Abstract: The paper introduces a simple method of determining the phosphorus in flax lecithin. At first the sample was combusted by oxygen bomb ashing combustion, then the products were absorbed by water, finally, the content of the phospho- rus was determined by P-Mo-blue spetrophotometry, the measure wavelength is 690nm, the result showed that there is a good linear relation between absorbance and concentration at the range of 0.4×10-4～3.2×10-4mg/ml, r =0.9994; the paper also investigate the influence of the developing time on determining result, choose the best boiling water bathing time, precision and accuracy experimental result meets the requirement, the average recovery rate is 99.7%, RSD =1.46%; the phosphorus content of the sample is 4.68%, exceeding 2.70% of the index number of the national standard. The method is accurate, simple, feasible, suitable for determination of the phosphorus content in the flax lecithin.

Key words: oxygen bomb, ashing, spectrophotometry, flax lecithin, phosphorus content