Assessing Accuracy of an Analytical Method in silico: Application to “Accurate Constant via Transient Incomplete Separation” (ACTIS)

Analytical methods may not have reference standards required for testing their accuracy. We postulate that accuracy of an analytical method can be assessed in the absence of reference standards in silico if the method is built upon deterministic processes. A deterministic process can be precisely computer-simulated thus allowing virtual experiments with virtual reference standards. Here, we apply this in silico approach to study “Accurate Constant via Transient Incomplete Separation” (ACTIS), a method for finding the equilibrium dissociation constant (K_d) of protein–small molecule complexes. ACTIS is based on a deterministic process: molecular diffusion of the interacting protein–small molecule pair in a laminar pipe flow. We used COMSOL software to construct a virtual ACTIS setup with a fluidic system mimicking that of a physical ACTIS instrument. Virtual ACTIS experiments performed with virtual samples — mixtures of a protein and a small molecule with defined rate constants and, thus, K_d of their interaction — allowed us to assess ACTIS accuracy by comparing the determined K_d value to the input K_d value. Further, the influence of multiple system parameters on ACTIS accuracy was investigated. Within multi-fold ranges of parameters, the values of K_d did not deviate from the input K_d values by more than a factor of 1.25 strongly suggesting that ACTIS is intrinsically accurate and that its accuracy is robust. Accordingly, further development of ACTIS can focus on achieving high reproducibility and precision. We foresee that in silico accuracy assessment, demonstrated here with ACTIS, will be applicable to other analytical methods built upon deterministic processes.