string[] strngSep1 = str.Split(';');
 ds = new DataSet();
 int counter =1;
        foreach (string strng in strngSep1)
 
        {
 
    SqlDataAdapter adap = new SqlDataAdapter("Select Fecha, Valor from datos where " + strng + " and NumEstacion = @StationID and Fecha between @start_DateTime and @end_DateTime", con2);
 
         adap.SelectCommand.Parameters.Add("@start_DateTime", start_query_date);
 
   adap.SelectCommand.Parameters.Add("@end_DateTime", end_query_date);
 
            adap.SelectCommand.Parameters.Add("@StationID", station_var);
 
      
                adap.Fill(ds, "Table" + counter.ToString());
counter++;