Medical brain notes 14

  INTRODUCTION Metallic salts (or metallic compounds) after dissolution in appropriate solvents when introduced into a flame (for instance : acetylene burning in oxygen at 3200°C), turns into its vapours that essentially contain mostly the atoms of the metal. Quite a few such gaseous metal atoms are usually raised to a particular high energy level that enables them to allow the emission of radiation characteristics features of the metal : for example-the characteristic flame colourations of metals frequently encountered in simple organic compounds such as : Na-yellow, Ca-brick-red ; Ba-apple-green. This forms the fundamental basis of initially called  Flame Photometry,  but more recently known as  Flame Emission Spectroscopy (FES).   It is quite evident that a relatively large proportion of the gaseous metal atoms shall remain in the ground state  i.e.,  in an unexcited form. It has been observed that such ground-state atoms shall absorb radiant energy...

  THEORY The underlying principle of  Flame Emission Spectroscopy (FES)  may be explained when a liquid sample containing a metallic salt solution under investigation is introduced into a flame, the following steps normally take place in quick succession, namely :   ( i ) the solvent gets evaporated leaving behind the corresponding solid salt,   ( ii ) the solid salt undergoes vaporization and gets converted into its respective gaseous state, and   ( iii ) the progressive dissociation of either a portion or all of the gaseous molecules gives rise to free neutral atoms or radicals.   The resulting neutral atoms are excited by the thermal energy of the flame which are fairly unstable, and hence instantly emit photons and eventually return to the ground state ( i.e.,  the lower energy state). The resulting emission spectrum caused by the emitted photons and its subsequent measurement forms the funda-mental basis of FES.   Bohr’s Equation : ...

  INSTRUMENTATION There are  two  types of  Flame Photometers  that are used invariably in  Flame Emission Spectroscopy  (FES), namely :   ( a ) Simple Flame Photometer, and   ( b ) Internal Standard Flame Photometer.   These  two  typical instruments shall be discussed briefly here highlighting their various components and procedural details.   1. SIMPLE FLAME PHOTOMETER   The line-sketch of a simple flame photometer is shown in Figure 25.2.   In general, Flame Photometers are designed and intended mainly for carrying out the assay of elements like : Sodium, Potassium, Calcium, and Lithium that possess the ability to give out an easily excited flame spectrum having sufficient intensity for rapid detection by a photocell.   Procedure :  The compressed and filtered air (A) is first introduced into a Nebulizer (E) which creates   a negative pressure (suction) enabling the liquid sample (C) to gain en...

  APPLICATIONS OF FLAME EMISSION SPECTROSCOPY IN PHARMACEUTICAL ANALYSIS   A few typical example of  ‘flame-emission spectroscopy’  are given below.   1. ASSAY OF SODIUM, POTASSIUM AND CALCIUM IN BLOOD SERUM AND WATER   ( i )  Standard potassium and sodium solutions, approximately 500 ppm :  Weigh accurately 0.95  g  of dried KCl and 1.25  g  of dried NaCl into separate 1-litre volumetric flasks. Dissolve in water and dilute to the mark.   ( ii )  Standard calcium solution, approximately 500 ppm :  Weigh accurately 1.25 g of CaCO 3 , which has been dried at 110°C, into a 500-ml breaker. Add about 200 ml of DW and 10 ml of conc. HCl. Cover the breaker with a watch-glass during addition of acid to prevent loss of solution as CO 2  is evolved. After the solution is complete, transfer it quantitatively into a 1-litre volumetric flask and dilute to the mark with DW.   ( iii )  Radiation buffer* for sodi...