Craig, it is likely that the phenidone in solution A has oxidized. When mixing the stock solutions and the working solution, it is important to use deionized or distilled water that has been boiled to remove dissolved oxygen.

Other potential problems are the small quantity of phenidone required (with consequent measurement difficulties) and the difficulty encountered in dissoving it in water.

I prefer to weigh the phenidone myself on a small electronic scale (about $30. on eBay) and dissolve it and the catechol in a small amount of dry methanol before adding them to the boiled water. Done this way, Solution A should last 6 months to a year.