BACKGROUND The determination of kalium and phosphorus in plant samples is usually carried out by high-pressure sealed microwave digestion-inductively coupled plasma-optical emission spectrometry (ICP-OES).However, complex matrices can increase the difficulty of digestion, such as peanuts, walnuts, and other samples containing high oil and grease macromolecular polymers, which are difficult to digest quickly and thoroughly, easily leading to low results.

OBJECTIVES To improve the efficiency for the determination of kalium and phosphorus in plants.

METHODS Sulphuric acid-hydrogen peroxide digestion and high pressure sealed microwave digestion were used to convert the elemental phosphorus into phosphate and the kalium into free potassium ions to form a single-phase monovalent digestion solution.

RESULTS Validation of the actual sample analysis showed that: (1) For high oil and grease samples, the sulphuric acid-hydrogen peroxide digestion method can directly digest the sample by destroying the outer layer structure of the plant by strong acid, causing rapid charring of the organic matter, followed by rapid digestion (about 2.5h) by dropwise addition of hydrogen peroxide, which is safer and more thorough; whereas the high-pressure sealed microwave digestion method is more time-consuming (about 4.5h).Compared with the results of most scholars, the sulphuric acid-hydrogen peroxide method is recommended, because its accuracy is better than that of the high-pressure sealed microwave method.(2) For non-oil samples, both treatments are suitable and there is no significant difference between the results of kalium and phosphorus determination, with the high-pressure sealed microwave digestion method being recommended for its low reagent consumption, low blank value and ease of operation.The results of the two methods are in good agreement with the experimental results of most scholars.(3) The limits of detection for kalium and phosphorus by the sulfuric acid-hydrogen peroxide digestion method were 0.006mg/L and 0.001mg/L, respectively.For the high oil and grease samples, the RSD ranged from 1.32% to 1.98%, the repeatability r ranged from 2.90% to 8.21% and the error of determination ranged from-0.007% to-0.025%.For the non-oil samples, the RSD ranged from 0.51% to 0.87%, the repeatability r ranged from 0.77% to 5.08%, and the error of determination ranged from-0.002% to 0.010%.The limits of detection for kalium and phosphorus by high pressure sealed microwave digestion were 0.005mg/L and 0.001mg/L, respectively.For the high oil and grease samples, the error of determination for kalium and phosphorus ranged from-0.012% to-0.028%;for the non-oil samples, and the error of determination for kalium and phosphorus ranged from-0.010% to 0.001%.

CONCLUSIONS The sulphuric acid-hydrogen peroxide digestion method is capable of rapidly digesting high oil and grease macromolecular polymers, but it is affected by the complexity of the samples and the external environment.With the development of science and technology, direct solid injection with artificial intelligence will be the future trend.