[Materials for carrying out external quality control in the determination of total protein]

Quaternary bis-ammonium compound No. 82 (QAC-82) is a highly effective antibacterial biochemical stabilizer of total protein. In concentrations of 3.4-13.6 mmol/liter, it preserves the content of protein in the blood serum for 40 days at 18-20 degrees C. For preparing reference material, 5 ml human or animal serum is added to 95 ml 5.25 mM aqueous solution of QAC-82, mixed, stored at room temperature, and used for assessing the quality of total protein measurements by the biuret method.