Detectors of gc

Detectors of Gas chromatography

1. SUBMITTED BY MALAY PAUL SUBMITTED TO T. MENAKA M.PHARM 1 st SEMESTER DEPARTMENT OF PHARMACEUTICS MALLIGE COLLEGE OF PHARMACY A PRESENTATION ON DETECTORS OF GC 1 20-04-2021

2. DETECTORS They are considered as heart of apparatus Detectors sense the components as they leave from the column When carrier gas is passing through column, number of signal produced are proportional to the concentration of components 2 20-04-2021

3. IDEAL REQUIREMENTS OF DETECTORS Applicability to wide variety of sample High sensitivity to even small concentrations Rapidity to response Non destructive to sample Simple and easy to maintain Inexpensive 3 20-04-2021

4. Types of detectors A)katharometer or Thermal conductivity detector B)Flame ionisation detector C)Electron capture detector D)Argon Ionization detector 4 20-04-2021

5. Katharometer/Thermal conductivity meter 5 20-04-2021

6. Katharometer /thermal conductivity detector It is based on the fact that the rate of loss of heat from body depends upon thermal conductivity of surrounding gas and effluent present in gas The rate of loss of heat is proportional to amount of component present It consists of two chambers of small volumes,made within a metal block,each containing a resistance wire with high temperature co-efficient of resistance 6 20-04-2021

7. Continued… The resistance consists of reference (R) and sensing element(S) which are connected to two arms of wheatstone bridge The carrier gas passes in both the cells When sample component enters sensing cell,the temperature of filament change due to difference in thermal conductivity of sample that of carrier gas 7 20-04-2021

8. Continued… As a result resistance of s varies and the bridge becomes unbalanced The off balance is signalled to recorder,which draws elution curve for chromatographic separation It responds to all substance except carrier gas Sensitivity depends on type of carrier gas ,filament current temperature , and flow rate of carrier gas 8 20-04-2021

9. Advantages Applicable to most compounds The sample is not destroyed . Simple,easy to maintain and inexpensive 9 20-04-2021

10. Disadvantages Low sensitivity Affected by fluctuations in temperauture and flow rate Biological samples cannot be analysed 10 20-04-2021

11. FLAME IONISATION DETECTOR 11 20-04-2021

12. FLAME IONISATION DETECTOR In this the effluent from column is mixed with hydrogen and is passed through a jet which is burned in presence of external air The platinum jet serves as one electrode and collector electrode as the other A potential of about 400V is applied across two electrode through dc supply ,which lowers the resistance between electrode and allow flow of current 12 20-04-2021

13. Continued… The ions and free electrons generated in pure hydrogen flame produces current The produced current passes through collector electrode to external resistor,which is sensed as voltage drop ,amplified and finally sent to an output device or recorder 13 20-04-2021

14. DRAW BACK : The sample may be destroyed by flame some compounds cannot be detected like hydrogen,oxygen,carbondioxide , carbonmonoxide etc 14 20-04-2021

15. Advantages This detector is extremely sensitive and background noise is low ,hence microgram quantities of the solute can be detected Stable and insensitive to small changes in the flow rate of carrier gas and water vapour Responds to most of the organic compounds 15 20-04-2021

16. ELECTRON CAPTURE DETECTOR 16 20-04-2021

17. ELECTRON CAPTURE DETECTOR In this effluent from column is passed between two electrodes One of the electrode consist of radioisotope that emits high energy electrons( β -particles)as it decays These electron bombard with carrier gas and sample resulting in formation of positive ions ,radicles and thermal electrons by series of collisions 17 20-04-2021

18. Continued…. The application of potential difference to electron capture cells allow collection of electrons that constitute base line signal when only carrier gas is passed It responds only to those compounds whose molecules have a affinity for electrons Example: chlorinated compound , alkyl lead etc 18 20-04-2021

19. Advantage and Disadvantage The advantage of this type of detector is it is highly sensitive ,even nanogram quantities can be detected But disadvantage is that it can be used only for compounds with electron affinity 19 20-04-2021

20. 20 20-04-2021 ARGON IONIZATION DETECTOR

21. ARGON IONIZATION DETECTOR This type of detector depends on excitation of argon atoms by particles from Radioactive substances. The high energy particles ionize argon atom and hence they are excited to Metastable state. 21 20-04-2021

22. These molecules collide with sample molecules and ionize them. These ions when reach to detector will cause increase in current . Hence compounds can be detected. 22 20-04-2021

23. REFERENCES A review article on gas chromatography Instrumental method of analysis by Willard Slideshare.gas chromatography. 23 20-04-2021

24. THANK YOU 24 20-04-2021