Final answer:
Gravimetric analysis is the most accurate method to determine total solid content in a fuel sample as it measures mass changes after separating the substance from the sample.
Step-by-step explanation:
The most accurate testing method to determine the total solid content in a fuel sample is gravimetric analysis. This method involves treating the sample to enact a physical or chemical change, allowing separation from other components.
The total solid content can then be accurately quantified by measuring the mass of the residue after the treatment. Combustion analysis is a specific type of gravimetric analysis used to assess the elemental composition of hydrocarbons by burning the sample and weighing the resulting gaseous products such as carbon dioxide and water. These gravimetric methods offer precision and reliability in quantitative chemistry and have been used as standard practices in analysis.