[PASCO Spectrometer and Colorimeter: A Comparison]
Hi, this is Tom Loschiavo, Chemistry Education Manager at PASCO scientific.
I'm here today to talk about the Colorimeter and the Spectrometer,
to make sure you have all the information you need
to make the best decision for your lab and teaching classroom.
Both of these devices are very useful in studying colored solutions:
Colored solutions like copper sulfate, or dyes,
plant pigments, or crystal violet.
First we'll talk about the Colorimeter.
I have a Colorimeter Bluetooth-connected to SPARKvue,
but it also works with Capstone.
One of the great features of the Colorimeter is that it's a quick one button calibration.
I simply put in my blank,
push the button,
and allow it to calibrate,
so that I get 100% transmittance and zero absorbance
for the four LEDs that are present:
the red, green, blue, and orange LEDs.
In SPARKvue, right from the home screen, I can put in a sample,
in this case, some crystal violet.
I can see that the crystal violet absorbs mostly in the green part of the spectrum,
with the 565 nm absorbance being the highest.
For the Spectrometer, I can also do an initial analysis of a colored solution.
The Spectrometer will work with its own app,
called the Spectrometry app.
I would do the same thing I did with the Colorimeter:
I would blank it using a reference, in this case, a water sample,
putting it in so that the white light source points through the sample to the detector.
Then I would calibrate my reference, turning the lights on and off.
Once I have that calibrated, I can put in a colored solution,
And I can see a full spectrum of the sample,
from 380 to 915 nm,
Not only do I see the full spectrum,
I can pick any wavelength of that full spectrum to do further analysis.
In this case, the peak wavelength for study would be around 582 nm,
which is close to the wavelength we saw with the Colorimeter,
but we get a little more precision in terms of the wavelength that we get to pick.
The other nice thing about the Spectrometer, in terms of simply analyzing solutions,
is the Spectrometer has built-in fluorescence support.
Not only is there the white light source,
there are also green and purple excitation LEDs for fluorescence.
I can put in a sample that will fluoresce, like olive oil or Fluorescein,
and I can go to the Fluorescence page in the Spectrometry app,
and I can see the fluorescence wavelength of that particular sample,
in the 670 nm or so range of the spectrum.
So a little extra functionality with the Spectrometer and the full visible spectrum.
But both of these are great tools for initial analysis of colored solutions.
[Concentration and Absorbance]
The other great thing that both the Colorimeter and the Spectrometer allow us to do
is look at concentration and absorbance relationships,
commonly known as Beer's Law.
In chemistry, we could use crystal violet to do that,
or copper sulfate, or any colored solution.
In biology, you will typically see that with DPIP studies
of light reactions involving photosynthesis.
With the Colorimeter we'll check that out first.
I filled these different concentrations of crystal violet into some cuvettes,
and I created a page in SPARKvue that has a graph of concentration and absorbance--
green absorbance for crystal violet--
and a table of those same concentrations and absorbance for crystal violet.
So I go in and I start my data collection,
and I keep my absorbance values for each of those known standards.
As I keep those in the table, the graph will automatically populate.
I can see this relationship between absorbance and concentration.
To further quantify that relationship I can use my graph tools, like my linear fit,
and I can apply that fit to the data.
Then the students can measure the absorbance of an unknown sample of crystal violet.
Based on the graph and their fit they can determine the concentration of that unknown.
With the Spectrometer you can do those exact same things.
In fact, in the Spectrometry app there is a specific Concentration section.
Just like in the SPARKvue page,
I can have concentration and absorbance values in a table.
They'll auto populate onto a graph of absorbance and concentration.
I can apply a linear fit to those values.
The other nice thing about the Spectrometry software is
that I can take an unknown sample,
and that unknown analysis is built right into this page.
I can insert my unknown, start my data collection,
and save my data.
Based on the graph, or their fit line, or the slope and intercept,
students can determine what the concentration should be.
That unknown value is automatically added to the graph,
and the students can get an idea if their estimation or calculation was correct,
so they get a little bit of student feedback.
