conditions for a first trial run.
Suggest a suitable detector - give reason.
Would a TED detector be suitable for use in this analysis? Why?
(iv)
Suggest instrumental ways to determine the following ions in mixtures with each other (a) Na+ and Li+
(b) Cd2+ and Zn2+
(c) Cl- and SO-
(v)
(a)
(b)
(c)
(vi)
KOH is used as a preliminary column treatment in various CE methods. What is
the purpose of this?
Why is it not used when we are separating the anions in a mixture?
Why is a surfactant sometimes used as part of the buffer?
Say something about preparing the sample for analysis. (What do you need to
add?)
The development of GC and HPLC methods can often be very time consuming with many
different conditions which can be varied. In addition, separations can be optimised by the
correct choice of column. It would not only be time consuming, but very costly, if one
had to try a variety of columns to optimise a separation.
(a)
(b)
(c)
List the parameters that can be varied with respect to column make-up.
What can one do to find optimum conditions for a separation without having to
spend a lot of time in the lab?
What experimental information would be necessary to do what you have described
in (b)?
Chemistry 360 - April 1995 - T. Smith-Palmer
Page 3
(vii) Suggest what conditions could be changed in the following chromatograms to get
adequate resolution in as short as time as possible.
[4]
4.
Do either of the following:
(i)
(a)
What factors influence the nuclear stability of atoms?
(b) Predict how 2F should decay.
(ii)
[4]
[5]
[4]
The tritium (H) decay rate of a sample is 15, 260 min-1. Its half-life is 12.26 g.
What is the tritium content of the sample?
5.
Do one of the following:
(a)
Describe Liquid Scintillation Counting.
(b)
Describe Neutron Activation Analysis.
6.
Do EITHER (a) OR (b)
(a)
Draw graphs showing the voltage ramps used in sampled direct current (TAST) and
differential pulse polarography. Label the axes. Indicate when current is measured. Why
is differential pulse polarography more sensitive then direct current polarography?
Distinguish between capacitive and faradaic current.
(b)
What is a junction potential?
What is activation overpotential? How and why does it change with current density?
In deciding what potentials are necessary to carry out a real electrolysis, why is a lot more
information than just standard reduction potentials necessary? What extra information
would you need?
7.
Do EITHER (a) OR (b)
(a)
How long should a constant current of 100.0 mA be passed through a solution to prepare
100 mL of a solution of 0.0100 M Ni2+ using an anode of pure nickel?
Why not increase the current and prepare the solution in a shorter time?
F = 96, 485 C mol-1
(b)
At what value should the cathode potential be controlled if one desires to separate 0.05 M
silver from a 0.005 M solution of Cu2+ ions?
Ag+ + e-  Ag
E = 0.799 V
Cu2+ + 2e  Cu
E = 0.337 V
Justify your choice of voltage.
Chemistry 360 - April 1995 - T. Smith-Palmer
[5]
8.
Page 4
(a)
The use of gc. ms. is now fairly commonplace. What are some of the problems
involved in interfacing gc and ms, and how have they been solved?
[2]
(b) The use of hplc ms is rapidly increasing. Why does this technique pose more of a
problem than does gc mc.
[4]
(c)
Describe one of the more popular interfaces for HPLC MS.
Chemistry 360 - April 1995 - T. Smith-Palmer
[5]
9.
Page 5
Look at the following spectrum:
Write down the sequence of steps you would use to analyse the spectrum. go through each step
you mention. There is no nitrogen present.
[9]
[5]
10. Often there is more than one way of analysing a particular mixture. Assuming you have
access to both instruments, discuss the factors which might influence your choice of: (Choose
3).
(a)
(b)
(c)
(d)
HPLC and MECC to separate a mixture of analgesics.
Reversed phase or Normal phase HPLC to separate a mixture of organics.
HPLC or GC to separate fatty acid methyl esters (fairly non-polar).
IC or CE to separate a mixture of anions.
11.
(1)
(2)
(3)
Describe one of the following:
Quadrupole mass filters
Chemical Ionization
Double focusing m.s.