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Предмет:
Файл:English in Analytical Chemistry communicating about Methods & Techniques. Учебное пособие. Книга для студента
.pdf
2 Now look through the steps provided below. Read them out and translate into
Russian if necessary. Put them into the correct order.
Take a strip of filter paper
Put a drop of ink into the center of the line
Observe how water starts moving up by capillary action
Take a jar containing solvent [water]
Detect components [dyes] in the analyte [ink] because of different solubility
Put the filter paper into a jar
See different colors
Draw a line with a pencil closer to the lower edge of the paper
Let it dry for some time
3 Close the book and try to speak on paper chromatography procedure from
memory.
Reading and Speaking
4 Read the text and draw the academic vs. chemistry mind map for the words
highlighted in red.
1. Divide the words into two columns: “Academic” – for the generic terms that
could be used outside the scope of analytical chemistry – and “Chemical” – for specific
terms that reflect certain aspects of AC (types of analysis, methods, typical actions,
etc.).
2. Provide a simple English synonym for each word if it is possible. If not, draw a
schematic picture to visualize the word or download an associative picture from the
Internet (if you decide to make the mind map in e-format). Make sure all of the words
are put into their root forms.
Academic words are generally used in a scientific context and suit various
areas of science – whereas chemistry terms are used in a specific chemistry-oriented
context only. If it is difficult for you to remember a simple synonym, resort to
https://www.thesaurus.com/ or https://context.reverso.net/. However, do not use for
synonyms the words you do not know yet!
Example:
ACADEMIC CHEMICAL
TO TRAVEL = TO MOVE DYE
Paper Chromatography
Background
In paper chromatography there is what is described as the stationary
phase, which is the adsorbent, and the mobile phase, which is a liquid solvent (or
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mixture of solvents), used to carry the sample solutes under analysis along the paper.
Usually, one uses chromatography to detect the components of a sample, which are
separated depending on how much soluble these are in particular solvents and hence
how far they travel along the chromatography paper. Samples are usually of organic
matter (not ionic salts), which dissolve in certain polar solvents (namely water) or nonpolar (organic) solvents.
Principle
In order to make the technique more scientific rather than a mere interpretation
by sight, what is called the retention value (Rf value for short) was applied in
chromatography. A particular compound will travel the same distance along the
stationary phase by a specific solvent (or solvent mixture) given that other experimental
conditions are kept constant. In other words, every compound (dye, pigment, organic
substance, etc.) has a specific Rf value for every specific solvent and solvent
concentration. Rf values come very handy for identification because one can compare
Rf values of the unknown sample (or its constituents) with Rf values of known
compounds.
Calculation
The Rf value is defined as the ratio of the distance moved by the solute (i.e., the
dye or pigment under analysis) and the distance moved by the solvent (known as
the solvent front) along the paper. Both distances are measured from the
common origin or application baseline, that is, the point where the sample is initially
spotted on the paper.
Due to the fact that the solvent front is always larger from the distance travelled
by the solute, Rf values are always between 0 – one extreme where solute remains
fixed at its origin and 1 – the other extreme where the solute is so soluble that it travels
as far as the solvent. Rf values do not have units because it is a ratio of distances.
Because mixture solvents are often applied, Rf values are usually written as the
following examples:
Rf = 0.66 (60% ethanol) – if % is given, it is assumed that the mixture is in water,
hence, 60% ethanol and 40% water;
Rf = 0.78 (ethanol – methanol mixture {1:2}) – a mixture of 1 part Ethanol and 2
parts Methanol;
Rf = 0.25 (ethanol – methanoic acid – acetone mixture {4:3:1}) – a mixture of 4
parts ethanol, 3 parts methanoic acid and 1 part acetone. Note that mixture compounds
with larger proportions are placed first in the mixture sequence.
(based on S. Misfud’s Paper Chromatography)
5 Think of a word from the mind map you have devised. Prepare several riddles or
puzzles via Power Point Presentations or simply by doodling pictures in your
copybooks. Make your co-students work out the words relying on the visual
prompts.
52
6 Look at the riddles below. Work out which word or word combination it stands
for.
ACADEMIC
1.
2.
3.
