A dilution, in chemistry, is a process that reduces the concentration of a substance in a solution. It is defined "serial" when the procedure is repeated several times to rapidly increase the dilution factor. This is quite a common practice during experiments that need very diluted solutions with maximum precision; for example those that have to develop concentration curves on a logarithmic scale or tests that determine the density of bacteria. Serial dilutions are widely used in biochemistry, microbiology, pharmacy and physics laboratories.
Steps
Method 1 of 2: Perform a Basic Dilution
Step 1. Choose the correct liquid for dilution
This step is crucial; many solutions can be diluted with distilled water, but not always. If you are diluting a bacterial or cell culture, then you must use the culture medium. You must use the liquid of your choice for all dilutions in the series.
If you are unsure about the type of fluid, ask for help or do an online search to see if other people have already done the same type of procedure
Step 2. Prepare several tubes with 9 mL of dilution liquid
These represent the dilution blank. You will need to add the concentrated sample in the first tube and then proceed to a serial dilution in the following ones.
- It is worthwhile to label the various containers before starting, so as not to get confused once the procedure has begun.
- Each tube will contain a solution ten times more diluted than the previous one, starting from the first one that contains the pure product. So the first dilution container will have a solution with a concentration of 1:10, the second 1: 100, the third 1: 1,000 and so on. Consider in advance the number of dilutions you need to avoid wasting tubes or liquid.
Step 3. Prepare a test tube with at least 2ml of concentrated solution
The minimum quantity necessary to proceed with serial dilution is 1 ml. If you only have 1ml of concentrated solution, you won't have any more left. You can label the tube that contains it with the abbreviation SC, i.e. concentrated solution.
Mix the solution thoroughly before starting the procedure
Step 4. Make the first dilution
Transfer 1 ml of concentrated solution (contained in the SC tube) to the tube labeled 1:10 and which contains 9 ml of dilution liquid. For this, use a pipette and remember to mix the solution thoroughly. At this point there is 1 ml of concentrated solution in 9 ml of liquid, so you can say that you have performed a dilution with a factor of 10.
Step 5. Make the second dilution
To proceed with the series, you must aspirate 1 ml of diluted solution from the 1:10 test tube and transfer it to the second tube which reads 1: 100 and which contains 9 ml of liquid. Remember to mix the solution well before each transfer. Now the 1:10 tube solution has been further diluted 10 times and is in the 1: 100 tube.
Step 6. Continue with this procedure for all tubes you have prepared
You can repeat it as many times as necessary, until you get the dilution you need. If you are performing an experiment that involves the use of concentration curves, you can use this method to create a series of solutions with dilution 1; 1:10; 1: 100; 1: 1,000.
Method 2 of 2: Calculate the Final Dilution Factor and Concentration
Step 1. Calculate the final dilution ratio of a series
You can find this value by multiplying the dilution factor of each tube up to the final one. This calculation is described with the mathematical equation: Dt = D1 x D2 x D3 x… x D where Dt is the total dilution factor and D is the dilution ratio.
- For example, suppose you performed a 1:10 dilution 4 times. At this point you just need to enter the dilution factor in the formula and you get: Dt = 10 x 10 x 10 x 10 = 10,000.
- The final dilution factor of the fourth tube in the series is 1: 10,000. The concentration of the substance at this point is 10,000 times lower than that of the original undiluted solution.
Step 2. Calculate the concentration of the solution at the end of the series
To arrive at this value, you need to know the starting concentration. The equation is: C.the final = Cinitial/ D where Cthe final is the final concentration of the diluted solution, Cinitial is that of the starting solution and D is the dilution ratio determined previously.
- Example: If your starting cell solution had a concentration of 1,000,000 cells per milliliter and your dilution ratio is 1,000, what is the final concentration of the diluted sample?
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Using the equation:
- C.the final = Cinitial/ D;
- C.the final = 1.000.000/1.000;
- C.the final = 1,000 cells per milliliter.
Do Serial Dilutions Step 9 Step 3. Verify that all units of measurement match
When doing the calculations, you need to be sure that you have always used the same unit of measurement from start to finish. If the initial data represent the number of cells per milliliter of solution, the results must also indicate the same quantities. If the initial concentration is expressed in parts per million (ppm), the final concentration must also be indicated in ppm.
