National Pingtung University of Science and Technology
Department of Tropical Agriculture and International Cooperation
Biochemistry Lab Report:
Experiment 1: Micro Pipetting Tutorial
Instructor:
Dr. Albert Linton Charles
Group #5
Sunita Subedi (B10622053)
Chet Narayan Gyawali (B10622057)
Simran Kayastha (B10622062)
Ribesh Dhungana (B10622072)
February 22th, 2019
Experiment 1: Micro Pipetting Tutorial
1. Introduction
Classification and principles of micro pipette (pipette) first appeared in 1956, by the German Institute for
Physiological Chemistry, scientists Schnittger invention, then, in 1958, Eppendorf, Germany began producing
button-type micro pipette to become the world's first production of micro pipette company. Much of
biochemistry, molecular biology involves working with very small volume. Typically, samples volumes and
reagents are measured in microliters, or 1/1000 of a milliliter, which is abbreviated L. These small volumes
are measured with a tool called a micropipette. Pipettes come in several designs for various purposes with
different levels of accuracy and precision from single piece glass pipettes to more complex adjustable or
electronic pipettes. In this experiment, we will learn how to use pipettors of various sizes and measure their
accuracy, precision and calibration.
1.1 Pre-Lab Questions
a) What is the usable range of a p- 1000 Eppendorf Pipetman?
Ans: The usuable range of a P- 1000 eppendorf Pipetman is 200-1000l.
b) What is the difference between accuracy and precision?
Accuracy and precision both terms are applied to any experimental measurements. Accuracy is a measure
of how close experimental measurements agree with known values. For example, we are attempting to measure
two different volumes of water with our micropipette and two with our graduated pipet. Perfect accuracy would
have us measure the exact volume we desire each time. However, the volume of water that we actually measure
will be close but probably different from these volumes. The farther away from the correct volume, the lower
the accuracy of our pipets and/or our technique will be.
Precision is a measure of how close the experimental measurements agree with each other. The closer
each measurement is to the other measurements, the more precise the measurements. For example, if the
micropipette is set to the same volume (300 µL) and four measurements are taken at this volume, a standard
deviation can be taken of these five measurements. The smaller the standard deviation, the more precise the
micropipette is.
c) What should 100l of water weigh?
Ans: The weight of 100l water is 0.1 gram.
1.2 Principle
A pipette tip constructed like a syringe is used. The pipette tip thus contains its own piston, which is
operated by the pipette mechanism. Because of this unique mechanism, positive displacement systems are
usually closed systems, that is, they cannot take tips from other systems.
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1.3 Objectives
The main objective of the lab experiment is to become familiar and adept at using micro pipettors and
check the calibration of the pipettors.
2. Materials and Methods
2.1 Materials
Equipment:
a)
b)
c)
d)
e)
100- and 200- L pipettors
1000 L pipettors
Yellow and white pipette tips
Deionized water
Weighing Balance
Figure 1: Pipette
2.2 Methods
A: Precision of P- 100 or P- 200 pipettor:
At first, we acquired a P-100 and P-200 pipettor and with a correct size tip as shown in “Figure:2”. The
pipette was set to 1000 L. The weighing cup was placed on the balance and tared the weight to zero. 100 L
of deionized water was drawn into the weighing cup and dispensed it onto the weighing cup as shown in
“Figure:3”. The weight of the water was recorded. The procedure repeated twice. We weighted 100 L for three
times to measure accurate result up and compared the data.
B: Precision of P- 1000 pipettor:
At first, we acquired a P-100 and P-200 pipettor and with a correct size tip as shown in “Figure:2”. The
pipette was set to 1000 L. then weighing boat was placed on the balance and tared the weight to zero. 1000
L of deionized water was drawn up and dispensed it onto the weighing boat as shown in “Figure:3”. The
weight of water was recorded. The procedure was repeated more two times. Again, the pipettor was set to 100
L and the weight of the liquid was checked three times. 200, 500 and 750 L of water were drawn up just to
see what they look like in the tip. The analysis of results questions was checked making sure that we have all
the data needed the pipettors was adjusted to the highest volume size and the pipettors were put carefully away.
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Figure 2: Inserting
Tip in a pipettor
Figure 3: Weight deionized
water
3. Results and Discussion
3.1 Results
A: precision of P-100 and P-200 pipettors
a) The weight that we measured was recorded for the three trials of 100 l:
Weight 1 (x1) = 0.10g
Weight 2 (x2) = 0.10g
Weight 3 (x3) = 0.10g
b) The average of three trials is
∴
x1+x2+ x3
3
=
0.1=0.1=0.1
3
= 0.1g
c) The % error between the average of the three trials and the true value was calculated:
∴ % error = |
𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑤𝑒𝑖𝑔ℎ𝑡−0.1𝑔
0.1
0.1𝑔−0.1𝑔
| 0.1 |
=
=0
| × 100%
× 100%
d) The mean deviation for the three trials
∴ Mean deviation =
∑ | 𝑋𝑖−𝑋𝑎𝑣𝑔|
3
4
|0.1−0.1|+|0.1−0.1|+|0.1−0.1|
=
=0
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B: Precision of P- 1000 pipettor
a)
The weight that we measured was recorded for the three trials of 1000 l
Weight 1 (x1) = 0.99g
Weight 2 (x2) = 1.00g
Weight 3 (x3) = 1.00g
b) The average of three trials is
∴
x1+x2+ x3
3
=
0.99+1.0+1.0
3
= 0.99g
c) The % error between the average of the three trials and the true value was calculated:
𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑤𝑒𝑖𝑔ℎ𝑡−1.00𝑔
| × 100%
1.00𝑔
0.99𝑔−1.0𝑔
=|
| × 100%
1.00
∴ % error = |
= 1%
d) The mean deviation for the three trials
∴ Mean deviation =
=
∑ | 𝑋𝑖−𝑋𝑎𝑣𝑔|
3
|0.99−0.99|+|1.0−0.99|+|1.0−0.99|
3
0.02
=
3
= 0.006
C: the weight that measured for the three trials of 100 l using the P- 1000 was recorded.
