Prevent Unwanted Comma

This may not be possible on the server side, so apologies if this is the
wrong group for this post.My form consists of an unknown number of pairs of text boxes. They are named textbox_a and textbox_b. I then split the comma separated list
that gets posted:

textbox_a = split(Request.Form("textbox_a"),",")
for i = ubound(textbox_a)
...insert into db

then do the same for textbox_b

If anyone puts a comma into one of the text boxes, this will result in
unmatched pairs. How can I deal with the comma, or prevent it?