Welcome to Chem 370 Lab!

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<h1 style = "text-align: left; color: #C1A875;">Chem 370</h1>
<h1 style = "text-align: left; font-weight: bold; color: #C1A875;">UV-visible Spectroscopy</h1>

**Dr. Al Fischer**   |  Western Carolina University

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# lab 1 | **spectroscopy**

**Spectroscopy** is the study of the interaction of *light* and *matter*.

.image-credit[[Philip Ronan, Gringer](https://commons.wikimedia.org/wiki/File:EM_spectrumrevised.png) / [CC BY-SA](https://creativecommons.org/licenses/by-sa/3.0)]

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# lab 1 | **uv-vis (absorption)**

**Spectroscopy** is the study of the interaction of *light* and *matter*.

You’ve done UV-vis absorption spectroscopy in Quant, IR/NMR in o-chem.

.image-credit[David Harvey, [Analytical Chemistry 2.1](https://commons.wikimedia.org/wiki/File:EM_spectrumrevised.png) / [CC BY-SA](https://creativecommons.org/licenses/by-sa/4.0)]

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# lab 1 | **uv-vis (absorption)**

The plot of absorption vs. wavelength (energy) is called a **spectrum**.

.image-credit[David Harvey, [Analytical Chemistry 2.1](https://commons.wikimedia.org/wiki/File:EM_spectrumrevised.png) / [CC BY-SA](https://creativecommons.org/licenses/by-sa/4.0)]

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# lab 1 | **uv-vis (fluorescence)**

Some molecules also emit light (luminesce) after absorbing a photon.

.image-credit[Granger et al Instrumental Analysis. / Fair Use]

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# lab 1 | **uv-vis (fluorescence)**

The detector is placed at 90 degrees to the light source for luminescence spectroscopy.

.image-credit[[Venier](https://www.vernier.com/product/go-direct-spectrovis-plus-spectrophotometer/) / Fair Use]

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# lab 1 | **spectrophotometer**

- Use in fluorescence mode. 
- Measure fluorescence at $\lambda\_{ex}$ = 405nm and $\lambda\_{em}$ = ~450 nm (you should determine this first).
- Save three measurements of $\lambda\_{em}$ = ~450 nm for each sample.

.image-credit[Granger et al Instrumental Analysis. / Fair Use]

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# lab 1 | **standardization**

You must **standardize** the spectrophotometer using (5) **external standards** and a blank.

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# lab 1 | **standardization**

Check the precision of your standards by calculating the $R^2$ value. (1 = perfect)

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# lab 1 | **quality control**

Check the accuracy of your standards by analyzing a quality control sample (**QC**).

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# lab 1 | **glassware**

Use volumetric glassware!

Remember to fill to the right mark (TD vs TC) and record the uncertainty in your lab notebook!

.image-credit[David Harvey, [Analytical Chemistry 2.1](https://commons.wikimedia.org/wiki/File:EM_spectrumrevised.png) / [CC BY-SA](https://creativecommons.org/licenses/by-sa/4.0)]

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# lab 1 | **detection limits**

- (Lower) Limit of Detection: $ LOD = \frac{3\sigma}{m}$

- Limit of Quantitation: $ LOQ = \frac{10\sigma}{m}$
    
<img src="/assets/images/lab-2/harvey_fig416.png" style = "height: 250px; margin-left: auto; margin-right: auto; display: block; margin-top: 50px">

.image-credit[David Harvey, [Analytical Chemistry 2.1](https://commons.wikimedia.org/wiki/File:EM_spectrumrevised.png) / [CC BY-SA](https://creativecommons.org/licenses/by-sa/4.0)]    
    
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# lab 1 | **getting started**

- You may work in pairs to prepare standards if you wish.  But each students should run their own standards/samples individually.
- Create individual lab notebooks.
- Keep glassare clean and **organized**
    - Wash with Alconox and warm water, 3X DI rinse.
    - All Instrumental I supplies are in back left corner of lab.
- Run a blank (3X) 5 standards (1X each), a QC (3X), and a sample (tonic water, 3X) -- you have 3 weeks for this!
- Your goal today is to get a standard curve with an $R^2 > 0.9990$.  If you do not achieve this you should write a short summary of what went wrong in your lab notebook and what you plan to do differently, and then try again (either today or next week).
- ***You should turn in a draft lab notebook showing either a passing standard curve or a failing standard curve and plans to improve it today on Canvas so I can give you feedback.***

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# lab 1 | **getting started**
    
**Safety:**

- All wastes go in the waste container (in hood).
- Wear gloves and goggles (standards are acidic).
- Ask if you are unsure about anything!

**Lab Notebook + Data:**

- Turn in notebook at end of lab with today's work
    - You should have blanks, 5 standards, a QC, and (if time) sample data
- You will peer review other notebooks
- You may have to redo the experiment if your results are not good
- Final notebook + (high quality) data due in 3 weeks