Class: BE209
Group: R7
Members: Robert Bowles, Nicole Hadi, Kevin Kedra, Naomi Saint Jean,
Eric Sussman
Date: December, 2002
Introduction
Spectroscopy is the field concerned with the dispersion of light
into its component colors by a certain substance. More specifically,
it deals with the ability of a substance to absorb and emit characteristic
wavelengths of light.
One important application of spectroscopy is to use the optimal
absorbance wavelengths to determine concentrations using the Beer-Lambert
Law. This law states that the absorbance for a particular substance
is proportional to the concentration of that substance. Spectrophotometers
are the devices used to collect data pertaining to spectroscopy.
They consist of 4 main parts- a light source, a monochromator used to separate
white light into component wavelengths from which one wavelength can be
chosen, a cuvette, and a phototransistor, which is the device that measures
the intensity of the transmitted light. One specific type of spectrophotometer,
colorimeters, use filters instead of monochromators to select the wavelength.
Colorimeters are widely used in the clinical laboratory setting, to identify
the concentrations of substances contained in blood, urine, and other body
fluids. The filter can be chosen based upon the color of the solution.
In order to obtain effective results from a colorimeter, the sample
that is being tested must be diluted. Otherwise, no light would be
transmitted to the photometer. Once the absorbance value of the diluted
solution is obtained, the corresponding concentration can be read off of
a calibration curve, and then multiplied by the proper dilution factors
to achieve the original concentration value.
The main objective of this experiment was to construct a circuit
which behaves like a colorimeter and could measure the concentration of
hemoglobin (optimal absorbing wavelength of 416nm) using the red diode
(~650nm), and bromocresol green using the green diode (~510nm). Photocells
were used as photometers and diodes as a combination of the light source
and the filter. In addition, the ability to measure concentrations of hemoglobin
similar to those found in human blood was investigated.
We hypothesized that using the colorimeter linear plots of absorbance
versus concentration will result from using the green diode for hemoglobin
and the red diode for bromocresol green. Using the filter paper method,
a linear plot of absorbance versus concentration will result to which unknown
samples can be compared.