Ethanol is now added to some brands of petrol in order to replace some of the hydrocarbons with a renewable resource - VCE - SSCE Chemistry - Question 2 - 2004 - Paper 1

To determine the most suitable analytical method for testing the presence of ethanol in petrol, we must consider the properties of ethanol and the sensitivity of the methods available.

1. Gas Chromatography (GC): This method is widely used for separating and analyzing compounds that can be vaporized. It can effectively determine the presence of ethanol in petrol due to its capability to analyze volatile compounds with high precision.

2. Paper Chromatography: While this method is useful for separating and identifying small quantities of compounds, it is generally not suitable for analyzing complex mixtures like petrol. Its sensitivity and resolution are not optimal for this application.

3. Flame Tests: This technique is primarily qualitative and used to detect certain metal ions based on their characteristic colors in a flame. It is not suitable for detecting organic compounds like ethanol.

4. Atomic Absorption Spectroscopy: This method is primarily used for detecting metals and metalloids in a sample and is not applicable for organic substances like ethanol.

Given these considerations, the best method for detecting ethanol in a petrol sample is gas chromatography.