  Explicit analytical expressions for the drag and diffusion coefficients of a
spherical particle attached to the interface between two immiscible fluids are
constructed for the case of a small viscosity ratio between the fluid phases.
The model is designed to explicitly account for the dependence on the contact
angle between the two fluids and the solid surface. The Lorentz reciprocal
theorem is applied in the context of a geometric perturbation approach, which
is based on the deviation of the contact angle from a 90{\deg}-value. By
testing the model against experimental and numerical data from the literature,
good agreement is found within the entire range of contact angles below
90{\deg}. As an advantage of the method reported, the drag and diffusion
coefficients can be calculated up to second order in the perturbation
parameter, while it is sufficient to know the velocity and pressure fields only
up to first order. Extensions to other particle shapes with known velocity and
pressure fields are straightforward.
