Question 1

What is the difference between Nessler and Salicylate methods for ammonia?

Accepted Answer

The Nessler method (Method 8038) measures ammonia-nitrogen in the range 0.01 to 2.50 mg/L NH3-N using Nessler reagent (potassium tetraiodomercurate) which produces a yellow-orange color proportional to ammonia concentration. It is the most sensitive ammonia method available for the DR300 and is appropriate for drinking water and low-level environmental monitoring. However, Nessler reagent contains mercury compounds and is a hazardous waste requiring proper disposal. The Salicylate method (Method 10031) measures 0.4 to 50.0 mg/L NH3-N using salicylate and cyanurate chemistry that produces an indophenol blue color. It is mercury-free, has a longer reaction time (15 minutes), and is preferred for wastewater compliance monitoring and samples with higher ammonia concentrations.

Question 2

What is the ammonia measurement range of the Hach DR300?

Accepted Answer

The DR300 Ammonia model supports two methods with different ranges: Nessler Method 8038 for Low Range (LR) measurements of 0.01 to 2.50 mg/L as NH3-N, and Salicylate Method 10031 for High Range (HR) measurements of 0.4 to 50.0 mg/L as NH3-N. Results are reported as ammonia-nitrogen (NH3-N), not as total ammonia (NH3). To convert NH3-N to NH3: multiply by 1.216. To convert to NH4+: multiply by 1.288.

Question 3

Why is the 15-minute wait mandatory for the Salicylate ammonia method?

Accepted Answer

The Salicylate method (Method 10031) develops color through a two-step enzymatic reaction pathway: ammonia first reacts with salicylate in the presence of a hypochlorite-releasing reagent to form a blue indophenol compound. The full color development requires 15 minutes at temperatures above 20 degrees C. Reading before 15 minutes produces a falsely low result because the reaction is incomplete. Reading after 20 minutes may show slight color fade. The acceptable read window is 15 to 20 minutes after the start of color development.

Question 4

What is ammonia-nitrogen and how is it regulated in wastewater?

Accepted Answer

Ammonia-nitrogen (NH3-N) measures ammonia expressed as the nitrogen it contains, rather than as the total ammonia molecule weight. It is regulated in wastewater discharge permits because ammonia exerts oxygen demand in receiving waters (nitrification) and is directly toxic to aquatic organisms at elevated concentrations. The toxicity is pH-dependent: unionized ammonia (NH3) is significantly more toxic than ionized ammonium (NH4+). Most NPDES permits specify NH3-N effluent limits, often with seasonal limits that are more stringent in summer when receiving water temperatures are higher and toxicity is greater.

Question 5

Can the Hach DR300 Ammonia be used for drinking water nitrification monitoring?

Accepted Answer

Yes. The Nessler method (LR, 0.01-2.50 mg/L NH3-N) is sensitive enough for drinking water distribution system nitrification monitoring. Nitrification in chloraminated distribution systems produces ammonia as a byproduct when nitrifying bacteria oxidize the ammonia in chloramine. Typical trigger levels for nitrification investigation are 0.1-0.5 mg/L NH3-N above background. The LR DR300 Ammonia at 0.01 mg/L detection limit can detect these changes.

Application	Typical Range	Method	Why Monitored
Drinking water source	0.1–5.0 mg/L	Nessler LR or Salicylate HR	Source water quality; affects chloramination chemistry and chlorine demand
Chloraminated distribution system	0.01–0.5 mg/L	Nessler LR	Nitrification monitoring; rising ammonia signals nitrifier activity consuming chloramine
Wastewater influent	15–50 mg/L	Salicylate HR	Influent loading characterization; process control for biological nitrification
Wastewater effluent	1–10 mg/L	Salicylate HR or Nessler LR	NPDES permit compliance; most discharge permits have NH₃-N limits
Nitrification/denitrification process	1–30 mg/L	Salicylate HR	Biological process control; optimize aeration and carbon source addition
Aquaculture/fish hatchery	0.01–1.0 mg/L	Nessler LR	Ammonia toxicity to fish; unionized NH₃ is the toxic form (pH-dependent)
Industrial process water	Varies widely	Select by concentration	Contamination indicator; process chemistry control

