Method for measuring contents of total nitrogen and total phosphorus contained in seawater substrate sludge by adopting combined digestion

The invention relates to a method for measuring the contents of total nitrogen and total phosphorus contained in seawater substrate sludge by adopting combined digestion, comprising the following steps of: weighing 1.0 g of air-dried sample screened through a phi 0.5 mm sieve; adding 8 mL of sulfuric acid and 2 mL of hydrogen peroxide, carefully and uniformly shaking, and placing overnight; slowly increasing temperature till the sulfuric acid is smoky; slightly cooling, then adding a plurality of drops of hydrogen peroxide, and continuously heating till the solution is colourless or off-white; slightly cooling, adding water, and heating to boiling; taking down for cooling, nondestructively transferring a digested solution into a 100 mL volumetric flask, adding water, fixing volume, and standing for clarification or filtering by using phosphate-free filter paper; then sucking 10.0 mL of sample solution containing 0.05-1.0 mg of the phosphorus into a 50 mL volumetric flask, adding waterto 20-30 mL, carrying out