In our lab we analyze water and wastewater by a spetrophotometric method.
There is a publication called Standard Methods for the Examination of Water
and Wastewater which includes most of these methods. It seems that you
could use this type of protocol for the supernatant and the washings,
although the sensitivity is only 1-10 ug or higher. As for the yeast, there
should be some digestion procedure that you can modify for extremely small
samples, microchemistry.
Good Luck,
Robert Kirkland
