Folin method
1. (for acetone) aerate the acetone into a solution of sodium bisulfite and then determine the amount of nephelometric comparison with a standard acetone solution using Scott and Wilson reagent. 2. (for amino acids in blood) make 10 mL of protein-free blood filtrate slightly alkaline to phenolphthalein. Add 2 mL of beta-naphthaquinone solution and place in the dark. The next day add 2 mL of acetic acid–acetate solution and 2 mL of 4 per cent thiosulfate solution. Dilute to 25 mL and compare the blue color with a standard amino-acid solution similarly treated. 3. (for ammonia nitrogen) sodium carbonate is added to the urine to free the ammonia, which is aerated into standard acid and titrated. 4. (for creatine) precipitate the proteins of the blood with picric acid and filter. To the filtrate add sodium hydroxide and compare color with a standard solution of creatine. 5. (for creatine in urine) change creatine into creatinine by heating at 90°C for three hours in the presence of third normal HCl. Determine creatinine by picric acid and alkali and deduct the preformed creatinine. 6. (for creatinine in urine) to the urine add picric acid and sodium hydroxide and compare the red color with a half normal solution of potassium bichromate. 7. (for ethereal sulfates) remove the inorganic sulfates with barium chloride and then the conjugated sulfates after hydrolyzing with boiling dilute hydrochloric acid. 8. (for inorganic sulfates) acidify the urine with hydrochloric acid, precipitate with barium chloride, filter, dry, ignite, and weigh. 9. (for protein in urine) add acetic acid and heat, wash, dry, and weigh the precipitate. 10. (for total acidity) add potassium oxalate to the urine to precipitate the calcium which should otherwise precipitate at the neutral point, and titrate with tenth normal sodium hydroxide, using phenolphthalein as an indicator. 11. (for total sulfates) boil the urine for thirty minutes with dilute hydrochloric acid, precipitate with barium chloride, filter, dry, ignite, and weigh. 12. (for urea and allantoin) decompose the urea by heating with magnesium chloride and hydrochloric acid, distill off the ammonia, and titrate.

Medical dictionary. 2011.

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