L histidine his

All chemicals used were of analytical grade and were used as received without any further purification. All solutions were prepared with deionized water of resistivity not less than 18.2 MΩ cm^−1, which was purified by the WaterPro RO system (Labconco Cooperation, Kansas, MO, USA).
Both glucosamine and calcium nitrate were purchased from Merck KGaA (Germany). The stock solutions of glucosamine (1000 mg/L) and Ca²⁺ (1000 mg/L) and standard solutions of calibration curves were prepared with deionized water in volumetric flasks and stored at 4°C before further use.
L-arginine (Arg), N-cyclohexyl-3-aminopropanesulfonic acid (CAPS), L-histidine (His), and tris (hydroxymethyl) aminomethane (Tris) used for background electrolyte (BGE) and sample preparation were purchased from Sigma–Aldrich (Singapore). Otherwise, acetic acid (Ace) and trichloroacetic acid (TCA) were purchased from Merck KgaA, Germany. The BGEs were prepared by adding Ace into Arg, Tris, His, and CAPS solutions, followed by pH adjustment with acetic acid using a HI 2215 pH meter (Hanna Instruments, Woonsocket, RI, USA).
Fused silica capillaries (50 μm i.d., 365 μm OD) were purchased from BGB Analytik AG (Böckten, Switzerland). Before use, the capillaries were conditioned by flushing with 1 M NaOH solution, deionized water, and then the BGE.

All chemicals were of reagent grade and DI water (Purite, Neptune, Watrex, Prague, Czech Republic) was used for stock solution preparation and dilutions. 10 mM stock solutions of inorganic anions were prepared from their sodium salts (chloride, nitrate, nitrite, all from Pliva-Lachema, Brno, Czech Republic). Lithium lactate was from Pliva Lachema, Brno, Czech Republic. BGE for CE measurements was prepared daily by diluting 200 mM stock solution of L-histidine (HIS, Sigma-Aldrich, Steinheim, Germany) and 50 mM solution of dl-glutamic acid (GLU, Sigma, Steinheim, Germany) to the required concentration. Cetyltrimethylammonium bromide (CTAB, Sigma-Aldrich, Steinheim, Germany) was prepared as a 10 mM stock solution in 5% acetonitrile and was added to the BGE to yield the final concentration of 30 µM. A 7% (w/v) solution of [tris(hydroxymethyl)methylamino] propanesulfonic acid (TAPS, Sigma-Aldrich, Steinheim, Germany) was prepared by dissolving 0.7 g of TAPS in 10 mL of DI water.

L–Histidine (His, 99%) and Glycine (Gly, 99%) were purchased from Sigma-Aldrich, Shanghai, China. Zinc(II) chloride (ZnCl₂, 98%) was purchased from J&K Scientific Ltd, Beijing, China. Copper(II) chloride dihydrate (CuCl₂·2H₂O) (99%) was purchased from Sinopharm Chemical Reagent Co., Ltd, Beijing, China. All samples were used without purification and preprocessing. All salt solutions and other aqueous solutions were prepared with 18.2 MΩ, 3 ppb TOC Milli–Q water (Millipore, Burlington, MA, USA).