You will need to use a Calculated Field and formulas using the LEFT, MID and RIGHT operators.

LEFT({Item #} , 4) will give you the first 4 characters
RIGHT({Item #} , 4) will give you the last 4 characters ( if you use all 16 characters in your item)

MID({Item #} , 5, 6) will give you 6 characters starting a the 5th one