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Start the year with the right technique

For standard pipetting use Forward Technique:
Recommended for aqueous solutions, such as buffers, diluted acids, or alkalis, this technique is commonly used when pipetting and mixing a sample or reagent into another liquid.

For solutions with high viscosity or tendency to foam use Reverse Technique:
This technique is commonly used with air displacement pipettes, and is recommended for precisely pipetting small volumes. Reverse pipetting avoids the risk of sample splash, foaming, or bubble formation.

Learn how to further improve accuracy and precision ›

Isn’t all labware the same? No, and let us explain why

There are a lot of plastic labware choices, but the quality of your work often depends on using quality plastic labware. Even though they may look alike, not all labware products are created equal. Lower-cost alternatives come with a nice price, but remember that old saying, “You get what you pay for.”

Regulatory Standards:
High-quality plastic labware must meet accepted ASTM and ISO accuracy standards and be made from laboratory-grade plastic materials that won’t leach impurities into your reagents and samples. Containers should provide guaranteed leak-proof performance to keep you safe from exposure and your work safely contained. 

Learn more about Nalgene quality ›

What type of liquid are you pipetting?
Aqueous solutions work well with standard pipette tips. For viscous and “foamy” solutions or small volumes, consider low-retention tips for maximum sample delivery. Filter/barrier tips are recommended for solutions containing nucleotides, radioactive compounds, and where contamination control is critical.

What are you pipetting to/from?
Standard tips are great for microplates and microcentrifuge tubes. For taller vessels like tubes, flasks and bottles, extended length tips keep the pipette shaft from touching the inside walls allowing access to the bottom while preventing carryover contamination.

How concerned are you about contamination?
Filter tips help prevent contamination by blocking aerosols and preventing liquid from accidentally splashing the inside of the pipette. Filter or barrier tips are recommended for sensitive assays like PCR, genetic studies, forensics, and radioisotope sampling.

What pipette are you using? 
Tips that are designed and manufactured for your specific pipette provide an optimal fit, but high quality universal tips - such as ART pipette tips, are also a good option.

Is this an extremely sensitive application?
Individually wrapped sterile tips are ideal for sensitive applications requiring aseptic conditions.

View the quick reference chart 


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Recommendations for pipetting different compounds

Solution/compound
Pipette
Pipette Tip
Pipetting Technique 
Aqueous Solution
Buffers, Diluted Salt Solutions
Air displacement Standard Forward
Viscous Solutions
Protein and nucleic solutions,
glycerol, Tween 20/40/60/80
Air displacement
Positive displacement
Standard or wide orifice 
Low retention

Positive displacement
Reverse
Volatile Compounds
Methanol, hexane
Air displacement
Positive displacement
Filter barrier
Positive displacement
Reverse
Body Fluids
Whole blood, serum
Air displacement Standard or wide orifice tip Heterogeneous*
Nucleotide Solutions
Genomic DNA, PCR products
Air displacement
Positive displacement
Filter barrier or wide orifice
Positive displacement
Forward
Radioactive Compounds
Carbonate, H-thymidine
Air displacement
Positive displacement
Filter barrier
Positive displacement
Forward
Acids/Alkalis
H2, SO4, HCl, NaOH
Air displacement Filter barrier Forward
Toxic Samples Air displacement
Positive displacement
Filter barrier
Positive displacement
Forward or reverse

*With blood or serum reverse technique is another option. During the aspiration and dispensing, use very slow plunger movements. When aspirating, hold the tips in the liquid for a few seconds, after the plunger is in the upper position. Also, when dispensing, move plunger slowly and wait a few seconds when plunger is in the down position.


Proven Steps to Improve your Pipetting Accuracy

Step 1

Aspirate and fully expel an amount of the liquid at least three times before aspirating for delivery. Failure to pre-wet the tip increases evaporation within the tip air space, which can cause significantly lower delivery volumes. Pre-wetting increases the humidity within the tip, thus reducing evaporation.

Step 2

Allow liquids and equipment to equilibrate to ambient temperature prior to pipetting. The volume of liquid delivered by air displacement pipettes varies with relative humidity and vapor pressure of the liquid – both of which are temperature-dependent. Working at a constant temperature minimizes variation of pipetted volume.

Temperature differences cause thermal expansion and shrinking in the air space. After temperature equilibrium, the influencing factor is liquid density. Cold liquid is more dense and hot liquid is less dense compared to room temperature liquids.

Step 3

Before dispensing, carefully remove droplets from the outside of the tip by touching off the side of the reservoir, being sure to stay clear of the tip opening to avoid wicking liquid out of the tip. After dispensing, and before releasing the plunger, deliver any residual liquid remaining in the tip by touching the tip to the side of the container. Surface tension will help draw the remaining liquid out of the tip.

Step 4

Depress the plunger to the first stop, immerse the tip into the liquid, and aspirate by releasing the plunger. Remove the pipette from the liquid and depress the plunger to the second stop to dispense the entire contents. Standard (or forward) mode pipetting yields better accuracy and precision than reverse mode for all but viscous or volatile liquids. Reverse mode often results in over-delivery. Hence, it’s recommended to evaluate the effect of possible over-delivery in the experiment and make adjustments if needed.

In this experiment 200µL of  viscous liquid (glycerol) was pipetted 10 times by using both forward and reverse pipetting techniques. The pipette used was adjusted for glycerol using forward pipetting. The chart describes the accuracy and precision obtained with both techniques.

Using the reverse method a smaller deviation between doses was observed and therefore reduced imprecision.

The reverse method gave bigger doses as the liquid column in the tip is taller and therefore the liquid amount above the dose presses a larger dose out.

Step 5

After aspirating, and before removing the tip from the liquid, pause for one second. Make this pause as consistent as possible. Liquid continues to flow into the tip for a short time after the plunger stops. At the same time, evaporation within the tip is occurring. Pausing consistently balances these two effects and ensures correct aspiration.

Step 6

When aspirating liquid, hold the pipette vertically and pull the pipette straight out from the center of the reservoir. This technique is especially important when pipetting small volumnes (less than 50µL). Holding the pipette at an angle as it is removed from the liquid alters the aspirated volume.

Step 7

Hold the pipette loosely and utilize the finger rest. Remember to return the pipette to the pipette stand between deliveries. Avoid handling pipette tips or reservoirs with bare hands. Body heat transferred during handling disturbs temperature equilibrium, which leads to variations in delivered volume.

Step 8

Before aspirating, immerse the tip adequately below the meniscus. Too little immersion, particularly with large volume pipettes, can lead to aspiration of air. Too much immersion can cause liquid to cling to the outside of the tip. Contacting the container bottom with the tip may restrict aspiration.

Step 1: The tip is immersed to the correct depth and correctly held vertically.

Step 2: Inaccuracy doubles when immersing the tip too deeply.

Step 3: Inaccuracy increases three to five times by immersing too deeply while holding the pipette at a 30-40° angle.

Step 9

Use high-quality tips intended for use with the pipette. System tips are designed to work with their matching pipettes. Mismatched tips and pipettes can result in inaccuracy, imprecision, or both. Quality system tips provide an airtight seal, are made of superior materials, and are free of molding defects. They also ensure dependable liquid delivery.

Step 10

Depress the plunger smoothly until coming to rest with a light and consistent force at the first stop. Immerse the tip, and  then release the plunger at a constant rate. Repeatable actions produce repeatable results.