Accurate evaluations of the field shift and lowest-order QED correction for the ground $1^{1}S-$states of some light two-electron ions

Mass-dependent and field shift components of the isotopic shift are determined to high accuracy for the ground $1^{1}S-$states of some light two-electron Li${}^{+}$, Be${}^{2+}$, B${}^{3+}$ and C${}^{4+}$ ions. To determine the field components of these isotopic shifts we apply the Racah-Rosental-Breit formula. We also determine the lowest order QED corrections to the isotopic shifts for each of these two-electron ions.