Alkylphosphonic acids (APAs) are degradation products and chemical markers of organophosphorous (OP) nerve agents (chemical warfare agents). Anion exchange disk-based solid phase extraction (SPE) has been combined with in vial solid phase derivatization (SPD) and GC-MS analysis for the determination of APAs in aqueous samples. The optimization of critical method parameters, such as the SPD reaction, was achieved using statistical experimental design and multivariate data analysis. The optimized method achieved quantitative recoveries in the range from 83% to 101% (n=13, RSD from 4% to 10%). The method was sensitive, with LODs in SIM mode of 0.14 ppb, and demonstrated excellent linearity with an average R(2)>or=0.99 over the concentration range of 0.07-1.4 ppm in full scan mode and from 0.14 ppb to 14 ppb in SIM mode. For forensic applications, aqueous samples containing APAs at concentrations exceeding 14 ppb were concentrated and target analytes were successfully identified by spectral library and retention index matching. Method robustness was evaluated using aqueous samples from the official OPCW Proficiency Test (round 19) and all APAs present in the sample were conclusively identified. The SPE disk retained the underivatized APAs in a stable condition for extended periods of time. No significant losses of APAs from the disk were observed over a 36-day period. Overall, the method is well suited to the qualitative and quantitative analysis of degradation markers of OP nerve agents in aqueous matrices with simplicity, a low risk of cross-contamination and trace level sensitivity.