first hand you can assume it is the same. Then you should check how sensitive are results on changing the values.

I agree with Titus; a robustness (= sensitivity) study on the effect of the imaginary component is essential in any method development. Couple of useful rules of thumb:

• If the material is large (> 40 lambda; 25 um for a He-Ne laser; ISO13320:2009) then there's likely to be very good robustness to change in optical properties as the particle is essentially opaque to the incident radiation
• A dry measurement will always have better robustness to RI changes as the relative refractive index is always higher in air than in a fluid
• Note that carbon black and activated carbon are similar (typically the real part is around 1.5 - 1.6)  but much different from graphite (1.83?) and diamond (2.42) which are other forms of carbon

Couple of background webinars:

June 22nd 2010  Determination of the optical properties of CeO2 and CaCO3 by the volume concentration experiment - the 3 S's, Beer-Lambert and Mie

https://www.brainshark.com/malvern/vu?pi=zF2zI6Y3fz5chz0&tx=preview

June 27th, 2006 Optical Properties - use and abuse  http://tinyurl.com/jo2u6p9

Dear Aisyah,

I think you can use infrared internal reflectance spectroscopy (IRS) for analysis.

I agree with Alan for detailed information regarding the refractive and absorption index for commercial coconut activated carbon.

Regards,

Gowhar

while I am not sure your question has been answered, I have used this for my research: Article Investigation of optical and dispersion parameters of electr...

They don't mention what the feed stock is though.