Writing an Experimental section

 

Content of an Experimental section

  • The journal accepts either "Material and Methods" or "Experimental" as synonyms for the title of this section.
  • Materials and experimental details should be described in sufficient detail to enable others to repeat the experiments. See Appendix B for lists of minimum required details for common methods.
  • UniProt Accession IDs and/or protein IDs (http://www.uniprot.org/) should be provided for all proteins that are purified and/or characterized.
  • Always provide the composition of buffers and other solutions. If a solution is a commercial product with unknown composition, provide identifying product information.
  • Names of products and manufacturers should be included only if alternate sources are deemed unsatisfactory.
  • Provide the model and manufacturer for major analytical equipment.
  • Provide the name, manufacturer, and version number of major software used to process data.

Style of an Experimental section

  • Divide this into separate sub-sections, each of which describes an experimental procedure performed.
  • Always write methods in the past tense, passive voice.
  • Do not rewrite the detailed procedures in your handout. Succinctly provide the minimum practical detail that the reader can reproduce your work.
  • Simply provide the final concentrations of components in a system rather than a list of stock solutions and individual volumes. Only state the stock concentrations and volumes if different methods for arriving at the same final conditions will actually generate different results.
    • Correct and preferred: "Reactions were performed at 25 °C in 50 mM Tris-HCl (pH 7.1) with 4.0 μM imiginin, 20 μg/ml imaginase, and either 0 or 150 mM MnCl2."
    • Correct but unnecessary: "Reactions were performed at 25 °C in by mixing 500 μl of 100 mM Tris-HCl (pH 7.1), 10 μl of 400.0 μM imaginin, 100 μl of 200 μg/ml imaginase, and either 0 or 250 μl of 500 mM MnC2 to a final volume of 1000 μl using buffer to make up the difference."
    • Incorrect: "Reactions were performed at 25 °C by mixing 500 μl of 100 mM Tris-HCl (pH 7.1), 10 μl of 400.0 μM imaginin, 100 μl of 200 μg/ml imaginase, and either 0 or 250 μl of 500 mM MnCl2." This example is ambiguous because it leaves-out the final volume. Please aoivd this common mistake.
  • Whenever hazardous materials or dangerous procedures are utilized, the necessary precautions should be stated.
  • Explain the procedures for data analysis. You must define any non-standard units (e.g. enzyme units) and provide the statistical basis of measurements (e.g. "values are the mean of three replicate measurements," "uncertainty is the standard deviation of values").
  • Please use the Equation Editor in Word to draw equations. However, you may draw equations by hand. Center equations on their own line with an equation number in parentheses to the right. Italicize all variables in an equation and in the body of the report.
  • In the Experimental section, you may use formulas for common inorganic reagents such as NaOH, HCl, H2SO4, MgSO4, etc., and for common organic solvents with very few carbons such as CH2Cl2 (dichloromethane) and CHCI3 (chloroform). Do not use formulas if they are not readily interpretable or if they take as much space as the name itself (e.g., use n-hexane, not CH3CH2CH2CH2CH2CH3).
  • Uncertainty on values is not required the Experimental section because quantities are assumed to represent typical values with assumed uncertainty in the last digit.

Below is a student example of a well-written Experimental section: