Gas chromatography GC is an analytical technique used to separate, identify, and quantify the components in a mixture of volatile compounds. To determine the percentage composition of a mixture containing three unknown compounds, follow these steps:1. Sample preparation: Prepare the sample by dissolving it in a suitable solvent, if necessary. The sample should be in a liquid or gaseous state and should not decompose at the temperature used in the GC analysis.2. Injection: Inject the sample into the gas chromatograph using an appropriate injection technique, such as split, splitless, or on-column injection. The sample is vaporized and mixed with an inert carrier gas, typically helium or nitrogen.3. Separation: The sample-carrier gas mixture is passed through a column packed with a stationary phase. The stationary phase can be a liquid or solid material coated on the inner surface of the column or packed in the column. The compounds in the mixture interact with the stationary phase and are separated based on their volatility and affinity for the stationary phase. The more volatile and less polar compounds will elute come out of the column first, followed by the less volatile and more polar compounds.4. Detection: As the separated compounds elute from the column, they are detected by a suitable detector, such as a flame ionization detector FID , thermal conductivity detector TCD , or mass spectrometer MS . The detector generates a signal proportional to the concentration of the compound, and this signal is recorded as a peak in a chromatogram.5. Identification: Identify the unknown compounds by comparing their retention times or mass spectra if using an MS detector with those of known reference compounds. This can be done by injecting the reference compounds individually under the same conditions as the unknown mixture and comparing the results.6. Quantification: Calculate the area under each peak in the chromatogram, which is proportional to the concentration of the corresponding compound in the mixture. The percentage composition of each compound can be determined by dividing the area of its peak by the total area of all peaks and multiplying by 100.7. Validation: To ensure the accuracy of the results, it is essential to validate the method by analyzing samples with known compositions and comparing the results with the expected values. Additionally, the linearity, precision, and accuracy of the method should be evaluated.In summary, gas chromatography can be used to determine the percentage composition of a mixture containing three unknown compounds by separating the compounds based on their volatility and affinity for the stationary phase, identifying them using reference compounds, and quantifying their concentrations by calculating the area under their respective peaks in the chromatogram.