Background: Simple, sensitive, and economic colorimetric device based on a smartphone digital image coupled with Color Grab™ application was developed for DCH drug determination. The method is based on the diazotization reaction of benzocaine with DCH drug to obtain an orange azo dye. Method: Variable parameters such as volumes of reagents, the internal walls and ambient light have been analyzed and optimized. From the optimized conditions, a calibration curve was created by the effective intensity (IG) of an orange azo dye, a correlation of determination is 0.999 and limit of detection 0.808 mg/L. Result: The results of the Smartphone method were statistically compared with the reference method using a t-test and found to be a good agreement. Conclusion: This method requires neither solvent extraction and temperature control, also it has achieved an extensive linear range and low limit of detection compared with different methods reported in the literature.