The NR latex sample (high ammonia latex, 60% of dry rubber content (DRC)) was purchased from Thai Rubber Latex Corporation (Thailand) Public Company Limited.A 5.0 g of NR latex was stirred to evaporated ammonia for 20 min. Then, a 0.03 g of the NR latex was weighed in the test tube and 5.0 mL of ammonium persulphate solution was added followed by digested in a thermoreactor at 100 C for 70 min. The colorless solution was obtained after sample digestion. After the solution was cooled down, it was diluted to 10.0 mL with de-ionized water in volumetric flask. A 1.6 mL of the molybdenum blue solution was added in 10.0 mL of the resultant solution and the solution was stood for 10 min followed by phosphate determination using UV-Vis spectrophotometer at 880 nm.