<p>The accurate and selective determination of morphine in biological and pharmaceutical samples remains a critical challenge due to matrix interferences and the need for highly sensitive detection methods. While traditional techniques such as GC-MS, HPLC-UV, and LC-MS/MS offer high sensitivity and selectivity, they often require complex sample preparation, expensive instrumentation, and extensive calibration procedures. In this study, we employ rank annihilation factor analysis (RAFA) in combination with kinetic spectrophotometry to enhance the accuracy and robustness of morphine quantification. RAFA effectively eliminates matrix interferences and resolves overlapping spectral data, thereby improving both sensitivity and selectivity compared to conventional spectrophotometric and chromatographic methods. The Marquis reagent, as a simple, known reagent, was used to acquire kinetic-spectrophotometric data for rank annihilation factor analysis of morphine in several unknown samples. Marquis reagent is composed of a mixture of formaldehyde and concentrated sulfuric acid. Usually, different compounds produce different color reactions when using this reagent. The proposed method was first investigated using simulated data before a couple of tested opiate samples were analyzed by the proposed method to further investigate its performance. The proposed method was also successfully applied to determine morphine in a human urine sample.</p>