Flex :: Select / Set Style To DataGridColumn After Passing DataProvider

I have a Datagrid thats being populated by different Arrays... (headers/columns change for the same DataGrid)... I would like to Select a Column of the Datagrid after it was generated by the Dataprovider and Bold it, and place it as the 'last column"

This is what I have.... and throwing an error:
private function populateGrid(evt:Object):void {
dg.dataProvider = evt as Array;
if (dg.columns.length > 0) {
for (var i:int = 0; i < dg.columns.length; i++) {
if (dg.columns[i].dataField == '_user_total') {
DataGridColumn((dg.columns[i].dataField)).setStyle('fontWeight', 'bold');
}}}}

This way I would like to have One Datagrid (for different Arrays) )without having the Columns fixed and declared (like in MXML), but dynamic, and would like a 'specific' column to be Bolded, and placed as the last column, in this example, the column with dataField _user_total.