a) The weight that we measured was recorded for the three trials of 1000 l
Weight 1 (x1) = 0.99g
Weight 2 (x2) = 1.00g
Weight 3 (x3) = 1.00g
b) The average of three trials is
∴
c)
x1+x2+ x3
3
=
0.10+0.10+0.10
3
= 0.10g
The % error between the average of the three trials and the true value was calculated:
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∴ % error = |
=|
𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑤𝑒𝑖𝑔ℎ𝑡−1.00𝑔
1.00𝑔
| × 100%
0.10𝑔−1.0𝑔
| × 100%
0.10𝑔
=0%
d) The mean deviation for the three trials
∴ Mean deviation =
∑ | 𝑋𝑖−𝑋𝑎𝑣𝑔|
3
|0.1−0.1|+|0.1−0.1|+|0.1−0.1|
=
=0
3
3.2 Discussion
The micropipette is a reliable precision instrument that has been used to accurately measure small
volumes of liquids (volumes typically vary from 5 to 1000 l) and trusted many years in biochemistry, molecular
biology and other fields. Micropipette can deliver accurate and precise volume of solution. Accuracy is a
measure of how close a measured value is to the accepted or “true” value. It is related to the percent error
between the average volume of solution measured experimentally and the volume that was expected (the
accepted value). Precision measures the closeness of a set of values obtained from identical measurements of
the same quantity. It is the measure of reproducibility of a measurement (whether it’s accurate or not). The
percent error between the average volume of solution and standard deviation are used to compare accuracy and
precision respectively.
In our experiment we use three types of micropipettes i.e. P-100, P- 200, and P-1000 l. We placed an
appropriate tip on the end and push down gently plunger of the micropipette to suck the correct volume of water.
When we push down the plunger of the pipette there would be vacuum created in the tip and water could drawn
up. The volume to be taken up is set by turning the plunger on the top of the micropipette and reading the
numerical settings displayed. A setting of 100 l is equal to 0.1 g. A setting of 1000 l is equal to 1.0g. Although
micropipettes are usually quite accurate when first purchased, they can eventually develop problems with use
so always need to put original position after use.
3.3 Post-Lab Questions
1. Which of the two pipettors that you used was the more accurate? Explain.
Ans: From the result P-100 l pipette is more accurate. In 100 l the percentage error is zero whereas at P- 1000
l the percent error is 1% so P- 100 l is more accurate.
2. Which of the two pipettors that you used was the more precise? Explain.
Ans: In our case, P- 1000 l pipette is more precise. The mean deviation for the three trials of P- 1000 is 0.006
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and the percent error is 1%. Whereas at P- 100 l the mean deviation and percent error is zero.
3. Without checking the accuracy of a given Pipetman, would you predict that it is better to use a P-200 or P1000 to pipet 100 µL? Why?
Ans: If longer pipette is used, then we might end up measuring an error and lack precision. Therefore, it will be
better to use P-200 pipette to measure 100 µL and use P-100 to measure less than 100 µL.
4. Is a Pipetman more like a serological pipet or a Mohr pipet? Why?
Ans: Pipetman is more like a serological pipet, as it expels the liquid completely out of it all the way to tip.
1. How do you make 200 mL of a 0.1M solution of a substance that has a molecular weight of 121.1 g/mol?
Given,
Volume of liquid (V) = 200 mL = 200\100= 0.2 L
Molarity of solution (M) = 0.1 M
Molecular weight (MW) = 121.1 g/mol
Weight of solute (W) = X
We know that,
Molarity (M) = Number of moles / volumes of solution in L
Or, molarity (M) =
𝑋
weight of solute in gram (W)
MW×volume of solution in L
Or, 0.1 M = 121.1×0.2
𝑋
Or, 0.1 M = 24.22
Or, X = 0.1 × 24.22
Therefore, X = 2.422 gm
4. Conclusions
From this experiment, we were able to use micropipette and compare the precision and accuracy of the
different kind of micropipettors. From the result, we concluded that the pipettor with shorter tubes could give
more accurate results than longer tube. Micropipette needed an appropriate tip to suck the water up. Use of
pipette is very essential in all of experiments, as the accuracy of the measurement of different liquid increases
the more reliable the data will be.
5. References
1. Experiments in Biochemistry, 2019. Albert Linton Charles. National Pingtung University of Science and
Technology.
2. Post lab No.3: https://www.chegg.com/homework-help/questions-and-answers/chapter-1-biochemistryboot-camp-33-34-37-4-without-checking-accuracy-given-pipetman-would-q23527957. Retrieved on
February 25, 2019.
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