Dynamic Pivot Table - Incorrect syntax near '+ @cols +'.

When trying to build dynamic pivot tables, I keep getting the error message "Incorrect syntax near '+ @cols +'."  

I've pasted the query below exactly like I am trying to run it. 

Any help would be greatly appreciated.

DECLARE @cols NVARCHAR(2000)
SELECT  @cols = COALESCE(@cols + ',[' + COMPM_ID + ']',
                         '[' + COMPM_ID + ']')
FROM    EDW.Excalibur.DetailSalesSuspenseComponents
ORDER BY COMPM_ID
SELECT *
  FROM (
    SELECT
      DSS.GSL_ID,DSSC.COMPM_AMOUNT, DSSC.COMPM_ID
FROM EDW.Excalibur.DetailSalesSuspense DSS
LEFT OUTER JOIN EDW.Excalibur.DetailSalesSuspenseComponents DSSC
ON DSS.DSS_ID = DSSC.DSS_ID
WHERE DSS.PER_END_DATE >= '04/30/2012'
AND DSS.PER_END_DATE <= '04/30/2012')
  AS PivotData
  PIVOT (
    SUM(COMPM_AMOUNT)
FOR COMPM_ID IN ( '+ @cols +' )
  ) AS PivotTable