Hello some parts of one question I have from my homework are: a) Why would the mass spectra of Caffeine from GC and LC-M

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Hello some parts of one question I have from my homeworkare:
a) Why would the mass spectra of Caffeine from GC and LC-MS beso different.
b) When one mixes 12C and 13C caffeine it will couple largepeaks in pairs like 194/197, 109/111, 82/84, 67/68 e.t.c. How couldthis isotopic pattern help with the assignment of the structure ofthe fragments?
c) When a GC-MS integrates and if the peak and area of ananalyte are too small how can the concentration be increased at thedetector? Consider that there was a liquid-liquid extraction priorto running the GC-MS, within these factors consider thedistribution coefficient, sample preparation and finally sampleinjection.