[sweetyee]

I am attempting to analyze total nitrogen in fish fecal using a chn analyzer. The results obtained is in % in a g of sample(correct me if i'm wrong). Let's say it gave a 3-4% of N reading. Does that means in ppm (mg/L) is 30,000-40,000 ppm of TN since 1%=10,000ppm? Do i need to multiply the 3-4%  with protein factor of 6.25 to get the exact value of TN for the fish fecal? I'm getting contradicting opinions from my superiors. Please advise.

[gritch]

Man do I hate ppm notation, it just seems so ambiguous to me. I would go with  100 000ppm for each 1%. Using grams-grams measurements 1ppm would be 1μg per 1g of sample.
1% would be 0.1g per 1g or 100 000μg per 1g or 100 000ppm.

I did a quick look up of the 6.25 factor and it seems to be the standard method for determining protein content from nitrogen content. I assume it is based on the average number of nitrogen atoms per protein. I'll admit biochemistry of any sort is sort of out of my expertise but I don't think you need this 6.25 factor in this case.

[Borek]

I would go with  100 000ppm for each 1%. Using grams-grams measurements 1ppm would be 1μg per 1g of sample.
1% would be 0.1g per 1g or 100 000μg per 1g or 100 000ppm.

You better count your zeros. 0.1 g in 1 g is 10%, not 1%. 1% is 10 000 ppm, not 100 000 ppm.

[JGK]

Man do I hate ppm notation, it just seems so ambiguous to me. I would go with  100 000ppm for each 1%. Using grams-grams measurements 1ppm would be 1μg per 1g of sample.
1% would be 0.1g per 1g or 100 000μg per 1g or 100 000ppm.

I did a quick look up of the 6.25 factor and it seems to be the standard method for determining protein content from nitrogen content. I assume it is based on the average number of nitrogen atoms per protein. I'll admit biochemistry of any sort is sort of out of my expertise but I don't think you need this 6.25 factor in this case.

It also depends on the source of the protein

 
Wheat and most cereals it is 5.8
Rice, 5.95
Soya 5.7
Most legumes and nuts, 5.3
Milk, 6.38
Other foods, 6.25.

In mixtures of proteins, as in dishes and diets, the factor of 6.25 is used. ‘Crude protein’ is defined as N × 6.25.

The Analytical Methods Comittee of the Royal Society of Chemistry have produced a Technical Brief for nitrogen factors in meat & poultry http://www.rsc.org/images/nitrogen-factors-technical-brief-7_tcm18-214878.pdf