I'm currently trying to set up an offline UV digestion of organic phosphate using potassium persulfate as a digestion reagent. The goal is to produce orthophosphate which can react with ammonium molybdate for detection (fairly standard stuff). I'm currently using glycerol phosphate calcium salt as a check standard to verify it's working. This procedure worked without issues for several months during the Fall. However, for several weeks now it continues to fail as little to no orthophosphate is produced. I have verified the problem is with the digestion of the organic phosphate. Does anyone have any thoughts as to what could cause this issue?

I have:

Acid washed everything

Tried multiple UV lamps and tried exposure times ranging from an hour to a day

Altered ratios of digestion reagent and glycerol phosphate

Tried a heat catalyzed digestion (which also appears to fail???)

used new tubing, and potassium persulfate