SW-846 Chapter 3 and Method 9056A don’t address holding time for nitrate in soil; what is the recommended holding time?
If nitrogen speciation in soil is needed (i.e., nitrite and nitrate), it is important to analyze as soon as possible because of the possibility of conversion from nitrite to nitrate. Microbial activity can cause changes over time.
Method 9056A is not clear on the holding time for solid matrices. Some holding times for solids are based simply on holding times for aqueous matrices (e.g., metals holding time for soils and waters is 180 days) and others are based on assumptions about constituent stability in solid versus aqueous matrices (e.g., holding time to extraction for semivolatile organic compounds is 7 days for waters and 14 days for soils).
For analysis of nitrogen as nitrate using either SW‐846 Method 9056 or EPA Methods for the Chemical Analysis of Water and Waste (MCAWW) Method 300.0, a holding time not to exceed 48 hours from collection through extraction and analysis for speciation of inorganic nitrogen is recommended, considering that nitrogen species conversion can happen relatively quickly regardless of the matrix.
Other category: Holding Time & Preservation