With 5% acetonitrile, the Symmetry C18 column is likely to work also.
If you are not sure about the elution of the peak, you can also run a gradient to maybe 10% acetonitrile.
If two standards give you different peaks, I would go for a third standard from a third supplier. If I get a consensus peak from 2 suppliers. I would complain to the supplier that did not deliver the same product.
You can also try to derivatize it with DNPH, but since this is a dialdehyde, you have to have a good derivatization procedure to get both aldehyde functions. What are the details of the derivatization procedure? But anyway, this is an additional complication that may not resolve anything. What if you get DNPH derivatives from both standards? Then you knwo that you got aldehydes, but you still do not know which one is the right aldehyde.
Of course, if you would have access to other analytical tools such as MS, you could verify yourself, which is the right glyoxal.