Study on the Effect of Methods of Digestion of Cosmetic Samples on Their Results of Determination of Antimony,Cadmium,Chromium and Neodymium by ICP-AES

Different methods of sample pretreatment,especially ① the conventional wet digestion with HNO3 and HClO4;② the refluxing wet digestion with HNO3;and ③ the microwave assisted digestion with HNO3 and H2O2,were studied to find out their effects on the ICP-AES determination of Sb,Cd,Cr and Nd in various kinds of cosmetic samples,such as the water,emulsion,oil and powder based cosmetics.The action of hydrofluoric acid on the digestion of powder based cosmetics was also tested.The sample solutions obtained by any of the above methods were diluted to a definite volume and used for ICP-AES analysis.As shown by experimental results,digestion method ② and ③ were feasible to be used for various kinds of cosmetics.Hydrofluoric acid was necessary for dissolution of powder based cosmetics to break the crystal lattice of SiO2,especially in the determination of antimony;but it should not be used for samples containing neodymium,because insoluble fluoride precipitate of NdF3 was formed in the presence of HF.It was proved that by either the digestion method ② or ③,any of the Cd,Cr or Nd if present in the powder cosmetics could be extracted completely from the sample even without the addition of HF.Tests for recovery and precision of the proposed method were tested,values of recovery and RSD′s (n=11) found were in the range of 80.3%-118.5% and 4.25%-6.09% respectively.