I did antioxidant analysis which was catalase. My samples were rats liver. How can i proceed to analyse the end results if the absorbance rate was more than 1.2 (as suggested in the kit manual)? The manual suggested to dilute the samples, however all the reagents were almost finished. Need advice on this. Many thanks for your help.
To give you an appropriate answer, we need to have more information about the methode that you had used. For example, if you're essaying with Aebi methode, you need to check the blank absorbance, if it's higher than 0.700 or 0.800, you have to diminish the H2O2 concentration (0.400-0.500 of absorbance is acceptibale). However, if your method is based on the formation of formaldehyde from ethanol, here yes you should do a dilution of your samples, especially when working with some tissues.
Indeed, as liver, kidney and erythrocytes have a high catalase activity, you need to do a further dilution of these tissues homogenates (other to that done when preparing your homogenate) to have a linear decrease rate (in aebi method) or to get a value inside the standard curve (in ethanol/formaldehyde essay).
The ideal manner to proceed with all the cinetic methods, even if you're working with kits, is to do a preliminary test with one test sample (that you expect to have the intermediate activity between the groups) to define the adequate dilution before analysing all samples.
What kind of detector you used? A simple way is to use other wavelengths, which have lower absorptivity coefficients.