www.osti.gov/scitech/servlets/purl/799361

www.ncbi.nlm.nih.gov/pubmed/26653437

What I need is a simple method to estimate the quantity of petrolem remaind in the medium

The simplest method would be BOD (Biochemical Oxygen Demand), which is the amount of oxygen needed by aerobic biological organisms to dissolve (break down) organic material present in your medium (most commonly it is water). It is expressed in mg/L of oxygen consumed.

The quickest (and most commonly used) is the BOD 5 test, which is run for 5 days, at incubation temperature of 20 deg C, and most commonly the degradation is between 50 and 70 %. The longer test is 25 days, but it rarely done, due to long time needed to show the results.

I hope this helped you a bit... :) 

In petroleum pollution assessment, the most applied analysis is the GC-FID or GC-MS determination of the n-alkanes (they are the first hydrocarbons that are expected to be degraded). But if you don't have access to this kind of method, maybe the most simple analysis that usually is done in petroleum pollution assessment is the TPH (total petroleum hydrocarbon). It is done in many ways, but includes in general (I) an extraction (by a solvent), (II) a purification (that is not mandatory but usually is important, as a silica column for example), and (III) a determination that can be done by gravimetry (weight of dry extract). Wish you all the best, hope to help you a little, good luck 

thak you so much Marina Reback, if I have a unkonwn petroleum composition, Which stadards should I use?

The answer is BOD

Anirbid Sircar, Please,Could you explain more? Do you have a protocol ? I mean an article about that

You can use FTIR spectroscopy standard method for quantitative determination of total hydrocarbon in water (Standard Test Method for Total Petroleum Hydrocarbons (TPH) in Water and Wastewater with Solvent Extraction using Mid-IR Laser Spectroscopy, ASTM D 7678). This test method covers the determination of total petroleum hydrocarbons (TPH) in water, and waste water, that are extractable from an acidified sample (with Hydrochloric Acid) with a cyclic aliphatic hydrocarbon (cyclohexane, liquid- liquid extraction), and measured by IR absorption in the region of 1370 -1380 cm-1. 

Measured by IR absorption in the region of 1370 -1380 cm-1 which relates to the methyl group CH bending, directly correlates to the concentration of total hydrocarbons.  The Cyclohexane solvent has a cyclic structure and does not have any methyl groups, so does not show this peak.

This method covers the range of 0.5 to 1000 mg/L and may be extended to a lower or higher level by extraction of a larger or smaller sample volume collected separately.