L-TRYPTOPHAN

C11H12O2N2 

204.23 

L-Tryptophan, when calculated on the dried basis, contains 98.0~102.0% of L-tryptophan (C11H12O2N2).  

L-Tryptophan as white to yellowish-white crystals or crystalline powder. It is odorless or has a slight odor and has a slightly bitter taste.  

(1) L-Tryptophan solution is levorotatory. Add sodium hydroxide solution (1→5) to make the solution alkaline. The solution becomes dextrorotatory.

(2) Proceed as directed under Identification (2) and (3) in [DL-Tryptophan].  

(1) Clarity of Solution : Weigh 0.5 g of L-Tryptophan. and dissolve in 10 ml of 0.5N sodium hydroxide solution. The solution is almost clear, and its color is not darker than that of Color standard Solution C.

(2) pH : When L-Tryptophan proceed as directed under glass electrode method, pH of an aqueous solution (1→100) should be 5.5~7.0

(3) Specific rotation : L-Tryptophan is dried for 3 hours at 105°. Approximately 0.5 g is precisely weighed and dissolved in 40 ml of water by heating. After cooling, water is added to make 50 ml solution. Optical rotation should be [α](20, D)= -30∼-33°.

(4) Arsenic : Proceed as directed under Purity (3) in [DL-Tryptophan].

(5) Heavy metals : Proceed as directed under Purity (4) in [DL-Tryptophan].

(6) Chloride : Proceed as directed under Purity (5) in [DL-Tryptophan]. 

When L-Tryptophan is dried for 3 hours at 105°, the weight loss should not be more than 0.3%. 

When thermogravimetric analysis is done with approximately 2 g of L-Tryptophan, the amount of residues should not be more than 0.1%. 

Approximately 0.3 g of dried L-Tryptophan is precisely weighed and dissolved in 50 ml of glacial acetic acid by heating. After cooling, titrated with 0.1 N perchloric acid solution (indicator : 10 drops of α-naphtholbenzene solution). The end point is where the brown color of the solution becomes green.

      0.1 N perchloric acid 1 ml = 20.42 mg of C11H12O2N2