53
CHEMICAL
1.
2.
3.
54
7 Now answer the questions to the text.
1. Give definitions of stationary phase and mobile phase.
2. What are the functions of stationary phase and mobile phase?
3. What is the purpose of chromatography as a method?
4. What kind of samples are used in paper chromatography?
5. Why do we apply retention value (Rf)?
6. Why is Rf so handy?
7. Is Rf always the same?
8. How is Rf calculated?
9. What is the Baseline?
10. What are the Rf values?
11. How do they write the mixture sequence (what is the priority)?
Further Reading and Speaking
8 Work with a partner. Match the words and their definitions.
1. Chromatography A. A graphical representation of detector response in
chromatography, a measure of effluent concentration of
an analyte versus effluent volume or time
2. Mobile phase B. A physical method of separation in which the
components to be separated are distributed between
two phases: one of which is stationary and the other is
mobile
3. Stationary phase C. In chromatography or electrophoresis, a measure
of how effectively compounds are separated (adjacent
peaks are separated in the chromatogram or
densitometer scan)
4. Retention time D. In chromatography: (buffer) Liquid or gas phase
that carries the mixed compounds over/through the
stationary phase
5. Eluate
6. Chromatogram
7. HPLC
8. Resolution
9. Elute
9 Read the text and find Russian equivalents for the words highlighted in red.
Translate the sentences underlined into Russian.
It is the (1) preparative application of chromatography. It is used to obtain pure
chemical compounds from a mixture of compounds on a scale from micrograms up to
kilograms using large industrial columns. The classical preparative chromatography
(2) column is a glass tube with a diameter from 5 to 50 mm and a height of 50 cm to 1
m with a stopcock at the bottom.
E. In chromatography: phase where resin is packed in
column
F. Liquid chromatography method where a pressure
pump is used to move analyte through column
G. The time it takes an analyte to travel through the
column
H. The washings obtained by the elution process
I. To remove from an adsorbent by means of a buffer
or solvent
Column Chromatography
55
(3) Slurry is prepared of the (4) eluent with the stationary phase powder and
then carefully poured into the column. Care must be taken (5) to avoid air bubbles. A
solution of the organic material is pipetted on top of the stationary phase.
This layer is usually topped with a small layer of sand or with cotton or glass wool
to protect the shape of the organic layer from the (6) velocity of newly added eluent.
Eluent is slowly passed through the column (7) to advance the organic material. Often
a spherical eluent (8) reservoir or an eluent-filled and (9) stoppered separating funnel
is put on top of the column.
The individual components are (10) retained by the stationary phase differently
and separate from each other while they are running at different speeds through the
column with the eluent. At the end of the column they elute one at a time. During the
entire chromatography process the eluent is collected in a series of (11) fractions.
The composition of the eluent flow can be monitored and each fraction is
analyzed for dissolved compounds, e.g., by analytical chromatography, UV absorption,
or fluorescence. Coloured compounds (or fluorescent compounds with the aid of an UV
lamp) can be seen through the glass wall as moving (12) bands.
The stationary phase or adsorbent in column chromatography is a solid. The
most common stationary phase for column chromatography is C18H37, followed by
alumina. Cellulose powder has often been used in the past. Also possible are (13) ion
exchange chromatography, (14) reversed-phase chromatography (RP),
(15) affinity chromatography, or (16) expanded bed adsorption (EBA). The
stationary phases are usually finely ground powders or gels and/or are microporous for
an increased surface; though in EBA a fluidized bed is used.
The mobile phase or eluent is either a (17) pure solvent or a mixture of different
solvents. It is chosen so that the retention factor value of the compound of interest is
roughly around 0.75 in order to minimize the time and the amount of eluent to run the
chromatography. The eluent has also been chosen so that the different compounds can
be separated effectively. The eluent is optimized in small scale (18) pretests, often
using (19) thin layer chromatography (TLC) with the same stationary phase.
A faster (20) flow rate of the eluent minimizes the time required to run a column
and thereby minimizes diffusion, resulting in a better separation. A simple laboratory
column runs by gravity flow. The flow rate of such a column can be increased by
extending the fresh eluent filled column above the top of the stationary phase or
decreased by the tap controls. Better flow rates can be achieved by using a pump or by
using compressed gas (e.g., air, nitrogen, or argon) to push the solvent through the
column, which is called (21) flash column chromatography).
