I hope you meant sodium carbonate, not sodium chloride.
The only way the conversion would be incomplete is if you did not have enough maltodextrin. If you are worried, use more maltodextrin, or add a few drops of corn syrup.
Here is how it actually breaks down.....
30 mg of gold is about 0.00015 moles of gold atoms.
Gold is trivalent. So you need 0.00045 moles of maltodextrin.
Maltodextrin weighs between 540 and 3060 grams per mole (variable length chains of glucose)
Assuming the worst (all maltodextrin molecules largest possible), then you need 1.38 grams of maltodextrin to fully reduce all of the gold or only 81 mg of glucose.