LaMotte SMART 2 - Manual (Page 220)

INTERFERENCES: a. No interference from copper, iron, or silicate at
concentrations many times the concentration of sea water.
However, high iron concentrations can cause precipitation
and subsequent loss of phosphorus.
b. Salt error for samples ranging from 5% to 20% salt
content was found to be less than 1%.
c. Mercuric chloride, HgCl
2
, when used as the preservative,
interferes when the chloride levels are low (less than 50
mg/L). This interference is overcome by spiking samples
with a minimum of 50 mg/L of sodium chloride.
Phosphate–LR 2/3 Smart2 TEST PROCEDURES 2.04