Selection of Method
The open reflux method (B) is suitable for a wide range of wastes where a large sample size
is preferred. The closed reflux methods (C and D) are more economical in the use of metallic salt
reagents and generate smaller quantities of hazardous waste, but require homogenization of
samples containing suspended solids to obtain reproducible results. Ampules and culture tubes
with premeasured reagents are available commercially. Measurements of sample volumes as
well as reagent volumes and concentrations are critical. Consequently, obtain specifications as to
limits of error for premixed reagents from manufacturer before use.