Answer to Question #32124 in Organic Chemistry for SASAN

Question

I want to measure PAH in marine sediment sample.
I want to know, why I should measure organic carbon in my sample?

At first step of extraction PAH from sediment, I should dried samples in 60 degree of centigrade,
Does this temperature can have adverse effect on PAH in my sample?

Answer 1

The most common technique utilized for the extraction of PAHs from sediments was initially Soxhlet extraction. However, more recently, alternative methods have been developed such as ultrasonic extraction, microwave dissolution, pressurized liquid extraction (PLE) and supercritical fluid extraction (SFE), in order to reduce the volume of solvents used as well as the time required for analysis . Solid phase microextraction (SPME) techniques have also started gaining interest for sediment samples.

ΡΑΗs are organic compounds containing condensed aromatic rings in their molecules. The number and position of the rings as well as the number, position and nature of the atoms that can be present in the molecule affect the physical and chemical properties of PAHs, their environmental behavior and their interactions with biota and human. Carbon atom is presented in each ΡΑΗs compounds, so you must measure organic carbon in your sample.

This temperature (60°C) can not have adverse effect on PAH in your sample, as ΡAΗs have high melting and boiling points and low water solubilities. Their solubility in water decreases, while correspondingly their boiling and melting point increases, with increasing molecular weight. For example naphthalene (M_W = 128) has a water solubility value of 31 µg l^-1, melting point 80.5 °C and boiling point 218 °C, while chrysene (Μ_W = 228) has water solubility 0.006 µg l^-1 melting point 255 °C and boiling point 448 °C.