Interferent	Nessler LR	Salicylate HR	Treatment
Residual chlorine	Positive interference — destroys Nessler color	Destroys indophenol color	Add 1 drop sodium thiosulfate solution (3.5%) per 25 mL sample before testing; mix and proceed immediately
Turbidity	Positive interference at high turbidity	Positive interference	Filter through glass fiber or 0.45-micron membrane; correct for baseline turbidity with blank
Hardness (>500 mg/L CaCO₃)	Precipitate forms with Nessler; causes turbidity	Minor effect	Pre-treat with EDTA solution to complex calcium and magnesium; or dilute sample
Amines (primary)	Positive interference — react like ammonia	Some reaction	Distillation pre-treatment separates true ammonia from amines; required for highly contaminated industrial samples
Hydrogen sulfide (H₂S)	Interferes with color	Interferes with color	Acidify and aerate briefly to drive off H₂S before testing; re-check pH
pH outside 6–8	Affects Nessler reaction	Affects indophenol formation	Adjust to pH 7 ± 1 before testing if sample is strongly acidic or alkaline

Regulation	Basis	Typical Limit
Aquatic toxicity — chronic	Unionized NH₃ is toxic to fish; toxicity increases with pH and temperature	Site-specific; often 1–10 mg/L NH₃-N in effluent depending on receiving water
Oxygen demand	Nitrification by Nitrosomonas and Nitrobacter consumes dissolved oxygen in receiving water	Limits set to protect DO in receiving water; often seasonal (summer more stringent)
Nitrogen removal	Nutrient impairment of receiving waters; eutrophication concerns	Total nitrogen limits often accompany NH₃-N limits in nutrient-sensitive waters
Consult your NPDES permit for specific limit values. NH₃-N limits vary widely by receiving water classification, state, and seasonal conditions.

Item	Method	Hach Item No.	Notes
Nessler Reagent	LR (8038)	2119134	Contains mercury; hazardous waste disposal required
Mineral Stabilizer	LR (8038)	2355953	Added before Nessler; complexes interfering metals
Polyvinyl Alcohol Dispersing Agent	LR (8038)	2355953 (kit)	Disperses turbidity before Nessler addition
Ammonia Salicylate Reagent Powder Pillows	HR (10031)	2605345	First reagent added in Salicylate procedure
Ammonia Cyanurate Reagent Powder Pillows	HR (10031)	2605445	Second reagent; starts 15-minute timer
16 mm glass test vials	Both	2427700 (verify)	Used with cell adapter in DR300 compartment
Cell adapter	Both	Included with instrument	Required for 16 mm vials; do not omit
Sodium thiosulfate, 3.5% solution	Both (dechlorination)	2640349 (verify)	For dechlorinating chlorinated samples before testing
Confirm current item numbers at hach.com. For Nessler reagent disposal: treat as mercury-containing hazardous waste per local regulations.

Hach DR300 Ammonia Pocket Colorimeter: Complete Review & Reference (2026)

Two Methods, One Instrument — Choosing Nessler vs Salicylate

Ammonia in Water Treatment — Why It Matters

Ammonia Units — NH₃-N vs NH₃ vs NH₄⁺ Conversions

Nessler Method 8038 Procedure (LR: 0.01–2.50 mg/L)

Fill the sample cell to the appropriate volume

Add Mineral Stabilizer reagent and Polyvinyl Alcohol Dispersing Agent

Add Nessler Reagent — start 1-minute timer

Read within 10 minutes of reagent addition

Salicylate Method 10031 Procedure (HR: 0.4–50.0 mg/L)

Fill the sample cell to the specified volume

Add Ammonia Salicylate Reagent — mix

Add Ammonia Cyanurate Reagent — mix — start 15-minute timer

At exactly 15 minutes — zero with blank then read

Interferences — Both Methods

Wastewater Compliance Context

Reagents & Parts Reference

Related DR300 & Hach Instrument References