If you and your spouse file separate returns and one of you itemizes deductions, the other spouse cannot use the standard deduction and should also itemize. See IRS Publication 504 Divorced or Separated Individuals for more information.
To indicate that your spouse itemizes deductions:
If My spouse itemized deductions on their separate return is checked, itemized deductions will be forcibly entered on Form 1040 U.S. Individual Income Tax Return, Line 9. This will occur even if the itemized deductions are less than the standard deduction.
This will not occur if the same box is left unchecked. If the spouse chooses to use the standard deduction, the taxpayer is not forced to use the standard deduction. The taxpayer can use whichever is better for his or her situation. Choosing to itemize would then force the spouse to itemize.
If the taxpayer chooses to use the standard deduction to avoid forcing the spouse to itemize, the taxpayer may need to force the assumption of the standard deduction.
To take the standard deduction even though itemized deductions are larger:
Allocation of itemized deductions between the spouses is generally based on which spouse actually paid the expenses. If an expense was paid with funds from a joint bank account, then each spouse should claim half of the expense, unless one can prove otherwise.
Note that any link in the information above is updated each year automatically and will take you to the most recent version of the document at the time it is accessed.