An analytical method for the detection and quantification of silver docusate antimicrobial finishing in soil was developed through a combination of the QuEChERS extraction method and tandem mass spectrometry (MS/MS) quantification with isotopically labeled internal standard. First, the calibration system was established in the matrix where QuEChERS extraction removed docusate from soil. The addition of an isotopically labeled internal standard reduces ionization suppression due to instrumental fluctuation and run-to-run deviation. After establishing the calibration system, this quantification method was validated according to a guideline from the U.S. Food and Drug Administration. A series of variables for quantification were validated including coefficient of determination (R2 = 0.989 ± 0.002), percent error (% error = 3 ± 4%), coefficient of variation (% CV = 6 ± 1%), limit of detection (LOD = 8 ± 2 ng mL-1), lower limit of quantification (LLOQ = 27 ± 5 ng mL-1), recovery and matrix effect (matrix effect = 0.944 ± 0.026). Those parameters were obtained from the inter- and intra-day measurements for both calibration and the quality control standards. Later, samples extracted from a simulated landfill degradation of cotton fabrics applied with sliver docusate antimicrobial finishing were measured. It was observed that the concentration measured (51 ± 5 ng mL-1 or 252 ± 25 ng g-1) fell into the ranges defined by the method development with good precision (% CV = 4 ± 1%). Results from this study could further the understanding of textile landfill degradation and facilitate further study regarding docusate contamination in soil.