A colorimetric dry-reagent test strip for direct detection of the presence of hydrogen peroxide in strongly acidic solutions without the necessity of a pH neutralization step comprises a chromogen responsive to hydrogen peroxide, an enzyme peroxidase catalyst and at least one complexing agent chosen to protect an active site of the catalyst for an amount of time sufficient to allow for the catalytic oxidation of the chromogen. The test strip has particular value in the determination of peroxide-based explosive compounds, such as hexamethylene triperoxide diamine (HMTD) or triacetone triperoxide (TATP), which require a treatment with a strong organic acid to release the hydrogen peroxide to be detected, and typically requires neutralization of the acid before a conventional test strip can be employed. The invention dispenses with the need for such a neutralization step.