Sallum was part of Ottoman Tripolitania until December 1911. Then it was ceded to Egypt and never given back to Libya.
http://trove.nla.gov.au/ndp/del/article/58953411
http://paperspast.natlib.govt.nz/cgi-bi ... 223.2.44.2
Sallum is placed at the Gulf of Sollum.
I was not able to find detailed pre-1911 maps how big the effective territorial change was.