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    • CommentAuthorjuruble
    • CommentTimeFeb 26th 2008 edited

    This protocol explains: the basics of solution-making.

    Protocol revised: 2/26/2008

    Protocol written by: Julie Ruble (pictures by Dom Ippolito)



    1. Locate the recipe of the solution you need by scanning the "Recipes" category of the protocol website or using the "Search" tab.
    2. Collect all the reagents you need to make your solution.  Room temperature reagents will usually be located in the chemical cabinet (shown below) in alphabetical order while cold or frozen reagents may be kept in the lab fridge or small freezer, respectively.

      Fig. 1
      Figure 1. Chemical cabinet.

    3. Evaluate the amount of solution you should make.  For solutions used in large amounts (e.g. 20% Steinberg's, 1X PBS) it may make sense to mix up several liters at a time.  For solutions that degrade quickly (e.g. Testes Steinberg's, cysteine) or are used less frequently (e.g. disag, 0.1M PB) you may decide to mix up a smaller amount.
    4. If you are making a different volume of solution than the recipe specifies, do not trust yourself to make the calculations and convert the recipe as you go.  Calculate how much of each reagent you need BEFORE starting the recipe, writing down each new amount.
    5. Gather all your reagents and a bottle big enough for the volume of solution you are making and head over to the scale and pH meter. 


    Using the scale

    1. The scale can remain ON at all times.  TARE/ZERO the scale when you begin. 
    2. To measure chemicals, use white plastic "weigh boats" in the drawer closest to the fume hood.  Place a weigh boat on the scale and TARE/ZERO to remove its weight from the measurement.  Now you can use a metal scoop (located in the same drawer as the boats) to scoop a reagent into the boat until the screen reads the correct measurement.  Go slowly to avoid going over the correct mass, but if you do, discard the extra reagent onto a paper towel and weigh again. Do not pour extra reagent back into the original container.  When you reach the correct mass, pour this reagent into your bottle (Fig. 1), place the weigh boat back on the scale, TARE/ZERO and begin to weigh the next reagent the same way.  When finished weighing all reagents, throw paper towel with excess into trash carefully.  Dirty scoops go in the dirty dishes, used weigh boats go in the trash.

      Fig. 2
      Figure 2. Schematic diagram of making PBS. Reagents (circled in yellow) are weighed and placed (green arrows) into a bottle.

    3. If you get stray powder on the counter top or scale, dust them off. Don't leave a messy work area.


    Mixing the solution

    1. Once all the reagents are in the bottle, add the correct amount of liquid (usually distilled water, but check the recipe).  ONLY measure liquid with a graduated cylinder -- DO NOT use the markings on the bottle because they are not reliable. 
    2. Drop a spinvane (magnetic stirbar) in the bottle.  Spinvanes are found in the weigh boat drawer as well.  Place the bottle on the magnetic stir plate and turn in the stirrer -- NOT the heat (unless the recipe calls for heat). 

      A.Fig. 3   B. Fig. 3   C. Fig. 3
      Figure 3. Dropping the spinvane into a bottle of PBS (A), turning up the stir plate (B) and letting it mix (C).

    3. Allow the solution to stir until it is completely mixed.  While it is stirring, make a label with lab tape that includes the following information:  name of solution, date solution was made, date solution expires (if applicable), your initials, and the pH of the solution (if the recipe calls for pHing). 
    4. When the solution is completely mixed, let it continue stirring while you calibrate the pH meter and use it to check the pH (if the recipe tells you to).  See the "Using the pH meter" protocol for how to do this.
    5. Place the fully labeled solution in or on top of the lab refrigerator as appropriate (e.g. Steinberg's needs to be refrigerated, PBS doesn't).