Advances in Sample Digestion Using Microwave-ultraviolet Radiations: Phosphorus and Sulfur Determination in Animal Feed

Background: Conventional analytical methods for phosphorus and sulfur determination in several matrices present normally analytical challenges regarding inaccuracy, detectability and waste generation. Objective: The main objective is proposing a green and feasible analytical method for phosphorus and sulfur determination in animal feed. Methods: Synergic effect between microwave and ultraviolet radiations during sample preparation was evaluated for the first time for the animal feed digestion associated with further phosphorus and sulfur determination by ion chromatography with conductivity detection. Dissolved carbon and residual acidity in the final digests were used for the proposed method assessment. Phosphorus and sulfur values were compared with those obtained using conventional microwaveassisted wet digestion in closed vessels associated with inductively coupled plasma optical emission spectrometry and with those obtained using an official method (Association of Official Analytical Chemists International). Recovery tests and certified reference material analyses were performed. Animal feeds were analyzed using the proposed method. Results: Sample masses of 500 mg were efficiently digested using only 2 mol L^-1 HNO3. The results obtained by the proposed method were not differing significantly (p > 0.05) from those obtained by conventional and by official methods. Suitable recoveries (from 94 to 99%), agreement with certified values (101 and 104%), and suitable relative standard deviations (< 8%) were achieved. Phosphorus and sulfur content in commercial products varied in a wide range (P: 5,873 to 28,387 mg kg^-1 and S: 2,165 to 4,501 mg kg^-1). Conclusion: The proposed method is a green, safe, accurate, precise and sensitive alternative for animal feed quality control.