Can I calibrate my dewpoint instrument using certified bottled gas?

No. Unlike many gases, there is no such thing as a bottled dewpoint “standard.” Some gas suppliers will certify that the gas used to fill a cylinder has a maximum water vapor content (for example, 70ppmv or less). Note that this is a threshold value, not an absolute value with tolerances. Even if the water vapor content of the fill gas is precisely known, this does not mean that gas coming out of the cylinder is also at this value. Gas fill lines, cylinders, regulators, and other hardware all have the potential to hold or emit water vapor.