Chem 231

Lab Report Writing Guidelines

-adapted from Dr. Baker (Fall, 2005 class)

All reports for Chem 231 will be double spaced, with 12 pt Times New Roman font and 1 inch margins. Include your name, a title, a 2-3-sentence abstract, an introduction, an experimental methods section, a results and discussion section, and a short conclusion. Concise reports describe all parts completely are preferred over longer reports that add little to the understanding of what was done. Remember, your work in the lab is as good or bad as your lab report.

Abstract

A proper abstract is a concise summary of the paper (or presentation, or book chapter). It is not an introduction. The abstract should include a one sentence introduction to the experiment, a brief summary of the experiment, and a description of any important results that were obtained, including important numerical data. The amount of detail given in the abstract will depend on the allowed length.

An abstract needs to stand on its own. In general, references to other work should not be included unless there is a compelling reason to include one. References to figures and tables that may appear in the main body of the paper should not be made. If acronyms are used they must be defined the first time they are used. (Acronyms must always be defined the first time they are used unless they refer to commonly known measurement units). However, since the abstract stands alone, acronyms must be defined again in the main body of the paper, even if they have already been defined in the abstract.

Introduction

The introduction is used to tell the reader why you did the experiment. The two most important parts to the introduction are background on what has been done before and a clear statement of the purpose or purposes of the work undertaken. In research papers, this is normally accomplished by starting on the importance of the field of the research and then narrowing the scope down to the specific purpose of the experiments. On using new chromatography, this may include pointing out limitations of common methods or advantages of proposed methods. For example, an paper describing the measurement of phenols in water using solid phase extraction and HPLC could start by discussing why measurement of phenols in water is important (e.g. health concerns of phenols). Then it should discuss past efforts to measure phenols in water. If use of solid phase extraction is the novel part to the work, it should discuss limitations of past methods and advantages to using solid phase extraction (e.g. in similar samples for similar compounds). Important historical references regarding work related to your experiment should be in this section. If your experiment is testing a particular hypothesis or theory, it must be stated in the introduction. The results of your experiment should not be given in the introduction. There are usually no figures or tables in the introduction, unless it is referenced from some other source.

Parts of the introduction may be in the past tense and others in the present tense. If you are discussing a specific experiment or specific work that happened in the past, it would be presented in the past tense or mixed tense. For example, “Smith et al. (2003) found that time of flight mass spectroscopy works better than ion trap mass spectroscopy due the faster response time.” If you are discussing something in general, that is not linked to a specific reference, use the present tense. For example, “Isoprene is the most prevalent volatile organic compound emitted by plants.” A statement like this may be followed by one or more references if it is not general knowledge in the field.

Experimental Methods Section

The experimental methods section tells the reader how you carried out your work. This section should describe in detail: where chemicals were obtained and what quality they were, methods and equipment used, any parameters that were set for these methods or equipment, how instrumentation was calibrated, how experimental controls were set up, any sampling and analysis protocols that were used, calculations that are not routine, etc. The amount of detail given should not be more than is necessary for the reader to repeat what you have done in the general sense. For instance, if you are describing how calibration solutions were made, it is appropriate to say, “A range of Ca²⁺ calibration solutions from 1.00µM to 10.0µM were prepared using volumetric glassware by serially diluting the 5.00mM Ca²⁺ stock solution with deionized water.” (We assume here that the 5.00mM Ca²⁺ stock solution has already been discussed.) This amount of detail will allow anyone familiar with wet chemistry to make calibration solutions in the proper range. It would not be appropriate to say, “To make a 10µM Ca²⁺ calibration standard, 2.00mL of the 5.00mM Ca²⁺ stock solution was added to a 1000mL volumetric flask using a 2.000 mL volumetric pipet, and then the volumetric flask was diluted to the mark with deionized water.” This statement is wordy and unnecessary. However, if you are discussing a procedure that is new, extremely uncommon, or very sensitive to small changes in the procedure and may alter the outcome of the experiment, then this sort of detail may be appropriate. If some parameter was changed half-way through the experiment (and data is used from both before and after changing the parameter), then it should be mentioned in the experiment section. Why the parameter was changed should appear in the discussion section (a brief comment on why it was changed could be included in the experiment section to avoid confusion). None of your actual data or results should be presented in the experimental section.

Figures and tables may be used in the experimental section if they show how an instrument was set-up or a set of experiments that were conducted or solutions that were prepared in a more concise format than by description through text.

Most of the time, the experimental section will be written in the past tense. Any time you discuss something that was done in your experiment it should be in the past tense. However, if you are writing about something in the general sense, then the present tense should be used. For example, “Mass 67⁺ was used to monitor isoprene since it is the most prevalent mass produced in the electron impact ionization of isoprene.” The first part of the sentence is in the past tense since it refers to the experiment, the second part of the sentence is in the present tense, since it is a general property of electron impact ionization. Also, be sure to write what you did and not just what the experiment instructions told you to do.

