427 PHC
ATOMIC EMISSION
SPECTROSCOPY
Direct-Current Plasma
 A direct-current plasma (DCP) is created
by an electrical discharge between two
electrodes. A plasma support gas is
necessary, and Argon is common.
 Samples can be deposited on one of the
electrodes.
 Insulating solid samples are placed near
the discharge so that ionized gas atoms
sputter the sample into the gas phase
where the analyte atoms are excited.
Direct-Current Plasma
Spark and Arc
 Spark and arc excitation sources use a
current pulse (spark) or a continuous
electical discharge (arc) between two
electrodes to vaporize and excite analyte
atoms.
 The electrodes are either metal or
graphite. If the sample to be analyzed is a
metal, it can be used as one electrode.
 Arc and spark excitation sources have
been replaced in many applications with
plasma or laser sources, but are still widely
used in the metals industry and for the
analysis of metallic elements in solid
samples.
 For non-conductive materials, the sample
is ground with graphite powder to make it
conductive.
 In traditional arc spectroscopy methods, a sample
of the solid was commonly ground up and
destroyed during analysis and placed into a cup-
shaped lower electrode.
 An electric arc or spark is passed through the
sample, heating it to a high temperature to excite
the atoms within it.
 The excited atoms emit light at characteristic
wavelengths that can be dispersed with a
polychromator and detected.
 As the spark or arc conditions are typically not well
controlled, the analysis for the elements in the
sample is qualitative. However, modern spark
sources with controlled discharges under an argon
atmosphere can be considered quantitative.
Spark and Arc
Flame emission spectroscopy
 A sample is brought into the flame as a gas or
sprayed solution. The heat from the flame
evaporates the solvent and breaks chemical
bonds to create free atoms.
 The thermal energy also excites the atoms into
excited electronic states that subsequently emit
light when they return to the ground electronic
state.
 Each element emits light at a characteristic
wavelength, which is dispersed by a grating or
prism and detected in the spectrometer.
Application:
 AES is useful for both qualitative and
quantitative elemental analysis.
 The plasma sources yield significantly better
quantitative analytical data than other
emission sources do.
 All metallic elements can be determined by
AES.
 Calibration curves are used for determination
of the concentration of trace elements in
different samples.
What is the difference between
atomic emission spectroscopy
and atomic absorption
spectroscopy?
 Emission spectroscopy is a spectroscopic technique
which examines the wavelengths of photons emitted by
atoms during their transition from an excited state to a lower
energy state. Each element emits a characteristic set of
discrete wavelengths. By observing these wavelengths the
elemental composition of the sample can be determined.
 Absorption spectroscopy measures the loss of
electromagnetic energy after it absorbs by the sample under
study. For example, if a light source with a broad band of
wavelengths is directed at a vapor of atoms, the particles will
absorb those wavelengths that can excite them from one
energy state to another.
AAS
AES
• preparation of samples
1.Reagents and chemicals:
a.Nitric acid conc.
b.Hydrochloric acid conc.
c.Deionized water (grade 1).
d.Hydrogen peroxide (30%).
e.Sulpheric acid conc.
f.Potassium dichromate solution 5%.
B- Equipment and instrument:
a.Pipettes 1-5-10-20 ml.
b.micro pipettes (10-1000 micro liter).
c.Flasks 1000-500-250-200-100-50-10-5 ml flasks.
d.Beakers 50-100-250-500 ml.
e.Oven up to 700 C.
f.Microwave oven for digestion.
g.Analytical balance.
• PROCEDURE:
1.Receive the sample.
2.Register the data in the Logbook.
3.For open system digestion Weight about 1-2 gram of the
sample.
4.For closed system digestion weight maximum 0.5 gram of
the sample.
5.The sample should be digested or ashed according to the
element been analyzed.
1.Standard Preparation:
a. Prepare your different standard concentrations
either from stock standard 1000-ppm stored in the
refrigerator, or from a suitable salt of the element.
b. It is recommended that you prepare 100-ppm STD
stock and make the dilutions out of it to minimize the
margin errors.
2.Sample Preparation:
• open system digestion
1.Take 1-2 gram\s of the sample in 250 ml flask
and add 20 ml of concentrated nitric acid.
2.Put it on a burner in the fume hood and heat.
3.Evaporate nitric acid till 3-5 ml is left.
4.Add 2 ml of hydrogen peroxide and continue
heating. Notice the white fume evolving (that’s the
nitric acid).
5.When the white fume stops, add 20 ml of HCl:
H2O 1:3 and heat again till it starts to boil.
6.Leave it for 2 minutes, then filter and complete to
volume with de-ionized water.
• Ashing:
i.Some samples are treated by aching method.
ii.Weight one gram and ash the sample in oven at
450ºc for organic samples and up to 800ºc for
inorganic samples.
iii.Remove the ash from the oven and diluted it with
20 ml of HCl: H2O 1:3
Note: use nitric acid instead of hydrochloric acid for
selenium Se
i.Filter the sample and complete to volume with deionized water.
a.As it is sample:
i.Some sample dose does not need to be digested
since its elements are free in the aqueous solution. It
will be analyzed as it is. If necessary, diluted with
de-ionized water.