[mercury]

Before a sample is ready for analysis by analytical instruments( ICP, etc), samples are prepared by acid digestion for oxidation of the organic constituents.But what are this "organic constituents" that we are oxidizing?and how exactly are the acids(nitric,HCl) reacting with this organic matter that makes organic constituents be eliminated from the sample?For example, fish samples.Samples are usually digested in close tight tubes, so how are these organic compounds eliminated?

[Yggdrasil]

Proteins, which can sometimes stick to surfaces through hydrophobic regions, will be hydrolyzed in the presence of concentrated acid, producing amino acids, which are much more easily washed away in aqueous solution.

[Borek]

Heated concentrated nitric acid used for digestion can oxidize organic compunds (carbon based after all - proteins, fat, hydrocarbons) to simple gases - CO², H²O, N².

[mercury]

" which are much more easily washed away in aqueous solution".what you meant by this?washed away?

[Yggdrasil]

Amino acids are very water soluble and are won't to stick to surfaces like proteins.

[Yggdrasil]

Amino acids are very water soluble and are won't to stick to surfaces like proteins.

is the reason above tell why we do acid digestion prior to analysis?pls explain further or recomend a website if possible.

I'm not sure why one does an acid digestion prior to analysis.  However, I found this site which may be helpful:

http://www.ivstandards.com/tech/reliability/part12.asp