Results/Data Section

The results/data section presents your data to the reader, but does not present an analysis of that data. Since this is sometimes difficult to do, it is common to combine the results section with the discussion section. Only show results that are pertinent to your experiment. If you made a mistake during the experiment, do not show the data from the mistake. Only show bad data if that data was used to direct the next step of the experiment. This would be common if your experiment involved method or instrument development.

Normally the results section will contain most of the figures and tables since this is an efficient way to present data. In general, figures and tables should always be used sparingly, and only if they result in a better presentation of information than can be accomplished in the text. More information regarding figures and tables are given below. Do not show the same type of data more than once unless there is a good reason to do so. If you are analyzing ten samples with various concentrations of phenols, there is no reason to present more than one of the chromatograms; in general, they all look the same. Similarly, there is no reason to show more than one calibration curve. A graph of concentration versus sample number, or time, or whatever is appropriate, would be more useful to the reader. Be sure to always use the appropriate number of significant figures in every number you report. Also be sure to include units with every number you report in the text, and in figures and tables. If the units require superscripts or subscripts, format these properly. There is no excuse not to when using a modern word processor. Avoid reporting raw data. For example, if you want to show the results of several chromatography analyses in a table, convert the area units to concentration (based on the calibration), or some other useful units before making the table. The exception to this may be if you are reporting the results of repeated standard analyses.

For the purpose of this class, I recommend putting raw data into an appendix at the end of the paper. This can assist me in checking if you carried out calculations correctly.

Discussion Section

The discussion section should be used to put your results into the proper context. It is commonly combined with the results section. The results of the experiment should be explained in a meaningful way. This may include: comparing your results with the results of others (in your class or from published work), comparing various results from your own experiment, explaining how your work demonstrates a certain scientific principle, or supports or disagrees with a particular hypothesis or theory, discussing the quality of your data and if the quality of the data is not as good as possible, why, etc. If you want to show the process of making specific calculations, put these in an appendix at the end of the report. Do not go through detailed calculations in the main body of the report; although, important equations that are used for making calculations may show up in the experiment section. Detailed calculations should only appear in the main report if the study involves novel equations. The discussion section of your report should be the most thought out, and the most interesting.

Conclusion

An effective conclusion is used to reflect on the experiment, to put your results in a broader context than in the discussion (for example, reduction of detection limits relative to past methods), to suggest improvements for future experimenters or for further studies. The intention of the experiment may be repeated (from the introduction) and whether or not the original goals were met can be discussed. You also have the opportunity to put your results in a broader context than in the discussion (e.g. what your results mean in terms of the field of work.

Helpful comments on figures and tables

-Only use a figure or table when necessary. Ask yourself if the information in the figure or table can be adequately described in the text alone.

-Label figures and tables separately and in order.

-A caption should be associated with every figure or table that does not rely on the text of the paper, although the reader can be referred to the text for more information.

-Every figure and table included in the paper must be referred to in the text, and must be referred to in order. If the figures and tables are embedded in the text, try to have the referral in the text come before the figure or table appears. Otherwise, it is acceptable for all of the figures and tables to be included (in order) at the end of the text.

-The first time that the figure or table is referred to in the text, the figure or table must be described. Describe what the figure or table is displaying, and then discuss the data in the figure or table. After this, it is ok to make a reference to the figure or table without a specific discussion of the data in the figure or table. Use the present tense when referring to the actual table or figure. For example, “Figure 1 illustrates how the helium carrier gas was used to desorb compounds from the sampling traps.”

-Use the correct or at least a reasonable number of significant figures in every number reported.

-Whenever possible, show uncertainty in your data. Use error bars on graphs to show uncertainty in each point, or to show variations from one analysis to the next. Be sure to explain you error bars or uncertainty in the caption.

-Units must be associated with every number reported. This may appear in the column heading for a table, or on the axis label in a graph. For chromatograms it is ok to use ‘detector response’ for the units of the y-axis, and area units for peak areas, however it is better if area units are converted to the final units used (the same units as the standards).

-Most software allows the user to format how data looks for printing. Spend the time to learn the software and make your data look the way you want it before printing it out.

-The font for all lettering should be the same as in the text whenever possible. Do not use smaller than 10 point font in figures and 12 point in tables.

-All lines and points should show up clearly. This includes axis and trend lines, and data points.

-Use all of your space. There is no reason to have a graph on half a piece of paper if the other half is empty.

-Use enough space to display the data well. Short and wide chromatograms do not do as well as tall ones.

Some common unacceptable errors for a lab report

-Having numerous and blatantly misspelled words.

-Using poor writing structure (not having periods after sentences, missing spaces, etc.).

-Not describing and discussing figures and tables that are included in the report.

-Poor labeling of figures and tables, for example, if multiple figures have the same figure number, or if the incorrect figure is given in the text.

-Being excessively redundant.

-Not reporting units (or incorrect units) and obviously reporting too many significant figures.

-Not using appropriate symbols, sub- and superscripts, and not using an equation editor to display equations.

All of these can easily be avoided by carefully reading your report before handing it in and having some pride in your work.