L-Cysteine CAS 52-90-4 (H-Cys-OH) Assay 98.5~101.0% (Titration) Factory High Quality

L-Cysteine contains not less than 98.5% and not more than 101.0% of L-Cysteine (C3H7NO2S), calculated on the dried basis.
Description L-Cysteine occurs as white crystals or a white crystalline powder. It has a characteristic odor and a pungent taste. It is freely soluble in water, and practically insoluble in ethanol (99.5). It dissolves in 1 mol/L hydrochloric acid TS.
Identification Determine the infrared absorption spectrum of L-Cysteine as directed in the potassium bromide disk method under Infrared Spectrophotometry <2.25>, and compare the spectrum with the Reference Spectrum: both spectra exhibit similar intensities of absorption at the same wave numbers.
Optical rotation <2.49> [a]20D:+8.0 ~+10.0° (2 g calculated on the dried basis, 1 mol/L hydrochloric acid TS, 25mL, 100 mm).
pH <2.54> The pH of a solution prepared by dissolving 1.25 g of L-Cysteine in 50 mL of water is 4.7 to 5.7.
Purity (1) Clarity and color of solution-Dissolve 1.0 g of L-Cysteine in 20 mL of water: the solution is clear and colorless.
(2) Chloride <1.03>-Dissolve 0.30 g of L-Cysteine in 10mL of diluted nitric acid (1 in 4), add 10mL of hydrogenperoxide (30), heat for 20 minutes in a boiling water bath,cool, and then add water to make 50 mL. Perform the test using this solution as the test solution. Prepare the control solution with 0.35 mL of 0.01 mol/L hydrochloric acid VS (not more than 0.041%)
(3) Sulfate <1.14>-Dissolve 0.6 g of L-Cysteine in 30 mL of water and 3 mL of dilute hydrochloric acid, and add water to make 50 mL. Perform the test using this solution as the test solution. Prepare the control solution as follows: To 0.35 mL of 0.005 mol/L sulfuric acid VS add 3 mL of dilute hydrochloric acid and water to make 50 mL. Prepare the test solution and the control solution with 4 mL of barium chloride TS, respectively (not more than 0.028%).
(4) Ammonium <1.02>-Perform the test with 0.25 g of L-Cysteine, using the distillation under reduced pressure. Prepare the control solution with 5.0 mL of Standard Ammonium Solution (not more than 0.02%).
(5) Heavy Metals <1.07>-Proceed with 1.0g of L-Cysteine according to Method 4, and perform the test.Prepare the control solution with 1.0 mL of Standard Lead Solution (not more than 10 ppm).
(6)Iron <1.10>-Prepare the test solution with 1.0 g of L-Cysteine according to Method 1, and perform the test according to Method A. Prepare the control solution with 1.0mL of Standard Iron Solution (not more than 10 ppm).
(7)Related Substances-Dissolve 0.10 g of L-Cysteine in N-ethylmaleimide solution (1 in 50) to make exactly 10 mL, leave for 30 minutes, and use this solution as the sample solution. Pipet 1 mL of the sample solution, add water to make exactly 10 mL, pipet 1 mL of this solution, add water to make exactly 50 mL, and use this solution as the standard solution (1). Separately, dissolve 0.10 g of L-cystine in 0.5mol/L hydrochloric acid TS to make exactly 20 mL. Pipet 1mL of this solution, add water to make 100 mL, and use this solution as the standard solution (2). Perform the test withthese solutions as directed under Thin-layer Chromatography<2.03>. Spot 10mL each of the sample solution and standard solutions (1) and (2) on a plate of silica gel for thin-layer chromatography. Develop the plate with a mixture of1-butanol, water, and acetic acid (100) (3:1:1) to a distance of about 10 cm, and dry the plate for 30 minutes at 809C.Spray the plate evenly with a solution of ninhydrin in a mixture of methanol and acetic acid (100) (97:3) (1 in 100), and then heat at 80℃ for 10 minutes: the spot obtained from the sample solution corresponding to the spot obtained from the standard solution (2) is not more intense than the spot from the standard solution (2). Also, the spots other than the principal spot and the spots mentioned above from the sample solution are not more intense than the spot from the standard solution (1).
Loss on Drying <2.41> Not more than 0.50% (1 g, in vacuum, phosphorus (V) oxide, 3 hours).
Residue on Ignition <2.44> Not more than 0.1%(1 g).
Assay Weigh accurately about 0.2 g of L-Cysteine, place itin a stoppered flask, and dissolve in 20 mL of water. Dissolve 4 g of potassium iodide in this solution, immediately place in ice cold water, add 5 mL of dilute hydrochloric acid and exactly 25 mL of 0.05 mol/L iodine VS, leave in a dark place for 20 minutes, and then titrate<2.50>an excess amount of iodine with 0.1 mol/L sodium thiosulfate VS (indicator: starch TS). Perform a blank determination using the same method.
Each mL of 0.05 mol/L iodine VS＝12.12 mg of C3H7NO2S
Containers and Storage Containers-Tight containers.