may be detected by measuring the change in solution ph associated with product formation or using a ph stat method a practitioner skilled in the art could detect the ammonia product using a number of other ammonia detection techniques it is important to note that ammonia is sometimes present in food and feed samples for example milk can contain significant levels of ammonia gt 1 ppm therefore detection of low quantities of ammonia produced by the enzyme in milk and other food matrices is nontrivial food matrices may contain agents which can interfere with ammonia detection e g glycine therefore it would be highly desirable to develop a method for preparing a sample in some embodiments a method may include preparing a sample to remove endogenous ammonia and or interfering agents e g substances which may interfere with the enzymatic reaction and or detection of the ammonia a sample may be prepared prior to the enzyme reaction to detect melamine is conducted in some embodiments sample preparation may include solid phase extraction spe spe may be conducted using a cation exchange resin e g strata x c while cation exchange spe based sample preparation methods are currently used for preparation of samples for melamine analysis by mass spectrometry current methods utilize high levels of ammonia to elute the melamine from the spe column since ammonia based methods such as these are not compatible with our enzyme based detection scheme since ammonia would increase the background signal and potentially inhibit the enzyme the elution step of the spe scheme described herein does not employ ammonia in some embodiments a sample preparation method.