To determine the percentage composition of caffeine in a sample of coffee using liquid chromatography, follow these steps:1. Sample preparation: First, prepare the coffee sample by extracting caffeine from it. This can be done by mixing a known amount of coffee with a suitable solvent e.g., water, methanol, or a mixture of both and filtering the mixture to remove any solid particles. The resulting filtrate will contain the dissolved caffeine.2. Liquid chromatography setup: Set up a liquid chromatography system, which typically consists of a solvent reservoir, a pump, an injector, a column, a detector, and a data acquisition system. Choose a suitable column and mobile phase solvent for the separation of caffeine from other components in the coffee sample.3. Calibration: Prepare a series of standard solutions containing known concentrations of caffeine. Inject these standards into the liquid chromatography system and record the peak area or peak height of the caffeine peak in the chromatogram. Plot a calibration curve by plotting the peak area or height against the concentration of caffeine in the standard solutions.4. Sample analysis: Inject the prepared coffee sample into the liquid chromatography system and record the chromatogram. Identify the caffeine peak in the chromatogram based on its retention time, which should be similar to that of the caffeine peak in the standard solutions.5. Quantification: Measure the peak area or height of the caffeine peak in the coffee sample chromatogram. Use the calibration curve to determine the concentration of caffeine in the sample.6. Calculation: Calculate the percentage composition of caffeine in the coffee sample by dividing the concentration of caffeine in the sample by the total concentration of the sample including caffeine and other components and multiplying by 100.For example, if the concentration of caffeine in the coffee sample is 10 mg/mL and the total concentration of the sample is 100 mg/mL, the percentage composition of caffeine in the coffee sample would be 10/100 x 100 = 10%.