Guinier peak analysis for visual and automated inspection of small-angle X-ray scattering data

The Guinier region in small-angle X-ray scattering (SAXS) defines the radius of gyration, R (g), and the forward scattering intensity, I(0). In Guinier peak analysis (GPA), the plot of qI(q) versus q (2) transforms the Guinier region into a characteristic peak for visual and automated inspection of data. Deviations of the peak position from the theoretical position in dimensionless GPA plots can suggest parameter errors, problematic low-resolution data, some kinds of intermolecular interactions or elongated scatters. To facilitate automated analysis by GPA, the elongation ratio (ER), which is the ratio of the areas in the pair-distribution function P(r) after and before the P(r) maximum, was characterized; symmetric samples have ER values around 1, and samples with ER values greater than 5 tend to be outliers in GPA analysis. Use of GPA+ER can be a helpful addition to SAXS data analysis pipelines.