Henry's function

Henry's function (related to electrophoretic mobility) is given by (Eq. 2 in ):

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle f(\kappa a)= 1 + \frac{1}{16}(\kappa a)^2 - \frac{5}{48}(\kappa a)^3 -\frac{1}{8}(\kappa a)^4 \left[ \frac{1}{12}(1-\kappa a ) - \left( 1 - \frac{1}{12}(\kappa a)^2 \right) e^{\kappa a} E_1(\kappa a )\right]}

where $a$ is the radius of the particle, Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \kappa } is the Debye length and Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle E_1(\kappa a )} is the first order exponential integral.