Folin and Wu method
1. (for creatinine) the color produced by the unknown (protein-free blood filtrate or urine) in an alkaline solution of picric acid is compared in a colorimeter with the color produced by a known solution of creatinine or with a standard solution of potassium bichromate. 2. (for creatine plus creatinine) the creatine of a protein-free blood filtrate is changed to creatinine by heating with dilute hydrochloric acid in an autoclave, and the creatinine thus produced together with the preformed creatinine is determined colorimetrically after adding an alkaline picrate solution. 3. (nonprotein nitrogen) the total nonprotein nitrogen in the protein-free blood filtrate is determined by setting free the nitrogen as ammonia by the Kjeldahl process, nesslerizing this ammonia, and comparing with a standard. 4. (for protein-free blood filtrate) lake the blood with distilled water, add sodium tungstate and sulfuric acid, and filter. 5. (for urea) change the urea to ammonia by means of urease, and nesslerize. 6. (for uric acid) uric acid is precipitated from the protein-free blood filtrate or from urine by silver lactate, treated with phosphotungstic acid, and the blue color compared with the color produced by known amounts of uric acid.
Medical dictionary.
2011.