Comments made Fall 2007

Experiment #1: Thin Layer Chromatography:

I strongly recommend that you get acquainted with applying the solutions with the capillary tubes by practicing applying water to a paper towel first.  Do this before applying the solutions to the silica gel.  An improved technique would result in more precise measurements and thus more accurate results in calculating Rf values. PN

Speaking from experience it is important to follow the instructions on TLC in regard to marking the slide.  The solvents used in the experiment will cause pen ink to run and separate on the slide.  This can in turn affect your observed results.  So, always use a pencil to mark the start and finish lines on your TLC slides. AK

When drawing any of the starting or finish lines or measuring the distance for the Rf values, be careful with placing your ruler down on the slide.  This may cause the ruler to imprint itself on your slide.  This can also be prevented by waiting for your the solution on the slide to evaporate.  MB

Before coming to lab do a good amount of research on the polarity of your compounds AND the solvents.  If you know what you are expecting it will keep you from doing unnecessary TLC's just to get a relative feel for the polarity.  Also, mixing solvents is often the best way to perform a TLC, but you have to have a good idea of what polarity you are trying to achieve. SP

Make sure that you put the lid on your developing chamber once you put the silica gel slide in. If you don't, the solvent will evaporate and you won't be able to see it climb the slide. If you can't see the solvent climbing, you won't know when to take it out and where to draw your finish line. MW

This tip may seem obvious, but don't forget to mark your end line of solvent on your TLC slides. After waiting for them to develop, I was in a hurry to see what the spots looked like and forgot to mark where the solvent had ended. The solvent dries very quickly in open air and the "wetness" disappeared before I could mark the final line. Estimating where it could have been will distort your Rf values, and placing them back in the solvent to redevelop is time consuming, so don't rush!  BH

Make sure you carefully label each spot. I assumed that I would remember the order of each spot, and I ended up needing to re-do all of my TLC slides. Also, when labeling the TLC slides, use pencil. I used pen and the ink from the pen traveled up the slides. PH

make sure not to apply to much of each chemical to the TLC slide or else it can smear accross the slide making it hard to get a precise calculation. PL

It would be wise to have a good understanding of the characteristics that the functional groups play in this experiment- along with the solvents. To have a better understanding-read the chapters related to this in the text book. EC

Since this lab required that you record a lot of data, I would recommend that, during the experiment, you make your tables for your data first. I know it sounds trivial but I didn't and after I completed the experiment, I had an abundance of data and got annoyed having to write in two pages of results afterwards. I would say right all your info down as you go in your tables; it will save you a headache later. CR

Record all colors and smells of the different substances, they can help you later in identifying your unknown compound. Also make sure to record the number of your unknown to avoid later trouble when entering your results. YM

I suggest that when adding the solvent to the slide make sure that you drop the solvent onto the properly labeled spot or you can mix up your data. Also when labeling the slide, lightly mark the slide with the pencil or you will crack the slide. MFL

I would advise future students to make sure they mark down what solution is where when spotting the TLC slides. It is easy to get confused and forget which one you did first, second and third. Also make sure you have a good lab partner, because you will need their results, and if they have incorrect results, so will you! AP