I suspect you are trying to convert the amount of folate in your multi-vitamin to nanomoles per liter to see if you are taking to much folate. This is not possible with the information given for two reasons.
mcg stands for micrograms, which is a unit of mass. You can convert a mass (grams, micrograms, etc.) to moles if you know the molar mass of the chemicals spicies (e.g., folate). Molar mass has the units grams/mole. So, for example, mass (in grams) of folate divided by molar mass (in g/mole) of folate would give you moles of folate.
nanomoles per liter is a unit of concentration. Notice we have moles, but you also have liters, which is a unit of volume.
You can not conver mass (grams, micrograms, or whatever) of folate to moles/volume of folate without knowing volume. The volume part is an unknown variable because you don’t know how your body processes the folate with out actually measuring it once the folate is processed.
These woman in the article took some amount of folate (grams, micrograms, or whatever). The folate was process by the body, after which some concentration of folate remained in the blood stream. The scientist measured this concentration in the blood. The article goes on to say:
“But the researchers say they don’t know exactly why some of the women had such high levels in their blood. It could be that they consumed too many folic acid-fortified foods or took too many supplements. Or, they say, it could be that some women are genetically predisposed to absorbing greater quantities of folate or metabolizing it slower, leading to the excess. Or it could be a combination of the two.“
So, unless you know how your body processes an specific amount (grams, micrograms, etc.) of folate, and the resulting concentration of folate thereafter, you can’t determine an optimum amount (in grams, micrograms, etc) of folate you should consume.