Try reference:

https://www.inorganicventures.com/sample-preparation

I have used concentrated H2SO4 to prepare sample of TiO2 (P25) for ICP-OES analysis. I hope it will work for your other materials also. Follow the below steps with full precautions with the reaction taking place only inside a hood having proper ventilation.

DIGESTION in acid 

1. Take 5mg of your powder sample in a 20 ml vial with 2 ml conc. H2SO4 in it.

2. Stir the above mixture at 500 rpm @ 400 C.

3. You will observe an initial orange colour and acid starts to boil with fumes coming out ( WEAR MASK AND GLOVES, PROPER HOOD VENTILATION)

4. Stir the above solution until 1 ml acid is left and cool down. 

5. If you observe powder suspended, then add more acid (around 2 ml) and again stir.

6. If the amount of acid left is 1 ml, cool down the acid to RT.

Filtration of sample

1.Filter the above solution using a 400 nm syringe filter by adding 10 ml DI water.

2. The pH of the solution SHOULD BE NUETRAL or it will damage the ICP-OES sensor.

3. Finally dilute your sample in 10 ml  DI water.

4. Give your sample plus 10 ml DI water (background sample) to the operator for analysis.

NOTE: You must keep a note of all the calculation of acid added, sample taken in preparing your sample because the operator will ask so.

Good luck!

@ Saurav 

Thanks alot sir