oceanoptics(3) - BC367 Measuring Absorbance with the Ocean...

BC367: Measuring Absorbance with the Ocean Optics Spectrophotometers
Introduction:
The absorbance of a sample is given as A = log






I
o
I
,
where I
o
is the intensity without sample present and I is the intensity with the sample in the light
path of the spectrophotometer. This calculation is done at each wavelength in the spectrum. The
value of I
o
depends on wavelength and must be determined by placing a reference or blank
sample in the instrument. The terms reference and blank are used interchangeably. The reference
is usually a cuvette filled with only the solvent or the buffer for the experiment. The process of
acquiring the reference spectrum is called calibration in Logger Pro. Every time you switch
solvents or buffers, a new reference spectrum must be taken, so the instrument must be
recalibrated.
I. Getting Started and Calibration
1. First, open the Logger Pro 3 software. Then, in order, plug the spec power cord into an outlet,
plug the other end into the spectrometer where it is labeled “POWER,” and plug in the USB port.
2. The software should recognize the spectrophotometer automatically, showing the colors of the
visible spectrum in the data window with Wavelength as the horizontal axis. If the visible
spectrum is not displayed, first check your connections. If this doesn’t work, select Connect
Interface → Spectrometer → Scan for Spectrometers from the Experiment menu. If you find the
visible spectrum display annoying, turn it off by clicking on the graph and the going to “options”
 “graph options.” Unselect “Draw visible spectrum.”
3. Select Set Up Sensors → Spectrometer: from the Experiment menu. The Spectrometer dialog