Unless you are looking for very rough answers, you may not get the accuracy you want with this method.
First off, you are mixing (if I'm following you correctly) two highly concentrated materials to get your answer. That's going to add a large amount of error to any test you make, because it will take only a tiny bit of acid or base to make a big difference in the answer you get.
Also, NaOH is deliquescent and highly reactive. This means as you expose NaOH to the open air -- whether the NaOH is in solid form or a liquid solution -- it simultaneously absorbs large amounts of water and quickly reacts with CO2. That is why NaOH solutions are notoriously difficult to accurately measure, even in the laboratory.