Automated flash chromatography systems attempt to minimize human
involvement in the purification process. Automated systems may include components
normally found on HPLC systems ((22) gradient pump, (23) sample injection
apparatus, UV detector) and a fraction collector to collect the eluent. The software
controlling an automated system will coordinate the components and help the user to
find the resulting purified material within the fraction collector. The (24) software will
also store results from the process for archival or later recall purposes.
(based on P. Kumar – Top 12 Types of Chromatographic
Techniques)
10 Work in pairs and give definitions to the words whose Russian equivalents
you have managed to figure out in exercise 9.
56
11 Now answer the questions to the text in Task 9.
1. What is the practical application of column chromatography? Why is it called a
preparative technique?
2. How is the eluent applied in column chromatography?
3. What are the stationary and the mobile phases in column chromatography?
4. Why is the faster flow of eluent required? How can this be achieved?
5. What is an automated system in chromatography and what is the function of
it?
6. Why do they use cotton wool or sand?
7. How do they collect eluent?
8. How do they monitor the composition of the eluent?
9. What are the criteria for choosing the eluent?
10. Write down what occurs in column chromatography step by step (5 steps at
least).
12 Watch the video on types of chromatography and redraw the classification into
your copybooks or notebooks. Then answer the questions below. Follow the link:
https://disk.yandex.ru/i/kE6PZWgIwLR4uQ
The speaker represents the Indian variant of English language. This might
make the watching process both entertaining and hard. To run the subtitles, follow the
link: https://disk.yandex.ru/d/CJNDMILzoH6rAQ
Types of Chromatography (video)
1. What are the main types of chromatography? What are they based on?
2. Which solvents are used in liquid chromatography?
3. What are the two subtypes of gas chromatography? Give the definition of
each.
4. What are the four subtypes of liquid chromatography (LC)?
5. Give definitions and Russian equivalents of 1) ion exchange chromatography;
2) exclusion chromatography; 3) partition chromatography; 4) thin layer chromatography
(TLC).
6. Which type of liquids can be used in LC? In which types are they used? What
is the difference between them? Provide examples.
7. What are the stationary phases for partition (paper) chromatography and TLC?
13 Read the text and match topic sentences A-E with paragraphs 1-5. Explain the
words in bold.
Topic sentence is the most important sentence of a paragraph. It states the
main idea and tells readers what the rest of the paragraph is about.
Chromatography
(1) Chromatographic separations utilize the selective partitioning of the
sample's components between a stationary phase that is immobilized within a column
and a mobile phase that passes through the column.
57
(2) A solute's retention factor is a measure of its partitioning into the stationary
phase, with larger retention factors corresponding to more strongly retained solutes.
The column's selectivity for two solutes is the ratio of the their retention factors,
providing a relative measure of the column's ability to retain the two solutes. Column
efficiency accounts for those factors that cause a solute's chromatographic band to
increase in width during the separation. Column efficiency is defined in terms of the
number of theoretical plates and the height of a theoretical plate, the latter of which is a
function of a number of parameters, most notably the mobile phases' flow rate.
Chromatographic separations are optimized by either increasing the number of
theoretical plates, by increasing the column's selectivity, or by increasing the solute
retention factor.
(3) Gas chromatography is useful for the analysis of volatile components.
(4) A stationary phase of opposite polarity, which is bonded to a particulate
material, is packed into a wide-bore column. HPLC can be applied to a wider range of
samples than GC; however, the separation efficiency for HPLC is not as good as that
for GC.
(5) Other separation techniques, however, find specialized applications. Of
particular importance are: ion-exchange chromatography for separating anions and
cations; size-exclusion chromatography for separating large molecules; and
supercritical fluid chromatography for the analysis of samples that are not easily
analyzed by GC or HPLC.
(6) Positively charged solutes elute first, with smaller, more highly charged
cationic solutes eluting before larger cations of lower charge. Neutral species elute
without undergoing further separation. Finally, anions elute last, with smaller, more
negatively charged anions being the last to elute. By adding a surfactant, neutral
species can be separated by micellar electrokinetic capillary chromatography.
