Safe, Simple Na+ measurement

Hi all,

I'm looking into a project measuring the amounts of sodium sequestered in yeast vacuoles.

Unfortunately, I'm working in a biology lab with limited chemical expertise and equipment. Additionally, I have a tiny (nonexistent) budget, so buying an ion-selective electrode is out of the question. I've found some tests in the literature involving ion exchanges, but nothing that involves safe, cheap reagents that could be brought into a bio lab without a fume hood. I can probably find the use of that kind of basic equipment if I ask nicely, though.

Does anyone know of a safe and cheap technique for measuring sodium concentration? Titration, precipitation, something else I've never heard of, it doesn't matter as long as its (relatively) safe and doesn't cost too much.

Thanks!