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The Spectronic 20 (Spec20) is the most common type of spectrophotometer used in labs today, and is the one you will use in your CHM1046 labs.

The spectrophotometer is an instrument that measures the amount of light that passes through a medium at a specific wavelength. According to Beer’s law, the amount of light absorbed by a medium is proportional to the concentration of the absorbing material or solute present. Thus the concentration of a colored solute in a solution may be determined in the lab by measuring its absorbance of light at a given wavelength.  Wavelength (often abbreviated as lambda) is measured in nanometers (nm).  The spectrophotometer allows the operator to select a wavelength to pass through the solution.  Usually, the wavelength chosen corresponds to the absorption maximum of the solute. Absorption is indicated with a capital “A”

1. Display: 20-character, 2-line LCD

2. Soft key 1: Function varies depending on screen; generally Escape, Back up or Clear

3.Soft key 2: Function varies depending on screen; generally Enter, Accept or Continue

4.Scroll keys: Used to scroll through menus and enter numeric values

5.Wavelength controls: Increase and decrease the wavelength setting

6. 0 Abs/100%T: Automatically sets the instrument to zero absorbance (100%T)

7. A/T/C: Switches between absorbance, %transmittance and concentration modes

8. Utility: Accesses instrument set-up, diagnostics and other functions

9. Print: Sends currently displayed data to selected printer

Keyboard layout

The Genesys 20 – Absorbance and %Transmittance measurements

1. Press A/T/C to select the absorbance or %transmittance mode. The current mode appears on the display.
2. Press nm   or nm   to select the wavelength.

Note: Holding either key will cause the wavelength to change more quickly.

3. Insert your blank into the cell holder and close the sample door

Note: Position the cell so the light (indicated by arrow in drawing) passes through the clear walls.

4. Press 0 ABS/100%T to set the blank to 0A or 100%T.
5. Remove your blank and insert your sample into the cell holder. The sample measurement appears on the LCD display.

The Genesys 20 – Concentration measurements using a standard

1. Press A/T/C to select the concentration mode The current mode appears on the display.
2. Press nm  or nm  to select the wavelength.

Note: Holding either key will cause the wavelength to change more quickly.

3. Insert your blank into the cell holder and close the sample door.

Note: Position the cell so the light (indicated by arrow in drawing) passes through the clear walls.

4. Press 0 ABS/100%T to zero the blank, then remove the blank and insert your standard.
5. Press the Standard soft key and use the and keys to enter the concentration of the standard, then press the Set C soft key to calculate and display the factor for the selected standard.
6. Remove the standard and insert your sample into the cell holder. The calculated sample concentration appears on the LCD display.

The Genesys 20 – Setting absorbance and % transmittance

In addition to taking absorbance and %transmittance measurements, you can also set specific values for the absorbance or %transmittance on the display.

1. Press the  and  keys to set the absorbance or %transmittance value on the display.
2. Press the  and  keys to adjust the absorbance or %transmittance to the desired value.
3. Press the Set A soft key or the Set %T soft key to set the value and return to the main display.

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