Abstract: There is described a concentrated photographic silver halide developing solution which comprises from 50 to 150 g/liter of an ascorbic acid type compound of the general formula I: ##STR1## or alkali metal salts thereof, in which the group R represents a hydroxylated alkyl group, and at least one basic compound the anion of which is carbonate, sulphite or hydroxide of which the cation is an alkali metal, especially sodium or potassium, the total sodium to total potassium ion ratio in the concentrated developing solution being from about 50:50 to 0:100 (mole: mole).Preferably the concentrated solution is entirely aqueous but it may comprise a proportion of water-miscible organic solvents such as ethyl alcohol, or glycol solvents.

Abstract: Hydrogen peroxide can be detected using a pyrolytic graphite edge electrode when cytochrome c peroxidase and an aminoglycoside are both present in the system.