A centrifuge is a piece of laboratory equipment commonly used in chemistry and molecular biology. The centrifuge is roughly circular in shape, with circular holes for microtubes arranged around the perimeter. Balances the centrifuge by placing the sample-filled microtubes and balance tubes opposite each other in the centrifuge rotor. When the centrifuge is properly balanced, the center of gravity of the centrifuge and the test tubes it contains will be located in the center of the centrifuge.
Steps
Part 1 of 3: Prepare the Centrifuge and Fill Microtubes
Step 1. Make sure the centrifuge is on a level and stable surface
Most centrifuges are the size of a toaster oven and sit on a counter, table, or other laboratory surface. Before worrying about adding liquid to the centrifuge, make sure the surface of the centrifuge is completely level. An inclined surface will deflect the results or cause the equipment to fall to the ground.
- If you have a carpenter's scale handy, you can make sure the surface is completely level. Place the scale on the table or counter, and make sure the horizontal bubble is completely centered in the glass tube.
- If you are using a very large centrifuge that sits directly on the laboratory floor, you can skip this step.
Step 2. Select the correct size microtubes for your centrifuge
Different size centrifuges will use different tube sizes. In general, larger centrifuges use larger microtubes. Placing the wrong size tube in a centrifuge could result in spillage or damage to the centrifuge or tube.
- If you are unsure about which size microtube to fit into which size centrifuge, consult a more experienced lab technician or review the manual for the centrifuge you are using.
- Most benchtop centrifuges use either a 1.5 milliliter (0.05 fl oz) microtube or a 0.5 ml tube.
Step 3. Fill all microtubes evenly
Use a laboratory dropper to pour exactly the same amount of liquid into each of the microtubes that you are going to put into the centrifuge.
For example, if you fill the first microtube with 10 milliliters (0.34 fluid ounces) of solution, make sure all other microtubes you plan to use for the experiment are filled with 10 milliliters (0.34 fluid ounces) of solution. A microtube filled with 9 milliliters (0.30 fl oz) or 11 ml could throw the centrifuge out of balance
Step 4. Fill all balance tubes to the same level
As the name implies, the balance tubes are lowered into the centrifuge to provide enough weight to balance the other microtubes. Use a laboratory dropper to fill the balance tubes with liquid, so that all the microtubes weigh the same amount.
- Or, if the microtubes have markings on the side that indicate the amount of liquid in the tube, make sure all tubes are filled to the same level.
- Balance tubes are commonly filled with water. However, if the solution you are going to use in the experiment has a density much higher or lower than that of water, use a liquid with a similar density in the balance tubes.
Part 2 of 3: Putting Tubes Into the Centrifuge
Step 1. Insert a counter balance tube to each microtube into the centrifuge
The center rotor of your centrifuge will have an even number of holes spaced around its perimeter. Choose a hole and firmly insert a filled microtube. Then, insert a balance tube into the hole exactly opposite to the hole that contains a solution-filled microtube. Adding 2 microtubes at a time will ensure that you add an even amount of weight to each side of the centrifuge.
By adding a tube of equal weight to each side of the centrifuge, you will keep the center of gravity exactly in the middle of the centrifuge rotor
Step 2. Turn the centrifuge rotor 90 ° and add 2 more microtubes
Insert these new microtubes halfway between the 2 microtubes you have already added. So if you added the first 2 microtubes at 12 and 6 o'clock, add 2 new microtubes at 3 and 9 o'clock.
Create a system to find out which tubes are microtubes and which are equilibrium tubes (if the liquids are the same color). You could put a small sticker on top of sample filled microtubes or use a blue marker to place a small dot on top of balanced tubes
Step 3. Continue adding equidistant microtubes and counter balance tubes
You can add as many microtubes as there are holes in the centrifuge using this system.
- Continuing with the example, after you've added microtubes at 3 and 9 o'clock, you could add 2 more at 2 and 8 o'clock, and another pair at 11 and 5 o'clock.
- If you have an odd number of microtubes, you will need to balance the centrifuge using an alternate setting.
Part 3 of 3: Balancing the Centrifuge with Other Settings
Step 1. Balance 3 microtubes by placing the tubes at even intervals
If you have 3 microtubes, you could create 3 balance tubes and place 3 pairs facing each other. Alternatively, balance the centrifuge without using balance tubes by placing the 3 microtubes at 2, 6, and 10 o'clock.
Clock positions work well when balancing a 12-hole centrifuge. Other common sizes include 24 and 30 hole centrifuges
Step 2. Place 5 microtubes with a balance tube
To equilibrate the centrifuge using 5 microtubes, first fill 1 equilibrium tube with water. Then put 3 tubes at 11, 12 and 1 o'clock. Place the other 3 tubes at 5, 6 and 7 o'clock. The balance tube can be located in any of these positions.
Balance the centrifuge with 6 microtubes using the same setup, but swap the balance tube for a microtube filled with sample
Step 3. Place 7 microtubes and 1 balance tube in the centrifuge
Position 2 sets of 4 microtubes so that the sets are offset against each other and center the weight on the centrifuge. Place 4 microtubes (including balance tube) at 11, 12, 1 and 2 o'clock. Then, place 4 more microtubes at 5, 6, 7, and 8 o'clock.
You can balance a centrifuge using 8 microtubes in the same setup. Just replace one of the microtubes with a tube filled with sample
Advice
- When adding microtubes and balance tubes to the centrifuge, it may help to imagine a straight line passing between each new pair of tubes you insert. If the imaginary line does not pass directly through the center of the centrifuge, the rotor will not be evenly balanced.
- The centrifuge shakes the balanced test tubes at a very high speed (up to 13,000 revolutions per minute) to separate liquids of different densities. If the centrifuge is not balanced correctly, it may damage the equipment or ruin the results of the experiment you are about to run.