The other nice thing about this page is that there is a built-in live scan,
so you see the full spectrum at all times.
You can see that full spectrum changing.
You can easily toggle between absorbance and transmittance,
so the students can determine if the relationship between transmittance or absorbance
and concentration is linear, and therefore more useful in doing their analysis.
Both of these tools are great for doing concentration and absorbance studies.
The Spectrometer has little extra features
to make it easier for implementation and understanding for your students.
[Reaction Kinetics]
One of the other useful applications of both the Colorimeter and the Spectrometer
is to do some kinetics studies.
In this case, again, I used my crystal violet.
I reacted it with some sodium hydroxide
in order to determine the rate law and order of the reactants of the crystal violet.
In the case of the Colorimeter, using SPARKvue software,
I have a green absorbance versus time page setup.
I simply added some sodium hydroxide to the crystal violet,
put it in, started collecting data, and allowed this graph to populate.
To do the kinetics studies you want to be able to look at not only the absorbance,
but the natural log and the inverse of the absorbance,
to see which one of those is the straight line, to determine the order of the reaction.
Both SPARKvue and Capstone allow us to make calculations.
In this case, I created some calculations: inverse and natural log.
I can apply those calculations onto the graph.
In this case, I put them onto the same graph using a multi-y feature of SPARKvue.
I see my green absorbance,
my inverse absorbance,
and my natural log of absorbance.
I notice that the natural log of absorbance is the straightest line,
indicating a first order reaction
And again, we can quantify that a little bit more using the fit tools,
in this case, a linear fit on that particular set of data.
The Spectrometry software also allows us to do the same kinds of studies with the Spectrometer.
Take a sample of crystal violet, put some sodium hydroxide in, let that reaction run.
Again I get my absorbance and my time.
In this case, because it's a Spectrometer, I could have picked any absorbance wavelength,
but I picked the maximum wavelength that we established earlier on.
The nice thing about the Spectrometer is that I could view this as absorbance versus time,
easily as transmittance versus time,
or as concentration versus time.
The reason I can do that is because the Spectrometry software
calculates the concentration based on the slope and intercept
from that Concentration experiment page.
I want to be able to relate absorbance or concentration, natural log, and inverse very easily.
The Spectrometry software allows me to do that, too.
I can quickly toggle through my QuickCalcs.
Here's my absorbance,
here's my inverse,
and here's my natural log.
Again, this one looks nice and straight.
I can apply a linear fit to this,
and again, see that relationship to quantify the order of the reaction,
and the rate constant, or pseudo rate constant in this case, for that particular reaction.
The other nice thing with the Spectrometry software is I have that inset,
so I can see the full spectrum changing as the reaction's happening.
You can actually perceive that peak changing over time in the inset,
as well as seeing the absorbance or concentration change over time.
So both of these tools are very useful for kinetics.
The Spectrometer has a few extra features that allow you to make some easier calculations
and determine those relationships in a meaningful way.
[Emission Spectra]
There's an additional feature for the Spectrometer
that takes advantage of the fact that it is a full spectrum analysis.
It can use the optional fiber optic accessory cable.
Put it into the sample holder
and point it at light sources.
By doing that--we're looking at Helium--
I can go to the Analyze Light page
and I can look at the full visible spectrum of the emission of that particular element.
You can take advantage of the customized features within the Spectrometry software.
From there I can use the Coordinates tool.
I can select those peaks that are on the spectrum,
and I can see not only the wavelength,
but then I can have students apply some mathematical relationships,
and determine the frequency and energy of those emissions,
and relate that to atomic theory.
If you want to learn more about our Colorimeter and our Spectrometer,
there are lots of online resources at pasco.com, including videos.
If you want to get your hands on the Spectrometry software, but don't have a Spectrometer yet,
you can download the free software from our website.
There are also some sample files where you can get some data and play with it.
I encourage you to investigate other ways to do spectroscopy in your classroom
using the Colorimeter and Spectrometer.
This has been Tom Loschiavo at PASCO scientific.
Feel free to reach me with questions or comments at chemistry@pasco.com.
I encourage you, as always, to "Think Science".