Chemical Destruction of Nitrite (NO₂⁻) – Most Common Method
Technique: Sulfamic Acid Treatment (NH₂SO₃H)
Purpose: Remove nitrite without affecting nitrate.
Reaction
NO₂⁻ + NH₂SO₃H → N₂(g) + SO₄²⁻ + H₂O
(Nitrite → nitrogen gas)
Procedure
- Add 10–20 mg sulfamic acid per 50 mL sample (adjust per nitrite load).
- Mix vigorously for 2–5 minutes.
- Nitrite gets destroyed completely.
- Filter (0.45 µm) and inject.
Notes
- Nitrate remains unaffected.
- Does not introduce interfering anions except slight sulfate.
- UV Irradiation for Nitrite Destruction
Effective for low–to–medium nitrite levels
Working principle:
UV light (254 nm) photodegrades nitrite → NO + NO₂ → nitrogen oxides → escape.
Advantages
- No chemical addition
- No additional ionic background
Disadvantages
- Not effective for high nitrite (>20 ppm)
- Requires UV reactor or spectro-irradiation chamber
Separation by Ion Chromatography Conditions (Suppressing Co-Elution)
Optimizations
- Use carbonate/bicarbonate low carbonate (1.8/1.7 mM) eluent
- Increase column temperature (35–40°C)
- Use longer column (e.g., IonPac AS23 → AS11-HC)
Advanced Suppression Techniques
- Gradient IC (AS11-HC) to separate acetate, formate, nitrite, nitrate
- 2D-IC (Heart-Cutting) for complex effluent
- Longer column + lower flow rate
Result:
Improved retention resolution → no overlap → no interference.
Reducing Nitrate to Nitrite (For Nitrite Analysis Only)
Used when you want total nitrite (NO₂⁻ + NO₃⁻ → NO₂⁻).
Method:
- Use Cadmium column reduction
- Then measure nitrite via colorimetric (Griess method)
Not for IC, but included for completeness.
Precipitation / Ion Exchange Clean-up
A. Cation exchange + anion exchange cartridges
Useful for industrial effluents with high inorganic load.
- Use strong base anion exchange resin (SBA) to selectively retain nitrite/nitrate.
- Or retain organic acids while nitrate elutes.
Silver precipitation
- AgNO₃ reacts with Cl⁻; useful only when chloride is causing interference.
- Not recommended for nitrate/nitrite correction.
Suppressing Interference in Colorimetric Methods
Griess reaction (Nitrite method):
Interference by nitrate → minimal
Interference by:
- Ascorbic acid
- Sulfide
- Iron
- Organics
- can be suppressed by:
- EDTA addition
- Filtration + carbon cleanup
UV nitrate measurement (220 nm):
- Interference by organics → corrected using A_corrected = A_220 − 2 × A_275.
. pH Control for Stability
Nitrite is unstable at low pH → can degrade.
Best practice:
- Keep samples at pH 7–9
- Add 1–2 drops of buffer (borate or carbonate) if required
- Analyze within 24 hours
Sample Dilution & Matrix Management
When concentration is too high (e.g., 2000 ppm nitrate)
Interference is reduced by:
- Diluting 10–100×
- Filtering 0.2–0.45 µm
- Degassing sample
Advantages
- Best solution when matrix is extremely loaded.
- Problem Best Suppression Technique
- Nitrite interferes with nitrate
- Sulfamic acid treatment High nitrate suppressing nitrite peak
- Dilution + column optimization Co-eluting nitrate/nitrite in IC
- AS11-HC gradient / 2D-IC Organic matrix interference
- UV/H₂O₂ or activated carbon High chloride causing IC distortion
- Silver precipitation (Ag⁺) Unstable nitrite
- Maintain pH 7–9, analyze fast
Principle
- Anions are separated on a hydroxide-eluent IC column and detected by suppressed conductivity. Quantification is done using external calibration with acetate standards. Sample pretreatment (filtration, possible cleanup) removes particulates and interferences.
Scope & Purpose
- This SOP describes a validated procedure for the determination of acetate ion in aqueous samples
- (drinking water, wastewater,
- industrial effluent, process waters)
using suppressed anion IC with conductivity detection
It is suitable for concentrations from ~0.05 mg/L to 1000 mg/L (with dilution)
Safety
- Consult Safety Data Sheets (SDS) for all chemicals (sodium hydroxide, sodium carbonate, sodium acetate standards, sulfamic acid, acids/bases).
- Use PPE: lab coat, chemical-resistant gloves, safety goggles.
- Handle NaOH and concentrated eluents carefully (corrosive).
- Dispose of IC waste and concentrated eluents per institutional hazardous waste rules.
- Work in well-ventilated area
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What is Sodium Acetate Used For
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