TE Growth Factor Concentration ACTIVITY
BACKGROUND
One common means of measuring the level of a chemical relies on an indirect measurement. Chemists can
employ “reporter” molecules that complex with the target chemical (in this case, growth factor). Often, the
interaction between the reporter and target chemical results in the production of a color. The amount of color,
assumed to be a reflection of the amount of target chemical present, can be quantified by varying methods,
including spectroscopy. A spectrophotometer is a machine that passes a beam of light of a specific wavelength
through an aqueous sample. The amount of light absorbed by the reporter/pollutant complex (absorbance) can
be measured, as can the total amount of light able to pass completely through the sample (transmittance).
In this activity, students are challenged to determine the concentration of growth factor within a tissueengineered scaffold This determination will require the generation of a standard curve, commonly described as
a data set that correlates a particular measurement with a selected independent variable. For example, suppose
that a marine biologist wanted to determine the size of fish without the tedium of catching them and measuring
them. Prior to this, a data set was collected, comparing the length of a fish and its swimming velocity. This
information was graphed as follows:
Swimming Velocity Correlation
18
velocity (m/s)
16
14
12
10
Series1
8
6
4
2
0
0
20
40
60
body length (cm)
Notice that there appears to be a direct (linear) relationship between these two characteristics. Thus, if one
value (such as the y coordinate, or swimming velocity) is measured, the other value (the x coordinate, or length
of fish) can be determined by deducing the value from the graphed line. For instance, if the fish is clocked at 8
m/sec, the standard curve reveals a fish size of about 20 cm length. In this activity, a standard curve will reveal
a linear relationship between absorbance (y) and the concentration of pollutant (x).
PROCEDURE (suggested; can be modified by student)
1. Label 8 test tubes (provided by the instructor) with selected concentrations. Use a 100 ppm, 50 ppm, and 0
ppm, as well as 5 other concentrations between 0-50 ppm.
2. Obtain at least 50 ml. of the 100 ppm stock of reporter/GF solution.
3. Using pipets, water, the test tubes, and the stock solution, create the desired concentrations of solutions for
your standard curve. It is recommended that calculations be based on a final tube volume of 5 or 10 ml (for
ease of calculations).
4. After the spectrophotometer has been primed (warmed up), determine the absorbance of each solution.
Your instructor will announce the appropriate wavelength for the analysis.
5. Record the following information in a neat, organized table: the volume of water, volume of 100 ppm
stock, the resulting concentration, and the absorbance.
6. Obtain an environmental sample extract from your instructor. Measure the absorbance.
7. Graph your data. Remember to label axes, graph title, and position of sample extract.
8. Determine the concentration of GF in the sample extract.
Growth Factor ASSESSMENT ACTIVITY
Tube number
Volume of 100 ppm
stock (mL)
(Reporter Molecule)
Volume of
water (mL)
Resulting
concentration
(ppm)
Measured
absorbance
1
2
3
4
5
6
7
8
Formula to calculate various concentrations of solution:
mL stock solution
total volume in tube *
[conc. stock soln]
[new concentration]
=