this is my code for reference
double[] xy = new double[] { Longitude, latitude};
// z values if any. Typically this is just 0.
double[] z = new double[] { 0 };
// Source projection information.
ProjectionInfo source = DotSpatial.Projections.KnownCoordinateSystems.Projected.World.WebMercator;
// Destination projection information.
ProjectionInfo dest = DotSpatial.Projections.KnownCoordinateSystems.Geographic.World.WGS1984;
// Console.WriteLine("Coordinate (WGS1984) = (" + xy[0].ToString() + ", " + xy[1].ToString() + ").");
DotSpatial.Projections.Reproject.ReprojectPoints(xy, z, dest, source, 0, 1);
// Console.WriteLine("Coordinate (World.WebMercator) = (" + xy[0].ToString() + ", " + xy[1].ToString() + ").");
The above code written in lon, lat system but with a little modify, you do.