Reference Material (RM) 8634 is a NIST particle standard produced from abraded ethylene tetrafluoroethylene (ETFE), a chemically inert polymer, that will help standardize and allow more accurate monitoring of subvisible proteinaceous particles in biotherapeutics. These ETFE particles resemble proteinaceous particles in biotherapeutics because they are translucent, with a refractive index similar to that of proteinaceous particles and have irregular morphology. RM 8634 has reference values for particle size distribution (PSD), in the range of (1 to 30) µm, and morphology (aspect ratio, compactness, ellipse ratio). The PSD values were obtained using flow imaging (FI), an in-house-devised stop-flow microscope (SFM), and a static optical microscopic technique. For morphological assessment of the particles, SFM, scanning electron microscopy (SEM), and static optical microscopy techniques were employed. All techniques employed were highly characterized for instrument biases and appropriate corrections were made; rigorous statistical analysis of the data was performed to obtain the reference values. This document briefly describes the preparation of the RM, data collection, data analysis, data compilation, and reference value assignment. Detailed procedures of how the analyst can use this RM to obtain PSD and morphology information, qualify instruments, reduce variability, and correct for instrument biases are presented. The document also describes how the analyst will be able to apply corrections, obtained from RM analysis, to protein-like samples to obtain more accurate PSD and morphology information than if the correction is based solely on polystyrene microspheres. Such a standard is the first-of-its-kind available to the industry. We envision that RM 8634 will drive industrial collaboration to better characterize and in turn, understand the implications of proteinaceous particles in biotherapeutics.
Special Publication (NIST SP) - 260-193
ETFE, flow imaging, particle, particle size distribution, protein particle, protein particle surrogate, reference material, standard