Electrophoretic separations also can take advantage of the ability of polymeric gels to
separate solutes by size (capillary gel electrophoresis), and the ability of solutes to
partition into a stationary phase (capillary electrochromatogra-phy). In comparison to
GC and HPLC, capillary electrophoresis provides faster and more efficient separations.
(based on D. Harvey – Analytical Chemistry 2.0)
14 Ask the question about the information underlined in the text.
A. Together, GC and HPLC account for the largest number of
chromatographic separations.
B. Chromatography and electrophoresis are powerful analytical techniques
that both separate a sample into its components and provide a means for determining
each component's concentration.
C. In high-performance liquid chromatography the mobile phase is either a
nonpolar solvent (normal phase) or a polar solvent (reversed-phase).
D. In gas chromatography the mobile phase is an inert gas and the
stationary phase is a nonpolar or polar organic liquid that is either coated on a
particulate material and packed into a wide-bore column, or coated on the walls of a
narrow-bore capillary column.
E. In capillary zone electrophoresis a sample's components are separated
based on their ability to move through a conductive medium under the influence of an
applied electric field.
58
F. The effectiveness of a separation is described by the resolution between
two chromatographic bands and is a function of each component's retention factor, the
column's efficiency, and the column's selectivity.
15 Check your understanding: read the text again carefully, looking up everything
you do not understand in a dictionary. Then find the words, which mean:
1. use (para 1)
2. become bigger or greater (para 2)
3. inactive (para 3)
4. productivity or capability (para 4)
5. usage (para 5)
6. quicker (para 6)
16 Fill in the correct preposition, then make sentences using the completed
phrases.
under on by of without into through in for (*2) to
to pass _____
to elute _____undergoing further
separation
_____ the influence
to account _____
to take advantage _____ the ability
to separate a sample ____components
to optimize _____increasing the
column's selectivity
to coat _____ a particulate material
to provide a means _____ determining
_____comparison____
17 Match the words from column A with the words from column B to make up
some frequently used collocations.
A B
retention plate
theoretical solvent
column’s column
nonpolar technique
wide-bore factor
separation field
electric selectivity
18 Choose a common word for each group to get collocations.
a) gas ..............
paper .............
b) selectivity .............
capacity .............
retention................
c) ................... selectivity
....................efficiency
………………ability
59
d) mobile ................
stationary ....................
19 Ask the question so that the part in bold is an answer.
1. Chromatography and electrophoresis are powerful analytical techniques that both
separate a sample into its components and provide a means for determining each
component’s concentration.
2. The effectiveness of a separation is described by the resolution between two
chromatographic bands and is a function of each component’s retention factor,
the column’s efficiency, and the column’s selectivity.
3. A solute’s retention factor is a measure of its partitioning into the stationary phase,
with larger retention factors corresponding to more strongly retained solutes.
4. The column’s selectivity for two solutes is the ratio of their retention factors,
providing a relative measure of the column’s ability to retain the two solutes.
5. Column efficiency accounts for those factors that cause a solute’s
chromatographic band to increase in width during the separation.
6. Chromatographic separations are optimized by either increasing the number of
theoretical plates, by increasing the column’s selectivity, or by increasing the
solute retention factor.
7. Gas chromatography is useful for the analysis of volatile components.
8. In high-performance liquid chromatography the mobile phase is either a nonpolar
solvent (normal phase) or a polar solvent (reversed-phase).
9. In capillary zone electrophoresis a sample’s components are separated based on
their ability to move through a conductive medium under the influence of an
applied electric field.
10. By adding a surfactant, neutral species can be separated by micellar electrokinetic
capillary chromatography.
Practice Makes Perfect
20 Watch another video describing a paper chromatography procedure in detail
and make a word-for-word script of it in writing. Look through the tough points
below and make sure you discern them properly while watching. Follow the link:
https://disk.yandex.ru/i/mM-wy3JI3lJZcw
Tough moments
00.12 wet erase marker
00.26 ...then what we’ll want to do
00.30 ...of water in it
00.52 ...some of them are heavier
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