I am trying to find COD of municipal leachate using closed reflux method but results are not coming to the expectation. Following some journals i tried leachate before and after treatment COD determination which is not giving the expecting results. Except the blank all became green at 60 dilution. If i go for 70 to 100 dilution it is not becoming green but results are unreliable. So if dilution factor increases whether i conclude results wont be reliable...IS standards 3025 (part 58 ) suggests to go with open reflux method for higher concentration...so i need answer for which method is best and why it is not coming in closed reflux method...whether answers are not reliable if dilution factor is higher?