INTRO TO SPECTROSCOPY

What is Spectroscopy?

There are about 12 types of spectroscopy. It involves ALL parts of the electromagnetic

spectrum We are specifically studying:

Atomic Absorption SpectroscopySending a beam of visible light through a sample and measuring how much of the light is absorbed by that sample.

Why?

By looking at the absorbance of light, we can determine the concentrations and types of a substance found in a solution.

Meaning… How much of THIS is in THAT.

And… What is THIS made of?

Who uses it?

Medical Field Radiology Technicians Astronomy Analytical and Physical Chemists Environmental Scientists and Chemists Quality Control Chemists Medical Examiners Forensic Scientists and Chemists Toxicology

Why is it called Spectroscopy?Spectroscopy = Spectrum = Electromagnetic Spectrum = LIGHT!

Atomic Absorption SpectroscopyUses the spectrum of VISIBLE LIGHT.

Wavelengths we will be measuring:

700 nm to 400 nm = 7 x 10-7m to 4 x 10-7m

We will be taking our readings in nanometers (nm)

Demo…

Let’s take a look at the instrument:

Spectrophotometer

How can we determine the concentration of a substance in a solution?

Table 2: The Absorbance Reading for Each Sample

Sample Absorbance Concentration (mol/L)

1 0.015 1.70E-07

2 0.089 8.50E-07

3 0.166 1.70E-06

4 0.829 8.50E-06

5 1.593 1.70E-05

Unknown 0.047 To be Determined

Make solutions of known concentrations using the substance you are measuring. Place them in spectrophotometer and read absorbance.

Make a Graph with a Linear Line

1.00E-07 5.10E-06 1.01E-05 1.51E-050

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

f(x) = 93835.5507492253 x + 0.00879215157137225R² = 0.999595610909128

Calibration Curve of Concentration Versus Absorbance for the Blue Dye No. 1 Solutions

Concentration (mol/L)

Absorbance

Now place your unknown in the spectrophotometer.

It will read the absorbance. Place the absorbance on your calibration curve to find concentration.

Unknown Absorbance = 0.047

1.00E-07 5.10E-06 1.01E-05 1.51E-050

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

f(x) = 93835.5507492253 x + 0.00879215157137225R² = 0.999595610909128

Calibration Curve of Concentration Versus Absorbance for the Blue Dye No. 1 Solutions

Concentration (mol/L)

Absorbance

Use your equation:

Use the equation of the line to find EXACT concentration.

Y=mx+b y = 93836x + 0.0088

Y= Absorbance X=Concentration

Looking Ahead:

Lab intro due on Monday to proofread

Collecting Samples (Next Tuesday)

Using Excel to make graphs and figures (Next Thursday)

How to calculate the concentrations of your known standard solutions (Next Thursday)

Using pipets and glassware to perform dilutions (Monday Sept 15)