Vernier Original LabQuest - Manual (Page 21)

LabQuest Reference
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modes.
View Full Spectrum
Once a spectrometer is calibrated, place a sample in the cuvette holder. Tap Collect.
Absorbance, Transmission or Intensity will be displayed as a function of wavelength. The
spectrum will be updated as quickly as possible, with the previous spectrum replaced by the
current one. When you tap Stop, the latest spectrum will be retained.
Change Wavelength
After observing a full spectrum sample (or if you already know the desired wavelength
setting), return to the Meter screen. Tap the meter, and choose Change Wavelength… to
reach a dialog where you can enter the desired wavelength in nm. This setting is used for
modes other than Full Spectrum, so that the LabQuest App reports the current reading at
the selected wavelength. This reading would then be collected as a function of time or
events.
Example Spectrometer Application: Beer’s Law
To illustrate the sequence of steps commonly used with a spectrometer, consider setting up a
Beer’s law experiment, where the ultimate goal is a graph of absorbance versus concentration
of a sample of nickel sulfate at the wavelength of peak absorption. Making use of the details
already given earlier, the general steps are as follows.
1. Prepare a selection of various concentrations of nickel sulfate, including a zero
concentration cuvette with only the solvent.
2. Calibrate the spectrometer using the zero concentration (blank) cuvette.
3. Place one of the non-zero concentration cuvettes in the spectrometer, and measure
the absorbance as a function of wavelength. From this graph, select the desired
wavelength.
4. Set the chosen wavelength for further single-wavelength data collection. LabQuest
App chooses the wavelength of maximum absorbance by default.
5. Change the data collection mode on the Meter tab to Events with Entry. Label the
Entry column as Concentration, with units of mol/L.
6. Start data collection; place the lowest concentration cuvette in the spectrometer.
7. Tap Keep; enter the concentration when prompted.
8. Put in the next sample, tap Keep, and enter that concentration. Repeat this step for
all samples.
9. Tap Stop.
10. Inspect your graph of absorbance versus concentration. If desired, fit a linear
function to the data. After a linear fit has been
performed, you can also interpolate between
data points using Interpolate from the Analyze
menu. This lets you estimate the concentration
of an unknown sample using a reading on the
meter screen.
Settings for Full Spectrum Mode
The Data Collection dialog for Full Spectrum Mode
contains several settings for advanced users.