analytical chemistry

2. Mujahid ali
Roll No: 44
B.s applied geology
Institute of geology, University of the Punjab Lahore

3. 1. Indicator – Quickest method.
 Indicator solutions change colors
when a molecule of interest is
present.
 Allows scientist to detect colorless
molecules in a solution.
 Examples: Bradford protein reagent
Diphenylamine (DPA) or Biuret
(NaOH+CuSO4).

4. 2. Spectrophotometer (Spec)
 An instrument that measures the
amount of light that passes
through (is transmitted through) a
sample.

5. Uses a type of light to detect
molecules in a solution
Light is a type of energy, and
the energy is reported as
wavelengths, in nanometers
(nm).

6. 1. Ultraviolet (UV)
Spectrophotometers.
 Uses ultraviolet light of wave lengths
from 200 nm to 350 nm.
2. Visible (VIS) Light Spectrum
Spectrophotometers.
 Uses visible light (white light) of wave
lengths from 350 nm to 700 nm.

7. R O Y G B I V

8.  Shines a beam of light on a sample.
 The molecules in the sample interact
with the light waves in of 3 ways:
 Absorb the energy
 Reflect the energy
 Transmit the energy between and
through the atoms and molecules of
the sample.

9. Consider blue molecules, all the
wavelengths of light are absorbed,
except for the blue ones.
The blue wavelengths are transmitted
or reflected off the molecules. If these
blue wavelengths hit a detector (such
as in the spectrophotometer or the
nerve cells in your eye), they appear
blue.

10.  Molecules are whatever color of
light that they do not absorb.
 Green molecules appear green
because they absorb most
wavelengths of visible light,
except the green wavelengths.

11. The spectrophotometer measures
the amount of light transmitted
through the sample
(Transmittance).
By using an equation (Beers law),
it converts the transmittance data
to an absorbance value.
It is quantitative analysis

12. The concentration of an unknown
sample can be determined by
comparing the absorbance data to
standards of known concentration.
The data generated with the set of
known standards is called a
standard curve.

13.  Inner parts
● Lamp
● Prism or grating that direct light of
a specific wavelength.

14.  Outer parts:
Sample Holder
Display
Knobs or buttons used to calibrate the
spec to measure the designated molecule.
Wavelength
Selection

16. Visible Spectrophotometer
White light hits the prism or grating,
it is split into the colors of the rainbow
(Visible Spectrum).
The wavelength knob rotates the
prism/grating, directing different
color of light toward the sample.

17.  The wavelength of light produced
by the tungsten lamp range from
about 350 nm (Violet light) to 700
nm (red light).
 The molecules in the sample either
absorb or Transmit the light energy
of one wavelength or another.

18.  The detector measures the amount
of light being transmitted by the
sample and reports that value
directly (% transmittance) or
converts it to the amount of light
absorbed in absorbance units (au)
using Beers Law.

19. 1. Determines the presence and
concentrations of samples.
2. Determines the purity of a
sample.
3. Look at the change of samples
over time.