GY-Glucosamine

 Item

Value

 Remarks

Appearance

 White to almost white crystalline powder

 HCl usually white crystals; sulfate double salt almost white

Odor/taste

 Odorless or slight odor; slightly sweet, slightly bitter

 Solubility

Freely soluble in water (HCl ~1 g/mL); slightly soluble in ethanol; insoluble in ether and chloroform

 HCl solubility markedly better than sulfate

 Rotation (free base)

 About +100° (water, dried basis)

Scattered literature values ; free base very unstable and rare commercially

Rotation (HCl)

+72° to +80° (testing); +70.0° to +73.0° (USP/industry); +71.0° to +74.0° (national standard WS1-XG-028-2001)

Three coexisting ranges ; contracts must state the governing version

 Rotation (sulfate-2KCl)

+47.0° to +53.0° (USP monograph, dried basis)

Vastly different from HCl — must never be mixed up

pH (aq.)

3.0~5.0  HCl 3.0–5.0 (some makers 3.5–5.0); sulfate-2KCl (2 % aq.) 3.0–5.0

 Free base is weakly basic; rarely used commercially

Melting point

 ~88 °C (decomp.); HCl ~190–210 °C (decomp.)

Strongly rate-dependent; not a sole identity basis

Bulk density

 0.5–0.8 g/mL (loose)

 Tapped 0.65–0.9 g/mL

 Hygroscopicity

 Fairly hygroscopic; marked weight gain above 60 % RH

 Keep sealed and dry; weigh quickly

Stability

 Solid stable; aqueous solutions brown via Maillard under heat/alkali/light

Discoloration accompanies assay loss and impurity rise

pKa / pKa

Amino ~7.8 (conjugate acid); hydroxyls ~12–13

 Lowest solubility near the isoelectric point