17
Magnesium (Mg
2+
): above 100,000 mg/L as CaCO
3
Molybdate Molybdenum: above 25 mg/L (as Mo‑MoO
4
) (positive error)
Sample containing up to 50 mg/L Mo‑MoO
4
may be measured if a reading is taken after 1 minute
instead of 3 minutes.
High Iron concentrations: up to 200 mg/L do not inhibit color development; above 200 mg/L color
development may be inhibited.
High sulfide concentrations (S
2‑
): high sulfide concentrations may interfere
To reduce sulfide: acidify the sample and boil for about 20 minutes, neutralize and adjust volume
before measurements.
Silica (SiO
2
): above 175 mg/L (as SiO
2
). May slow down color development (negative error)
MEASUREMENT PROCEDURE
INTERFERENCES
Alkalinity: above 2,000 mg/L (as CaCO
3
). May slow down color development (negative error).
To resolve this, neutralize the sample with diluted HCl
Calcium (Ca
2+
): above 10,000 mg/L as CaCO
3
Copper (Cu
2+
): does not interfere: reagent contains a masking agent.
• At the end of measurement, the instrument directly displays concentration in mg/L of iron on the
LCD.
