Flam emissionAtomic absorption phenomenonemissionabsorption Source of excitationflameHallow cathode lamp Role of flame1-Evaporation. 2-Atomisation. 3-Excitation. 4-Emission of radiation 1-evaporation..2-atomisation. No. of determined elements Alkali and alkali earth Metal (Na,K,Li) All elements
Flame emission Definition: determination of the concentration of an element by measurement of light emitted when the element is excited by energy in the form of heat. determinationconcentration elementmeasurementlightenergyheat
Why flame emission is used for limited no of elements? Because most elements except ( Na,k.Li) needs high energy for excitation, & in flame spectroscopy only relatively cool flame are used(natural gas-air flame o c)
applications Rapid determination of Na ions in the blood. In organic and inorganic analysis of alkali and alkali earth metals Flame emission can be used : - qualitative and quantitative. 1- qualitative (the substance emitted radiation at characteristic λ). 2- quantitative depend on the intensity of emission. Emission concentration. .
instrument The instrument consist of two parts: 1- burner and atomizer system ( pressure regulator, flow meter, nebulizer and burner) 2- optical system ( monochromator, detector, amplifier, recorder, in addition to mirrors )
1-Atomizer and burner: Atomizer : produce a fine and uniform spray of the sample solution ( mist) N.b : only liquid samples are used in this method. 2- burner: a- total consumption burner. b- pre mix chamber burner.
Total consumption burner:
A-Total consumption burner The sample is aspirated through a capillary to the tip of it where its break down into a fine mist by the stream of the oxidant. The mist + fuel & supporting gases are mixed in the flame. It is called total consumption cause the entire aspirated sample enters the flame.
Premix chamber burner: Aspiration of sample in to the nebulizer. In the nebulizer the sample is sprayed into very fine droplet ( mist). Large droplet will be drain out the fuel and the oxidant are mixed in the mixing chamber before they enter the flame head where the combust. only fine droplets remains and mixed with the Gases and enters the flame( 2-10% of the sample get atomized)
At the flame evaporation, melting, atomization and excitation of the atoms takes place. The excited atom emit radiation in which its intensity α concentration of the determent elements. The emitted radiation is filtered → D → R
Why a mirror is placed behind the flame : Cause the radiation from the flame is emitted in different directions & so the mirror will increase the amount of radiation falling on the detector.
Determination of Na & K 1- Determination of Na : Stock = 100 ppm. ( Nacl) mlsConc.% emission 2cxv = c-xv unkown67
Determination of K Stock 100 ppm mlsconc% emission 1Cxv = c-xv unknown62
Standard addition method Radiation intensityRadiation intensity after correction Sample alone5.1 Sample +0.1 ppm standard Ca 6.2 Sample ppm standard Ca 7.3 Sample ppm standard Ca 10.6 Flame alone0.7
Standard addition curve % E c
Atomic absorption It is a type of flame spectroscopy in which the absorption caused by atoms when introduced into the flame is studied, it is a method of elemental analysis. The process of atomic absorption spectroscopy (AAS) involves two steps: 1. Atomization of the sample 2. The absorption of radiation from a light source by the free atoms
spectroscopyAtomic absorption principleMolecular absorptionAtomic absorption Source of lightTungsten, deuteriumHallow cathode lamp Rang of λWide rangNarrow rang Absorption spectrumBroad absorption spectrum Line absorption spectrum
Applications Poisoning of heavy metals e.g Hg,Pb s of Analysis of certain drugs which contains metal e.g vit B12. In organic chemistry, its used for determination of all the elements in the periodic table
instrument 1- hollow cathode lamp. 2- burner ( as in flame emission). 3-optical system
Hollow cathode lamp It consists of: 1- a cylindrical metal cathode made of the same elements to be determined. 2- anode. 3- the lamp is filled with an inert gas ex: Ar or He..
Why The cathode is hollow ? to allow the atoms to deposit back on the cathode, thus increasing the life time of the lamp
hollow cathode lamp
Steps of atomic absorption:
The sample is aspirated, aerosolized and mixed with the combustible gases. The role of flame here is atomization. When a light beam from a cathode ( which is made from the same element to be determined ) passes through the flame the free atoms will absorb it. The light passing through the flame is received by the monochromator, transmitted to the detector which measures the reduction of the beam of light as absorbance
Determination of Zn by AAS stock = 10 ppm Conc. ppmmlsabsorption unknown0.46