Why was it important to filter and degas the mobile phase and the samples? how is the "reversed-phase" hplc used here different from "normal-phase" with regard to stationary and mobile phases, and order of elution? mobile phase composition (a) if the mobile phase composition was changed from 65: 35: 1 (v/v/v) to 75: 25: 1 (v/v/v) water: methanol: acetic acid, how would the time of elution (expressed as retention time) for caffeine be changed, and why would it be changed? (b) what if it was changed from 65: 35: 1 (water: methanol: acetic acid) to 55: 45: 1? how would that change the retention time and why?