Staining solution A
20 mL aqueous ferric chloride (0.21 M; 5.6% [w/v] FeCl3•6H2O)
1.0 g eriochrome cyanine R (C.I. 43820)
2.5 mL sulfuric acid (concentrated [95%-98% w/w])
H2O to 500 mL
Combine above reagents. The ingredients take 2-5 min to dissolve, with stirring. Filtration should not be necessary. The solution can be kept and used repeatedly for at least 8 yr.
