The best way to find out about an analytical method which is reliable is to look in to book entitled, "Standard Methods for the Examination of Water & Wastewater". This book will give you several options for COD measurement and then you can check which one of the methods suits your requirements or available facilities. the link to the book is: http://books.google.com.my/books?id=buTn1rmfSI4C&dq=Standard+Methods+for+the+Examination+of+Water+and+Wastewater&hl=en&sa=X&ei=SbPMUvfqFor5rQfBqIHABA&redir_esc=y
Yes, it is possible to measure COD in solid samples...For this purpose a modification of the open reflux method is described in the literature: oxidant at high concentration (1.2 N) and volume (20 mL) and titrimetric end-point...