Precolumn derivatization liquid chromatography method for analysis of dietary supplements for glucosamine: single laboratory validation study

A precolumn derivatization liquid chromatography (LC) method was developed for the analysis of various dietary supplement formulations and raw materials for glucosamine. A 1 mL sample or standard water solution (containing about 0.05 mg glucosamine) was mixed with 1 mL pH 8.3 buffer, 1 mL 5% phenylisothiocyanate methanolic solution, and derivatized at 80 degrees C in a water bath for 30 min. After derivatization, the solution was cooled in a cold water bath and centrifuged at 3000-5000 rpm. The clear upper layer was ready for injection. The LC system was equipped with a C18 reversed-phase column and an ultraviolet detector set at 240 nm. The column was developed with a linear gradient composed of 0.1% phosphoric acid in deionized water and 0.1% phosphoric acid in methanol. The method was subjected to Single Laboratory Validation. The method precision was 0.50% relative standard deviation, accuracy was less than +/-1.5%, method linearity in the range 0-2 mg glucosamine/mL was 1.00, the detection limit was 0.0705 microg/mL, and the quantitation limit was 0.235 microg/mL. Chondroitin sulfate, amino acids, and excipients did not interfere with glucosamine testing. After derivatization, both standard and sample preparations were stable for at least 48 h. Due to its high sensitivity, this method can be used to assay glucosamine in functional foods and pet foods. The validation data will be published separately.