Historical C, H, O Analysis

[Carvone]

Hi all,

 

I currently study starch, and a side project I am working on is researching the early history of starch research, which inevitably involves a lot of research about simple sugars (glucose and maltose) from learning that starch degraded with acid to sugars and with enzymes to glucose, maltose and various MW dextrins.

 

To be frank, I am quite amazed at what was known back 100 years ago considering the methods were very limited. Paper chromatography to separate the sugars was not available until 1943. Gas and liquid Chromatography came about 8 years later. Most of the experiments involved controlled degradation with enzymes or acids followed by analysis in a polarimeter (before & after methylation). However, another technique that is referenced a lot as early as the 1890s (that I have found) is the elemental composition (eg. % carbon, % oxygen and % hydrogen), which could be related to the molecular composition of glucose, maltose, etc. This was based on calculating the amount of CO2 and H2O I am guessing that was combusted from the original samples. However, nowhere could I find how the early carbohydrate chemists measured this so accurately, and I am very interested in this early technique. If someone knows how they accomplished this experiment with such great precision without such instruments as ICP-OES, I would really appreciate being educated about this.

 

Thank you.

Carvone

[John Cuthber]

Hydrogen was measured by oxidising a known mass of the compound and measuring the water produced. Similarly, carbon was measured by measuring CO2. Oxygen was traditionally measured "by difference"- i.e whatever wasn't H,N or C was assumed to be O.

Nitrogen was done like this

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

and sulphur by combustion and oxidation to sulphate.

The halogens were measured with some sort of variation on this

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

 

Many of these tests involved weighing the sample and products so once the chemists had a good balance they could get remarkable accuracy.

[Carvone]

Thanks John for your reply.

 

Yes, I did know about how C, H, and O were calculated from CO2 and H2O based on mass to mole conversions. I am very interested to know how these early chemists did this so accurately, and what method they used to convert their organic matter to CO2 and H2O, and then how did they trap these two substances (water and a gas) and then weigh them out. For example, how do you weigh a gas back in 1890? Perhaps they trapped the CO2 in some sort of balloon-like material (eg. goat intestine), and then measured the volume by displacement and converted this to mass or moles, but I am only guessing. I hope there is someone out there that knows how this was done over 100 years ago to be able to figure out the molecular formula of compounds.

 

For nitrogen, the Kjehdahl method was first used long before Dumas, and was developed by a chemist from the Carlsberg brewery named Kjehldahl (hey whaddya know!) in the 1880s in Denmark. The 3-minute Dumas method has now largely replaced the lengthy Kjehdahl method, which took half a day to perform and consumed quite a lot of chemicals, since it was based on acid digestion to liberate ammonia, trapping the ammonia in boric acid, followed by quantitative titration.

Edited March 18, 2012 by Carvone

[John Cuthber]

Water was trapped with P2O5 and CO2 with CaO or NaOH. The traps were weighed before and after use and the weight of CO2 or water measured as the weight gain.

[Carvone]

Water was trapped with P2O5 and CO2 with CaO or NaOH. The traps were weighed before and after use and the weight of CO2 or water measured as the weight gain.

 

 

Perfect thanks greatly John! Truly amazing to see what was learned so long ago using only wet chemistry methods!

Edited March 18, 2012 by Carvone