You have a mixture of particle types. Make use of various features in the analysis software provided by the vendor - for example, to establish if the round ones are silicone oil droplets. The other particles will need orthogonal verification for composition. Possibilities are contaminants such as rubber/plastic pieces. Simply looking at the image, low likelihood of the last 3 being protein particles. You can use a microscope with polarization to confirm certain features if they are glass. Finally, if you have access to FTIR imaging or Raman imaging, you may be able to confirm composition.

All the best.

Hello, Tapan K Das,

although used MVAS (the analysis software) filter these particles and contrast the figure below, I can not identified them exactly. I'm not sure whether the first 2 particles are silicone oil or others; and the last 3 are glass?It's a pity that I do not have a chance to detect my sample with FTIR imaging or Raman imaging.

Thanks for your answer!

Ci - It is difficult to confirm the composition but you might be able to use the first approximation for ID. For example, the first two are very likely silicone oil (and look for sources that have contributed to your formulation - such as syringe - many of which are siliconized). For the other particles also, you can generate hypothesis for root cause - such as if handling of glass vials contributed to glass pieces. If these were filtered by 0.2 um filter, then you can look for a limited number of sources (such as glass, syringes etc).

Regards

Tapan K Das, thanks.

And it's interesting that had not detected particles in the buffer solution(without containing protein).