C) Analysis of hexanal and heptanal was done using headspace solid phase microextraction (HS-SPME) with methyltrimethoxysilane-(3-mercaptopropyl)- trimethoxysilane coated fiber followed by quantification using gas chromatography flame ionization detector. Figure 2 shows the extraction efficiency (based on peak area) of the compounds using a sample volume of 10 mL, extraction temperature of 60 C and desorption time of 3 min. 160 140 120 100 peak area (PA) 80 hexanal 60 heptanal 40 20 0 15 20 30 40 50 60 70 Extraction time (min) Figure 2 Effect of extraction time on the HS-SPME extraction efficiency i) Discuss the effect of extraction time based on the result obtained in Figure 2. (6 marks) ii) Explain how the thickness of fiber coating affects the equilibrium time of the analytes in HS-SPME. (3 marks) iii) List 3 advantages of using the SPME technique