Dictionary g = new Dictionary();
g.Add("K", "k1");
g.Add("L", "l1");

var keys1 = g.Select(x=>String.Format("{0}=@{0}", x.Key));
var result1 = String.Join(",", keys1);
Console.WriteLine(result1);

var keys2 = g.Select(x=>String.Format("{0}={1}", x.Key, x.Value));
var result2 = String.Join(",", keys2);
Console.WriteLine(result2);