[10 mark b. (1) Describe, using the aid of a carefully drawn schematic diagram, the workings of a Gas Chromatography (GC) system. (ii) List three gases that are commonly used for GC and very briefly explain why these gases are suitable (iii) Briefly discuss two methods by which a sample may be introduced into a GC system [3 marks [4 marks c. (1) In High performance Liquid Chromotography (HLPC) gradient elution may be used over isocratic elution. Explain what is meant by the term gradient elution and what is meant by the term isocratic elution. Give reason(s) why gradient clution can be favoured over isocratic elution when performing HPLC [4 marks (ii) [3 marks