I think you might be looking at gas chromatography methods here.

Deni Ribicic With GC the concentration of the oil can be determined.

GCMS will quantify the aromatic and aliphatic constituent in the oil separately. However, I wish to quantify the concentration as a whole in category of (Pump oil, Engine oil, Diesel oil and Kerosene)

As I am aware GC-FID should be able to perform what are you looking for. I remember using it to quantify total hydrocarbon depletion in oil degradation experiments performed.

Look at this thread on RG;

https://www.researchgate.net/post/What_is_the_procedure_to_quantify_TPH_in_sediment_samples_using_GC_FID

Abdulkareem Aishat Yetunde You can extract the oil from water sample in hexane, evaporate it and weigh the residual oil quantity.

It can extract the oil drops using a suitable solvent like n-hexane then evaporate the solvent to mesure the volume of residual oil.