I am not a native English speaker. I have been given the task of reviewing a text written in English. I wonder if I by the following use of the word "disjunction", make myself guilty of the very same crime I accuse my reviewee of, namely that he is using a particular word in a wrong way, simply to portray himself as being eloquent. I claim that "quantitative is used in disjunction to qualitative".
You're simply looking for
"quantitative is used in contrast to qualitative"
"quantitative is the opposite of qualitative"
As you say, "wanted to let the respondent know that quantitative is most often used as meaning the opposite of qualitative when collecting data".
There is no disjunction, whatsoever, between "quantitative" and "qualitative". They are just two words. A disjunction is a "thing" - rather like these "things": "a debate", "tension in the air", "a war", "an ongoing argument".
Please note that your sentence
"quantitative is most often used as meaning the opposite of qualitative when collecting data"
is perfectly correct and accurately explains that quantitative is most often used as meaning the opposite of qualitative when collecting data.