If I itemize deductions on Federal tax returns, is it possible to use standard deduction on my state tax returns ? Married filing separate from Maryland.

Yes, you can choose to use the Standard Deduction in Maryland even if you itemized on the federal return.

See

"2. Itemized deductions.

Q: Can I claim itemized deductions on my Maryland return if I claimed standard deduction on my federal return?

A: No. You may claim itemized deductions on your Maryland return only if you claimed itemized deductions on your federal return. If you claimed your itemized deductions on your federal return, you may figure your tax using both deductions methods to determine which is best for you."

See page iii in Maryland 2019 Tax Booklet.

But you must read "8 SPECIAL INSTRUCTIONS FOR MARRIED PERSONS FILING SEPARATELY" on page 4 of the same link, because this describes special rules for taxpayers filing married separate.

It is my understanding that for tax year 2020,  Maryland will allow you to use itemized deductions even though you you used standard deductions for federal return. Turbo tax does not offer this option to the best of my knowledge.

Maryland requires taxpayers to use the same method of calculating deductions on their state returns as they do on their federal returns - standard deduction or itemized deductions (see Item 3 on the screen shot below)

TurboTax will allow you to file a federal return (using standard deduction) and a state return (using itemized deductions). It requires a desk version (CD/Download) of the TurboTax program. You have to prepare two returns with the same income information but with different deduction options.

From the Maryland 2020 State and Local Tax Forms and Instructions: