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I am currently doing a lab write up for biology, in which the purpose of the lab is to "Develop a Method for Measuring Peroxidase in Plant Material, and to Determine a Baseline." This is supposed to be accomplished by finding the relationship between time elapsed since the beginning of the reaction (in minutes) and the $\mathrm{pH}$ of the solution. However, I'm not exactly sure what is meant by a baseline.

The lab packet, which contains instructions and background for the experiment, has this description of a baseline:

Baseline is a universal term for most chemical reactions. In this investigation, the term is used to establish a standard for a reaction. Thus, when manipulating components of a reaction (in this case, substrate or enzyme), you have a reference to help understand what occurred in the reaction. The baseline may vary with different scenarios pertinant to the design of the experiment, such as altering the environment in which the reaction occurs. In this scenario, different conditions can be compared, and the effect of changing an environmental variable (e.g., pH) can be determined.

However, whether due to an ambiguous description, or due to an error in my thinking, I am still a bit confused as to (a) what a baseline is, and (b) how baselines are used.

If asked, I would guess that a baseline is either a specific set of conditions (like what you'd find in a control group of an experiment), or that it's the results you'd obtain from a specific set of conditions, but I'm really not sure. I don't understand it well enough to apply it in the next part of the lab, in which we are supposed to compare some part of the first section of the experiment (the baseline, I think) to some part of the second experiment, when the pH of the solution is changed.

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  • $\begingroup$ I am not sure how applicable my opinion would be. However, in spectrometry the baseline is a way to reduce white noise. In spectrometry, we take a spectrum of the conditions before analyzing the sample. We then substract this spectrum from the spectrum of the analyzed sample. I suppose you could do the same for your situation. Measure the pH of the solution for x seconds. Then add the reagents and measure for x seconds as well. Or the baseline in the lab could refer to the calibration of the probe. $\endgroup$ – CoffeeIsLife Nov 30 '16 at 6:41
  • $\begingroup$ I think it means a control (standard) sample that could be used for reaction purposes. Its definetly strange the way theyve put it tho. $\endgroup$ – Technetium Dec 1 '16 at 5:01
  • $\begingroup$ bgs.ac.uk/research/groundwater/quality/BaselineUK/… Maybe this can help $\endgroup$ – Mockingbird Dec 1 '16 at 11:12
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In the context of your lab, I think that the term "starting point for the experimental conditions" could fairly correctly be inserted in place of "baseline". Once you have measured the parameters of interest for the starting point of your experiment, then you have something, a baseline, for comparison to the measured parameters after you perturb your system or the conditions of the reaction or measurement. Without this baseline you cannot quantify the effects or interpret the meaning of measurements made under arbitrary conditions.

One comment to your question was "I think it means a control (standard) sample...". I'm not sure whether this is where the commenter was headed, but this is not a bad analogy. Here, your established baseline is like the standard against which you compare your future results.

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