There are many possible reasons for strange and unusable absorbance results, particularly when investigating these enzymatic cofactors. For initial troubleshooting, we recommend:

• Run a negative control to test instrument settings-photometer settings in particular may vary

• Check for precipitation, particularly when using tissue homogenizations, as particulate increases scattering

• Buffer levels too low or unsuitable buffer used-some formulations may cause enzymatic reactions leading to discoloration or frothing. See our buffer recipe and formulation resource in 'Additional Resources' below.

• If using an in-house procedure, try an NAD(H) assay kit suitable for your needs to investigate if the procedure or the material is the cause