for example, food or other organic substances.

The amount of water stored in a substance? I don't understand the question.

Depending on what you mean by water, heating the substance until the water evaporates, heating the substance in the absence of oxygen until all the oxygen leaves and adjusting for the produced gases, dunking it in a dissicating agent like concentrated sulfuric acid. Basically, take whatever you mean by water out, and measure what is left.

Depending on what you mean by water, heating the substance until the water evaporates, heating the substance in the absence of oxygen until all the oxygen leaves and adjusting for the produced gases, dunking it in a dissicating agent like concentrated sulfuric acid. Basically, take whatever you mean by water out, and measure what is left.

 

Dunk it in sulfuric acid? That would certainly do something to it, but dessicate it properly is not one of them. Personally, I'd store the food item under a good vacuum over P2O5 until the weight stopped going down. Gentle warming may also help drive off the last of it without causing degradation.

This is one way

 

http://en.wikipedia.org/wiki/Dean-Stark_apparatus

Herew's anothe

http://en.wikipedia.org/wiki/Karl_Fischer_titration

 

How hard did you look before posting?

This is one way

 

http://en.wikipedia.org/wiki/Dean-Stark_apparatus

Herew's anothe

http://en.wikipedia.org/wiki/Karl_Fischer_titration

 

How hard did you look before posting?

 

Probably didn't look at all.

 

Ah, the ole' Dean-Stark, haven't seen one of those in a while. Haven't run any condensations in a while I guess.

Standard protocols for biological samples is dry weight measurement using moderate temps (often around 65-85 ° to avoid loss). Depending on application freeze drying is also an option.