A method for the colorimetric detection of two compounds in a bulk sample comprises the steps of forming an aqueous solution of the bulk sample, inserting a single dip strip having a pair of test regions each having separate colorimetric indicator reagents for a different one of the two compounds to be tested for into the solution and then removing the dip strip from the solution, and observing the test regions for color changes denoting the presence of the two compounds. The methodology is especially adapted for the colorimetric detection of nitrates and chlorates, two components commonly associated with explosives and particularly homemade explosives.