Reassessment summer 2009

MS1005N General Biochemistry (Module Leader: Dr D. Perumal)

Summary

Component / Reassessment Task / Reassessment Environment (include length if exam) / Additional info
(optional)
CWK – Practical Report / Non time-constrained Practical Report – 1000 words / Handed in by standard deadline
EXU – Unseen Exam / Unseen time-constrained examination / Exam
(1 hour)
OTH – Practical Attendance / Not reassessed / n/a

Coursework Practical Report based on Practical 2:

SEPARATION OF ANALGESICS BY THIN LAYER ADSORPTION CHROMATOGRAPHY

Instructions:

  • The practical brief for Practical 2 is as on Page 18 of the 2008-09 Module Booklet. It is also included below.
  • You are required to write a full practical report (1000 words) using the results obtained during the practical. Please read the guidelines at the end of this schedule when writing up.

Practical 2

Introduction

Separation of compounds on a thin layer of supporting medium (i.e. TLC or thin layer chromatography) is very rapid and gives good resolution at low concentrations. Separation may be by adsorption, ion exchange, partition or gel filtration depending on the medium employed. Separated compounds may be detected by methods not possible on paper, for example with corrosive sprays; in this practical the isolated spots are visualised under ultraviolet (UV) light. Here analgesics are separated by adsorption on a thin layer of silica gel using an ethyl ethanoate/ethanol/ethanoic acid solvent mixture.

Method

TLC plates

Silica gel TLC aluminium sheets will be provided. Handle them carefully by their edges to prevent flaking.

Preparation of chromatography tank

Line small beakers with paper which as it becomes soaked in the solvent produces a saturated atmosphere. Add the solvent provided to the beaker to a depth of about 1 cm and cover with clingfilm.Beware of letting the silica come into contact with the solvent-saturated paper.

Chromatography

The following analgesics will be provided as standard solutions : ibuprofen; acetylsalicylic acid; acetaminophen; and caffeine. You will also be provided with 2 unknown test solutions.

Starting 1cm from the left spot the solutions at about 1.2 cm intervals and 1.5 cm from the base of each plate using fine glass capillary pipettes. The line on which you spot the solutions is called the origin. Use a hair drier (set to cold) to keep the spots as small as possible. Keep a record of the position of each standard and unknown. Draw a pencil line across the plate 7.5 cm from the origin.

Place each plate in a beaker containing the solvent and develop the chromatogram until the solvent front reaches the 7.5 cm mark. Dry the plate in a stream of cold air with the hair drier and locate the analgesics by placing the plates under a UV light source. The analgesics should appear as black spots. Mark their position by circling in pencil.

Treatment of results

Write up this work as a full practical report. Refer to the format in this booklet on the following pages. The report must be printed, and not handwritten.

In your report:

•Make a diagram of the chromatogram in your practical book. You may use a clear photocopy

•Determine the Rf values of each analgesic where

•Rf = Distance moved by each spot

Distance travelled by solvent.

•Identify the analgesics present in the unknown solutions by comparing Rf values with the standards.

•Look up and include the structures of the analgesics used.

•Discuss why the analgesics have separated on the chromatogram in the way that they have (particularly in the light of the above).

Useful reference

Cawley, J J (1995). The identification of aspirin-free Bayer products. Journal of Chemical Education 72(3) 272-273.

WRITING A PRACTICAL REPORT

The report must be printed, and not handwritten.

A practical report should include the following:

Title.
This should be as informative as possible and relate to the aim of the work. Where possible it should be of your own composition and not simply copied from the schedule.

Introduction.

An introduction should be concise and provide the background of the "problem", e.g. in the TLC practical report, you should talk about the structure and polarity of the compounds you analysed. A copy of the introductory text supplied to you in the practical schedule will not be awarded any marks. An introduction also is the proper place to define any specialist terms and abbreviations which will appear in the report, e.g. ATP (Adenosine Triphosphate). The last paragraph of the introduction should state the aim of the practical, i.e. you should say "The aim of this practical was...... " (but should not be copied from the schedule).

Methods.
either: you can write the description of the procedure(s) used in the practical, which must be sufficiently complete for others to be able to repeat the work, and must be written in the past tense, e.g. "The test tubes were placed in a water bath at 25oC...... " and NOT "I placed the test tubes in a water bath...... "

or: since the methods are outlined in the schedule, you can say "Refer to the practical schedule", but do not forget to include any changes that you made to the schedule.

