Mass spectroscopy

Instrumentation

1. INSTRUMENTATION OF MASS SPECTROSCOPY Presented By, Sachinkumar B 1 st Year M.Pharma Dept of Pharmaceutics Srinivas College of Pharmacy,Mangalore 1

2. Contents Definition Stages of instrumentation Ionisation Acceleration Deflection Detector 2

3. Mass Spectroscopy Definition: Mass spectroscopy is an instrumental technique in which sample is converted into rapidly moving positive ions by exposure to ionizing conditions which are separated and characterized according to their mass to charge ratio. Mass spectroscopy is widely used to determine and identify the elements present in samples and to determine their concentrations. Mass spectroscopy is the most accurate method for determining the molecular mass of the compound and its elemental composition 3

4. INSTRUMENTATION 4

5. INSTRUMENTATION-STAGES There are 4 main key stages in the instrumentation process for mass spectroscopy Ionisation Acceleration Deflection Detection 5

6. STAGE-1 : IONISATION The electron ionisation is the most common type ionisation The atom is ionised by knocking one or more electrons off to give a positive ion. (Mass spectrophotometer always work with positive ions) 6

7. The particles in the sample (atoms or molecules) are bombarded with a stream of electrons which come from a heated filament and to knock one or more electrons out of the sample particles to make positive ions Most of the positive ions formed will carry a charge of +1 These positive ions are persuaded out into the rest of the machine by the ion repeller which is another metal plate carrying a slight positive charge. 7

8. STAGE-2 : ACCELERATION The ions are accelerated so that they all have the same kinetic energy. 8

9. The positive ions are repelled away from the positive ionisation chamber and pass through three slits with voltage in the decreasing order. The middle slit carries some intermediate voltage and the final at ‘0’ volts. All the ions are accelerated into a finely focused beam. The speed of acceleration can be adjusted by changing the charge on the plate 9

10. STAGE-3 : DEFLECTION The ions are then deflected by a magnetic field according to their masses. The amount of deflection depends on the number of positive charges on the ion The heavier ions and ions with two or more positive charges are deflected the least (Ion stream C) 10

11. The lightest ions and ions with 1 positive charge are deflected most (Ion stream A) The ions at the correct mass and charge travel to the detector (Ion stream B) The amount of deflection depends on: The mass of the ion: Lighter ions are deflected more than heavier ions. The charge on the ion: Ions with 2 (or more) positive charges are deflected more than ones with only 1 positive charge 11

12. STAGE-4 : DETECTION The beam of ions passing through the machine is detected electrically. 12

13. The beam of ions passing through the mass analyser are detected by detector on the basis of m/z ratio. When an ions hits the metal box, its charge is neutralised by an electron jumping from the metal on to the ion. That leaves a space amongst the electrons in the metal, and the electrons in the wire shuffle along to fill it. A flow of electrons in the wire is detected as an electric current which can be amplified and recorded. 13

14. References Chatwal R Gurdeep, Sham K Anand; Text Book Of Instrumental Method of Chemical Analysis; Himalaya Publishing House,Delhi ; Mass Spectroscopy; 2007, Fifth Revised Ed,2.272-2.302. Sharma Y.R, Text Book Of Elementary Organic Spectroscopy, S Chand & Company Ltd, New Delhi; Mass Spectroscopy; 2007, Multicolour Ed, 291-353. 14

15. THANK YOU 15