If your marital status was Separated on December 31st, and you meet the requirements to make the claim for the Eligible Dependant Amount, then "yes", you can make this claim on your 2018 tax return. You can claim this amount for the full year, even if you met the eligibility criteria for only part of the year.
Then eligibility requirements are listed below: https://turbotax.community.intuit.ca/replies/2647984