Results.
This section must contain text that gives an explanation of the results. This should be concise and need not be complex. Numerical data are best presented in the form of tables or figures/graphs (or both as appropriate). Table or graph titles should be complete enough to be understood without having refer to the main text and explanatory footnotes are helpful.
Example 1- in a biochemical practical report a bovine serum albumin standard curve may have been prepared and could be entitled "Bovine serum albumin standard curve (at 540nm)". Axes must also be labelled appropriately giving units as required.
Example 2- in a microbiological practical report you may need to compare colony forming units (cfu) obtained for E.coli grown on different media. A suitable way to present this data would be on a table entitled "A Comparison of Colony Forming Units Obtained for E.coli Grown on Different Media", with footnotes under the table defining any abbreviations used, eg: "where NA is nutrient agar and EMB is eosin methylene blue agar".
A sentence or two of text leading the reader to an appropriately labelled graph or table is a good method of explaining your results.

Make sure any calculations are clearly explained.

Discussion.
In this section you should try to consider the implications of your results ie what the results mean/tell you rather than a recapitulation of the results section. You should also try to relate or compare your results with the general body of knowledge in the particular area that can be obtained from reference texts. In other words you should discuss you own data as compared with published data, and comment on the method(s) used in the practical. Sources of error and strategies for further work may be included here. The discussion should also contain a concise conclusion or statement that follows logically from the data obtained and discussion points eg "from these results it can be concluded that------" or "these results show quite conclusively that------".

Conclusion:

Conclusions(s) should follow logically from the data and discussion contained in the report. Distinguish clearly the conclusion(s) from the actual results. Briefly sum up the whole work.

References.
Quote any references, i.e. books, journal articles and web sites etc. that were used in writing up the report. References to support statements you may make should be cited in the text and not just in the reference list at the end of the report. Journal and text book references should be cited in the text in brackets following a particular statement and should give the author’s name and year of publication, eg for a journal reference "Drug resistance has become a major problem in the treatment of TB" (Rieder 1994). The full reference giving the authors, year of publication in brackets, title of article, name of journal, volume number and page numbers is then given in the reference list.

E.g. If while writing up this practical, you used an article from the Pharmaceutical Journal of January 13, 1990, volume 244 No. 6567, pages 58 to 60, written by Anil C. Mehta, you should quote it as:

Mehta, A.C. (1990). Writing Papers for Publications. Pharm. J. 244(6567): 5860.

If you use information from a text book, again you cite the author(s) and the year of publication in the text as above, and the full reference is given in the reference list (see below); eg for a text book reference, "Hydrothermal vents support large numbers of sulphur-oxidising bacteria" (Madigan et al 2000). The "et al " means "and others" and is used in the text when there are more than two authors, but all authors must be shown in the reference list (see below).
Book/ Journal references must be listed at the end of the report in alphabetical order according to the first authors name (see the reference list below).
Web site references should also be cited in the text where they are given a number according to the sequence in which they appear in the text and this number is shown in brackets eg "E.coli is a Gram negative rod shaped bacillus (1) and is a common contaminant of fresh water (2)."
Web site references are listed after journal/book references in the reference list. Students are reminded that referenced material should be predominantly from text books and peer-reviewed research papers, rather than web sites.

Example of referencing:

References
Madigan M. T., Martinko J.M. and Parker J.( 2000). Brock’s Biology of Microorganisms (9th edition). Prentice Hall International, p.354-346.
(i.e authors, year of publication , title of article, name of book, and page numbers).

Rieder, HL.(1994). Drug-resistant tuberculosis. Tuberculosis and Lung Disease,74:324-328.
(i.e author, year of publication , title of article, name of journal, volume number and page numbers).

(1)

Guide to microbiology on the net. Accessed December 13th 2005

(2)

Publishers web site for Brock. Accessed January 4th 2006

Marking Scheme

  • Title

(of students own composition as appropriate) 5%

  • Introduction (with Aim).

(Of students own composition i.e. not copied from the module schedule, To contain a clear statement of the aims of the investigation) 25% 25%

  • Methods.10%
  • Results (to include explanatory text).25%
  • Discussion (with Conclusion).30%

References 5%